CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS
Lobby => Amp and DAC Measurements => Topic started by: ultrabike on October 12, 2014, 08:11:17 PM
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This is a fairly interesting amp. This amp seems to be able to behave as a voltage source or current source depending on headphone out. I used my HD600s to check out both ports.
Out of the voltage out it sounds pretty pleasant. More lower end impact and fun factor. Still, I wouldn't call this as overtly colored sound at all. In fact I like what I heard quite a bit. Good amounts of power reserves (though they seem to get consumed rather fast... this is sort of a rechargeable amp which adds to it's uniqueness)
Anyhow, using the current out definitively adds quite a bit of hump. It's a completely different story now. Hell of a lot more gain too. This is not subtle.
Here are some frequency response plots of my HD600s out of the 2i2, Bakoon voltage out and Bakoon current out:
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7824;image)
Out of the voltage out I measured somewhere between 1.5 to 1.76 ohms output impedance. In current out all bets are off. There is a low and high gain switch which seems to do a whole lot of nothing when using the voltage outy. However, it does control gain of the current outy.
So from the voltage output I was able to get 3.39 Vrms into an open, 3.37 Vrm into a 300 ohm load, and 3.24 Vrms into 33 ohms.
From the current output in high gain mode I was able to get 9.78 Vrms into a 300 ohm load, and 3.3 Vrms into 33 ohms. In low gian mode I was able to get 5.57 Vrms into a 300 ohm load, and 0.626 Vrms into 33 ohms. Into an open I got all kinds of weirdness.
As far as THD, different results depending on the output port. All of the following were taken @ around 400mVrms and -6dBFS from the Focusrite DAC line out. Current output was in high gain:
THD 1 kHz 300 ohm (voltage out)
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7826;image)
THD 1 kHz 33 ohm (voltage out)
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7828;image)
THD 1 kHz 300 ohm (current out)
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7830;image)
THD 1 kHz 33 ohm (current out)
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7832;image)
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IMD (similar THD measurement conditions)
SMPTE 60Hz 7kHz 4:1 300 ohm voltage out
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7834;image)
SMPTE 60Hz 7kHz 4:1 33 ohm voltage out
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7842;image)
SMPTE 60Hz 7kHz 4:1 300 ohm curorent out
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7838;image)
SMPTE 60Hz 7kHz 4:1 33 ohm current out
(http://www.changstar.com/index.php?action=dlattach;topic=1825.0;attach=7840;image)
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If I was to nitpick Mr Bakoon HPA-01 it would be on the need to charge it before using it... There is IMO a high WTF factor with that. But then again, there is some uniqueness to it as well given it's current output port and IMO sounds pretty darn decent.
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Wow, that's a major difference in THD performance with current out. I wonder what's going on inside...
This is also one of those cases that if you were to look at static RMAA read-out, you wouldn't say there's much of a difference between .0181% and .0159%. Looking at the spectrum plot tells a whole different story.
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Current Out distortion measurements look amazing?
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Current Out distortion measurements look amazing?
Sadly, apart from the HD600, I didn't notice any other phones benefiting. Quite the opposite in fact. So something else is going on too. Looking at the distortion you'd expect a sea of clouds to part and let the rays of sunshine illuminate your recordings. Doesn't really happen.
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Well... Higher order harmonics perhaps look relatively clean from current out. However, for 300 ohms, IMD second order harmonics seems close. For 33 ohms it seems IMD second order harmonics are better on the current out though. Note something is up with noise floor with 300 ohms from the current out.
THD second order harmonics also look kind of close for 300 ohms. Again, noise floor seems higher with 300 ohms for current out. I dunno if current out likes highish impedance. Things got weird into an open.
(EDIT: yup, current out looks pretty clean compared to voltage out)
All that said coloration will happen with current out, and bass may get bloated too. I think there was a paper by Nelson Pass about current out stuff amps for speakers (which tend to be low impedance loads). He seemed to have built quite a bit of analog equalization stuff into them (perhaps due to similar coloration issues or to fine tune things). Maybe with certain loads there are some distortion gains to be had. Dunno, pure speculation on my part there.
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I'd be curious to see the behaviour with something like the Senn HD595/598 which has a much larger impedance spike. Or perhaps a multi-driver iem with wonky curves.
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Or perhaps a multi-driver iem with wonky curves.
I've done it with the UERM, it's awful. I'll have a review up next week. Just busy with other stuff atm.
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Well... Higher order harmonics perhaps look relatively clean from current out...
All that said coloration will happen with current out, and bass may get bloated too.
Wonder how figures would be with headphones with flatter imp. curves? Still have the PM-2?
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I remember reading a pretty technical discussion of the HPA-21 by a designer from Bakoon. I assume they are using the same (or similar) tech in the HPA-01. It might shed some light on this, I will see if I can find it again.
(apologies, this is from 6 moons, but i think it has some of the technical stuff in it http://www.bakoonproducts.com/review/hpa-21-review-6moons/ (http://www.bakoonproducts.com/review/hpa-21-review-6moons/) )
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Wonder how figures would be with headphones with flatter imp. curves? Still have the PM-2?
Both Bakoon and PM-2 are no longer in the premises. I would imagine with flatter imp cans things would be much less coloredt in current out. The fact that the Bakoon can function as a current source might actually play really nice with orthos, specially considering distortion results!
I think I was able to get about 320 to 330 mW (rms) in high gain into resistors: 9.78 Vrms into 300 ohms and about 3.3 Vrms into 33 ohms. That may mean that the max current into 33 ohms is about 100 mA rms.
Their website mentions they can do 1 W into 50 ohms. This is peak power based on what I got, and I think this can be achieved from either current or voltage out at least into 33 ohms also based on what I got.
Things proly get louder with the high-imp HD600s in current out because somehow current out does not seem as voltage limited as voltage out. But with ~33 or so cans things might not be too different volume-wise from either port actually.
Like I said before, I think this amp can supply a reasonable amount of power w/o too much effort... Though one has to crank it up once in a while.
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Tried to extract any useful technical information out of the 6moons article.
More and more people love the AMP-11R as headphone amp. We thus wanted a more affordable model superior even to the 11R for this specific purpose. With an output impedance close to 2.5MΩ, expect up to 1/10th the headphone distortion with the HPA-21's current-mode output. We believe this will be a true game changer. It's a larger one-box solution with internal battery power supply derived from our EQA-11R."
"As the HPA-21 drives headphones with current, impedance doesn't factor into the equation. We can expect far lower distortion. Such has been studied by Dr. Yoshiaki Muda of the Department of Electrical Technology at the Nara University of Education in his 1996 paper Transient and frequency response of the moving-coil loudspeaker current-drive and voltage-drive method*. During his experiment he found that when a speaker was driven from a current source, he could achieve up to 1/10th its distortion. The HPA21's current output achieves the exact same behavior. The major drawback of current drive for loudspeakers is that whilst there are continuous impedance changes across all audio frequencies, the current-driving force remains fixed. Therefore the unit’s impedance curve becomes the frequency response of the driver. Because of this it is not appropriate to use current drive for most loudspeakers whose impedance varies too greatly.
"Damping factor with a headphone amplifier is of less significance especially in current-drive mode. The formula for calculating damping factor is D=R/Z (damping factor = resistance of headphone/amp's output impedance). Since the HPA-21’s voltage output is about 1Ω, a 10Ω headphone encounters a damping factor of 10 whilst a 100Ω headphone sees 100. As we see the damping factor varied by a factor of 10. The HPA21’s current output is about 2.5MΩ. This renders damping factor effectively zero. Now the music signal itself becomes the drive current and it is unaffected by any other variables to generate much higher and more precise output drive."
If someone wants to give a shot translating the relevant parts of this white paper which was mentioned somewhere in there, please do: http://near.nara-edu.ac.jp/bitstream/10105/1560/1/NUE45_2_11-18.pdf (http://near.nara-edu.ac.jp/bitstream/10105/1560/1/NUE45_2_11-18.pdf)
Although I think I have a good idea of what it's getting at.
Anyway, I still have no idea how this device is built so that it can support both "modes", and then how one of these modes can measure so much differently. If I had to speculate, I would guess that one of these modes places the load in a feedback loop. Or there's some other feedback trickery going on here.
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Anax,
do your conclusions about other HPs not benefiting include the HD 800 as well?
Thanks
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Anax,
do your conclusions about other HPs not benefiting include the HD 800 as well?
Thanks
Sadly yes. Others might like the more compressed and slightly bassier output that sacrifices all the HD800's technical strengths, But I think they should just buy another headphone if they like that sound better.
I tested with HD800, HD600, Oppo PM2, HE5, UERM, ES5, CKM500. I was originally hoping it would be an option as an uber amp for portable IEMs. Sadly, it was just the opposite.
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Anax,
do your conclusions about other HPs not benefiting include the HD 800 as well?
Thanks
Sadly yes. Others might like the more compressed and slightly bassier output that sacrifices all the HD800's technical strengths, But I think they should just buy another headphone if they like that sound better.
I tested with HD800, HD600, Oppo PM2, HE5, UERM, ES5, CKM500. I was originally hoping it would be an option as an uber amp for portable IEMs. Sadly, it was just the opposite.
That was precisely why I asked the question. I read this exact sentiment (about the bass kicking harder) being expressed and was not sure about how the others (mid and treble) were preserved. Thanks again.
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That was precisely why I asked the question. I read this exact sentiment (about the bass kicking harder) being expressed and was not sure about how the others (mid and treble) were preserved. Thanks again.
I thought the HD600 in current mode offered the least amount of trade-off and actually recommend that pairing for sure. It's pretty cool for HD600 owners that want to travel trans/portably.
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If we're judging by the THD figures, then current output looks only okay (I have seen better numbers on high power speaker amps). The voltage output looks unacceptable for me, provided the higher frequency spikes aren't measurement artifacts. I'd look at square waves to see if the amp isn't actually ringing.
Here's a diy speaker amp driving 60W into 4Ohms.
(http://www.customworks.cz/wp-content/gallery/hypa170/1khz-39r-155v.png)
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Here is some reading material:
http://www.current-drive.info/9 (http://www.current-drive.info/9)
For HP amps the 'Grounded Load Operation' part will be aplicable.
Also relatively easy to 'switch' between feedback operations using this topology.
The 'extra opamp' in the feedback loop is most likely responsible for the added background noise of the high Z headphones as it needs to amplify the 'correction signal' more than for low Z headphones.
AFAIK most headphones are designed to be voltage driven (those that perform optimally on low output R amps).
Of course headphones with a flat impedance (orthos and some dynamics) won't react as much as those with wonky or largely varying impedances.
Some may prefer current driven over voltage driven systems as bass and upper treble is boosted.
Headphones that sound 'better' from higher output R amplifiers will probably sound 'better' on current drive amps.
Theoretically (speed related) current driven speakers/drivers will be faster (in rise/fall time) as the current drop caused by the rising impedance of a voicecoil will be compensated.
Unfortunately all resonances that show up in the impedance plot will also be exaggerated.
A blessing for some headphones/speakers perhaps but a nightmare for others.
For orthos though, where the current drive is probably just as good as voltage drive, there should not be that much difference except with this particular design as it clearly has lower distortion in current mode, FR wise nothing will change.
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Any idea on what sort of topology constitutes a "current mode" output?
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The drawing on the left (a) is voltage mode output, the one on the right (b) is current mode output.
The drawings are of 'basic' circuits of course.
(http://www.current-drive.info/files/currentdrive.ota.fi/kuvat/current-feedback.gif)
The voltage amp (a) puts out an output voltage (Uo) that is proportional to the input voltage (Ui) by keeping the differential voltage (Ud) the same.
The current sourceamp provides a current Io that is proportional to the input voltage (Ui) by keeping the differential voltage (Ud) the same Uo = Io x R.
The voltage across the load (the output voltage of the amp - Ud) is now determined by the impedance of that load.
Of course within the limits of the power supply voltage + sensing resistor R's voltage drop.
In the voltage output mode the output voltage is compared with the input (via voltage divider to set the gain).
The current source in the circuit above cannot be used for headphones with a common return wire as they would short the sensing Left and Right channel's sensing resistors thereby f-ing up channel separation.
Theoretically a current source has an infinite output Voltage and infinite output resistance.
Theoretically a voltage source has an infinite output current output and 0 Ohm output resistance.
In practice both circuits are of course limited by the power supply or circuit.
Below is the more practical solution when a common ground is needed (single ended headphone)
It is highly likely the HPA-01 is based on this type of circuit.
(http://www.current-drive.info/files/currentdrive.ota.fi/kuvat/grounded_load.gif)
The output current (voltage across R1) is now 'compared' to the input voltage (U R1 = the difference between - and + input + gain of A2 circuit).
The output voltage will thus vary depending on the load impedance and the driver voltage will therefore be determined by it's impedance.
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Ok, that's what I thought.
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Infinite output impedance. Explains the mega-bass boost on the HD600 measurement.
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Yes, it is to be expected from a current source. Also not sure what the STARI circuit is exactly all about, but they claim zero negative feedback, no slew rate, constant SNR, and all sorts of things:
http://www.bakoonproducts.com/technology/satri-advantages/
I also noted that measurements were at -6 dBFS of the 2i2 Line Out. From what I measured, it seems distortion is somehow a function of the input level, but don't think it's clipping at all. This sensitivity seems to be higher than in other amps I have measured for some reason. Good, bad or so-so, there is some weirdness to this amp.
Main complain I have with it would be the need to charge it before one can use it. No way to use it while charging.
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Infinite output impedance. Explains the mega-bass boost on the HD600 measurement.
I don't think the amp output impedance has anything to do with the bass boost... the HD600 has an impedance spike in that area, so since the amp is trying to keep current constant, it ramps up the voltage delivered in the midbass.
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Infinite output impedance. Explains the mega-bass boost on the HD600 measurement.
I don't think the amp output impedance has anything to do with the bass boost... the HD600 has an impedance spike in that area, so since the amp is trying to keep current constant, it ramps up the voltage delivered in the midbass.
There are more than a few ways to think of it
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The bass boost indeed follows the impedance plot exactly (this is what a current source does).
It couldn't do it this much without the very high output impedance and as the top of the headphone impedance is limited so is the output voltage limited.
The boost is higher than when a 120 Ohm output or (heaven forbid) a 600 Ohm output were used so in essence is as high as it is because of the high output R.
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Well I did say bass boost ... "on the HD600" implying specific to the HD600's impedance spike at ~ 100Hz
I never said bass boost on any random headphone.
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The bass boost on the HD598 should be fun. ::)
I expect it to be around +15dB.
(http://cdn.head-fi.org/7/74/900x900px-LL-74d84dbe_447246a6880823ad9e68d8aa869519e4.png)
As if you pull up the 100Hz slider to the maximum... that should sound fun ! :gross:
But then again... for those headphones it has a voltage output...
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Gaaaaaaaaaaa...
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ye... HD558s might be no go...
HD558 impedance plot:
(http://www.changstar.com/index.php?action=dlattach;topic=65.0;attach=4259;image)
HD600 impedance plot:
(http://www.changstar.com/index.php?action=dlattach;topic=987.0;attach=5272;image)
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Could the HD558 be even destroyed by an extremely inappropriate amp pairing? Like too extreme midbass for the drivers to take with some serious impedance mismatch...
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As if you pull up the 100Hz slider to the maximum... that should sound fun ! :gross:
That's pretty much how the original Beats Solo sounded.
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Could the HD558 be even destroyed by an extremely inappropriate amp pairing? Like too extreme midbass for the drivers to take with some serious impedance mismatch...
We could try it. I have a 558 I don't use laying around.
Honestly though, I have to say the HD600 sounds a lot better on the Bakoon current out than it looks. It's much more articulate than most would think looking at the plot. It's fast, hits hard. Not bloomy and fat so I wouldn't judge it too harshly. I do stand by my listening that I recommend the pairing for those who like that. It's not Wow, this sucks bass, but wow this is crazy, kind of slammin' bass.
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Well, the high order harmonics do seem to clean up on current mode...
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Interesting concept. A couple years ago I simulated similar ideas and got poor results.
After reading some of the www.current-drive.info website, I did some new simulations. I still got relatively poor measurements vs the same amp driving by primarily voltage and current. Plus, a massive loss in output increasing with frequency.
The claims on the website seem very far fetched. The reality is that modern conventional high fidelity amplifiers drive the loudspeaker with both voltage and current (aka. Power)
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Either way I think the amp will deliver power (both current and voltage) to the speaker.
Most drivers, given their frequency dependent impedance and sensitivity, seem to be designed for voltage drive. It kind of seems to boil down to what follows the impedance curve, the voltage or the current... add to that random sensitivity and voilá! ... err... and some random non-linear stuff here and there too...
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You know what - a fairly easy at home experiment is in order for all readers.
Simply apply a high resistance across positive and negative terminals of your amp, relative to your load.
So if you're using speakers & a speaker amp, apply say 2 x 40 Ohm resistors (5 x the nominal speaker impedance)
If you're using headphones, apply 5x the nominal impedance. eg. With my Senn HD800, 1.5k Ohm. W
What this does is send most of the current through the headphones / speakers, with much of the voltage dropped across the resistor.
Report back your findings
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Could the HD558 be even destroyed by an extremely inappropriate amp pairing? Like too extreme midbass for the drivers to take with some serious impedance mismatch...
No, it won't be destroyed, just sound very bloated, fat, bassy as the power (voltage) it can deliver is limited and the current at 90Hz will be the same as that on 1kHz (assuming both signals are present equally loud).
There is no impedance matching in headphones and speakers, there is for digital and HF (radio etc) transport.
In the audio range there is just voltage division.
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You know what - a fairly easy at home experiment is in order for all readers.
Simply apply a high resistance across positive and negative terminals of your amp, relative to your load.
So if you're using speakers & a speaker amp, apply say 2 x 40 Ohm resistors (5 x the nominal speaker impedance)
If you're using headphones, apply 5x the nominal impedance. eg. With my Senn HD800, 1.5k Ohm. W
What this does is send most of the current through the headphones / speakers, with much of the voltage dropped across the resistor.
Report back your findings
I think I understand, but if the purpose is to emulate current drive I think a smaller resistor should be used relative to the load, when connected in parallel to the load as I think you described. <- this proly only works with current drive, which maybe what you mean.
One can proly achieve something similar using similar values to what you describe but perhaps in series with the load... Like I think was done here: http://www.changstar.com/index.php/topic,1554.msg42053.html#msg42053
Also note the Bakoon delivers more power in current mode than in voltage mode. So not sure what they are doing still.
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Any 'normal' amplifier delivers a voltage.
The current that flows is a result of the impedance (phase and amplitude of the current) to the applied voltage (P=(U2)/R).
Of course the higher the current capabilities of the amp are the lower the impedance it can deliver that voltage to and the more power in low impedances it can deliver.
For higher Impedance speakers the 'limit' to what power it can deliver is usually determined by the max output voltage.
The current that flows with a given voltage defines the drawn power (power is not supplied, it is drawn).
All amps have limited output voltages and currents (and thus power) and are not necessarily related to its output resistance.
Of course this is just semantics but to me its like saying there is current on your wall socket.
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The resistor used should be even be higher but is impractical due to the max output swing one would get.
The resistors need to be placed in series.
A current source has an infinite (extremely high) output resistance which will be emulated by a high series resistance.
These resistors will just give you a glimpse what to expect, real current drive is even more exaggerating.
As said before (by quite a few) HP and speakers are designed to be driven from a voltage.
On the other side a lot of people like raised bass (as long as it doesn't become fat/muddy) and may prefer current drive simply as it sounds better to them (moar bass).
It is 'fake' though and could just as well turn up a bass slider of a multiband EQ with a normal (low distortion) amplifier and raise the treble a dB or 2.
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Any 'normal' amplifier delivers a voltage.
The current that flows is a result of the impedance (phase and amplitude of the current) to the applied voltage (P=(U2)/R).
Of course the higher the current capabilities of the amp are the lower the impedance it can deliver that voltage to and the more power in low impedances it can deliver.
For higher Impedance speakers the 'limit' to what power it can deliver is usually determined by the max output voltage.
The current that flows with a given voltage defines the drawn power (power is not supplied, it is drawn).
All amps have limited output voltages and currents (and thus power) and are not necessarily related to its output resistance.
Of course this is just semantics but to me its like saying there is current on your wall socket.
I got all of that... But one of the things that is sort of weird from the Bakoon clusteramp is that I was able to get 9.78 Vrms in current mode into 300 ohms. In voltage mode I was only able to get 3.39 Vrms into 300 ohms.
Seems like voltage output is limited and current out is not (in terms of voltage delivery). Distortion characteristics are also fairly different.
The resistor used should be even be higher but is impractical due to the max output swing one would get.
The resistors need to be placed in series.
As mentioned a lot of people like raised bass (as long as it doesn't become fat/muddy) and may prefer current drive simply as it sounds better to them (moar bass)
It is 'fake' though and could just as well turn up a bass slider of a multiband EQ with a normal (low distortion) amplifier and raise the treble a dB or 2.
Follow the series resistance + series connection stuff for voltage source type amps.
In the Bakoon maybe they are doing some resistor thing to emulate voltage out instead and maybe that's why things don't look so hot from that port...??
EDIT: OK, actually I don't think one can get the impedance effect with a small resistor in parallel to the driver when using voltage drive... but when using current drive one might... Still dunno exactly what the Bakoon amp is all about (how it works and all I mean).
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I got all of that... But one of the things that is sort of weird from the Bakoon clusteramp is that I was able to get 9.78 Vrms in current mode into 300 ohms. In voltage mode I was only able to get 3.39 Vrms into 300 ohms.
The output voltage has a limit as well (just like any other amp) which is about 10V in this case.
The power supply rails voltage thus will probably be +/-15V and the current limit is about 140mA (peak = 100mARMS)
It could be that in voltage mode the circuit is changed so much by the different feedback topology that this limits the output voltage in that mode.
It may also be (due to the amps topology) that to reach an output voltage above the 3V perhaps you need a higher input current/voltage (higher than the 2i2 provides)
Maybe drive it from the headphone out (if that has a higher voltage swing) or an amplifier that can provide a higher voltage.
Most likely both different outputs have completely different circuits with different limits.
Follow the series resistance + series connection stuff for voltage source type amps.
In the Bakoon maybe they are doing some resistor thing to emulate voltage out instead and maybe that's why things don't look so hot from that port...??
EDIT: OK, actually I don't think one can get the impedance effect with a small resistor in parallel to the driver when using voltage drive... but when using current drive one might... Still dunno exactly what the Bakoon amp is all about (how it works and all I mean).
They simply change the feedback point to achieve voltage gain.
When you parallel the output of the current section with a small value resistor it effectively lowers the impedance peak and thus the FR will become flatter BUT the output voltage will also be lower as part of the output current will flow in the resistor.
So yes, paralleling a resistor will make a current amp act more like a voltage amp (when small enough in a relative sense) while mounting a resistor in series with a voltage amp will make it act as a current amp.
To make a current amp act exactly like a voltage amp the parallel resistor should be < 1 Ohm and thus it will have almost no output voltage.
To make a voltage amp act exactly like a current amp the series resistor should be >100kOhm and thus it will provide almost no output current.
It appears to be a current amplifier without feedback, so not exactly the same as shown in the drawings I posted.
It looks like the 'heart' of the circuit is very similar to the inverting input of an 'opamp' (with the + input connected to ground) and the voltage follower output stage has been replaced by a current output stage. All internal stages are likely to have local feedback instead of overall feedback acc. to their vague description.
The circuit simply amplifies the input current. As transistors amplify currents in a rather linear way it is easy to make such a circuit perform nicely.
In a voltage input amp the input is voltage controled (as well as the output is a voltage control) and this has to be achieved with current amplifying devices.
FET's and tubes are input voltage and output current devices.
In voltage mode they may simply take their feedback point from another part inside the circuit.
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Yes, that's the reason that putting a resistor in parallel in the Bakoon amp doesn't seem to explain to me a whole lot. I measured 1.5 ohms and about 3.39 Vrms swing. That's a lot of current down a drain made up of possibly a bunch of resistors in parallel... About 7.7 Watts (and 2.26 Amps) of which only 38.3 mW go to the cans (assuming 300 ohms). Could be, but...
The other option is some unconventional topology stuffs, like some you mentioned, which one can only speculate.
End of the day, it may not have measured amazeballs either way, but it didn't sound awful out of the voltage out to me. Current out is not that bad either with certain cans like the HD600s. Just a bit bassy as should be expected. Like most folks have already said from first hand experience, current out is proly not for every can.
I feel the cool factor is there. The need to charge this thing up before every use subtracts a bit from that cool factor though. So does the price, but I'm cheap.
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do BOTH outputs work simultaniously or as soon as you plug one headphone in the other output is disabled ?
The current mode out also puts the whole 'damping factor/grip' thing and output resistance debate in a different light though.
Given the fact that a current out amp doesn't have a damping factor at all and output resistance is in the M Ohm range.
Cable resistance and inductance also do not play a role any more (in current mode) and cable capacitance will only become relevant far above the audible range.
I like to think of it as a novelty amp... it's not like everyone is suddenly going to make current out speaker- and headphone-amps all of a sudden as this would be 'new insights'.
The current source concept is already very old and not applied because headphones/speakers are designed to be voltage driven.
Even the old 5 pole DIN connector used 'current out' for the recording pins and voltage out for the output pins.
More of a gimmick than a real attempt to improve fidelity (although the manufacturer may be convinced it is).
I'll stick to voltage out amps myself with some 'current output alike' output customer selectable settings as well though.
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To make a voltage amp act exactly like a current amp the series resistor should be >100kOhm and thus it will provide almost no output current.
Solderdude: I don't understand how this would make a voltage amp supply any current through the load. How will it behave in a current drive mode with a huge resistance choking the current prior to the speaker/phones?
Correct me if I'm wrong, been a while since I studied Circuit analysis, if you parallel the load with a high value resistor, current will be choked through the resistor, most of the voltage will drop across the resistor as well. Thus the load will get less voltage drop, but still get the balance of the current. Output of course would be lower
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To make a voltage amp act exactly like a current amp the series resistor should be >100kOhm and thus it will provide almost no output current.
Solderdude: I don't understand how this would make a voltage amp supply any current through the load. How will it behave in a current drive mode with a huge resistance choking the current prior to the speaker/phones?
It's only theoretical hence the words: thus it will provide almost no output current.
IF you were to convert a voltage amp to a current amp the voltage rails would have to be very high in order to provide a current.
With 100kOhm the voltage rails would have to be a few kV in order to obtain practical values for headphones so not realsitic in any sense.
Of course using a 1k Ohm resistor in series with the output of a voltage amp will already transform it towards being a current amp.
A real current amp will have an Rout >1Mohm though (within the output voltage range it can operate in, outside of it the impedance drops dramatically).
In practice, with nominal impedances of around 30 Ohm you won't measure much differences between a real current amp and a voltage amp with 1k in series (except for output power).
For 300 Ohm headphones there will still be a difference unless you 'up' that 1k to say 10k or so.
The 100k was to make a point that converting a voltage amps into a 'real' current amp isn't really feasable in practice.
Correct me if I'm wrong, been a while since I studied Circuit analysis, if you parallel the load with a high value resistor, current will be choked through the resistor, most of the voltage will drop across the resistor as well. Thus the load will get less voltage drop, but still get the balance of the current. Output of course would be lower
If you parallel a load (assume 30 Ohm) with a high value resistor (say 300 Ohm) most of the current will flow though the 30 Ohm, after all they have the same voltage on them.
The amp will see a load of 27 Ohm and probably won't behave much differently.
Perhaps you meant: if you put a high value resistor in series with the load most of the voltage will drop across that resistor.
That would be correct and indeed the load would get almost no voltage across it BUT the current would always be virtually the same and thus act as a current source.
Example HD558: R load = 60 Ohm (call this A) and peak R load is 300 Ohm (call this B).
With a 120 Ohm 'source' and the voltage source being 10V
A would draw 10/180= 55.5 mA where B would be 10/420= 23.8mA so the current is not constant as Rsource is too small compared to R load differences.
Same example except R source = 10k
A would draw 10/10060= 0.99 mA where B would be 10/10300 = 0.97mA which is more 'constant'.
Same example except R source = 1M
A would draw 10/1000060= 9.999 uA where B would be 10/1000300 = 9.997 uA which is more even more 'constant'
The higher the series R will be the smaller the difference and the closer it gets to a real current source but also a lower current.
If you would like at least 10mA with a 1M R you will need 10kV input voltage.
This would be very dangerous when touching the terminals on open circuit.
The reason why the Bakoon can deliver more current while the max voltage is 10V is because of the circuit used.
The Bakoon simply isn't a voltage amp with a high output R but an actual current source.
For this reason it is likely the Bakoon has either 2 separate amp circuits (one current, one voltage) which would explain some of the findings such as THD or the current circuit has applies voltage feedback in some way or adds a fixed resistor + voltage follower for the output voltage stage.
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Maybe one of you guys should check out the Current Conveyor amp on diyaudio? Seems to be a awesome design for a voltage mode satri-style amp. I'm surprised it does not benefit orthos given ortho's relatively flat impedance.
http://www.diyaudio.com/forums/analog-line-level/223835-current-conveyor-voltage-amplifier.html
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I'm surprised it does not benefit orthos given ortho's relatively flat impedance.
That's exactly why there is no benefit (viewed objectively, so probably not while subjective determined by some).
A constant current (over the entire freq range) over a constant R (over the entire freq range) will yield a constant voltage (over the entire freq range) .
A 'normal' voltage amp will always give a constant voltage over an entire frequency range (regardless of impedance).
So both types of amps will both yield a flat frequency range with orthos.
Headphones with a varying impedance will show a flat (electrical measured) frequency response on a 'normal' voltage amp.
Headphones with a varying impedance will show a 'curved' (electrical measured) FR on a current output amp (an exact copy of the impedance plot) and thus altering the sound where with orthos (or other linear dynamics) the FR will be flat, as flat as from a voltage out amp.
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Maybe one of you guys should check out the Current Conveyor amp on diyaudio? Seems to be a awesome design for a voltage mode satri-style amp. I'm surprised it does not benefit orthos given ortho's relatively flat impedance.
http://www.diyaudio.com/forums/analog-line-level/223835-current-conveyor-voltage-amplifier.html
It's possible that other orthos might benefit from the topology that the Bakoon is utilizing. Mr. Anax only tested the....HE-5 and PM2 unless I'm mistaken.
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do BOTH outputs work simultaniously or as soon as you plug one headphone in the other output is disabled ?
Sorry, didn't try that. Only tested one output at a time. Someone else might chime in about that.
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The Satri circuit will be very similar to this (current conveyor)
(http://electronicdesign.com/files/29/21152/fig_02.jpg)
Y and X are inputs (inverting and non-inverting low Z as they are coupled in the emitters)
Z+ and Z- are current outputs (differential)
Audio GD also uses these circuits:
(http://www.audio-gd.com/audio/ACSS/ACSS.GIF)
a voltage output Satri based amp (diamond output buffer)
(http://cdn.head-fi.org/4/41/41d1bfc6_Sijosae-Satriv2.1.png)
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Maybe one of you guys should check out the Current Conveyor amp on diyaudio? Seems to be a awesome design for a voltage mode satri-style amp. I'm surprised it does not benefit orthos given ortho's relatively flat impedance.
http://www.diyaudio.com/forums/analog-line-level/223835-current-conveyor-voltage-amplifier.html
Mr. Anax only tested the....HE-5 and PM2 unless I'm mistaken.
You are correct sir.
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Is the Satri stuff similar at all to the Krell CAST and Audio-gd ACCS?
(having done very little reading on the subject matter... I just know (think?) they hold everything in the current domain)
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Yep, very similar.
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Would you be able to provide some non-salesbabble explanation for why those would be "better" than standard voltage driven connections?
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No, not really.
Most of the claims they have in their http://www.bakoonproducts.com/technology/satri-advantages/ (http://www.bakoonproducts.com/technology/satri-advantages/) seem a bit far fetched with a hint of truth in it.
Headphones and speakers are designed to be voltage driven.
As the amp has no damping factor those that care about this (think it is relevant which I don't) should forget about this topology unless it is voltage out.
THE SIMPLEST CIRCUIT = PERFECTLY LINEAR BEHAVIOR
It may have nice linear behaviour for a non feedback design but only in the current domain so for orthos there will be low (electrical) distortion and flat FR.
ZERO NEGATIVE FEEDBACK = NO DISTORTION
Nonsense....
NO SLEW RATE = NO INPUT AND OUTPUT DELAY
of course it has a slew rate but in A/us instead of V/us the thing is BW limited.
There is some delay (physics, propagation speed etc) but it is very small, not smaller than other designs having the same bandwidth.
NO INPUT SIGNAL LIMIT = THE WIDEST FREQUENCY RANGE
It should be noted that with a crisong impedance of most headphones (it is an inductor) the output voltage will rise.
So when using your NOS DAC those spikes you didn't want are amplified like crazy.
Above a certain frequency the output level drops again because of cable capacitance kicking in.
ONLY nice looking squarewaves when driven in a resistance which headphones are not.
The no input signal limit is true for every design.
If you want you can feed 100MHz in ievery amp, it just won't come out as 'loud' as a 1kHz signal though.
What they mean is that it doesn't have an input filter low pass filter which is recommended for most feedback based circuits.
FIXED OPERATING POINT = NOT AFFECTED BY OUTSIDE FACTORS
Willing to bet that not all transistors are created equal and there is some thermal drift.
How audible this is remains to be seen though.
There are lots of other designs that are pretty resistant against voltage rail changes and temperature (stable enough to not change properties)
I do wonder how it handles cell phone signals (it may well be affected by this outside factor as it is filled with PN crossings (they can act as detectors for HF signals)
As mentioned the idea isn't new and certainly not ground breaking and not exclusive for Bakoon.
They may have a slightly different implementation as the posted circuits but the essence remains the same.
Novelty thing ... but that was said about a lot of things in the past (internet for instance) ::)
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Thanks. I'm pretty good for deciphering metallurgical technobabble, but the EE stuff gives me headaches.
(says the guy who goes "nah I don't need to shut off the circuit breaker, I'll just wear rubber gloves instead" when replacing worn out AC receptacles...)
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I wanted to offer a few thoughts on how the amp actually sounds, although I do appreciate all scientific information (best nap I've ever had). I tried the hd600, hd800 and he560. IMO the best pairing out of the group was the planar mag, followed by the hd800 and then the hd600 (all using current mode).
The he560 was effortless and was able to bring out the best in this hp. No part of the spectrum seemed exaggerated and the amp seemed to let the hp do what it was intended to.
The hd800 was a much more dramatic experience. We all know that the hd800 can be the Chameleon of hp's depending on the upstream gear, but I honestly had no idea that the 800 could change this much. The treble was certainly somewhat rolled off, mids about the same and the bass became almost explosive. On bass heavy material it was nearly too much sub bass. But with acoustic, jazz and singer song writer stuff, I actually enjoyed it. I only had about an hours audition between all three hp, so I'd need more time to be comfortable with what I was hearing.
The hd600 sounded good but not great. I go to the hd600 for tone mostly. And the Valhalla 2 seemed to be able to achieve the tone I was looking for better. The Bakoon was still enjoyable with the 600 though. I did not have time to listen with voltage mode.
I might have another opportunity to pick up the Bakoon and have a longer evaluation period. So hopefully more to come.
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Just goes to show listening priorities are different. I think it turns the HD800 into shit.
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I rather liked the HPA-01 + HD800 + X-Sabre combo I heard. And there are a lot of amps I wouldn't touch with the HD800.
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I rather liked the HPA-01 + HD800 + X-Sabre combo I heard. And there are a lot of amps I wouldn't touch with the HD800.
Cool. I think it sounds like shit. I suppose not the worst shit I've heard with the HD800 but why you would even bnother to have an HD800 and use it in current mode for that sound boggles my mind. There are better and cheaper phones you could buy.
The HD800 simply does NOT improve in any single technical way upon listening in current mode. I've had cleaner, harder, tighter bass from tube amps and that's all the Bakoon compression effect does for the HD800.
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More bass and warmer sound. Think Leben or RWA, but done better.
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More bass and warmer sound.
Yes I know. The bass quality is worse though and it just sounds like less capable HE500. What's the point?
Plankton dies, space dies, air dies, imaging takes a crap, microdynamics gone, inner resolution gone. Pft, f*ck that.
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yes, but what you if want HE-500 like sound, but with superior comfort and deeper staging?
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You buy a PM2?
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yes, but what you if want HE-500 like sound, but with superior comfort and deeper staging?
I suppose if that's worth $2500 to someone.
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You buy a PM2?
Na. HD800 is more open.
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I found the coloration to be enjoyable on that rig. I wouldn't trade my gear for it, but it was still enjoyable, especially with the pop music they had available to listen to.
Would I use it to listen to my favorite classical pieces? No way.
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Not everyone is going after the HD800 for the same reasons. I know I'm not. Some people like the big soundstage, clear imaging, clean treble (I've come to the conclusion that the HD800's treble is extraordinarily clean despite being slightly elevated). Or maybe I need to hear it to really understand how it destroys all of the HD800's technical advantages ::)
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I found the coloration to be enjoyable on that rig. I wouldn't trade my gear for it, but it was still enjoyable, especially with the pop music they had available to listen to.
Would I use it to listen to my favorite classical pieces? No way.
I wouldn't listen to Godsmack, Michael Jackson or Daft Punk on it. Too compromised for me. I seriously don't get it.
I don't see how the coloration on the HD800 would be acceptable from the Bakoon amp, but not from the Eximus DAC which I know Marv hates. I think if you buy into one as okay, you have to accept the other.
We can agree it's not a Leben.
OJ, go pick it up from burn and see for yourself. If you can come back and tell me with a straight face, the HD800 is technically superior sounding in current mode than it is in voltage, I'll let you win the internet.
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Well different kind of coloration. Heh. Yosef Islam's Tea for the Tillerman was awesome with HD800 + HPA-01. Current mode for FTW!
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I wouldn't listen to godsmack on any system.
I did enjoy some Beyonce on there, though.
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I wouldn't listen to godsmack on any system.
I did enjoy some Beyonce on there, though.
That's quite a public admission. We truly live an open society these days. :P
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I think the Questyle cma800r uses current mode output. While Marv here didn't like the sound of this amp very much (too boring?), I think enhances all the strengths of the HD800. In particular accuracy in details extraction, imaging and staging, which happenens to be my favourite thing about the HD800. It doesn't add anything to the tonality, and some may want some extra bass in the HD800. I haven't heard many high end amps so that may be an factor here, but I think the current mode in the questyle is done very well.
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The Questyle CMA800R has voltage input and output but internally they use current gain circuits.
A give-away may be: It doesn't add anything to the tonality, and some may want some extra bass in the HD800.
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The Questyle CMA800R has voltage input and output but internally they use current gain circuits.
A give-away may be: It doesn't add anything to the tonality, and some may want some extra bass in the HD800.
Ah, I didn't know that! Thanks for the info!
I can understand why some may call it boring, but for now I like it. :) Not gonna lie, a future fully balanced ygg/rag combo sound really tempting :)p8
Sorry for the off-topic!
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'tis true. Questyle don't add anything extraneous and maintains a very good level of precision. Boring is better than "sizzly etched analytical SS abomination" or Leben CS-300 syrup distortion.