CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS

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Author Topic: Bakoon HPA-01  (Read 8927 times)

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Solderdude

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Re: Bakoon HPA-01
« Reply #20 on: October 13, 2014, 03:27:48 PM »
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.


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.



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.

« Last Edit: October 13, 2014, 04:54:32 PM by Solderdude »
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OJneg

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Re: Bakoon HPA-01
« Reply #21 on: October 13, 2014, 03:54:00 PM »
Ok, that's what I thought.
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Marvey

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Re: Bakoon HPA-01
« Reply #22 on: October 13, 2014, 04:24:27 PM »
Infinite output impedance. Explains the mega-bass boost on the HD600 measurement.
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ultrabike

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Re: Bakoon HPA-01
« Reply #23 on: October 13, 2014, 04:38:00 PM »
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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Armaegis

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Re: Bakoon HPA-01
« Reply #24 on: October 13, 2014, 04:56:36 PM »
Quote from: marvey on October 13, 2014, 04:24:27 PM
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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OJneg

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Re: Bakoon HPA-01
« Reply #25 on: October 13, 2014, 05:05:04 PM »
Quote from: Armaegis on October 13, 2014, 04:56:36 PM
Quote from: marvey on October 13, 2014, 04:24:27 PM
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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Solderdude

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Re: Bakoon HPA-01
« Reply #26 on: October 13, 2014, 05:08:34 PM »
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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Marvey

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Re: Bakoon HPA-01
« Reply #27 on: October 13, 2014, 06:50:51 PM »
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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Solderdude

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Re: Bakoon HPA-01
« Reply #28 on: October 13, 2014, 09:26:48 PM »
The bass boost on the HD598 should be fun.  ::)
I expect it to be around +15dB.



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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Marvey

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Re: Bakoon HPA-01
« Reply #29 on: October 13, 2014, 10:23:06 PM »
Gaaaaaaaaaaa...   
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