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Author Topic: SCHIIT VALI - measurements.  (Read 25546 times)

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Solderdude

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Re: SCHIIT VALI - measurements.
« Reply #50 on: October 16, 2013, 08:39:30 AM »
That may be due to a too high test voltage and current limiters kicking in.

Try to measure it at a lower voltage with say a load around 50 Ohms.
Maybe the numbers get better, focusrite claims <10 Ohms (which is a weird spec as 0Ohm would also be possible)
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ultrabike

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Re: SCHIIT VALI - measurements.
« Reply #51 on: October 16, 2013, 09:30:36 AM »
I'm actually using 100 ohm resistors. Tried with a variety of voltages ranging from 0.15 V to 1 V (Focusrite) and 0.25 V to 5.11 V (Vali)... Same results.

It could be I'm doing something wrong :-S. My dummy load is basically a 100 ohm resistor connected from the tip to the sleeve (gnd) of a 3.5mm jack, and another 100 ohm resistor from the ring to the sleeve of the same jack. I just apply the classic voltage divider equations with no load (open) and then dummy loads (voltage from either tip or ring to sleeve).

I'm also kind of surprised at the highish numbers I'm getting.

I just measured my BitHead for sanity check, and I'm getting 11 ohms :-Z
« Last Edit: October 16, 2013, 10:05:08 AM by ultrabike »
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Solderdude

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Re: SCHIIT VALI - measurements.
« Reply #52 on: October 16, 2013, 09:59:30 AM »
It isn't current limiting in this case.

10 Ohm output R is a bit on the high side for IEM's for instance, but considering the noise floor you can't use them anyway.

Most likely the 'power stage' is a follower circuit without any feedback.
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ultrabike

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Re: SCHIIT VALI - measurements.
« Reply #53 on: October 16, 2013, 10:07:03 AM »
Could be. Dunno.

As far as the output impedance, my HD558 are supposed to be somewhere around 50 ohms so 10 ohms is not optimal but not too bad. However, 15 ohms might start showing FR stuff up ... which kind of did.
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ultrabike

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Re: SCHIIT VALI - measurements.
« Reply #54 on: October 16, 2013, 03:47:45 PM »
I believe I had a problem with a non-negligible impedance cable adding resistance to the measurement. Here are the new measurements:

Total BitHead:< 5.6 ohms
Sansa Zip:< 0.7 ohms
Focusrite 2i2:< 11.7 ohms
Schiit Vali:< 6.4 ohms
« Last Edit: October 16, 2013, 03:55:55 PM by ultrabike »
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xnor

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Re: SCHIIT VALI - measurements.
« Reply #55 on: October 16, 2013, 04:29:54 PM »
Quote from: Solderdude on October 15, 2013, 02:35:49 PM
It's actually really good and mainly 2nd harmonic, the third is still visible but below the audible treshold so VERY natural and a just about audible 'addition'.
[...]
IMD also doesn't look bothersome to me at this level which might explain why it doesn't sound bad.

Why would the 2nd harmonic distortion product be pleasing but the much more offensive IMD at roughly the same level be less problematic?  ???

IMD products in the graph above are down what, roughly 45 dB? The 2nd harmonic of the 60 Hz tone is down roughly 50 dB.


ultrabike, could you please measure the FR with a load (HD5xx would be awesome)?
And maybe the loaded spectrum of 250 Hz + 400 Hz (sum to full scale) tones?

I agree, if it really is ~100 bucks it's certainly not a bad deal but ...
« Last Edit: October 16, 2013, 04:41:52 PM by xnor »
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ultrabike

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Re: SCHIIT VALI - measurements.
« Reply #56 on: October 16, 2013, 04:40:35 PM »
It may be the fact that those graphs are at 1 Vrms. At a less ear splitting level of 0.141 Vrms the main problem is that the noise creeps up relative to 1 Vrms, but the IMD products are reduced:

1) Noise Level at 0.141 Vrms



2) IMD+N Level at 0.141 Vrms



Quote from: xnor on October 16, 2013, 04:29:54 PM
ultrabike, could you please measure the FR with a load (HD5xx would be awesome)?
And maybe the loaded spectrum of 250 Hz + 400 Hz (sum to full scale) tones?

I agree, if it really is ~100 bucks it's certainly not a bad deal but ...

I'll see what I can do tonite mang.
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xnor

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Re: SCHIIT VALI - measurements.
« Reply #57 on: October 16, 2013, 04:46:25 PM »
What's the gain btw?

edit: thanks ultrabike.  p:3
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Solderdude

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Re: SCHIIT VALI - measurements.
« Reply #58 on: October 16, 2013, 08:56:39 PM »
Quote from: xnor on October 16, 2013, 04:29:54 PM
Why would the 2nd harmonic distortion product be pleasing but the much more offensive IMD at roughly the same level be less problematic?  ???

2nd harmonics are very natural sounding as there are but few pure sinusoidal instruments anyway.
IF IMD were present at the same (or even much lower) amplitude it would be very problematic and awful sounding so wouldn't be less problematic at all.

Quote from: xnor on October 16, 2013, 04:29:54 PM
IMD products in the graph above are down what, roughly 45 dB? The 2nd harmonic of the 60 Hz tone is down roughly 50 dB.

Can you tell me where you find high amounts of IMD in the plot ?

All I see is mainly 2nd harmonics of both tones and NO sign of IMD in the spectrum plot.
IMD products would be visible on both sides of the higher frequency at a distance of the lower frequency.
They aren't there at all.

The small 'peaks' around those frequencies are also present in the noise plot at equal levels so aren't IMD they might come from switchmode power supplies in the chain somewhere,.


These later impedance numbers seem more realistic.

Did you measure the voltages at the dummy load while they were connected via wires of at least 2 Ohm per lead instead of directly at the output plug of the amp ?



« Last Edit: October 16, 2013, 09:39:38 PM by Solderdude »
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ultrabike

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Re: SCHIIT VALI - measurements.
« Reply #59 on: October 16, 2013, 09:15:57 PM »
Quote from: Solderdude on October 16, 2013, 08:56:39 PM
All I see is mainly 2nd harmonics of both tones and no sign of IMD in the spectrum plot.
IMD products would be visible on both sides of the higher frequency at the distance of the lower one.

The small 'peaks' around those frequencies are also present in the noise plot at equal levels so aren't IMD.

I think I see what you are saying SD. Most of it is 2nd harmonic stuff it seems.


Quote from: Solderdude on October 16, 2013, 08:56:39 PM
These later impedance numbers seem more realistic.

Did you measure the voltages at the dummy load while they were connected via wires of at least 2 Ohm instead of directly at the output plug of the amp ?

Yup  facepalm. Also measured the wire impedance... north of 3.9 ohms :-0

New measurements made use of a much shorter cable and with < 0.3 ohms impedance (for convenience).
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