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Author Topic: Amp measurements: Obj2, Magni 2, Vali, Studio  (Read 3016 times)

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Marvey

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Amp measurements: Obj2, Magni 2, Vali, Studio
« on: July 23, 2015, 08:32:04 PM »
Did these for fun. I think most people here have had a chance to hear these amps for themselves.

Two tone tests
1kHz and 123Hz @ ~2V
0dbFS = 20 volts (using 10x probe so QA400 doesn't explode)
100 ohm resistor load.

Note that output had to be reduced with Obj2 to prevent clipping because of its retarded architecture.

Vali is not as bad it it looks. 2nd harmonics are -45db (0.5%) down, and IMD bands are -40db (1%) down. Lots of smaller IM bands from the HD distortion too! I won't kid you as I do feel this distortion is audible. This distortion doesn't take away that the Vali subjectively more lively and resolving, albeit slightly warmer and thicker compared to the excellent measuring Obj2.

P.S.

Distortion measurements should always be on a log scale, never linear percentage. We hear logarithmically, not linearly. Distortion graphs in linear scale can be very misleading and make things look better than they really are. Here are some examples:

http://www.changstar.com/index.php/topic,2105.msg59347.html#msg59347
http://stereos.about.com/od/Measurements/ss/Oppo-Digital-PM-1-Headphone-Measurements.htm#step5
« Last Edit: July 26, 2015, 07:48:05 AM by marvey »
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Solderdude

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Re: Amp measurements: Obj2, Magni 2, Vali
« Reply #1 on: July 23, 2015, 09:47:54 PM »
The distortion of the Vali might probably drop a lot when the output voltage is lowered by 10dB.

How does a TOTL EC amp measure comparatively ?
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali
« Reply #2 on: July 23, 2015, 11:18:46 PM »
I'll measure the Studio when I get a chance. It's at the lab. We are still checking it over since it was a first build in a new chassis that we just finished the day before the meet.

In the meantime, here is Vali 10db lower @ ~0.6V peak. Both IMD and HD are down another 6db. Same 100ohm load. Not going to bother with Magni 2 or Obj 2 since measurements were already awesome and distortion was far far below what people can hear.

M0 and M2 are the tones. M1 and M5 and their second harmonics. M3 and M4 are the IMD bands.
« Last Edit: July 28, 2015, 08:22:42 AM by CEE TEE »
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thune

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Re: Amp measurements: Obj2, Magni 2, Vali
« Reply #3 on: July 23, 2015, 11:27:13 PM »
Looking at the measurements: I kinda wish the second channel was connected, to look at the distortion of the crosstalk. John Atkinson has said that the distortion of the crosstalk can be pretty ugly, but he hasn't shown it. Seems possible that the distortion of the crosstalk in a channel could be worse than the inherent distortion of the channel itself, in some instances. Anyway, I should investigate this for myself.
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ultrabike

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Re: Amp measurements: Obj2, Magni 2, Vali
« Reply #4 on: July 23, 2015, 11:43:41 PM »
Noise profile and distortion for the Vali seem in good agreement with what I had before. Though I used slightly different voltage settings. When comparing to other measurements note the noisefloor is less than -130 from 20Vrms.

It is also nice to see a zoom in plot aroudn the 1kHz frequency. Previously I was using RMAA which did not allow that AFAIK.

The Magni 2 and O2 measurements seem pretty close. O2 seems to measure a hair better.
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali
« Reply #5 on: July 24, 2015, 12:06:16 AM »
Quote from: thune on July 23, 2015, 11:27:13 PM
Looking at the measurements: I kinda wish the second channel was connected, to look at the distortion of the crosstalk. John Atkinson has said that the distortion of the crosstalk can be pretty ugly, but he hasn't shown it. Seems possible that the distortion of the crosstalk in a channel could be worse than the inherent distortion of the channel itself, in some instances. Anyway, I should investigate this for myself.

Maybe later. I currently only have one set of differential /10 /100 probes.
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Solderdude

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Re: Amp measurements: Obj2, Magni 2, Vali
« Reply #6 on: July 24, 2015, 10:58:48 AM »
Quote from: marvey on July 23, 2015, 11:18:46 PM
I'll measure the Studio when I get a chance. It's at the lab. We are still checking it over since it was a first build in a few chassis that we just finished the day before the meet.


Thanks Marv, quite curious how TOTL measures.



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firev1

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Re: Amp measurements: Obj2, Magni 2, Vali
« Reply #7 on: July 24, 2015, 04:26:33 PM »
I assume you don't find the QA190 probe to make much of a difference even with low signal levels?
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali
« Reply #8 on: July 24, 2015, 05:53:19 PM »
Quote from: firev1 on July 24, 2015, 04:26:33 PM
I assume you don't find the QA190 probe to make much of a difference even with low signal levels?

Raises the noise floor about 5-10db on top of the QA400 (already crazy good) depending upon conditions.
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Marvey

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Re: Amp measurements: Obj2, Magni 2, Vali, Studio
« Reply #9 on: July 26, 2015, 08:07:19 AM »
Here is a follow up with the EC Studio (not yet in production). These measurements were taken at inside my home where the power is worse than where the prior measurements were taken. Same 100ohm load. Single-ended output. /10 probe.

So, you guys are probably thinking "Wow, horrible!". I bet some people are now thinking "These measurements totally explain why the Studio, a tube amp, sounds so great to these moronic audiophools. It's all that euphonic even order harmonic distortion! Yup! Yup! Distortion!"

Well, hold on a minute. Let's think about this. At 2V (probably really fricking loud), the 2nd harmonic (M1) of the 123Hz tone is -63db down. That's 0.07%. Maybe Anaxilus can hear this distortion, but I really doubt noobs like nwaguy has ears well trained enough to hear this. The 2nd harmonic (M3) for the 1Khz tone is even lower at -73db down. That's 0.02%. The IMD bands are -62 to -66db.

The only thing that looks funny compared to the other graphs, especially the SS amp measurements, is all the feathery crap that sticks out from the noise floor. Is this a big deal? Probably not unless your ear can make sound sounds 90db down from from the fundamental tones. The feathery stuff is basically the noise floor rising when there are signals present. It is true that tube amps are noisier, but you are not going to hear any noise from this amp with the volume at reasonable levels.

There is one thing I've learned. I have awesome test equipment that can measure stuff so far beyond what the human ear can detect.
« Last Edit: July 26, 2015, 08:40:00 AM by marvey »
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