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Garage 1217 Project Sunrise III measurements

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atomicbob:
This hybrid tube - mosfet ampifier has been providing me with considerable enjoyment for some time now. Here are some measurements I made today in a quest to dig deeper into why this amp sounds so good to me. The distortion is particularly good considering the low voltage plate tube front end and the no feedback topology. The listening station is a Mousai MSD192 (measurements found here), the PS3 and HD6x0 or D5000 headphones as the cans with most audition time on this system. I should think there would be more discussion of this amp given it has an exceedingly high performance/price ratio.

The data presented were collected as follows:
 
1.  PrismSound dScope III, picoscope 5243B
2.  DAC unbalanced output RCA
3.  100 Kohm load used for measurements
4.  44 KHz  sample rate, 24 bit depth
5.  USB input – Audioquest Forest
6.  Unbalance cable DH Labs Silver Sonic Air Matrix RCA
7.  Vaunix Lab Brick USB hub
8.  PS Vane 12AU7 used in PS3
9.  PS3 output set for 32 ohms

Picture of the Kitchen Counter Audio Lab


Tests were run at a gain consistent with my personal listening sound levels which is between 70 to 77 dBC SPL.

A 0 dBFS sinusoid at that gain is 700 mVpp:


There is a 1 dB imbalance between the channels at my preferred listening level. Not enough to concern me for recreational listening.

Square waves can reveal a lot about an amplifier's performance. For reference morphology, the signal generator waveform looped back to the oscilloscope input at 1 KHz, 700 mVpp.

Signal generator loop back to oscilloscope input for reference


PS3 square wave 20 Hz 700 mVpp 10 mS / div 100K load


PS3 square wave 20 Hz 700 mVpp 50 uS / div 100K load


PS3 square wave 20 Hz 700 mVpp 10 mS / div 50R load


PS3 square wave 20 Hz 700 mVpp 50 uS / div 50R load


Noting the Mousai MSD192 has an excellent 20 Hz square wave response and so too the PS3, we have a theme developing.

atomicbob:
Part B of measurements.

Here are 20 Hz square waves with an HD650 as the load:

PS3 square wave 20 Hz 700 mVpp 10 mS / div HD650 load



PS3 square wave 20 Hz 700 mVpp 50 uS / div HD650 load



dScope measurements

PS3 amplitude - phase - gain



PS3 signal to noise



PS3 THD+N  THD  nth harmonic distortion


Three things to note about the distortion measurements.
1) Distortion will be dominated by the tube chosen for the input gain stage.
2) The 3rd harmonic distortion is 20 dB lower than the 2nd harmonic distortion. My ear finds even harmonic distortion pleasing and odd harmonic distortion offensive. Thus the PS Vane 12AU7 is behaving the way I prefer in the PS3.
3) The PS3 does not use feedback to lower the distortion specs

editorial - I believe there is a tendency to focus too much on THD numbers rather than look at distortion spectrum and type such as even vs odd in an attempt to reduce a complex topic to a single number representing a sort of goodness rating.

atomicbob:
Part C of measurements










If you made it through all of the numbers and graphs, you can see why I think this hybid headphone amp rocks.

Ringingears:
Yes you would think there would be more discussion of Garage1217 amps in general.

Solderdude:
For those that like squarewave shots; a 10kHz and 100kHz squarewave (with 60 Ohm load)
(The 'noise' you see on the signal is from the scope, not there in reality)






Do note that L-R balance, Frequency Response, THD and harmonic character are all tube dependent as Bob already mentioned.
L-R balance differences I have seen vary between 0.1 dB and 2.1 dB with different tubes (all pulls).

Using an (old) Philips ECC88 tube and 32 Ohm load I measured FR:  -0.5dB: 10Hz - 150kHz / -3dB: 4Hz - 350kHz
With tubes like the ECC83 the FR can easily be reduced to -3dB: 5Hz - 15kHz so the FR range can vary substantially.

The amount of distortion greatly depends on the output level.
The lower the output level the lower the distortion.
At 'Normal' listening levels the THD levels are considerable lower b.t.w.

The schematics of SR-III are found here:
http://www.mediafire.com/view/06g72zyu2d32gp6/Sunrise_3.1_schematic.pdf

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