Salas DCG3 preamp (line & headphone)

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They are very clean for cheap closed back dynamics aren't they? Beyond being good in music, I was surprised on how much preferable I found them in watching movies vs my HD600s. Because they have the closed back oomph advantage for following the heavy cinematic FX better but without being characteristically closed cups resonance muddy they manage a very decent stage with sense of depth. The dialogue is always very distinct. Most closed backs are V shaped in response but this one isn't. It needs some initial play time to soften up the cushions and remembering to adjust so they touch and seal well especially below and behind the ear because they are long cups.
 
For the quick THD measurment I used my trusty Keithley model 2015-P, Audio Analyzer Multimeter & Generator. Indeed it is THD + noise. Once it is assembled in the case, with the normal supply I'll check using my CLIO system.

What main fuse rating do you recommend for 120Vac main? I'm using two 50VA transfo with your dual mono supply, using 115ma BIAS.
Thanks
SB
 
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The Keithley must be true enough for one Volt RMS because if you look in my post #1 second picture FFT for 1kHz with 0.00041% THD it also shows the THD+N which is 0.0037% for half a Volt RMS.

I would recommend 2.5A AC inlet fuse to can take about 20A at 0.1 sec inrush with ease during the eye blinking power on time that the trafos build up magnetic momentum.

For Europe I would recommend 1.25A AC inlet fuse for same 100VA total.
 
Ok, here we go, and before I begin with the measurements, let me comment on the complete unit presently playing on my bench, with my Pono player and Hires files.

To resume it is simply gorgeous!

Perfectly silent, Silky smooth highs, resolution, timing and flow, just perfect (Anouar Brahem - Eyes of Rita),

For the bass craving type, wow, powerfull bass, no problem there (Daft Punk - Random Access Memories),

Voices, just lovely (Diana Krall - MayFlower).

Even if the following measurements are just very good as well, it tells nothing if the amp is not musical. This one is, big time, a keeper and a reference piece. I'm happy :D
 
CLIO Measurements

Before anything check the CLIO noise floor at -111dBV, not perfect, can be better, but enough for the following ;) All measurements are at 1Khz

DCG3_GND IN_MAX VOL_Noise Floor: -95.2dBV. With headphone we hear nothing...

DCG3_Vout 1V_MAX VOL_No Load_THD: 0.002% In real life, nothing...

DCG3_Vout 1V_MAX VOL_No Load_IMD: 0.005%, Intermod (1 & 2Khz), very low as well

DCG3_Vout 1V_MAX VOL_33R Load_THD: 0.014% Into a punishing load, max volume, again not an issue. We can see that it is mainly 2nd harmonic, good...

DCG3_Vout 0.1V_MAX VOL_33R Load_THD: 0.003% at a more realistic level of 100mv

To resume, excellent performance :D
 

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An then my built. The amp PCB is mounted on a custom heatsink bracket (1/4" aluminum L-channel, cut to size, drilled and polished). The larger flat section si solidly bolted on the chassis bottom. The all case is acting as heatsink. The back acts also as some shielding for the amp. There are matching ventilation holes on the amp bottom cover, that match the heatshink fins.
 

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Then the rest is pretty standard (hi-end std I meant ;): Dual 50VA big transformer, dual mono DCSTB supplies, ALPS volume pot, my trusty Mogami shielded mike miniature cable. Cardas hook-up wires at key locations, CMC RCA connectors. There is also a preamp output on the back. I added a power-on blue led that illuminates the front power-on button.
 

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I'm also pleasantly surprise that with such massive power supply onboard, there is absolutely no noise to hear, always a critical point for my in an headphone amp. You're recommendation to use these 50VA transfo was well informed. These transfo largely overs-specs I thought at first, are the perfect choice for the supply. They are not working hard at all, and it probably contributes to reduce inducation AC field.

Naturally the supply design and amp CMRR are also certainly major contributors to this excellent performance.

I'm very pleased, it was money well spent ;)

I measured the heatsinks once stabilized with cover off, and with cover on. I got:

Power supply, central heatsinks, wt cover: 55C, no cover: 45C, this is Pas Labs Class-A terrority, I'll add ventilation holes!
Amp custom heatsink bracket, wt cover: 38C, no cover: 35C, my custom heatsink with chassis coupling is working pretty well and keeps the amp cool
 
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