Volume control for Modulus86

[Amnes]

Hi Tom,

From an engineers perspective - what do you reckon this pream is worth: RelaiXedSMD -- Documentation

for use with your poweramps?

 

[tomchr]

Looks pretty decent. Specs with measurements to back them up. I rather like that.

Personally, I'm not a fan of attenuators. I usually end up wanting an attenuation that's between steps - in particular at low volume settings. I'd prefer some sort of programmable gain amp. That's a personal preference, though.
I would also have chosen regular 1206 resistors rather than the MELF packages used. The rectangular packages are much easier to solder.

Overall, it looks like a pretty nicely executed preamp, though.

Tom

 

[danielwritesbac]

Personally, I'm not a fan of attenuators. I usually end up wanting an attenuation that's between steps - in particular at low volume settings. I'd prefer some sort of programmable gain amp. That's a personal preference, though.

So far as I know, the usual problems with attenuators include "hard sound," "loud mids," and "not enough bass." However, wrong SPL is rarely or maybe never reported in absence of those other problems.

To a practical extent, I theorize that if it was too loud, that was because it is wrong/offensive. See?

In recent years (or even a couple of decades) we have considered impedance mismatch of no practical concern, resulting in all of the above little troubles probably simultaneously.

Now wouldn't it be a lot nicer if we had a rather easy to use USB source that matched the amplifier? Just sayin.
And, you know, for some years (possibly decades) I've been wondering where that is.

 

[billshurv]

S

Now wouldn't it be a lot nicer if we had a rather easy to use USB source that matched the amplifier? Just sayin.
And, you know, for some years (possibly decades) I've been wondering where that is.

It's called an ODAC.

 

[tomchr]

So far as I know, the usual problems with attenuators include "hard sound," "loud mids," and "not enough bass." However, wrong SPL is rarely or maybe never reported in absence of those other problems.

My personal experience with a 24-step attenuator wasn't positive. The channel-to-channel matching was within 1 % so stellar. Much better than any pot. But the attenuator went from mute to 0 dB in uneven steps. AFAIR, the first step was -80 dB. Then -70 dB. Probably then -62 dB. Then the last 15 or so steps were all 2 dB steps. For background listening, I always ended up on either step #4 (too loud) or #3 (not loud enough). It was rather annoying. This was in the 1990ies, before micro controller based attenuators with many, many steps were introduced.

1 dB steps is probably good enough for my taste. I'd probably want the lowest step to be -80 dB, plus a mute setting.

To a practical extent, I theorize that if it was too loud, that was because it is wrong/offensive. See?

No I don't see... In particular as Sean Olive has documented through controlled experiments that loud sounds better. This is also known by just about every salesman in the HiFi business. When comparing two stereos, turn up the volume just a dB or two on the more expensive stereo. It'll sound better...

As for the perceived sound quality difference between an attenuator and a pot, I suspect the pot introduced some THD that happened to provide some harmonic extension. This made for better sound... The attenuator didn't introduce this THD, so the sound quality degraded with the attenuator.
Personally, I want my volume control to be transparent rather than an effects box, so I'd prefer the attenuator (provided it meets my specs listed above).

Tom

 

[tomchr]

Finally cleared a bunch of project backlog and had some time to work on the layout for the differential driver/preamp circuit.

PCB size: 3.0 x 3.0 inches (approx 75 x 75 mm).
Stereo board with PCB-mount XLR connectors. Includes on-board voltage regulation that can be bypassed if a clean ±15 V is already available.

The layout is 99 % complete. I need to let it sit overnight and return to it tomorrow. I generally find a couple of optimizations the following day.

Tom

 

[tomchr]

Just started a thread in the Vendor's Bazaar for the THAT Driver: http://www.diyaudio.com/forums/vend...l-driver-preamp-0-000021-thd.html#post4464688

Tom