Reducing overall volume range

[jcoman]

Hello, I have a RPi model B with a Polyvection PlainDAC (same chip as the Hifiberry, just a smaller form factor) driving a Sure Electronics class D (or T) 2x100W amplifier, and the overall volume level is a little louder than I would like. Normal listening range is about 15-30 on the volume knob and anything above 50 starts to get uncomfortable. I like to listen to the music really low at night, so the goal is to get more resolution down low and eliminate the upper (painful) volume levels.

I'm already supplying the amp with only 20V (range is 15-32), and the input gain on it is set to the weakest it can be, so I don't think I can change anything there. The DAC isn't the + version, so there is no hardware volume control option and I'm using Rune's software volume control. The speakers are built-in to the walls, and my guess is that they are just really sensitive.

Before I added the DACs, I was using the pi's default output (the hiss at low-ish volume levels was awful, and the intention was always to add DACs), and the overall volume level was lower than it is with the DACs (normal listening was ~40-60, and uncomfortable began around 80-90).

What would be the best way to lower the output volume? I have 4 of these setups running various zones in the house, so cheap would be good . The amps have an input impedance of ~60K from the datasheet, and I'm thinking I could just get/make a set of attenuators for the RCA (line level) cables, but a software method would be easier to implement .

I'm wondering though if a passive (resistor) attenuator might raise the average SNR because it would allow the DAC to run at a higher level for a given volume level?

Anybody have any ideas/thought?

[utschu]

Would it work by use of alsamixer which has to be started from the console?

[PeteB]

[jcoman]

[dunghnguyen]

@jcoman: you can try to plug in a keyboard into RPi, also connect its HDMI out to TV then logging in by user 'root' with password of 'rune' then simply typing the below command:

alsamixer

then you could adjust the original volume by using up/down arrow keys on the keyboard.

Hope this helps.

[jcoman]

@dunghnguyen: Thanks, but I tried that using ssh, and because i don't have the + version of the DAC (at least I think that's why) alsamixer just tells me "this device does not have volume control" or something like that. I can adjust the PCM (rpi native output) volume, but not the DAC's.

Thanks though

[dunghnguyen]

So it should have something instead, do u think so?

[jcoman]

The DAC I have doesn't connect to the pi with I2C, only I2S, so I don't think I should be able to control it from alsamixer (or the pi at all).

[PeteB]

@jcoman: I believe your DAC board may have a different dac chip, not identical to the DAC+ and the DAC+ Pro.

I read your other posts, & it looks like you are doing something similar. As for saving a few $, same here. I simply don't have the budget for 3~4 completely new sets of audio gear, so I am recycling older amps I already own and like, and same with speakers.

The scheme works great using a 25W receiver with a built in pre and volume knob. Not so much with a plain amp, especially not with 50+ wats per channel A/B amps.

A good passive volume control is not cheap, either, but: According to the DAC chip spec, the output can drive up to a 1K load (not tested yet). Therefore, building one from conventional components is not out of the question. I hope to get some time to try it, soon. Software OR hardware volume control at the chip, in this case (Pi, dac board, wallwart power supply), reduces mostly signal, not noise (tested).

In-line attenuators are your next best option, because they reduce the signal and noise proportionately, just like a passive volume control. Avoid the ones intended for cars audio...

I have tried these, and they are ok, not great, but fair to good (in my, biased, opinion):