Advise on a passive volume control
Aug 21, 2009 at 2:06 PM Thread Starter Post #1 of 13

technetium

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Well I have a integrated RWA sig. 30.2 connected to my audio-gd 19mk3 dac running from my computer.

My problem is that even on the lowest volume in foobar the sound levels are quite high, so I need a volume control. And since I live in Denmark I thought it would be easier to build a passive volume control than having my amp sent to the US and back, and most likely also a lot cheaper
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But I am new to DIY, so need a bit of advise.


I know that a passive volume control is easy to make, I have already ordered a case (small Hifi2000 case) and the connectors (neutrik) and a knob (big 40mm alu)

Now what I am not sure of is what value attenuator (10,20 or 50k) to use and what brand, I have been looking at Khozmo (100usd), Goldpoint (100usd) and the Dact ct2 (150usd).
What would you recommend?

The output impedance of my dac is 20ohm.

Secondly what kind of wire should I go for?

I have been looking at Kimber TCSS 19 AWG.

Thanx guys
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Aug 21, 2009 at 3:12 PM Post #2 of 13

ting.mike

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Normally a 10K attenuator is recommended for passive volume controls. The Khozmo is still quite new and nobody knows how good they are. Goldpoint and Dact is more reputable. I personally went with a CT2 for my Beta.

As for cables, I personally don't like the sound of Kimber TCSS, I think they're a bit treble happy. Depends on what kind of sound you're looking for. I actually prefer canare starquads to the more expensive TCSS. I think the canare are warmer and less fatiquing. They won't win any detail contest, though. But they're definitely not muddy.

If you want to minimize soldering and joints, you can do like what I did, solder the wires directly to the volume controls and put an RCA set on both ends (input and output):

Source>RCA===========Volume Control==============RCA<Amp

Here's a document from DACT regarding passive pre amps:
http://www.dact.com/html/passive_preamp.html

If you google "passive preamps" you'll find a lot more.
 
Aug 21, 2009 at 3:31 PM Post #3 of 13

linuxworks

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here's an idea: why have the volume control have MANY steps?

if you are ok with the software vol control for the most part, just make a voltage divider and give it maybe 2 or 3 steps! easier, cheaper, no fancy stepped attens needed and it could even be relay based if you wanted
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a 'high medium low' gain setting, so to speak. that might do it.

I like to find simple solutions to things....
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Aug 21, 2009 at 3:32 PM Post #4 of 13

technetium

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What does the value of the attenuator mean? Does 50k mean lower inital volume than e.g. 10k? or?

Okay but the TCSS are not to thick or anything? Its just if you look at e.g. the Khozomo then it only has small "legs" to solder on.

Well in terms of brand of cable I dont know how much I will be able to hear. It has to be great quality, but then the cable from the jack to the attenuator is only like 6-8 cm
 
Aug 21, 2009 at 3:35 PM Post #5 of 13

technetium

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Linuxworks, how would that look like? A three point switch with resistors on it or?

Secondly does foobar not lower the quality of the music when it lowers the volume, I thought that what foobar did was to reduce the numbers of bit in order to lower the volume.
 
Aug 21, 2009 at 3:51 PM Post #6 of 13

linuxworks

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I am guessing that foobar (being smarter than this) is going to dither-down the resultant wave and so it won't be nearly as bad as 'bit truncating'. my guess, though.

it really matters on COPY and not so much on LISTEN. my 2 cents
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in terms of the circuit, it would just be a binary atten, cutting maybe 5 and 10db (say). then you can combine the 2 atten elements and select a total of 5, or 10 or 15db of cut. that may be enough. or pick other elements; maybe 10, 20, 40 db. something like that. then switch in the ones you want to cut it down to 'useful range' and use the software vol control as the vernier adjuster, so to speak.

if foobar is letting the dac vary the volume, it could be bad. but a pc doing it in software is probably dithering properly and I would not worry about that, myself.
 
Aug 21, 2009 at 3:54 PM Post #7 of 13

linuxworks

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Quote:

Originally Posted by technetium /img/forum/go_quote.gif
What does the value of the attenuator mean? Does 50k mean lower inital volume than e.g. 10k? or?



no, the volume range is still 0..100%. ie, from near the grounded lug end to the other end.

you still 'carve up' the range into 'none' thru 'full'.

the issue about the impedance is the load it puts on the source (dac or whatever) and if the source can 'drive' something as low as 10k.

lower values keep the noise down a bit. think of the extreme: if you short the inputs on an amp or preamp, you get no noise and no hiss
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as you let the inputs float, you get tons of noise and hiss. those 2 extremes help illustrate that having a lower and lower Z value lowers the noise (as an input to a gain stage, this is typical).

10k-50k are typical ranges for vol control pots.

if your source can 'handle' 10k, go for that. lower is almost always better unless the source can't quite drive it.
 
Aug 21, 2009 at 4:08 PM Post #9 of 13

linuxworks

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depending on how much building you want to do, I could help with some relay atten circuits
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one I'm toying with, these days, is using latching relays. that's cool since you just use a momentary switch to 'set' the relay and then you remove power and it 'holds'. that would be perfect for your app. you wouldn't even need a controller, really; you could have an 'up/down' button on each relay item (2 pushbutton switches) and that would either select the atten element as 'inline' or 'bypassed'. put 2 or 3 of these in series and you have that ladder I was talking about.

the relays I am using are something like $4 each. they need 2 resistors per channel (l/r) per 'atten block' (relay). each relay handles l/r (dpdt).

it would be WAY cheaper to build a 2 or 3 bit atten from relays and R's than any kind of stepper. and way way more accurate than the best pot you could buy.
 
Aug 21, 2009 at 4:53 PM Post #10 of 13

technetium

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Well I am tempted, but a attenuator is a lot simpler, and I am new to DIY :wink: And then I wont have to rely on the volume control of foobar.
 
Aug 21, 2009 at 5:34 PM Post #11 of 13

linuxworks

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some people don't like not having steps between steps in attens
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with the 'decent software control' that foobar probably gives, I would think that its the better choice for your vernier needs; and you set the coarse level with the 2 or 3 bit atten section.

yours is way more expensive. but its your pocketbook, not mine
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Aug 23, 2009 at 12:38 PM Post #13 of 13

Billyk

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You could try one of these, Lightspeed attenuators. They are getting rave reviews. I have a set but have yet to put it together. Seems like it would be just the ticket for your application.
 

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