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Old 31st August 2007, 10:21 PM   #1
jaykick is offline jaykick  United States
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Default Adding volume control to Lite DAC-AH

I just took apart my Lite DAC-AH, and it looks like, with a minimal amount of metal work, I could fit an Alps potentiometer where the power button is. I figured I'd mount the pot. on the inner front panel. Although, the shaft may need to be lengthened somehow.

But the question is, where is the best place to insert this into the circuit? I was thinking between the DACs and the OP-Amps. But, I'm not sure where exactly to connect things, as I don't know how many layers these PCBs have. Two? I figured it would be a bad idea to insert it after the op-amps, as that could cause capacitance issues with some interconnects.

If anyone has any ideas, please share. I have a feeling this could be quite useful to many people. If you only have one source and one (or 2 monoblock) amplifier, this could get eliminate the need for a preamp/passive attenuator. My system is iMac > DAC-AH > 300B monoblocks, and using digital volume control isn't working well, since any noise from the DAC is being being amplified at full strength, and is quite audible sometimes.

Here's the schematic: http://www.audiodesignguide.com/DAC/...ircuit_new.JPG

thanks,

Jay
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Old 1st September 2007, 02:26 AM   #2
jaykick is offline jaykick  United States
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OK, I somewhat solved the problem, at least electronically. The left channel is easier to modify due to the way the PCB is laid out, so that's all I've done. First what I did was score the circuit board connection between the top of R35 and U14 pin 3. Then I put the potentiometer (an 80k Alps unit I happened to have) in parallel with R35 and took the output to the through hole next to R28, which conveniently runs to U14 pin 3.

Although it does work, when turning the pot. it goes from silent to almost a little too loud for normal listening very quickly. How could this be remedied? With a different value pot?

Jay
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Old 6th September 2007, 07:59 AM   #3
recca is offline recca  United States
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I'm about to add a 50K TKD Pot to mine, but I'm going to bypass the active output stage and put in a passive out using 2.2uF caps. Check out these threads for info on the passive output mod and the check for proper output voltage from the regulators.

http://www.head-fi.org/forums/showthread.php?t=200856

http://www.head-fi.org/forums/showthread.php?t=166545

I think I should add the pot after the Caps. If you know if that is correct that would be helpful.
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Old 8th September 2007, 04:01 PM   #4
Puffin is offline Puffin  United Kingdom
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I you are doing the passive mod, could you not put the pot before the caps by connecting to C12 & C13 ?
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Old 11th September 2007, 08:53 PM   #5
recca is offline recca  United States
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Quote:
Originally posted by Puffin
I you are doing the passive mod, could you not put the pot before the caps by connecting to C12 & C13 ?
I don't know. I'm a total Noob to something like this so I need some help. I'll try it though. Got nothing to lose at this point!

After reviewing the schematic, did you mean C38 & C39?
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Old 11th September 2007, 09:12 PM   #6
Puffin is offline Puffin  United Kingdom
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recca. If you look at the info for the passive mod you will see that the L&R outs are taken from the holes near C12 & C13. I don't know if this would work for a pot, but it's worth a try. You will need to pick up a ground for the pot.
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Old 11th September 2007, 09:20 PM   #7
recca is offline recca  United States
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Okay I see what you mean. That's where I tapped for the caps. Could I just the ground point I'm using for the RCA's right now?
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Old 12th September 2007, 06:04 AM   #8
recca is offline recca  United States
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Okay so here's what I did:

C12/C13 -> Pot -> Caps -> RCA's worked.

I used the ground for the +/- 15V pads for my ground.
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Old 12th September 2007, 08:16 AM   #9
Puffin is offline Puffin  United Kingdom
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recca. I logged off and went to bed early last night! Glad to hear it works. I assume you have not got the loudness problem with the pot anymore ? What value pot did you use ?
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Old 12th September 2007, 08:32 AM   #10
recca is offline recca  United States
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I think the OP had an issue with the volume. I actually do too, but I tried wiring in Shunt Mode which didn't seem to work. I'm going to rewire how its supposed to be done and go from there. My Trends blew up though so I have to wait for a new one.
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