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Building Second Cmoy Amp

post #1 of 11
4/16/10 at 2:35am
Thread Starter 
I just finished building my first CMoy Amp and it works!! This is my first DIY audio project and really my first foray into building any electronics, so I'm pretty stoked.

I am already thinking about building my second Cmoy and I have two questions:

1) I found soldering the EVJC20 pot pretty tricky. I tried looking for some advice on the net but couldn't find any. Does anyone have any tricks of the trade for this pot?

2) I would like to use a pot with an on/off switch. Does anyone have any suggestions as a replacement for the EVJC20?

Thanks for your help!
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post #2 of 11
4/16/10 at 5:58am
Quote:
Originally Posted by jcaps View Post
I just finished building my first CMoy Amp and it works!! This is my first DIY audio project and really my first foray into building any electronics, so I'm pretty stoked.

I am already thinking about building my second Cmoy and I have two questions:

1) I found soldering the EVJC20 pot pretty tricky. I tried looking for some advice on the net but couldn't find any. Does anyone have any tricks of the trade for this pot?

2) I would like to use a pot with an on/off switch. Does anyone have any suggestions as a replacement for the EVJC20?

Thanks for your help!
1) Considering the pins are all in a single line, I'd make a small breakout board from some perf board. Solder the pot to the board, leaving just enough to solder the wires to and bobs yer uncle. Should keep the size of the connections relatively small

2) ALPS Pot. This is the one most DIY'ers go for if they need a compact pot with on/off switch.

HTH
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post #3 of 11
4/16/10 at 1:31pm
Thread Starter 
Thanks for the reply. A couple of more questions:

1) The EVJC20 is a dual pot, where as the ALPS pot is a single(?). Can one solder both the left and right inputs into a single pot, or do you need to have a dual pot for stereo sound. If so, do I need to choose a pot with less/more impedence?

2) Do any of the ALPS pots have on/off switches as well (to be clear I'm looking for a pot that turns the amp off when the volume is turned all the way down)?

Thanks again!
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post #4 of 11
4/16/10 at 1:45pm
Alps makes that part in both single and multiple channels.

They also make it with and without switches!

I would check out Tangent's site. He has some nice PCB based projects that (IMO) make a much better second project than a second cmoy.
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post #5 of 11
4/18/10 at 3:24am
Thread Starter 
I think I installed the IC socket with the notch facing the wrong way. Is this a problem if I make sure to drop the op-amp in facing the CORRECT direction?
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post #6 of 11
4/18/10 at 7:07am
Building my first cmoy today, saw your post and wanted let you know Tangent sells the ALPS RK097 pot with built-in power switch. Now on to my post...
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post #7 of 11
4/18/10 at 9:13pm
On your second CMoy consider replacing the amplifier input capacitors with a 1K ohm resistor for each channel. I did this and the quality of the sound improved noticeably (I am using 32 ohm phones). This was a recommendation from either Pars or Fallen Angel or CFcubed if I recall correctly.

F
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post #8 of 11
4/19/10 at 9:35pm
the input capacitors are there for a reason. They are used to strip dc voltage from the input signal. If Dc voltage is applied to op amp inputs, it will amplify it Xgain times. Then 0.6 V DC offset with gain of 10 will come at 6 V from op amps output straight to headphones. It will burn most of the headphones voice coils almost instantly.

Most mp3 players don't have dc offset in their signal, so that mod will be safe. But measure first your sources dc offset, it would better be couple millivolts max if input capacitors are omitted.
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post #9 of 11
4/19/10 at 11:34pm
sorry to thread jack, is there a cmoy with a buffer stage that i buy the PCB from?
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post #10 of 11
4/20/10 at 3:20pm
Flux is the "magic" you need to solder wires to the pot! Or anything fine like that, especially SMD stuff once you get to that point. Tangent sells a bottlle that will last forever.
Here is the process that I use, practice it a bit and you'll be a pro in no time.
Strip and tin the wire, hold the wire against the pin on the pot, in the position you want it to be in when it is soldered, apply a small drop of flux to the joint, clean the tip of your soldering iron and touch it to the solder so as to pick up enough solder to make the joint, now touch that blob of solder to the wire and pin that you just fluxed, the solder should should almost immediately form the joint, remove the iron! Viola! a nice shiny, strong joint! This is an invaluable technique to learn.
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post #11 of 11
4/20/10 at 8:29pm
Spacehead, you are certainly correct about the purpose of th input capaitors. I should have discussed DC offset from the source in my note.

F
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