[btol]

Hi Everyone,   I'm a newb with very very little electrical knowledge having a go at the CMOY headphone amp. After a few glitches, I made it to setting up the enclosure and trying to figure out how to wire the panel components when I realized that I might have another issue.  I couldn't find the Alps pot online that Tangent recommends (Alps RK097) so I went to Radio Shack and purchased the substitute that he listed (271 1732). As I was cruising through the various cmoy forums to determine what lugs on the pot go to which part of the board, I ran into a site that said if the Shack pot is being used, R2 needs to be changed to a value between 200K and 1M. Apparently, there's a problem with the fact that the Alps pot is 10K while the Shack one is 100K. So I'm at a crossroads.   Do I go the R2 switch up route? If so, what values would you recommend that I change them to? Or is this false and I should just go ahead and use the RS pot without changing the R2's? I've also heard that cheaper pots like the Shack one can have issues when playing at lower volumes. Should I scrap the Shack pot altogether and try to track down the Alps one? Lastly, if I you think the Shack pot shouldn't be a problem, I'd greatly appreciate any advice on which of the lugs I need to use and where those should be connected to on the board and the various panel components (http://tangentsoft.net/audio/cmoy-tu...ayout-0150.pdf).  I went ahead and included pics of the substitute pot in case it's helpful.   Feeling a bit confused due to my lack of knowledge so thanks in advance for the help.

 

[wakibaki]

Go ahead and build the amp with the parts you have got. A 10k pot or higher values for R2 would be preferable in a sense, but the amp will still work OK. Lower values result in less hiss, if you find the hiss is unacceptable in practice, then try to get a 10k pot, but the difference will not be enormous.
 
There are 3 tags clustered together for each pot (6 if you count both pots). The 2 tags at the top (in the second picture) are for grounding the metalwork of the pots, you can ignore them.
 
The middle tag of each group of 3 is the wiper, it goes to the arrow connection in the diagram, one for each channel.
 
If you hold the pot as it would be installed in an amp, with the shaft pointing towards you and the tags rotated to the bottom, then the left-hand tag gets connected to ground and the right-hand one gets the signal.
 
w
 
You may notice some imbalance between the channels at low volume, but wait and see. If you're lucky the pots will be well enough balanced.

 

[btol]

Thanks, Wakibaki!
 
I was starting to get a little worried about getting a response - I imagine head fiers have had their fill of cmoy threads. 
 
Your instructions are VERY detailed so I appreciate that.  I'll work on this over the course of the week and report back this weekend (hopefully sooner).  Here goes...

 

[nikongod]

Quote:

There are 3 tags clustered together for each pot (6 if you count both pots). The 2 tags at the top (in the second picture) are for grounding the metalwork of the pots, you can ignore them.
 

 
EEEEh, on some pots they are for hooking up a "loudness" or other volume-related EQ control. Ignore them yes, but never ground. 

 

[wakibaki]

Quote:

 
EEEEh, on some pots they are for hooking up a "loudness" or other volume-related EQ control. Ignore them yes, but never ground. 

 
Nikongod is correct that the 4th. terminal on some pots is used as part of a 'loudness' control, however it appears from the picture that at least one of the additional tags connects to the metalwork. 'Loudness' taps are generally offset towards the low end of the travel (which these would not be if they are loudness taps) and considering that some pots do have a tag intended for grounding the case I thought it a needless complication to enter into an investigation of all this in an already wordy post.
 
It's typical of forums like this that you can't get an answer to a simple question but when you do someone will contrive to raise an objection in the least favourable of terms, and without taking the time to offer a comprehensive explanation which would relieve me of the effort of making a further post.
 
Whatever the case in this instance you can ignore the additional tags.
 
w

 

[btol]

Hi again -
 
I avoided the two tags, followed as instructed, and...success!  I didn't hook up the i/o jacks yet but I hooked the pot up to the ground and inputs on the board then used the alligator clip test per Tangent's instructions (the only difference being that I alligator clipped the ins from the source patch cable to the pot's inputs instead of the board's) and the pot works!  There was a slight hiss when I turned it up to louder volumes but I think that's my ipod or my music files.  I tried my ipod unamped at full volume and sure enough, there was a milder version of the hiss.  There's also some slight crackling when I turn the knob but I'm hoping a little deoxit can fix that.
 
Thank you for the help!
 
So now I'm going to do a test with the pot mounted into the Altoids tin to make sure there are no issues with it being in the tin.  One problem I've been running into is the stupid little piece of metal sticking out of the front of the pot.  If you look at the bottom of the two pics that I posted, it's on the lower left hand side, on the rim of the pot and just to left of the threads on the knob.  When I previously tried mounting the pot into the tin, that piece of metal causes the pot to mount in a crooked fashion when the nut is fully tightened.  If I loosen the nut a little, I can get the pot to straighten out but that causes the pot to jiggle around every time I turn it.  Am I doing something wrong?  Is there a way to tighten the nut fully and still get the pot to mount flush with the tin or should I punch another hole into the tin so that the obtruding piece of metal doesn't get jammed on the tin's inside wall?
 
B

 

[Avro_Arrow]

You can either punch a hole for the tap or get rid of the tab.
The tab help locate the pot and keeps it from rotating if the nut gets loose.

 

[btol]

Got it, Avro.  How do you recommend I cut it off without damaging the rest of the pot?  Just a pair of beefy wire cutters?  I'd like to avoid punching another hole into the tin.
 
B

 

[Avro_Arrow]

You can probably just bend it out flat or use beefy wire cutters.
Don't saw it off.

 

[btol]

The wire cutters worked like a charm!  Much appreciated!