[robzy]

Hey guys, i just finished building my first CMoy and i love it

Its nothing special - standard 1% resistors, standard capacitors and an OPA2132PA.

Firstly, would the potentiometer be okay as a volume control:

http://www1.jaycar.com.au/productVie...=&SUBCATID=802

Also, how on earth do i hook up the potentiometer?! I have a single gang, normal size, potentiometer here that i am trying to hook up to a single channel but nothing i do seems to work.

Input jack: Circuit board:
(left) ----= =--- (Where the left channel usuall connects to, a capacitor)
(ground) --= =---- (ground)
(right) ----= =--- (Where the right channel usuall connects to, a capacitor)


and if the potentiometer has 3 prongs, 1 being left, 2 being centre and 3 being right, what do i do with that all??? I have tried connecting the left channel from the input jack into prong 2 and connecting prong 1/3 to the capcitor, but the volume doesnt change

, i am well and trully confused.

Lastly, if i just plug headphones in and walk around the room with the cmoy plugged in, when i go around to light switch and other things there tends to be a lot of static - now, i did put lots of soldier on but i dont think it woulda been that much more than i meant to.

Thanks a heap

Any help would be much appreciated,
Rob.

 

[Megaptera]

There's been some good talk about that particular pot lately, but I don't know how many people here have tried it.

Quote:

Also, how on earth do i hook up the potentiometer?! I have a single gang, normal size, potentiometer here that i am trying to hook up to a single channel but nothing i do seems to work. Input jack: Circuit board: (left) ----= =--- (Where the left channel usuall connects to, a capacitor) (ground) --= =---- (ground) (right) ----= =--- (Where the right channel usuall connects to, a capacitor)

Which are you trying to do, hook the pot up to one channel or both? I'm afraid your diagram is confusing me a little. You've got a mono pot (single gang) that can only do one channel at a time, so if you're connecting that, ignore the right channel stuff completely. One pin will be signal in, one will be ground, and one will be signal out. If you want to do both channels at once, which you do, you need a dual gang/stereo pot.

Basically, which pin does what can be read on the pot's datasheet, or you can use a meter and experiment. The in/out can actually be reversed (it just affects which way you turn the knob to lower the volume), so it shouldn't be too hard to find that part out.

From there, you want to connect the signal input and signal ground to the appropriate pins on the pot, right from the jack. The pot's output pins and ground pins will then go to the amp board's input.

Quote:

Lastly, if i just plug headphones in and walk around the room with the cmoy plugged in, when i go around to light switch and other things there tends to be a lot of static - now, i did put lots of soldier on but i dont think it woulda been that much more than i meant to.

Sounds like interference. Is your amp cased up yet? If not, it's nothing to worry about yet -- a metal case will probably block most of it. If your solder joints look blobby, it won't hurt to clean them up, of course

And welcome to Head-Fi, too

 

[robzy]

Thanks for that

(And thanks for the welcome)

So for example if my pot has a pinout(?) like this:

\ | /
(1)(2)(3)

which would be signal in, which signal out, and which ground (And i understand that 1 and 3 might need to be reveresed) And yes, i also understand that i can only do one channel atm, im just waiting untill i obtain a dual gang pot, is the one that i give the url to in my previous topic okay?

(Does that diagram mke more sense? :S)

And as for the interfereance, that would make sense, atm its in a makeshift plastic case, proper metal tin coming soon though

 

[Earwax]

The pot you linked to is a linear taper, you really want to find one with an Audio taper instead.

 

[Sal]

If the light switch is a dimmer switch, it will thow out a lot of RF interference. If I plug in an electric guitar in a room with a dimmer switch, the noise will very easily be heard through the amp. Now that's an extreme case, but illustrates how much noise some electric devices can radiate.

Metal cases help a lot to block those kinds of interference, but it is also important to use shielded wire within your headphone amps or very short wires and to ground the proper parts of the circuit well.

 

[robzy]

Quote:

Originally Posted by Earwax The pot you linked to is a linear taper, you really want to find one with an Audio taper instead.

Would that be a log pot? Or would i have to get one that specifically has an audio taper?

Sal, yes, it is a dimmer. *looks at the wire in his CMoy*, might be worth investing in sheilded wire

 

[Megaptera]

I would wait and see how well the metal case works on blocking the interference before rewiring it. If it's still a problem, but only a problem in certain locations, it may or may not be worth rewiring the entire amp. I'm guessing that the wire you've got in there would fall under "really short wire" -- the interconnects would be picking up more noise than the hookup wire.

If you wanted to try (warning: science teacher mode) an experiment, you could wrap the plastic-case in aluminum foil and see if it does anything. And the interconnect. I'm not sure if it would do much good, but at the very least it stops the mind-control rays from Saturn...

Quote:

which would be signal in, which signal out, and which ground

The diagram is clearer, but unfortunately without a datasheet or trial and error your guess is as good as mine. Do you have a model/type? The datasheet would be the first place to look, since it can vary from model to model. If I were to guess, I'd say the ground pin is probably the middle pin here.

Just out of curiousity, why are you connecting the mono pot? There's no practical benefit, other than experience -- You'll have one channel going at full gain and the other attenuated, not an evenly matched mono signal in both channels. Aside from just learning how to wire pots and the simple pleasure of soldering two things together, you're probably better off leaving out of the circuit until you get a stereo pot.

 

[robzy]

Quote:

Originally Posted by Megaptera Just out of curiousity, why are you connecting the mono pot? There's no practical benefit, other than experience -- You'll have one channel going at full gain and the other attenuated, not an evenly matched mono signal in both channels. Aside from just learning how to wire pots and the simple pleasure of soldering two things together, you're probably better off leaving out of the circuit until you get a stereo pot.

It might be a week before i get my dual gang pot and even when i do i still need to know how to wire it up. Origionly though i did just want to do it to see if i could get some kind of volume control. I guess ill just wait though.

Thank you everyone for your help, its great to see a forum with people this helpfull

Rob.