[till]

Hi all,
as my first project, I just assembled a CMOY according to Tangent´s excellent tutorial and the original CMOY article on Headwize, it is a Levallois variant with Meier crossfeed. The problem is that I can only get it to work at full volume or at a ridiculously low volume. The potentiometer I used is a dual 10k log.
If I use only four wires (no ground, just input and output for each channel), I get full volume regardless of how I turn the pot.
If I wire the remaining two pins to the ground, I can hear a very faint sound, but only with cheap low-impedance earbuds and the pot turned fully counterclockwise.

As discussed in this thread
http://www5.head-fi.org/forums/showt...threadid=43566 ,
the resistance between input and output decreases when turning the pot clockwise, Rmax being about 9K for each channel. R between output and ground increases when turning clockwise, but Rmax is only 30 ohms here. So I assume that my input signal is leaking to the ground, but I have no idea how to prevent this.

Hints, anyone?

Till

 

[guzzler]

what pot are you using? If it's for a small CMoy, give me a PM as I've still got a few of the good quality, very small Panasonic EVJs which are otherwise impossible to get in Europe left over from a group buy and i'd be happy to ship a couple out to you

g

 

[till]

The potentiometer is a Radiohm JP160KC - big, cheap and made mostly out of plastic. Its size causes no problem because the case I picked is fairly big (an Altoids box would not be sufficient for all the components). But as soon as my next project is underway, I might be very interested in the Panasonic pots

 

[Pars]

Quote:

Originally posted by till <snipped> The potentiometer I used is a dual 10k log. If I use only four wires (no ground, just input and output for each channel), I get full volume regardless of how I turn the pot. If I wire the remaining two pins to the ground, I can hear a very faint sound, but only with cheap low-impedance earbuds and the pot turned fully counterclockwise. As discussed in this thread http://www5.head-fi.org/forums/showt...threadid=43566 , the resistance between input and output decreases when turning the pot clockwise, Rmax being about 9K for each channel. R between output and ground increases when turning clockwise, but Rmax is only 30 ohms here. So I assume that my input signal is leaking to the ground, but I have no idea how to prevent this. Hints, anyone? Till

A couple of things. First, without the pot being hooked to ground, all you are doing is placing a variable resistor in series with the input... this will not provide any ( or much) volume control. A pot works like a variable voltage divider... as the resistance from the amp input to ground increases (and the series resistance decreases), more of the input signal is delivered across the iinput to ground, hence voltage iincreases.

That said, you have a problem if your Rmax from the input to ground is only 30 ohms. It should be about 9K. Check the wiring diagram for this pot again.

 

[till]

Quote:

Originally posted by Pars A couple of things. First, without the pot being hooked to ground, all you are doing is placing a variable resistor in series with the input... this will not provide any ( or much) volume control. A pot works like a variable voltage divider... as the resistance from the amp input to ground increases (and the series resistance decreases), more of the input signal is delivered across the iinput to ground, hence voltage iincreases. That said, you have a problem if your Rmax from the input to ground is only 30 ohms. It should be about 9K. Check the wiring diagram for this pot again.

Thanks for the help. I let it sit for a while, and now the problem is gone (I get 9K to ground) - it seems that I had a short to another compoent somewhere (I have a multi-board design) that wasn´t impressed at all by my wriggling of the main board. Anyway, now that the amp is running, I am quite content with it and myself

But the pot has to be replaced, there is a difference in volume between the channels. And some noise in one channel which seems to originate from the pot. I´ll get a better one, cheap pots just don´t seem to be the way to go...