Cmoy Headphone amp

[Puffin]

I have built one of these using a schematic. I am having some problems getting a stereo output. If I join one of the input channels to the headphone socket ground I get stereo. If not I only get mono.

I also have an issue with the volume pot. At low volumes it is mono, bit louder, stereo, bit louder, mostly in right ear.

I have a DC reading mis-match at the headphone out of 23mv on one channel and 182mv on the other.

Can anyone help?

[Atilla]

Ok, all of this sounds wrong, so you'd better start posting the exact schematic you used, some photos if possible, and a little more detail on what you have connected where.

[Puffin]

Schematic/layout here

http://bp2.blogger.com/_0URxOBSyTPQ/...b_standard.jpg

[Atilla]

I think this schematic can be very confusing. For one, it can lead you to believe that a single 10k potentiometer is enough for both channels, which is wrong. For stereo, you obviously need a dual potentiometer, one that controls both inputs with the same knob.


What kind of potentiometer are you using?

[Puffin]

I am using a dual pot.

[Artie]

Hey Puffin. Your first paragraph suggests that perhaps two different problems may exist. It sounds like maybe you have one input reverse-phase. Probably in the wiring of the input volume control. The source device will use a common ground, so when you touch one input to ground, you get both channels.

An out-of-phase condition is much easier to identify with speakers, because the bass cancels. But not so with headphones.

It also sounds like you may have greater gain in one channel than the other. But then again, this may just be a quirk of the mis-wiring.

So . . . I'd double check the pot wiring real close first. (Input wiring too.) See what that does, then recheck your resistor values if there's still a problem.

Hope this helps.
Artie

[mjf]

hello.
ground connection between the two 9v batteries?
greetings............

[Atilla]

There is a virtual ground, based on the resistor dividers and the caps. The schematic looks fine, I guess it's only the wiring that is mistaken. Check carefully how the inputs and outputs are wired.

[Puffin]

Thanks for all your replies. I have been looking at the thing and trying various wiring combinations for the last 2 nights. I may have to start from scratch again.

I'll let you know how I get on.

[lgreen]

Puffin, sometimes those minijack and 1/4" connectors are funny and don't conduct consistently. I have a miniplug that is new from digikey and does not conduct on the left channel unless bent a certain amount but it looks perfect.

You may want to check you connectors if your wiring looks ok. Or post a pic of your wiring and people here will look at it.