I can confirm that a suitable replacement volume or balance control is 502-0312 NTE Electronics 50K OHM 1/5W LINEAR. It isn't an exact replacement as it has a slightly shorter D shaft but it's enough for both set screws to secure the knob. As a bonus the knobs now have a smoother weighted feel so it could be considered an upgrade. There's still an issue when the volume is set all the way down where sound still passes through and the balance is off. All is well when the volume is slightly raised. I tried adjusting the four trim pots but it didn't make much difference and I set them back to the original settings.
I've been trying to revive an Iris preamp that was non-functional. Apart from a blown fuse and a burned tantalum cap on the remote input board I didn't see anything else odd about it.
The symptom is this:
Channel Right tracks properly with regards to volume.
Channel Left does not. If you nudge the volume pot even a very small amount the volume in the right channel jumps to 3/4 volume immediately.
Nudging it back just a tiny bit causes the left output to drop back to barely audible. So a very very small increase in the volume pot cause the volume to jump drastically, but only in the left channel.
I verified that the pot is tracking correctly out-of-circuit.
I also replaced the usual 4.7 and 2.2 uF Tantalum caps that often cause issues.
Can someone point me in the right direction?
I am having trouble deciphering the schematic - it's quite complex with regards to the optical photo resistive volume controls.
Oh, and to be sure it wasn't related to the remote input board I removed it from the preamp. Same issue.
The symptom is this:
Channel Right tracks properly with regards to volume.
Channel Left does not. If you nudge the volume pot even a very small amount the volume in the right channel jumps to 3/4 volume immediately.
Nudging it back just a tiny bit causes the left output to drop back to barely audible. So a very very small increase in the volume pot cause the volume to jump drastically, but only in the left channel.
I verified that the pot is tracking correctly out-of-circuit.
I also replaced the usual 4.7 and 2.2 uF Tantalum caps that often cause issues.
Can someone point me in the right direction?
I am having trouble deciphering the schematic - it's quite complex with regards to the optical photo resistive volume controls.
Oh, and to be sure it wasn't related to the remote input board I removed it from the preamp. Same issue.