First time post here. I'm having some interesting issues with my first DIY project, an LM6172-based CMoy design. (I thought, perhaps too audaciously, that the challenge of getting that chip to work would be more rewarding than reproducing the original circuit.) The amp is based on the schematic provided on the Tangent "Working with Cranky Op-Amps" page, with an LM317/TLE2426 power supply regulated down to 14V from a DC wall adapter (currently 24V). I am using a pre-patterned perfboard with pads arranged in the breadboard style, and my layout is as shown on the cartoon image I've linked to below.
My layout: https://www.dropbox.com/s/rqu1oedi2xsda4m/cmoy_layout.png (black lines are insulated wires, blue lines are jumpers/leads, purple lines are out to the headphone jack. The power section is not complete as shown, but the IC's are in those places in the power supply on the actual PCB.)
My problem is an intermittent noise in only the left channel (this channel is actually on the left in the layout pictured). It is rather "static-y," sounding like a more mellow version of a piece of paper being ripped in half. It's quiet, unnoticeable except during quiet passages of music (and of course when no input signal is provided). It comes and goes without any apparent pattern, typically in small pulses that range from a fraction of a second to a few seconds in length. The circuit may go minutes without making any noise at all. I don't believe the amplifier is oscillating badly, as music still sounds good, the chip is not getting hot, and current through the circuit is well below its maximum.
I have tried a couple things to get rid of this, including increasing the gain (R4 to 620K, rather than 470K) and grounding the unused PCB pads near the offending channel. Neither of these helped. Since the amp sounds fine with an OPA2134 chip, I'm hesitant to try soldering this chip to the board until I understand better where the noise signal is coming from. Any ideas as to what is causing the noise and/or why the circuit is picking it up would be very welcome. Perhaps some type of interference? I am kind of a big noob as far as circuits go, so many thanks in advance in case anyone has an idea.
(I'd also be interested in any feedback on the layout of the circuit as well---though I do understand that a patterned board like this might be problematic with a high-speed op-amp!)