Rockford Fosgate T30001

[Perry Babin]

Did you check U100-U107 for DC offset?

[seankane]

Yes I did and they had none but I will re-check today since I made an error in my last pin configuration when checking the others. Just to double check and confirm.

[Dr Zeus]

I had a similar issue with one of these amps. I somehow get the feeling people try to over-drive the input on these with bass boost, eq boost, full gain, and easy clipping. Something tells me the TL072 opamps cant take that much abuse, possibly due to regulated voltage levels or lack of protection on the opAmp inputs.

I even found one time that DC offset wasnt an issue, but the sound passing through was. If you throw a sine wave through the RCAs, you should be able to see the same wave of different amplitude on your scope; that is depending on the crossove and switch settings. In any case, if you have a sine wave on any of the opamp input pairs or outputs, then all 3 audio pins on that side of the opAmp should likely read something of the inputed sine wave. Again, I've found at least one case where a stuborn opamp had sound on input pins but nothing on output - not even DC, and the opamp was bad.

[Perry Babin]

These amps have problems with DC offset in the op-amps because there are so many in series and any amplification boosts the offset from the previous stages.

The op-amp will only have signal on all 3 pins of one channel if the non-inverting input has signal driven into it. If the non-inverting input is grounded (and therefore has no signal) and the input is fed into the inverting input, there will only be signal on the output of the op-amp unless the op-amp is driven into clipping. Then you may see signal on the inverting input but it will likely be very distorted.