Rockford T30001bd

[shawnk]

Hey guys!

I have this T30001bd amp here that I have recently repaired the output stage.

The amp is working fine thus far (low level testing) save for one problem. I'm getting a pretty nasty turn on spike which is quite audible through the speaker. When the amp first powers up, the "protect" l.e.d. is engaged for aproximately two seconds as the rail caps are charging, then the amp comes out of protect and the "power/blue" l.e.d. engages and this is when I'm getting the audible spike (over 1vdc).

I've checked the other threads pertaining to the T30001 but didn't find anyone having the same problem.

Any insight would be appreciated!!!

 

[Perry Babin]

Is the spike less if you set the subsonic filter on?

 

[shawnk]

It's the same in either position.

Thanks for the reply Perry!

 

[Perry Babin]

Do you read more than about 0.05v DC on the output terminals of any of the audio op-amps in the amp?

 

[shawnk]

Yes actually. I'm getting between .5v-.6v on all of them. That's also for both output 1 & 2 These figures don't change even when adjusting any of the pots/switches/etc.. if that helps in advance?

Thanks!

 

[Perry Babin]

If you're getting 0.5-0.6v on pins 1 and 7 of all of the 8-pin audio op-amps, you may have a ground problem. Where was the black probe when you measured the voltage on the op-amps?

 

[shawnk]

Just went back and I'm getting the same results. I did however, notice that U105 U106 & U107 are in fact effected by the gain pot. However, only pin 7 of U105 is effected by the gain and pin 1 rests @ 0.58v like the rest.

I'm using the B- terminal on the amp for the meter's neg. probe

Thanks

 

[Perry Babin]

Try using the negative speaker terminal.

 

[shawnk]

Same results bro

Thanks

 

[Perry Babin]

Connect the input RCA shield to the main ground terminal and re-check them.

 

[shawnk]

Ok, I grounded the RCA shield and now both outputs of U100 through U104 rest @ 0.04 - 0.00v

Both outputs of U106 & U107 vary with the gain

Pin 1 of U105 is 0.00V and pin 7 varies with the gain

Thanks

 

[shawnk]

Still having a hard time tracking down this audible spike. Even when jumping the RCA shield to ground the spike is still present.

Without the jumper in place, the outputs of most of the op amps resort back to ~0.5-0.6v.

Another oddity I have discovered is a strange voltage swing on the speaker outputs when adjusting the gain pot (no signal applied) I was slowly adjusting the gain pot to find the associated op amps and noticed the subwoofer was oscilating (very slowly, but easily visible) I then metered the outputs when adjusting the gain pot and noticed a voltage swing from 0.0.25vdc to ~14vdc then drops back to its resting point of ~0.0.25v when I stopped turning the pot. There's something odd happening in this input stage :-\

 

[Perry Babin]

Does U105, pin 7 vary (DC) when you adjust the gain?

Does the subsonic filter make a difference in the swing when you adjust the gain?

 

[shawnk]

Yes, the subsonic filter does effect the voltage swing. With the switch "on", there's not nearly as much of a "swing"

With the switch off, I'm reading -.04v to -1.0v @ pin 7 of U105... adjusting the gain from min to max.

With the switch on, I'm reading -0.0v to -.123v @ pin 7 of U105... adjusting the gain from min to max.

(RCA shield as ground reference)

Thanks

 

[Perry Babin]

You need to leave the ground jumper on for these tests. Rockford floats the RCA shield about 1/5v above the amp ground for some of the op-amps. Others are referenced to the main ground. When you plug the RCAs in from a conventional head unit, they are pulled down to the level of the main ground.

 

[shawnk]

I didn't mention it, but the jumper was still in place for these readings.

Thanks

 

[shawnk]

Shameless bump

 

[Perry Babin]

Do you have a scope?

 

[shawnk]

I do.

 

[Perry Babin]

For the DC surge that you have when you adjust the gain, I'd suggest replacing any op-amps that have more than 0.02v of offset. I think you'll likely have to replace most of the op-amps in the crossover, subsonic and gain circuits.

Do that and see if that decreases the pop.