Fender Ultra Chorus - Noise

[dyermaker8]

Ok,. I'm stumped. I'm getting bad-noise/static/hum from the right speaker only when the chorus is OFF,. ,. when the chorus is on everything is peachy,. I've traced the signal and the noise appears to start when I hit pin 6 on a tl072 which is marked on the schematic as u7b. But for some reason that seems a little off to me,.

Am I on the Right track? If so is there an easy to find substitue for a TL072C?

Thanks,
Dan

[Jam]

Try each speaker connected to the left side and if speaker is weak and distorted Replace it If you didnt try it

[dyermaker8]

no go,.its a solid state amp,. i'm troubleshooting using a signal tracer with amps speakers disconnected,.

[Enzo]

TL072 is just a general purpose dual op amp IC. You can find them anywhere. In their absence, you could substitute anytime with a 4558 or 4560 or 4580 IC, or even a 5532. There are many. The 8-leg dual op amps all have the same connections and are more or less interchangable. The guitar amp is not a critical application, so use what you have.

Mouser sells them for cheap. Wherever you order them, watch the package, the physical shape. Your amp uses the ful size DIP package, not the tiny SOIC.

Mouser stock number:
511-TL072CN $0.52 each 10 for $4.00.
513-NJM4580D 0.34 each

SOme ICs like the 4580 are made by more than one company, so there are extra letters, but they are all interchangable. NJM4580 = RC4580.

[dyermaker8]

Fun stuff,. I've swapped the opamp out out with 2 different 4558's and..well ,.its different. i'm not seeing the hum,. but now the gain is messed up on the right channel,. with the chorus off i'm getting nothing,. with the chorus on its probably a 1.4 of what it was with the tl072,. if i switch back to the tl072 the gain comes back,. but so does the noise. bummer,.

Thoughts anybody?

[dyermaker8]

Oops,. scratch that last one,. I went back to the 4558 and the gain problems is such,. with chorus on,. everything is fine,. similar to my initial issue,. but with the chorus off,. gain drops way way down,. probably an 8th of the left channel.

[dyermaker8]

One thing I've noticed ,. only signifigant difference between the two opamps,. reading dc at pin 6 ,. the tl072 reads .01v with chorus on and 1.96v with chorus off,. the 4558 reads .05v with chorus on and -16v with chorus off! pretty big difference,.

gratefull for any and all help,.
dan

[dyermaker8]

A Little more detail,. I'm really digging here,. on to some AC readings,. with chorus off,.

with the TL072 installed the right channel power transistor 2(Q11) reads 7v-0v-9v and transistor 1(Q10) reads 10v-100v-9v

with the 4558 installed the right channel power transistor 2(Q11) reads 0v-0v-0v and transistor 1(Q10) reads 0v-90v-0v

as far as ac on the opamp itsself,. with chorus on or off,.
pin 5 on either shows 40v pin 6 with the TL072 installed shows 4v with the chorus off. all other pins in any configuration show 0v.

Anybody?

[dyermaker8]

In the latest news,. I ventured out to purchase a TL072 and I have the same problem as the original TL072,. so nevermind all the jazz about the 4558,. now i'm just trying to figure out where i'm getting noise in the chorus circut when the chorus is switched off,. arghh,.

[dyermaker8]

ok., guess i'll go back to college.