Stereo micro amp, weird sound

[Bagge]

I just finished building the stereo microamp into a Hammond 1590B box. I use it as a preamp for my Ibanez semiacoustic. It does give a wider sound.
However, when I crank the volume up, it gets this weird sound like a heartbeat. Although I've built a few projects before, I lack the theory part of electronics. I hope some of you can help me with the issue. Could it be the opamp ( 4558)?

Byt he way its the schematic from Tonepad http://www.tonepad.com/project.asp?id=28

[petemoore]

Did you PCB it?
 I ask because layout and wires may cause that. Certain wires shouldn't run closely parallel to one another.
 You could try a cap across the V+/V-...I do kwik test right at the battery clip...try 47uf or 100uf there...put _ on cap to _ on battery same for +'s.
 Are you using a wall wart?...try a battery
 If you have spare OA...might as well try another one.
 Are b oth sides doing that?

[Bagge]

Thanks for replying

Yes I did pcb it, and I do have long wires inside. The weirdest part though is, that when I use channel one cranking channel two volume up also affects the signal and causes the heartbeat sound in channel one. Could I try tlo72 instead as a dual opamp?

[Bagge]

Uhm..
It seems I used a different diode than suggested at +9v. The schematic said 1n4001, I used 1n4007. Could this be the issue?

I do use battery

[MartyMart]

Uhm..
It seems I used a different diode than suggested at +9v. The schematic said 1n4001, I used 1n4007. Could this be the issue?

I do use battery

That should be fine, 1N4001/2/4/6/7 will just offer "beefier" protection to reversed current.
The "motorboating" as its called,  should be stopped with the advice given
ie: shorter wiring, power and I/O wires separate or possibly screened and the 100uf power filter is always a good idea IMO.

Cheers,
Marty.

[Bagge]

When the boat comes in.

Gee, what a night. I wanted to try the TLO72, but when I tried to remove 4558 the socket went off. I don't use holes in the pcb, but solder directly on the board. So I had to remove it all, and start all over. Anyway, I did finish, and shortened the wires; no big difference. The 100uF cap did lower the boat sound, but didn't remove it. I tried TLO72, and there were no "motorboat" at all. The level was also reduced some.
I found out that my output cap is a polarized 1uF instead off nonpolarized 1uF from the schem. Would that cause the sound? Tomorrow, I'll try some shielded wire for i/o.

[petemoore]

I don't see why not. LF oscillations that change with volume control can be other things, OA and caps tend to want to 'choose' a frequency sometimes...sometimes not...
 But that cap is worth swapping for the specified one...that's how I'd see if that's it.

[Paul Perry (Frostwave)]

I suspect the problem is that the power supply isn't handling the maximum current load, so the power rail wobbles. (whihc would explain how one channel affects the other).
Some op amps (like the TL072) are more resistant to supply line wobbles than others, so...

[Bagge]

So a wallwart instead of battery may solve the problem? Otherwise I'll have to live with the boat or switch to TLO72, though it's not quite the same sound.

[Bagge]

It seems the microamp is debugged. No more "motorboat".
I changed the output cap from polarized elect 1uF to a foil cap 1uF. I resoldered ground wires to jacks. I tried a new battery. The battery clip neg. wire went off, and it got me thinking that it may have shorted at a point. But its fixed now. I'm not sure what did the trick, but now I'm getting curios. I think I'll put it on stripboard so I can easily try different components. Maybe it's the caps that makes the difference?

Thanks for leading me on the way!

[petemoore]

Finding problems...losing solutions...happens all the time.
 Wh-If 'it' works, I generally move on...maybe stick it back on a WWart one time to see what changing PS did.