Oscillation

[poobah]

Are R22 & R23 wirewound resistors? If so, make sure they are non inductive.

You can test by shorting (jumper) from B of Q12 to B of Q13... temporary.

[amplifierguru]

Hi raveenvijendren,

Is R24 a wirewound? Is it inductive? Try replacing it with a same value 1W or 2W carbon film or metal film.

If still a problem with slight oscillation , try paralleling another with it, totalling 4 ohms. It may be due to component spreads one channel stability is a little less benign than the other.

Cheers,
Greg

[raveenvijendren]

Good Day,

All the resistors I used in this amplifier is the cheap carbon resistors with 5% tolerance(not exactly high fidelity). No wire wound or metal film(too expensive and I'm 16). What about Mr. Thanh's idea of:

Q12 Q13 ,protection tst
a 40n cap from B to C
a 47p cap is parallel with R10


Anyway, I am not an expert, so I will try everything I get from you all, and hopefully be able to null the oscillations. Thank you very much for the help.

[thanh]

I weren't using those cap in my amp before . My amp became a occsilator after I had added the protection circuit . I went to www.diyaudio.com , and a guru recomend me that thing

[poobah]

Raveen,

I suspect that the protection circuit, Q12 & Q13 may be your oscillation. Try the jumper form B/Q12 to B/Q13... it will turn off the proctection circuit and prove where the problem is located.

Protection circuits like these are strong cause, sometimes, of oscillation.

[raveenvijendren]

Good Day,

I would like to apologise to everybody in this thread about my oscillation problem. I tested the amplifier PROPERLY this time, and I only found about 0.8 mV of noise and about 4 mV of hum present(on both channels). No 20 MHz Oscillation. The reason I saw the oscillation was because I connected the amplifier to a Philips CD ROM headphone output. What a cheap junk that thing was. I read the scope properly this time and found that the CD ROM outputs a 1.25 MHz sinewave in the headphone out. My silly mistake of connecting the amplifier there. Very sorry for troubling everyone in this thread.

On the other hand, everyone here has given me very useful information regarding amplifier oscillations. Thank you all so much and again, I am very sorry for the inconvenience caused by my sloppy troubleshooting. Thank you.

PS: Please be careful where you connect you amplifiers.