Oscillations in output waveform

[svkr2k]

Hi all,

Oops ! I forgot to ground the heatsinks !!!

Today, I connected the heatsinks to ground and everything works fine !
Thanks for everyone who gave me ideas.

I still have one issue: Low frequency "Hum" is audible when I set the volume to higher side. (Probably, mains frequency???) Any ideas to adoid this?

Regards,
Raj.

[sgrossklass]

See whether it's still there with the inputs shorted.

I never noticed this thing only has a specified damping factor of 20 at 8 ohms (0.4 ohms R_out). Funny little amp.

[gootee]

Originally Posted by svkr2k

Hi all,

Oops ! I forgot to ground the heatsinks !!!

Today, I connected the heatsinks to ground and everything works fine !
Thanks for everyone who gave me ideas.

I still have one issue: Low frequency "Hum" is audible when I set the volume to higher side. (Probably, mains frequency???) Any ideas to adoid this?

Regards,
Raj.

See if the hum is still there with nothing connected to the inputs.

If not, then it could be that the input signal/gnd pairs have too much enclosed loop area. And it could also be that some conductor pair with mains frequency has too much enclosed loop area.

[svkr2k]

Originally Posted by sgrossklass

See whether it's still there with the inputs shorted.

I never noticed this thing only has a specified damping factor of 20 at 8 ohms (0.4 ohms R_out). Funny little amp.

Hi sgrossklass,
I couldnt understand what you mentioned on damping factor, could you please explain. Thanks a lot !


All,
I believe I should mention this ... I replaced all electrolytics with common grade (probably industrial) and not "audio grade" capacitors. Is this okay? Or how will this affect the performance of the amp?

Thanks !!!
Raj.

[gootee]

The electrolytic caps will probably be fine. I would worry more about the matching of the transistors you replaced.

Did you try testing for hum with the inputs open (not connected) and with the inputs shorted, as we asked?