[tamtamstudio]

:oops:
thank you very much..
the ripple is 0,77V

is it correct?

[peterc]

What is the ripple before & after the reg?

[tamtamstudio]

:?:  ok, I've got hallucinations..

My DMM sign:
0,25V after TL783, after 5 sec (and goes up ...)
0,3V before TL783

strange?

[jensenmann]

I have 0.18V ripple before (220uF filtercap) the regulater and 0,0000V after (another 220uF smoothingcap) the regulator. For the measurement you have to wait around a minute until the tube is heated and the quiescent current is biased.
But anyway, obviously you´d better change your regulator.

[tamtamstudio]

:wink:  I think is a good idea.. I'll tell you

[tamtamstudio]

:grin:  Finally solved problem!
At first i changed the rectifier without success.
Second, I changed the caps! Was quite Perfect!
now the sound is perfect, no 100Hz hum noise. Thank yu guys for the suggests!

[Greg]

Congrats on the fix...

[jensenmann]

:thumb:
Well done

[analogical]

Tam, which caps did you replace?

[maxheadroom]

it must be C14 and C15. increasing the values gives better ripple values.

[analogical]

Ok, ready to tackle my hum issues.  Firstly, C14 and 15 are the nice big ones; I don't imagine the trouble is having too small of caps here.

It passes audio just fine, save for the hum as seen below.
The volume knob does change the volume of the hum. The 140 @ -44db is with the gain and output knobs most of the way up.



Any advice on what to look for? Ripple was the first to check. What are the acceptable voltages? PSU B+ and where else to look?

Also upon first power up, R33 got real hot once, but now it's ok.

Any help would be appreciated.   :oops:  thanks!

[MrShhh]

#1 culprit is heater noise
#2 would be xfmr location
#3 would be ground loop between source and amp and output listening device (headphone amp or stereo amp and speaks
#4 would be inadequate filtering-but if you followed the schemo, this is a non issue
#5 would be excessive lead length and location on input wiring.

There is a #6: EMI from the power switch inducing hum on the channel 2 output pot/front panel pcb. This gave me 100Hz hum on the right hand channel only.

I had zero ripple on the HT, 2mV on the heater supply, perfectly clean left channel, but annoying hum on the right when the output pot is above halfway on all gain settings.

Moving the power switch & pcb away from each other eliminated the hum. Grounding or not grounding the power switch or pot casing made no difference so next I insulate then shield the power switch with metglas foil and hey presto...the hum is gone for good. 2 zero hum channels at all gain/output settings.

[SaMpLeGoD]

Hello, i'm having the same humm problem... I think is the ripple also, can I put some caps in paralel with C14, C15? to rise the value of the caps and get rid of the ripple? or do I really need to change that big one (yes, my is 2 in one big cap) for two with higher value?
Thanks,

Eddie

[Kingston]

measure the hum with some free FFT tool (like your DAW and some VST plugin like voxengo span) and your soundcard. otherwise you are just guessing.

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