Not enough NFB... OT problem?

[Ralle]

That would be the 27k resistor ( or 47k, 100k for that matter ), yes it's ok, and the nfb is wher it should be, but my suspision is that it's not the right amount of nfb for that setup...
Just to be clear: the nfb gets thrown back from the ot seccondary thru 27k and on trhu the 10k/100nF to the pi stage...
Where it gets thrown back, is where I suspect is something wrong... it doesn't get thrown back hard enough, or pushed back due to not enough amplitude from the ot... that's my theory... but a theory is just what it is, so...
I have borrowed a 50w superlead from a friend of mine, too see if what I'm seing on the scope is correct, for reference...

[Haze13]

Mmmm... NGB is formed by the 27k (47k-100k) and the 5k pot with a cap to ground... If the 5k pot is no longer the 5k or the cap is no longer the 0.1uf, then there will be less feedback, which will result as more gain from the PI.
Correct me if I'm wrong of course

[Ralle]

Well, a resistor or pot is more likely to brake (larger value ) than short, wich will result in a larger signal into the pi... and the .1uF cap could short or leak, wich would result in less presence from the cap...
But that's not the case here. Think of the nfb circut as intact... fully fuctional as it is. It's the signal going thrue the nfb that is too low... I was thinking more in line with the ot secondary having issues throwing back the signal thrue the nfb...

[Tazin]

Wouldn't there be a noticable decrease in the amps volume if the OT secondary was at fault?

[danman]

If I am thinking correctly Ralle, the NFB circuit simply taps a bit of the AC signal voltage, before it reaches the speaker, and sends it back to the PI. If all components in the circuit are functioning properly, the voltage should reach the PI. How much voltage reaches the PI would be determined by the size of the NFB resistor and which impedance tap on the OT it is connected to. Like Tazin mentioned above, if there was a problem with the NFB signal, the OT secondary would also have to be affected.

[Haze13]

Ralle, caps can increase their value when they are dying, it will result in higher filtration and less signal to the PI -> more gain:)

What impedance do you use for the speaker connection? 16ohm? Is it the same for the NFB?

[Carbia]

Can you post an image of what you see on the scope?

[Ralle]

I'm running an 8 ohm cab with 16 ohm nfb tap...
Regarding caps, I know that electrolytes tend to decrease in value when dying... does that applie tp coupling caps as well?

I can't post the pic... it's a bmp file...

[Carbia]

open the image on Paint and "Save as" JPG

[Ralle]

Ok... I'll try that...
No, that didn't work either... the board attachment quota has been reached...
What do I do now?

[Haze13]

photobucket...