Negative Feedback Question

knowledge base for the classic Dynaco ST70

Re: Negative Feedback Question

Postby Shannon Parks » Sat Sep 24, 2005 7:11 am

BAMA wrote:I built ST70 from scratch using the schematic in the manual I found in this forum without using the board. I finished putting all but I am having problem...

When I turn on the amp with shorted RCA input, all I get from the speakers are only vibration. But I disconnect negative feedback from 16ohm tap and turn on amp with CD input, I can hear music but it is really low. I guess the problem is something to do with the negative feedback but I do not know what to do... Does anyone know what can be the problem and what I need to do to fix the problem?

Thanks in advance.


Hi BAMA,

Is this the diytube schematic or another? As to the vibration aka oscillation, swap the signal wires going to the EL34's like an 'X' to swap the phases around so that you can get negative feedback instead of positive feedback from the 16 ohm tap.

Why you have very low music with no feedback I don't know. Could you take some close up photos of the guts and mail them to me for posting? Needless to say, double check all the hookups and resistor and cap values.

Shannon
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