Bad Power Transformer On Hamptone JFET Mic Pre?

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lightandmind

Member
Joined
Jun 9, 2012
Messages
13
I bought a mic preamp kit from Scott Hamptone a while back and I love this thing but it stopped working after about a week, I kind of a newb and Scott doesn't seem eager to help me troubleshoot so here I am.

Neither audio channel is working, the pilot light does not come on, but the 48v phantom power lights light-up when pressed. I tested the psu according to the schematic and it seems that I'm reading really low on everything compared to Scott's reference points starting with around 34vdc at V1, (R34), and ending with the meter reading -.5 at V9, (R52), would that be the power transformer you think?

IMAG0076.jpg
 
do you know the transformer specs? you may have bad/failed bridge rectification.  If your careful you can unplug the secondaries off the transformer  and hook them up to a dmm. measure the AC off the secondaires, if it fits with in spec then it's not the transformer. The big clue is the fact your getting around half the voltage you need at V1. there is not much upstream from that other then the psu transformer, the rectifier diodes and the resistor r34.

Also I at first would be more concerned with the voltages at the end of v9 as that is what powers your circuit, the 48V is for phantom for the mics the 24V runs the circuit.
 
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