Spectral dmc 20, phono help.


2001-11-16 8:30 pm
I have the phono board of the DMC-20 and I’m planning to run it by itself. I don’t have the actual preamp, just the phono pcb.
Anybody who knows the +/- feed voltages for the DMC20 phono board?

Never mind the attached photo☺️


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Mjona: thank you for the link.
Useful info I get:

Phono module Output Voltage:
17.7 VRMS, 50 V P-P max.

Assuming this refers to the actual phono pcb output.

Do we think the same as regular amplifier; rail voltage +/- 26-30 to get 50Vpp?

It would not be a bad idea to trace the circuit out to get an idea on its' workings.

Assuming this circuit has the form of an op.amp with a bipolar transistor output stage - there will be some voltage drops across these and any series resistors connected between the emitter and the output.

If the impedance of the RIAA is low the current draw and with Class A operating the output current demand and associated circuit voltage drops may require rail voltages in the region you mention.

The thought occurs that in the input LTP there would be a trim pot to set the output dc offset voltage - your module might have this correctly set up or at least within that zone. I have a hunch that might not be the case if the supply rail voltage is too low.

To pursue that you could look at setting up a test pair of LM317/LM337 with trim adjustments to experiment with.

I am assuming there are no voltage regulators on the phono pcb - if there are that might provide you with another clue.