Standel preamp module

[g1]

Then you must suspect the new module and proceed as 52Bill suggested in post #58.

[52 Bill]

52 Bill, I built the first version from the Standel website. My signal starts dropping off after the output of the first transistor. I built this circuit using NTE 159 for the first stage and NTE 129 for the second stage. [ATTACH]32966[/ATTACH]

I'd guess that the bias of the first stage is off. Did you use a 470 ohm or a 330 ohm resistor for the emitter circuit? What are the dc voltages at the Collector, the Base and the Emitter?

[jvm]

I used a 330 ohm resistor. Q1 voltages are: E-.49V, B- 1.12V, C- 11.46V

[52 Bill]

I used a 330 ohm resistor. Q1 voltages are: E-.49V, B- 1.12V, C- 11.46V

And the voltages for Q2?

[jvm]

Q2 voltages are: E-10.3V, B-10.7V, C-26.3V

[52 Bill]

Q2 voltages are: E-10.3V, B-10.7V, C-26.3V

I think that the base voltage or the emitter voltage is off. I think that the B-E voltage differential should be higher.

What value resistor did you use for the Q2 emitter resistor 2K2 or 22K? I can't tell if there is supposed to be a decimal point there or not. The second version schematic is a 2K2.

In fact how hard would it be to rebuild the circuit into the second version schematic? Keep the cap values as they are for testing, just change the stage to the direct coupled configuration. Just a thought.

[jvm]

Well, the owner of the amp decided to use it as a speaker cabinet. I unhooked the preamp feed so he can plug into the power amp via the line out jack also. I still have my homebrew module so I'll see if I can figure out the issue with it. Thanks for all the help everyone.

[52 Bill]

Sorry to hear that. My thoughts are that the transistors weren't turned on (biased) enough and when the audio signal was added to the circuit, it would cause the transistor to turn off, shutting down the audio signal.

Part of the problem seems to be the poor quality schematics. Some of the resistor values are a bit hard to figure out. It may be that the reason for the second module version was to fix the very problem that yours had.

I don't know what you tried doing to the circuit, but if you play with the resistor values, try and get the B-E voltages up to at least 0.5-0.7 negative volts.