Electronics > Beginners
Trimpot rating when in place of two resistors??
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Ian.M:
It looks like the upper resistor should be in the 1.5K to 2.5K range.  If you've got a 10K multiturn pot, patch that in as R11 in the original schematic.   Initially set it to zero before power-on, and with no load and no signal check the quiescent current by measuring the voltage between the NPN and PNP output stage emitters.  Turn it up till you get 100mA (136mV)*, switch off and note the resistance value. Turn it back to zero and repeat to get the resistance when the quiescent current first starts to rise (1mV between the emitters). 

Once you have that data, tell us and we can suggest resistor values and circuits to allow you to trim the bias over a reasonable range while applying a low level 1KHz sinewave input and monitoring the crossover distortion with the amp's normal load connected.

* 100mA should be safe as long as the output transistors are properly heatsinked.
Gyro:
Well if the OP wasn't confused before (he was)...  ::)
Ian.M:
Yes and so was I, as can be seen above.  :-[  Without knowing what other hacks are in the original build and not on the schematic,  :-DMM usage is required to avoid  :-BROKE with loss of magic smoke.

O.T. this forum needs a magic smoke icon!
Robbie010:

--- Quote from: Ian.M on February 13, 2019, 09:52:21 am ---Yes and so was I, as can be seen above.  :-[  Without knowing what other hacks are in the original build and not on the schematic,  :-DMM usage is required to avoid  :-BROKE with loss of magic smoke.

O.T. this forum needs a magic smoke icon!

--- End quote ---

If it helps, I have drawn up the full schematic in LTSpice (to the best of my ability) and added known values and ratings where possible. Unfortunately, I am not skilled enough to run this as a spice model but it does represent the full amplifier circuit.

Attached.
Robbie010:
Sorry, just thought I may as well provide the original DIY instructions for building the amp.....
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