I started building last week and completely forgot about the Q1&2 orientation note in the assembly instructions.
Followed the sch and the PCB and got it all wrong. Voltages and offsets all over the place.
Traced out all the emitter locations from the PCB and confirmed which way around all the transistors needed to go. Lot of hours !
Today I found the assembly instructions after I almost finished doing the second PCB. and testing first the input LTP alone and then testing with the input + VAS LTPs alone. Both passed. I finally have the transistors oriented correctly.
BTW, I used a ZTX751 for Q16. The Eline has a higher dissipation of 1W instead of 600mW. The Eline has a cbe pin out (same as BC5xx) whereas the 2N have ebc pin out.
I selected a matched pair of 3.9mA Idss for Q1&2 (but installed BC182 for testing) with the intention of operating them @ between 1.6mA (41%) and 3mA (77%) depending on what I measure on the scope. 3mA for Q1&2 = ~10mA through Q16.
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Have built up three different versions (AAK, AAK DTV, Rudi) and all have a problem with ringing on low voltage squarewave.
One version was outright oscillation and after many changes to increase compensation I have got it working reasonably well but still see a tiny ringing when I add 100nF to the output, both before the output inductor and after the output inductor.
They are all lying on the bench waiting for a eureka moment.
I have all three drawn into LTspice files. But I still have not found out how to add good models into the file so that all can run the asc with the same models.
I'm hoping to post these and ask for help in analysing the stability margins for each or any of the designs.
One version was outright oscillation and after many changes to increase compensation I have got it working reasonably well but still see a tiny ringing when I add 100nF to the output, both before the output inductor and after the output inductor.
They are all lying on the bench waiting for a eureka moment.
I have all three drawn into LTspice files. But I still have not found out how to add good models into the file so that all can run the asc with the same models.
I'm hoping to post these and ask for help in analysing the stability margins for each or any of the designs.
Hi AndrewT,
Can you please provide more details on the setup that made it oscillate so I can try to duplicate it. Any information on the modifications you tried with the results would be helpful. I'll work on trying to come up with a solution. I also have a close friend who's a great audio analog design engineer that I'm sure can solve it if I can't. Thanks!
Best regards,
Al
Can you please provide more details on the setup that made it oscillate so I can try to duplicate it. Any information on the modifications you tried with the results would be helpful. I'll work on trying to come up with a solution. I also have a close friend who's a great audio analog design engineer that I'm sure can solve it if I can't. Thanks!
Best regards,
Al
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