That pcb layout certainly leaves a lot to be desired. I'd never try to build a 1MHz bandwidth circuit
like that. Give the capacitor increase a try and see what happens.
I didn't design the board.
Viktor was kind enough to share his files with me. All I changed were some pad sizes and lead spacing on some of the components.
I'll try the cap change tomorrow.
Viktor was kind enough to share his files with me. All I changed were some pad sizes and lead spacing on some of the components.
I'll try the cap change tomorrow.
Use some old speakers just in case, since you don't have a scope.
See if it behaves any differently with the larger capacitor value.
Hi Viktor,
The offset constantly fluctuates from 1.5mV to almost 5mV.
Bias constantly fluctuates as well +-5mV.
Try placing a small plastic or cardboard box over the pcb to reduce the air currents,
to see if the input stage is the problem.
Hi rayma,
I soldered three 100pF ceramic caps in parallel to the underside of the board today, but I haven't had a chance to test it.
I have to disconnect my only PS from my op-amp preamp and turn the voltage up to 22V in order to test this circuit.
I'll try placing a box over the board as well.
I soldered three 100pF ceramic caps in parallel to the underside of the board today, but I haven't had a chance to test it.
I have to disconnect my only PS from my op-amp preamp and turn the voltage up to 22V in order to test this circuit.
I'll try placing a box over the board as well.
I tested the circuit with 300pF plus the 4.7pf, which I left in place.
No change, the hum and RF interference are still quite noticeable with the volume all the way down.
No change, the hum and RF interference are still quite noticeable with the volume all the way down.
Ok, either it wasn't unstable before and had different problem, or it still is now.
!
I do not have this problem. In my case, the offset constantly fluctuates from -0.9mV to -1.6mV. If you have 1.5mV to almost 5mV you answered why bias fluctuates +5mV. Are the transistors matched?
Send us few pictures.
I do not have this problem. In my case, the offset constantly fluctuates from -0.9mV to -1.6mV. If you have 1.5mV to almost 5mV you answered why bias fluctuates +5mV. Are the transistors matched?
Send us few pictures.
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