I have added the cathode stage but there is a severe problem with a popping sound coming once every second. I will try to find the cause of that before any further work
Probably a low frequency oscillation through the power supply.
Increase the supply capacitance values, and/or add supply decoupling between the first and second stages.
In a bad case, also reduce the value of the coupling capacitors between the first and second stages.
Increase the supply capacitance values, and/or add supply decoupling between the first and second stages.
In a bad case, also reduce the value of the coupling capacitors between the first and second stages.
Exactly. This is motorboating, and it can be caused by PSU coupling between the first two stages. Adding the missing decoupling RC for the first stage should fix it.
Or ditch this poor design and use something that’s going to work.
EJP
Or ditch this poor design and use something that’s going to work.
EJP
I have been reading on valvewizards homepage and made some changes, specially to the buffer stage (like grid stopper and moving the output capacitor), se below. I have now included the power supply in the schematic.
It works, but only when one channel is driven. When I try using both channels the sound commes and goes. No popping or anything. Just the sound that should be there but pulsating in volume with a resonanse at about 2-3 Hz or so (give or take).
It works, but only when one channel is driven. When I try using both channels the sound commes and goes. No popping or anything. Just the sound that should be there but pulsating in volume with a resonanse at about 2-3 Hz or so (give or take).
Your output coupling cap is grounded at the output by the volume potentiometer? You have it wired correctly?
I would also de-couple the two amplification stages, as EJP already suggested. Since the input stage only requires something like 0.5mA, you can use a fairly high value resistor (at least 47k Ohm) here to get the PSU noise down for the input stage as well. You will need another capacitor after it.
I didn't have that in the simulations I posted earlier, but of course I do that too. I am using a linear voltage regulator (LR8) instead of an RC network just because I love the added complexity. 😉
I would also de-couple the two amplification stages, as EJP already suggested. Since the input stage only requires something like 0.5mA, you can use a fairly high value resistor (at least 47k Ohm) here to get the PSU noise down for the input stage as well. You will need another capacitor after it.
I didn't have that in the simulations I posted earlier, but of course I do that too. I am using a linear voltage regulator (LR8) instead of an RC network just because I love the added complexity. 😉
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You need a grid stopper on V2, and/or decoupling to V1 plate. But I still don’t know why you have all this gain. That’s part of the problem.