Is this a phase inverter problem?
Moderators: pompeiisneaks, Colossal
Is this a phase inverter problem?
So a week or two ago, my build that I finished a couple months ago started acting funny. The tone and volume both went down the drain. After poking around, it sounded like it was a loading issue. I think it might be the phase inverter, but I wanted to see if I understand things right. I am using a cathodyne phase inverter, which should be roughly unity gain, is it not? I ask because when I poked around with an audio probe, I listened to the output from the preamp after the last coupling cap and then on each phase inverter output after the coupling caps there. The volume after the phase inverter is at least a few good dB lower than after the preamp coupling cap. If it is 6 dB down, then that is a gain factor of .5, right? Does that seem a little low for a cathodyne phase inverter? Could this also cause loading? If this isn't it, then I guess I am on to the power amp to look for something to cause loading.
Exact science is not an exact science
Re: Is this a phase inverter problem?
So it was working originally and now it isn't? I'd look for under-rated components that could fry in a short time: a resistor with too small a power rating, or a cap with too low a voltage rating.
The cathodyne inverter approaches unity gain; in practice it's a little lossy, but it shouldn't be so negative that you can hear it, let alone estimate the decibel loss!
Not that it matters, but for power or amplitude, -6dB is .25 -- one quarter as loud. For voltages, -6dB is .5.
The cathodyne inverter approaches unity gain; in practice it's a little lossy, but it shouldn't be so negative that you can hear it, let alone estimate the decibel loss!
Not that it matters, but for power or amplitude, -6dB is .25 -- one quarter as loud. For voltages, -6dB is .5.
Re: Is this a phase inverter problem?
Thanks for the tip, I will start checking components. I don't think the loss is near 6 dB, I just needed a refresher as to whether I need to be thinking voltage or power. Time to check resistors, caps, etc. If it is a bad resistor, will the resistance rating be infinite?
Exact science is not an exact science
Re: Is this a phase inverter problem?
Did you try a different PI tube?
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Is this a phase inverter problem?
Checked the PI, was a good tube. Turns out it was a problem with the NFB. Feels good to get it tracked down. Rewired the NFB and it works great again. Thanks for the help and replies.
Exact science is not an exact science