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Old 2nd November 2021 | Show parent
Gear Head
Heterodyning or Intermodulation Distortion can occur when two or more signals are mixed through a non-linear device. LIKE YOUR EAR. Your ear is a nonlinear device where heterodyning (intermodulation distortion) does occur. Messy indeed.

Transient response is one of the performance requirements any Pro Audio vacuum tube design should have built in. A lot of it depends on the audio transformers used. There are many things I had to consider when designing this preamp. LOTS of things. Safety issues included.

Sagging power supplies are sometimes there on purpose, designed in. I thought about doing that, but decided against it. My preamp power supplies are fully regulated, even the HV B+. I use a higher than usual High voltage to get the sound I wanted. A lot of guitar amps use starved plate designs. It is a sound. I just wanted a much more robust design. My design can maintain the proper design internal voltage on the 120 Volt setting anywhere from 80 Volts to 135 Volts. I am sure it will handle higher and lower voltages than that. I just don't claim that. Same for the 240 Volt setting.

I have been recording field festivals where the power line voltages went down to 80 volts. They were then adjusted with a Variac.

I leave the studio on 24 hours at a time with no oscillation, within or outside the audio bandwidth. The proper design of a HV power supply takes that into consideration. That is all you need to have a power supply turn into a UHF oscillator. That is just good design. Also, the ability to operate for days with all the vents closed off and the room temperature at 90F is an important thing to design in. I had great mentors I could go to for advice. They kept me out of trouble. Maybe even had me over build too much, but better safe than sorry.

In some of your comments you seem to be talking about solid state preamps or HIFI systems. I am not commenting on them.

Jim Moss

Originally Posted by kludgeaudio ➡️
From intermodulation effects that you don't see. From slew limiting. From transient effects like power supplies sagging. Maybe it breaks out into oscillation after running for an hour but you never notice that on a short test. What you describe is a very good test, but not a universal test. There are a lot of tests that can measure that stuff, but you need to know to use them first.