Signal isolation, transformer coupling and optos

[Steve Conner]

Oh, the irony!

I've used those OEP audio line transformers with some success. I added them to the inputs of my tube hi-fi amp for extra irony. Lundahls would have been nice, but they were a bit too expensive, and probably overkill considering the performance of the rest of the amp.

The model I used had a resonant peak of several dB at about 25kHz when loaded with 50k ohms. I had to load it with 10k to flatten the peak out. Even so the skirt of it gave a slight boost to the top octave. These are the kinds of tradeoffs discussed by Dai H. above.

[guitician]

Peaks may be a good thing depending where they are in the bandpass. I know Ampeg used a big inductor in the V4 for it's midrange control. Maybe using some sort of variable tuned circuit with the inductance could be a tone control option.

[R.G.]

There's another way to go about this.

Duotriodes are fairly well matched. Use a whole duotriode at the input as a differential amplifier and do the design for good common mode noise rejection.

We think of tubes as expensive today. In fact, they are incredibly cheap compared to what they cost back in the Golden Age in constant dollars (or pesos, rubles, RMB, pounds, Euro-equivalents...). I have sometimes dispaired at what amplifiers could have been if they had used another half-tube at the inputs and gone differential. It was just too expensive.

[R.G.]

There's another way to go about this.

Duotriodes are fairly well matched. Use a whole duotriode at the input as a differential amplifier and do the design for good common mode noise rejection.

We think of tubes as expensive today. In fact, they are incredibly cheap compared to what they cost back in the Golden Age in constant dollars (or pesos, rubles, RMB, pounds, Euro-equivalents...). I have sometimes dispaired at what amplifiers could have been if they had used another half-tube at the inputs and gone differential. It was just too expensive.