FET preamp Observations and potential enhancements

[ChrisM]

No phase reversal, yet your looking at the Dumble style common source gain stage?

[glasman]

No phase reversal, yet your looking at the Dumble style common source gain stage?

Totally aware of the phase inversion. That is why I designed a single supply opamp version of the preamp.

But for completeness I wanted to evaluate both solutions.

FWIW the opamp version has several advantages and a couple of disadvantages.

Pros

1. Wider supply range (10 to 30volts or so). No having to screw with bias voltage for various supplies.
2. No phase inversion
3. Wider bandwidth.
4. True gain control capability

Cons

1. Higher part count
2. Single source complicates input and output.

[glasman]

After evaluating both preamps, the opamp version (to my ears) wins hands down over the FET.

The OPA134 is a really nice choice, not as "cork" snifffy as some of the other options out there, but it is also a lot more natural sounding than some of the higher end amps.

YMMV.

[boldaslove6789]

The phase reversal isn't such a disadvantage when using lapsteels like the Supro/Kay Rocket. They have single coils that are split in half and cancel the hum but switch phase. There is often phase problems with lapsteels because of some of their weird configurations.