JFETs in Bass Amps

[Quilly]

I'm hearing a lot of good things about the use of JFET transistors in solid state guitar amps, particularly the Orange super crush 100. Apparently they have very similar tonal characteristics to valves (without all the drawbacks). Just wondering if these are used in bass amps at all ? 

would they work etc. ? 

[paul_5]

They're everywhere in solid state gear - common opamps (TL072/ TL074) are JFET based chips, so I would imagine the majority of solid state preamp will have them in.

[rmorris]

Yes - widely used in bass and guitar amps.

Either in terms of jfet input opamps as paul-5 has said.

Or as discrete jfets eg classic Trace Elliot preamps (not sure about later stuff) but much of the Clive Button stuff.

Apart from the overload / distortion characteristics - they are well suited to passive Hi-Z pickups since they tend to have lower current noise than bipolar solutions - and so develop less noise with the resistance of the Hi-Z pickup. For Hi-Z pickups this is basically more important than the voltage noise where they are worse than bipolar solutions.

Unfortunately the lowest noise jfets are now difficult to obtain eg Toshiba SK170 and associated dual jfet are obsolete. Equivalents are manufactured by Linear Systems - LSK170 / LSK389 - but purchasing and availability can be challenging esp for small quantities.

fwiw similar applies to the lowest noise bipolar transistors that were originally produced for the mass phono pre-amp market and are now discontinued.

On the upside the classic TL07x and LF351 jfet opamps have been superseded in performance by eg OP134 etc.