Hello

Any opinions or suggestions about this hybrid tube preamp ?

Here's the circuit with parts values.

Thank

Bye

Gaetan

 

My opinion is that a tube amp is an archaic amplifying device, and there is no good reason to use one (unless of course you have that magical "Golden Ear" that can hear the difference).

 

Looks OK. Biasing seems unusual, eg, static grid bias at ~ -18V.

Same for plate current, looks right on.

Regards, Dana.

 

Hello

I have done a Ltspice simulation using 12AU7 tube and with differents values for somes parts.

The thd spectrum look good.

Any thought or suggestions about it ?

Thank

Bye

Gaetan

 

I am not sure about this one. I do quite a bit with tubes, and have made hybrid preamps, but my general approach has been to replace a fet front end with valve. Maybe a backward step, but it does work well and one big advantage is that front end overload damage is unlikely (I should say most of my work is with RF). I can see that the input circuitry is similar to tube circuitry. Putting aside the information given for the moment, I see one good reason for using fet input is lower noise. I suppose my thought would be to see the results compared with a purely tube design though, as I don't really see the point of sacrifice of (possible) advantages of tubes and placing one in a less advantageous position with attendant complexity.

Tracy

 

Hello,

I would have expected a capacitor between the pot and the gate resistor of jfet.


I think that without the capacitor the DC settings of the jfet will be influenced, depending on the pot setting.

Bertus

 

Hello Bertus

Yes, I should think about that, I will do it.

Thank

Bye

Gaetan

 

Some old people like the vacuum tube distortion because that is what they heard 55 years ago. The distortion will be much worse at higher levels.

 

Theese old people is more drawn to the fact that tubes are "warmer". (Yes, actual temperature, not the sound)
All to often they confuse the two terms.

Somebody bring them wood-amps?

 

Even harmonics distortion produced by a vacuum tube are exactly octaves apart and do not sound awful, but should not be there. Odd harmonics distortion is not musical (sounds awful, something like a buzzer) and is usually caused by push pull tubes close to and beyond symmetrical clipping.