6SN7 6N8S preamp suggestions

[merlin el mago]

6SN7 6N8S schematic preamp suggestions

An externally hosted image should be here but it was not working when we last tested it.

I'm looking for high gain, high input impedance, low output impedance, low noise design with only 2 tubes so one per channel.

Ideas and suggestions will welcome.

 

[denny9167]

6SN7 6N8S schematic preamp suggestions

An externally hosted image should be here but it was not working when we last tested it.

I'm looking for high gain, high input impedance, low output impedance, low noise design with only 2 tubes so one per channel.

Ideas and suggestions will welcome.

I've had good experiences with the SRPP,I haven't tried the other configurations. Just be sure to elevate your heaters. Thanks

Denny

 

[merlin el mago]

Thanks Denny, could you post your schematic used and let me know: gain, input/output impedance, etc?

 

[denny9167]

Thanks Denny, could you post your schematic used and let me know: gain, input/output impedance, etc?

Sure, I have the pic attached. Since the 12AU7 and 6SN7 are so close I made the substitution. The sound is really quite nice. Since the 6SN7 is an 8-pin octal you will have to change pin-out arrangment. I don't remember the gain, but it should be sufficent for what your looking for.

BTW, this schematic is designed to give you elevation on those heaters! Thanks

 

[merlin el mago]

Looks nice and very easy to do, surely I will try, thank you.

 

[tinitus]

been thinking if srpp would be good or maybe even ideal to drive a low impedance trafo output
which could be balanced 600/600 ohm

 

[merlin el mago]

I don't want to use output transformer.

 

[ruffrecords]

Use a mu follower. More gain, much less distortion than and SRPP and still the low output Z. Run the 6SN7 at around 5mA.

Cheers

Ian

 

[Davec113]

Use a mu follower. More gain, much less distortion than and SRPP and still the low output Z. Run the 6SN7 at around 5mA.

Cheers

Ian

I would agree, I had a mu follower pre using 6DJ8s and it had 28 dB gain very little distortion.

 

[vconsumer]

Use a mu follower. More gain, much less distortion than and SRPP and still the low output Z. Run the 6SN7 at around 5mA.

Cheers

Ian

Put a CCS on the plate of the voltage amplifier, bias it with LEDs, direct couple the two halves, and a put CCS on the mu follower. You will have a nice preamp.

 

[merlin el mago]

Use a mu follower. More gain, much less distortion than and SRPP and still the low output Z. Run the 6SN7 at around 5mA.

Cheers

Ian

What about this schematic with R4, R6 400-500 ohms?
B+ 360V?
I have 240VAC tx, Salas shunt regulator spends 20V in-out so I have maximum 315-320Vdc regulated wich value for R8 have I to use to have 250VAC?
Schematic can be improved?

Put a CCS on the plate of the voltage amplifier, bias it with LEDs, direct couple the two halves, and a put CCS on the mu follower. You will have a nice preamp.

I will use Salas high voltage shunt regulator.

 

[ruffrecords]

Put a CCS on the plate of the voltage amplifier, bias it with LEDs, direct couple the two halves, and a put CCS on the mu follower. You will have a nice preamp.

Why complicate a simple mu follower so much? The improvement in performance will be negligible and with two stages there will be far too much gain.

Cheers

Ian

 

[ruffrecords]

What about this schematic with R4, R6 400-500 ohms?
B+ 360V?
I have 240VAC tx, Salas shunt regulator spends 20V in-out so I have maximum 315-320Vdc regulated wich value for R8 have I to use to have 250VAC?
Schematic can be improved?.

For a 6SN7 I would use 1K for R4 and R6, change R5 to 10K, R7 to 220K and C2 to 220uF.

Cheers

Ian

 

[merlin el mago]

For a 6SN7 I would use 1K for R4 and R6, change R5 to 10K, R7 to 220K and C2 to 220uF.

Cheers

Ian

B+?
R8?
heaters?

Cheers

Felipe

 

[ruffrecords]

B+?
R8?
heaters?

Cheers

Felipe

Mu followers are quite tolerant of B+ so anything between 275V and 325V will be fine. I am a great believer in well smoothed supplies and I would use sever RC filters cascaded. Heaters in a 6SN7 mu follower need to be elevated to about 75V to avoid exceeding Vhk ratings. Heaters for this kind of preamp can be ac or dc. My HT250 PCB will provide a well smoothed HT and heater elevation on a single board:


http://www.ianbell.ukfsn.org/EzTubeMixer/

Cheers

Ian

 

[vconsumer]

Why complicate a simple mu follower so much? The improvement in performance will be negligible and with two stages there will be far too much gain.

Cheers

Ian

Not complicated. A handful of inexpensive parts and very little real estate would get the job done. Besides, the OP said he was looking for high gain.

Have you tried it both ways? I have, and the difference was more than negligible.

 

[merlin el mago]

Are necessary R8 & C3 with Salas shunt HV regulator?

 

[merlin el mago]

Not complicated. A handful of inexpensive parts and very little real estate would get the job done. Besides, the OP said he was looking for high gain.

Have you tried it both ways? I have, and the difference was more than negligible.

Could you draw a schematic to see how complicated is to implement?

 

[vconsumer]

Just replace the 47k resistors in the schematic above with CCSs. While you're at it, try the loctal 7N7 in place of the 6SN7.

 

[merlin el mago]

Just replace the 47k resistors in the schematic above with CCSs. While you're at it, try the loctal 7N7 in place of the 6SN7.

Wich schematic?