6SN7 6N8S preamp suggestions

[merlin el mago]

Thanks Ian for your patient & kind support I will let you know how sounds when finished but surely sounds very good because I have done othe mu-follower with ECC81.

 

[ruffrecords]

Thanks Ian for your patient & kind support I will let you know how sounds when finished but surely sounds very good because I have done othe mu-follower with ECC81.

The 6SN7 has a very low level of inherent distortion so it usually sounds very clean in a mu follower. Good luck.

Cheers

Ian

 

[merlin el mago]

Thanks again Ian.

Cheers

Felipe

 

[merlin el mago]

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

Have I to elevate heaters to 75V in both tubes, right?

Cheers

Felipe

 

[Uunderhill]

100K log pot at input is OK.

Cheers

Ian

I'm still learning here - so please be patient.

As I've just heard with a solid state amp - changing the input resistors from carbon to metal film makes a dramatic improvement to the sound quality.

Turns out there is far more to resistor noise than the old text book description of thermal noise.*

Those rotating DACT volume controls get horrifically expensive (rotating selector switches with banks of metal film resistors).

For the 100K volume control - Is there anything you would recommend - at a sane price ?





* This is a great little artical on resistor noise
Resistor Types--Does It Matter?

 

[merlin el mago]

Can I measure heater elevated 75V without valves connected or is necessary have the valves connected?

 

[Jay]

Hi Merlin, you haven't mentioned what the amplifier will be? You seemed to care enough with output impedance and mu-follower, I guess you have solid state amp there?

I'm interested in better than the aikido tube preamp to drive solid state output...

 

[merlin el mago]

Yes is to drive SS class A power amps: Borbely, Pass, Thereshold....

 

[Jay]

Yes is to drive SS class A power amps: Borbely, Pass, Thereshold....

And have you tried the Aikido or the grounded grid? I think the Aikido is the new benchmark for that kind of job. I have many tubes waiting for a more suitable circuit myself

BTW, the last mu-follower I built was 6J5 driving Hitachi dual differential lateral mosfet amp.

 

[merlin el mago]

Can I measure heater elevated 75V without valves connected or is necessary have the valves connected?

I used R1 75K connected to B+ 300V, R2 25K paralleled with 22uF450V, I measure ground to between R1 & R2 but can get only 0V instead 75V

 

[merlin el mago]

I tried grounded grid clone but isn't a line pre amp is a buffer = no gain

 

[Jay]

I tried grounded grid clone but isn't a line pre amp is a buffer = no gain

Aikido has slightly too much gain. Isn't that what you're looking for? To lower the gain you need more expensive tubes.

 

[merlin el mago]

Aikido has slightly too much gain. Isn't that what you're looking for? To lower the gain you need more expensive tubes.

What about a voltage divider soldered at the input.

 

[merlin el mago]

When I connect the 75V dc elevated heaters to gnd heaters the voltage drops to 0V

 

[merlin el mago]

Fixed the issue, gnd heater was connected to gnd chassis instead to leave gnd floating, now I have elevated heaters to 75V

 

[merlin el mago]

Measurements B+ 300V, heater elevated 75V, heaters:

Right channel
Across R4 1K 3.84V = 3,84mA
Between anode lower valve R5 100K & C1 0,1uF 164,7V
Between R6 1K & R5 10K & R7 220K 127,2V

Left channel
Across R4 1K 3.88V = 3,88mA
Between anode lower valve R5 100K & C1 0,1uF 165,9V
Between R6 1K & R5 10K & R7 220K 127,8V

I believe measurements are ok, now I soldered the volum pot and check with scope before listening.

 

[merlin el mago]

Scope measurements ok, tomorrow I will listening with Erno Borbely 75W RMS class A mono power amps.

 

[merlin el mago]

Simple sounds amazing, highly recommended

Tubes used Russian 6H8C Photon, B+ regulated with Salas SSHV2.

 

[ruffrecords]

Simple sounds amazing, highly recommended

Tubes used Russian 6H8C Photon, B+ regulated with Salas SSHV2.

Excellent. I am glad you like it.

Cheers

Ian

 

[Jay]

Simple sounds amazing, highly recommended

Tubes used Russian 6H8C Photon, B+ regulated with Salas SSHV2.

Cool. The PS may have big contribution. Any comparison with other preamp?