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Tubenstein 28th March 2012 11:51 PM

Is that a SRPP circuit with 6SN7?
My friend has told me recently for a SRPP preamplifier that has 2 x 6SN7 per channel, normally a 1 x 6SN7 is enough in SRPP circuit, how come having 2?

He has the actual preamplifier and he has sent me a description: "The audio circuit has two dual-triode 6SN7 tubes per channel. The lower tube is set up as a long-tailed differential pair. one of the grids is grounded, the other is the input grid from the volume control. Input signals are amplified by this stage and converted to differential (push-pull, or balanced ) outputs by this circuit. One half of the second dual triode is the follower for the one half of the lower tube, and the second half of the upper tube is the follower for the other half of the lower tube.

Refer to HeadWize - Project: An OTL Tube Headphone Amplifier by Kurt Strain for an example of a single-ended mu follower stage. Imagine that the lower tube is a differential pair and there is a second follower above the other half of the differential pair. Two tubes, single-ended input, balance d outs."

Can anyone explain to me what is it about? I'm really curious how a SRPP with 2 tubes (4 triodes)?


Wavebourn 28th March 2012 11:58 PM

It is a differetial amplifier described, wih cathode follower outputs. It is not a SRPP.

Tubenstein 29th March 2012 12:08 AM


Originally Posted by Wavebourn (
It is a differetial amplifier described, wih cathode follower outputs. It is not a SRPP.

I found the link of my friend's unit:

SA-11 Upgrades

And start under the section Basic Upgrade (3rd paragraph of the website).

Wavebourn 29th March 2012 12:13 AM

Hmmm... How long do you think elecrolytic capacitors in such close proximity with radiating heat tubes will live before asking for one more $5,000 upgrade?

Tubenstein 29th March 2012 12:19 AM

That's why I found sound crazy since it has Black Gate cap in there for the upgrade more than 10 years ago!!

DF96 29th March 2012 09:45 AM

The 'basic upgrade' section says that the original circuit is cathode-coupled and the modified circuit uses an SRPP. Is your unit original or 'upgraded'. By the way, this is not an upgrade but a redesign.

I note with amusement that after the 'upgrade' the unit can achieve astonishing performance: distortion less than 1% at 1V out! This is only an order of magnitude worse than a much simpler circuit can achieve - truly 'high end'.

Tubenstein 31st March 2012 11:30 PM

Aikido instead??
My friend who is my tech and I told him everything about this mod, his response is why not an Aikido with 6SN7 and adjust the power supply circuit and that's the end of it!

What do you think??


DF96 1st April 2012 03:11 PM

I think I am wondering why you seem to want to do a tour around possible preamp architectures, without saying what you want this preamp to do. It was cathode-coupled, possibly modded to SRPP, now you want to look at Aikido. Throw cathode follower, low-mu grounded cathode, and ring-of-three with NFB into the ring and you have covered all the common possibilities.

Tubenstein 1st April 2012 04:14 PM

Because someone I know who has stock Counterpoint SA-11 but Alta Vista no longer offer the mod. And he is seeking comment but couldn't write English by himself. So if you are in my position, will you give him a hand???

I know a person recently has the SA-11 refurbish his "modded" unit but sounds like he didn't want to give out the circuit.

Tubenstein 1st April 2012 04:16 PM

I personally has Curcio Daniel II type preamp and my friend just ordered Salas SSHV2 for me, do i can upgrade mine.

Another preamp I might go ahead to build it is a transformer coupled linestage.

Aikido with SA-11 power supply is too many tubes and too much heat. Not my cup of tea!

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