6N23P-EB SRPP DAC output stage.

[Mario_JR]

Hello diy friends o/.
This is my first post here on tube section, so be nice with me
Just a little history...
A couple of months ago I was searching for R2R DAC with a tube output stage. Found one model from an ebay seller called raindrop (really nice guy) that uses a 6N11 SRPP output stage.
Decided to buy, but to my surprise the DAC did not sound good at all..after some searching (superficial) I found the culprit could be the cheap chinese 6N11. Why not to tube rolling? Found some 6N23P-EB and tried to run them without any circuit change ( YEs that was stupid ) and now I have a signal of 33Vrms on the output...that could kill a small animal LoL.

I need some help to setup it correctly, specially the gain and the correct impedance load support .

Any volunteers? Gonna draw the actual schematic to the 6N11 =)


Thanks. Best regards

[TheGimp]

We will need a schematic to help.

[DF96]

The gain of an SRPP is set mainly by the mu of the lower triode so higher mu means higher gain. However, the 6N11 is supposed to be equivalent to 6N23p so there should be no major change.

[Mario_JR]

Hi guys, Im sorry for the delay.
Here we have the schematics. The interstage transformer is 90:2600
Measured 0,146Vrms on the I/V resistor of dac that is in parallel with the transformer.

What I need to do to use a 6N23P-EB with a output of ~2,5Vrms



Mods.PNG


Thanks alot!

[TheGimp]

Whoa!

90:2800 is 1: 28.889, so you are driving the input of the bottom triode with 4.36Vrms? (28.889 * .146Vrms= 4.36Vrms).

Then you have the gain of the SRPP.

This looks like way too much gain.

[Mario_JR]

Originally Posted by TheGimp

Whoa!

90:2800 is 1: 28.889, so you are driving the input of the bottom triode with 4.36Vrms? (28.889 * .146Vrms= 4.36Vrms).

Then you have the gain of the SRPP.

This looks like way too much gain.

Yes you are correct.
Is that circuit ok?

[TheGimp]

While The Valve Wizard example with an ECC83 shows a gain of 25 which is significantly less than Mu (ECC83 Mu=100).
The Valve Wizard- SRPP

What is your load impedance for the output? What are you driving?

[Mario_JR]

Originally Posted by TheGimp

While The Valve Wizard example with an ECC83 shows a gain of 25 which is significantly less than Mu (ECC83 Mu=100).
The Valve Wizard- SRPP

What is your load impedance for the output? What are you driving?

Its driving for now a solid state headphone amplifier, about 50K Ohms

Gonna take a look at the valvewizard =D.

Thanks!

[revintage]

Mario!

90 to 2600 is surely your transformer impedance figures so turns ratio will be 1:5,37 which makes sense. The typical gain of a SRPP is in the ballpark of mu/2. So ouput level should be something like ,147*5,37*33/2=13V. Question is though how much the transformer in parallell with the I/V resistor loads the DAC. 47k secondary loading indicates it isn´t by much.

Are your figures right or is this a bad design?

[Mario_JR]

Originally Posted by revintage

Mario!

90 to 2600 is surely your transformer impedance figures so turns ratio will be 1:5,37 which makes sense. The typical gain of a SRPP is in the ballpark of mu/2. So ouput level should be something like ,147*5,37*33/2=13V. Question is though how much the transformer in parallell with the I/V resistor loads the DAC. 47k secondary loading indicates it isn´t by much.

Are your figures right or is this a bad design?

When paralleling the IV resistor the dac sees a very low load, it produces a 0,082Vrms . I dont know if the transformer choose was clever...
My figures are right, despite being for the 6n11, and I want to run a 6n23.
I dont know much about tubes, but I think that design is wrong.