Schade Common Gate (SCG) Preamp

[manniraj]

@ra7 can you please edit the 1st post with the links to the post suggesting the upgrade options and also the buffer option as it would help others too.

Thanks

 

[rickmcinnis]

I would greatly enjoy attending and meeting you and the others but I do not like travel. My house and stereo need me. Always work to be done on both.

Luckily for you, you are in the neighborhood!

I am sure a splendid time will be guaranteed for all.

 

[ElArte]

I was going to go, but I figured I am too much of a noob for such high society.

 

[ra7]

You are too modest. All are welcomed and you’d fit right in.

 

[rickmcinnis]

ra7,

The new version of the circuit looks like it would be much easier to make without a PCB than the original.

Is the schematic posted close to what the final will be or should I wait? You have mentioned changes to the power supply.

If I attempted point to point for the first stage it might be nice to use the buffer boards.

Are those still available?

Now that I have figured out how to use the line stage in my system with gain AND the fact that I managed to make a mess of my original PCBs I am anxious to give it a try.

Took me much too long to realize all I needed to do was attenuate the output from the DACs.

Thanks and take care,

 

[marconi118]

why did you added q13 and r17?

 

[manniraj]

If someone is interested in a fully build SCG here is my sale post for reference - https://www.diyaudio.com/community/threads/thread-watched-schade-common-gate-scg-preamp.404081/

Thanks

 

[ra7]

why did you added q13 and r17?

Not sure I understand. Which schematic are you referring to?

 

[ra7]

ra7,

The new version of the circuit looks like it would be much easier to make without a PCB than the original.

Is the schematic posted close to what the final will be or should I wait? You have mentioned changes to the power supply.

If I attempted point to point for the first stage it might be nice to use the buffer boards.

Are those still available?

Now that I have figured out how to use the line stage in my system with gain AND the fact that I managed to make a mess of my original PCBs I am anxious to give it a try.

Took me much too long to realize all I needed to do was attenuate the output from the DACs.

Thanks and take care,

Hi Rick,

Now that BAF is done (and I've recovered from the high), I am switching my full attention to finishing the new boards. The buffer boards have been sent. Can you hold on for a couple more weeks for the new board? Buffer boards are available. I will send you a PM.

Thanks!

 

[ra7]

@ra7 can you please edit the 1st post with the links to the post suggesting the upgrade options and also the buffer option as it would help others too.

Thanks

Link to Part 1 upgrade has been added to the first post. Going to keep Part II under wraps for now.

 

[marconi118]

last complete schematics post 1238

 

[ra7]

Q13 is part of the new CCS. R17 sets the current. A fixed resistor has replaced the pot. Two resistors provide flexibility for J113 variations, so you don't need to select parts (though you can do that, if you like).

 

[marconi118]

what are the advantages of the new CCS compare to the simple one using only DN2030?

 

[ra7]

For lower bias currents, say, below 25 mA, J113 is better than the DN series for capacitance. More bandwidth, less distortion. But you need the upper FET to shield the J113 from high voltage. It is a cascoded CCS with depletion mode devices that can operate at lower currents. You could also use an LND150 in place of the JFET.

 

[rickmcinnis]

Glad to hear you had a great time at BURNING AMP.

Of course, I will do as you ask. Without your blessing I am in the dark!

Very excited by what you have wrought - evolution is fun.

Take care, ra7

 

[metaphile]

I was fortunate enough to be at Burning Amp this year and had the opportunity to hear ra7 demo the SCG in combination with a few amps, including the Total Domination VFET amp. I was already intrigued by the design and following this thread - but now I am even more interested in building one than I was before. I really enjoyed the sound.

Looking forward to the next iteration of this project.

 

[ElArte]

I am in the process of completing a headphones-focused build under the guidance of master @ra7.
It’s getting very close.
I’ll post pictures when it’s finished.

 

[ra7]

Thank you! So glad that it sounded good in that space--was a little nervous how the response shaping would work. Also, the SCG definitely was behind the sound. It was the Miro TDA 1541 DAC into Nelson's FE 2022 (transparent plus gain) into the SCG driving an F4.

 

[pinholer]

Don't forget the custom, modified dust caps on the JBL woofers!

 

[ra7]

That was the secret sauce