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[Dave Amels]

What do you guys think about this mod:

[zmix]

Dave,
I cannot find a copy of the original head amp for comparison.  Do you have one that you could post?

[QUEEF BAG]

it's on the studer ftp site-

ftp://ftp.studer.ch/Public/Products/

in the analog recorders folder, near the bottom

[zmix]

Modded from this?:

[zmix]

QUEEF BAG wrote

it's on the studer ftp site ftp://ftp.studer.ch/Public/Products/ in the analog recorders folder, near the bottom

Thanks for the link!!!

[Dave Amels]

That's the original... You beat me to it.  Thanx.

Also.  The EQ returns to R19 on the mod like the original.

[Dave Amels]

I have some comments on it but I'll let others go first.

[Dan Kennedy]

Cascode stage cathode current thru head?

[Larrchild]

Just use a FET like everyone else does, lol.

[mgod]

A friend of mine says he recognizes that circuit. Interesting.

[Larrchild]

Is the very top resistor NFB? And if so, how does the 47n cap on the left not ground it?

[johnR]

Larrchild wrote on Fri, 19 November 2010 23:48

Is the very top resistor NFB? And if so, how does the 47n cap on the left not ground it?

It looks like that resistor might be providing dc bias for V2A. Otherwise V2A's grid would be tied to the grid of the input valve (through a 680K resistor) which I don't think would allow V2A to turn on.

[johnR]

The way this is drawn makes it look like the input valve's cathode is grounded through whatever is plugged into the input connector. My head is starting to hurt.

Edit: Oops, missed Dan K's post. Beat me to it.

[Larrchild]

I was thinking that if it was bias, it would be fed from a decoupled rail. Not the plate of 3rd tube.

[johnR]

Larrchild wrote on Sat, 20 November 2010 12:30

I was thinking that if it was bias, it would be fed from a decoupled rail. Not the plate of 3rd tube.

Is that a 100 ohm resistor on the plate of the output tube? That would make the plate not too far off rail voltage. The bias voltage would be ac decoupled by the 0.47uF cap.