Pro Audio Design Forum

Check out the Archiver USB preamp. This thing is full of 2SK389s.

http://www.hagtech.com/pdf/archiverman.pdf

The schematics are on page 7.

http://www.hagtech.com/pdf/archiverman.pdf#page=7

Cute the way the FETS are drawn as triodes.

That particular node (Rgain) is not the best place to do stuff in series or parallel. In the 1510 (and most CFB mic preamps of similar topology) even a small amount of stray capacitance to ground ~1-2 pF is going to create issues. In series, a few thousand uF are required to make changes. I agree wi...

I got to play with this a little this weekend by scabbing into an eq. Not really needed as the opamp I used recovers quite nicely on its own. It does make for a nice effect when abused (!) I 'nested' a few sets across the feedback path and could get a nice and smooth limiting effect. I want to try ...

Those Elco shafts are pretty hard aren't they? Stainless steel IIRC?

Crusty - Thanks for checking in. I disabled the global servo but not the Vos buffer. There was no correction. Although I didn't publish the numbers and only measured it at only a couple of sample points, the Vos buffer (OP07, trim and resistors) didn't appear to be the primary source of drift. Most ...

If you are talking about that diode break where above a P-P voltage another feedback path becomes active, that will was done to sound better that hard clipping, and IIRC with the 570- series gain cells the could get nasty if they are overdriven. So it was a lesser evil decision ands only expected t...

Thanks everyone. I fired up the desk lamp and temperature probe. With the global servo defeated I looked at the offset drift in the 1510 output op amp with it operating at 6 dB gain. At 69 degrees F the output Vos was a trimmed -0.11 mV. At 129 degrees -1.15 mV. It took about a 34 degree C rise to &...

Thanks Crusty. The switch I used is indeed break-before-make. Between every gain step there is a brief return to unity gain. The temperature drift of the THAT1510 isn't characterized in the data sheet. My concern would be with the Vos of the internal output op amp and the OP07 driving the ref pin. D...

I see a lot of questions here and elsewhere asking about servos for the THAT1510 and THAT1512. This post will discuss an improved servo circuit which has the goals of reducing switching clicks during gain change and eliminating a large value Cgain. An added benefit of this circuit is that output of...

I stumbled on this listing the other day and thought of our mastering engineers and preamp builders:

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... FP:US:1123