Pro Audio Design Forum

Using the T-bias scheme, what impedance will a mic see? I'm concerned about loading dynamic and ribbon mics. I have built a preamp around the 1510 using two 3.3k resistors to ground using the rule of thumb that the input impedance should be 10x the mic impedance (I do have a 600-ohm mic, AT804, and...

Here's one way to operate and bias a THAT1646 for single supply operation: https://www.ka-electronics.com/images/jpg/THAT1646_Single_Supply.jpg Image courtesy of THAT Corporation If the input is at or near the same DC potential as Vref (the one-half Vcc potential at the output of U2A) then C2 and R1...

raf wrote:I need to re-pitch the output device pads... I used 0.1" thinking they were TO220, they are, what TO126?

They are an insulated TO-126 on a 2.28 mm pitch. 0.1" may be close enough.

Thanks Roger and Doug.

I had a chance to check the PC board a few weeks ago and run a few measurements. The output Vos was <5mV. The orginal slew rate was thought to be ~4V/us but when re-measured turned out to be ~8V/us. This is consistent with the THAT1646 when driven in the "common mode" configuration. The RM...

What was the harmonic content of the fields? Could it be an issue of core saturation?

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 ...