Pro Audio Design Forum

... to 2K2 or so to the shorted one, the actually DC that winds up on the unshorted input is modest. There is a small amount of time for the tracking servo to follow but the TC is around 50 ms. To be really hard on the part I tried it without any protection diodes. Still it was quite fun trying to ...

Hi Wayne, I haven't got past my very basic 1512 -> servo'd outpt (OP77) -> 1646 design. I had a hard drive crash this week which has cost me a lot of time, which is why I haven't been back to post. :evil: I did get to run the basic preamps last Sunday ...

My basic preamps with output-servo'd 151x are up and running, and on a first listen seem pretty uncoloured. More serious tests today! Thought I'd post up the resistor table calculations I came up with. These are for the 1512 with 12 and ...

... 500K input resistor due to Ibias with a TL071. OP07s are cheap and you save a $3 trimmer. This is why you wouldn't want to use a TL071 as an input servo (plus also noise). As an output servo it's OK if you don't mind the trim.

If Cgain is used the output Vos, without any correction will be < +/- 5 mV. With Cgain a servo is unnecessary. Adding a servo will actually increase offset. I'm not sure a trimmed TL071 is much better as it can be trimmed, but the drift is high. The output offset servo ...

... & Mediatechnology's post, and that makes sense. The gain was relay controlled and I did not use Cgain. The only time I could see or hear the servo working was while changing gain. After the servo settled all was good AFAIK. I think you will be surprised how these sound! That's good to know. ...

... OP77. OP77 seems to be a later version of the 07 with a low offset voltage so looks ideal. The OP27 will have too much bias current IIRC for 100K servo resistors. (Input servo.) The OP77 ought to be fine. The reference I made to the bifet follower was if flying rails were used. As JR said you ...

... the 1510 and the 1646 would have to be very large (47uF/100V) and would have a lot of stored charge. I was actually planning on using the output servo circuit to avoid using a cap at all! Is there any reason this won't work? I recall we had a discussion about this in the past, but can't recall ...

... Despite its use of a preamp IC (vs. discrete) it's not exactly a low cost circuit either: The support ICs, at least if a LT1012 is used as the servo, is more expensive than the preamp IC itself. My thinking was it would make a good dual (or M/S) rack-mount or lunchbox format unit. I don't see ...

... If the offset turns out to be far less than the rather large correction it's capable of supplying, the current injection resistors (and servo noise contribution) can probably be raised considerably. You'll see in the demo board from THAT the correction resistor is two orders of magnitude ...