Modding a Tab V74a

[embee]

I recently got myself a TELEFUNKEN V74 tube line amps. Rumours are that they can be modded to achieve mic pre specs with up to 30dB gain.

From what I understand, there are two possibilities:

A)
if you take a peek at the schematic you will see a 200K
resistor wired from the top of the I/P trannie's secondary to the control grid
of the first tube. Replacing the 200K r with a piece of wire (or shorting out
the little bugger) will give you more gain and get you closer to that of a real
pre.
B)
adding a proper mic input tranny.

Does anyone here have any experience with these units? Are they worth modding?
thanks very much in advance.

[rob]

I don't have any direct experience with these, however examining the schematic tells me that you'd be hard pressed to get the 40 or more dB of gain you require for a mic preamp. There are a couple of simple things that can be done to squeeze a bit more than unity gain and adding a high ratio input transformer would give more again, but the more you do to keep getting gain the less and less of a telefunken it becomes.
The main thing that hamstrings the gain is the cathode follower output stage.

[Kurt]

Could you just stick a fixed 20db boost after it? The Altec pre I got from this board did that, I think it's 40 db in the little plugin modules and a fixed 20 db in the mixer that follows.

[embee]

Yes i think im just gonna keep the v74 for running/splitting line signals through or possibly summing if i could get hold of another one.

Would anyone know how to open up the frequency response anymore on this unit i understand it can also be done?

[adamcal]

I went through all this with my V74's with Ross Giles, in the end we decided that where just better off left alone as 10db line amps, if you want mic amps, get v72's or 76's.

having said that, there are many hot output mics that will work great with these, such as Beta52's (in a loud kick) and neumann 149's.

[rick]

or you could just run the 1176 as a pre by itself and forget the telefunken