AudioBanter.com - View Single Post - Recommend a ~$400 2-channel tube mic-preamp?

(Scott Dorsey) wrote in message ...
Garthrr wrote:
In article , (Scott Dorsey)
writes:

With the Aphex 107, you can bypass the tube stage. You lose only about 10 dB
of gain and it sounds a whole lot better.

How complicated is it to do that? Could it even be done in such a way as to
allow one to switch the tube in and out?

It's not that bad... I think we discussed it here back when the 107 was a
much more popular unit than it is today.

The tube stage is running with very low voltage, but it's not really in
starvation mode because it's also running without any plate resistor at
all. Instead, there is an I/V stage made with an op-amp that takes the
signal off the plate. Bypassing the whole RPA is a matter of removing
the tube and putting a capacitor between the grid line and the output of
the I/O op-amp.

There is also a little trimmer point inside there that controls the
linearity. Aphex sets it at the factory for a particular distortion
level, but you can turn it up or down too.
--scott

I did the two mods. With the trimmer, you can have a more dynamic
sound but it becomme harsch.
After that i founded a test point on the output of the Input op-amp. I
disconnected the switch jack that i disn't use and i connected the
test point to this jack (without any cap because the asymetrical input
of my Tascam has already a cap). So on the switch jack i have an
output of the first stage of the 107 (i think nok to drive long lines
because not symétrical and sure not a very low impedance) and on the
output jack i have the normal output.

The result ? The level is 12 db lower, but i discovered that the input
stage was beginning to clip with in input level 10 db higher than the
clip level with the complete 107... so i lossed 2 db...
And the sound is really more natural. Not harsh on the violin and the
trompet. It's A LOT better, really less distortion... with less noise.

Jean-Marie Mathieu