100 mm fader + 20 dB gain line level?

[audiothings]

greetings.

don't think i've ever posted in this forum before... i know absolutely nothing about electronics.

i have recently started using ribbons and dynamics and my pair of extremely low output avensons a lot... and i hope to solve two problems with a device i have in mind...

1. i need about 15-20 dB more, of clean gain... my current pres, rme quadmics, get distractingly noisy when driven above 50 dB or so.... and when recording soft sources with low output mics, 50 dB is not enough. (i found the MH ULN-2 to be much quieter under similar circumstances, but i don't own one).

2. i want to have a fader box in front of me... i'd love to ride the gain during tracking, and using small rotary pots for the purpose is far less than intuitive.

putting the above together, i want a fader box (maybe 4 channels) that will allow me to ride the gain and add upto 15 dB of extra gain, when required.

if this is all i want to do, how complicated will it turn out to be? what are the potential pitfalls? what i can already guess is that i'll need a line level opamp (not thinking of tubes right now) which will give me the requisite gain, and a fader that will trim the resultant output. what more do i need to know... where should i start?

here in india, i can get a very competent tech guy to put something together for me, but i'd like a few pointers to start my research, for while the tech guys here will do a clean job, the concept and possibly the bulk of the schematic will have to come from somewhere else.


thanks,

audiothings.

[Matt Syson]

Hi
Adding a stage with a fader and 15 - 20dB of gain is no particular problem except the noise.
With a ribbon mic you need to be thinking either a transformer or a preamp intended for ribbon level and impedance.
The transformer approach has a certain simplicity about it and say 10dB of gain here would improve the signal / noise somewhat (not necessarily 10dB worth).
Adding the gain after the existing preamp will tend to bring the noise up as well.
It is 'traditional' to get the first gain stage do do the majority of the work, mainly because it is the best way!
I would suggest tackling this in 2 directions, transformer (or optimised preamp) at the front and a fader with up to say 6 dB gain available at the other.
Matt S

[audiothings]

thank you for your reply matt.

I would suggest tackling this in 2 directions, transformer (or optimised preamp) at the front

Do you mean adding a transformer before the mic pre? Can I just slap in, say, a Lundahl 1538 XL before the pre? (You can probably make out I am clueless about these things). Apparently said transformer can add upto 14 dB of gain when "Jumpered for a 1:5 ratio".

and a fader with up to say 6 dB gain available at the other.

where does this 6 dB come from? transistor? opamp?

BTW, the "SysonStein" and Rack System are looking damn interesting... all the best with them.

Thanks again.

[Matt Syson]

Hi
Yes the Lundahl transformers are very high quality and selecting one with a variety of ratios available would allow some experimentation. It may be that you can't use a 1:5 ratio because the impedance of your existing mic amp input is too low. Lundahl's website has some useful info about their transformers. Whatever you do with it you won't damage anything so you can experiment.
Regarding the fader and amplifier, I was meaning a fader followed by an amplifier, with a modest gain, say 6 - 10dB. This would 'buffer' the medium impedance of the fader, so it would then be able to 'drive' some cable and also give you some gain. The amplifier could be transistor, IC or valve, it is up to you. If you are not really into electronics too seriously I would suggest a little amplifier kit from Velleman. I think theirs uses a TLO71 but once you have it working you could swap it for something a little better, NE5534 (with an extra capacitor from pin 5-8) to stabilise it.
If I did not spend so much time on Gerarslutz then Sysonstein would be completed by now!!
Matt S