Ribbon mic recording preamp... Discuss design

[garyk]

I have not managed to get an authoritative answer to this yet...even from techs with much more skill than me.

What do I need in a mic pre (recording) for ribbon mics?

I have a high end tube pre that just doesn't cut it for ribbon mics.
The standard pre in my little Soundcraft Spirit Folio sounds better.

I thought about building a pre especially for ribbons, but what design?

I guess two things spring to mind:

a) that you need more gain (generally) for ribbon mics (so needs to be quiet too?)
b) that the input matching (impedance? reactance?) may be more critical

Anyone have ideas, schematics, or other input for this?

I have collected a few transformers that I occasionally put between low impedance ribbons and pre's to get better matching, but I am interested to have opinions on all this.

Thanks
Gary

[EC8010]

Ribbon microphones include a matching transformer within the microphone, so although the ribbon is only about 0.2 Ohm or so, it typically appears as 200 Ohm via the 1:30 transformer. Despite this, they're generally low output and a 4038 typically needs 70dB of gain on the desk compared to 60dB for a condenser. What this all means is that your primary concern is low noise. Input impedance of the pre-amplifier is not critical, just so long as it doesn't load the microphone down, so >2k.

I can only assume that if your "high end tube pre" doesn't sound good with a ribbon then it isn't really "high end" at all.

There have been a number of threads on microphone pre-amplifiers, so do a little more searching. I would warn you that a microphone pre-amplifier and an RIAA pre-amplifier are the two hardest analogue audio challenges. (RIAA pre-amplifier techniques are very similar, so have a look at them as well.)

[garyk]

yeah..it is a challenge...as I say, no-one has really given me a definitive answer yet.

A few manufacturers say that their products are good with ribbons, and yes, 70 - 80dB clean gain seems to be the target. Some say the Telefunken V76/77/78 are very good with ribbons.

There may be some logic in what the input to some of the pre's has...eg transformer coupled, etc.

The tube pre I own IS really very high end, and works brilliantly for most applications and most mics...but I just don't find it good for ribbons for some reason.

The guy that makes the pre didn't have an answer (and he is well respected).

And, yes, the mics all have step-up trannies, but I still use some low ratio ones in between now and again to see if makes any improvements.

gary

[EC8010]

Another thought, I suspect that a mic pre-amplifier that sounds good with ribbons will have a transformer coupled input.

[garyk]

that's my thinking, too, (although I don't think my little Soundcraft desk has them, still sounds good) (and my tube mic pre DOES have them ......mmm...sigh....) and the exact nature of the trannies may be critical in this case.

The Telefunken gear has very specific types of trannies (in and out) that gives the modules much of their legendary character.

This is true of most tube gear....you can quite easily use a particular circuit design to get a result, but the sonic footprint has a LOT to do with the sound of the iron.

Gary