Ribbon mic with Mackie Preamp

It's a little slow here today - either that or posts are being deleted as quickly as they're being posted.  

Thought I'd put up another worthless poll.

I should have a pair of Oktava ML52 ribbon mics on Monday.  All I have for mic preamps are a Mackie 1402 VLZ Pro and a 1402 VLZ.  Am I going to be able to use the mics?

What's your opinion?
If you'd like to place a bet that your vote is correct, post a reply saying what option you picked, and the amount you are willing to wager on your pick (virtual money only - AudioMastersBucks only - no exchange rates will be calculated).  When the poll expires - or maybe before - I will let the results be known and will divide the sum of all bets placed among those who voted correctly to see who won what.

Hehe! Based simply on engineering principles, and gear psychology, answer two, (which at present has 100% of the votes, of course) is the only possible answer - apart from a few options not in the poll, that is. The obvious missing one is

I'll hate them so much that they'll be on Ebay in a week.[/list:u]

I voted 3, in the hope that it is physically possible to record with your current pre-amp.  If so, this is a perfectly possible answer

The obvious missing one is

I'll hate them so much that they'll be on Ebay in a week.[/list:u]

The poll is about the preamp/mic relationship - not the mics themselves.  You're option is certainly a possibility though.

I found this site with MP3 and WAV samples of a bunch of different mics on some - uh - questionable material.  The ML52 is one of them along with a Royer 121 and an AEA R-84 (there may be other ribbons, but these are names I recognize).

From what has been said before about the ribbon thickness, the results seem fairly predictable - a little bit darker than the other ribbons, but a similar character in the sound - and a very different sound than the condensers.  At this point I expect they will be a welcome addition.

The obvious missing one is

I'll hate them so much that they'll be on Ebay in a week.[/list:u]

The poll is about the preamp/mic relationship - not the mics themselves.  You're option is certainly a possibility though.

It's okay - I was only joking!

You'll have to increase the gain level somewhat from the settings you'd normally associate with a large diaphragm condenser mic, but there should be enough gain for most practical purposes, I would have thought. In principle, ribbon mics should work best with current-input preamps like the JoeMeek ones. This is a combination that I haven't tried yet - there are one or two things that I need to attend to first before trying this - I have an idea that may get around a number of known ribbon system problems relating to transformers, but this will require a mod to a mic, and they take longer to do.

It's okay - I was only joking!

I figured as much.  We need a TIC smiley.

Mic. preamps are pretty basic electronically and easy to make good, unless you make them out of the cheapest components to begin with, like manufacturers for consumer mixers used to do until a few manufacturers like Mackie decided to use standard pro-level electronics for the growing 'pro-sumer' market.

I bet one would find it hard to tell a basic Mackie mic. preamp from a transparent boutique preamp.  So although i voted for choice #2, i bet anyone would have a hard time telling the difference without an instant A/B comparison, and even then might prefer the Mackie sound [or whatever] over the more expensive preamp on certain source material, in particular with a blind test.  

Mic. preamps are pretty basic electronically and easy to make good...

You think so? I think you'll find that the really good ones aren't simple at all. And they're not basic either. There are some serious compromises going on, and if you want a noise and overload performance that will do justice to a half-way decent mic, you'll find that you have to make rather more effort than you might think you would to achieve it. And not all topologies suit all mics, either. What's good for a condenser mic is very unlikely to be optimal for a ribbon mic at all. Don't get fooled by those silly schematics you find on the web - most of them are hardly a beginning.

The Mackie preamps are good - there's no doubt about that. But some of the sonic qualities of really expensive mic preamps take more than a quick A/B/X test with dubious source material to determine - the qualities of some of them are quite distinguishable, and with the right source you might be rather surprised at the differences.

But what do I know? After all, I've only been designing and building them for 30+ years...

Ya and i guess it's relative.  I mean poeple have known how to make a good mic. preamp for 30+ years and designs keep getting better, but until recently mic preamps on mixers have been a major compromise, due to cost, but presumably Mackie and others now know how to make at least one great neutral preamp design cheaply.  

And then there are the variable impedance mode preamps.  I'm not sure what to think about them...    I guess i might want that for use with the ribbon mics.    A.R.T. makes a dual variable-impedance preamp.

The current Mackie design is no secret - I have a copy of the schematics, and it follows one of the classic semiconductor design topologies, with quite a bit of care taken over the layout.

All of the variable impedance mic preamps are still voltage-input preamps. Whilst it's quite correct that the loading on the mic can make a difference to the reflected damping in the capsule (this does not apply to condenser mics), it's by no means certain that this is the optimum way of extracting information from it. The only person who has recognised the other possibility and made a practical design out of it is Ted Fletcher, with the JoeMeek preamps. The fundamental difference is that these are current input preamps, not voltage input ones. It makes virtually no difference to a condenser mic, but a world of difference to a dynamic one, and by extension, a ribbon mic. For one thing, it virtually removes all of the effects of capacitance from your mic cable at a stroke... which means virtually no cable noise. Since by virtue of their very low impedance, ribbon mics generate a significantly lower level of self-noise, and have a relatively low energy transfer level, anything like this should make a significant difference to the results.

What I want to know (and this is the bit that's going to cause a rebuild of a microphone) is whether by using a current transfer technique on the ribbon element directly, we can cut out the otherwise inevitable transformer. Because in theory we should be able to lose it, in a way that wasn't possible when the mics were first invented. A current input stage with valves is an interesting idea, but the nature of their characteristics seems to preclude a practical one completely!

There's no real mystery about the current input technique - it has a number of industrial uses, and the firm I work for some of the time for has been using the technique for years. But it's conceptually harder to grasp, and this seems to have put off virtually all audio designers except Fletcher. I have to tell you that when I mentioned the technique to him, his eyes lit up, because people don't talk to him about it very often. He waxed eloquent for quite a while, and confirms absolutely the difference in performance it can make to any dynamic device - but freely admits that there's virtually no difference on a condenser mic. To me, everything he said made good engineering sense, so it's got to be worth a try - because a ribbon capsule is the ultimate current output device. It has an impedance fractionally above 0 ohms, and produces virtually no voltage output at all as a direct consequence of this. Normally the transformer raises the effective impedance to about 30 ohms, and in the process provides a small voltage swing. What I want to produce is a 'virtual' transformer, if you like, that has none of the disadvantages of a real one. It has been noted by all ribbon mic designers that the transformer plays a significant role in the quality of output from the device, so I'd like to see if we can't improve them even more.

But I have to say that current input stages are not entirely trivial to design - a whole different set of parameters come into play.

I've had modifications done on several of the early '60's Altec mic-pre's designed to optimize use with both ribbons & condensers . . . designs are of course voltage input.  Unmodded the preamps (again perhaps obviously) work fairly well with ribbons . . . but the overall performance enhancement is enough that I'm intrigued by your current input mod to the mic itself

One of my workhorse mic-pres is the API 3124 and I've never felt that it showcases the ribbon's to their best advantage . . . in the studio this is not a big problem but unfortunately I'm crazy enough to carry some difficult to replaces 44's and Pevey velocity mics into remote situations (and have gotten impressive enough results that at least one touring act is toying with using ribbon mic's & old valve preamps as their primary reinforcement)

is the mod you're thinking about one that could be applied generally to any ribbon mic?

not appealing for trade secrets or tech details, just wondering if I should start the search for a broken (i'm not likely going to release a 44a for a speculative mod) vintage ribbon . . . (my equipment budget is set for this year and there is certainly a price point above which an interesting idea starts to be less attractive . . . if & when you work out the details I'd be interested in at least hearing a price)

I like ribbon mics and feel I've used them with good effect on a wide (and broad) range of material.  I'll also be the first to admit that I lack the technical chops to know if my internal belief that impedance matching between vintage ribbons and modern solid state preamps being a bit problematic has any credibility . . . but it feels like it does . . . and has 'felt' that way since before I even knew what a mic-pre was (or why I couldn't just plug my guitar into the console (electrons are electrons after all) and supervise the session from the control booth rather then depend on unsympathetic idiot willingness to trigger the talk back).  

So while I can't visualize what the mod would look like it is an idea that intrigues me.

Well, it's not a trade secret any more (although it virtually was at one stage), and I have a very good idea of how TF did his version (okay, I took one to bits and reverse engineered the input - only slightly naughty...) - but it won't quite do for what I have in mind. When I said 'replace the transformer', that's exactly what I'm going to do - and this implies that you get an active ribbon mic - which is at present unheard of, AFAIK.

There are several reasons for doing it this way - phantom power is easily available nowadays, and taking the direct connections to the ribbon down the mic cable is not a particularly desirable thing to do, even though it's possible. So the (very small) active front end is going to be in the case where the transformer would have been. This makes it a relatively complex retro-fit. Fortunately, I have a candidate mic for the purpose - an old Reslo with an open-circuit primary on the transformer. This is effectively useless without either a new tranny or a modification, so a mod it is going to be. It's not one of my mics either, but I am related by marriage to its owner, so I have to be a little careful with it... because this mic is rare. Have you ever seen a Reslo SR1? It's got a ribbon twice the length of all the other Reslos I've ever seen - about 2" long. And apart from the fact that it doesn't work, it's immaculate - original box, leaflet, the lot.

So I've located some bipolar I/Cs with a low current noise spec, and they should arrive next week sometime. Then all I have to do is play around with the topology, and find out what actually works. Since the ribbon is a current generator, and therefore susceptible to interference fields, I suspect that a simple current input won't do, because it's inherently unbalanced. And if anything is going to take some sorting out, it will be this aspect of it, I fear. So please don't hold your breath.

Oh yes, your basic question! Yes, this should work on any ribbon mic, although there is one thing that will have to be adjusted in pretty much every case to get the response correct, I think.

So while I can't visualize what the mod would look like...

As small as I can make it - it really can't be any bigger than the transformer it has to replace.

The only update so far is that I've had another word with my bro-in-law about his mic, and under the circumstances, he says that he's absolutely happy for it to be used as a test bed for this project. Not that he really has a lot of choice...

A current input indeed does make sense for a ribbon its basic principle is F=BxIxL (Lenz). Just like a transconductance amp make sense for a ribbon speaker.

I'm very curious about your results Steve, keep us informed. Not sure if interference fields are going to be a big problem, the impedance of the ribbon is very low after all.

PS: there are ribbons with an active head amp, but I doubt they are current based: http://www.royerlabs.com/SF-24.html

PS: there are ribbons with an active head amp, but I doubt they are current based: http://www.royerlabs.com/SF-24.html

Yes, I hadn't noticed that they were actives. But I think you're right - since they are using FETs as input devices, they are almost bound to be voltage amps - which is what I'm trying to avoid. Since most of the extant literature compares bipolar and FET performance in voltage amp terms, it's rather hard to second-guess what will happen with a current amp configuration, because we're looking at a completely different noise generation mechanism. I suspect (but I'm not absolutely sure yet) that the bipolar technology will win out, and since this doesn't cause any immediate configuration difficulties, that's where I'm starting from. And in noise performance terms, I think that this is going to push my B&K measuring amp to the limits of its performance - we've had these problems with current sources before!