what kind of Mic input trafo would you like in a console

I am debating mic input trafos on a console as currently in the whirwind of instalation is a new Pre and EQ design for the sony 3056. The eq's are slowly progressing as I got a baiscly front pannel layout almost complete that looks nice and have a schemo I am working out.

But what do people like in trafos and why. this isn't a color VS no colour sort of thing. This is a what sounds good to you and why? Keep in mind that this will ultimately be tied to a 990 footprint opamp. Not a 990 but thinking of one from JLM. :thumb:

I have had a few ideas in mind but lack of time has me wanting to cut the fat and get to the point.

I'm wondering about bayerdynamic transformers as I have a feeling they would be quite nice and be unusual not in any console I know of. opinions

Avalon uses lundhals in their M3 mod for said console. which is possibility.

Sowter makes a nice neve style but the specs are 1:4 not 1:10 which I would rather have a 1:10 so I can pull roughly close to 70 db max gain out of the Mic pre.

Jensens been done and are to $$ for what is needed. they are clean but looking for a bit more color.

suggestions and why?

There's a reason you don't find the little Beyers in consoles: they saturate at the drop of a hat. [EDIT: And as cropped up in the discussion of New York Dave's MILA preamp, they have high DC resistances, which means they are comparatively noisy.]

If Jensens are too pricey, I'd go for Lundahls.

Peace,
Paul

JLM 1:4 or Beyer, if you want even more 'sound'. Even with 1:4 you should still be able to get more than 70db total gain out of the channel. What kind of topology are you thinking? Surely youll have to have more than 1 opamp per channel...


M@

[quote author="pstamler"]There's a reason you don't find the little Beyers in consoles: they saturate at the drop of a hat.[/quote]

I thought many famous consoles used Beyers. Helios, MCI, Phillips and many others I cant think of...

The low headroom thing is certainly true but in actual practice this is less of a problem than youd expect. I have 7 mic pres with Beyer input transformers and I love them. 6 of them are Phillips A class (similar to the first part of the Neve BA183 circuit) transistor pres and theyre my main drum pres. Ive tried them with input pads but I always prefer the sound without. The other is an MCI 400 channel which is one of my fave pres for...just about anything. I rarely use the pad with it, even with fair hot output mics and I never have problems.
Theyre also the input transformer for the repro amp in Ampex 440 tape recorders. Soundguy reckons they are a weak point because of their lack of headroom, but Ive read about problems with the repro amp circuit distorting horribly when overdriven, so Im not convinced yet.
Noise wise, I dont know. My Phillips pres are all BC109s and carbon resistors so the electronics are too noisey to tell, but the MCI is fairly quiet.

I can definitely vouch for the sound of this transformer though, for rock and roll especially but certainly not limited to that!


M@

Studer mixers uses Beyers.

Many Studer recorders uses Beyers.

Ntp 179-160 uses small Beyers for input - though in an ingeneous coupling.

That kinds says it all for me :razz:

Jakob E.

[quote author="mattmoogus"][quote author="pstamler"]There's a reason you don't find the little Beyers in consoles: they saturate at the drop of a hat.[/quote]

I thought many famous consoles used Beyers. Helios, MCI, Phillips and many others I cant think of...

The low headroom thing is certainly true but in actual practice this is less of a problem than youd expect. I have 7 mic pres with Beyer input transformers and I love them. 6 of them are Phillips A class (similar to the first part of the Neve BA183 circuit) transistor pres and theyre my main drum pres. Ive tried them with input pads but I always prefer the sound without. [/quote]

Do you happen to have some schematics of those Philips pre-amps ?
The combination of Philips (my employer) and Beyer (the stuff in my junkbox) sounds interesting, would be nice to have a look at those.

Have even no idea how that stuff looks like - probably greyish, but that's all I can think of. Got any type-no's ?

Thanks,

Peter

www.recordingconsoles.net has a good pic-collection:

http://www.4sync.com/rc/picdisplay.asp?itemkey=459
http://www.4sync.com/rc/picdisplay.asp?itemkey=115

Jakob E.

I really like these beyer transformers. I haven't had any problems with saturation (saturation is not always a bad thing!), and they are probably good if you a looking for a bit of colour / saturation with lower level sources. A pad should help keep it clean if need be anyway.

[quote author="clintrubber"]Philips (my employer) and Beyer (the stuff in my junkbox) [/quote]

Peter, where in Holland are you working?

My friend was recently researching at Philips Natlab Research in Eindhoven. Secret research!

Please don't call the box with Beyer transformers a "junkbox"! It is a treasure chest!

The Beyer "peanuts" do have a reputation for saturating at fairly low input levels. Beyer's own max input level spec is 300mV at 30Hz. Assuming that they mean RMS and not peak--they don't specify--that's -8dBU, well below what a hot mic on a loud instrument can produce. And the max level will be somewhat lower than that at 20Hz, of course.

The "peanuts" also have a reputation for poor low-frequency response. This doesn't show up in bench tests (at least not mine) because the frequency response is very good down to 20Hz when driven from a 200-ohm resistive source. But I've never met a mic with a purely resistive source impedance, so it may not perform as well with some real-world mics.

As for sound: I'll let you know. I haven't even had a chance to listen to the MILA-1 yet, although it measures very well. Soundguy make a very good point in the "records that sound like crap" thread, that we need to keep differences in personal taste/experience in mind when discussing the subject merits of transistors, chips, transformers and so on. For example, Scott Dorsey's (from Usenet) hatred of Beyer inputs is well-known. And Paul doesn't seem to care much for them, either. But unless I'm mistaken--and I hope Paul will correct me if I am--both of these fellows work primarily with acoustic music. The same qualities that may render Beyer inputs lacking for, say, bluegrass or folk recording could be the very things that endear them to someone else who records a different sort of music.

At any rate, it's pretty impressive that Beyer was able to make a transformer as good in such a tiny package. They used special techniques that were detailed by Beyer engineers in an AES article many years ago.

[quote author="NewYorkDave"]...we need to keep differences in personal taste/experience in mind when discussing the subject merits of transistors, chips, transformers and so on. For example, Scott Dorsey's (from Usenet) hatred of Beyer inputs is well-known. And Paul doesn't seem to care much for them, either. But unless I'm mistaken--and I hope Paul will correct me if I am--both of these fellows work primarily with acoustic music. The same qualities that may render Beyer inputs lacking for, say, bluegrass or folk recording could be the very things that endear them to someone else who records a different sort of music.[/quote]

I think you're correct, although Scott records more loud electric stuff than I do these days. But my experience with these trannies -- from the Ampex MX10 mixer days -- is that they saturate pretty unpleasantly from just a vocal through a condenser mic. Not a nice, euphonic saturation like I've heard with, say, Neve stuff, but something that sounds more like a not-very-good fuzzbox. What they did with a National steel guitar was not pretty. When I replaced the Ampex's iron with Triad A11J's, boy did the sound get better. It still had some iron sound, but in a very good way.

Peace,
Paul

I got ten of 'em (new in the package) for less than $15 each in a group buy, so I've got to learn to love 'em somehow :wink:

[quote author="pstamler"]they have high DC resistances, which means they are comparatively noisy....[/quote][quote author="pstamler"]they have high DC resistances, which means they are comparatively noisy....[/quote]

[quote author="NewYorkDave"]...the frequency response is very good down to 20Hz when driven from a 200-ohm resistive source. But I've never met a mic with a purely resistive source impedance, so it may not perform as well with some real-world mics.
[/quote]

Can someone possibly elaborate on DC resistances on mic transformers / source impedances being more resistive?

Does resistance on the transformer simply cause loss, or what is it that spoils the noise figure?

What difference does it make if the source (mic) impedance is more resistive? Is this because the "resistance" effectively varies with frequency when the source is closer to a purely err.. capacitive and inductive (ie. the opposite of purely resistive) source.



Sorry for my badly written questions - I have a terrible hangover and my brain is slow...

[quote author="gyraf"]www.recordingconsoles.net has a good pic-collection:

http://www.4sync.com/rc/picdisplay.asp?itemkey=459
http://www.4sync.com/rc/picdisplay.asp?itemkey=115

Jakob E.[/quote]

Thanks Jakob ! :thumb:

Beyers may have a technical rep that is this or that, but they have a sound which compared to modern transformers can ONLY be described, even by the biggest monkey out there, as shitty. Small shitty transformers. The thing about beyers that is really really really cool is where they'll place upper midrange material and how much lows they roll off. When things were recorded with the intention of going to vinyl, those transformers must have been looked at like magic, they just by accident put you where you needed to go. Now that our bandwidth is so much wider today you can only really look at a transformer like that as effect. Ampex machines are full of them, helios consoles, Ive got some melcor stuff with them, beyer made lots of different types and to my ear they all have a similar thing. The magic of any transformer and really the whole purpose of using one IMO is not so much the sound they impart but where they place things psycho acoustically and this can NOT be matched with any active circuitry I have ever come across. Beyers put things in a unique place and sound pretty crappy in the process. If you know the sound of a lundahl, just invert it and you sorta get the idea of what a beyer can do for you. Beyers are hardly unusual, I suspect that most people that have been stuck with them are just trying to forget about them. Or maybe thats just me...

dave

thanks guys. Big thanks dave. definately something to think about... Beyers came to mind as they were different. at current leaning towards Stevens and billington trafos if I can ever get a sample to test and a data sheet. :roll:

Hey Jakob,

Which Studer mixers used Beyer transformers?


T

[quote author="rodabod"][quote author="pstamler"]they have high DC resistances, which means they are comparatively noisy....[/quote]Can someone possibly elaborate on DC resistances on mic transformers / source impedances being more resistive?

Does resistance on the transformer simply cause loss, or what is it that spoils the noise figure?

What difference does it make if the source (mic) impedance is more resistive? Is this because the "resistance" effectively varies with frequency when the source is closer to a purely err.. capacitive and inductive (ie. the opposite of purely resistive) source.[/quote]

Here's the story. There are typically three sources of noise, broadly speaking, in a microphone preamp. The first is the active stage, be it tube or solid-state. The second is the microphone; it has an output impedance which has a resistive component, typically 150-200 ohms. The third noise source consists of resistances.

All resistances generate what's called "Johnson noise" or "thermal noise" as a result of molecules jumping around at random due to the fact that they're not at absolute zero.

An example: let's say you have a tubed preamp. The tube itself generates noise; this can be modeled as a "noise resistance". That's the resistance which would generate a particular amount of Johnson noise if it was at the grid of the tube. You calculate the equivalent noise resistance by the formula R = 2.5/gm where gm is the tube's transconductance in mhos -- excuse me, Siemenses. I'll use the old name because it's easier to type.

So let's say the tube has a gm of 1.45 millimho (mmho), which is typical for a 12AX7 at 0.8 mA bias current. The equivalent noise resistance is 2.5/.00145, or 1724 ohms. Put that into the calculator's memory.

That's the first item of noise: the noise of the active device. Next comes the source resistance. That's your microphone, transformed through a transformer. Let's say the microphone is 150 ohms, and you're using a 1:10 transformer that's unloaded (just to make things easier). The microphone's resistance will be stepped up by the square of the turns ratio, or 100, so it's 15k at the secondary. Put that into the stack too; so far you're up to 16724 ohms. If that was it, your noise would be proportional to that number.

But that's not it; there are resistances. First, there's the plate resistor, but you can essentially ignore that. (A story for another day.) Then there's the cathode resistor; if that's bypassed, though, you can ignore it too, as the bypass capacitor shorts out its resistance.

What you can't ignore are the DC resistances of the transformer's primary and secondary. Let's say the primary resistance is 100 ohms and the secondary resistance is 3k. (I'm pulling those figures out of the air.) Add the secondary resistance to your stack of noise generators. Now for the primary. It's 100 ohms transformed up by the square of the turns ratio, or 100x, so it appears at the secondary as 10,000 ohms. Add THAT to the stack.

Now the total resistance is no longer 16724 ohms, but 29724 ohms. That's almost double what you'd have with a perfect (resistance-free) transformer.

Your total noise from the circuit is proportional to the square root of the total noise resistance (in a tubed or FET circuit, at least), so if the resistance goes from 16724 to 29724, the noise will increase by sqrt(29724/16724), or about 1.33x, or about 2.5dB. That is how tranformers with high DC resistances increase the noise of real-world circuits -- just by adding more resistance, which generates more noise. Some tranformer makers list this as a "noise figure" -- the excess noise generated by the real transformer as opposed to a perfect, noiseless transformer with zero resistance in primary and secondary.

Peace,
Paul

[quote author="pstamler"]
All resistances generate ..."thermal noise" as a result of molecules jumping around at random due to the fact that they're not at absolute zero.

Let's say the primary resistance is 100 ohms and the secondary resistance is 3k. (I'm pulling those figures out of the air.) Add the secondary resistance to your stack of noise generators. Now for the primary. It's 100 ohms transformed up by the square of the turns ratio, or 100x, so it appears at the secondary as 10,000 ohms. Add THAT to the stack.
[/quote]

Ah! Forgot about thermal noise from sources other than the obvious... Thanks for your excellent description!

Roddy

Excellent description, Paul!

Like New York Dave I also got some Beyer transformers through Kubi's group buy. So far I've only used one 1:7 transformer. I recently found a broken MB (now MBHO) small diaphragm condenser. Got it for 5 euros at a flea market. :wink:

Since the electronics pretty much sucked anyway - apparently it was designed for hifi use - I built a new preamp/impedance converter. I followed pretty much the Neumann KM84 circuit using the Beyer 1:7 input tranny backwards. The mic sounds pretty cool. The self noise is about 20 dB-A, I would guess. That's not quite as low noise as a modern condenser mic, but I doubt it has anything to do with the tranny. The diaphragm is relatively small (low output) and I didn't include a DC converter for higher polarization voltage.

A couple of weeks ago I bought a Beyer M500, a handheld ribbon mic for vocal use. I'm amazed at how low noise it is. I have a number of chinese ribbon mics and I've also used Oktava ribbon mics. The Beyer feels louder, because it's designed for close miking. It requires about 6 dB more gain than a Shure SM58. If you use it at the same distance you would use a "normal" ribbon, you realize the output is really as low as on other ribbons. What really surprised me is the low noise floor. Even more so because the ribbon is pretty short and narrow. So I suppose the Beyer trannies used in ribbon mics must be really cool. :thumb: I wish I had some of those trannies as upgrades for chinese ribbon mics...

Beyer transformers: some guys love 'em, some guys hate 'em, some guys use 'em cause they got 'em for cheap. It just goes to show, there's no universal standard for "good" in audio...