UM-57 (Don't let this happen to you!)

[Gus]

I am not 100% sure why the 582 circuit is the way it is.

For cardiod only microphones I like not using an input cap it seems to have lower noise.

The cathode resistor not being bypassed lowers the gain a little. The tube used is 1/2 of a 12AT7.

IIRC Oliver posted at one of the forums that good alloy lams were not alway advailbe on the other side of the wall. Someone else at the old place posted that the feedback used here is alot like the feedback app posted at Lundall the 5402 transformer I think Sorry I forgot who posted that, it was a good find.

Maybe this is a clever way to use feedback to help a transformer with not so good lams and "burn up" some tube gain?

This is on my list of circuits to build and try out.

 

[peter purpose]

What a scumbag... I hope his earholes turn to arseholes and **** all over his shoulders.

 

[dale116dot7]

A fingerprint is a resistor in parallel with the high-value resistor, it happens to any resistor (even a 10 ohm resistor) but it doesn't matter until you are up there in resistance.

Almost certainly that's a Chinese capsule. A real Neumann capsule uses a plastic clamping ring, though from what I remember, the UM57 should use a glued diaphragm. The hole pattern isn't right either - it's the K67/87 pattern.

 

[jrmintz]

Thanks everyone. I broke the news to the guy who owns it, haven't heard back from him yet.

I hope his earholes turn to arseholes and **** all over his shoulders.

That's a hell of an image, Peter :green:

 

[toby]

my not be the right time to ask but who here has experience of a REAL um-57, how does yours sound Volki?

 

[soundguy]

Ive used two UM57s in the past and they were both kinda soft sounding, I couldnt find a good place for either on the records I was doing with them, but that shouldnt mean anything, we all have different taste. I think both mics probbably could have benefitted from a rebuild. I have two cmv 563's that are really similar, really soft sounding and need to have all the capsules cleaned. Id personally prefer to use new soundelux mics that mess around with old aging inconsistent mics like these UNLESS they have been rebuilt by a professional. Of course the rotting inconsistencies can be viewed as a really cool thing by some, the mics certainly didnt/dont sound bad, but when I listen to them I know they are only giving me maybe %60 or %70 of what I know they were probably designed to do. I would say in general, when it comes to condensers, Im not a real big fan of vintage mics that havent been rebuilt, they all tend to tell the same story.

dave

 

[tommytones]

I agree with Dave. Old mics are really subjective to their condition. I've had the pleasure of using some rebuilt UM57's. ..power supply was the biggest change. It was almost a complete redesign and it made a big difference I must say. I don't think I'd say they were soft sounding. Very similar to some M269c's I've used but the UM57 seems to have a rather distinct sound to it. Hard to pin point. Great mid range. I like them very much.

 

[toby]

cheers guys,

think i'll rebuild a couple more old, cheaper, mics for before i get one then :sad:

 

[soundguy]

dont let my advice talk you out of a vintage mic, afterall, its a likely good investment the way things have been going. The point is, with a vintage mic, unless you trust the seller extraordinarily, you really need to listen to the thing to have any idea what it sounds like. I cant understand the people who pay top dollar for vintage OLD mics on ebay without being able to listen to them. It may be good, but there are WIDE variations between one good U47 and another "good" U47.

dave

 

[volki]

toby, i actually haven't a/b'd any other LD tube mic's with my um57 yet, and as for some other mic's, i only had brief encounters, so i couldn't give a comprehensive opinion. I just fixed up my two m582 though, and since i have um70 capsules (containing the m7) to screw on there, i should be doing some a/b'ing soon there.

the cmv563 with m7 or m7s should sound similar to um57, yet not identical, since the capsule grill is totally different, which is likely to result in a sonic difference. the head amp circuit is the same, though.

about old gefell stuff in general, they especially are said to have large unit-to-unit variations due to material shortage on the other side of the iron curtain. the xformer ratio would vary, so would the material for it's lamination, and even the capsule would be made using a different metal sometimes. still they don't have a bad rep overall, and i really do like mine. only bad thing about my unit is that i did end up having all the trouble you're likely to encounter with vintage mic's. after i had it for a while, i sent it to gefell for inspection, and it turned out the membrane had perforations due to age. also the contacts from head amp to capsule were intermittent. eventually i had the capsule reskinned, but not with original PVC, but mylar-equivalent PE (sounds goot, too). later on, i had to resolder a loose contact in one of the connectors, and recently i got intermittent crackling and noise just sometimes, which obviously is to be attributed to the somewhat wierd mod's that my psu turned out to have, probably having cold solder joints or something. oh well. i still like the thing :grin:

 

[volki]

some more thoughts on the m582 circuit, if anyone interested.

lately i spoke to a renowned mic tech who is in contact with the company's developers etc. - he said that the fact that the m582 doesn't have a grid resistor is due to the fact that behind the iron curtain at the time, there weren't any sufficiently small resistors available to fit in between the capsule and the tube socket!! can you believe it. - so they just used the grid-cathode stray resistance for biasing, and since this rendered the thing an EXTREMELY hi Z input circuit, they put a couple of additional bypass caps in the place to prevent RF interference or oscillation. just compare the circuit to the um57 / cmv563, it's basically the same (plus grid R, minus the extra C's)

because of the missing grid resistor, the bias point obviously can shoot off into nirvana with very high AC voltages (settling takes quite a while), thus the m582 is likely to shut off at very high SPL or connecting/disconnecting a capsule with power applied to the head amp. - nowadays miniature R's are available though, so a mod shouldn't be a problem. :green: