u87 output transformer

Hi Guys,


I was wondering if anybody knows what the turns ratio is for u87 output transformer? I am considering modifying my u87 guts now I have the Innertube retrofit. I know that TAB funkenwerks do an upgrade transformer, but I was wondering what else might be available? Cinemag and Sowter do something, but size and/or ratio might be wrong.

Actually whilst I'm at it, does anyone know the ratios of any other mic output transformers, such as Neumann u47(tube) u67/m269, m49? Howabout Haufe T14/1 (C12/C28/ELA m251?)

HaufeT14/1 would just fit in the battery compartment, I think . . .


Any help warmly appreciated!


ANdyP

Do you have the docs on the retrofit? I have a toasted Fred Cameron U87 and the docs on it are not available anywhere, maybe this is close.....

Hi,

I don't have documentation, and was very politely declined when i emailed Steyne at Innertube! All is potted, and I don't imagine un-potting it in a hurry! Sounds amazing btw . .


ANdyP

Most likely a triode plate out to a transformer. The tricky part is making it fit a 87 body and connecting to the capsule housing part.

Pick a capsule, pick a tube, pick a B+, How muck lows or highs, pick a transformer, alloy(s), inductance, physical size, ratio low and high range of the input resistance of the pres it will be used with etc., caps to taste.

Does the innertube circuit have more highs than a u87 with stock electronics? If so I would guess the simplest circuits would be a cathode follower followed by a cathode biased plate out. Do the patterns still work? Lower voltage around 100VDC or higher 180VDC or greater? Does it work with the different versions of the 87?

One can change things in a stock 87 circuit first you need to ask yourself what don't you like?

Any pictures of the inside of the F.C. mod?

Kubi has buckets of info on the Haufe and stuff.

It might already be wired for cathode follower, is your output too hot when close micing?
If so, it is probably stock and would benifit greatly with a cathode take off.

Hi Gus,


Innertube has more extended top end than stock u87, but I think the is some compensation for the capsule rise - perhaps a small cap to ground before output transformer ala analag 6au6 mic. (?) Pattern select no longer works, with external continuously variable pattern from omni to fig 8 ala m49. There are two different retrofits, one for u87, and one for u87ai. I haven't measured plate voltages yet. Both halves of the 6922/E88CC/CCa tube are needed. I think that originally they used 6072, which I haven't tried yet. Mic is a tad noisey, and I have tried more than 20 different tubes! Best sounding/quietest is a National CCa that was very reasonably priced. Very expensive Siemens E88CC was as quiet, but sounded really bland - quite cold in fact. I have more tubes to try including Mullard E188CC and several flavours of Telefunken. (just moved house - dunno where they are!) Stock EH Sovtek 6922 was a tad noisey, and a bit "tired" . . .

I am very lucky to have a "redundant" u87 innerds to play around with. I have been following several threads here and at Klaus's forum, and removing the NFB network and associated "brown book" components makes loads of sense. I read somewhere that the Haufe output transformer is far from ideal. Not many things will fit(TAB funkenwerks obviously will, but $190!), and I was looking to see if anything else might do? T14/1 is small enough, I think, and €40, and no-one can argue that they don't sound good(C12/251/CM61/C28)

Dear CJ,


I'll pm Kubi. Yes. it is hot hot hot! Nothing my pre's can't handle though.


KIndest regards,

ANdyP

The output on the Cameron is of the Cenimag / Jensen variety, but the ID is sanded off.... it fits nicely in the base of the mic, but this one has no circuit board, all components are on the tube base.

I am not a fan of 6dj8 type tubes in microphones I have tried them in builds maybe I have not found the right circuit yet. Stock is a EH tube?

Have you tried a tube like a NOS 12at7 ONLY do this if you can change the heater connections to the tube socket? Is there switches or jumpers to change the heater pins because a 6072a and a 6dj8 have a different heater, shield hookup

Can you tell if there is a transformer in the innertube? If not maybe the 2nd 1/2 is a CF and the transformer is in the power supply

If both halfs are used can you ohm the tube socket and find any pins connected together this is to see if maybe a direct coupled CF or maybe there is a low pass RC filter between the first stage and the CF if it has one. A gain stage then a CF to say a 4:1 would make a hot output microphone.

I would guess the stock 87 transformer is better than a T14/1.

I might argue the very good capsules are the beauty in the C12 etc and maybe a different transformer than the t14 might sound better

Removing some of the parts does not make sense to me ADJUSTING some values makes sense to me. I would not remove the filter the 87 capsule sounds to harsh without it.

The ITA is a cathode follower.

http://www.twin-x.com/groupdiy/displayimage.php?pid=2729&fullsize=1

A basic idea for using an U87Ai and both halfs of a dual triode. One can build other circuit. Find the Neumann U87Ai schematic for the capsule section pins.

I used the pattern control as a rear capsule dropout switch and the pad should still work with a U87Ai.

Just a idea I did not place values on some things and the ones listed are just a starting point. I was Lazy 60VDC is 1/2 of 120VDC and a fairly common charge voltage and a bunch of tube microphones use around 120VDC B+. It might not even sound good. C1 needs to be picked for the plate output R at the operating point.

4:1 is just a starting point

Might have issues I have not built it just drew it up.

For the nady 1050,1150,apex460 modders look close at C1 and think about the stock circuit and capsule

hi Gus,


many thanks for your thoughts! Gotta say, I am actually not that interested in changing Innertube innerds, especially if to go to 6072 would need some soldering! It sounds trully awesome, Maybe it could be improved with another tube . . . There is an on-board transformer, think it is a Cinemag.(?) Agree that capsule could be harsh without filter, and plan to use a passive filter, cap to ground ala Analag 6au6 circuit. just keep changing the value til it rocks. It is not my contention that stock u87 transformer is not good, but I have heard it mentioned several times, and I think that Klaus uses a custom job from TAB. T14/1 is just an idea, since it is relatively cheep, and small! I intend to try each possible change one at a time. Nothing is irreversible afterall! Any suggestions are most welcome.


Kindest regards,


ANdyP

I am not telling you to change the innertube. I was just posting ideas. The simple schematic is an idea for a tube circuit for a 87.

Anyway I don't believe a lot of stuff I read about microphones on the web or tapeop or. I like to test check what ever I read if possible.

How is the microphone awesome if it has noise?

Hi Gus,

on a close source it is fine, but i would not use it at a great distance. Also, I have to say that noise is not really an issue whilst making pop records! It is noisier than my Sela T25, Neumann u47 tube, and Schoeps CM61. Definately noisier than it was as u87. Still acceptable though. I would ALWAYS prefer noisey-but-warm, sympathetic, non-sibillent mic over something quiet, but cold, brittle, and .un-appealing. Otherwise, I'd never use ANY ribbons, or for example any C12's, which are definitely not that quiet in my experience, even with 5* GE 6072's. Just my experience "in the trenches under fire" . . . .

KIndest regards,



ANdyP

Dear Gus,


thanks for sharing!


Kindest regards,


ANdyP

Hi Bockaudio,


thanks!


Kindest regards,



ANdyP

http://www.twin-x.com/groupdiy/displayimage.php?pid=2729&fullsize=1

Click to expand...

looks a lot like the U95 circuit

[quote author="strangeandbouncy"] Otherwise, I'd never use ANY ribbons, ...[/quote]

Hi Andy,

In this case look to your preamps - (good) ribbon mics have very low self noise.

Stewart

Zebra, hi,

with all due respect, i've been making records for 24 years. ALL ribbons are very insensitive. All ribbon mics(that I've used) need plenty of gain. Noise Is a function of of gain. I consider Neve, audix, helios, BBC, API, Glensound, RCA, EMI Redd, Cranesong, SSL, Calrec, etc etc(ie, the pre's i use daily) to be generally speaking, state of the art, and erm . . . low noise. However, if you regularly need 60+dB of gain, you WILL hear noise! I use STC, RCA, Coles, B+O, Royer and Beyer, . . . . . ( the mics I use daily). I don't know of anyone using such mics for, say, a quiet classical quartet. or as ambience in a very quiet recording. I know I wouldn't! Unless I wanted a hurricane blowing through the recording. As I said, I mainly make pop records, where noise is not really that significant a feature, but still, i would NEVER mic up say, an acoustic gtr with a ribbon mic, no matter how good it sounded, since the noise would be bound to be overpowering in the mix, considering the amount of compression I am EXPECTED to use!


Granny and Eggs spring to mind . . .


No offense intended!


ANdyP

Have you tried the Shiny Box ribbons?

i do not know how the dude does it, but they are pretty dang quiet.
Might be an amp inside the mic.

And only 200, 400 and 400.

The 200 dollar is my favorite, thank you.

CJ.

hi. I have . . . . and their on my Xmas list! (santa, I've been `good . . .)


Kindest regards,



ANdyP