Ribbon...transformer...rewinding

Hi there,
I have a grampian ribbon mic that came in for re-ribbon but it also has a broked secondary on the o/p transformer. The primary (ribbon side) is OK. The sec. winding is actually 50kOhm on this model (it has rediculously fine hair-like wire), and I was wondering if this is a good opportunity to try to rewind it for 200 ohms output. The lams slide out easily and the plastic bobbin is intact. I have little experience rewinding trafos so I need to know what I'm letting myself in for here.

Does anyone have any thoughts on this, in particular what kind of wire I would need to get for this. I have a salvage transformer from a shure 949 mic which I would be willing to use as a donor - could the wire from this be suitable or is that too simplistic.

What else would I need to do? For a 0.3 ohm ribbon to 200 ohm I calculate a turns ratio of 26, so I can measure the turns on the primary by using the PRR/cj method of wrapping 1 turn around, and then wind the secondary accordingly.

Any other ideas? I know the rewound trafo won't sound like the original, but at least it could be a low cost way of resurrecting the mic.

Cheers & thanks in advance
Stewart

OK, some interesting stuff here....

http://www.groupdiy.com/index.php?topic=2017&postdays=0&postorder=asc&start=15

[quote author="zebra50"]Hi there,
I have a grampian ribbon mic that came in for re-ribbon but it also has a broked secondary on the o/p transformer. The primary (ribbon side) is OK. The sec. winding is actually 50kOhm on this model (it has rediculously fine hair-like wire), and I was wondering if this is a good opportunity to try to rewind it for 200 ohms output.
Stewart[/quote]

Hey Stew,

I don't get how the hell ribbon trafo could brake--must be whether machanically damaged, or soldering--check it first.
Don't rewind it, I'm tellin' ya bro--one day you will need it... like I need it now... desperately :sad:

Hi Marik,
I just sent you an email about this - yeah, mechanical damage.

look how this mic element was when I received it.



There is damage to the trafo at the pins that connect to the secondary.

I have rebuilt the element and put in a ribbon. It seems a shame not to get it working somehow.

[quote author="zebra50"]Hi there,
I have a grampian ribbon mic that came in for re-ribbon but it also has a broked secondary on the o/p transformer. The primary (ribbon side) is OK. The sec. winding is actually 50kOhm on this model (it has rediculously fine hair-like wire),

Use simple common - collector buffer in the mic

xvlk

I know you can get 42 and 43 ga. magnet wire that some guitar pickup winders use. That is certainly hair like. If the wire is just damaged at the pins, maybe try to solder it back on . Is that feasible?

[quote author="thomasholley"]I know you can get 42 and 43 ga. magnet wire that some guitar pickup winders use. That is certainly hair like. If the wire is just damaged at the pins, maybe try to solder it back on . Is that feasible?[/quote]

The challenge though, would be to take off enamel insulation from the wire that thin, and my guess, very short end. I recall, I read somewhere, there is something (was it aspirin??? or some kind of chemical?) you put on the wire end, and then heat it up and enamel flakes off.
Anybody knows, or remembers?

[quote author="zebra50"]50kOhm on this model (it has rediculously fine hair-like wire), and I was wondering if this is a good opportunity to try to rewind it for 200 ohms output. [/quote]

Hi zebra and Marik,
here is simple fantom buffer for high-impedance mic.

(you must cut and paste link to the browser)

http://mujweb.cz/www/xvlkxvlk/buffer.gif

It uses fantom resistors for work. Only four
discretes, isn t it pretty ?

With it your ribbon will have the same gain as condensers.

xvlk

[quote author="Marik"][quote author="thomasholley"]I read somewhere, there is something (was it aspirin??? or some kind of chemical?) you put on the wire end, and then heat it up and enamel flakes off.
Anybody knows, or remembers?[/quote]
Marik, If you want to solder thin wires, you use pure
polyvinylchloride. It is used for make tubes for water-closed
waste.
Only put wire on PVC and solder it.
xvlk

You can take the enamel off with 600 grit sand paper and a light touch. Soldering also has to be at low temperature because this wire melts easily as well.

Thanks for the suggestions.
Wires are too short to solder, I'm afraid. I tried that first. Although I can unwind one end easily by a turn or so, the other end lies at the bottom of the winding & is impossible to get at.
My plan is to use PRRs idea in the other thread to wind a new primary around an old shure mic trannie I have. This lets me use thick, more easy to handle wire. I'll let you know how it goes.

xvlk
thanks for posting this circuit. I'm not sure I understand how it works. Is it for 48V phantom power? What type of transistors are they? What is the thing marked TR - is that the ribbon or the transformer?
Stewart

[quote author="zebra50"]xvlk
thanks for posting this circuit. I'm not sure I understand how it works. Is it for 48V phantom power? What type of transistors are they? What is the thing marked TR - is that the ribbon or the transformer?
Stewart[/quote]
Yes, it is phantom circuit.
if you not use 48 V, only recompute bias resistors value,
after formulas included.
Transistors are good low noise high beta, BC560C i.e.;
Tr is your high impedance ribbon transformer.

This circuit is symmetric common collector follower.
Emitor resistors are hiddden , they are part of phantom power
in the console. Collector power is that ground.

Transistors must be paired and mounted together with silikon vaseline,
for good thermal contact. Or use monolithic ones.

[quote author="zebra50"]My plan is to use PRRs idea in the other thread to wind a new primary around an old shure mic trannie I have. This lets me use thick, more easy to handle wire. I'll let you know how it goes.[/quote]
To wind low-impedance primary as outer coil have two effect:
high resistance per turn (that wounded transformer will have bad noise- figure) and secondary high impedance winding is inner == higher
winding capacitance. Not recommend it.

PRR, some questions ? Nice ribbon ZEN, isn t it?
xvlk

Thanks. I get that.
But the high impedence secondary is broken - that's the problem I have to solve.
Cheers!
Stewart

You might have an interwoven winding stucture, pri-sec-pri sec, etc, so rewinding might be a problem.
If not, it would be fairly easy to stick a few turns of #39 on there and see what your voltage ratio is.
Sometimes the PRR trick works beautifully, othertimes I have had to unwind the transformer to get the turns, usually on a high ratio tranny like 1:10 is when things don't add up right.
This is a linkage issue. When it works good, you do get exact turns.
When you don't hook up well, you get inconsistent numbers.
And noise can be a problem when measuring millivolts.

You can try to sand the enamel off the real thin stuff as you will compromise the mechanical strenght by taking away a little of the already thin copper.
I think te best way is to get a bigger piece of buss wire hot, melt some solder on it, then stick the thin wire to the buss wire, the ol "hit and git" method.

I would undwind the secondary if you can not repair it, and see where it leads to. If it finishes at one of your terminals, you are in luck. If it splices further into the winding....

Hope this helps and you could use the Schure wire to rebuild.
cj

Guys;
Turn your solder iron temp up or use a solder pot.
The enamal will burn off and if solder is applied it will tin and
wow great connection. This and a solder dip pot is how every
magnetics house does it. You are making a simple thing hard.

Depends on the gauge. 48 ga. will vanish before your eyes the second you hit it with the iron.
Imagine a hair coming in contact with the iron.
Can be very trick and very frustrating.
Absolutely the worst part of diy x-formers, lead breakout and soldering.
I mean, after all that careful tedious winding, you can't wait to hear it!
:guinness:
I remember a mechanical stripper we had, it was three blades hookeg up so that as you increase the rpms, the blades closed down on the enamel and you just pulled the wire thru and presto!
Reminded me of a hellicopter.

Thanks for all the tips. I could solder one end (the outside) OK but the wire was broken off too short to get too and it would have meant unwinding the whole thing. I'm not that brave (yet).

I got the mic working. I used PRR's suggestion. I removed the lams from the shure xfo, wound 10 turns of thick xfo wire around the outside, then relammed. Checked out with a turns ratiop of 1:49 - about twice what I wanted and there was no room to put another 10 turns on. Fortunately the 'secondary' had a centre tap so I just wired one half of the secondary to the output. The mic works fine - sounds pretty good, in fact. Definitely worth exploring.

Cheers!
:thumb:

nice info here
thanks
ts

[quote author="CJ"]and soldering.
[/quote]
what ????
use Aspirin instead of colophony...

xvlk

zebra50 said:

PRR/cj method of wrapping 1 turn around, and then wind the secondary accordingly.

Click to expand...

CJ said:

Sometimes the PRR trick works beautifully, othertimes I have had to unwind the transformer to get the turns, usually on a high r

Click to expand...

Hi,
it's an old thread but is there a chance someone can explain what is PPR's trick/method?

thank you