Aiwa HI-Z Ribbon mic - gut or what?

[mitsos]

A friend asked me to "fix" an Aiwa VM13 ribbon mic. I will upload some pics I took as soon as my internet allows me.

The problem that needs fixing is that the mic never gets used  ;D  Sounds nothing to write home about, whether that's an impedance thing or not, guess we'll find out.  My buddy is not averse to gutting it and making a "modern" ribbon out of aftermarket motors/trafos. 

As I see it, there are 3 ways about this:
1. Stock motor/new trafo
2. New Motor/stock trafo
3. New Motor / New trafo

I think the trafo need changing for sure, looks like it has 2K secondary DCR! so, option 2 is out, but I'm wondering if I should keep the stock motor and put in a new trafo for it or get a new motor AND trafo and build a whole new mic inside this thing.  In either case, I could use some enlightenment as to how to choose a trafo ratio/DCR, etc based either on this motor or one of the DIY options out there.

BTW, has anyone tried these motors?
http://make_a_ribbon_mic.tripod.com/noisyhaus/

thanks!

 

[zebra50]

I would say swap the transformer (or see if there is a different tap to it).

I don't know the VM13, but these old Japanese ribbons are usually quite nice. The VM15s are great mics.

So please don't remove the old motor in favour of a standard china motor! If you really don't like it then sell it (to me!), and buy a china mic.

Stewart

 

[mitsos]

I would say swap the transformer (or see if there is a different tap to it).

That's my first option for now, too.  BTW, how does one keep polarity correct here? Top of ribbon is positive or bottom?

I don't know the VM13, but these old Japanese ribbons are usually quite nice. The VM15s are great mics.

I'm still unable to upload pics to a hosting site, but dropbox seems to work sort of, so here are some pics to download (although it may take a while for the links to work, with my "high speed" internet):

https://dl.dropbox.com/u/16176593/Aiwa%20VM13/back.jpg
https://dl.dropbox.com/u/16176593/Aiwa%20VM13/front.jpg
https://dl.dropbox.com/u/16176593/Aiwa%20VM13/motor_back.jpg
https://dl.dropbox.com/u/16176593/Aiwa%20VM13/motor_front.jpg
https://dl.dropbox.com/u/16176593/Aiwa%20VM13/motor_top.jpg
https://dl.dropbox.com/u/16176593/Aiwa%20VM13/motor_top2.jpg

I'm hoping this one will improve with the new trafo. The old one is tiny and a very weird output impedance.

So please don't remove the old motor in favour of a standard china motor! If you really don't like it then sell it (to me!), and buy a china mic.

well, I'm not really sure what to expect, the motor is very strange looking, with the back almost completely closed by the two C magnets. I wasn't really going to do a china motor, I was looking at a couple of the DIY options available (mainly arthur ficher and the noisyhaus link above) in case the mic didn't improve much with just a trafo swap, but I'd definitely prefer to keep the stock motor.

thanks!

 

[zebra50]

The mic looks great, the motor will work just fine - maybe not totally hi-fi, but for my tastes it will be much better than those DIY options.

>BTW, how does one keep polarity correct here? Top of ribbon is positive or bottom?

Depends on the magnets.

The easiest way to check the polarity is to wire the whole thing up and then check against a known good mic (SM57 or whatever). Then just flip the wires at the output if you got it wrong first time. For some reason this happens more than 50% of the time.....

 

[rafafredd]

Great looking 77 knockout!

 

[Rossi]

Before you make any modifications, you should plug your mic into a Hi-Z instrument input. Most current audio interfaces and preamps have something like that for DI recording bass and guitar. Usually these are 500k or 1 Meg input impedance, which should be fine for your Hi-Z ribbon. Maybe it sounds totally usable that way.

Or you could construct an active impedance converter to go between your mic and your mic pre. Put it in a box and leave your mic unaltered.

 

[mitsos]

update... part of the issue was the original ribbon had a slight tear near the bottom.  It took me a long time to get ribbon material here, in the meantime I wound a new transformer on some 80% DU lams, 1:37 or so.  Re-ribboned the motor today, output was clean but pretty low... One option would be to rewind the trafo I guess, but then I figured the old magnets are also much weaker than newer ones, and I happened to have some neodymium "sticks" about the same length as the front of the motor, so I stuck one on each side and voila.. output went up to a more usable level.  Quick test, seems like it might work nicely on vocals!