Hey, Does anyone have any info on a suitable transformer for a ribbon mic that I’ve built? The cheaper the better, as I’ve checked out a couple that seem good (like Cine Mag) but they are still around $40. Which isn’t too bad, actually, but you know…

I wouldn't cut on spending when it comes to your transformer. It is one of the most important factors in ribbon mic design where matching impedances is very important since it can have a big effect on volume / frequency response / signal to noise ratio, etc. You should check the resistance of your ribbon transducer to find the right ratio to use too. Search on google for prodigy audio forum and use their forum to get info. Also, search for sowter, lundahl and jensen transformers. How did you make your ribbon mic anyway?

Well, basically I took 2 plastic light switch covers and sandwiched 2 magnets between them. (The magnets are the length of the covers and run vertically). There is a space between the magnets, and I ran a strip of silver foil between them, being careful not to rip it. (no easy feat). I then hooked up 1 wire to each side of the silver foil. This contraption is mounted on a plastic radioshack box with “Lâ€

Wow, that's some way to make a ribbon mic! Here's a good website that could be handy for you: http://www.lkmusic.co.nz/ribbonfix.htm

Make dure you use the right kind of foil. You are looking in the range of 0.5 to 3 microns thick. I use 0.6 micron stuff (ie. aluminium leaf) which is roughly the same as is used in STC / Coles mics.

Ribbon output is linearly related to mass (in theory) so halving mass will double the output - ie. thin foil is good in this respect.

Also, transient response is also related to mass, so thinner foil will give a give a better representation of treble and will generally sound better.

My method of corrugation of the ribbon, I use two gears (actually two telescope lens cases) and mesh them together covered in meths (alcohol) and run the ribbon through.

Let me know how you get on with finding a transformer. I'm actually on the lookout for one too.

Thanks for the info Rod! I am actually using aluminum leaf, and I have been using the tone wheel of my keyboard to corrugate the strip. Is it easier to use a fluid to do this? I have been doing it dry. (that sounds weird)

Tonewheels... What a good idea! Are you using the cotton bud technique or have you got two tonewheels which you mesh (is that possible)?

Its good to hear that you are using aluminium leaf. I have had some very good results using it despite the fact I have heard other people say that thicker stuff is better (they usually are incapable of corrugating the thinner stuff).

If it is working dry, then that is great. You just need to do whatever is best for you. Applying a little alcohol to you tonewheel befor you sit the foil on it will cause the aluminium leaf to stick to it (in a strange way). I find this makes things slightly easier since the foil is less likely to move or corrugate unevenly. You need to wait for the alcohol to dry before removal.

Make sure there are no rips or cracks in your ribbon when you are finished. You can check this by holding your ribbon assembly up to a bright light (assuming it is fig. of eight - yours might be cardioid-ish if it is mounted on a box).

Not cheap but great:

Lundahl LL2911, built specifically for ribbon mics. Up to 1:37.

$60 from here.

Hey--
Don't let anyone fool you. There are actually good, inexpensive transformers available.
You don't say what ratio you want, but Edcor and OEP are both cost-efficient audio transformers. Edcor is made in the US, and EOP is made in the UK. OEP used to make trafo's for some of the Neve consoles.

The down side of the Edcor is that its unshielded, and pretty large, but specs are actually very good, and they're $8. They have surprisingly good frequency response, and pretty low distortion.

The OEP's are available by special order through Newark. You must select the "include non-stock items" box when searching. They have that "Neve" type sound--a very rounded top end. They're about $16, and have a three week lead time from Newark

http://www.edcorusa.com/transformers/audio/matching.htm

http://www.oep.co.uk/audio_transformers ... rmers.html

Good luck!

thanks Puff Pastry! I don't think I would have ever discovered those transformers on my own. If they do sound like a Neve board, I would be pretty impressed.

Are those transformers not all microphone preamp input transformers?

Make sure you get a transformer with the correct load for your ribbon. If you don't, you'll end up with a terrible signal to noise ratio and other problems.

For maximum energy transfer, I think you want a transformer primary impedance to match your ribbon impedance (between 0.5 to 2 Ohms).

Also, the impedance ratio is the square of the voltage ratio, so for instance, a common 1:32 ratio transformer will cause a 1024 multiplication in ribbon impedance, so for a 1 ohm ribbon, you would get a 1024 ohm output impedance which is not good. You'd be aiming to get the output impedance in the range of 200 Ohms.