Lundahl 1:110 ribbon trafo

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El Fito

Well-known member
Joined
Apr 23, 2005
Messages
53
Location
London, UK
Guys

I have just spoken to Per Lundahl, who's told me that Lundahl has just developed a 1:110 trafo, which is suitable for use in ribbon mics, provided there is an active output stage between the trafo and the output.

This all sounds very exciting and could potentially overcome the objections regarding the painfully low output of ribbon mics.

Two points about this new trafo:

1- How would you envisage the circuit for the active output stage?; and

2- What are your initial ideas/impressions about a trafo of this kind?
 
Hey, that's good news! I suppose all you need is a simple impedance converter. That's how the Royer active ribbons work: a high turns ratio transformer plus an active impedance converter, supposedly FET based.

Take a look at PRR's Phantom Mic Booster in the active ribbon thread p. 4
http://headfonz.rutgers.edu/BR-pre.gif
That's pretty much what you need. Perhaps the circuit could be optimized to some degree for this particular transformer.
 
naa.. 1:10 wouldn't qualify as a novelty.

Lundall are wierd enough to do a genuine 1:110 :razz:

Your 1 Ohm ribbon would translate into around 12KOhms, which makes sense with an internally mounted buffer amp...

Jakob E.
 
fito

nice discovery.... :grin:
this looks really cool... i talked to clarence cane and he said he uses the lundahl trafo's.

thanks for the info .... you've been scarce lately ....
nice to see you posting .... :grin:

later
ts

PS :grin: lol... you get that fox? lol ... :grin:
 
Wes Dooley I believe told me that some of his AEA RCA-like ribbons are abour 0.2ohm, so this would mean an output Z at the secondary of about 2.4k. So it would be a good noise match to a 2SK170, or a good bipolar run at optimal current. I suspect you could still tolerate some gain in the buffer amp as well and not overload.
 
thats pretty cool news, Id certainly be into trying that out. I would say, however, that in my experience the low output of ribbon mics is more the exception than the rule with the ribbon mics I have used- most ribbon mics I use have an output that is similar in use to what youd get out of a sm57, so for most things that arent whispy female vocals, any old preamp is generally fine. Part of the cool thing about using a ribbon mic in the first place is being able to run a preamp wide open which most definitely adds character, I think somehow this idea gets overlooked especially when people cry about low output which is honestly something I rarely am faced with. Not evey mic needs the output of a condenser, not every mic needs to work on every source, but you know, that said, it would be real cool to check out the new lundahl as an alternative choice for a different color. Not every ribbon mic needs this though to be a useful and functional tool.

I wonder how big the transformer is- not all ribbons have the largest cavity in the world to house a larger transformer.

dave
 
Hmmm, what is the perm of that amorphous stuff?
Is KevinC still kickin?

Amorphous needs a bigger space because of air inbetween the thin layers, so the transformers that use this stuff end up a bit bigger than their permalloy counterparts, but with a ribbon mic, you are not going to saturate the core.
 
Well it seems to me that 1:110 is an EXTREMELY high turns ratio and quite unusual. Given the very low source impedance of a ribbon element, it may be easier to pull it off. It should be interesting to see what he comes up with.

As always; did I mention that I hate transformers? <grin>
 
> 1:110 is an EXTREMELY high turns ratio and quite unusual. Given the very low source impedance of a ribbon element, it may be easier to pull it off.

Turns-ratio is never the real problem. We only think it is because we usually have some specific primary impedance in mind. But the real killer is: how high is the impedance of the highest-Z winding? If it is more than 10K or 50K, response becomes less than hi-fi. You may need to stay down lower for very extended bandwidth.

At very low impedance, you can end up with wire too fat to bend around a core. Parallel turns or ribbon wire can take you very far. If the secondary is ~2KΩ, we are probably looking at 2,000 turns there. Then a 1:100 ratio implies 20 turns on the primary. For a small core, the length of turn is around 1 inch, say 2 feet for 20 turns. If the source is 0.2Ω then we would love copper resistance below 0.02Ω. 10Ω per 1,000 feet comes to #19 copper. #18 copper is readily available. At 1mm diameter it is a bit stiff for a small core. Anyway we do want to interleave away some leakage inductance. Three 20-turn windings of #24 between four primary windings should give good coupling, low loss, and not require heroic winding force.
 
I think I learned more about transformers from that one post then I have frrom all the theory I have read. For some reason that little blurb just pulled it all together for me and made it all make sense. Thanks.

adam
 
Also considered is how flat the wire will lie. You need a nice flat bed to start off with if you are going to wind a ton of thin wire layers.
 
I think the C would still be small from a audio band resonance standpoint.

I'm thinking the geometry might favor the packing of the layers of the secondary, compared to a circular geometry heavy wire taking up its space. I guess a square or rectangular wire would be fine as well, such as are used for voice coils sometimes.
 
Speaking of taking up space, I was talking with my xfmr guru last night and he told me that Koss, Sony, AKG headphones, Shure SM57 coils, etc; are all wound on the same Swiss winding machines. Some applications use a heated mandrel to melt the varnish off the wire as you wind, which saves space and holds things together. Interesting. I guess flyback and yoke coils are done in a similar manner. I do not kbnow how the turns keep from shorting, something about the varnish only melting on the sides of the coil.
 

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