Lundahl LL2911 in ribbon mics, thanks to Kevin Carter

[bradzatitagain]

Michael, Thank you for these good links! Good reads, all of them.

This activity is sort of like Miata racing or urban Toyota
customization.

Ain't it?

What's your present ML52 output impedance and what impedance do you find the mic loads best at after the addition of 18 guage wire and the Lundahl? Did you wire the Lundahl for 1:32 or 1:18?

Have you guys ever used Plasti-dip, meant for use as hand tool handle covering? Comes in small pots with pop off lids and in spray cans. Maybe not dense enough.

rgrds,
Brad

 

[Michael_Joly]

First, a tip of the hat to ribbon "motorman" Marik (again!) who's always pushing the DIY ribbon envelope - this time by considering ribbon output impedance.

Bradsatitagain,

I followed Lundhal's schematic and put all of the windings of the LL2911 in parrallel for a 1:37 ratio.

I run the ML-52 into a Studio Projects VTB-1 based on a glowing review by Harvey Gerst. "...the sound of the RCA 77DX in particular was spectacular thru the VTB1..."

Though his comment "...The low impedence setting definitely did the best job for all the ribbon mics..." has always puzzled me. The VTB-1 is spec'd as 300 Ohms input Z (low) or 2000 Ohms input Z (high) - I prefer the high impedance input setting of the pre because I assume I am loading the mic less. Marik, what do you make of this?

Brad - regarding ML52 grille resonance. There are three contributors to this resonant system: the vertical fins, the curved top fins and the horizontal ring between those two sets of fins. I attacked the grille one set of resonators at a time then measured the resonance reduction of each mod. First cut out the vertical fins and replaced with stainless steel mesh, then epoxy'd the curved top fins to the underlying wire mesh to lower amplitude, frequency and Q of this resonance. Finally, at that point, I then discovered the horizontal ring itself was a resonator and could only be damped by grasping it with my thumb and index finger - felt, rubber bands, hose clamps and lead foil all did not work.

re: your comment about the mic sounding like sticking your head in a plastic bucket - the resonances I described above are very high-Q, centered around 240Hz and can be reduced by at least 10dB by removing the stock grille. I did not measure how far below normal speaking level these resonances reside, but they are near enough to be heard as coloration of program material when excited by that same program material.

So Marik's advise to toss the top is right on.

 

[Michael_Joly]

Marik,

I re-read your comments about series vs. parallel and input / output ratio but I'm not following how the impedance of the Oktava ML-52 is transformed as you state.

Could you walk us through this? It's been a long long time since I did any DC theory

How does the input impedance load of the pre-amp get reflected back to the ribbons? What are the implications for transformer primary and secondary winding resistance and input/output voltage ratio?

 

[Gus]

I have worked on electro optic system that that was built on a optic table that floated on air supports. During the systems life parts were changed, One part when from being a steel weldup to a cast Al. Needless to say there where vibration problems besides the Al being 1/3 as dense some of the casing had to many air voids. The air voids where the greater part of the problem

What I think the major problem is with the Oktavas cast? bodys is what ever the metal is it is full of voids. You can have cheap metal and damp it however it needs to be as void free as possable. One why to test for this is the wine class type test. If you ping a wine glass with a high Q you can damp it touching the lip. Most metals if void free will damp kind of like this. The oktava does not damp much at all no matter what you do. I have coated the insides of the body edge damped it nothing stopped the ringing.

The only octava I will play with now it the 012 but then some of different plastics used at the capsule seem to be hyroscopic.

 

[Marik]

[quote author="Michael_Joly"]

I run the ML-52 into a Studio Projects VTB-1 based on a glowing review by Harvey Gerst. "...the sound of the RCA 77DX in particular was spectacular thru the VTB1..."

Though his comment "...The low impedence setting definitely did the best job for all the ribbon mics..." has always puzzled me. The VTB-1 is spec'd as 300 Ohms input Z (low) or 2000 Ohms input Z (high) - I prefer the high impedance input setting of the pre because I assume I am loading the mic less. Marik, what do you make of this?

[/quote]

Michael,

It's always pleasure talking to you and it is great that you found the way here :thumb: :guinness:

Harvey's comment... Well... It means... It means that obviously he has different... ears and sound aesthetics than us, if it makes any sense :grin:.
In fact, I always kinda hesitant to comment on sound for that very reason, and Harvey himself always emphasises that it very much depends on performer, instruments, room, monitoring, etc.
Also, we don't know what micing was he using. Ribbon mics tend to sound their best with more distance, where their huge proximity effect is much less of an issue. But even at 3-5' proximity still plays its role.
The effect of loading, when impedance of the pre through sec. and primary of the transformer comes back to the ribbon, mainly affecting two things--its bass response (kinda high pass, considering proximity), and IMO, also "chokes" the sound.
Both, stock ML52 and RCA77 are very colored microphones. We already know why ML52. RCA is because of very dense silk, which works as a pop/wind filter. BTW, RCA's frequency response specified for ribbon unloaded. In Harveys situation some additional loading probably helps to overcome some flaws of his specific situation, and probably suits more to his style of music, and his mix.
Anyway, for my taste, I prefer it unloaded, even though in this case transformer probably does not have its flattest response and may be there is some ringing.


[quote author="Michael_Joly"]
I re-read your comments about series vs. parallel and input / output ratio but I'm not following how the impedance of the Oktava ML-52 is transformed as you state.
Could you walk us through this? It's been a long long time since I did any DC theory
How does the input impedance load of the pre-amp get reflected back to the ribbons? What are the implications for transformer primary and secondary winding resistance and input/output voltage ratio?
[/quote]

Yes.
The impedance vs. voltage ratio is squared, so if we have 1:32 voltage ratio, impedance ratio will be 1:1024. As ribbons inductance is very low, it is safe to say that its impedance is equal to its resistance. For maximum energy transfer, primary of the trafo resistance should be the same as of the ribbon. IIRC, I measured ML52 ribbon DCR as 1.2 Ohm, but now, for some reason used 1.12 Ohm of the primary, which nevertheless is very close--now the impedance ratio we've got is 1.21.2x1024)=1.2:1228, for the secondaries in series.

 

[bradzatitagain]

[quote author="Michael_Joly"]First, a tip of the hat to ribbon "motorman" Marik (again!) who's always pushing the DIY ribbon envelope - this time by considering ribbon output impedance.

I followed Lundhal's schematic and put all of the windings of the LL2911 in parrallel for a 1:37 ratio.

So Marik's advise to toss the top is right on.[/quote]

10-4 that. Thanks fellows, I'm happy to eavesdrop on this one. New head grill on the way. Already removed the hf resonators/wind blast protectors on the motor, those cad plated goal post lookin' things, took off the grill, planted it behnd a Steadman pop filter and talked into it: plastic bucket miraculously has been removed from my bean. Lundahls plus the Cinemag RCA44 xfrmrs are on the way. Still think these guys were a bargian @ $160 each, the xfrmrs put them at street price about a year ago and the head grills will just be more thick brass pipe stock ordered along w/more of the same for other things. I'll report back when they're done.

rgrds,
Brad

 

[bradzatitagain]

[quote author="Gus"] What I think the major problem is with the Oktavas cast? bodys is what ever the metal is it is full of voids. You can have cheap metal and damp it however it needs to be as void free as possable. One why to test for this is the wine class type test. If you ping a wine glass with a high Q you can damp it touching the lip. Most metals if void free will damp kind of like this. The oktava does not damp much at all no matter what you do. I have coated the insides of the body edge damped it nothing stopped the ringing.

The only octava I will play with now it the 012 but then some of different plastics used at the capsule seem to be hyroscopic. [/quote]

I like Michael Joly's sculptural "voyages" w/Oktavas as pictured on the homerecording thread. The MC219s are $40 at my local GC until they're gone; worth it for the capsule & mod'd electronics alone, even if considered inferior by the multitudes. I got a couple despite wide net advice to walk past them. If they were $100 I would have, $40 makes my trigger finger too darn itchy. Even as a basis for a homebrew Lomo type LD head for the 012s or MXL603s.

 

[labcoat man]

This really is a great thread thanks for the valuable info! I'm a newbie carrying a few impedance issues with the LL2911 and I thought Id throw in my story.

Basically I modded an old lustraphone ribbon mic with a new LL2911 transformer. Pleased with the results on my ART TUBE MP (input impedance of 2k) I was a bit bummed out when the lustraphone sounded dull and useless through my beloved Ampex MX10 tube mixer.... the reason is Im pretty sure is that its 250 ohm input impedance is just too low for the Lundahl 1:37 set up.

Im a bit in the dark electronically but there are a few questions Id love to know the answers to.

On reading this thread Im guessing the impedance of the mic is around the 600 - 700 ohm mark....(based on a ribbon impedance of about .5 ohms which I think is about right?) two questions I have are....

Is there any quick fix for impedance matching one of the Ampex mic pre inputs (eg, with a resistor set up) to improve the result/ increse impedance the mic sees, or is there a good simple transformer replacement I could perhaps look at?
or is it far more complicated than that. There dosen't seem to be any mic transformers with an input impedance of 2k around.

Secondly... I have an old SSL pre with a Jensen 115k mic transformer at the front... the Jensen specs on this transfomer indicate a low impedance input of 150 ohm and yet the results from the ribbon mic are much better, clearer and more open than through the ampex. I think I must be confusing the input impedance of a transformer with that of the whole mic pre... ?.. anyway...

any ideas or thoughts would be appreciated of course!

Thanks

Tim

 

[skipwave]

[quote author="labcoat man"]There dosen't seem to be any mic transformers with an input impedance of 2k around.

I think I must be confusing the input impedance of a transformer with that of the whole mic pre... ?.. anyway... [/quote]

Mic pres tend to spec the output impedance of the microphone that the pre is expecting to be connected to, say 150-250ohm. The actual input impedance will be higher, possibly utilizing the ten-to-one approach so 1500-2500ohm. There is lots of info around about transformer secondary loading, and how that reflects a fixed impedance back to the transformer primary (input). keep in mind that the impedance ratio is the square of the turns ratio.

Hope that helps. Pstamler has posted lots of great explanations here on this subject.

 

[W DeMarco]

I have had a few killer conversations with Carter. Very helpful and interesting!

 

[labcoat man]

Thanks Skipwave, that helps,

I wondered about that, so its heartening to know that maybe my
ampex mx10 has an actual load impedance of around the 2kohm mark,
rated for 200ohm mics....

the world of impedance has got me spinning, I understand very simply that its important not to try and drive low impedance loads with high impedance sources and that the reverse can apply in extreme cases. Beyond that I think I better defer to the experts.

From Malik's post I kind of figured that the mic's output impedance would be the result of multiplying the 37 (turns ratio) squared by the impedance of the ribbon (from memory I measured it once at around 0.5 ) thats how I came up with the impedance of 684 ohms.... I could well be wrong....

I don't have the schematic that indicates the 1:18 strapping on the LL2911 transformer the only strapping I got was the 1:37, if anyone can help me out that'd be great. might be worth a shot to try and make it more compatible.

cheers

Tim

 

[kevinc]

If you want to try 1:18, which will sound somewhat different for sure, make the following wiring changes to the primary side of the transformers.

Remove the wires between 8/7 and 9/10 and between 1/2 and 15/16. Add wire from 9/10 to 15/16. Now you have 2:37 to try.

Make a recording before and after so you can hear the difference clearly.

 

[labcoat man]

Thanks Kevin much appreciated!
Ill give it a try.
Tim