Lustraphone stereo ribbon mic - testing the phase question

Hi
Just bought this old Lustraphone stereo ribbon mic in mint condition in an original case.
Did not expect it to work after all these years.
To my surprise it sounds superb and the capsules are well balanced!
Is there a quick way to test the phase between the 2 channels?
Thanks
Max

Assuming they are configured Blumlein, shove the mic into a speaker with each transducer at equal distance, 45 degrees off-axis.

Record a transient and compare waveforms. Alternatively, listen to the output summed, and try reversing polarity on one channel whilst still listening. Out of phase should be obvious.

Grab a reference mic (eg. an SM58 or whatever) if you want to compare overall phase of the mic (in case both are reversed!)

Roddy

Thanks! I'll try that.
These are great mics and its a revelation for me. I've had a BM5 few years back and it
didn't sound anything like that.
Cheers
Max

Hi Max,

Nice to hear you've got a good one. If you decide to peek inside, we'd love to see some photos!

Cheers.

Stewart

Thanks,
This mic sounds so nice I can't risk opening it. it is probably similar to the mono version.
how common are these mics ? I think the design is really special.
Does anyone here have one ?
I measured 110 ohm on the output, what impedance does it make ?
cheers
Max

Generally speaking, it's not a great idea to put a multimeter across the output of ribbon mic, as the impulse from some meters can put a strain on the ribbon.

That's the theory anyway. However I recently tried to make a movie of the effect to post here, and failed completely.

110 ohms DCR is pretty high for a transformer output, which would suggest it is a high-Z mic. But if it sounds good in your setup, then I wouldn't worry about it.

Ah, good to know that! ... it survived the blast ...
so you tried to film it, why didn't it work?

Hi everybody, I've recently bought the same microphone (well, at least the VR65/NS version, yours may be the more fancy VR65).

Mine is also in good condition and both ribbons seem to work perfectly and be matched (as fas as I can tell). I have not opened it, as when I unscrewed the cover of the topmost microphone it did not come out very easily. Like the original poster I was a bit afraid to damage it and did not persist. I might try again and post pictures here if I am successful.

I have dug up lots of info by searching online, including a very interesting review from Gramophone magazine in the 1960s:

http://www.gramophone.net/Issue/Page/August%201960/98/853202/#header-logo

I have tried to attach a picture of my microphone. It's surprisingly similar (at least in appearance) to the latter B&O stereo Blumlein design.

This microphone was apparently designed by an Austrian designer called George Pontzen and interestingly appears to pre-date the Olufsen Blumlein microphone by a couple of years. It is indeed designed to work as Blumlein (although the angle between the ribbons is adjustable, so you can go for different angles).

The frequency range should flat between 40hz and 13khz although the Gramophone reviewer says it is only 6db down by 16khz (in comparison to an AKG C12, which should be flat in this range) and the bass response does go down to 30khz and is similar to that of the C12.

My microphone is low impedance (it had in-line hi-z transformers originally, which I replaced by direct XLR connections). It has very low output, but on the other hand has very little self-noise.

Lustraphone mostly produced home-recording microphones, but this was by far the most expensive in their range. The retail price for the original version was around £31 in 1959 (£15 for the simpler version VR65/NS). In comparison an STC 4038 had a retail price of £43 in 1963 (according to the list price on the Coutant website: STC brochures).

I have also posted a couple of samples over at Gearslutz:

http://www.gearslutz.com/board/5801742-post2.html

http://www.gearslutz.com/board/5804068-post4.html

I like mine very much and can't wait to try it out on a variety of sources. Let me know how yours works or if you find out anything else about it.

Regards,

Santiago

Hi Santiago

Thanks for sharing all this info. Very interesting review!

Not sure which version is mine it is not written on it. also it is missing the external transformers.
Sound is great, there's a slight 50hz hum but the gain and volume on my pre are fully up.
I used to have a bm5 but this one is much nicer sounding and looks amazing. It will be interesting to find
out if there are any other stereo ribbons from this time or earlier (50's).

Do you know if the two channels can be paralleled so a higher level can be obtained.

Cheers
Max

Hi, you don't miss much by not having the transformers, they are fairly normal hi-z transformers. I think I will wire them to female XLR so that I can use them to connect mics to amps (not something I often do, but well).

Do you have each of the two outputs wired to xlr? the cable should have an earth connection, so that should be a first step to getting rid of the 50hz hum. Mine does not have any hum as far as I can tell.

Connected to my RME Fireface I have managed to use it on relatively quiet sources ok. The two recordings I put up on Gearslutz are of fairly quiet sources, (glockenspiel, archtop guitar and voice), but obviously with such a low output it will behave better with louder sources such as vocals, guitar amps, a drumkit, a full band or a string section.

Certainly if you get the two ribbons facing in the same direction and pan the recorded tracks in the center you should be able to get a louder signal with respect to the pre-amp noise from having the pre-amp at maximum gain (assuming that the self-noise of the mic is low, as it seems to be). [later edit: er, actually that would also probably cancel out most of the signal itself, so it's probably better to get them facing on different directions]

The VR65 (not the simpler NS) had a complicated matrix you could connect it to that would allow you to change the phase of one of the microphones, sum the signals to mono, etc, etc,

Zebra50 knows a nice very simple mod which consists in humbucking each ribbon motor by adding a parallel wire to the motor wiring (I'm not a very technical person but it was something along these lines). This gets rid of a lot of hum and noise and does not otherwise affect the sound, so it's highly recommended. Whenever the ribbons of my Lustraphone finally give up the ghost I might ask him to do it as well as the re-ribboning.

yes, I've replaced 2 DIN plugs with 2 XLR's, cable earth goes to xlr earth (body).
I get hum both with my valve preamp and mixer.

I've been thinking of building one of these boxes so I can sum the signals and change the phase.

sounds like mine is a VR65.

Hi Santiago,

Good to see you here & thanks for sharing the info. That's a nice looking microphone you've got there!

In terms of summing the two signals, of course if you've the extra channels (digital or tape), this can be done AFTER recording, which will give you added flexibility, and will save the effort of building a dedicated box.

The extra wire mod humbucking idea can work nicely, assuming it wasn't done in the factory.

How far does the top element rotate? If it goes a full 180 degrees you may be able to partially humbuck by rotating anti-parallel, and then try flipping the phase.

Stewart

Hi Stewart, that's a clever idea. Unfortunately the elements can only rotate from 0 to 100 degrees.

Looking online I have found this reference to one of these Lustraphone stereo microphones being affected by a magnetic field in the room where they were used, which led to hum.

http://www.sweetwater.com/forums/showthread.php?7945-Coincident-microphones-and-polar-diagrams (the third post has the information on the Lustraphone)

That could explain why maxkriza's mic hums and mine does not (i.e:, perhaps his room has a stronger magnetic field than the one where I record?). As fas as I know that could be solved by the humbucking mod. Pictures from the motor would help determine whether the mic already has that type of wiring.

Regards,

Santiago

Hi Santiago
I searched the Lab and couldn't find anything regarding this wire mod.
I don't think my room is the problem as I'm using other mics that doesn't hum (Beyer M160 etc').
cheers
Max

maxkriza said:

I searched the Lab and couldn't find anything regarding this wire mod.

Click to expand...

Might not be in the title, but it has certainly been mentioned. To see the idea, have a look at this RCA77 at Countant.org



You can see that the top of the ribbon is connected to TWO wires, which run down either side of the motor assembly. It's even shown in the schematic:

Thats cool, thanks.
I guess I need to open it now and check ... not too keen on that.
Hum seems a bit lower when mic is mounted horizontaly.
What will be your choice preamp for this mic type?
Cheers
Max