Some 87 Transformer Choices

[Wordsushi]

My main observation is about the difference I noticed between the responses of the transformers. I had the same feeling when I switched from a transformer with a smaller core to the UTM0587.
3U is richer in mid-highs and highs, harmonics, seems more incisive, faster (yes, transients), in the face, ideal for VO. UTM sounds more forgiving, more suitable for singing perhaps.
(Cinemag 13113 sounds very accurate, clean and Hi-Fi, Neutrik NTE10-3 (very small) quickly enters saturation, somehow it reminds me of the 50's.)
You probably used post-processing, but the sound of 3U gzt-87 always rings in my head, obsessively. It's perfect for VoiceOver

Been thinking about what @micolas wrote in the 87 body thread about these transformers. Of these, the 3u is the one I like best, and now I'm wondering if the reason I've never loved the sound of my D87 in an SYT-5 body is because of the Cinemag and how clean it is.

So, now I'm thinking of swapping out the Cinemag for something else, but before I just put another 3u in there I was wondering if anyone has tried Moby's BV-13?

 

[oscarhuang]

https://www.neumprospares.co.uk/shop/Neumann-U87-Ai-Transformer-90415-p396412795

 

[Wordsushi]

I suppose there's no better substitute than the original.
I still would like to know at some point how Moby's BV-13 compares to what's out there. All things considered, I'd rather give him my money than Sennheiser.

 

[micolas]

@oscarhuang ,

some time ago they no longer had the transformer available at:

https://www.neumprospares.co.uk/shop/Neumann-U87-Ai-Transformer-90415-p396412795

 

[micolas]

I suppose there's no better substitute than the original.
I still would like to know at some point how Moby's BV-13 compares to what's out there. All things considered, I'd rather give him my money than Sennheiser.

Some important voices claim that the transformer in the U87ai is a bit small. Maybe the Neumann engineers wanted an earlier saturation of the magnetic core, for more character.
But I also think that we have to experiment with various transformers, everyone has their own preferences.
I admit I'm curious how the Moby BV-13 sounds.
For fun I want to inform you that I tested in the U87ai circuit, 110v/12v mains transformers of very low power,
DI-box transformers modified by me for 9.5:1 ratio, or others built entirely by me. From very small cores to large ones. They all worked, better or more bizarre (some had strange resonances on some frequencies, or very non-linear behavior). What I want to emphasize is that we have to experiment, especially in combination with various other components, capsules, bodies, adjustments, etc.
DIY!

 

[LevinGuitar]

Maybe it was about saving costs? Since the BV13 was used in a smaller body microphones too. Not sure but guess the BV13 was already in use before the U87 release?

If so, is the 9.5:1 ratio really the exact needed for the first U87 variant with all gain factors in mind, and the next ones? Who is good with maths here?

Also the battery compartiment needed it's space

 

[micolas]

Is the 9.5:1 ratio really the exact needed for the first U87 variant with all gain factors in mind, and the next ones? Who is good with maths here?

Well, I also wondered why in the 87 circuit the transformer must have a 9.5:1 ratio.
I thought: it's about the output impedance of the jFET and the output impedance of the microphone. Or the resonant frequency of the transformer. Or something else. But some microphones have an output of 50ohms, others 250ohms. And mic preamps have 1.5 Kohms input, others 3.5Kohms. All these variations produce different colors of sound.
Very good! Let's color!!!
I put the nte10-3 dwarf in 7:1 configuration in 87ai. It sounded excellent at a moderate level, with nice saturation, nice mids (more pronounced than in its 10:1 configuration).
I put the M-audio Nova transformer, about 4:1ratio, like Sterling ST-77, it sounded darker, with attenuated highs. I did all kinds of absurd tests, some worked, some didn't produce anything musical.
The time has come for extreme experiments!
In the classic jFET+BJT+transformer 2:1 without DC/DC converter, with max 43v on the capsule, I put the gate resistor 1G directly to GND, I replaced the source resistor with a semi-adjustable 15Kohms in series with 1Kohm put directly to GND as well 22uF capacitor.
I removed the BJT from the circuit and connected the primary of the stock transformer through another 10uF capacitor in series with the existing 6.8uF (at the output of the BJT) , so as not to change the phase of the microphone.
jFET was stock 2SK30A Y
The resistor that fed the audio part of 4.7K was replaced by 68K.
I changed the 20K drain resistor to 10K.
I redid the BIAS on the jFET:
Us=0.89v Ud=12.14v , that's how I liked the sound.
De-emphasis network C=270pF.
The capsule bias voltage increased to nearly 46V.
Decent noise, I would say 17dB (compared to B2-PRO).
Output level slightly lower than U87ai.
Good headroom.
Sound in the U87 vintage area, warm, round, mellow.
Transformer ratio 2:1
The microphone is a Fame bought used for under 20 euros (included transport).

 

[Khron]

connected the primary of the stock transformer through another 10uF capacitor in series with the existing 6.8uF (at the output of the BJT) , so as not to change the phase of the microphone.

So that results in an effective value of about 4uF ( 6.8 * 10 / (6.8 + 10) ) How high did that push the resulting high-pass frequency?

 

[micolas]

How high did that push the resulting high-pass frequency?

On the voice I felt less bass compared to the stock microphone, but I liked the more '60s character, it made my voice younger, so I didn't increase the capacitors values. I like to use a microphone at 3..4 inches, it gives me a kind of privacy, closer connection with the microphone, so it stays that way. I haven't used it, but it will be needed in a situation. It has a different sound than the other several dozen microphones in my collection. I was amazed how good a low-tech transformer, a cheap stock capsule and a Chinese jFET (which may not even be written on it) can sound, probably defying some electronic theories (I think the drain current exceeds the recommended in this topology)
Some said that a low transformer ratio would force the jFET.
Well, to force him!
For decades I used power amplifiers that were boiling, 10-12 hours continuously.
Let it be, if necessary,
Hot Microphones!