U67 de-emphasis network

[ZHOUJUN]

What I am talking about is quite obvious when listening to this comparison by the reseller of Ruud's circuit (Vintage U67 vs. Ruud67 ) - knowing the Ruud67 is equipped with a chinese K67 in this case and might sound different with a proper capsule (I am using Arienne's K87):

The difference made by the microphone capsule is more obvious than any other accessory. I found that there are differences between many of Neumann's original K67s, but they are far less obvious than other capsules. Perhaps these subtle differences I hear are the result of natural aging over the years.

 

[Paul W]

Guys, doesn't the dynamic/harmonic behaviour of the BV12 transformer's primary : tertiary "translation" also factor in when tapping the signal there for NFB re-injection? Apart from the questions considered here regarding the role of the capsule itself.

I found myself using my 67-ish mics following RuudNL's alternative schematics with great results in situations, where a vintage U67 would sound a tad bit too pre-compressed for me (e.g. classical Grand Piano). Ruud used a usual transformer and taps the NFB signal directly after the coupling capacitor:
https://groupdiy.com/threads/u67-ish-microphone.75162/

Maybe there are other reasons, why those "alternative" 67ish mics sound less compressed (which of course can be a good or bad thing, depending on what you're after), but I am wondering, how the tertiary winding might play a role in this?!

I would naively think that negative feedback from the tertiary transformer winding would tend to make the transformer more transparent in normal uses; whatever color the transformer might tend to add to the output on its own, the negative feedback would tend to cancel it out. (Isn't that the point?)

But if that's true, why bother with transformer-coupled output and more expensive transformers with tertiary windings?

What am I missing?

 

[soliloqueen]

What I am talking about is quite obvious when listening to this comparison by the reseller of Ruud's circuit (Vintage U67 vs. Ruud67 ) - knowing the Ruud67 is equipped with a chinese K67 in this case and might sound different with a proper capsule (I am using Arienne's K87):

wouldnt trust mic and mods comparisons. their u87 one is just the same file with compression

 

[Roman B.]

wouldnt trust mic and mods comparisons. their u87 one is just the same file with compression

Sure, I don't trust them, either, but this comparison sounds pretty much the way I have experienced both mics to sound like, at least with vocals in close proximity. So please let's not discuss M&M and their policies any further as in so many other threads - I didn't intend to open this can of worms again.

 

[Roman B.]

Meanwhile I think my sound observation comparing Ruud's 67ish mic and "true" U67s is way more related to the higher current that is being shoved through the EF86 tube in the Neumann original. There we have a B+ of 210V and a plate resistor of 150k, while Ruud's mic uses the "Chinese" standard 120V and 100k, surely resulting in a cleaner sound.

So correcting myself, I don't think that the NFB plays a large role in terms of more or less percieved compression/saturation - regardless of being fed by a tertiary winding or tapped at the coupling capacitor.

 

[Khron]

the higher current that is being shoved through the EF86 tube in the Neumann original

Higher, how? 210V B+, minus the 75V anode voltage, gives 135V, right? Divide that by 150k anode resistor, gives 0.9mA. That's "higher" than what, exactly?

 

[Roman B.]

Higher, how? 210V B+, minus the 75V anode voltage, gives 135V, right? Divide that by 150k anode resistor, gives 0.9mA. That's "higher" than what, exactly?

Your way of asking rethorical questions that make other people feel like total morons, reminds me of my old maths teacher. Sooo 20th century


But sure, just as the old bastard you're right. My head wasn't working. I was calculating with just 60V anode voltage...

So well, forget what I said. Sleep deprivation again, our baby puked away the whole night...

 

[MaxxDM]

I would naively think that negative feedback from the tertiary transformer winding would tend to make the transformer more transparent in normal uses; whatever color the transformer might tend to add to the output on its own, the negative feedback would tend to cancel it out. (Isn't that the point?)

But if that's true, why bother with transformer-coupled output and more expensive transformers with tertiary windings?

What am I missing?

It was designed to be used in less than perfect situations, and that winding helps to improve things when it comes to load mismatch.

Also using an EF86 is not exactly the 'best' choice for a microphone. I think it may have been conceived primarily as a practical microphone

My theory years ago was that the extra winding also introduces an element of phase rotation, which makes the top end softer. I think the U67 was the first large Neumann condenser designed to be used close to the source, which obviously can sound sharp.

Not sure how much phase rotation is actually involved, come to think of it, but probably some?