DIY TG Microphone?

So it's got a fancy EQ and a dedicated PSU. It's also solid state, using TG circuits and people seem to like it. There aren't many that kind of solid state LDCs, it would be interesting to build one. TGM uses 4-pin mic cable so I assume it's PSU supplies about 60V (good for capsule bias) to the mic (like the mics modded and built by Rens Heijins, http://www.rensheijnis.com/microphones.htm).

So what kind of circuit would be best if you wanted to get U47 type sound using K47 type capsule and U47 body shell and grille? Output transformer or solid state output driver?

mhelin said:

mics modded and built by Rens Heijins, http://www.rensheijnis.com/microphones.htm).

Click to expand...

This site offers solutions for problems that exist only if original design is bad.
Criticizing phantom power, SMD... is just technically unjustified.
All the claims about improvements are pure BS.
"softness...robustness...relaxed projection...reaction time...realistic" are marketing terms that don't belong to a technically oriented group such as ours.
Nice builds, though.

Hey, the guy's gotta have something "worse" to compare his stuff to - duuuuh ;D

If it's just as good (if not better), then what's he left with as his "claim to fame"?

Jokes aside, yeah, i'm becoming increasingly "allergic" to marketing BS myself, as time passes...
I've also noticed a certain... disdain(?) for non-standard cabling and things like that. I guess i just don't like being locked into custom systems / setups or something.

abbey road d enfer said:

This site offers solutions for problems that exist only if original design is bad.
Criticizing phantom power, SMD... is just technically unjustified.
All the claims about improvements are pure BS.
"softness...robustness...relaxed projection...reaction time...realistic" are marketing terms that don't belong to a technically oriented group such as ours.
Nice builds, though.

Click to expand...

More on topic though... Is there such a thing as "A" U47 sound? Given that all the old ones are in various states of health and/or cleanliness, and there may well be night-and-day differences between any two of them.

Not sure if or how well regarded the newer Telefunken ones are, though.

Khron said:

Not sure if or how well regarded the newer Telefunken ones are, though.

Click to expand...

No "prestigious" user ever admitted they sound like "a" vintage U47.
There was a shoot-out some time ago (that was before I got fed up with the snobbery and resigned most of my accounts) and the only conclusion was that no two U47 sounded identical; each one had its personality.
I'm convinced if Elvis or Patsy Cline were doing the shootout, all the mics would sound good.

"The sonic improvements of active powering are:

- clearer placement of musical instruments within the stereo sound field"

I think we are getting into quantum physics theritory, where sound waves become particles!

That works excellent especially with mono sources ;D

kingkorg said:

"The sonic improvements of active powering are:

- clearer placement of musical instruments within the stereo sound field"

I think we are getting into quantum physics theritory, where sound waves become particles!

Click to expand...

Well, if there isn't a market for your products, you will have to create a market to make some money...

With U47 sound I mean huge proximity effect and range, meaning the bass respose is great even from a distance, good transients (no prolems with plosives or sibilants),  smooth frequency response though a tad mid forward, with velvety smooth top-end. The mic breathes with the singer.

Obvious limit with the P48 phantom powering is the lack of the power. You don't have much more than 0.5 watts available. Using proper high efficiency DC/DC converter for powering the amplifier instead of a resistor and zener you could obviously get much more out of it but I haven't seen it done for powering the amplifier section. With more power available you could play with the classic Class-A circuits, obviously you can't put LO1166 inside mic but maybe into PSU.  Anyway, you get the idea. In same cases you could bypass the mic pre altogether like is done with the REDD microphone though using tubes: https://chandlerlimited.com/redd-microphone/
The TG microphone though has lower output level:
https://chandlerlimited.com/tg-microphone/


There are also the 3U audio Warbler mics which have different voicings available, that would be another thing to consider:
http://www.3uaudio.com/cp.asp?id=685

Quite too often the microphone sound is tried to be explained using a two dimensional frequency response plot. However, there are resonances which cannot been seen in 2D snapshots and which color the sound a lot, also those problems cannot be fixed using EQ unless they are purely minimum phase symptoms. So you can't "voice" a mic with a K67 capsule to one with K47 for an example, might get half way though.

mhelin said:

With U47 sound I mean huge proximity effect and range, meaning the bass respose is great even from a distance, good transients (no prolems with plosives or sibilants),  smooth frequency response. The mic breathes with the singer.

Click to expand...

In terms of proximity effect, it depends only on the mechanical construction of the capsule; as long as it has the same dimensions, it will be identical. The rest is a matter of tuning; note that most existing U47's diaphragms are not as taut as they used to be.

Obvious limit with the P48 phantom powering is the lack of the power. You don't have much more than 0.5 watts available. Using proper high efficiency DC/DC converter for powering the amplifier instead of a resistor and zener you could obviously get much more out of it but I haven't seen it done for powering the amplifier section.

Click to expand...

Why would you want to do that? Half a watt is plenty to generate 8mW that correspond to +4 dBu into 200 ohms.

With more power available you could play with the classic Class-A circuits,

Click to expand...

Most of the classic P48 mics (U47 FET, U87, C414, Schoeps...) are class A .

obviously you can't put LO1166 inside mic but maybe into PSU. 

Click to expand...

LO1166 is a transformer. What's it got to do with available power?

mhelin said:

With U47 sound I mean huge proximity effect and range, meaning the bass respose is great even from a distance, good transients (no prolems with plosives or sibilants),  smooth frequency response though a tad mid forward, with velvety smooth top-end. The mic breathes with the singer.

Click to expand...

This could be atributed to the fact the k47 capsule is leaning slightly towards figure of eight pattern compared to k67 for example. I believe its super cardioid, but might be hyper, not sure.

kingkorg said:

This could be atributed to the fact the k47 capsule is leaning slightly towards figure of eight pattern compared to k67 for example. I believe its super cardioid, but might be hyper, not sure.

Click to expand...

That's an interesting observation, might be the drilling pattern and internal chambering of the K47 creates longer delay time around diaphragm compared to a K67 type capsule. Shotgun mics and other higher order mics like microphone arrays also have this feature.

abbey road d enfer said:

This site offers solutions for problems that exist only if original design is bad.
Criticizing phantom power, SMD... is just technically unjustified.
All the claims about improvements are pure BS.
"softness...robustness...relaxed projection...reaction time...realistic" are marketing terms that don't belong to a technically oriented group such as ours.

Click to expand...

You shouldn't be so harsh, IMO. I believe technically oriented group see that the phantom powering has some limits. Just to be clear, I don't justify PR's mumbo jumbo.

moamps said:

You shouldn't be so harsh, IMO. I believe technically oriented group see that the phantom powering has some limits.

Click to expand...

I agree that P48 has limitations, but which ones are really a hindrance? If a designer needs more than the 300mW available to deliver comfortable output to the load, there is something wrong. Either he is not competent enough, or he is designing for an unjustified target, or using a typology that is not adequate. The example of trying to put a Neve preamp in a microphone body is a plain aberration, technically-wise as well as operationally.
Putting a Chevy big-block in a lawn mower is a technical feat, but a pig practically.
There have been debates over active ribbon mics, that would benefit from operating at elevated current, however, the optimal designs still cannot get rid of the transformer; coupled with an input stage operating at about 1-2 mA makes them compatible with P48.

mhelin said:

That's an interesting observation, might be the drilling pattern and internal chambering of the K47 creates longer delay time around diaphragm compared to a K67 type capsule. Shotgun mics and other higher order mics like microphone arrays also have this feature.

Click to expand...

The k47 and M7 capsule backplate have both blind and through holes.  The blind creating the internal chambering and the through variants creating the pattern.

The reason that a k47 if wired strictly as cardioid will have a slightly figure 8 pattern is due to these through holes.

In a k67 and ck12 typr the through holes are interleaved meaning that they travel through to the centre of the backplate and then the wave is interupted by the opposing backplate, no wave can actually make it through to the opposing diaphragm.  This though is not the case for the k47 as is is a single backplate configuration so the wave is only interupted by the opposing diaphragm not the backplate iteself.

A perfect cardioid pattern can he acheived in a k47 or m7 capsule utilising voltage bias for polarity but the standard rear diaphragm linear voltage swing of 0v - 2x polarising voltage will not give a true cardioid pattern at 1:1x polarising voltage. 

Cardioid for a k47 and m7 style capsule is reached at approx 0.75 x capsule bias on the rear diaphragm.

Hope this is informative.

Cheers

Wow, thanks for this info!

It would be super easy to fine tune this effect with a k47 in a tube mic with continuous pattern select knob like in Rode mics.

Possible phantom 48 issues

Something other than 48VDC supply feeding the phantom resistors
Resistors not matching
Resistors not proper wattage rating when pin 2 or 3 shorted to ground
Supply not able to supply 10mA

If you look at older circuits they can be under 2mA with no DC to DC converter and an output transformer
transformerless can need a higher current than 2mA.

I like some of the transformerless circuits people post about not liking on the web.

When I build an external powered solid state microphone it is because I want to do something that draws more POWER than phantom can supply. This can be a solid state circuit working as a mix of what I think are the best parts of solid state and tube circuits

I have been working on P48 transformerless circuits don't dismiss them.

Gus said:

Possible phantom 48 issues

Something other than 48VDC supply feeding the phantom resistors
Resistors not matching
Resistors not proper wattage rating when pin 2 or 3 shorted to ground
Supply not able to supply 10mA

Click to expand...

Don't put the blame on phantom power; put the blame on bad implementation.

If you look at older circuits they can be under 2mA with no DC to DC converter and an output transformer
transformerless can need a higher current than 2mA.

Click to expand...

between 2 and 10 mA, there is ample room for making it right.
A very hot mic level is actually less than 1mW, drawing less than 1mA. Why would a transformerless circuit draw much more?

I like some of the transformerless circuits people post about not liking on the web.

Click to expand...

Too often, people judge a book by its cover. Tubes and transformers are Good, SS and no tranny is Evil. 

When I build an external powered solid state microphone it is because I want to do something that draws more POWER than phantom can supply. 

Click to expand...

OK, but don't blame phantom power, that is perfectly adequate!

  This can be a solid state circuit working as a mix of what I think are the best parts of solid state and tube circuits

Click to expand...

We all agree that tubes need an external PSU (bar exceptions). When you say "the best parts of solid state and tube circuits", I would question the pertinence of these circuits in a microphone. The Fairchild 670 is certainly one of the most-reverred piece of gear; is it pertinent to build one into a microphone?

  I have been working on P48 transformerless circuits don't dismiss them. 

Click to expand...

  I certainly don't dismiss transformerless circuits; I'm a fan. I believe some of the best things that happened in audio in the last decades are the possibility of getting rid of transformers and finally being done with tape. I loved tape machines, but not their limitations and constant need for attention.

abbey road d enfer

I think you are misunderstanding what I meant in my posts. I am not blaming the phantom power specs.

When I posted about phantom issues it was about the preamp or interface not supplying correct P48 power.

The R in some P48 RC filters needs to be taken into account. More current draw = a lower voltage at the "top" of the phantom resistors

Transformerless microphones can need more of the available current for a low output resistance.

Think of the microphone to preamp as a Wheatstone bridge circuit. You want a perfect match(next to impossible) or a low output resistance feeding a high input resistance for better CMRR . You can need more current to get a lower output resistance with good drive with a transformerless circuit. For example increasing the EFs current for lower output resistance or using an opamp that has good drive.

FWIW I've used my Frankentube phantom powered tube mic (ca.10ma) with several other regular phantom powered mics at the same time into Presonus 1818vsl and never had any issue.

Gus said:

abbey road d enfer

I think you are misunderstanding what I meant in my posts. I am not blaming the phantom power specs.

When I posted about phantom issues it was about the preamp or interface not supplying correct P48 power.

The R in some P48 RC filters needs to be taken into account. More current draw = a lower voltage at the "top" of the phantom resistors

Click to expand...

That is a bad implementation of P48. The voltage that feeds the 6.81k resistors must be perfectly regulated, in addition to be clean.

Transformerless microphones can need more of the available current for a low output resistance.

Click to expand...

Output impedance is remotely related to the current draw. For example, in the Schoeps circuit, it is possible to replace the emitter followers with Szlikai pairs, that reduce the output impedance from a few dozens of ohms to a few 1/100th of ohms, with a negligible current increase. Lowering the output impedance is more a matter of topology than brute force.