Cinemags

[CJ]

:green:

 

[AnalogPackrat]

Welcom to "Name that victim!" with your host CJ! So, which one is it? No center taps...hey, that looks like the CMMI-10C I recently acquired! This isn't part of the V72 set from a Mr. Boogie, is it? Can't wait to see what you find...

 

[CJ]

Holy Jeezzuss! Give that man a cigar!

:thumb:

Errr, you don't happen to know the winning lotto numbers for saturday nite, do ya?

 

[AnalogPackrat]

Don't I wish! I just happened to have my CMMI-10C sitting right here beside my computer and the light just went on. Mr. Boogie had you down for one set of the V72 iron he sold and I got the other one. Gonna be a late night?

 

[mikka]

Tidy work, CJ!

 

[Winston OBoogie]

...

 

[fazeka]

Hi WOB,

I hope to build your RED47 soon and wanted to know what kind of IP and OP trannies to use? I wish to use the Cinemags, but am not sure which ones.

Can I sub in a 6DJ8 for the E88CC?

Best,
Chris

 

[Winston OBoogie]

...

 

[matta]

Hey Winston,

Slightly OT but how is Rev2 of your Pre coming along? I dare call it my its
old name for fear you might be threatened by some suit with a suite against
you for copyright infringement of something they never really owned. But
anyways, how it is coming along?

It is actually rather weird since I first stumbled across your pre when you
were playing around with it with Peff and he posted some notes on his site,
small world I guess.

Cheers

Matt

 

[Guest]

[quote author="analag"]

[/quote]
Only one shot from my bad head.
Resistors forming negative feedback must
be comparable to noise resistance of input element.
I not know transconductancy of your triode, but
500 Ohm of input noise resistance of tube, 1k of differential
connection,
200 ohms of mic, 1:5 transformer = 5 k, noise figure can
be limitely 10*log10((1+5)/5) = 0.75 dB
and you totally degrade it by that 100k R13 to 13 dB

Use R13 = 1 k , R15 = 3 k and may be O.K., noise figure will be 1.5 dB
cathode follower allows that load.

xvlk

 

[CJ]

Igor, put that into Laymen's terms and I will let you move back to the Gaza.

cj

 

[Brian Roth]

[quote author="analag"]I find the Cinemag line of transformers to be of good quality and reasonable cost, so much so that I designed this tube pre around two of their offering. CMMI-5C for input and CM9589 for output.
Gain is fixed but can altered by making R13 adjustable e.g. as in a potentiometer.

Analag[/quote]

My so-far limited experience with Cinemag has been excellent. I needed some mic input trannies for some Electrodyne 712L modules that had been "robbed" by a previous owner, and Cinemag was most helpful. Reichenbach was the original OEM supplier!

As for the posted tube preamp circuit, I am a bit leary of the 1K (R18) in series with the phantom supply. A "high current" mic, pulling say 10 mA, would cause a 10V drop across that resistor. I would tend to think maybe 100 Ohms would be a better choice.

Of course, the absolute worst-case current draw for a phantom powered mic input is approx. 14.1 mA...and that's when XLR pins 1, 2 and 3 are all shorted together.

I bring this up because of a very dim memory of a factory service bulletin that MCI issued for early (black face) models of the JH-400 desks. They had a relatively high series R on the phantom line in each module, and certain mics were "starved".

There is also something to be said for a "slow ramp-up" when firing up the phantom line on a preamp. Oliver Archut of tab-funkenwerk has discussed this topic in other forums.

Bri

 

[analag]

I always go from 52V and use the appropriate resistor to bring it close to 48V, but that's just me.

 

[Brian Roth]

[quote author="analag"]I always go from 52V and use the appropriate resistor to bring it close to 48V, but that's just me.[/quote]

But, what would be the appropriate resistor value?? Some mics pull less than 1 mA (example...a U87 at 0.8 mA) while others might pull closer to perhaps 8 mA. I couldn't quickly find an example of the latter, but a 414 is spec'ed to draw 4.5 mA.

Bri

 

[analag]

If you are building to power a wide variety of mics a lower value resistor could be used which wouldn't sink the voltage too much coming from the regulator....probably 68 ohms and a larger cap. Just enough to soften the surge. I think the standard phantom power voltage resides between 45V and 52V.

 

[Samuel Groner]

Oliver Archut of tab-funkenwerk has discussed this topic in other forums.

Could you point me further with that? We discussed it here, but IMO no convincing results yet.

Samuel

 

[Brian Roth]

[quote author="Samuel Groner"]

Oliver Archut of tab-funkenwerk has discussed this topic in other forums.

Could you point me further with that? We discussed it here, but IMO no convincing results yet.

Samuel[/quote]

From the PSW forum:

http://recforums.prosoundweb.com/index.php/t/3244/4437/?SQ=b6a59dfaafc6db8ac40859c2a49d67d5

http://recforums.prosoundweb.com/index.php/mv/msg/1097/0/16/4437/?SQ=e13d9f5b4cfd9c6ced97725816a2524c

Bri