UM57/ CMV 563 sound so boring, whats up?

[volki]

gus xvlkk etc .-
so the bottom line is that the resistor is there for both optimal noise and
better headroom with the supposedly "bad" xformer? xvlk could you elaborate, which parameters of these circuit would affect noise performance most?

as for the xformer - i figure a "standard" mod then would be to get a different xforer, connect it directly to ground, and bypass the cathode? which of course woudl sound pretty different - more k2 ;-)

btw. i heard that oliver/funkenwerk makes custom xformers for these mic's and others.

badger -
whew, you seem to have xformer data inside info that most of us germans don't...? =oP

60v -> 80v polarization voltage should yield about 3db less noise, but will change the sound somewhat. (different electrostatic attraction with the membrane)

regarding m69x schematics - PM me if interested. the circuit is a little similar to the tube'd one covered here...

 

[hitchhiker]

hi Jens,

thanks for the clarification. I've had mine apart because one likes to quit
after working fine for about 15 minutes. They are N61 and have no transistor circuits.

Lance

 

[Joechris]

Gus, I would realy like to hear your mod tips for the U87. I have two of them,
and I have not used them for a long time. I compeared them with a blueberry, and sorry to say, they went back to rest. Is there a way to make
this classics rise again........ :roll:

jo

 

[Guest]

[quote author="volki"] xvlk could you elaborate, which parameters of these circuit would affect noise performance most?
[/quote]
Everyone knows, that bypassing of cathode resistor by capacitor
results as positive feedback. (Gain rises)
Why not to do positive feedback directly from output ?
Everybody knows that feedback is efective at circuit parameters
inside it.
And inside CMV feedback is transformer.
I not mean, that CMV trafo is shit. Nice thin permalloy inside it.
And this trafo inside (only by primary, but is) POSITIVE feedback
can rise some transformer related distortion.
But some positives of CMV topology.
Positive feedback going to the cathode resistor make it smaller,
and in middle frequencies dependent to the LOAD IMPEDANCE.
It means, that GAIN of the mic and his sonic properties can be
changed by LOAD impedance. If someone draw thevenin
equivallent of mic, then output impedance will be smaller than
plate resistor//plate resistance of tube itself.

Other positive of topology is, that new cathode resistor
(by feedback) will have smaller noise ratio than termic noise of resistor
alone.

It can be interesting to change transformer couplíng cap (I have read
it here), and to test different load. (some 200 Ohm input
impedance of preamp).

There is out of logic to change polarisation voltage from 60 to 80 V because of worse stability of capsule (it is out of permitted voltage)
Some gain is uninteresting, because of other noise sources (acoustic resistance control of gradient part of the capsule). And these capsules are
sensitive much.

For someone (me) is can be interesting to use the some capsule (M7,8,etc???) and to make new body. Some like source follower.

xvlk

 

[hitchhiker]

here's the N61 power supply for the CMV563.

http://www.geocities.com/pepperplace/CMV.html

hey kubi, could you add this to your schematics collection?

note: if you close the pop up to quick it says page not found.

Lance

 

[[silent:arts]]

N61 Schematic
N61V Schematic

 

[Gus]

the transistor gain circuit inside the PS does not look bad.

 

[soundguy]

Can that just be bypassed completely and use more gain from the mic pre, or is it doing something besides what I think its doing?

dave

 

[[silent:arts]]

Just remove the TV61 pcb out of the N61V, and you will have a N61.

I have an (Gefell) N61V with removed "V", and an (original Neumann) N61, and can't find any difference. Haven't removed the TV61 my own so, recieved it like that.

regards
volker

 

[Gus]

It looks like it could be a simple thing to bypass the gain stage. just copy the n61 wiring. The voltage to the microphone should stay the same because the power for both the microphone and gain stage comes from the str (125V reg of some kind?).

The tube looks like it uses just under 1ma, 125V -120V gives about a 5 V drop across the 5.6K .

Gain of the stage looks like 47K/10K = x 4.7

Looks like a new supply would be easy to make 3 trem 317 for the fil. I would use 4,700 before the reg and 2,200 or> after the reg. Maybe a new HV section using zener(s) to reg to 125VDC instead of the STR and 47uf caps instead of the 20ufs

 

[andre tchmil]

thanks for the clarification. I've had mine apart because one likes to quit
after working fine for about 15 minutes. They are N61 and have no transistor circuits.

Hitchiker.
Replace the big green resistors near the capsule and you problem is gone.
I think it's only one that causes thatb problem, but while you're at it.......

 

[hitchhiker]

hi Andre, The problem power supply quits with my second mic hooked to it also.

Both mics work well with my second supply.

The problem must be in the power supply. Right?

Lance

 

[jensenmann]

Gus wrote

The tube looks like it uses just under 1ma, 125V -120V gives about a 5 V drop across the 5.6K .

The schem says 5.8V for heating. You can adjust it with a pot in the PSU. When adjusting it you should measure the voltage in the mike, so you have the voltage drop of your cable excluded.

Can anybody tell how the preamp sounds? I have only the N61 and never heard the V-version?
jens

 

[volki]

the only attribute i've ever heard about that preamp is "noisy" :green:
but it wasn't meant as a high quality pre, anyway. just additional preamplification if used directly with a power amp, as for public address etc.

looking at the schem, it unbalances the connection from mic to PSU, no? and the o/p connector in the PSU, too... so it's best bypassed, by bridging pins 1 ,2 and 5 from in to out, and cutting off the internal connections from 5 to 1,

 

[hitchhiker]

hey Dave,

I plugged the output of my 563 directly into a Quad Eight ca-127 "sans
mic input tranny" and it was a big improvement . Clear and sparkly.On the schematics it looks to me like the mic has an output tranny but I'm not sure what the output impedence is. I also tried it into the PRR bjt version of the ESP #66 transformerless mic pre of late and it worked well here too.

Maybe plug yours directly into a DOA , or maybe you've tried this?

Lance

 

[hitchhiker]

I terminated the cmv563 output at the QE ca127 input with 2k2 because of
transformer ringing. Much smoother and still clearer than the use of the
lundahl input transformer I had here.

 

[Guest]

[quote author="hitchhiker"]I terminated the cmv563 output at the QE ca127 input with 2k2 because of
transformer ringing. Much smoother and still clearer than the use of the
lundahl input transformer I had here.[/quote]
EXCELLENT!
and is CMV still boring, or not ?

I mean that can not be boring after good termination, because of rise harmonics and lower
noise due to internal positive feedback.

xvlk

 

[andre tchmil]

euh, explain please.
where to mod. ?

 

[Guest]

[quote author="andre tchmil"]euh, explain please.
where to mod. ?[/quote]
For me?
in the 2k2 mic trafo termination.

xvlk

 

[hitchhiker]

hi Andre,

No mods. I'm terminating the output transformer of the cmv563
(pins 2 & 3of the bal jack) and going straight into the QE ca-127 amp.

That is, I'm not using a mic input transformer. The termination is best at the input of the amp .The transformer output of the cmv is designed to see
a mic pre input of aprox 2k I figure and the input of the QE ca-127 is 33k
and this allows the transformer to over react so to speak and you get
transformer ringing. I always hear it as a harsh high end but I think it effects the low end just as bad.

hi xvlk,

The mic is maybe still boring to some people . If you like clear, natural
but still punchy enough mids to have authority then you will be happy.

Happy New Year All!

Lance