Upgrading a Neumann Gefell CMV 563

I want to give my CMV a little love. My mic is completely stock. It works fine and sounds pretty good, but I know it's out of spec and I want to get it sounding as good as possible. I know a recap of the mic and power supply are in order, but I am not sure what kind of caps I should put in the mic. I would like to put the nicest components I can into the mic within reason, but I am having trouble finding good quality caps in the values I need that will fit into the mic. Also, I hear a lot of people replace the resistors. Would it be recommended to stick with wire wound resistors or will normal resistors do the trick?

Are there any other areas for improvement on this microphone? Has anyone played with the component values to get any improvement in sound?

Sorry for all the questions, I am relatively new to all of this stuff.

First I would leave it alone and think about what you are asking.

  How do you know it is out of spec?  How do you know if a recap of the power supply is needed?  If you information is from the web question it, even question this post.

  Sometimes well made electros last many years.  To check repair properly you will need access to a good cap checker something that measures value, DA, ESR and leakage at working voltage.  You will also need a schematic with voltages marked or the tube curve for the tube in the microphone to calculate the operation points of the circuit.

If you improve it it might lose value.

Search CMV at this forum

I have read every post regarding the CMV on this board, and the general consensus here and everywhere else is that these mics are good on their own but have a lot of room for improvement. I am more concerned with sound quality than historic or monetary value of my microphone. I plan on keeping it around, so I am open to anything. The mic does sound really good, it has a solid low end with a rather neutral top end which I really like. It is a bit noisy though and it lacks the presence of other tube Neumann's I've heard. I may have access to a good cap checker at my school's shop so I will take it there and see what I can find out. I know for a fact that C1 is visibly leaking, and since there are only 3 caps in the mic I figured I would replace them all. I have already bought a NOS tele EC92 which made a noticeable improvement in sound quality. I am mostly interested in what brand/type capacitors are recommended by those who have recapped their CMV's.

The power supply caps may be ok but I figured I would just replace the caps in there while I was at it. I am using a  step up transformer to get my 120v to 220v, I don't know how much of a difference that makes in the sound of the mic. Oliver at tab funk recommends his drop in replacement, saying that using step up transformers "doesn't really cut it for studio use, mostly creating more noise and other problems." I did try to buy his transformer but he never got back to me, so I went with the step up route. The noise isn't atrocious, it's still totally usable.

Check your voltages B+ and heater under load.  If you are using a 1:2 step up transformer use a variac before the step up transformer to get to 220AC to the power supply. Sometimes in the USA the wall voltage can be 124VAC and X 2 = 248VAC about a 13% increase in voltage.  You could have too high a voltage at the filament.  This depends on the type of supply you have and if you can adjust for it in the power supply.

Ian said:

Oliver at tab funk recommends his drop in replacement, saying that using step up transformers "doesn't really cut it for studio use, mostly creating more noise and other problems." I did try to buy his transformer but he never got back to me, so I went with the step up route. The noise isn't atrocious, it's still totally usable.

Click to expand...

I wonder what kind of noise that would be. I might overlook something, but I don't see any reason against a (good quality) step up transformer. I would have to look up what I did to my CMV, but there are anyway not many caps inside. I remember I replaced the 1uF coupling cap with some film type. My CMV is somewhat noisy, but sounds terrific - so I was wondering if it is possible to do a split signal path with a transformerless fet circuit and then make the output switchable between both. But I haven't yet thought about whether that would add an additional load to the capsule or if if the then somehow connected gate of the fet and the grid of the tube would introduce some kind of noise to each other...

Another thought would be to check the individual parts of the circuit. They sometimes didn't have too great quality of parts in the former GDR, so maybe it might also pay of to replace some resitors (especially the multi-megohm) or other than the typical electrolytic caps. Of course only if originality doesn't count...

Michael

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Hey all, sorry to necrothread but I've got a question about the tubes in the CMV563 power supply. Anyone know a source for the gr 27-56 tubes? I just picked up a nice looking cmv563 to finish out a pair and it's dead but swapping my old power supply awakens it so I know the prob is with the power supply from the one I just bought. I figured if the caps are out of spec at least the thing would make sound so I'm assuming the prob is with the tubes and bouncy shipping. Anyone have any ideas? Thanks!

Before you go spending money, your best bet is to measure some voltages and post them up here. I'd be surprised if it makes the mic quit completely.

There may well be a case for getting rid of that tube anyway - I'll have a fiddle with mine when I get some free time and see what I can come up with.

Good idea, thanks...

Here's what it measures going clockwise from top with the middle pin at the end
1) 7.7 v
2) 85v
3) 84.5v
4) 7.7v
5) 85v
6) 5v

All AC and I didn't test under load which I imagine does make a diff because my GOOD power supply tested weird to me too...
1) 3v
2) 45v
3) 27v
4) 3v
5) 27v
6) 2.5v

So (while not under load) my good supply has about 1/2 the voltage vals of the bad supply.

Very weird - we should be looking at DC voltages here.

What are these voltages referenced to? That is, what is the black leg of the multi meter attached to?

Should be refenced to pin 1...



Unloaded you should see something over 130V on pin 3, and a little over 6V on pin 4.

6) 5v

Click to expand...

What model of the PSU have you got? Is it the multi-pattern version for UM57?

I've just got the regular n61 supplies, the middle pin on the connector I guess isn't being used. That said, I remeasured using the correct ground reference re: your post and my "good" one measures fine, the bad one is 0v all the way around (DC). Also, the pilot light doesn't come on. The guy I bought it from swears up and down that it was working great right before he shipped it and the pilot light was not burnt out. It was packed well too, lots of bubble wrap, no indications of dropped box, etc, no reason to suspect foul play. Anyway, thanks for the schematic, any more ideas?

Here's the schemo for N61.

bkbirge said:

, the bad one is 0v all the way around (DC). Also, the pilot light doesn't come on.......any more ideas?

Click to expand...

If the light, 120V and 6V supplies are gone then i would first check internal and any external fuses, and make sure the mains cable is good.

Another possibility is that the primary of the power transformer is fried, AND the pilot lamp is blown.

Or a broken wire inside from the power socket to the transformer/fuse/pilot light.

OK, "fixed", thanks for all the help! Turns out I'm just an idiot. The old bakelite ended power cable actually has a button that kills power. I thought it was part of the bakelite mold but when there was no continuity from one end to the other I looked closer. Pressed the button and voila everything is nice. Thanks for the schematics!

My CMV 563 was modified by Peter Drefahl http://www.drefahlaudio.com/mic/mainmic.html. He changed the resistors to modern lower noise types and did some mechanical repairs  at the capsule. I use his PSU to power the mic. A short while ago I got an (internal) good looking N61 too. I checked out the voltage (mic must be connected) an it works fine 120V/5,8V on PIN 3/4 against PIN 1 (0V). You can set the heaters voltage (important) internal by the trim pot to 5,8V. The anode-voltage can be a little bit higher I would change the PSU- capacitors only if you have any problems (buzz, leakage).

It's right - the CMV 563 +M7 has a flat frequenzy curve, it sounds not so open in the highs. But IMO that's no problem in the mix, I raise the highs with EQ just enought I need. I love it on vocals with cleaner preamps or in combination of an clean preamp at first followed by an V72.

Today there are many good engineers around the town Gefell, where the CMV 563 was build after WW2. Last year I visited MICROTECH Gefell (they build great Mics). They have an anechoic room to test the old mics too. Another good adress is Thiersch Elektroakustik with usefull modifications of the M7.