Gefell MV692 disassembly instruction

[bezen4uk]

Hi guys,
There is step by step instruction how to open these mics.
Many thanks to Sredna for a key advice.

 

[mylesgm]

Having four of these lovely mics this is incredibly useful...

 

[hobiesound]

funny because i did this with my mv692 a few days before you posted this.

now if someone could do a step by step on converting these to P48 that would be super!

greetings,

Thomas

 

[spreemusik]

now if someone could do a step by step on converting these to P48 that would be super!

Step 1: Send them to Gefell
Step 2: Pay around 80€ a piece
Step 3: Get them back in perfect refurbished condition.
Not DIY, I know, but it was definitely worth it.

 

[bezen4uk]

Hi hobiesound,
I did it this way (circuits in attach):
*remove D1/2 and C12 (usually D1/2 is transistor connected as diode);
*place 24 kOhm resistor instead of C12;

Good luck.

 

[bezen4uk]

Compare with original circuit MV692-48 (look at resistor R8).

 

[hobiesound]

Yeah i've seen both schematics. I've been thinking about having mine sent to MTG for a long time now got a quote and all.. they even told me a now laquer of the body and refurbishing the electronics is all included in the price....
Just waiting till i snatch a second m692 on evilbay (got 1 mv692 and 1 mv691). Great company to deal with they even look up the date when the individual parts were made if you ask them nicely.

greetings,

Thomas

 

[hobiesound]

anyone know how much a reskinning costs at thiersch? i know gefell used to charge 220,- euro ex vat in 2008 for a new m70 membrane . I've always wondered why people always recommend thiersch when talking about reskinning of old gefell mics. Since it would be more obvious to have it done by the the people who manufactured the thing in the first place? I've got a hunch he's cheaper  .

greetings,

Thomas

 

[Sredna]

Well, Mr Tiersch used to work for MTG, he actually was one of the developers for the SMS70 system.(MV692 etc.)

Mr Tiersch charge (Sept. 2010) €50 for 48Volt/XLR conversion.(PM 750/ 860, MV 691/692)
Reskinning is €59 for M 70/94 (SD) and €120 for Um70/M71 (=M7). All prices without VAT.

One difference getting the 48V/XLR conversion done by MTG is that you get a completely new
body tube and a nice special design XLR connector.

Doing the conversion self is not that difficult, fitting the XLR connector requiers some skills though...
I attatched the circuit used by MTG, the zener is a 12V, the transistor is a 60Volt NPN and the capacitor is a tantalum one. MTG use SMD parts...

 

[mrclunk]

Anyone know how a Gefell PM750 comes apart?
I'd like to mod mine to 48v (or check it hasn't already)

 

[Sredna]

There's a small screw just over the connector, remove it, take a firm grip on the bright metal windings of the connector and carefully slide the connector/amp part out.

The headbasket is threaded on the upper part of the body, just screw it off to get to the capsule and the capsule holder with the front end of the amp (FET, hi-ohm resistor, first cap).


Good luck!

Anders

 

[mrclunk]

There's a small screw just over the connector, remove it, take a firm grip on the bright metal windings of the connector and carefully slide the connector/amp part out.

The headbasket is threaded on the upper part of the body, just screw it off to get to the capsule and the capsule holder with the front end of the amp (FET, hi-ohm resistor, first cap).

Thanks Anders,
I was worried if i pulled the connector it would pull the whole capsule and assembly through the mic tube..

I've emailed Thierch to see how much he'd charge for the mod/service anyway, we've a few u87 P48 that i'd like looked at too so might make sense to get them all done at the same time.
cheers
paul

 

[Sredna]

Looks like it's modded, the radial cap close to the transformer is new.
Normally there's a 66nF there for hi pass (proximity filter), 10uF makes it linear.

There's actually a pad in there as well but it's nessesary when using the PM750 capsule.
When using other capsules from the SMS70 series, omitting the pad gives you more headroom.

Tiersch makes a neat conversion, he removes the windings and puts a metal ring over there.

Aren't there techs in UK that does U87?

 

[mrclunk]

Yes it has been modded. Well spotted!
Thats a 10uf pana fc cap.
The seller said its had the 10dB pad a LF filter removed. I'm told the capsules an M94 but it only has a serial number.
It all looks in good shape.
Just waiting for the conector to turn up and then i'll convert to 48v myself i think.
The 48v to 12v circuits is simple, just a tight squeeze to fit it in. 

Aren't there techs in UK that does U87?

yeah but i trust the Germans more!

 

[Sredna]

The PM750 is (as you know) meant for singing but more versatile witout the HP and pad,
so that's a good and easy mod.

The capsule is indeed mechanically like an M94 but not electrically, the real M94 has a 10M resistor between the membrane side and capsule housing (=GND). The reason is that the M94 can take
just 40V polarizing voltage but the other capsules in the SMS70 series use 60V.

The PM750 capsule lacks this resistor because this is already taken care of by R2 in the microphone amp. (see schematic)

If you remove R2 you could use the other capsules with full potentional.
(can't use the old capsule anymore though...)

If you use the mike mostly for instruments maybe it's an idea to cut off the lower part of the
headbasket and move the amp front end (FET, R1) to the main amp assembly.
That way you'll principly have an M692 but without the pad/HP switches and be able to use
the M70, M71, M73 and M93 capsules.

yeah but i trust the Germans more!

What I meant was that do you trust the german (and british) post? 

 

[mrclunk]

Thanks for the explanation and schematic!
I do intend to use this for instruments rather than vocals. I'm thinking it'll be nice for acoustic guitar, strings, harp etc..
I'll leave the head basket 'as is' for now but i'll try removing the internal foam, should make it a little more 'open' sounding.
If i like this one i'll get a few more so i have a pair.
Hopefully the connectors will arrive tomorrow and i can fire it up!

 

[mrclunk]

Built the conversion circuit into the mic.
FYI. used a 13V zener and a BC548b NPN transistor.  Output measures 12.3V.
Just waiting for my Tuchel connectors to arrive and i can give it ago...

If anyone need the 7pin conector this guy has them.
http://www.ebay.co.uk/itm/140733224739?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_3814wt_932

 

[paulcheeba]

No I was just talking about taking the basket off to get to the M7 but thanks and I’m glad it sparked a fruitful conversation!