Need MXL V67i Tube Schematic

[commanderberti]

can anyone help me? thanks

 

[cyrano]

I've just added a reversed schematic to the MXL thread:

https://groupdiy.com/threads/mxl.84887/

 

[Khron]

I believe the OP was looking for the "V67i Tube"; that reverse engineered schematic seems to be of the older / original (?) "V67". Apparently there's also a "V67i" non-tube.

MXL seem to enjoy making a VERY confusing-sounding lineup...

 

[cyrano]

Thanks, Khron. I missed that part.

And, yes, MXL has a confusing way of naming their products. Anyhow, I don't have these other schematics. Sorry.

 

[Khron]

can anyone help me? thanks

Then again, you could consider posting some well-lit, well-focused photos of the mic circuitry, along with a description of the issues you're facing..?

 

[commanderberti]

Andererseits könnten Sie in Betracht ziehen, einige gut beleuchtete, gut fokussierte Fotos der Mikrofonschaltung zu posten, zusammen mit einer Beschreibung der Probleme, mit denen Sie konfrontiert sind..?

Das Problem ist, dass kein Ton herauskommt. Netzteil, Schlauch und Kabel sind gut. Pad-Schalter, Tiefpass und Capslule-Schalter machen Geräusche am Schalter. Ich glaube, die Kapseln haben keine Spannung...

the problem is der is no sound coming out.. PSU, tube und cable are good.. pad switch , Low Pass and capslule switch are making noise at switch.. I think the capsules has no voltage… tube B was 200v.. heater 6,3v.. tube works .. on bothe capsule i can mesure no voltage, if i remove the bode.. a hum came, if i remove the mic grill, more hum noise.. so everything seams to be ok.. but .. no sound .. if i talk to the capsule..

 

[Khron]

That's not exactly a photo of the mic circuitry, is it?

Apologies if i wasn't clear enough - i meant photos of the front and the back of the "main" board (with the tube removed), and now that i see it, the switch board as well.

on bothe capsule i can mesure no voltage, if i remove the bode.. a hum came, if i remove the mic grill, more hum noise..

That's an accurate assessment though, even if you will definitely NOT be able to measure ANY voltage directly on the capsule (due to several resistors in the 100Meg-1G range, much higher than your multimeter's input impedance).

 

[Migs 31]

Das Problem ist, dass kein Ton herauskommt. Netzteil, Schlauch und Kabel sind gut. Pad-Schalter, Tiefpass und Capslule-Schalter machen Geräusche am Schalter. Ich glaube, die Kapseln haben keine Spannung...

Guten Morgen,

It is perfectly normal that you get humm as soon as you remove the body and then the grill.
That is supposed to be a Faraday cage effect, metal body/grill protecting the circuit from humm.
A fellow member recently described how to use a metal bin/trash can to test the mic inside it...

In those cheap MXL mics a few things can go wrong:

- Could easely be the Valve/tube - I had a 12AT7 China dying after few hours.
You can change it for any 12AT7-12Au7-12AX7 or ECC 81/82/83 borrowed from a GT amp.
Just to test, see if its not that. Then buy the correct type, if thats the problem.
Thomann had some decently priced ones, last time I checked.

- If its not the Valve/Tube check with a magnifying glass the soldering,
wires from capsule to PCB, they are so thin sometimes & can break easily .

- If not then the PCB. Look for obvious bulged out El. caps,
if you have cheap Tantalums in it, they could have gone short circuit.
Check for cold joints/broken solder points with a glass.
Oh! clean the back of PCB's with Isopro. or Ethanol Alcohol & Toothbrush.
I have seen lots of dirt and residue resin in some of those cheap mics.

I worked on an MXL V67G long ago (the FET version-no valve).
I got so frustrated with the poor quality.
I ripped the PCB inside and made into a U87 type instead.

Your one has a LED in it ?!?

Good luck to you.
M

 

[Voyager10]

There's a schematic for the V77S tube mic on the recordinghacks page: MXL V77S Tube | RecordingHacks.com - I'm guessing the V67 will be similar.

If there's a lot of hum with the screening removed, it suggests the tube itself is basically working - something is amplifying a high-impedance signal. If so it's either a problem with the polarisation voltage, or with the capsule itself.

 

[RuudNL]

This one? (It doesn't have the "i"...)

 

[Khron]

This one? (It doesn't have the "i"...)

... And not a tube mic

 

[commanderberti]

Einen Schaltplan für das V77S Röhrenmikrofon gibt es auf der Recordinghacks-Seite: MXL V77S Tube | RecordingHacks.com - Ich vermute, dass das V67 ähnlich sein wird.

Wenn es bei entfernter Abschirmung viel Brummen gibt, deutet dies darauf hin, dass die Röhre selbst im Grunde funktioniert - etwas verstärkt ein hochohmiges Signal. Wenn ja, liegt es entweder an der Polarisationsspannung oder an der Kapsel selbst.

There's a schematic for the V77S tube mic on the recordinghacks page: MXL V77S Tube | RecordingHacks.com - I'm guessing the V67 will be similar.

If there's a lot of hum with the screening removed, it suggests the tube itself is basically working - something is amplifying a high-impedance signal. If so it's either a problem with the polarisation voltage, or with the capsule itself.

yes i think the tube is working.. so this mic has 2 seperatly capules.. i think it is a problem with the polarisation voltage oder withe die capsule switch

 

[commanderberti]

That's not exactly a photo of the mic circuitry, is it?

Apologies if i wasn't clear enough - i meant photos of the front and the back of the "main" board (with the tube removed), and now that i see it, the switch board as well.



That's an accurate assessment though, even if you will definitely NOT be able to measure ANY voltage directly on the capsule (due to several resistors in the 100Meg-1G range, much higher than your multimeter's input impedance).

 

[Migs 31]

yes i think the tube is working.. so this mic has 2 seperatly capules.. i think it is a problem with the polarisation voltage oder withe die capsule switch

Ok,

Maybe bypass the capsule switch, then? Maybe?

I read somewhere that your mic has a Warm and a Bright side?
Hence the LED, to tell you which side is on (I guess) & the letters Wm-Brt.
Interesting concept, all though not a "classic' valve design.
We are still looking for the V76i TUBE schematic.

M

 

[Voyager10]

OK, from those photos it's nothing like the various V67s, as there's no (visible) output transformer. At least 3 transistors on the main circuit board, so, what, a tube first stage followed by a Schoeps-style transformerless output??

I'd still guess it's a problem with the polarisation voltage. There are a lot of wires between the main PCB and the switch PCB. Is it possible any have broken? Often they look OK but have just broken at the solder joint, you may need to wiggle them to be sure.

 

[commanderberti]

OK, from those photos it's nothing like the various V67s, as there's no (visible) output transformer. At least 3 transistors on the main circuit board, so, what, a tube first stage followed by a Schoeps-style transformerless output??

I'd still guess it's a problem with the polarisation voltage. There are a lot of wires between the main PCB and the switch PCB. Is it possible any have broken? Often they look OK but have just broken at the solder joint, you may need to wiggle them to be sure.

i think the same.. yes this mic is transformer less.. i have mesuring every kabel from cabsule to pcb.. also the switches.. all seams to be ok.. i think it must be a smal problem.. contact problem or so an PCB.. (polarisation voltage came not to the capsules.. so if both cabsules ar not working i think it is ab common ground problem.. so a schematic wehre helpfully.. )

 

[kingkorg]

i think the same.. yes this mic is transformer less.. i have mesuring every kabel from cabsule to pcb.. also the switches.. all seams to be ok.. i think it must be a smal problem.. contact problem or so an PCB.. (polarisation voltage came not to the capsules.. so if both cabsules ar not working i think it is ab common ground problem.. so a schematic wehre helpfully.. )

It is unlikely both sides of the capsule are not working. You can't measure the voltage on the capsule, you have to check before 1G resistors that go to the capsule. Check the switch itself if it is working.

 

[Gus]

I would guess it is lke a MXL690 or V69 transformerless circuit with an added switch for the capsule sides.

Is the capsule side selection switch any good?

 

[Gus]

What is the marking on the output transistors and does it have a 170 JFET?

I would try a new tube first.

It might have the the two triodes in parallel setup like a about gain of 1 inverting charge amp first stage into a Schoeps like output stage like a MXL transformerless microphone I started to trace sometime ago(I stopped because the output was covered in epoxy and it was not worth the time to finish tracing it).
IIRC that microphone had about 180VDC B+ if you are measuring about 200VDC maybe the tube is not conducting

 

[commanderberti]

What is the marking on the output transistors and does it have a 170 JFET?

I would try a new tube first.

It might have the the two triodes in parallel setup like a about gain of 1 inverting charge amp first stage into a Schoeps like output stage like a MXL transformerless microphone I started to trace sometime ago(I stopped because the output was covered in epoxy and it was not worth the time to finish tracing it).
IIRC that microphone had about 180VDC B+ if you are measuring about 200VDC maybe the tube is not conducting

i have already change the tube , this was my first action.. no sound from the capsules..