its the MXL V67 mod thread again

[Andybot]

Hi,
im going to mod my v67 and wanted to get some opinions from people who had done the various mods that can be done on these. Im mainly looking to reduce my workload and only replace those parts that are going to improve the mic, the mic i have seems to suffer from what i can best describe as high end fizzle.

So who re-laminated the the trafo and would you recommend it or replace it?
Which capacitors are the most critical to replace?
Is a capsule change going to help or just be expensive?

I attached the schematic.

Thx

 

[pasarski]

Is a capsule change going to help or just be expensive?

It'll probably make bigger difference than any other mod.

Check here Rossi's ideas about taming the harshness http://www.groupdiy.com/index.php?topic=35464.0

 

[Andybot]

Thx Pasarski,
i will check that out.

I have read that a peluso capsule was tried by some, never heard any feedback on the mods.
Has anyone here done a capsule mod on this mic?

Thx

 

[Marik]

Hello Andybot,

It is very fashionable to curse that capsule, but in fact, it is just fine and was used in many even high end microphones (Manley is one example).

The circuit includes EQ used in Neumann U87. You can tweak it for your liking, if you wish. The transformer has only 2:1 ratio (actually, even somewhat lower), so they had to use emitter follower. I'd take the EF out and make U87 circuit and pair it with a good 10:1 transformer. There were quite a few discussions as for how to properly bias the FET. You can use the existing PCB, with minimal modifications.

Best, M

 

[mista min]

Hey Marik,

I found my way to this place and I see you said some pretty interesting things about the circuit.  Could you possible elaborate on what you are saying because i'm not very good at this just yet and would love to know more about what you mean.  Which values are the EF.  I'm not very good at reading FET circuites just yet.

Thanks a lot  ;D
min

p.s.  Marik is right about the capsule being good and not the weakest link.  Honestly I'd think it would be a waist of a capsule to do that... :-\

 

[Andybot]

Thx Marik,
i have been reading the old discussions, they make me feel old as i read them when they first
were posted without understanding much. Thanfully with a k i understand more now.

Is there an emitter circuit 101 somewhere on the web pertaining to mics?

Thx for your Time
A

 

[mista min]

Hello Andybot,

It is very fashionable to curse that capsule, but in fact, it is just fine and was used in many even high end microphones (Manley is one example).

The circuit includes EQ used in Neumann U87. You can tweak it for your liking, if you wish. The transformer has only 2:1 ratio (actually, even somewhat lower), so they had to use emitter follower. I'd take the EF out and make U87 circuit and pair it with a good 10:1 transformer. There were quite a few discussions as for how to properly bias the FET. You can use the existing PCB, with minimal modifications.

Best, M

Marik,

I looked up a lot about this mic and read Idk how many pages of META, but I haven't found any info on the EF for this mic or circuit.  Could someone please share a link or give us a clue?  Also, what changes need to be made to the circuit to use the 10:1 transformer.  Also, about changing the FET isn't the stock one lower noise then the U87?  I don't know if I wanna go through with changing the FET and rebiasing... I couldn't fing it in the META... link perhaps?

Thanks a lot,
Marcos

 

[mista min]

So are these the EF?


c11
r14
r12
r11
r13
c10
L2
L1

I keep looking at the circuit and I am thinking R12 and R11 aren't part of the EF.

What changes should I make to the circuit concerning values if I wanna swap transformers? 
Does R8 and C8 need to change in value?

Sorry, I searched and searched and couldn't find Gus's examples of a transformer swap in this microphone.

Thank you,
Marcos

 

[tmuikku]

Marcos:
try Googling "pnp emitter follower", thats the "EF"

As Marik wrote, that emitter follower is used here to make impedance smaller so that 2:1 transformer can be used (10:1 transformer is more expensive?). Maybe there is some other benefits ( read cost savings )? I'm trying to look at the schematics and got interested, I'm not very good with transistors either Hopefully Marik or some other guru will enlighten a bit more!

Compare the v67 circuit to u87 circuit as Marik suggested.
One schematic here: http://recordist.com/ampex/schematics/neumann/u87sch.jpg


edit:
Multiple edits later another edit (Gosh I'm bad at expressing myself  8)):
By saying Smaller impedance in the first sentence I ment that the EF stage provides high input impedance so it is easier load for the jfet than a 2:1 transformer. EF stage has low output impedance so EF stage can drive 2:1 transformer. All this means the EF stage is a buffer between the fet and 2:1 transformer... Is this correct statement, any gurus online ?

 

[mista min]

Marcos:
try Googling "pnp emitter follower", thats the "EF"

As Marik wrote, that emitter follower is used here to make impedance smaller so that 2:1 transformer can be used (10:1 transformer is more expensive?). Maybe there is some other benefits ( read cost savings )? I'm trying to look at the schematics and got interested, I'm not very good with transistors either Hopefully Marik or some other guru will enlighten a bit more!

Compare the v67 circuit to u87 circuit as Marik suggested.
One schematic here: http://recordist.com/ampex/schematics/neumann/u87sch.jpg


edit:
Multiple edits later another edit (Gosh I'm bad at expressing myself  8)):
By saying Smaller impedance in the first sentence I ment that the EF stage provides high input impedance so it is easier load for the jfet than a 2:1 transformer. EF stage has low output impedance so EF stage can drive 2:1 transformer. All this means the EF stage is a buffer between the fet and 2:1 transformer... Is this correct statement, any gurus online ?

I can see the logic in that statement because that is how it is on the Apex 460, but that one has a 10:1 transformer ??? ??? ???  Still, I will have to read the schematics on paper because on the computer screen it starts to get all...

Anybody, wanna help?  Maybe Andybot has some ideas????  Thanks!

min

 

[Andybot]

I wish i could add more but im out of my depth already. I have begun reading about transistors,  biasing  and looking at sample amplification circuits to try to grasp whats going on better. Like i say though im already out of my depth.

If anyone does have a suggestion of a book that may help? it would be greatly appreciated, the one im reading is very badly written and is troubleshooting manual for receivers.

Thx all

 

[mista min]

Well, I printed the circuit and began to run the copies with highlighters.  And am realized what maybe everybody else already saw, but took me a while to notice.

I wrote what I found to be the same in both circuits.

MXL  =  U87

C5    =  C9
R17  =  R13
C13  =  C11
R16  =  R15
C14  =  C13
R15  =  R16

and

C6    =  R12

I haven't made it far enough in the circuit to find more and maybe I'm totally off... But I don't see how.  I will figure this out one way or another!   But any help would be appreciated.  Any ideas?  I think C9, R13, C11, R15, C13 and R16 are the EQ in the U87 since it is exactly the same in the V67G.  Any clues could help!  Lets figure this out guys!   We newbies ca do it!

Peace,
min

 

[Andybot]

Hi,
im wondering if someone might take that v67 schematic and draw around those parts that are the eq, i dont think your right in your analysis Mista Min but i dont know enough to add much further.

From looking at the schematic for the v67 im wondering if c13 and c14 are a part of the eq circuit or part of the power supply.

I am however going to do some vocals with my v67 and then relaminate the transformer and do some more vocals so i will post the results later.

Anyone who might be willing to point out the eq circuit in the v67 schematic will get bigs ups from me.

Thx 

 

[mista min]

i dont think your right in your analysis Mista Min but i dont know enough to add much further.

Well, I honestly don't really know.  But I think you might be correct in saying I am wrong because it's looks like too much work for just the eq... oh man,... I really don't know enough  ???

Just trying to help with what little I understand.

Did you already change all the capacitors and resistors?

 

[mista min]

I found this thread... need to finish reading it, but it has some good info in it.

http://recording.org/diy-pro-audio-forum/40994-chinese-mic-mxl-v67-improvements.html

 

[Andybot]

Hi mista min,
dont get me wrong you may very well be correct, but i think that area has more do with balanced outputs than any eq'ing. Id like to find out though.

The mods i have done so far are a swap of C2 to a 1000pF polyester 630vdc cap which, although i didnt record anything to compare to , was to my ear an improvement in the clarity of the mic.

I just finished changing the laminations on the trafo and actually recorded a before and after to compare anything that changed . What i recorded was a female voice and an old gibson acoustic.  Again i felt the mic improved in clarity, felt the sound had more depth and less color so what i was listening back to through the monitors was what i heard in the room. Its a voice and a guitar that i have been recording for years and im very familiar with so i was impressed with what the lamination change did.

Ill check out the article you posted. Whatever happened to flatpicker?

Im just going to make slow changes and ab them as i go.
I think next ill change out the electrolytics .

Thx
A

 

[oragall]

the mod more easy its replace the caps, of these the most important is change to 1uf polyester cap.

 

[Andybot]

Hi,
so i finally had time to compare the circuits of the mxlv67 and u87 and i think now i can see what
the mod suggested by Marik would entail.
Does anyone have a suggestion for the transformer for this mod, on the mxl its stuck on a little cavity of its own and i assume thats where the new one would have go.

A link or part number for a transformer that could be used for this mod would really help me out.

Thx Again
A

 

[mista min]

Marik sells one in the white market that is 10:1 and fits in there.  And honestly sounds to me a bit better then a Lundahl according to the audio clips in that thread.

 

[Andybot]

Thx, i will check it out.A