MXL V67 mod: Is it possible to install Ge Trans for D2?

[orpheusmaximo]

Hi.
I'm a Germanium Transistor enthusiast. I want to mod my MXL V67 ( mostly re-cap it ). Question: Could I exchange D2 ( 2SA1015 in the schematic I have ) for a PNP Ge, granted that I would install a trim pot for R7 ( or R6 ) to re-bias it?  Also a trim pot for R10 could be advisable? Anyone can help me with this?  Thanks!

 

[ln76d]

What's the PNP Ge?
Germanium transistor?

 

[orpheusmaximo]

At the moment I have ( from my Fuzz Face builds ) some 2n404.

Also NPN I've got some AC 88 and AC 176 ( just saying, maybe build a whole new mic circuits around these? ).

Also some Ge diodes.

Thanks for the reply.

P.S: If besides these you feel there's a better Ge fit for D2, would appreciate the info, the idea would be to fit the 2n404 as D2. Planning on maybe putting a trans socket for D2, is that a good idea? So I would be able to try different trans, and then adjust the trim-pot (s) for best sound.

 

[ln76d]

Oh men, i'm not familiar to the germanium transistors.
You need compare the specs of both.
I didn't noticed before that you wrote about your Germanium Transistor enthusiasm, so my question looks stupid
To be honest - this is not the best part of the circuit to get any improvement in sound.
You can always throw out whole emitter follower and 2:1 transformer, put 10:1 and make it some u87 style.
For other improvements - i would replace C8 with 1uF foil cap (max 3.3uF) and for better low end response increase C1 to 100nF.
C4 to ground, R5 to ground, R7 and R6 - change for potentiometer wired as variable resistor, remove R4 and C2.
If you are using original capsule, you could try C3 from 270pF to 330pF range.

 

[orpheusmaximo]

My intent is more in relation to timbre than anything else ( Ge always brings a "metallic highs" and "rubbery lows" to audio circuits, at least as Guitar fx are concerned , I just fear ending up with a noisy mic.
I guess you can just undo the changes if it doesn't work.

 

[orpheusmaximo]

One more thing to take in account: The V67 is ALWAYS my 2nd microphone, mostly addressing bass frequencies, connected to a Bellari 105 valve pre ( and I'm very happy with the results, though I believe I could make it more customized, more/defined lows and a "thinner grain distortion" on highs ):

For vocals, 1st. mic is Neum. TLM 103 into a Chandler Pre
For Guitar  cab, 1st mic is Shure SM57beta into a Chandler Pre

So please take this in account. I don't want a U87 clone ( not necessarily, though I may get another MXL to try that mod ), but a more rounded V67 for my specific needs. Thanks.

 

[orpheusmaximo]

One last question: Besides clumsy set-up, is there any other reason for not installing outside pots for R7 ( or R6 ) and R10, so as to adjust as necessary on-the-spot ( right before pressing REC ), specially if intending to swap D2 for different transistors? Thanks.

 

[Matt Nolan]

My intent is more in relation to timbre than anything else ( Ge always brings a "metallic highs" and "rubbery lows" to audio circuits, at least as Guitar fx are concerned , I just fear ending up with a noisy mic.
I guess you can just undo the changes if it doesn't work.

Considering that D2 is an emitter follower, its contribution to the timbre of the mic will be very small.

 

[gary o]

Interesting read I have been interested in messing with a V67 for while now but not got one.....IM about to throw together a point to ppoint U87 circuit for my friend we using a Fame C05 as doner body I believe the circuit is same as v67, I have a few capsules laying around tim capsule neumann ,rk47 ,adk, Violet design, 93 k67,and cheapys & other diy mics, u87i, u47 ish, Elam and so on good stuff basically, I did a day of swapping capsules in mic circuits every combo sent files blindly to my friend.... basically he blindly and me were blown away with this circuit as is no mods (yet) could not believe it ! it beat the tube mics using same capsules in many cases .....it sounded great with chunger cheap K67 $39 Fame was only £35, Im gonna swap a few caps for fun, I keep coming to that same conclusion about capsule being king, makes me laugh when some one seeks out a brand of capacitor that was in a U47 to get that sound when they using a capsule made by a guy in his garage ( not that I dont admire these guys).Anyway we gonna keep Fame/V67 circuit mostly standard coz we like it... perhaps its the de emph that is different from the 87 that we like well we like both more audio crayons to scribble with best £35 spent for long time.

 

[midwayfair]

Germanium tends to handle low-impedance sources decently. Most of the issues with noise occur with higher impedance sources and become more apparent with more gain.

Here, the source impedance is low, and the transistor is purely an emitter follower, with about 2V on its emitter.

There's no gain in the system. So the higher capacitance of germanium (which is why the highs usually sound softer) won't do anything.

There's still leakage current, and this could add noise but it won't be that bad since ... there's no gain.

The reason some circuits have less low end with germanium is because the input impedance is probably lower than with some other devices. Usually you see this in guitar pedals, where the transistors are thoroughly abused. There's no gain so the input impedance of that stage is pretty close to the value of the base resistor, which is not that high to begin with.

What I'm getting at is that there's no benefit to a germanium transistor here, only the possibility for a downside (more noise).

If you want to play with the frequency response, there are plenty of other components in the circuit to mess with that will have a much, much larger effect.

 

[ln76d]

So everyone confirmed whote i wrote
There's no need to copy U87 circuit as a "clone".
Most chinese microphones which are based on U87(deemphasis input stage)/C414 (emitter follower output stage) circuits sound better converted to the lower output like in U87.
Values of capacitors and capacitor-less input as i described is far away from U87 sound.

 

[midwayfair]

There's no need to copy U87 circuit as a "clone".

Well ... the Aurycle is cheaper than the V67g, and you don't have to desolder anything but can just build it right the first time. The circuit sounds just fine with a handful of modifications to reduce the noise (particularly removing the test signal input components ...) and a better capsule. The transformer is fine (and at 2:1 it's "doing less" to the sound in any case) and most of the passives can be upgraded for pennies. The circuit is capable of better signal:noise than the u87's circuit since you aren't losing 8x of gain from the step-down transformer.  Is leaving out an emitter follower better or worse in terms of noise than turning your average preamp up another 18dB?

 

[ln76d]

When you are loosing  "8x of gain" mostly those cheap capsules sound little bit better
Good microphone doesn't mean only noisless and sterylised!
Transformer "sound" and little bit of coloration can sometimes make really great microphone from a junk.
Where's the problem with preamp? Most decent preamps can handle really weak signal levels - also mostly you don't need pad at louder sources. Compare 1mV/Pa coil dynamic microphone to the 8mV/Pa U87. Did you ever had problem to use dynamic microphone?

 

[orpheusmaximo]

I'm here reading and learning folks! Keep on giving the wisdom on the mic mods please!

 

[Gus]

did you do a search of this site?
Something to look at
http://groupdiy.com/index.php?topic=47569.0

 

[orpheusmaximo]

Nice. So far I like the:

Replacing C8 with 1uF foil cap (max 3.3uF) and for better low end response increase C1 to 100nF.
C4 to ground, R5 to ground, R7 and R6 - change for potentiometer wired as variable resistor, remove R4 and C2.
If you are using original capsule, you could try C3 from 270pF to 330pF range.

So at first I plan to:

Change C1 C3 C8 ( install sockets and try different values )

Variable resistor for R6 / R7 - C4 to ground, R5 to ground - remove R4 and C2.

Socket D2 and try different trans.

Eventually I may get to C2 C4 C6 ( install sockets and try different values )

Personally, specially if Ge for D2, I wonder if R10 shouldn't also be a variable resistor.

 

[ln76d]

R10 can be variable resistor - why not?
C2 - set low frequency corner - the best capacitor here - no capacitor
C4 - don't bother with it
C6 - you can try 68nF - 100nF

Instead the socket you can use rotary switch.
You can connect specific values and switch it in working circuit - it's real a/b comparison.
You can also make connection of parallel capacitors.

 

[orpheusmaximo]

Thanks! The body of the mic lacks space for all the pots I would like to install ( at least two pots and a rotary switch ), so sockets seem to be the best way.

 

[ln76d]

I had in mind only to use switches for testing process

You can connect every switch using wires and for tests use microphone without the outside pipe.
When you will find proper value, then you can use single capacitor, normally placed, on PCB

 

[orpheusmaximo]

Got it! Question: In relation to R10 as variable resistor, don't you think it would give some control to what goes through to D2, and thus it's impact in the circuit?