Oktava mkl2500

Hi, I had fixxed 2 (MKL-2500) mic hum problems. Both were in the mic cable end. One of the pins was grounding due to poor soldering. If you moved the cable end it would short or open and work. All better now. A better made cable may be in order down the road. From what I've read this seams to be a common problem, (they must have started the newguy out on cabels!)

I will say that I like the mic and feel it was well worth the issue and price.


Later
 
PhilGood said:
Though I have to admit my homemade ELAM 250 kicks booty!!!!
Click to expand...

...and there's already a waiting list for your next production run...(can we get custom colors?!!!)...
 
kidvybes said:
...and there's already a waiting list for your next production run...(can we get custom colors?!!!)...
Click to expand...

Funny... I first went with brushed aluminum body and gold grill, then almond body and gold grill, now I'm thinking dark green or black. Can't decide!
 
I posted this a while back inthe mp3 section, but here is a tune with female voice using an mkl2500. I cut a little high shelf eq .

FWIW the guitar (me) was AT4040

mkl2500 vocal
 
one thing i quickly learned about the 2500 is that you will need a shockmount.
picks up vibrations like nothing i've ever seen.
 
giraffe said:
one thing i quickly learned about the 2500 is that you will need a shockmount.
picks up vibrations like nothing i've ever seen.
Click to expand...

The June 05 Recording had a great DIY for mods on the 219 and 319 by Scott Dorsey.

Some mods could be used on the 2500
I think if you cover the inside of the body with sone silicone RTV calk it may help.

I should have my MKL2500 early next week.




Also I found this on the net
http://www.omnipressor.com/Other/Othermicpix/MKL2500schem.jpg
http://www.prodigy-pro.com/forum/viewtopic.php?t=509
 
timboZ said:
The June 05 Recording had a great DIY for mods on the 219 and 319 by Scott Dorsey.

Some mods could be used on the 2500
I think if you cover the inside of the body with sone silicone RTV calk it may help.

I should have my MKL2500 early next week.

Also I found this on the net
http://www.omnipressor.com/Other/Othermicpix/MKL2500schem.jpg
http://www.prodigy-pro.com/forum/viewtopic.php?t=509
Click to expand...

That's a great idea, but I wonder if the silicone RTV would withstand the heat over time?

FWIW, the accelerator used to make silicone RTV cure quickly is an acid and is very corrosive to metal... that's what it gives the RTV that sour, tart, eye-burning smell.

I'd suggest using the electronics grade silicone RTV, used for attaching coils and other things to PCBs. It takes a lot longer to cure, but it smells much better and won't eat the shell or insides of your mic. ;)

GREAT links too, by the way!
 
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giraffe said:
one thing i quickly learned about the 2500 is that you will need a shockmount.
picks up vibrations like nothing i've ever seen.
Click to expand...

What is the metal Oktava uses for their bodies? Tin? I've never heard a metal ring so easily! Someone could probably have a good business making replacement shells of a different material.
 
YES. Get one while you can.

A tube mic for the price of a SM58. Hell get 2.
I just unboxed mine yesterday. Sounds great so far.
 
MKL2500 Schematic

I'm new here but I have two MKL2500's and last night I spent 20 minutes generating a preliminary schematic. The schematic for the new versions differ
from the post sited here quite a bit. See the attached file.
No longer a cathode follower
No Dc current flowing through transformer
Potential Mods
Replace 680pf ceramic connected to grid to a 680pf polyprop, the 1uf electrolytic in serries with the transformer to a Mylar and bypass the cathode Cap with as large a value film that will physically fit. I'm not done with the schematic but intend within the next week to finalize all of the values.
Hope this help those of you that are interested in modifying thes Mic.
 
I spent some time and finalized the schematic with some recommended changes that seem to work well. Referring to the attached schematic
* C4 is changed to a Polypropolyene (See MK319 thread)
* C2 1uF Stacked Film is added in parallel with the existing cathode
bypass cap
* C3 is changed to a 1uF Mylar/polyester
* C1 added, is the 1uF electrolytic that was removed from the
tranformer and moved into the C3 position.This provides some local
energy storage and a low Impedance to a reasonably high frequency
which will improve the transient (time domain) response of the circuit.
If anyone has any comments I'd appreciate hearing from you.
Vince
 

Attachments

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VinceNY said:
I spent some time and finalized the schematic with some recommended changes that seem to work well. Referring to the attached schematic
* C4 is changed to a Polypropolyene (See MK319 thread)
* C2 1uF Stacked Film is added in parallel with the existing cathode
bypass cap
* C3 is changed to a 1uF Mylar/polyester
* C1 added, is the 1uF electrolytic that was removed from the
tranformer and moved into the C3 position.This provides some local
energy storage and a low Impedance to a reasonably high frequency
which will improve the transient (time domain) response of the circuit.
If anyone has any comments I'd appreciate hearing from you.
Vince
Click to expand...

Looks good Vince - nice job!
 
Vince, if pins 2 and 7 are inseperable in an EF95 (U.S. equivalent) then isn't the tube wired in pentode mode? If you used a CV10100, you could wire it exactly like a U47.

Also, the heater voltage seems low. Are they trying to under heat like a U47?
 
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Thanks for your responses kid klash and Phil Good

Phil Good
You are correct that the suppressor grid is internally connected to the cathode and that it does not represent a true triode connection, thanks you for the correction.
The EF86 or the tube you suggested (do you have any data on it as I am not familiar with it) would definitly push this mod toward the topology of the U47.
The undervoltage applied to the heater is normally done to reduce the tube noise output, although I don't know if it has any other effect on the sonics; maybe someone can comment on that.
Some other notes on the Mods: I will try to post some photo,s regarding the placement of the new components as it was quite a tight fit.
The addition of C1 seems to have increased the gain somewhat ( I need to go back and recheck this) leading me to believe that before this change the high impedance of the PSU allowed for a (sneak) feedback path from the plate through the capsule and back to the grid. In keeping with the U47 approach, feedback of this type will not be used.
If anyone has the opportunity to A-B these mods with some known reference mic we could use that input to help tweek the sound although the ultimate limiting factor may turn out to be the capsule.
Vince
 
Sorry Correction
..........(sneak) feedback path from the plate through the capsule bias network and into the grid.
Vince
 
Hello all
The preceived gain increase was one of those late night abberations. The gain before and after the Mods is within 1dB.
Vince
 
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