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Parts for Scott Dorsey/Oktava mod
Old 9th February 2006
  #1
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Parts for Scott Dorsey/Oktava mod

I remember seeing a thread about parts being available for the MK-012 mic mod. Anyone know about this?
Old 9th February 2006
  #2
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Old 9th February 2006
  #3
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You can get the 2SK170 FET at

http://www.mcminone.com/

Good luck finding the 1G resistors, but they aren't needed IMO and I've tried both ways...

I recommend using a silver mica for the capsule to FET coupler cap, but Dorsey recommends something else. Just use the same value as is in it now or as on the schematic if you have a copy. I also tried other types including polystyrene (an audiophool favorite) for the capsule coupling cap and it totally ruined the sound IMO, so I'd stay away from those.

I put in polypropylenes in mine to replace the tant cap that drives the pnp (which BTW can be replaced with a BC560 pnp if you like) , but IIRC it made no audible difference.

So I'd say do the FET and the capsule coupler cap and call it a day...
Old 12th February 2006
  #4
Gear Nut
 

Another source....

You should be using the 2sk170BL - which is a lower noise 2sk170.

I bought mine from tech-diy.com, and it was $3.80 for 4 of them.

http://www.tech-diy.com/smallsignal.htm

You should also be aware that the pin layout is different on the 2sk170 than on what in originally in the mic. Dorsey's article does not really address this. Install the new FET with the flat side facing the post where the leg of the FET connects to the teflon post and resistor - and use the MIDDLE leg to go to the post - the other 2 will fall into place. The original had one of the end legs going to the post.

I also used the 1g resistors - I wasn't sure what was in there, and had a pair of mics both with different resistors. Why not? Also used the panasonic tant to feed the second op amp.

I used a .001 polyester from the capsule to the FET (standard green chiclet type) and I like it.

The other caps in my mics were OK - it did not have the wet slug tants in there - so I left them alone.

After the mods, the mics sound much better. More open, better top, less boxy. They were muffled and boxy as hell before, so I would call this mod well worth it.

I've got more expensive mics, and before the mod I considered these to be useless, and was saving them for when I needed a condensor I could destroy (snare mic...) Now they might actually be useful for something. Gonna try them on overheads next week...

Regarding the ebay parts kit, I think there's about $10 or so worth of parts in the kit if you replace everything, so it's probably worth paying $15 to get them in one shipment at one time. But if you need to do 2 or more mics, I would source them yourself...

Mike
Old 12th February 2006
  #5
Gear Nut
 

PS

One more thing. I either got the 1g resistors from mouser or digikey (can't remember which).

Not a problem, and a good idea IMO - at least Dorsey seems to think it is....

Mike
Old 12th February 2006
  #6
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Thanks, Mike, for the heads up on the FET position. I hope this gets rid of the lower mid/upper bass tubbiness.
Old 12th February 2006
  #7
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Tubby...?

Quote:
Originally Posted by tenor39
Thanks, Mike, for the heads up on the FET position. I hope this gets rid of the lower mid/upper bass tubbiness.
Well, compared to my AKG 451s, the oktavas have a bit more bass, but I don't know if I would call them tubby. More like warm or full.

What really put me off of them before the mod was the really boxy plasticy upper mids, and very muted highs.

All in all the balance between low, mid and high is much better after the mod, plus they are much less noisy.

I would guess that some experimentation with that coupling cap would yield a vareity of tones, but I liked the first one that I tried, so I left it alone...

Good luck with this!
Old 15th February 2006
  #8
Gear addict
 

Quote:
Originally Posted by mikelevitt
You should be using the 2sk170BL - which is a lower noise 2sk170.

...Also used the panasonic tant to feed the second op amp...


Mike

That's just flat wrong.

The "BL" is a I(dds) grade - it has NOTHING to do with lower noise...

There are NO op amps in a MC012...
Old 15th February 2006
  #9
Gear Nut
 

Considering that.....

Quote:
Originally Posted by sekim
That's just flat wrong.

The "BL" is a I(dds) grade - it has NOTHING to do with lower noise...

There are NO op amps in a MC012...
It was the middle of the night when I was writing, and I meant "transistor" not op amp...

I have no idea what an "I(dds) grade" is...

I am not an electronics engineer...

I guess you win. Thanks for the helpful post.

Now back to reality. Dorsey says to use the BL - to quote him "And no, other 2sk170 variants will not work." So I guess it is pretty important to get the BL.

I am trying to be helpful here, and have no desire to join in a pissing match. The guy is trying to rebuild some mics here, and I am trying to help.

So shoot me!

Mike
Old 15th February 2006
  #10
Gear addict
 

Quote:
Originally Posted by mikelevitt
Now back to reality. Dorsey says to use the BL - to quote him "And no, other 2sk170 variants will not work." So I guess it is pretty important to get the BL.
Any 2SK170 will work (there's actully quite a few part numbers that are suitable). SD recs the BL because it has a decent chance of not needing to adjust the bias point, but there's no guarantee that it won't need to be done even with a BL...especially since Oktava is well known to put "whatever is close" in, and that includes any resistors that affect the bias point (especially when they used alternate FET's). I've done other "grades" (one is not better than the other - only different) of the 2SK170 and these particular ones worked without re-biasing in these particular mics that had the right bias resistors in them. But the bottom line is it's best to check the operating conditions after replacing the FET. If you want to know how to check the bias on a MC012 let me know and I'll post...

BTW - many MC012's don't even need a FET replacement. The problem is there's no telling what they put in any particular day with the earlier ones, some were cr@p, some were actually great...It's the coupler cap between the capsule and FET that's the real culprit IMO. The 1G resistors aren't needed - especially if you're going to a .001uF for the capsule coupler. The output caps are an issue as well though not nearly so much as the coupler. Also, I'm not interested in any pissing match either, life's too short for that, sorry if I came across otherwise...
Old 15th February 2006
  #11
Gear Nut
 

No worries!!!

Quote:
Originally Posted by sekim
Any 2SK170 will work (there's actully quite a few part numbers that are suitable). SD recs the BL because it has a decent chance of not needing to adjust the bias point, but there's no guarantee that it won't need to be done even with a BL...especially since Oktava is well known to put "whatever is close" in, and that includes any resistors that affect the bias point (especially when they used alternate FET's). I've done other "grades" (one is not better than the other - only different) of the 2SK170 and these particular ones worked without re-biasing in these particular mics that had the right bias resistors in them. But the bottom line is it's best to check the operating conditions after replacing the FET. If you want to know how to check the bias on a MC012 let me know and I'll post...

BTW - many MC012's don't even need a FET replacement. The problem is there's no telling what they put in any particular day with the earlier ones, some were cr@p, some were actually great...It's the coupler cap between the capsule and FET that's the real culprit IMO. The 1G resistors aren't needed - especially if you're going to a .001uF for the capsule coupler. The output caps are an issue as well though not nearly so much as the coupler. Also, I'm not interested in any pissing match either, life's too short for that, sorry if I came across otherwise...
Hey, thanks for the info! Sorry for the paranoid reaction!!! I really don't know very much about electronics, I'm just a good google searcher...

I've only rebuilt the 2 oktavas that I have, but I did notice that the 1g resistors were different on both mics, and bizarre looking with no markings. And since my meter can't measure resistance that high, I just figured it would be safe to change them out.

Would love to know how to check the bias, and also the theory at work in this part of the circuit.

I would also be curious as to your thoughts regarding the effect of the value of the coupling cap on the frequency response of the mic.

Bottom line for me is that I think this mod is really worthwhile.....



Mike
Old 15th February 2006
  #12
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BradM's Avatar
Quote:
Originally Posted by sekim
You can get the 2SK170 FET at

http://www.mcminone.com/

Good luck finding the 1G resistors, but they aren't needed IMO and I've tried both ways...

I recommend using a silver mica for the capsule to FET coupler cap, but Dorsey recommends something else. Just use the same value as is in it now or as on the schematic if you have a copy. I also tried other types including polystyrene (an audiophool favorite) for the capsule coupling cap and it totally ruined the sound IMO, so I'd stay away from those.

I put in polypropylenes in mine to replace the tant cap that drives the pnp (which BTW can be replaced with a BC560 pnp if you like) , but IIRC it made no audible difference.

So I'd say do the FET and the capsule coupler cap and call it a day...
When you say ruined the sound, what do you mean exactly? I put polystyrene in mine and I don't think anything sounds bad. What am I missing? What's the tonal difference between using silver mica vs. polystyrene?

Brad
Old 15th February 2006
  #13
Gear addict
 

Quote:
Originally Posted by Brad McGowan
When you say ruined the sound, what do you mean exactly? I put polystyrene in mine and I don't think anything sounds bad. What am I missing? What's the tonal difference between using silver mica vs. polystyrene?

Brad

The green "chiclet" isn't polystyrene, it's a polyester or polypropylene. It should be a decent sounding cap for this application (though I haven't tried one myself). There are some parms that make it less than ideal for such a high impedance use, but the same holds true for silver mica... And the polystyrenes have parms that appear ideal, yet they sound horrible IMO...
Old 15th February 2006
  #14
Gear addict
 

Quote:
Originally Posted by mikelevitt
...I did notice that the 1g resistors were different on both mics, and bizarre looking with no markings. And since my meter can't measure resistance that high, I just figured it would be safe to change them out.

Would love to know how to check the bias, and also the theory at work in this part of the circuit.

I would also be curious as to your thoughts regarding the effect of the value of the coupling cap on the frequency response of the mic.
One of these resistors (actually 650M) + the capsule coupling cap (850pF) together form a hi pass filter that can be calculated using: cutoff frequency = 1/(2piRC).

I'll post the bias info later tonight since I'm at the office right now and don't have the schematic handy...
Old 15th February 2006
  #15
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BradM's Avatar
Quote:
Originally Posted by sekim
The green "chiclet" isn't polystyrene, it's a polyester or polypropylene. It should be a decent sounding cap for this application (though I haven't tried one myself). There are some parms that make it less than ideal for such a high impedance use, but the same holds true for silver mica... And the polystyrenes have parms that appear ideal, yet they sound horrible IMO...
Excuse my ignorance. But what's a parm?

Can you be more explicit about why you think the polystyrene sounds horrible? Does it make the sound too grainy? Too cloudy? Does it lose detail? What exactly is it that you don't like specifically?

Brad
Old 15th February 2006
  #16
Gear addict
 

Quote:
Originally Posted by Brad McGowan
Excuse my ignorance. But what's a parm?

Can you be more explicit about why you think the polystyrene sounds horrible? Does it make the sound too grainy? Too cloudy? Does it lose detail? What exactly is it that you don't like specifically?

Brad

parm = parameter, i.e. individual specification item

To my ears the polystyrenes were very constricted sounding i.e. the mids and upper mids were all wrong. I tried a couple of different ones and pulled them each after 30 seconds of listening - they were that bad to me...

But again, this is not what your green "chiclet" is. I've not tried those, but given that they're widely used "in the signal path" in all sorts of gear, I'm not surprised that you're satisfied with the sound.
Old 16th February 2006
  #17
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BradM's Avatar
Quote:
Originally Posted by sekim
parm = parameter, i.e. individual specification item

To my ears the polystyrenes were very constricted sounding i.e. the mids and upper mids were all wrong. I tried a couple of different ones and pulled them each after 30 seconds of listening - they were that bad to me...

But again, this is not what your green "chiclet" is. I've not tried those, but given that they're widely used "in the signal path" in all sorts of gear, I'm not surprised that you're satisfied with the sound.
I'm not using a green chiclet. I'm using a 1000pf Xicon polystyrene. They look like little clear bugs.

Brad
Old 16th February 2006
  #18
Gear addict
 

Quote:
Originally Posted by Brad McGowan
I'm not using a green chiclet. I'm using a 1000pf Xicon polystyrene. They look like little clear bugs.

Brad
Ooops, it's the other guy that's using the green "chiclet".

Anyway, what I posted before concerning my perception using them (polystyrene)...

I don't recall what brands these are and they aren't marked. Interestingly, I have a couple of Adcom power amps and one has polystyrene in the drivers and the other uses something else and I hear the same constrained sound in the amp with the polystyrenes. But in all fairness, I haven't changed them out so I can only guess as to whether that's causing it.

Of course what I hear as "constrained" may be something that sounds right to you, so if you're satisfied with the sound I'm certainly not going to tell you that you should change your caps. Who knows? You might not like the sound of silver mica. But if someone isn't satisfied with their mic, I say try the silver mica first.
Old 16th February 2006
  #19
Gear Nut
 

It's me...

Quote:
Originally Posted by Brad McGowan
I'm not using a green chiclet. I'm using a 1000pf Xicon polystyrene. They look like little clear bugs.

Brad
I'm the guy using the green chiclet (polyester). Sounds nice in the mic. No uppper-mid weirdness at all...

Mike
Old 16th February 2006
  #20
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BradM's Avatar
Quote:
Originally Posted by sekim
Ooops, it's the other guy that's using the green "chiclet".

Anyway, what I posted before concerning my perception using them...

I don't recall what brands these are and they aren't marked. Interestingly, I have a couple of Adcom power amps and one has polystyrene in the drivers and the other uses something else and I hear the same constrained sound in the amp with the polystyrenes. But in all fairness, I haven't changed them out so I can only guess as to whether that's causing it.

Of course what I hear as "constrained" may be something that sounds right to you, so if you're satisfied with the sound I'm certainly not going to tell you that you should change your caps. Who knows? You might not like the sound of silver mica. But if someone isn't satisfied with their mic, I say try the silver mica first.
Well I'll definitely keep this tip in mind. Does anyone have a part number for the green chiclet? I may order some and try them.

Brad
Old 16th February 2006
  #21
Gear Nut
 

Xicon...

Quote:
Originally Posted by Brad McGowan
Well I'll definitely keep this tip in mind. Does anyone have a part number for the green chiclet? I may order some and try them.

Brad
I am pretty sure that they are xicon PF series, available at mouser. I actually got mine from a "5 pounds of capacitors" bulk bag that I bought on ebay.... so I am not exactly sure what brand they are, but they look like xicon.

Mike
Old 16th February 2006
  #22
Gear addict
 

As for biasing, if you have a copy of the schematic with numbering on it, you want vary R3 (39K) and R5 (82K) such that the junction between Q2 and R7 (7.5K) gives 7.63 vdc when the circuit is hooked up to phantom power.

You need to vary these resistors so that R3 + R5 always = 121K (within 5% ).

This assumes that Q2 is properly biased with R3+R5 and R6 (36K), which should be a safe assumption for a working mic that you want to change the FET...

If you need a copy of the schematic, PM me and I'll send you a copy.
Old 16th February 2006
  #23
Gear Nut
 

Thanks!!

Quote:
Originally Posted by sekim
As for biasing, if you have a copy of the schematic with numbering on it, you want vary R3 (39K) and R5 (82K) such that the junction between Q2 and R7 (7.5K) gives 7.63 vdc when the circuit is hooked up to phantom power.

You need to vary these resistors so that R3 + R5 always = 121K (within 5% ).

This assumes that Q2 is properly biased with R3+R5 and R6 (36K), which should be a safe assumption for a working mic that you want to change the FET...

If you need a copy of the schematic, PM me and I'll send you a copy.
Very cool, thanks! I have the schematic, from Dorsey's article...

Mike
Old 16th February 2006
  #24
Gear addict
 

BTW - for the heck of it, I cobbled together this circuit from scratch and stuck it in a 319 and it makes a nice sounding mic. I like it on guitar cab and some vocals.
Old 16th February 2006
  #25
Gear Nut
 

I believe it....

Quote:
Originally Posted by sekim
BTW - for the heck of it, I cobbled together this circuit from scratch and stuck it in a 319 and it makes a nice sounding mic. I like it on guitar cab and some vocals.
I believe that would sound pretty good. I've been thinking about transplanting it into a couple of chinese mics that I just can't bear to listen to, but I have the feeling that the problem there is in the capsule as well as the electronics...

Thanks for all of the info!!

Mike
Old 16th February 2006
  #26
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sorry for beeing stupid, but can someone give link to the mod itself?
Old 16th February 2006
  #27
Gear Nut
 

the link

Quote:
Originally Posted by lowswing
sorry for beeing stupid, but can someone give link to the mod itself?

http://www.tbrstudio.com/index1.php

Then you have to click on the help section, and there is a PDF of the article in there.

Mike
Old 16th February 2006
  #28
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cheers thumbsup
Old 11th December 2006
  #29
Gear Addict
 

Quote:
Originally Posted by mikelevitt View Post
http://www.tbrstudio.com/index1.php

Then you have to click on the help section, and there is a PDF of the article in there.

Mike

Hi Modders,

I just came accross this Oktava 012 modding, and since I have a few myself, I am very curious to start modding them. The above link does not work anymore. Could anyone please send me the article?

Thanks in advance,

Lucas
Old 14th December 2006
  #30
anyone know where to get 2sk170BL in europe?
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