Oktava 012: building a new preamplifier

[mark88]

Hello to the community!
I have the idea to build some preamplifiers for the Oktava 012 capsule. My first idea was to buy the stock microphones and mod them, but after a few inquiries I decided to build them (they will cost much less).

I'm following the article by Lucas Adamson ( http://oktavamk012rebuild.blogspot.it/2012/01/introducing-oktava-mk-012-mc-012-ok-so.html ) and the Scott Dorsey mod ( http://www.recordingmag.com/resources/resourceDetail/315.html ).

My question is about what components should I use: is it relevant to say that some of the components suggested by Scott Dorsey are chosen for its dimensions (other won't fit in a original oktava tube) but I'm planning to build a completely new preamplifer, so no space problems here.
I have a friend which has the possibility to rewrite the PCB and make it printed from a online service.

schematics:

Capacitors:
C1: Dorsey specifies a "Panasonic COG ceramic types, usually an 820 pF value" while Lucas uses a "820pF Silver mica input DC blocking cap". Which would be the best? I read that the silver mica could be brighter on the final sound.

C2: I found the Vishay 1uF 160v MKP. Would be ok?

C3,C4 (and C5): Dorsey specifies Vishay BCC electrolytic capacitors ( http://www.digikey.it/product-detail/it/MAL202138689E3/4073PHCT-ND/263276 ) while Lucas uses Panasonic FC capacitors, which are bigger ( http://www.digikey.it/product-detail/it/EEU-FC1J680/P10341-ND/266350 ).

C6,C7,C8: 10nF are specified on the schematics, while Lucas uses 47nF 63v Wima Polyester MKS02. Are them ok?

Transistors: the Q2 is ok (Toshiba A1015Y) ?


This is my actual list, the same of Lucas Adamson's blog, with reference (Q1...ecc) and prices from the sellers in Euro:

Transistors:
1x Toshiba 2SK170 BL Q1 6pc 10.62 Ebay
1x Toshiba A1015 Y Q2 10pc 5.08 Ebay
Capacitors:
1x 820pF Silver mica C1 5pc 13.79 RS
1x Vishay 1uF 160v MKP C2 5pc 7.87 Ebay
2x  68uF 63v Panasonic FC C3,C4 10pc 3.90 DigiKey
1x  47uF 63v Panasonic FC C5 5pc 2.00 Digikey
3x 47nF 63v Wima Polyester MKS02 C6,C7,C8 15pc 8.19 Farnell
Resistors:
4x 1GOhm  MOX200001007JE R1,R2 20pc 59.40 Digikey
1x 39R0 1% 0.6W Vishay R3 50pc 2.95 RS
1x 7K5 Welwyn RC55Y R4 5pc 7.15 Farnell
2x 13K0 Welwyn RC55Y R5,R6 10pc 12.90 Farnell
1x 39K2 Welwyn RC55Y R7 5pc 6.50 Farnell
1x 84K5 Welwyn RC55Y R8 5pc 1.38 RS
1x 36K0 Welwyn RC55Y R9 5pc 0.60 Digikey
1x 51R1 Welwyn RC55Y R10 5pc 3.42 Farnell
1x 33M0 Vishay 0.5W R11 10pc 1.88 Farnell


---------------------------------------------

About the preamplifier, I found 20mm Aluminium pipes from a local store, which should match exactly the silver Oktava capsule set.
I will use Neutrik connectors (NC MX, silver ones).
My mainly problem is how to fix the capsule on the head of the aluminium pipe.
I attached a scratch, which is similar to the original Oktava microphone.



Thanks you!
mark

 

[mark88]

no suggestions?

 

[Krumlee]

All of your choices seem good to me. I guess from the quantities that you're planning to build five mics? Interesting recommendation from Dorsey to use 2x 1G resistors in series. I'm really curious to hear what difference that makes to the sound compared with 1G. I'm sure it's good advice - he knows his stuff.

Also, are you really buying from Digikey, Farnell and RS? You could probably find acceptable substitutes from just one or two suppliers. Otherwise you're going to be paying a lot in shipping.

The thing about a lot of the component choices (especially capacitors) is that they're a matter of taste. Some people actually like the tone of tantalum capacitors, others prefer something else. C1, C2 and C3 are the important ones. I'd go with the 1uF Vishay for C2. And either choice for C1 is fine - if you use ceramic then it must be C0G type.
Personally I don't think those Welwyn resistors are worth the money - most metal film resistors sound the same to me - but buy the expensive ones if you want.

The thing that makes the real difference to the mic tone is the capsule. I'm not familiar with the Oktava capsules, but they have a good reputation.

Make sure you clean the boards really well (use isopropyl alcohol) before and after you solder them - especially around the FET.

 

[Rossi]

Frankly, I don't think this project is worth the trouble. Original 012 amplifiers aren't that expensive, and their parts are not that bad - at least on the ones I own. The component quality may have been worse when Dorsey wrote his article quite some years ago.

Use the search function to find discussions on the 2SK170 and its high input capacitance (which is undesirable for a mic head amplifier).

Don't rely on that blog recipe, I don't think this guy knows what he's talking about, and I'm pretty sure his super-pimp 012 performs worse than a stock original. For instance, the filter caps on the output are pretty big already at 10 nF. Upping them to 47 nF will cut some treble and, what's worse, introduce HF distortion.

Also, I wouldn't recommend combining two 1G resistors the way this guy does. Theoretically 2G may give a litte lower noise. In reality, you won't hear a difference. The shrink tube looks like a good idea, at first, but it may contain carbon fibers which could reduce the resistance drastically to no more than a few megaohms. Such low resistance would cause noise you WILL hear.  I've had a piece of black colored rubber from a capsule mount that measured 1M, that's 1000 times lower than a 1G resistor.

 

[Krumlee]

Also you can buy bare pcbs quite cheaply if you didn't want to make them yourself. Check here http://www.ebay.co.uk/itm/Oktava-MK-012-MC-012-Replacement-PCB-/111447737675

I kind of agree with Rossi - if you're new to mic building then doing a mod project first would be easier. You start with a working mic, and you can understand its strengths and weaknesses, and experiment with small changes to build your knowledge and experience. It would also help you decide if it's worth building them yourself. But it's your project.

I'll promise you one thing - it will take much longer than you think...

 

[mark88]

Thank you all, you are very useful.
I'm planning doing this project mainly because buying the original preamps and then mod them, will cost me more (I need 4 new microphones). The second reason, because I have a friend who is a electronic engineer, so he knows how to draw pcbs and solder them. My work will be mostly on the mechanical part (making the tube and the connections).
But I'm taking into account to buy only the stock ones and stop.



So... about capacitors... maybe I can swap the silver mica one for a ceramic COG or it would be better a polypropilene? (like the PHILIPS KP 820pF 250V Axial Polypropylene film capacitor). I have not found a ceramic COG type .... could You help me finding one?
And for C6-8 could you give me a replacement for the wima caps?

Then, for the resistors: ok for the 1GOhm ones, I could swap the expensive Welvyn with comparable ones. About the tolerance values what I have to find? 5% is ok?

About the FET: Dorsey specifies the Toshiba 2SK170BL... it is not fine? Also OKtava seems starting using it in the recent microphones. And the A1015 is fine, or better the one specified by Scott Dorsey?


I have a question: I have the idea, that the reduced space inside the original oktavas could raise the microphone noise. Is it right? Should I take this into account when drawing the new pcb and leave some space around the fet especially?

Last question.... I'm planning to make the preamp tube with 20mm aluminium pipes: there is difference into using brass ones, about shielding of magnetic fields? I read something on it.


Thanks!

 

[pasarski]

You probably don't here the difference between capacitors you mention. There's so much more in building mics than the capacitor types. For example, keeping the high Z area clean, preferably floating or built on a high resistance material (teflon etc.) is much more important than choosing between silver mica or polypropylene.

EDIT: Every mod I've done to my 012's have made the mic worst or no difference what so ever.

 

[mark88]

You probably don't here the difference between capacitors you mention. There's so much more in building mics than the capacitor types. For example, keeping the high Z area clean, preferably floating or built on a high resistance material (teflon etc.) is much more important than choosing between silver mica or polypropylene.

EDIT: Every mod I've done to my 012's have made the mic worst or no difference what so ever.

thank you. so you suggest to keep clean around the FET 2sk170? what you mean for "Z area"?

 

[Rossi]

Don't underestimate the mechanical part. It's not easy to build a microphone tube that fits, and the capsule connector won't be easy either. Do not solder to the capsule terminal; it is connected to the backplate and if you by applying heat you might melt the diaphragm which is only microns in front of it.

I own two 012 bodies, one modded one stock. I can't tell them apart. Replacing stock parts with high quality or esoteric parts seems like a sure way to improve a mic, but it's not. Been there done that. It's just a convenient way, when you don't know how the circuit works.

The sound and performance of a circuit is mostly in the design itself. Good designs rarely rely on particular parts. And that's certainly true for the 012 preamp. This is a Russian mic, designed during the cold war, when quality parts were scarce. So what do you do? You come up with a design that's largely independent of particular parts and will work fine with just about anything available.

 

[mark88]

Don't underestimate the mechanical part. It's not easy to build a microphone tube that fits, and the capsule connector won't be easy either. Do not solder to the capsule terminal; it is connected to the backplate and if you by applying heat you might melt the diaphragm which is only microns in front of it.

I own two 012 bodies, one modded one stock. I can't tell them apart. Replacing stock parts with high quality or esoteric parts seems like a sure way to improve a mic, but it's not. Been there done that. It's just a convenient way, when you don't know how the circuit works.

The sound and performance of a circuit is mostly in the design itself. Good designs rarely rely on particular parts. And that's certainly true for the 012 preamp. This is a Russian mic, designed during the cold war, when quality parts were scarce. So what do you do? You come up with a design that's largely independent of particular parts and will work fine with just about anything available.

I thank you, what you wrote is really interesting. When You talk of design, you mean the position of the components, its spacing? Could You explain me?


About the quality of the modding I'm sure of the improvement: my friend - the other person who is involved in this project - has 4 Oktava 012, two stock and two modded. And after the mod of the second pair the sound has clearly improved.
So what we are thinking to do is only to copy the original oktava design - replacing some components - mainly because the updated ones do not enter in a normal oktava pcb. And then for a price reason (the new preamp will cost us less than a stock with the modifications).
thanks


----------------


at the moment this is the project:

 

[Rossi]

No, I'm not talking about the circuit layout but about the way this circuit is constructet. The way it works. There are various ways to construct a mic amplifier, and the 012 is just one. It's actually about the simplest transformerless head amp possible: just one FET and one BJT, no DC converter for capsule polarization. It does have its shortcomings, for instance its SPL capability is fairly limited. Still, given its simple construction, it works well and it sounds pretty good.

I'm not saying you can't improve this circuit, but, it's hardly worth the trouble. IMHO, a little crunch is part of the Oktava appeal. BTW you can fit an MKS-2 1u polyester cap into the stock body, if you want a cleaner sound.

Whenever you do mods, do a blind comparison. When you know which is which, you will always prefer the modded one. Who would admit, even to himself, to have spent days working on mods that don't really improve the sound? But that's what often happens when you replace parts. We've all been there, believe me.

 

[mark88]

No, I'm not talking about the circuit layout but about the way this circuit is constructet. The way it works. There are various ways to construct a mic amplifier, and the 012 is just one. It's actually about the simplest transformerless head amp possible: just one FET and one BJT, no DC converter for capsule polarization. It does have its shortcomings, for instance its SPL capability is fairly limited. Still, given its simple construction, it works well and it sounds pretty good.

I'm not saying you can't improve this circuit, but, it's hardly worth the trouble. IMHO, a little crunch is part of the Oktava appeal. BTW you can fit an MKS-2 1u polyester cap into the stock body, if you want a cleaner sound.

Whenever you do mods, do a blind comparison. When you know which is which, you will always prefer the modded one. Who would admit, even to himself, to have spent days working on mods that don't really improve the sound? But that's what often happens when you replace parts. We've all been there, believe me.

thank you.
do you think i have the possibility to build a good microphone? I'll surely follow the dorsey mod and the original schematics.

 

[Rossi]

Of course it's possible, but I have no way of knowing if your skills will suffice since you have no previous experience. Building a mic may not be the easiest beginners project, even though this circuit is quite simple and has a low component count. You have to work very clean, and make sure no parts make contact with the body tube. The small diaphragm body format can be tricky. Building this circuit for a large diaphragm mic with an existing body would be a much easier start.

 

[mark88]

Of course it's possible, but I have no way of knowing if your skills will suffice since you have no previous experience. Building a mic may not be the easiest beginners project, even though this circuit is quite simple and has a low component count. You have to work very clean, and make sure no parts make contact with the body tube. The small diaphragm body format can be tricky. Building this circuit for a large diaphragm mic with an existing body would be a much easier start.

Ithank you for your advice. Indeed I'm planning to buy components for 5 microphones, and use the first as a prototipe (I'll build only the pcb) for making a bit of practice and a quality control.
But I have a bit of soldering skills and, i think, good manual skills for building the microphones; this is the first time I build audio stuff, but I'm a musician and I repair my instruments every day.


I have a question: could you suggest me a replacement for the C1 (820pf) and C6-7-8 ?
And about the resistors - to buy less expensive stuff - I have to look only for the same Ohm value, or should I take care of other parameters?

 

[ricardo]

I have a question: could you suggest me a replacement for the C1 (820pf) and C6-7-8 ?

This is a critical component.

The BEST capacitor here is NPO/COG Ceramic

Silver Mica's are noisier & polystyrenes are microphonic.  But you may like more noise & microphony.

2sk170 is noisier than J305 for this application

Golden Pinnae stuff for the other parts usually won't make things worse or better.

 

[mark88]

I have a question: could you suggest me a replacement for the C1 (820pf) and C6-7-8 ?

This is a critical component.

The BEST capacitor here is NPO/COG Ceramic

Silver Mica's are noisier & polystyrenes are microphonic.  But you may like more noise & microphony.

2sk170 is noisier than J305 for this application

Golden Pinnae stuff for the other parts usually won't make things worse or better.

thank you. A specific model? I found Panasonic, TDK, Murata... which one is best? http://www.digikey.it/product-search/it?FV=fff40002%2Cfff8000b%2C3400e4%2C1140050&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=50

And for the C6-8 capacitor?

 

[Rossi]

Silver Mica's are noisier & polystyrenes are microphonic.  But you may like more noise & microphony.

I have no experience with silver mica, but I've testet just about everything else. Polypropylene is what sounds most like a naked wire to me [there are mic circuits that can do without an input cap, but this is not one of them]. In my experience C0G ceramics sound a little bit brighter and crunchier, although I like this quality with the Oktava capsules. So I'd also recommend C0G for this project. However, multilayer ceramics are about the worst sounding mic input caps, and it's often impossible to distinguish various types of ceramic caps.

Theoretically polystyrene is about the best dielectric, and many people around here seem to like it. I've not had bad experiences with microphony, but sound wise I don't really like polystyrene in this application.

Polyester is also a bad mic input cap material, but it can be very good further down the signal chain.

I've come to the conclusion that generalizations don't help; you really have to test each application separately. The same cap can be good or bad in different applications. For instance, polypropylene makes a terrible tone cap in a guitar. 

BTW, the exact value of the mic input cap doesn't matter as it is way oversized. You can use anything from 820 to 1500 pf. Even 470 p will do. But don't use physically big caps; it shouldn't touch the body tube (or anything else for that matter).

 

[mark88]

Silver Mica's are noisier & polystyrenes are microphonic.  But you may like more noise & microphony.

I have no experience with silver mica, but I've testet just about everything else. Polypropylene is what sounds most like a naked wire to me [there are mic circuits that can do without an input cap, but this is not one of them]. In my experience C0G ceramics sound a little bit brighter and crunchier, although I like this quality with the Oktava capsules. So I'd also recommend C0G for this project. However, multilayer ceramics are about the worst sounding mic input caps, and it's often impossible to distinguish various types of ceramic caps.

Theoretically polystyrene is about the best dielectric, and many people around here seem to like it. I've not had bad experiences with microphony, but sound wise I don't really like polystyrene in this application.

Polyester is also a bad mic input cap material, but it can be very good further down the signal chain.

I've come to the conclusion that generalizations don't help; you really have to test each application separately. The same cap can be good or bad in different applications. For instance, polypropylene makes a terrible tone cap in a guitar. 

BTW, the exact value of the mic input cap doesn't matter as it is way oversized. You can use anything from 820 to 1500 pf. Even 470 p will do. But don't use physically big caps; it shouldn't touch the body tube (or anything else for that matter).

Many thanks for this explanation. So any of these would fit fine? http://www.digikey.it/product-search/it?pv14=2&FV=fff40002%2Cfff8000b%2C3400e4%2C1140050&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=50


And for the C6-7-8 10nF which of these would fit? http://www.digikey.it/product-search/it?pv3=3&FV=fff40002%2Cfff8000b%2Cfffc0038%2C34003e%2C1140050&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=50

 

[ricardo]

Silver Mica's are noisier & polystyrenes are microphonic.  But you may like more noise & microphony.

Theoretically polystyrene is about the best dielectric, and many people around here seem to like it. I've not had bad experiences with microphony, but sound wise I don't really like polystyrene in this application.

Polyester is also a bad mic input cap material, but it can be very good further down the signal chain.

I've come to the conclusion that generalizations don't help; you really have to test each application separately.

NPO/COG ceramics do what capacitors are supposed to do AND NOTHING ELSE.  They don't sound brighter, darker bla bla.

This stuff about Silver Mica et al is tested .. including the propensity of Polystyrenes to microphony.  You can test this yourself.  Replace your capsule with a (shielded) polystyrene capacitor of the same capacitance and tap the resulting assembly.  You need to use a circuit that doesn't have other microphonic bits in the signal chain.

Guru Scott Wurcer did this for his Linear Audio articles but the results appeared in MicBuilders.

 

[mark88]

Ok I made a new list on your suggestions, with reference to Digikey product page:


Toshiba 2SK170 BL http://www.ebay.it/itm/2SK170-BL-TOSHIBA-Low-Noise-Audio-Amplifier-N-Channel-TO-92-J-FET-/111343523766?pt=UK_BOI_Electrical_Components_Supplies_ET&var=&hash=item19ec9757b6
Toshiba 2N5087 http://www.ebay.it/itm/5-x-TRANSISTOR-2N-5087-2N5087-/400728260714?pt=Componenti_elettronici_attivi&hash=item5d4d44006a

CAP CER 820PF 100V 5% NP0 RADIAL http://www.digikey.it/product-detail/it/RCE5C2A821J0M1H03A/490-7493-1-ND/4277410
1uF 160v Vishay MKP1839 2.5% http://www.ebay.it/itm/4x-VISHAY-ROE-MKP1839-1-uF-160V-ROE-ERO-Polypropylene-/251254674181?pt=UK_Sound_Vision_Other&hash=item3a7ff21305
CAP ALUM 68UF 63V 20% AXIAL http://www.digikey.it/product-detail/it/MAL202138689E3/4073PHCT-ND/263276
CAP ALUM 47UF 40V 20% AXIAL http://www.digikey.it/product-detail/it/MAL202137479E3/4047PHCT-ND/263257
CAP CER 10000PF 100V 10% RADIAL http://www.digikey.it/product-detail/it/K103K15X7RH5TH5/BC1120CT-ND/286742

1GOhm  MOX200001007JE http://www.digikey.it/product-detail/it/MOX200001007JE/MOX200J-1000ME-ND/705445



Which specifications should I care of choosing the other resistors? Tolerance and power?
Thanks