advice for first tube mic clone build

[kip.duff]

Hello forum.

I have spent yesterday and part of today looking at DIY tube mic build forums- all new to me.  I have limited elctronics design skills but have building skills- my current hi-fi are kits from Bottlehead based on 300B tubes, and for speakers, Altec A7 VOTTs, Altec 604-8H, Fostex/Nagaoka folded horn.  Career mechanic.  Looking for advice along these lines:

a) I want to build a tube mic clone
b) am researching reasonable mods for my Rode K2 (Mullard CV2492 and 1961 Valvo tubes on their way already)

a) it appears I have one of approx three classic mic styles to choose from for the build 1) U47/M49 Neuman  2) U87/U67 Neuman, and 3) C12/251 AKG.  So I am going to describe my intended use.  Simple home audio hobby setup.  I am playing harmonica and keyboard thru Rivera Sedona 55 ES tube instrument amp.  I am playing Telecaster thru 1965 modded Fender Super Reverb and Fender Deluxe Reverb Reissue.  I do not play agressive rock- more bluesy, single, pure non-overdriven notes- and using pretty much native reverb.  No vocal or acoustic needs.  At this point recording thru Scarlet 2i2 into Mac mini and Logic Pro X.  Which (if any) of these three vintage microphone styles might be better suited for my use?  All good?

For simplicity's sake, I am close to ordering one of the complete kits from micparts like V-251 or V-47.  I would prefer not to be building from scratch, sourcing components one by one from different sellers.  Not necessarily against getting something like an Apex 460 as starting point though. 

Anyway, after more reading, I realized I might be better off using a Maiku capsule as a starting point for the build.  Would one of the Maiku capsules be compatable and a smart mod choice for one of the MP kits?

b) the Rode K2 seems to be unique circuitry- and appears heater voltage is 5V(!?)  If I'm correct, this is to keep the mic cooler?  Doesn't affect sound?  Is Maiku capsule a smart mod?  I got this mic cheap and am waiting for tubes to get a better idea if I like it.

Thanks, Kip......
       

 

[moamps]

...based on 300B tubes, and for speakers, Altec A7 VOTTs, Altec 604-8H, Fostex/Nagaoka folded horn...

So you have a huge living room 

b) the Rode K2 seems to be unique circuitry- and appears heater voltage is 5V(!?)  If I'm correct, this is to keep the mic cooler?  Doesn't affect sound?  Is Maiku capsule a smart mod?  I got this mic cheap and am waiting for tubes to get a better idea if I like it.

I would try CT12 (http://www.timcampbell.dk/index2b.htm) capsule in Rode first, and better (Tfk) tube also. I can't comment Maiku.

 

[kip.duff]

moamps:

Using one set of speakers at a time.  Oddly, A7's work well in small room.

Telefunken?  Should try one also.  But so many different vintages, plant locations.  I like their logo. 

CT12 capsule $385- not sure the K2 warrants that investment.  But I don't know the potential of the K2.....

 

[analogguru]

..... Altec A7 VOTTs....

As the name says VOTT = Voice of the THEATRE (or cinema).  IMHO for studio-/home-use they sound terrible and EVERY cheap chinese mic is sufficient for them, you won't hear any difference, everything sounds like the same sh*t.  And yes, I have experience with them.  In the studio where I started to work in 1979 they had them as control monitors.  The first thing I did was that I bought with my private money immediately two 3-way-HiFi-speakers for ~ $ 350,--/pair because I couldn't stand the terrible sound of the A7.... yes, they are loud, designed for THEATRE or cinema, but the compression drivers into a horn like in the A7 are a torture to my ears....

 

[moamps]

CT12 capsule $385- not sure the K2 warrants that investment.  But I don't know the potential of the K2.....

If you will not be satisfied with this combo, you can buy parts for C12  and use CT12 there. It can be very good mike.

I have once opportunity  to listen A7 VOTT driven with 2A3 SEP amps. Very detailed, fast and big sound.  I liked it.

 

[kingkorg]

I personally wouldn't touch K2. It is a great mic.

Don't know where you live but some of Apex variations like this one are great to start with, and then you can turn it into anything you want:
https://www.gear4music.com/Recording-and-Computers/SubZero-Tube-Microphone/154R

 

[kip.duff]

If you will not be satisfied with this combo, you can buy parts for C12  and use CT12 there. It can be very good mike.

Makes sense.

I have once opportunity  to listen A7 VOTT driven with 2A3 SEP amps. Very detailed, fast and big sound.  I liked it.

They are my favorite speakers so far- most "air" I've ever heard.  Maybe the types of music I listen to favor them also- not much "rock".  I think old style tube anps like you mentioned favor these speakers.  I had to rebuild the X-overs- Russian PIO surplus capacitors worked real good there.  Still need a lot of work- may have to scratch build better X-overs and substitute  Emilar horns.

 

[kip.duff]

I personally wouldn't touch K2. It is a great mic.

I appreciate the input.  I need to do extensive work improving/learning recording technique with it.

Don't know where you live but some of Apex variations like this one are great to start with, and then you can turn it into anything you want:
https://www.gear4music.com/Recording-and-Computers/SubZero-Tube-Microphone/154R

Yes- Apex 460B available Amazon Prime $249.  I've seen many of your posts!  Definitely been considering.  Still leaning towards trying out the MP V-47 kit- get everything I need at one time.  This kit comes with different circuit than 460 though- might limit my mod options later.

Also,  just discovered  the great Matador C12 build thread- however, not sure if CT12 capsule is in stock right now.

 

[Tim Campbell]

Currently the lead time for my CT12 is 4 weeks or less. I've had many customers exchange my capsule for the stock one in K2's and they've been surprised by what a world class mic it can become. Really Rode's achille's heel is their capsules. Even the NT1 becomes a great mic with a capsule change.

 

[mhelin]

SELA T12 would be a nice and easy beginner's mic:

https://groupdiy.com/index.php?topic=62601.0

Circuit can be built on tube socket, but you have to figure out how to attach the socket inside the body. You could use Tim's CT12, but would need to modify the capsule connection to get omni as well as cardioid directional patterns and use either a switch on mic or a reed relay to switch between the patterns.

 

[kip.duff]

SELA T12 would be a nice and easy beginner's mic:

https://groupdiy.com/index.php?topic=62601.0

Circuit can be built on tube socket, but you have to figure out how to attach the socket inside the body. You could use Tim's CT12, but would need to modify the capsule connection to get omni as well as cardioid directional patterns and use either a switch on mic or a reed relay to switch between the patterns.

Thanks- very interesting: 62V plate and 5V heater!  Sure is simple circuit- but appears to need a bit of modding/fabricating expertise.

 

[kip.duff]

Currently the lead time for my CT12 is 4 weeks or less. I've had many customers exchange my capsule for the stock one in K2's and they've been surprised by what a world class mic it can become. Really Rode's achille's heel is their capsules. Even the NT1 becomes a great mic with a capsule change.

Thanks Tim.  Current price and shipping?

 

[kingkorg]

Tim, i believe k2 has polarisation voltage of 70v, wouldn't it have to be modified for your capsule?

 

[Tim Campbell]

kip.duff please email me at [email protected]

kingkorg you're right in that I'd prefer 55v but I not sure anyone who has swapped them out has done that mod.

 

[ln76d]

I would said a little bit opposite. Capsules aren't bad (depending on revision and definately not their center terminated k67 type) but most of the circuits are horrible. It isn't CK12 type capsule, rather like many chinese edge terminated k67. Still it can sound truly good outside the rode circuits After many years of NT1 (a) manufacturing they finally improved circuit (which what's funny use exactly all the mods i was making for the years in NT1a). Finally polarisation voltage is in decent range (65V instead 75V), more linear response etc. It is decent microphone for the money but not my thing completely.
For K2, this microphone truly sucks due to transformerless circuit, this is common for transformerless tube  mikes (or there is any fan of m147/m149 or lauten etc? ), but of course it isn't only related to output buffer. Currently working on a pair, but here's different goal - completely new circuit with 6au6 pentode and transformer at the output. Then owner will decide does he like it or will swap exactly to Tim CT12   Anyway, i tested original circuit with original CK12 and this is a little waste of potential of the capsule in my opinion. Still K2 have really great enclosure and the psu is also truly good design.
PSU use negative voltages in both sections. For my needs high voltage section need to be converted to positive. Heater voltage in both PSU on my bench is -5.8V. It can be easily reset inside PSU - there's trimmer potentiometer for that.

 

[ln76d]

Tim, i believe k2 has polarisation voltage of 70v, wouldn't it have to be modified for your capsule?

The two i currently have are polarised with 60-65V (don't remember exactly, now both circuits are disassembled), but if i remember correctly some NTK and K2 which i reworked few years ago were over 70V.

 

[Tim Campbell]

In76d I'm sure it's just because of our different disciplines. I'm no electronic genius but I have a lot of experience with Rode capsules. I have about 50 of them here. When they switched distributors in denmark I got their old distributor's stock of NOS and problematic capsules. They may not be the very worst capsules I own but they are far from the best.

I've made capsules specifically for a number of NT1a's to be used as omni room mics that really transformed them into unbelievably good ambient mics. I'm sure with your tweeks they would be even better.

 

[ln76d]

Dear Tim,
of course and i'm not "electronic genius" also, just love microphones  
I would say that these capsules are much different than for example your CT12 (which i truly love as stated many times before).
There were different revisions of these capsules, i hope that there were revisions and not just poor quality control Since last nt1 capsule is named HF6 so i believe that there were other hf Anyway they can sound very different. Some have more bumped high frequency area, some different dip in midrange. I spot also different shims between halfs etc. as also single sided version have resonator backplate instead back half with diaphragm which also makes it different sounding from typical double sided, which you can find in NT2a or K2 etc.
For example mentioned my thread with T12 circuit ended up with single sided Nt1a capsule. It fit the circuit and body which i used. Is it the best microphone in the world? Of course not, but truly usefull tool for tracking guitar (acoustic and electric with  amp also), some vocals, ambience, toms etc. I love to have various type of microphones in my studio for every occasion and source.
NT1 circuit for omni - why not and for ambience yes of course ;D For NT1a i would keep original 75V connected to backplate and both diaphragms connect to input - this should give really good omni response.  For ambience recording there's no need to extend low end in NT1a.  This microphone  unfortunately have pretty bad headbasket.
I asked you some time ago about cardioid versions of your capsules, but topic died  - do you think would this be possible to reduce some costs and make single sided cardioid only version?  Maybe something with just second half made of acryl like rode did? Just idea I have some plans for a pair of CT12 for my personal use in the near future, cardioid only would be best for this, especially if there would be a chance to reduce some costs
And yes, i still remmeber that i promised you something and i will keep my word, just have some problems to send it from a long time (i will explain soon in PM) 

 

[Recording Engineer]

For K2, this microphone truly sucks due to transformerless circuit, this is common for transformerless tube  mikes (or there is any fan of m147/m149 or lauten etc? ), but of course it isn't only related to output buffer.

Way too broad in my option... I’m not saying that mods, along with the addition of a transformer, probably wouldn’t vastly improve the mics mentioned (along with many, many, many others), but I certainly hope most would agree, the simple fact that a mic is transformerless, is not a factor of suck.

 

[ln76d]

Way too broad in my option... I’m not saying that mods, along with the addition of a transformer, probably wouldn’t vastly improve the mics mentioned (along with many, many, many others), but I certainly hope most would agree, the simple fact that a mic is transformerless, is not a factor of suck.

Not the main factor, but pretty important - that's why i wrote before - "but of course it isn't only related to output buffer".
Take for example M147/M149 - ultra great metal work, one of the best capsules ever made and truly good tube (i used it and its twin 6112 in different builds) - so what sucks here?