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gabasa

Mic Project Idea
« on: November 13, 2016, 01:50:25 PM »
Hi All,

I'm fairly new to this forum, but I have a project idea and wanted to get your opinions on whether or not you think it's good and feasible.

I have a pair of AKG C480b mic bodies that are dead.  I do not want to repair them because it would cost too much to get new PCBs installed by AKG.  On the other hand, I have a pair of great AKG C460b mics with JW mods with a small collection of AKG capsules.

I would love to design some replacement PCBs for the 480 bodies, so that I have a pair that is different than, but just as good as my modded 460s.  I have 8 capsules, so complementary mic pairs seem like a cool idea.  I could either design PCBs with a transformerless Schoeps circuit, or maybe straight up KM84 circuits if I can find a transformer that fits the AKG body.

What do you think?  Is this a great idea worth pursuing, or not worth the effort?

Thanks.


RuudNL

Re: Mic Project Idea
« Reply #1 on: November 13, 2016, 02:29:07 PM »
Of course this can be done! Only the space inside a pencil microphone is very limited.
I did the same some time ago. I used a (slightly modified) Schoeps circuit, complete with a DC/DC converter for the polarisation voltage. (Top is the original, bottom is the modified microphone.)
There is a solution for every problem!

http://www.vansteenisaudio.nl

ln76d

Re: Mic Project Idea
« Reply #2 on: November 13, 2016, 03:43:15 PM »
Make tube mikes instead FET ;)

Gus

Re: Mic Project Idea
« Reply #3 on: November 13, 2016, 05:47:58 PM »
Why not fix it it does not look like it would be hard to repair
http://recordinghacks.com/microphones/AKG-Acoustics/C-480-B

gabasa

Re: Mic Project Idea
« Reply #4 on: December 05, 2016, 09:21:34 PM »
Well, it looks like this project is going to move forward; Russell Tech is actually going to work on a pcb for this one!

I've been looking at components.  The capsule is obviously the AKG ULS series, and it looks like the AMI T8 output transformer is a good fit, which has the 7:1 ratio of the KM84.  There's more than one good choice for the capacitor on the capsule, like Amtrans AMCH copper foil or RelCap polystyrene, but I guess many choices will be able to fit.

Beyond this, the 1uf coupling cap is probably the most important passive component choice.  Would anyone here be able to recommend a polypropylene  film/foil that would be small enough to fit inside the AKG body?  If not, maybe a pair of 0.47uf in parallel?  What are some good choices for this capacitor?  Should I consider metallized perhaps?  I think that Wima has a small MKP2 that would fit.

This is going to be fun.  I look forward to comparing these when completed to my modded C460B mics.

Thanks

gabasa

Re: Mic Project Idea
« Reply #5 on: December 05, 2016, 10:28:53 PM »
RuudNL, thanks for posting those great photos!  What mics did you start with?  I wonder how the surface mount components that Schoeps uses today compare to what you used in your project.

ln76d

Re: Mic Project Idea
« Reply #6 on: December 06, 2016, 07:23:46 AM »
Well, it looks like this project is going to move forward; Russell Tech is actually going to work on a pcb for this one!

I've been looking at components.  The capsule is obviously the AKG ULS series, and it looks like the AMI T8 output transformer is a good fit, which has the 7:1 ratio of the KM84.  There's more than one good choice for the capacitor on the capsule, like Amtrans AMCH copper foil or RelCap polystyrene, but I guess many choices will be able to fit.

Beyond this, the 1uf coupling cap is probably the most important passive component choice.  Would anyone here be able to recommend a polypropylene  film/foil that would be small enough to fit inside the AKG body?  If not, maybe a pair of 0.47uf in parallel?  What are some good choices for this capacitor?  Should I consider metallized perhaps?  I think that Wima has a small MKP2 that would fit.

This is going to be fun.  I look forward to comparing these when completed to my modded C460B mics.

Thanks

It's not clear what you want to make.
Russell have MK12 boards and schoeps topology for electret.
Then you wrote about transformer and km84.

It's not clear for me also, how the 460 capsule is build.
It looks like it's separated from ground - there's "center", "ring" and "ground" connection in  the capsule.
If so, you don't need any input capacitor. If not, then i would use 470pF (max 1nF) NP0/C0G for C1.
For the C4, output of KM84, i would reccomend MKT over MKP.
Evox Rifa MMK is really good choice for that topology. For this one, to fit, it should be placed horisontal.
You can use values from 470nF - 1uF.
If you want to use pad, then NP0/C0G for C9.
Also two most important capacitors are C2 (feedback cap) and C3.
For C2 3.3pF NP0/C0G, for C3 4.7uF Epcos MKT (also mounted horisontal - sme size as MMK) or 10uF Elna Silmic II (good bipolar 4.7uF-10uF could be also used).
For transformer i would suggest 3U Audio GZT-47.
Should fit without any problem, have proper ratio, and 3U Audio transformers are really high quality.

Re: Mic Project Idea
« Reply #7 on: December 06, 2016, 09:43:49 AM »
"For transformer i would suggest 3U Audio GZT-47.
Should fit without any problem, have proper ratio, and 3U Audio transformers are really high quality."

Fascinating, 3U Audio for the past 6+yrs utilize AMI transformers for their higher end (more expensive microphones).
http://3uaudio.com/cp.asp?id=610

micaddict

Re: Mic Project Idea
« Reply #8 on: December 06, 2016, 10:00:27 AM »
"For transformer i would suggest 3U Audio GZT-47.
Should fit without any problem, have proper ratio, and 3U Audio transformers are really high quality."

Fascinating, 3U Audio for the past 6+yrs utilize AMI transformers for their higher end (more expensive microphones).
http://3uaudio.com/cp.asp?id=610
Yup.

AMI trannies are not necessarily (!)  better than GZ's own, but many buyers simply prefer American over Chinese.

For a while Guosheng also used Sowters in some of his more expensive mics, but from what I recall he was less in tune with those.

ln76d

Re: Mic Project Idea
« Reply #9 on: December 06, 2016, 05:00:17 PM »
Fascinating, 3U Audio for the past 6+yrs utilize AMI transformers for their higher end (more expensive microphones).
http://3uaudio.com/cp.asp?id=610

You know, simple marketing :D
Not always go in pair with better quality ;)


gabasa

Re: Mic Project Idea
« Reply #10 on: December 06, 2016, 05:31:59 PM »
It's not clear what you want to make.
Russell have MK12 boards and schoeps topology for electret.
Then you wrote about transformer and km84.

Thanks everyone for all the great comments!

Sorry if I was unclear.  Russell told me he'd be interested in designing a pcb for this project, so that a KM84 circuit can fit into the AKG body.  I hope that this clears things up.

ln76d, am I correct in thinking that you prefer polyester film caps in mic circuits?  Has anyone tried polyester foil, such as the Nichicon QYX?  I think that Marantz used these caps a lot in their older stereo receivers.
http://www.nichicon.co.jp/english/products/pdfs/e-qyx.pdf

Cheers!    :)

ln76d

Re: Mic Project Idea
« Reply #11 on: December 06, 2016, 07:38:59 PM »
You can build it on perfboard without any problem.
This way would be easier to fit all components you want to use.
I prefer good polyester as the output capacitor before transformer.
My favourite type is metal paper, but you wouldn't fit it inside that microphone.
I did many A/B tests, especially in tube microphones.
Polypropylene are worst a sounding in this part of the circuit.
Why? I don't know.
Am using polypropylene caps in many different circuits, so i'm not against polypropylene at all, but in this case it doesn't sound good.

For Nichicon, i didn't used it, it's some standard cap, with poor datasheet and the first line of description - "inductive construction" sounds not good :D
Am using some electrolytics from nichicon, but i was really dissapointed with their fine gold, muse, kt.
If you like datasheets, you can only compare dielectric loss tangent.
http://banelec.online.fr/fab/evox%20rifa/Film%20Capacitors%20-%20General%20Purpose.pdf
BTW. there's no value as 1uF, so max you can use is 470nF (or two in parallel) if you would like to use "original" value.
It doesn't mean anything if Marantz use it in their products. Probably was cheap enough :D
For my excuse, i need to say that i was newer a fan of Marantz stereo, especially these made in (at least) last 20 years :D

Phrazemaster

Re: Mic Project Idea
« Reply #12 on: December 06, 2016, 09:39:54 PM »
Yup.

AMI trannies are not necessarily (!)  better than GZ's own, but many buyers simply prefer American over Chinese.

For a while Guosheng also used Sowters in some of his more expensive mics, but from what I recall he was less in tune with those.
I found it fascinating that Klaus claims the only transformer he ever thought was indistinguishable from an original old Neumann was one that Ollie built (AMI).
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micaddict

Re: Mic Project Idea
« Reply #13 on: December 07, 2016, 03:57:11 AM »
I found it fascinating that Klaus claims the only transformer he ever thought was indistinguishable from an original old Neumann was one that Ollie built (AMI).

Yes, IIRW it was made with original laminations and all.
Perhaps Klaus will chime in.

BTW my post wasn't meant to put down AMI trannies in any way.
But that was clear probably.  :)

Re: Mic Project Idea
« Reply #14 on: December 07, 2016, 10:58:03 AM »
Yes, IIRW it was made with original laminations and all.
Perhaps Klaus will chime in.

BTW my post wasn't meant to put down AMI trannies in any way.
But that was clear probably.  :)

Hi Micaddict,
For the benefit for everyone in the audio recording community, I would like to try and clear any and all misinformation or misunderstanding's concerning AMI/Tab-funkenwerk and transformer laminations.  To my knowledge, when Oliver spoke of original laminations, It was only concerning UI30 laminations used in the BV8.  Is there any other "original lamination NOS" reference that was made by anyone at AMI/Tab? 

Hello IN76d,
Based on your various post I've read, I firmly believe you are a helpful resource to the community and I do not wish continuing adversarial gestures. It provides no benefit to our community!
I think we can both agree, anyone pursuing the art of manipulating electrons, will inevitably formulate some very strong opinions.

I do not know if Oliver disrespected you or anyone else in some way?  I do know some statements made about Oliver are simply not true.  "Oliver's interests are only Commerce"  It's absolutely true, for a company to exist it must make a profit.  However, if we look at the following facts....

-Oliver never really wanted to run a company, however in the mid '90's when Oliver started doing historic V72/76 and microphone repairs and racking for locals in the Pacific NW, there was not a single company in existence where he could buy quality replacement transformers.  (maybe a private individual somewhere existed)

-The way Oliver manufactured transformers is very time consuming, (it's not simply... use an off the shelf bobbin place it on the machine and start winding, there is a lot of prep and post winding tasks involved)  Over the years the prices have become less expensive due to efficiencies in manufacturing.

-As many customers all over the world have experienced Oliver provided these historic repair services at a incredible prices.  (Yes many times he was slow in completing the repairs) However often he would feel bad about his untimeliness and offered free shipping, even some repairs/mods were free.

-In the early 2000's a historic corporation with financial means, solicited an offer to Oliver to give up his business and get out of their way. Oliver could have made $$, however he made the decision to continue to help small audio companies to provide an alternative for the benefit of musicians, artist, producers without a "rockstar budget". 
Oliver continued to provide expertise and assistance to individuals and startup companies often at little to no immediate financial gain, and is one of the reasons we have soo many options today.

-Oliver was not perfect he had many flaws (he would never admit it.... a lot of stubborn German in that 6'10 stature)

I could make a few more points, however I have a responsibility to get back to....
I say all the above in the sincerest hope it will be received in a positive manner!  With soo much stupidity and hate happening on this planet, our community should not participate in such behavior.

-Cheers to everyone,
Dennis Maximova

ln76d

Re: Mic Project Idea
« Reply #15 on: December 07, 2016, 07:09:27 PM »
Dennis - please check PM ;)

gabasa

Re: Mic Project Idea
« Reply #16 on: December 08, 2016, 01:17:56 PM »
Thanks everyone for the helpful info, especially all the capacitor recommendations.

Damn, I feel like I've been bitten by the DIY bug.  Now I feel like getting a used MXL ldc and gutting it.  I can do the same circuit as above, but with space for large components.....

 ;)

ln76d

Re: Mic Project Idea
« Reply #17 on: December 08, 2016, 06:40:46 PM »
Nah, for ldc you can make it better ;)

gabasa

Re: Mic Project Idea
« Reply #18 on: December 24, 2016, 12:24:42 AM »
Thanks everyone for your suggestions.  Something came to mind tonight.  I think that the AKG capsules polarize at 62V, but I believe that the KM84 circuit is 48V.

Will the AKG capsules work with the Neumann voltages, and if so, will this affect the sound?  Perhaps the pcb for this project would have to have a voltage converter for the proper AKG polarization voltage.

Dylan W

Re: Mic Project Idea
« Reply #19 on: December 24, 2016, 05:10:06 AM »
You might look at using 0.1uf C0G capacitors in parallel. Mouser carries both 50V and 100V parts in the 1206 form factor. If you're willing to do a little SMD, you should have no trouble fitting 10 in parallel on the back of the PCB.

IIRC, they're around a buck each, so at $10 for a 1.0uf cap you're still well in under the price of most fancy foil caps.