S16 - tube microphone (6028/408 and 6AK5/5654)

[ln76d]

[PROJECT FINISHED]

S16 - Cardioid pattern

Below schematics for:

S16MP - Hypercardioid, Cardioid, Omni patterns

S16H - Hypercardioid, Cardioid patterns

S16O - Cardioid, Omni patterns

AKG 2072 Z 0009 "Teflon CK12"
6028 JAN ECG
10:1 Beyerdynamic
MXL 770 body
0.5uF MP capacitor
3.3uF Evox Rifa MMK

MXL headbasket!
First internal mesh need to be removed completely!
Second internal mesh need to be removed from the front side of the capsule!

Simple as hell!

Sound good enough to keep it

I tried many configurations of resistors, voltages, capacitors, capsules, transformers etc.
Tried chinese k67, k47, Rode NT1 edge terminated capsule and for this circuit AKG fit well.
I will try again NT1 capsule, which is also really good. If i will keep AKG i will probably make omni switch.
With AKG polarisation voltage could be around 80V but then microphone output is too high.
Transformer ratio could be a little bit higher like t14/1.
First i tried 6:1 and 7:1 and i couldn't find optimal configuration for it.

Update:
Select C3 for low end response between 1uF-2.2uF.
You can try 1G for R1 - only for single - cardioid - pattern version S16.
Important change for MP and H versions.
Added O version.
MP version - updated to V2 - simplified pattern switching with use SP3T type.



I did test with 5654 - 6AK5W military tube - works wonderful!
To use it, heater voltage need be changed to 5-6V so it's easier make PSU from typical chinese

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All microphones projects:
https://groupdiy.com/index.php?topic=62423.0
https://groupdiy.com/index.php?topic=62441.0
https://groupdiy.com/index.php?topic=64687.0
https://groupdiy.com/index.php?topic=62601.0
https://groupdiy.com/index.php?topic=63436.0
https://groupdiy.com/index.php?topic=63682.0
https://groupdiy.com/index.php?topic=62262.0
https://groupdiy.com/index.php?topic=62682.0

 

[Matt Nolan]

Looks cool. Sounds like it sounds cool too. What is your source for the Beyerdynamic transformers?

Thanks,
Matt.

 

[ln76d]

Thanks.
I bought them long time ago on ebay.
There was a guy, from germany, who was selling a lot of it, but he was hard to talk.
I wanted to buy 30 or so transformers of one type and finally i couldn't...
I don't know if he still sells it.
What i can recommend for microphones - RFT Funkwerk Leipzig, Stela, Kolleda.
Unfortunately i have no more 10:1 for this project so i used Beyer.
These transformers are great as hell! Linear in both ways, but with some "their own" sound.
Beyer also is linear in both ways but from 25Hz.

Today i will test again a little bit lower plate resistor and NT1 capsule.
6028 is hard tube to work with it -  in case of microphone circuits.
Fixed bias is not recommended by RCA in datasheet and in any condition it doesn't sound good.
I will put some photos later and sound samples around next week.

 

[Matt Nolan]

OK. Thanks. You've mentioned them a couple of times lately and I thought perhaps there was a source for new ones, like Beyerdynamic spare parts / service or something. But I couldn't find this myself.

 

[ln76d]

Here's what i get from beyerdynamic:

"Please find attached a scan of our last “large” transformer catalogue from 1995. We actually discontinued most models, we just build very few units for our ribbon microphones and some industrial customers."

You could ask them, maybe still they made something usefull. They have really great customer service.

This guy have few:
http://www.ebay.de/sch/mellow48/m.html?item=272209749244&hash=item3f60f724fc%3Ag%3AzXUAAOSwq19XDSxa&rt=nc&_trksid=p2047675.l2562


I need to test Neutrik "cheap" transformers in microphone circuits. For some other applications these were really good.
I have information, that they are (or were) made by Haufe.

 

[dmp]

The little Beyer transformers are great as a mic output. I've made several mics with them.
The 6028 is suddenly a very popular tube for mic builds. Why would the tube have a problem with fixed bias?
The U47 configurations these are being used in are close to fixed bias using the filament current.
The only truly fixed bias mic circuit I know of is the U67.

 

[ln76d]

Hey Dan,

i also used many beyers with different ratio and for microphone applications these fit well
The 6028 is very popular for one type microphone  build
I didn't found any other circuit where it is used.
If the "Telefunken" US use one tube as replacement for VF14 - i don't know what they doo, because it has different specs and everything else
I think that using a pair like in MK47 - it could sound better, but overall i doubt it's good replacement anyway.
I only once have opportunity to use original U47 so i have no true comparison.
There are tubes like 5840, 6072, E80F, EF86, EF12 or even ECC81 which whatever connect them they sound mostly good.
In one configuration sounds better, in other worse but overall decent.
With 6028 finding proper configuration is really hard - in most of connections sounds like crap
"Fixed" bias (like u47) or without cathode cap it sounds really weak.
Cathode capacitor also gives lower impedance which is important here.
I tried philips (8 pcs) and western electric (2pcs) and they worked really similar.

 

[ln76d]

Since i choosed "Teflon" CK12 (NT1a capsule will go to another project), here's schematic for multi-pattern option.

Hypercardiod - Cardiod - Omni

I could make figure of eight, since it use dual backplate capsule, but to be honest i don't need another figure of eight
Much more often am using hypercardioid or supercardioid.
Also it is easier when the microphone body is small
For figure of eight  could be used a little bit modified ELA M251 switching schematic.


Update:

C2p - changed for 3.3pF (it can be even 1pF if you will find some).
Select C3 for low end response between 1uF-2.2uF.
Update to V2 - simplified pattern switching with use SP3T type.

 

[ln76d]

My final build

My last DP3T died today, so i made cardioid/hypercardioid with SPST switch.

Update:

C2p - changed for 3.3pF (it can be even 1pF if you will find some).
Select C3 for low end response between 1uF-2.2uF.

 

[midwayfair]

You fit this in a 770? 

uhhhhh ... will you be offended if I say "pics or it didn't happen"?

 

[ln76d]

Of course not

I wanted go to sleep, but speciall for you i did pics.

It's unfinished - i need to make a mount for transformer etc.
It's really a lot of space
With PCB there could be even much more.
Am using big caps and most of resistors is also big (first transformer was much  bigger).
I will not share pictures of the electronics, because it's to messy
I designed layout for something completely different and after many changes i get this.

With 990 you could build some microphone with 5840/EF732.
When i finish my "something à la M49" you will see what's a really lack of space

 

[ln76d]

For PSU i recommend some generic chinese PSU like for example:

http://www.thomann.de/de/the_tbone_psu_sct_700.htm?ref=search_rslt_t.bone+sct_109920_10

There's no problem to drop voltage from 150V to 100V and for heater using voltage doubler and  7818 regulator which have same pinout as 7806 used in original PSU.

My PSU is also from some chinese microphone but i have luck, because it have extra "60V AC" (measured 73V AC) winding so i  had no problem to get 100V from it.

 

[midwayfair]

That's an amazing ... and inspiring amount of squeeze. Great work!

 

[ln76d]

Some updates, pics of final build below.

 

[ln76d]

Here's full set.
Sound samples someday

 

[shot]

Lovely! 

How did you print the lettering on the PSU?
I reckon you went for something cheap&DIY, but it looks very solid!

 

[ln76d]

Thanks

Letters are from original PSU and in fact not adequate
Whole circuit inside the box is rebuild

DIY?

Yes

Cheap?

Not exactly

Final version use 1000$ mike capsule, resistors from the beginning are mostly vintage (few times than dale metal film), transformer - depends where you buying, rest of the parts (except tube socket) definately not made in china.
Body - ok cheap chinese (like most around here - all these pretending u47 or c12 etc.)  - for me it need to be at least visualy acceptable.  Even with 100$ NT1a capsule - sounds great.

This is only example - i truly don't care about prices or etiquetes.

For me need to be usefull tool, good sounding tool.

I wanted only to show, that everybody can build his own microphone, even "design" it.

It's a hype for all these clones with all these yucky color boards - which mostly even doesn't looks like original unit and sound galaxy faaaar from it (yes i know what am writing).
What for call it u47, c12, m251 if these microphones aren't it?

Why not build something different, find own sound?
It's so great feeling, when you build microphone from a scratch, do a lot of tests to improve the sound and it's good
It think it's better than make a monkey job and make kit from instructions even not knowing how it works,

I don't want to offend anyone or his builds but guys - this is groupdiy not groupkitdiy!

We need some fresh air! Ideas! Improvements! Deteriorations! And everything else which isn't only instructions following!

But it's only my two cents before the sleep

Good night everyone.

PS. Shot - this week i will get new tube socket for S216, so i will try to finish it

 

[ln76d]

A what the hell - let's make cardioid/omni version also.

 

[ln76d]

Updated info in first post on another suitable tube - 6AK5.
This circuit could be even much better tuned for 5654/6AK5, but i'm to tired with tuning this mike
But after change of the heater it works really great
After i finish three other microphones i have idea for new microphone using two 5654!
After simple test i can say that this is one of my favorite tube for microphones!
Very pleasant, smooth and other bullshit