How to tame some highs from a k67 type capsule?

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rbaker

Well-known member
Joined
Apr 27, 2005
Messages
147
Location
Los Angeles
I've seen many people mention how the amp circuit for a k67 capsule usually helps to smooth out the freqency response because the capsule is a bit bright.

I'm wondering if anyone could help me figure out how to do that (and then tell me why so that I understand it?)

I modded a mic for a friend...it's the basic nady tcm1050 (this one is actually a ppa, but the circuit is the same)

Here's the basic schematic for what I did. The bv314 transformer is made by oliver from AMI/Tab. Basically a bv8 core, but with a t14 winding to match the impedance of the 6072.

http://www.ryanbakerproductions.com/micschematic.jpg

Again if someone could tell me what and where to put it and then maybe how to figure it out for myself next time so that I don't need to ask... :grin:

edit: I DO have a peluso 367 capsule in it.
 
If you've got a TAB transformer in there, and some valuable hours invested, TRUST ME when I say that that you probably won't get what you want from a Nady 1050 capsule.

You now have an easily-identifiable paper-thin link in an otherwise strengthened chain.

Even with "shaping" the response to correct for the intrinsic alight HF climb, if it's that 'harshness' that you speak of, you need to get to know someone like John Peluso.

Toss the capsule. Unelss EVERYTHING in that mic was basically free, and you are ready to value your time as worthless.

Keith
 
I'd take Keef's advice.

Also, there was a thread where Wavebourn and Keef discussed taming filters used in mics using the K67-type capsule. It was pretty interesting.
 
for a quick try insert a 680pf (or 500pF) styro from plate to ground.
but i agree on the capsule. also a new "teflon" akg ck12 could sound nice with the transformer/tube.

-max
 
I think this should work. Please comment if you see something wrong with this approach. It's a different tube but the concept is more or less the same.

mic_feedback_2.gif


It will change the sound of the amplifier slightly for better or worse because of the feedback.

-Okko
 
[quote author="omeiko"]I think this should work. Please comment if you see something wrong with this approach. It's a different tube but the concept is more or less the same.

mic_feedback_2.gif


It will change the sound of the amplifier slightly for better or worse because of the feedback.

-Okko[/quote]

Your capsule has no DC bias. I'd remove C9 or at least shunted it by resistor.

EF86 is a nice toob for such a purpose. :thumb:
You may consider using it with lowered filament voltage, say 5.7V (7805 with one diode in a ground leg)
Also, with such huge grid leak resistor probably you don't need resistors in cathode.
 
Actually, we had the same problems in modding this mic with this schematic over at the HomrecordingBBS and the EVE recording forum. The problem lies with your removal of C6 and C7, because they have a lot to do with the balance of the mic. Mine was brittle without those. Put some decent caps back there and the sound will change dramatically. It's really that easy.
Craig
 
rbaker

First what are you trying to change/improve the sound of the microphone for? Voice etc.

I see a few things I would not do with the modded schematic.

Why did you remove c6 and c7?

Is the tab transformer installed?

Okko

Whats up with the cathode leg of the circuit? why do you have it set up like that?
 
yes those were recommendations from dave way back when. As you can probably tell I don't know much about the circuit, but I'm trying to learn.

The mic is is primarily for vocals, but is used for other things as well.

It sounds really good...it's very smooth and that transformer helped a lot over the cinemag that dave originally recommended. (yes the tab transformer is installed) It's just a little bright. Not brittle, just bright.
 
What was the original B+ voltage of the microphone if you changed it?

What are the DC voltages at the plate and cathode?

If you changed the voltage you might want to adjust the bias point with changing R7

A 47uf or bigger cap across the cathode resistor R7 should be fine if you want to add one back.

Do a search for 1050 and TCM1050 here look for Marik's posts with leaving in the CF.

What cinemag did you have installed? 2480?
 
I never (knowingly) changed voltages or removed resistors. I only took out those 4 caps, replaced the 5th one, changed the capsule, tube and transformer.

Yes I had a 2480 in it before. It sounded nice, but this one just seems to have a cool thickness to it.
 
Interesting about the voltages. My 1050s had 200VDC and 6.6VDC stock and the tubes were soldered in.
 
this mic was actually a PPA (pacific pro audio) ld-2be but it's the same circuit. The body is a little different. It has the mount of the tcm1050, but it's a little skinnier and taller (not as tall as the apex 460)
 
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