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Author Topic: Warm Audio WA-67 - C9 capacitor value  (Read 718 times)

ilcaccillo

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Warm Audio WA-67 - C9 capacitor value
« on: January 27, 2022, 10:05:34 PM »

Hi,
I'm working on a Warm Audio WA-67 microphone which is a clone of the Neumann U67.
The electronic circuit is a straight copy of the U67 besides one component, and that is C9.

In Neumann U67 the coupling output cap C9 is either 0,5uf or 1uf, but in the Warm WA-67 the C9 value is 4,7uf.

I would like to ask you what might be the reason for using a 4,7uf capacitor instead of 0,5uf (or 1uf) ?
What is the expected sonic impact of increasing C9 value to 4,7uf?

Thank you so much
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klaus

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Re: Warm Audio WA-67 - C9 capacitor value
« Reply #1 on: January 28, 2022, 10:18:01 AM »

IF and this is a big if, the circuit and component values are 100% identical between the original and the copy mics, increasing the coupling capacitor five fold would considerably increase the level of very low frequency content in the copy mic.

But I am skeptical that we are actually comparing similar circuits. The transformer alone is such a beast to duplicate, let alone the capsule...

You can easily substitute the 4.7mfd cap with with a 1.0 or 0.5mfd and listen to the results. Your ears will tell whether that is an improvement or a detriment.

In addition, you can also call the company that makes the copy mic, and test their willingness to engage a curious customer on this level of inquiry.
It sure will tell a lot how serious they take their customers' intelligence and how much they respect inquisitiveness.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

ilcaccillo

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Re: Warm Audio WA-67 - C9 capacitor value
« Reply #2 on: January 28, 2022, 08:24:19 PM »

Hi Klaus,
thank you so much for your reply

IF and this is a big if, the circuit and component values are 100% identical between the original and the copy mics, increasing the coupling capacitor five fold would considerably increase the level of very low frequency content in the copy mic.

But I am skeptical that we are actually comparing similar circuits. The transformer alone is such a beast to duplicate, let alone the capsule...

Yes, component values are almost 100% identical.
C12, C13, C14, C15 and C16 capacitors are 2200pf instead of 2000pf, which is negligible.
C17 is 100pf, a pretty standard value in U67
and C9 is 4,7uf 160v.
I traced the circuit and all the other components have exactly the same values as the U67 schematic.

Transformer is a Lundahl LL1965B.

Capsule is a 3U Audio "flat K67 type", it's a capsule made similar to the K67 but with less holes in the backplate to achieve a flatter and with less high boost than a standard K67.
This choice of capsule it's a bit strange since the C17 value is 100pf, I don't see the point because it will just make the microphone darker and not take full advantage of the Emphasis/De-emphasis circuit that is part if the U67 sound

You can easily substitute the 4.7mfd cap with with a 1.0 or 0.5mfd and listen to the results. Your ears will tell whether that is an improvement or a detriment.

I will do that for sure, will try the stock 4,7uf value versus U67 1uf or 0,5uf value and see which I prefer.
I will have to replace stock C9 4,7uf capacitor anyway since its voltage rating is only 160V, and at power up and power down that capacitor is hit with a much higher voltage than it's rating.


In addition, you can also call the company that makes the copy mic, and test their willingness to engage a curious customer on this level of inquiry.
It sure will tell a lot how serious they take their customers' intelligence and how much they respect inquisitiveness.

I did that actually, I sent them an email. They told me they would get back to me but it has been 2 weeks and no reply.
Maybe they didn't like my inquiry or maybe they will reply at some point, I don't know yet.
But I'm pretty sure they are not much interested in customer inquiries about the circuit of their products and are more interested in just marketing and selling.
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RuudNL

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Re: Warm Audio WA-67 - C9 capacitor value
« Reply #3 on: February 20, 2022, 09:54:17 AM »

They may have increased the value to 4.7µF to shift the C-L resonance frequency (Output C + transformer inductance) to a subsonic frequency.
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