All things "C12 output capacitor"

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kingkorg

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Every mic that I have built sounds slightly different after a few days of use.


I can absolutely confirm this is true. I do measurements daily, and i have to re-calibrate the setup before every measurement, otherwise i get all kinds of artifacts.

However it is almost always due to capsule/environment changes. Humidity, air pressure, temperature and even the objects around. If i'm within a meter from the mic my body position will affect the response. Position of the mic stand and how it's angled... All of these make very audible and measureable changes in mic performance. Several db of difference in very sensitive areas.

I've been struggling for the longest time with multi pattern mics because of remaining charges on capsules even when pattern is changed. Sometimes there is no path for the capsule to discharge depending on topology. There is good chance everyone has been using a wide (or hyper) cardioid while they were thinking they were using cardioid. And suddenly the day after the mic sounds different.

One of the reasons i never use multi pattern LDCs. At least not the conventional ones. The other being you get mediocre responses with anything other than cardioid, and all sorts of phasing issues where "electrical" pattern fights the "mechanical".
 

Delta Sigma

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I have heard differences between caps but thinking back, it's likely the slightly different value that caused the audible difference.

I find that when I make a component change, I fall victim to confirmation bias on first listen. My rule now, is to listen the next day to the A-B recordings and I have a different conclusion the next day.

The fixation on output caps is strange. I have fixated on it in the past. I'm not sure why we focus on it. I've never heard an output cap change the sound the way capsule or transformer swap does.

Recently, I've purchased multiple values of caps between 0.5 and 1uF so I can experiment with difference values.

I swapped a film cap for an MP in my first build (U67) and thought I heard a huge difference. I think it measured at 0.7uF though. I should find those files one day and listen back to see what I hear now!
 

Purplenoise

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Sep 19, 2019
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I can absolutely confirm this is true. I do measurements daily, and i have to re-calibrate the setup before every measurement, otherwise i get all kinds of artifacts.

However it is almost always due to capsule/environment changes. Humidity, air pressure, temperature and even the objects around. If i'm within a meter from the mic my body position will affect the response. Position of the mic stand and how it's angled... All of these make very audible and measureable changes in mic performance. Several db of difference in very sensitive areas.

I've been struggling for the longest time with multi pattern mics because of remaining charges on capsules even when pattern is changed. Sometimes there is no path for the capsule to discharge depending on topology. There is good chance everyone has been using a wide (or hyper) cardioid while they were thinking they were using cardioid. And suddenly the day after the mic sounds different.

One of the reasons i never use multi pattern LDCs. At least not the conventional ones. The other being you get mediocre responses with anything other than cardioid, and all sorts of phasing issues where "electrical" pattern fights the "mechanical".
Very true. Never gave any thought to this multi pattern mic issue but it makes sense. I’ve had several occasions that I thought something was wrong and after flipping the pattern switch a couple of times everything sounded normal again. Thought I was imagining things.
 

inkster

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Aug 10, 2009
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I have had to replace that cap in a C12 when it took out the transformer, Chris at vintage windings did a great job rewinding the transformer and I dissected the original, pulled out the guts and stuffed it with a new PP film cap...sounds great, the studio has 3 and I have never heard any of the engineers mention that it sounded different.
I never use high voltage NOS caps without testing them on a proper leakage tester(built my own) at operating voltage. Most of the vintage caps I test are leaky.
 

tomas.borgstrom

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I'm convinced that I can hear differences between capacitors but I know the psychologic factor is substantial. As said before the capsule, tube and transformer is so much more important. Here are my findings regarding the output capacitor in tube microphones:

Polyester - Good quality (typically made in Germany) polyester work really good and I think it should be the first choice, but some brands can sound muddy for example Tropical fish.

Polypropylene - Perhaps a little cleaner but not better to my ears, sometimes worse.

Polycarbonate (I've tried ERO/ROE) - great sound

"Hifi-capacitors" - Generally don't fit in microphones and the few polypropylene I've tested sounded ok, no more no less. I was very excited when I once tried a Jupiter copper foil paper wax. That time the psychology didn't work because I didn't like it at all. It sounded really strange, like the high end was out of phase or something.

MP - Siemens, Bosch and RFT sound really good, little slower but still clear. Its an uncertain path and not worth the effort if you don't have a special interest in testing different components. They are old and often out of spec. The other day i measured three NOS Bosch MP 0,5uF. All were between 1-2uF and had 6-8% leakage. The russian sealed ones seems reliable and the sound is ok but I'd rather use polyester.

I would like to know why Neumann and AKG back then didn't choose polyester on the output when it became availiable in the sixties (MP in U47, M49 and C12 - Wet tantalum in Elam - Bipolar electrolytic in U67/M269).
 

Drea

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I never heard any difference! (But maybe I only used 'good' capacitors...)
But what is a good capacitor. Some are very clean lot of punchy attitude. Other has more crunchy gritty sound with a kind of compressed (tape sound somewhat) . I like the original bosch and Telefunken square capacitor. Strange is that the eru mkt1813 400v is very clean but The vishay 1813 250v very crunchy. The yellow in the picture are out of specs a lot I can’t use it. The green russia is somewhat okay.
I like the bad quality capacitors in mics , I can listen a lot longer to that kind of sound. If it sounds good it is good.
 
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tomas.borgstrom

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Here's an old paper in Swedish about capacitor quality and dielectric absorption. In short the performance of polypropylene is superior and the two MP that are measured (Hunts and WKG) are much worse than the rest, check out the table in page 6.
 

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kingkorg

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But what is a good capacitor. Some are very clean lot of punchy attitude. Other has more crunchy gritty sound with a kind of compressed (tape sound somewhat) . I like the original bosch and Telefunken square capacitor. Strange is that the eru mkt1813 400v is very clean but The vishay 1813 250v very crunchy. The yellow in the picture are out of specs a lot I can’t use it. The green russia is somewhat okay.
I like the bad quality capacitors in mics , I can listen a lot longer to that kind of sound. If it sounds good it is good.
This would be extremely easy to test. however i am not aware of any scientific explanation which explains how capacitors in tube mic could do anything like that. Tube microphones have specification of something like 1% thd at 130-140db. Even at 1% there is no audible compression, nor really crunchiness that can be perceived. ''Strange is that the eru mkt1813 400v is very clean but The vishay 1813 250v very crunchy.'' If this is true, and components are in order, there is something really wrong with those mics, and it has noting to do with the caps. TUBE MICS ARE NOT GUITAR AMPS!
 

Khron

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Here's an old paper in Swedish about capacitor quality and dielectric absorption. In short the performance of polypropylene is superior and the two MP that are measured (Hunts and WKG) are much worse than the rest, check out the table in page 6.
... And that's likely with capacitors that were brand new at the time, not 50-70yo and miles out of spec (by now)...
 
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