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Analog audio interrupter problems

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Intra

Tue Sept 11 2012, 12:38AM

Registered Member #2694 Joined: Mon Feb 22 2010, 11:52PM
Location: Russia, Volgograd (Stalingrad).
Posts: 97

Guys, I got a big problem here))

With grand support of Greg, I was made comparator+limiter audio interrupter. Actually, I walk around all public circuits of this stuff and all of it can't be match for me, or just not work, but Greg was help me with most important thing to me - >1kHz cut off (I use TO247 IGBT). After this, I plug in it on my drsstc and plug my Ibanez into the interrupter. I set burst lenght 70-80% of usally midi mode and playing guitar about 5min. After this, my mmc was really hot and some caps lost capasity. Drsstc resonance was fall and streamer slowly getting low. I think, it so, because interrupter doing big polyphony, 6 strings on guitar+1/2,1/3,1/4.. and more subgarmonics on each string. Something about 50-70channel polyphony. Perhaps, it's pretty hardcore for coils this type, but awesome analog guitar sound doesn' make me rest.

How can I make this thing working out? Have you got something to calculate mmc heating of rms current?
And, I don't want to switch this way on midi-pickup system with fiber transmitter onboard, because I really like this analog subgarmonics.. ^,..,^

Steve Conner

Tue Sept 11 2012, 07:34AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

You need to reduce the duty cycle on your interrupter or make a better MMC. :p

Turning down the tone control on your guitar may help by removing the highest harmonics.

Intra

Tue Sept 11 2012, 08:40AM

Registered Member #2694 Joined: Mon Feb 22 2010, 11:52PM
Location: Russia, Volgograd (Stalingrad).
Posts: 97

I'm already thinking about growing up mmc, but which model of caps could be better in my case? Do you have a formula for calculations current and heating? Should I use something better than CDE caps? In your DR I saw non-CDE big brick cap))

Steve Conner

Tue Sept 11 2012, 10:07AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

You can't calculate the RMS current without knowing more about the signal. One approximation I often use is:

Irms = 0.5*Ipk*sqrt(Burst length * BPS)

but we don't know either your burst length or BPS.

Unfortunately that big brick cap failed. :( It started to make crackling sounds and leak wax. I'm now using 2 strings of 10 "RS" brand PP film/foil caps.

Intra

Tue Sept 11 2012, 06:03PM

Registered Member #2694 Joined: Mon Feb 22 2010, 11:52PM
Location: Russia, Volgograd (Stalingrad).
Posts: 97

"RS" brand? I found only stock market)) Can you post number of model or number of model's photo or datasheet link?

Steve Conner

Tue Sept 11 2012, 09:16PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I couldn't find any information on the caps. I had hundreds at one time, but I resold them all. They are 0.47uF, 1000V and were probably made for RS by Arcotronics or LCR. I don't think RS sells them any more, but the CDE 942 series probably has a similar part. Most DRSSTC builders use the 942C20P15K which is 0.15uF, 2000V.

Intra

Tue Sept 11 2012, 09:34PM

Registered Member #2694 Joined: Mon Feb 22 2010, 11:52PM
Location: Russia, Volgograd (Stalingrad).
Posts: 97

942C20P15K could be match for this type of interrupter, if I make my calculations right? I ask, because somebody might definitely know it match or not.

Steve Conner

Wed Sept 12 2012, 07:24AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Again, we can't say because you didn't give us any information on your primary current, duty cycle or burst length of your interrupter. If you don't know, try to measure it with a scope.

Intra

Wed Sept 12 2012, 12:45PM

Registered Member #2694 Joined: Mon Feb 22 2010, 11:52PM
Location: Russia, Volgograd (Stalingrad).
Posts: 97

Primary current is 350A on the Suntan 3A154K caps in 6 string and 3 caps per each string, Duty cycle is 5%, burst lenght is 30-40uS, igbt bridge irg4pc50ud, Fw=100kHz. I found a problem in that config. Now, I have 700A current(actually, I just set OCD on 700A, but not testing yet), 942C20P15K in 6 string and 3 caps per each string, duty cycle 5% and I don't now yet my burst lenght in new config.

Maybe just calculate mmc on maximum duty cycle and maximum in my case bps(I got a 1kHz cut off)? Then, anything polyphony with definetly current and burst lenght will make nothing and mmc could be live a long time. What do you think about it?

Intra

Sun Sept 16 2012, 03:22PM

Registered Member #2694 Joined: Mon Feb 22 2010, 11:52PM
Location: Russia, Volgograd (Stalingrad).
Posts: 97

What about B25856-J7505-J003 caps? Look like his RMS current significantly more.

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