Is this cap ok for audio?

Cassiel · 27th January 2006, 12:36 PM

I have several of these. I opened one and there is a 750k resistor acrosss the cap...is this normal?

I want to use them for power supply duties - before and after the choke.

http://pg.photos.yahoo.com/ph/stella...bf.jpg&.src=ph

Cassiel · 27th January 2006, 01:58 PM

If that 750k a bleeder resistor? Value seems high...
Shall i keep it?
Any harm in removing it?

I never use bleed resistors.

Thanks,

Al.

kevinkr · 27th January 2006, 02:09 PM

Looks like a motor start or snubber capacitor. (or SCR phase control cap?) It's a 250V~ rated AC cap, but I sure wouldn't trust what appears to me to be a 1/4W resistor, probably rated for much less than this. I would definitely remove in this instance, also I would keep the dc across this cap to no more than say 300Vdc to play it safe.

I assume you were joking about bleeder resistors? I generally use them, (or design circuit elements that perform the same task) but choose values that result in 1 - 2mA of load current at most when the supply is operating.

Kevin

Cassiel · 27th January 2006, 04:11 PM

Thanks Kevin... yes i believe they are motor start caps. I have read ppl are using motor run not motor start caps in their amps. I really don't understand the difference but i just want to know if this cap is better than a regular electrolytic.
If it's not it would be stupid of me using it as it needs a lot of space.

I have removed the resistors.
Maximum voltage is ok....B+ will be 230 Volts.

kevinkr · 27th January 2006, 04:14 PM

Hi Stalker,
The best way to find out I think is just to try it.. I can't see any reason for it not to be reasonably good.

Kevin

Cassiel · 27th January 2006, 04:19 PM

Thanks again Kevin. I will try them.

Tweeker · 27th January 2006, 05:09 PM

Motor run caps tend to be of very durable metal can polypropylene in oil construction, motor starts are usually electrolytic. I wouldnt put more than VAC RMS *1.4 = VDC on a motor start cap, but theres nothing wrong with them as electrolytics go. They are big because they are bipolar.

A motor run cap is usually good for VAC RMS *2 = VDC. Motor runs also have good sonic qualities and are suitable for use in crossovers etc.

tubelab.com · 27th January 2006, 06:08 PM

In AC (motor) application current flows in the cap. Motor start caps are designed to create a phase shift to start the motor. They handle large currents for a few seconds and then, no current. Some of these are indeed non polar electrolytic.

A motor run cap passes current continuously. They are made to handle this. To pass current without dissipating much power (most of the current is reactive) the ESR and DF are low. These are good qualities for audio use.

Cassiel · 27th January 2006, 07:11 PM

Cap says MKP. Can this be an electrolytic?

They seem to work allright...no strange noises.

Thanks Tweeker and Tubelab, great info.

Tubelab i have to say this: you're a joy to read. Never too much, never too little; all to the point and well explained. I have learnt a lot reading your posts. Don't ever leave this forum.

Tweeker · 27th January 2006, 07:19 PM

MKP is metallized polypropylene film.

Are there any polarity markings on the cap?

27th January 2006, 12:36 PM	#1
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	Is this cap ok for audio? I have several of these. I opened one and there is a 750k resistor acrosss the cap...is this normal? I want to use them for power supply duties - before and after the choke. http://pg.photos.yahoo.com/ph/stella...bf.jpg&.src=ph

27th January 2006, 02:09 PM	#3
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Looks like a motor start or snubber capacitor. (or SCR phase control cap?) It's a 250V~ rated AC cap, but I sure wouldn't trust what appears to me to be a 1/4W resistor, probably rated for much less than this. I would definitely remove in this instance, also I would keep the dc across this cap to no more than say 300Vdc to play it safe. I assume you were joking about bleeder resistors? I generally use them, (or design circuit elements that perform the same task) but choose values that result in 1 - 2mA of load current at most when the supply is operating. Kevin __________________ www.kta-hifi.net

27th January 2006, 04:14 PM	#5
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Hi Stalker, The best way to find out I think is just to try it.. I can't see any reason for it not to be reasonably good. Kevin __________________ www.kta-hifi.net

27th January 2006, 05:09 PM	#7
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	Motor run caps tend to be of very durable metal can polypropylene in oil construction, motor starts are usually electrolytic. I wouldnt put more than VAC RMS 1.4 = VDC on a motor start cap, but theres nothing wrong with them as electrolytics go. They are big because they are bipolar. A motor run cap is usually good for VAC RMS 2 = VDC. Motor runs also have good sonic qualities and are suitable for use in crossovers etc. __________________ Be sure your foil hat has a good low impedance ground.

27th January 2006, 06:08 PM	#8
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	In AC (motor) application current flows in the cap. Motor start caps are designed to create a phase shift to start the motor. They handle large currents for a few seconds and then, no current. Some of these are indeed non polar electrolytic. A motor run cap passes current continuously. They are made to handle this. To pass current without dissipating much power (most of the current is reactive) the ESR and DF are low. These are good qualities for audio use. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

27th January 2006, 01:58 PM	#2
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	If that 750k a bleeder resistor? Value seems high... Shall i keep it? Any harm in removing it? I never use bleed resistors. Thanks, Al.

27th January 2006, 04:11 PM	#4
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	Thanks Kevin... yes i believe they are motor start caps. I have read ppl are using motor run not motor start caps in their amps. I really don't understand the difference but i just want to know if this cap is better than a regular electrolytic. If it's not it would be stupid of me using it as it needs a lot of space. I have removed the resistors. Maximum voltage is ok....B+ will be 230 Volts.

27th January 2006, 04:19 PM	#6
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	Thanks again Kevin. I will try them.

27th January 2006, 07:11 PM	#9
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	Cap says MKP. Can this be an electrolytic? They seem to work allright...no strange noises. Thanks Tweeker and Tubelab, great info. Tubelab i have to say this: you're a joy to read. Never too much, never too little; all to the point and well explained. I have learnt a lot reading your posts. Don't ever leave this forum.

27th January 2006, 07:19 PM	#10
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	MKP is metallized polypropylene film. Are there any polarity markings on the cap? __________________ Be sure your foil hat has a good low impedance ground.

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