You Be the Tech

triodesteve · 8th March 2004, 03:28 PM

Sort of like; "You make the Call" from old NFL games.
I need help and I'm not sure where to turn. I have a N.E.W. DCA-33 amp that is having a problem. NEW went out of business quite a while ago, and justifiably so it seems, as my amp was pretty much stolen from Nelson's A40 (although he is too much a gentleman to say it). The difference is that it runs of of 4 12v SLA batteries.
Here's the problem.
A few weeks ago the amp would buzz lightly on turn on..not loud, but noticable on quiet passages. The buzz seemed to go away after 15 minutes or so. Then the other day, I noticed that the level (volume) from the amp dropped way down, and stayed down.
I measure the batteries and they are a healthy 26v. That tells me that the charging circuit is operating fine and probably not the cause of the noise, it is switched out of the circuit at power up anyway. After eliminating that, there isn't a lot left that is common to both channels in the amp except for a big cap...a Nippon 27000uf 50vdc.
My questions are two. Can a bad cap lower the output of an amp...surely it can make an amp buzz right? And two, if this doesn't seem to be the problem can anyone reccomend a brave ss tech who can poke around without a schematic?
Thanks,
Steve

kilowattski · 8th March 2004, 07:37 PM

Steve,

Can you disconnect the battery charger and run the amp with the batteries only? This will let you know if the problem is charger related. If the hum goes away with the charger totally disconnected the problem is obviously charger related. I assume the large capacitor you refer to is part of the charger circuit? It is possible that the capacitor is pulling down the dc supply if it is in the circuit all the time.

triodesteve · 8th March 2004, 08:50 PM

Guy, thanks for your help. No, I can't seperate the two. If the amp is not plugged into the wall it won't work at all. The more I look at it, the cap is part of the charging circuit and not the audio. The thing is that with all the relays in there....6 I think, I would surely think that the charging circuit would be completely out of the picture..bummer.
Steve

kilowattski · 9th March 2004, 01:45 AM

Steve,

What physical size is the capacitor? I have some spare electrolytics hanging around. I think as a matter of fact I have a 27000uf 50 wvdc cap I could donate to you if you pay for shipping. All we need to do is see if the cap will physically fit.

triodesteve · 9th March 2004, 02:34 AM

It's 3" long and about 2"wide. But it has screw lugs..is that the right term?
Thanks,
Steve

kilowattski · 9th March 2004, 05:12 AM

The capacitor I have is larger but you are welcome to it if you wish. Just pay for shipping.

triodesteve · 9th March 2004, 01:42 PM

Thanks for the offer Guy...give me a day to try to figure this out and I'll get back to you on your generous offer.
Steve

8th March 2004, 03:28 PM	#1
triodesteve diyAudio Member Join Date: Oct 2002 Location: Walla Walla. WA USA	You Be the Tech Sort of like; "You make the Call" from old NFL games. I need help and I'm not sure where to turn. I have a N.E.W. DCA-33 amp that is having a problem. NEW went out of business quite a while ago, and justifiably so it seems, as my amp was pretty much stolen from Nelson's A40 (although he is too much a gentleman to say it). The difference is that it runs of of 4 12v SLA batteries. Here's the problem. A few weeks ago the amp would buzz lightly on turn on..not loud, but noticable on quiet passages. The buzz seemed to go away after 15 minutes or so. Then the other day, I noticed that the level (volume) from the amp dropped way down, and stayed down. I measure the batteries and they are a healthy 26v. That tells me that the charging circuit is operating fine and probably not the cause of the noise, it is switched out of the circuit at power up anyway. After eliminating that, there isn't a lot left that is common to both channels in the amp except for a big cap...a Nippon 27000uf 50vdc. My questions are two. Can a bad cap lower the output of an amp...surely it can make an amp buzz right? And two, if this doesn't seem to be the problem can anyone reccomend a brave ss tech who can poke around without a schematic? Thanks, Steve

8th March 2004, 07:37 PM	#2
kilowattski diyAudio Member Join Date: Aug 2003 Location: Long Island, New York	Steve, Can you disconnect the battery charger and run the amp with the batteries only? This will let you know if the problem is charger related. If the hum goes away with the charger totally disconnected the problem is obviously charger related. I assume the large capacitor you refer to is part of the charger circuit? It is possible that the capacitor is pulling down the dc supply if it is in the circuit all the time. __________________ ----------------------------------------------- Kilowattski

9th March 2004, 01:45 AM	#4
kilowattski diyAudio Member Join Date: Aug 2003 Location: Long Island, New York	Steve, What physical size is the capacitor? I have some spare electrolytics hanging around. I think as a matter of fact I have a 27000uf 50 wvdc cap I could donate to you if you pay for shipping. All we need to do is see if the cap will physically fit. __________________ ----------------------------------------------- Kilowattski

9th March 2004, 05:12 AM	#6
kilowattski diyAudio Member Join Date: Aug 2003 Location: Long Island, New York	The capacitor I have is larger but you are welcome to it if you wish. Just pay for shipping. __________________ ----------------------------------------------- Kilowattski

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8th March 2004, 08:50 PM	#3
triodesteve diyAudio Member Join Date: Oct 2002 Location: Walla Walla. WA USA	Guy, thanks for your help. No, I can't seperate the two. If the amp is not plugged into the wall it won't work at all. The more I look at it, the cap is part of the charging circuit and not the audio. The thing is that with all the relays in there....6 I think, I would surely think that the charging circuit would be completely out of the picture..bummer. Steve

9th March 2004, 02:34 AM	#5
triodesteve diyAudio Member Join Date: Oct 2002 Location: Walla Walla. WA USA	It's 3" long and about 2"wide. But it has screw lugs..is that the right term? Thanks, Steve

9th March 2004, 01:42 PM	#7
triodesteve diyAudio Member Join Date: Oct 2002 Location: Walla Walla. WA USA	Thanks for the offer Guy...give me a day to try to figure this out and I'll get back to you on your generous offer. Steve

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