Jump to content


DC-300A "popcorn" noise


  • Please log in to reply
4 replies to this topic

#1 JWS

JWS
  • Members
  • 2 posts

Posted 31 October 2005 - 09:07 PM

Hi,

About 15 years ago, I bought a nearly mint condition early 70's DC-300A amplifier at a garage sale. I even got the original instruction manual with it. I've used it for a number of applications over the years, including DJ use and home audio use; it's been a dependable and great sounding amp. It was strong enough to easily burn out a pair of 15" Kicker car woofers (I was on a tight budget at the time, and I had to use non-pro speakers). Those poor speakers were smoking! It even had enough power to damage the 4" voice coil on a used 15" Peavey Black Widow speaker I bought later. And I've yet to hear the DC-300A distort! I've never abused the amp, but the original owner was in a local rock band, so who knows how rough he was on the amp.

About 5 years ago, while using it in my home audio system, it began making a raspy "popcorn" sound through the speakers (Allison CD-9 speakers). It only lasted for a few seconds, and I couldn't tell which side it was coming from. A few months later it did it again, and I unhooked the amp and put it away, until now.

I'm interested in using this amp again, and I'm wondering if the noise is due to a bad output transistor? Is this a potentially expensive repair? When I bought it, it had the mono single channel modification done to it already, but it was in stereo mode when the popping sound occurred.

I'd like to know what everyone thinks, and if the amp is repairable. This is one of my favorite pieces of audio equipment, so I'd like to get it running back up to factory specs. The amp still sounds great, but the popping can be unnerving!

For the curious, the rest of my home equipment (I don't do the DJ stuff anymore): Denon 1650 CD player, Electro-Voice MS-820 Monitors, Golden Tube SE-40 Amp, Allison CD-9 speakers, Rotel turntable with Grado cartridge, Yamaha Natural Sound Preamp, Tara Labs cables.

#2 Wilder Bill

Wilder Bill

    Power User

  • Members
  • PipPipPipPipPip
  • 48 posts

Posted 03 November 2005 - 05:52 AM

My guess is that the random poping is from caps discharging.
There are three small electrolytics on the small predriver board in the middle of the amp. In time they can dry out and cause trouble.
If you can handle a screwdriver and a soldering iron, then you can cchange theem yourself for about $5.
If that doesn't do it, it won't hurt and they are past due anyway.

#3 Wilder Bill

Wilder Bill

    Power User

  • Members
  • PipPipPipPipPip
  • 48 posts

Posted 03 November 2005 - 05:54 AM

My guess is that the random poping is from caps discharging.
There are three small electrolytics on the small predriver board in the middle of the amp. In time they can dry out and cause trouble.
If you can handle a screwdriver and a soldering iron, then you can cchange theem yourself for about $5.
If that doesn't do it, it won't hurt and they are past due anyway.  tongue.gif

WATCH WHICH WAY THE STRIPS ARE ON THOSE! THEY ARE POLARIZED.

#4 JWS

JWS
  • Members
  • 2 posts

Posted 05 November 2005 - 01:28 AM

Thanks for the info!

I'm glad to hear that it's probably a minor problem. Since the amp is over 30 years old, I think I'll just send it to Crown for service and have them do a thorough "tune-up" of the amp. I'd like to get it running like new, and I'm afraid I might cause more harm by tinkering with it. I'm still impressed with the DC-300A's ability to peak at 800 watts output, but I was really stunned when I just learned that Crown's I-Tech amps crank out over 8,000 watts now, and weigh about half as much as my amp does!

#5 Wilder Bill

Wilder Bill

    Power User

  • Members
  • PipPipPipPipPip
  • 48 posts

Posted 05 November 2005 - 08:48 AM

That ITech IS awsome!

I think I am most imressed with the 300s ability to go into a rack, work every day for 20-30 years and then just want a little attention...which, by rights it should have had WAY earlier!
While you have it in for a check up, I'd go ahead and get the filter caps replaced, too. They are just as old and prone to the same problems with time, but at higher voltage.
IF you don't have the IOC and/or bridging switch and might want them, they can do that, as well while it's there.
For many applications they don't make any difference.

What you can't get is liposuction.  sad.gif
It'll still way a ton, but if you don't move it around, who cares?  laugh.gif