Crown D-150A power amp problem

tubular bob · Posted: Nov Tue 03, 2009 12:36 pm

I recently acquired a Crown D-150A power amp that has some serious distortion in the lower frequencies. Any ideas as to where to start looking for problem areas?

Thanks in advance!
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Dave Doughty · Posted: Nov Tue 03, 2009 1:29 pm

I would first check or replace the electrolytic filter caps in the power supply.

Dave

Johnnysan · Posted: Nov Tue 03, 2009 2:07 pm

Check for connections that were never soldered at the factory. I picked up a D-150A from a guy who said there was no output (I figured blown output transistors). Turns out the cables going to the binding posts were never even soldered.

SMITHY · Posted: Nov Tue 03, 2009 7:32 pm

As old as it is i would replace all of the elec . caps. i did in my two Mc's MC2100 and they sound great much better i used Vishay/Sprague and Nichicon low impedance from Mouser . SMITHY

Bruce Hagen · Member Joined: 15 Jun 2006 Posts: 2001 Location: NE Ohio

Crown has a parts department yet. 219-294-8000. May not be (219) though as some of the area codes have changed. If you need a print I think that I have it. Just advise.

Offer on print rescinded. Seems I've lost my 150A manual. If anyone has a D150A manual to spare and would like to trade for an other Crown manual I have several different duplicates.

Please rescind the recinded.
Have the manual again if anyone needs same.
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Bruce

tubular bob · Posted: Nov Wed 04, 2009 2:40 am

Thanks for all the replies. I love this place!

When I get a chance in the near future, I'll open it up and see what I can find. If there are no obvious problems, like unsoldered connections, I'll replace the electrolytics.
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Bob www.tubularradio.com

"Investing in the future by preserving the past"

tubular bob · Posted: Nov Thu 05, 2009 1:30 am

Bruce,
Does your schematic have a note that states a 1 0hm resistor (if I recall, it's R9) will help with low frequency oscillation? I originally called this problem a low fequency distortion, but it does seem to be more of a low frequency oscillation.
Any experience in this area?
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Bob www.tubularradio.com

"Investing in the future by preserving the past"

Bruce Hagen · Member Joined: 15 Jun 2006 Posts: 2001 Location: NE Ohio

Don't remember. Manual sent.
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Bruce

N7RHU · Posted: Nov Thu 05, 2009 3:40 am

Crown service manuals for discontinued models, including the D-150 are available free from the factory site:

http://www.crownaudio.com/gen_ ... gacamp.htm

--Chuck

tubular bob · Posted: Nov Thu 05, 2009 12:42 pm

I already have the orginal manual for my D-150A. I am asking if anyone has had experience in the area of low-frequency oscillation or distortion on this particluar model.

Thanks.
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Bob www.tubularradio.com

"Investing in the future by preserving the past"

Dave Doughty · Posted: Nov Thu 05, 2009 12:46 pm

Does the oscillation occur all by itself or do you have to have audio playing to make it happen? Is it constant or intermittent?

Dave

tubular bob · Posted: Nov Thu 05, 2009 1:36 pm

Dave,
I have noticed this while playing audio and have not taken time to test otherwise. It seems to be more constant than intermittent, although it also seems to be very dependant upon the type of signal, it occurs with a lot of lower fequencies (bass). I am using Electrovoice Sentry III speakers and do not have this problem with other amplifiers.

Any suggestions as to where to look for the problem in the chassis?
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Bob www.tubularradio.com

"Investing in the future by preserving the past"

Dave Doughty · Posted: Nov Thu 05, 2009 2:08 pm

As suggested earlier, I would suspect bad (high ESR) filter caps in the power supply. Be sure all of the connections are tight first.

Amazingly, I find that I have the complete service manual for this unit (even though I don't have the amp). There are 5 or 6 schematic revisions including the note about R-9. Oscillation must have been a common problem with certain speaker set-ups. But I can't find R-9 in any of the schematics.

Dave

tubular bob · Posted: Nov Fri 06, 2009 12:45 pm

Dave,
It appears to me that the R9 is installed between the chassis ground and the line ground. Does that make any sense?
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Bob www.tubularradio.com

"Investing in the future by preserving the past"

desertbard · Posted: Nov Fri 06, 2009 2:16 pm

Dave Doughty · Posted: Nov Fri 06, 2009 2:42 pm

OK - Now I see it. The first three schematics I have show a 2.7 ohm resistor for R9 which was changed to 1 ohm in the fourth schematic. It doesn't make sense but it might have something to do with ground loops in certain situations.

In this case, Bob means "line ground" is the power supply DC common return (after the power transformer), not the AC line neutral or third-wire ground. The chassis, however, is connected to the AC mains third-wire ground.

In any case, I don't believe R9 has anything to do with the low frequency oscillation problem.

Bob - if you are saying that music with lots of bass causes the oscillation to start and then stay constant, I still feel the problem is one or both large filter caps in the power supply. I just repaired a Hafler amp with a similar (but not exact) problem. These amps operate nearly class B so the current demand is always changing. The amp will become unstable due to aging caps before you notice any hum due to poor filtering.

I found that Mouser has the best price for these large-value caps.

Dave

desertbard · Posted: Nov Fri 06, 2009 2:57 pm

Right on. For some reason I could not think of the phrase "grounding loop" so I took the long winded approach to get the information across.

Joe
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tubular bob · Posted: Nov Mon 09, 2009 12:17 pm

In doing some shopping for the caps, I have found that Mallory is still making the "CGS" screw terminal type, which appears to be the OE supplier on this example. I'll just get a couple coming and see how this effects its performance.

I'll post to let you know what happens. In the meantime, I'm going to be busy trying to fix the IC-150 preamp problem I created. (see other post in this section)
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Bob www.tubularradio.com

"Investing in the future by preserving the past"

Dave Doughty · Posted: Nov Mon 09, 2009 1:51 pm

I noticed the screw terminal type caps are very expensive. For my Hafler, I used the kind made for PC board mounting and soldered lugs to the terminals so I could then use the original connections. The new caps were considerably smaller than the old ones. I removed the original mounting brackets and used industrial Velcro to mount them. The price of the new caps was about $8 each.

Please don't blame me if the caps are NOT the problem. Further troubleshooting with an oscilloscope or ESR meter would be needed to confirm bad caps are the cause.

Dave

tubular bob · Posted: Nov Sat 14, 2009 2:20 am

I received the $50.00 caps today from Crown and got them installed. I believe I've helped the oscillation/distortion problem but until I get my IC-150 preamp fixed, I'll have to wait to see just how much I've helped it. ther still seems to be some distortion, but it's really hard to tell without a preamp.
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Bob www.tubularradio.com

"Investing in the future by preserving the past"