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View Full Version : Any recommendations for a new, cheap 125W power amp? Parasound? B&K?, Rotel?



Tweak48
02-19-2005, 08:55 AM
I've got to replace the Citation 22 which I use to power the woofs in my JBL L-300 Summits (biamped setup). I don't think its worth the $275 estimate to fix, given how flakey the 22's have been. I'm also tired of getting burned on used amps/preamps on eBay.

So what about the Parasound HCA-1000A or the B&W 125.2??? Would one be better than the other in the <800hz range?

I'm looking to spend about $600 plus tax and license. Any other recommendations? Thanks in advance.

4313B
02-19-2005, 09:27 AM
Post what is wrong with it here and see what everyone recommends.

Don't throw it away. At the very least part it out.

Tweak48
02-19-2005, 09:59 AM
Post what is wrong with it here and see what everyone recommends.

Don't throw it away. At the very least part it out.

Giskard-

I definitely won't throw it away. Probably put it back up on eBay (with full disclosure) for $100. Both channels still work, it's just that there is low level intermittant noise on both channels from time to time. Always at start up, then can clear up a play fine for an hour and get noisy again. Noise can be "pink" noise transients or whistling.

I'm an old Heathkit-Hafler kit builder, so I could replace a known bad part, but have no trouble shooting experience or equipment other than a digital volt meter and a soldering gun. :blink:

hector.murray
02-19-2005, 10:59 AM
Did they tell you what was wrong when you got the estimate? If'n you were a couple thousand miles closer I'd loan you a scope.

Ian Mackenzie
02-19-2005, 02:18 PM
Sounds like an aged part, potentially a capacitor although output transisters can exhibit this behaviour.

If its both channels and you are certain its not comming from the source start looking at the power supply. If there is mains supression capacitor have a look at that.

Ian

Tweak48
02-19-2005, 02:37 PM
It's definitely not a source problem. I disconnected the inputs to verify that. <O:p</O:p

The noise is never simultaneous on both channels. It can be one or the other at any given time, with the noises I described above. <O:p></O:p>

The shop never did take a look at it. They just said their nominal repair bill on a large power amp is $250 to $275.<O:p</O:p

I wish you guys could stop over and take a listen to it. Anyone got a Starfleet Transporter??

jtgyn
02-19-2005, 08:38 PM
G'Day,
I agree with Ian that is probably a leaky cap.

"Always at start up, then can clear up a play fine for an hour and get noisy again"

I would start looking at the coupling caps first from this description.

Does anyone have a schematic for this amp?

Do a simple test and check for DC on the outputs on power up.

Disconnect the inputs and connect a small resistor across both the outputs (just like the speaker... any value from 10 to 5k ohms should be O.K.)

Connect your meter in DC volts mode across the resistor and watch the output volts when you power the amp on. This should settle to <100mv within 1 min. but should not be more than 500mV.

Leave the amp on and have a look every 10min. and check the voltage is not wandering more than +-100mV.

You could use a cheap speaker from an old radio instead of a resistor and when the noise starts look an the voltage.


Regards Scott

P.S. If you can fix the amp I would recomend that all the old electrolytic caps get replaced.. it should not cost very much. (excluding the main power supply caps)

Edit to correct errors.

johnaec
02-19-2005, 08:47 PM
Back to replacements - the JBL 62XX series shows up on eBay a lot at very reasonable prices.

John

4313B
02-19-2005, 09:00 PM
Does anyone have a schematic for this amp?

http://manuals.harman.com/HK/Owner%27s%20Manual/Citation22-24%20om.pdf

http://manuals.harman.com/HK/Service%20Manual/CITATION%2022%20sm.pdf

jtgyn
02-20-2005, 04:31 AM
G'Day,
Thanks Giskard!

Tweak48...

I suggest as a starting point that you remove the main amp coupling caps C401 & C402 and see if the noise persists. (Note the polarity of the cap on the board if it is not marked on the board)

Regards Scott

sonofagun
02-20-2005, 06:16 AM
Hey, this is exciting...remote electronic servicing...

stay tuned for episode 42...invasion of the oscilloscopes! :applaud:

Say, whatever became of SWTP?

GordonW
02-20-2005, 09:33 AM
IMHO, in that price range, ESPECIALLY on bass, the NAD 272 power amp slays all comers. Not by a small margin, either. Awesome control, 2 ohm stable all day and night, extremely well-damped and noise-free. We sell those amps at work... and I have yet to see a speaker they COULDN'T drive to the nines...

Regards,
Gordon.

Tweak48
02-20-2005, 10:26 AM
Thanks for the tips, you guys.

Later today after I run a few errands, I'm going to run the diagnostic suggested by jtgyn (http://audioheritage.org/vbulletin/member.php?u=447)<SCRIPT type=text/javascript> vbmenu_register("postmenu_43630", true); </SCRIPT> and will report back.

It looks like caps C401 & C402 are on the dirver board. Between the main and driver boards, it look like there are over 40 electrolytic caps. Provided I can eliminate the noise problem, are you guys suggesting I should replace all the caps, or just the coupling caps? If so, can you point them out for me??

Giskard, as for you suggestion in another thread to adjust the bias (due to my complaint about the heat), the service manual describes a simple procedure, which even I can do.

Bryan

sonofagun
02-20-2005, 11:19 AM
Stay tooned...

Episode 43...

Revenge of the...:blink:

Tweak48
02-20-2005, 04:58 PM
The test load in the form of a speaker was a great idea. I could watch things on the meter and listen to the noise at the same time.

Right channel was the worst: Would start at 200 MV; quickly swing up to 400 with brief peaks at 1.9 or so. I could see deflection of the cone from time to time

Left channel hung around 500 MV most of the time, but had some noise as well.

I curious as to why this noise isn't at greater amplitude. It seems to be at the same level (Very Noticeable); independent of the input signal level.

What next???

jtgyn
02-21-2005, 12:46 AM
G'Day Tweek48,
I suggest removing the input coupling caps. This will remove any leakage due to them and the signal switching stuff on the inputs.

The amp of course will not work with an input.


I would strongly suggest that you use a cheap speaker to do this. 500mv is rather high for the dc level and could damage the speakers.

Firstly track down the noise problem then you can adjust the DC level and bias.

Before you replace all the caps, it is really good to find the offending part. (I find a small pleasure in taking it all out on that part)

BTW don't do this in bridge mode.

Regards Scott

rbrooks7
02-21-2005, 07:20 PM
An easy way to test the caps to see which is the problem is to get out the blow dryer and heat them up one at a time. Any that make th problem better or worse should be replaced. Just take a marker and put a mark on the top of the can and go on to the rest. I've worked as a repair tech for a while and have used this method several times. It works better to heat the caps with a soldering iron, BUT MAKE SURE THE IRON AND AMP ARE ISOLATED WITH A TRANSFORMER.

As for a replacement amp, Rotel amps are well built and bullet proof, and the prices are good. Also, Crown makes their XLS series which start around $400.