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Old 4th January 2007, 07:59 PM   #1
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Default Blown output transistors crest amp

Hello guys, I have a question for you. I have a Crest amp that is very low in volume. It sounds like 200 watts as opposed to 540 watts, both channels work fine. I sent it to my repair guy to have it checked out. Where would you start on a repair like this. Would you look for blown heatsinks or transitors? Would you check the output module first? I know it could be multiple things. I looked under the amp before I sent it and nothing looked burned on the boards. I just wanted to know how would you begin on a job like this. What are important parts to check out? thanks Ern
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Old 5th January 2007, 12:56 AM   #2
anatech is offline anatech  Canada
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Hi Ern,
The first thing I would do is measure the output power and measure the distortion. Measuring the voltage supplies would give your repair guy an idea of what the actual output power should be.

-Chris
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Old 5th January 2007, 01:18 AM   #3
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Thanks Anatech, I'll tell him about that. He is a general repair guy, he fixes stereos vcr's and tv's. I hope he knows what he is doing. the guy who sold me the amp hasn't returned my messages, I bought it on ebay. Thanks, Ern
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Old 5th January 2007, 01:42 AM   #4
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Hi Ern,
Finding a problem that doesn't exist takes a lot of bench time. It may not sound like full power, but it may deliver it. In the event that there is a problem, a distortion test or simply looking at the waveform will generally give the tech some clues.

-Chris
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Old 6th January 2007, 05:22 AM   #5
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So it is possible for an amp to be delivering the full amount of wattage eventhough it sounds like it's not. I know it isn't delivering 540 watts because I compared it to my other Crest watt version of the same series. It sounds Even less than 200 watts. I read other posts and they said power amps can be very unforgiving and should be properly serviced. This amp was run day and night. It recieved alot of abuse. I understand why you guys charge alot, finding the problem can take time. Thanks Chris
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Old 6th January 2007, 04:34 PM   #6
anatech is offline anatech  Canada
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Hi Ern,
I was only trying to say that your tech should verify the performance (or fault) before spending a lot of time on it.

-Chris
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Old 7th January 2007, 03:39 AM   #7
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I happened to think of Crest amps in another context, then saw this thread.
1) You do not have blown outputs. Amps do not continue to function with blown output devices.
2) Amps do not lose power from being played, no matter how hard or how long. (We'll leave the question of bias drifting for another time--Crest is Class D.)
3) Do not be surprised if your amp is functioning properly. Those who think all amps sound the same are...well, let's just say they exist, and leave it at that. It's possible that this amp sounds different from what you had expected, without necessarily being defective.
4) The idea of trying to judge power by ear is foolhardy. First, note that tube amps often sound more powerful than their ratings would suggest. Second, the power supply has a lot to do with how "loud" an amp sounds. Third, 540W is not that much louder than 200W...it's a log scale, not linear.

Grey
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Old 7th January 2007, 05:50 AM   #8
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GRrollins you noted it could be the power supply. I know something is wrong with the amp. I took the amp apart and cleaned it completely from the aluminum heatsinks to the fans and even the boards. I didn't see anything burned. I did notice the ceramic heatsinks were a grey light brown and a few had been replaced, but those were a bright white.
You mentioned it could be the power supply? Do power supplies go bad? This amp was run day and night in a casino, it is from the Stardust that closed down a few months ago. The seller said he didn't get to test the amp with speakers, he only turned it on. I know the amp isn't performing to it's potential because I own A Bgw that is 230 watts at 8 olms per channel. My speakers are 250 watts rms. This amp clipped at times. I needed more power. I decided to purchase a used 7001 Crest which is 550 watts at 8 olms per channel. When I tried out the Crest it was less powerful than the Bgw. I had to put the volume on the mixer up three or more notches for sound almost as loud as the Bgw. That didn't sound right to me. Even my brother noticed the amp was not perfroming to it's potential. A 220 watt Bgw can't be louder than a 550 watt Crest. This is my second Crest amp. I love the thick, tight, tube like, low end bass of Crest. My local repair shop wasn't able to find anything visably wrong with the amp. They wanted to see the schematics and told me about adjusting the gain. My gutt feeling was they were not to knowlegable about this amp. I decieded to take it somewhere else. What could be causing this problem? I am probably going to take it to Audiospecialist.com on monday to have it repaired. Thanks for the reply Ern
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Old 7th January 2007, 09:14 AM   #9
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You are confusing gain with power.

Since the amp sounds OK, and the shop says it is OK, crank up the gain on your mixer until the clip light comes on.

I bet it is louder than the BGW at that point.
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Old 7th January 2007, 09:49 AM   #10
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Yea, but then that would mean the amp is working to hard. The shop said they couldn't find anything visably wrong, but they still wanted the schematics and said some adjustments could be done to it.
That is exactly what they told me. I saw some adjusters that require a philips screw driver on each board attached to the aluninum heatsinks, but I'm not about to mess with those. I'm going to let the techi handle it.
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