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Crest 8001 4 ohm bridge

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levyte357- View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357- Quote  Post ReplyReply Direct Link To This Post Posted: 30 August 2020 at 12:23pm
Originally posted by csg csg wrote:

Thomann TSA4-1300 bridged will drive 2 off 8ohm drivers with “surprising” results, for modest money and 3 year warranty. Well worth a try, if you don't like it, you just send it back. I doubt you would.


Got my mind made up mate.

Will try one of the most serious lightweights ever made, then if that doesn't give me what I want, will try transformer.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tilla Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 12:20am
Hi guys,

 I was hoping you could help me out here. I have two of these amps. One had a burnt output relay on one side which was an easy fix the other one i had to rebuild one output stage completely. It had a burnt pcb at place and many output transistors and resistors failed. Long story I put it all back now and both channels works fine. I am wondering however what the next steps will be. I d need to test the amps somehow, how do i do this without the load resistors. Will I need to bias all channels, the one a rebuilt perhaps is a no brainier but how about  the others  ? How do I know if capacitors failing, without removing them one by one and testing them?   I would like the amps to be safe to operate the least of course if i could restore them to factory spec that would be amazing   for now however safety is my first concern. 
  One thing I noticed the amp that i fixed on one channel seem to not to have a working soft start. What I mean is as soon I press the power on button at the front all the relays pull in including the output relays and the supply relays. It also causes a pop on the connected speaker. How do I start investigating this?

  I consider myself lucky to be able to have the none working side fixed so far as I have no previous experience in fixing amplifiers. I do have a large bag enthusiasm thought and i am good at taking my time when it comes to complex issues like this. It took me about 3 months to get to this stage.  I have the time and the patience I only need your advice which of course will be highly appreciated .
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tilla Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 2:35pm
Following up from my questions. I started looking around on eBay for dummy loads. I m not sure if what I am looking at is actually suitable for this purpose. Would these work: 
https://www.ebay.co.uk/itm/Resistance-Dummy-Load-Audio-1000W-4-8-16-ohm-aluminium-shell-braking-resistor-UK/223769625570?var=522499714303

I am thinking of buying two 8ohm ones. With that I could test both side @ 8hms at the same time or one side @4ohms with them in parallel Will the above resistors work I wonder?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 3:34pm
Yes - those look ok.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote tilla Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 3:49pm
Perfect! Thanks Earplug !  Got a pair of those. Looking forward to start testing. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 4:08pm
No problem. And maybe screw them down onto some Alu - and/or stick a fan on them. They can get hot.   Smile


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Post Options Post Options   Thanks (0) Thanks(0)   Quote tilla Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 4:26pm
Good Idea, I have a couple of spare fans at home I will stick them on top. How would I go about testing the amp with these. Is there a  suggested time limit I can ran the amp with these or as long as the amp able to ? ( I suppose this is the aim of the test isnt it ) What is too hot for these ?  How will i notice when something starts going wrong if anything ?  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 4:48pm
Originally posted by tilla tilla wrote:

Good Idea, I have a couple of spare fans at home I will stick them on top. How would I go about testing the amp with these. Is there a  suggested time limit I can ran the amp with these or as long as the amp able to ? ( I suppose this is the aim of the test isnt it ) What is too hot for these ?  How will i notice when something starts going wrong if anything ?  



When testing, I usually let the amp under test run for 20-30 minutes. That should show up any problems.

And you know something's going wrong when the magic smoke appears!!  LOL

OR:-

Get a couple of these to keep track of the temperatures -








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Post Options Post Options   Thanks (0) Thanks(0)   Quote tilla Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 6:07pm
Originally posted by Earplug Earplug wrote:

Originally posted by tilla tilla wrote:

Good Idea, I have a couple of spare fans at home I will stick them on top. How would I go about testing the amp with these. Is there a  suggested time limit I can ran the amp with these or as long as the amp able to ? ( I suppose this is the aim of the test isnt it ) What is too hot for these ?  How will i notice when something starts going wrong if anything ?  



When testing, I usually let the amp under test run for 20-30 minutes. That should show up any problems.

And you know something's going wrong when the magic smoke appears!!  LOL

OR:-

Get a couple of these to keep track of the temperatures -

https://www.ebay.com/itm/1Pc-Digital-LCD-Display-Thermometer-Temperature-Meter-Temp-Sensor-With-Probe/193007314151?hash=item2cf021e4e7:g:ykIAAOSwwgddNXOk - https://www.ebay.com/itm/1Pc-Digital-LCD-Display-Thermometer-Temperature-Meter-Temp-Sensor-With-Probe/193007314151?hash=item2cf021e4e7:g:ykIAAOSwwgddNXOk




Thanks again Earplug much appreciated.  I have an infrared thermometer which i was planning to use and will also get a couple of the ones you suggest. That looks a very handy tool for such cheap money.  in anyways I suppose I want to see if all output  transistors warm up and have the same temperature between them, correct ?  Ive seen videos guys touching transistors and testing by hand. How hot are they meant to be ? Or its the only important thing is they all are roughly on the same temperature ? 



Edited by tilla - 24 November 2020 at 6:08pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 24 November 2020 at 6:51pm
The output transistors should all be around the same temperature. It would be odd if one was a lot hotter.

Testing (carefully) by hand is ok - but I think that 40º or 50º will burn, so using a probe is far better.   Smile


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