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Amp Internals 2

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stagefumer11 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stagefumer11 Quote  Post ReplyReply Direct Link To This Post Posted: 09 November 2013 at 2:08am
Well intresting quick tests on the Wharfedale s2500, 1 output transistor is dead and the obvious blown resistor blocks.

Also, they shorted out and removed the right hand channel thermistor!!!! :(
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AudioSystemsEngineer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AudioSystemsEngineer Quote  Post ReplyReply Direct Link To This Post Posted: 11 November 2013 at 11:00pm
Thanks for those photo's - you saved me the job of taking the lid off mine.
I just bought one from the U.S. expecting it to have a switched mode power supply that i could change to 240V (as in the SPX90).
I can see there's no room to fit a step down transformer in the case, so its either and external in the rack (messy) or i have to replace the internal mains transformer with a pair of torriods (+/- 15V and 5V).
which basically serves me right for not thinking before i bought it ;-)


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Post Options Post Options   Thanks (0) Thanks(0)   Quote topsound Quote  Post ReplyReply Direct Link To This Post Posted: 12 November 2013 at 10:30am
Dear SUBBASS,
i ask you to HELPme..
I ahve a problem wwith my Chevin A500...
I ask you if you send me some details photos of the small circuit near FAN motor.....
This circuit have small heatsink.....and i need to look the type of componens mounted on
this circuit board.....
Important for me are the photos of the DIODEs, RESISTORs and Capacitors.....
Thanks
Simone
Italia.
santsim@libero.it
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JR.junior View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JR.junior Quote  Post ReplyReply Direct Link To This Post Posted: 12 November 2013 at 11:13am
Try reach him via PM box!
Support the scoop technology, larger mouth plays louder!
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Biggus View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Biggus Quote  Post ReplyReply Direct Link To This Post Posted: 12 November 2013 at 11:23am
He won't be able to PM as less than 10 points.
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WILL* View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WILL* Quote  Post ReplyReply Direct Link To This Post Posted: 14 November 2013 at 12:02am
the t.amp TA2400, what did you think about it?



he have 2kW RMS in brigde mode?Big smile
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AudioSystemsEngineer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AudioSystemsEngineer Quote  Post ReplyReply Direct Link To This Post Posted: 14 November 2013 at 12:17am
These are an (almost exact) copy of the QSC RMX2400 series.
also appear branded 'c-mark' and 'audiohead'.
they are a dual rail Class-G design (a high-speed FET switches the supply rails from ~50V up to ~80V as the input waveform passes  a pre-set point).
This results in lower power dissipation in the output stages (so they can get away with fewer devices).
They use a crow-bar to limit the output current - which is pretty crude.
personally, i wouldn't run these into less that 4 Ohms / channel (8 Ohms Bridged) and make sure the clip lights just blink in load sections. (the clip leds sense the error voltage - so they are a pretty good indicator of distortion / when the amp is struggling). 
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 14 November 2013 at 12:21am
When considering this amp do remember it was for a time about the cheapest amp you could buy, watt for watt.
Yours appears to have Nippon Chemicon capacitors? Never seen those before in one of these, they normally use cheap chinese grenades.
K. Edwards Electronics Engineers

North Staffordshire

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AudioSystemsEngineer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AudioSystemsEngineer Quote  Post ReplyReply Direct Link To This Post Posted: 14 November 2013 at 12:46am
i hated working on the audiohead 4000 - they didn't follow QSC's design of 3 rails...opting for a nice explody 2 rail solution.
also, the +/- 15V rails for the input signal part are derrived by using 15V zeners + big red-hot resistors.
this means you can't run it up on a variac because there isn't enough voltage for the op amps.
2 ways round this...
1. disconnect the resistors and use a seperate 15V psu, or.
2. bypass the resistors with a lower value (but remember to take the bypass off later !! )
I should also mention, if the amp has been run at continuous clipping... the clip LED's or their series resistor will die.

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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 14 November 2013 at 2:21pm
Originally posted by AudioSystemsEngineer AudioSystemsEngineer wrote:


I should also mention, if the amp has been run at continuous clipping... the clip LED's or their series resistor will die.


LOL! That piece of design genius deserves a prize....
Studio45 - Box Builder Commotion Soundsystem -Mobile PA
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JR.junior View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JR.junior Quote  Post ReplyReply Direct Link To This Post Posted: 14 November 2013 at 4:00pm
LOL
Support the scoop technology, larger mouth plays louder!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 14 November 2013 at 4:23pm
"also, the +/- 15V rails for the input signal part are derrived by using 15V zeners + big red-hot resistors"

Built in obsolescence. I´ve even seen that one in a couple of Crown amps, who you´d think would know better.

Ouch 


Earplugs Are For Wimps!
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