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Old 21st May 2008, 10:39 PM   #1
weissi is offline weissi  Europe
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Default "Blazer" amp from ebay

Anyone experienced to comment this amp? Cheap on Ebay.....

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PCB's are of good quality, shipping is a little bit on the expensive side (not if you're from the -region )

Is there a reason to design an amplifier with those extremely slow drivers while the output transistors are one of the fastest available

Oh, one shouldn't belive those wattages stated in the schematic
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Old 22nd May 2008, 01:40 AM   #2
CBS240 is offline CBS240  United States
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Hi

The input transistors and cascode devices are drawn backwards in the scematic, C E is reversed. Matters not though as long as the PCB is correct.
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Old 22nd May 2008, 02:26 AM   #3
Leolabs is offline Leolabs  Malaysia
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Also wrong on the input network section,both caps should be connected parallel from the input instead of one of them connected to ground.
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Old 22nd May 2008, 11:01 AM   #4
bluevas is offline bluevas  Indonesia
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AV400 with Bipolar output???
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Old 22nd May 2008, 12:32 PM   #5
weissi is offline weissi  Europe
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Yepp, Schematic is not correct, possibly because the seller wants to avoid "clones"
PCB is correct...
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Old 22nd May 2008, 01:14 PM   #6
teemuk is offline teemuk  Finland
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In addition to things pointed out already I don't see how that bias circuit could ever work. I hope the circuit on the PC board has not the same mistakes as the schematic.
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Old 22nd May 2008, 01:58 PM   #7
weissi is offline weissi  Europe
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Yes, seems to be a bit "dangerous". The trimpot needs delicate setting, extreme settings will result in

(Here too, the connection of the transistor is not drawn correctly, Base is connected to the wiper of the trimpot, so it's working. As stated, trimpot setting is delicate due to missing safety resistors)
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Old 22nd May 2008, 05:21 PM   #8
CBS240 is offline CBS240  United States
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Hi

That trim pot on the emitter of the Vbe multiplier is not correct as you have pointed out. Changing emitter resistance changes the temperature coefficient. However, you stated the base is connected to the wiper, this is not correct either. The trim pot should be between the base and emitter, perhaps in series with a fixed resistor to set a minimum value. If the pot wiper goes open, a common problem, then the Vbe multiplier turns off resulting in outputs. With the pot between base/emitter, if the wiper goes open, the Vbe transistor will saturate and the outputs will turn off. It is hard to see that part of the PCB in the photo because of glare, if it is not correct, then perhaps you can modify it.

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Old 22nd May 2008, 07:09 PM   #9
weissi is offline weissi  Europe
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Thanks for the input. I think I'll have to modify the VBe circuitry to have the standard topology (2 SMT resistors will do the trick).
Another option is to use those Thermaltrak transistors that I've for months now in my parts bin

regards, Markus
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Old 23rd May 2008, 05:54 PM   #10
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Hai weissi, actually thats pcb are came from indonesia ( BEL Produck: Bogor Electronics ) I am have already build ( many, more than 20 paer ) thats, all for PA system put volume control in input for reduce hum! ( vol max, hum! ) and use good quality device! i not comment wit spec of power out put ( 400 W just from 2 paer transistor, and 70 rail voltage ( sorry my english is poor!)
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