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Old 26th July 2011, 12:54 PM   #11
Dr_EM is offline Dr_EM  United Kingdom
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I'd go for a 2x12VAC transformer personally, as the Op-amp for the signal processing might not like +/-22V DC rails. Not seeing any regulators in here.
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Old 26th July 2011, 01:00 PM   #12
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nice, thanks, how do idecide which is +12, and which is -12 actually at the board?, easy to sort trans end, cheers, can't beleive the help i'm getting
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Old 26th July 2011, 02:11 PM   #13
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Dr.EM View Post
I'd go for a 2x12VAC transformer personally, as the Op-amp for the signal processing might not like +/-22V DC rails. Not seeing any regulators in here.
Hi Doc,
I took a chance with saying use a 15v tranny as I spotted two zener diodes near the opamp and I'm assuming these are for regulating the supply to the opamp.

Easy to check for definite though. If they are, then one end of each will go to ground and the other ends will go to pin 8 and pin 4 of the IC.
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Old 26th July 2011, 02:14 PM   #14
Mooly is offline Mooly  United Kingdom
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Originally Posted by richa View Post
nice, thanks, how do idecide which is +12, and which is -12 actually at the board?, easy to sort trans end, cheers, can't beleive the help i'm getting
It's AC from the tranny so there is no plus and minus as such. It's 15-0-15. As long as 0 is connected to the correct point on the PCB then the two 15's are the same and either can go to either point on the PCB.

The 1N4002 is just a higher rated (voltage rating) than a 4001. Makes no difference to the tranny type here.
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Old 26th July 2011, 02:51 PM   #15
johnr66 is offline johnr66  United States
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I have to agree with the 12-0-12 volt transformer recommendation. They are typically 25.2 volts (12.6-0-12.6) and will output between 17 and 18 volts per rail at idle (DC side of PS). With 10 watts at 4 ohm rating and the light heatsink, I can't see using higher rails.
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Old 26th July 2011, 04:15 PM   #16
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thanks once again for all your help everyone , will get new transformer tomorrow, and report back, hope to then uprate heatsink e.t.c and hopefully all will be well, it's an ok amp (or was!!) on the pre amp side with good clean channel and decent overdrive for originally very little money and is ideal plugged into my desk can't see the point (lack of any funds anyway) in buying anythig new and it's very small, hope to also take off dedicated pre out , onc again thanks to all for your help
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Old 3rd October 2011, 11:17 AM   #17
masood is offline masood  India
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dear all,
i have built mapin 50 w maplin amplifier.when i on the power supply the transistor became very hot.please give me the voltages at transistor i means fault finding probe.thanking you
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Old 3rd October 2011, 01:02 PM   #18
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hi masood, yes i had the same problem when i first built these, you must recheck your soldering, and recheck power supply. they work well when built, but get a bit warm, also recheck components are in right place. i did all of the above and presto they worked,,. hope this helps
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Old 16th October 2011, 11:52 AM   #19
masood is offline masood  India
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Thumbs up sick amplifier

thanks richa i shall find fault finding after some times many many thanks
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Old 5th November 2011, 11:29 AM   #20
masood is offline masood  India
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dear sir,
please help me for50w maplin amplifier .please send me the construction manuals and voltages at various pace,my preset2.2ohm does not show the ampr. trans. bd711 began to warm.thanking you
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