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Old 27th October 2004, 11:15 PM   #1
zionz is offline zionz  Argentina
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Unhappy Help with amp circuit.

Hello all, i have made an amplifier of a circuit i found in the net, the site where i found it say it can deliver 260w at 8R load (the URL is: http://www.pablin.com.ar/electron/ci...p260/index.htm is a spanish website) everything looked good until i tryed it, the problem is that the sound is very low (suposing the amp delivers 260w), and it sound very distorted. I rechecked the componentes lots of times, and also replaced the transistors twice but i had no sucess, the only thing im thinking now is if the circuit is right, im new in electronics so i don't understand very much. Maybe someone can just fast check the circuit schematic an tell me if it have some sense at least (i suspect about the 47r 5W resistors). Any help would be very appreciated.
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Old 28th October 2004, 12:16 AM   #2
quasi is offline quasi  Australia
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Whoa....

These resistors should be 0.47 ohm. There is a misprint on the schematic.

This amp will deliver about 110 watts maximum into 8 ohms.

There are much better circuits around. I'll post a few links later.

Cheers
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Old 28th October 2004, 01:51 AM   #3
quasi is offline quasi  Australia
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Hey Zionz,

I had to rush out before so my answer was too brief.

This cct is just plain bad and incomplete with too many errors to fix.

Honestly remove the good parts from the board and use them in a different design.

I'm not one of the smarter people in this forum but I can still spot a bad design.

Check out other designs in this forum including my final version in the thread "power amp under development".

Sorry

Good Luck & Cheers
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Old 28th October 2004, 02:20 AM   #4
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Thumbs up hi

There is also a 10ohm in serial with speaker...without a coil.
You should realy try some younger project. The amp you are building is maybe 20 years old...and most primitive.
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Old 28th October 2004, 02:21 AM   #5
zionz is offline zionz  Argentina
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Thank you for the answer, i have searched and found some circuits in the forum that look good, i will try with them now.
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Old 28th October 2004, 02:33 AM   #6
paulb is offline paulb  Canada
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Try an ESP P3A.
www.sound.au.com
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Old 28th October 2004, 03:19 AM   #7
Eva is offline Eva  Spain
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That circuit is a bit outdated but it should work fine after correcting a couple of mistakes included in the schematic :

- This 10 ohm 5W resistor [the one in series with the output] must have a 1 to 5uH inductor of in paralell with it. To make such an inductor wind about 10 turns of enamelled copper wire [or plain wire] around a 1cm former. The wire should be of enough gauge to pass speaker current with negligible voltage drop. A jumper of wire should also work as a quick fix but the amplifier may get unstable

- Those 47 ohms resistors are actually 0.47 ohms 5W resistors and should be replaced

Some additional notes :

The 12K resistor is optimum for an operating supply voltage of +-35V [around +-40V when idle]. For other supply voltages its value should be adjusted until the same voltage drop is measured across both 270 ohm resistors

The 2.7k resistor should be also adjusted for different supply voltages until 250mV to 300mV are measured across the 47 ohm resistor

It's not recommended to mount the leftmost BD139 on the main heatsink, use a separate small heatsink instead. This is also true for the other BD139/BD140 transistors

It's recommended to use a 220 ohm trimmer in paralell with a 220 ohm resistor instead of the 82 ohm resistor to provide some bias adjustment. Make sure the potentiometer is adjusted to its minimum resistance before powering up the circuit. Also make sure that the bias diodes [three in series] are thermally coupled with the main heatsink and placed near the power transistors, so any change in transistor temperature is quickly sensed by the diodes

Power output should be around 100W at 8ohms and 175W at 4 ohms with +-45V unregulated suppllies

Good luck

It should be a shame for the webmaster of www.pablin.com.ar to publish such faulty schematics and false power ratings. I recommend mailing them some complaints
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Old 28th October 2004, 01:48 PM   #8
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Default EVA, i've just readed your thread...you miss the output coil

This kind of design gives extraordinary bass.

I love this design, it is alike AKSA, but Hugh have their secrets that i cannot talk.

It is very good, and can be exceptional, but have to meet hugh and talk with him.

You find the one.....THIS IS THE AMPLIFIER THOPOLOGIE!

You can see that SANYO STK chips are using exactly that circuit inside...and they know very well what they are doing.

YOU GET IT!

Regards, i am happy!

Carlos
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Old 28th October 2004, 02:01 PM   #9
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Default EVA, i have been working hard in this kind of amplifier

It is a distant cousin of AKSA.

I tried to make Aksa better, but i could not.

I suggest you to:

- Remove the input capacitor, or reduce it to 47 pf
- Remove differential emitter resistors, the small ones
- Reduce value of the Miller cap.
- Try some electrolitic in parallell with 47ohms (220uF) or remove it, put a short in its place
- Remove the 390 ohms resistor if shorted the 47 ohms..it is to reduce voltage to other stages...having not 47 ohms...lower colector voltage, will not need the 390...or use 56 ohms....and the same to up transistor (up driver)
- Reduce the criminal 56 pf capacitors used in drivers.... reduce the more you can till reach 10 pf each one without oscilate.
- Have some secret to make in output....but i cannot say...sorry. It is not my intelectual property.

Those TIP darlingtons i use everyday..... explendorous punch in bass..... you can also increase the supply to 40 volts....those darlingtons will dissipate 200 watts without trouble...so, 100 RMS is not a problem.

People talk about crispy highs in those darlingtons...reducing caps that crispy highs disappear.

Hugh Dean is the man that can talk monthes without stop about that thopologie

regards,

Carlos
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Old 28th October 2004, 03:00 PM   #10
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Default ZIOMS, Shalom... sorry EVA, i was confused...not your thread

So, my Israel friend, read the text as made to you...as i made this confusion....readed EVA, and see some Spanish amplifier somewhere and made the confusion.

regards,

Carlos
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