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Old 3rd March 2010, 06:45 AM   #1
sekhar is offline sekhar  India
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Thumbs up amp for everybody

hi,
I have included 2 bjt based design both complementary & quasicomplementary
for evaluation and testing by everybody .The main motive behind this thead is to make a amp with commonly available parts with good sonics and reliablity
Plz fee free to give comments and modifications required for the given amps ........ AS this is a "Amp for everybody" let us design this amp together.....
Both the amps have been simulated under Multisim 10.1 and they have reasonable good thd ratings *(0.005 for complementary & 0.08 for quasicomplementary) I had following question for the board.....

1.how power will these amps handle safetly ??
2.Can supply rail voltages be increased & by how much ??
3.How can a OPS be included in the design??

COMPLEMENTARY
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QUASICOMPLEMENTARY

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Regards
SEKHAR
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Old 3rd March 2010, 06:58 AM   #2
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bias needs re design ....choise of outputs is very low fi ....

to my opinion one amplifier at plan A that is so simply made will work without curent sources in the fron end almost the same good ....

to design a sophisticated front end to drive 2N3055 is not realy wise ....

in any case and given the facts as is these amps may stand up to 50+50 volts i think and may be a bit more ....

then again keeping the outputs safe can only be done with VI limiters and there will come the question what you realy like to do ..... a high end device with good sonics and good sound or a safe amplifier with full safety at all times
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Old 3rd March 2010, 08:06 AM   #3
sekhar is offline sekhar  India
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to sakis
out here at my place only 2n3055 & 2N3773 is available I know 2n3055 is not that good of a device but i am help less..... Other than o/p device how stable will this amp be.........
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Old 3rd March 2010, 09:41 AM   #4
godfrey is online now godfrey  South Africa
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Hi Sekhar

It should be stable.
Maybe the changes below can help?

A) Add a capacitor at the input to filter radio interference and also to make sure the input transistor has a low impedance at it's base at high frequencies.

B) Bias circuit:
1) Don't need the diodes.
2) Use a smaller pot (e.g. 1K) to adjust the output transistor bias current.
(should be about 50% for the complimentary circuit, about 25% for the quasi)
3) Add a capacitor to keep impedance low at high frequencies.
Fixing the bias should make distortion much better for the quasi.

C) I don't understand why this capacitor is here?

D) A trimpot like you show will allow adjustment for minimum distortion, but only for people with expensive test equipment. A fixed resistor is simple and nearly as good.

Regards - Godfrey
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Old 3rd March 2010, 10:08 AM   #5
nikwal is offline nikwal  Sweden
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3n3055 reminds me of my youth, like 25 years ago, did'nt even want to use it back then hehe.. Besides, can do simpler circuit with fewer components with irf(p) ,even fully complementary.
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Old 3rd March 2010, 05:14 PM   #6
sekhar is offline sekhar  India
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thanks Godfrey did make the necessary changes.
completed making the pcb will upload in a matters hrs ............. if any body is interested in making a low fi amp ur most well come.............


regards
sekhar
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Old 3rd March 2010, 07:00 PM   #7
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The way I am reading these circuits is they look more like development amlifiers - hence pot for DC offset adjust on current mirror

I am seeing the two diodes as constant current sources for the collector for the BD 139 if mounted to heatsink for thermal impedance tracking

The 100pf at the bias chain linked between base collector of the driver attenuates the ability of the chain to operate beyond the reactive impedance "Xc" drops below 800Ω beyond 2Mhz - preventing RF instability - this is generally only done in the big power amplifiers used for power concert rigs (1000Watt to 5000Watt RMS) , because long multicores that feed signal can be 100 meters long from the main control desk - presenting a potential antenna to the amp stack - in this case input caps are not enough - clamping gain is far more effective. Not so necessary in domestic equipment where the feed is only carried on cable no more then 2 meters long and is screened properly.

With all due respect here - I think the devices used are a bit 1970's
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Old 3rd March 2010, 07:18 PM   #8
sekhar is offline sekhar  India
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every body seems to very unhappy about the output devices , so kindly suggest some diff output devices suited for the design .......................

regards
sekhar
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Old 3rd March 2010, 07:22 PM   #9
sekhar is offline sekhar  India
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neways the pcb files for the complementary amp

PCB
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SIlKSCREEN
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have fun

regards
sekhar
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Old 3rd March 2010, 08:14 PM   #10
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A personal preference of mine is in epitaxy planar transistors such as 2SA1216 and 2SC2922 complementaries -#

Sorry about being a bit unkind to older technology, but there is something a bit Tweed Jacket and Pipe about the ubiquitous 3055 these days --- from the era of Slippers, Roberts radios, Gramophones and Celestion Dittons hehee
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Last edited by PhaseLockLoopy; 3rd March 2010 at 08:20 PM.
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