Nothing to do this weekend?...here is a toy for you, have fun! - diyAudio
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Old 28th January 2006, 02:44 PM   #1
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Default Nothing to do this weekend?...here is a toy for you, have fun!

Of course, changing parts, maybe some adjustments will be needed.... the first transistor base resistors and the 220K ohms that is going to the up power transistor will help you if needed.

If you do not apreciate the VBEs in the output, you can arrange lower VBEs, and also Bias current, reducing the 82 ohms resistor, the one in series with silicon diodes (1N4148, 1N4001...everyone)....increasing this resistor the bias will be increased....1.250 Volts from base to emitter, related the darlington units can be fine....check the current....everything between 20 miliamps and 300 miliamps will be fine...observe the sonics...i prefer to use 300 miliamps..but those things are personal.

here is some test....introductory text down here:

Having nothing to do this weekend, here is some toy for you, better than do nothing
and be invited by your wife to visit her uncle or mother.

A very old fashioned amplifier, very nice to observe sonically how we have evoluted
(or not!) related audio design and performance.

You can construct as spider, P2P or point to point soldering “spider type” arrangement, and can use some supply you already have…those simetrical plus and negative 35 will fit perfectly…use only the positive half and ground.

Other supplies will fit…you can use the one you have…..but, carefull when going upper than 35 volts, because of the transistors, in special the output units that will not hold the power…and the smaller ones can not hold the voltage…have to check with care, your option of transistors.

You can use other darlingtons…everyone you have, respecting the power and voltage…and not having darlingtons, you can do them…. Use a power one and a smaller transistor…colector to colector, the small transistor emitter to the big transistor base, join the colectors and the power unit emitter will be the resultant emiter….

To make better, connect a 50 ohms resistor from the small unit colector to the power unit emitter (or Power unit base to emitter).

Colector will be the joined colectors
Base will be the small transistor base
Emitter will be the power emitter.

Ready, you made you Darlington…also you can use a diode…but you can forget too.

This amplifier will produce around 25 watts over 4 ohms, using 35 volts supply…and can go higher than 40 watts using higher supply voltages….remembering that using 8 ohms speaker, the power will be divided by a ratio of 2.

Just to have fun…doing nothing…try this toy.

Regards,

Carlos
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Old 28th January 2006, 02:54 PM   #2
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Default This is some very old amplifier, sold as Kits in Brazil, since the seventies

It was very cheap, and many models where produced, using TIP3055 and others transistors..... they disappear and return with other name...something very standard that cost from 10 to 20 dollares one channel kit, inside a transparent plastic bag, having parts and board..

Heatsinks, insulators, transformers, cables, switches, rectifiers, supply filters and all stuff are not sold....because of that, it is usually very cheap, the only way to sell transistor kits here is to produce them cheaper than an LM1875 Chip kit.

regards,

Carlos
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Old 28th January 2006, 03:39 PM   #3
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Some kinda El Cheapo amp.
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Old 28th January 2006, 04:05 PM   #4
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Hey Carlos, still again some four transistors miracle ?
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Old 28th January 2006, 04:26 PM   #5
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Default This is "Big indian magic!".... some of those transistors have two hidden inside.

Big magic..... and just one of those darlingtons also produces a nice class A sound too.

hehe

Carlos
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Old 29th January 2006, 12:24 AM   #6
CBS240 is offline CBS240  United States
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Hey Carlos,

How is bias through those darlingtons in class AB after a little heat is generated? Any occilations with the output cap inside the FB loop? Hey, could be a good breadboard amp...to study temp affects on bias of darlingtons. Very important concept indeed. Maybe best modified to class A? Certainly low cost though and that is always good.
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Old 29th January 2006, 06:36 AM   #7
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Default Hellô....adjust the 82 ohms resistor, the one in series with the diodes, measuring

Voltage over the emitter resistors.... adjust to have voltage in both emitter resistors, this way, both transistors will be conducting...this will be around 20 miliamps, and the current will be sligtly different related up and down transistor.

10 milivolts measured over 0.47 ohms resistor will something very near 20 miliamps.... 300 miliwatts will be dissipated into each transistor in stand by mode.

Heatsink size needed is 400 squared centimeters to each channel, to face the worst possible condition of work.... 4 fins, each one squared shape, 4 inches size..or other combination of fins, that presented area in contact with air reasonable.

regards,

Carlos
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Old 29th January 2006, 06:39 AM   #8
lgreen is offline lgreen  United States
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Default schematic

Carlos, I see that you have learned to draw schematics on the computer. Nice work! But I miss your old hand drawn schematics on paper, although these are much easier to read.

I'm busy this weekend but might try that one someday.
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Old 29th January 2006, 06:55 AM   #9
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Default Tekko, CBS240 and Igreen, than you by your presence in this weekend toy to produce

Some fun, to avoid to visit Wife's mother, or to make some other boring thing that happens when we have nothing better to do.

Well, brothers, thank you by the attention to this very simple schematic, you are kind to support this toy.

My Multisim was deleted from the computer, since i perceived that it was using too much of my time... this way i used the paint program, the windows accessorie to sketch this for you.

I hope someone felt good watching it, and maybe doing it.... very simple and intersting toy....nothing impressive, just to construct fast, to compare and produce some laughs...hehe..... this is the point...start with a smile, and them laugh...a need in our life, to be happy....i think when you started to laugh from yourself, no one will have the power to stole you happyness anymore....and better...people will not try to stole, they love happy people!

regards,

Carlos
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Old 29th January 2006, 07:13 AM   #10
Eva is offline Eva  Spain
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Carlos:

Go on, restore the multisim!!
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