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ke4mcl 1st March 2011 01:37 AM

any single 2n3055 audio amp schems out there?
i did some digging around for an audio amp schematic using a single 2n3055 in the output and much to my surprise, i couldn't find any.

im looking for something simple to build as a utilitarian amp for PA use for example. yes, there are other ways to go about this but i want to use a single 2n3055 in the output.

anybody got any links to some schems?

ontoaba 1st March 2011 02:19 AM

You may using it in classA emitter follower with resistor in emitter connected to ground, says 5W or 10W output and it will OK for 2N3055.

RJM1 1st March 2011 07:54 AM

4 Attachment(s)
Something like this? 6W class A. Power supply peak current 7.7A.

RJM1 1st March 2011 08:22 AM

4 Attachment(s)
Loop response, Loop response 2p feedback cap, Loop response 50p feedback cap
Frequency response 2p feedback cap.

RJM1 1st March 2011 01:29 PM

Change Q2 to a TIP31.

toprepairman 1st March 2011 06:51 PM

I'd use a transformer to couple the output or load it with a choke.

wg_ski 1st March 2011 11:31 PM

A second 2N3055 is cheaper than a transformer. Cheaper than a 25 watt resistor, too.

ontoaba 2nd March 2011 12:04 AM

"A second 2N3055 is cheaper than a transformer. Cheaper than a 25 watt resistor, too"
There still many fakes TOSH 2N3055 much cheaper than TIP3055.

Hi, RJM1, any opamp like TL071 will also work fine. It is ClassA, no crossover and already with high linearity, weaken the feedback or using feedback from 2n3055 base (with base resistor) output may also has better sound, even with lower linearity.

ke4mcl 2nd March 2011 03:52 AM

fake 2n3055's is right! i've resorted to getting mine from junked pro PA gear.

thanks for the info. will print some of those schems tomorrow and take a closer look. i have to admit i was thinking they be simpler much like SE tube amps are.

quikie22 2nd March 2011 05:05 AM

Go look at the Pass Zen amplifier for inspiration. You can safely replace the MOSFET with a bipolar resistor but of course with some changes in the component values. You should be able to replace the current source with a Resistor of about 10-20 ohms (or a suitable bulb with the requisite resistance). Trimmer pot should be at its minimum at turn on and adjusted to give an idle current of around 1.5-1.8 amps. I would place a 0.5ohm resistor at the emitter of the 2N3055 and use that to measure the current (V=IR, so for 1.8 amps and 0.5 ohm resistor, this would give 0.9V across it). You will need a HEFTY heat sink as this thing runs reallly hot.

I have one of these done up using the 2N3055. It sounds pretty good considering the low cost of parts and the simplicity. Bass is good, but I highly recommend good capacitors, Elna cerafines with 10000uF and 50V rating would work fine as output caps. It does not sound as fast as a MOSFET circuit but it has nice warmish sound somewhat like a tube-amp but with good definition and detail (definitely impressed my "audiophile" friends). I have tried with and without feedback and still prefer without feedback.
As gain is low, you should be looking at an appropriate preamp to go with it. The Bride of Zen would be a good accompanying project. (The BOZ will bring back some speed to the sound without interfering with the niceness of the tone)

There is a turn on thump, so you should be thinking of a delay circuit.

The part of the schematic of interest is the lower half of the circuit involving the IRF 140 only. The 9240 and MPSA part are the current source circuit, which help to linearise the circuit but which I replaced with a load resistor/bulb as in the Zenlite series of amplifiers)

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