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Old 22nd September 2003, 04:10 PM   #11
belg is offline belg  Belgium
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hellow again

does someone has online companies that can deliver the output transistors that i need for the p3a amp from esp?

i can't find them on farnellindustries and not even on the official site of OnSemi

i'm talking about the MJE15035 and the MJL...

i also sent a mail to farnell to ask them about those transistors and they don't have them.

thx
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looking for schematics for a 4x80W rms amp, a good power supply and 2 pre amps
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Old 29th September 2003, 10:07 AM   #12
Paulr is offline Paulr  United Kingdom
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Default Output Transistors

With regards to the new transistors for the P3a try http:\\www.onsemi.com . As a student constructing a genuine project you should have no problem getting samples of the transistors shipped to school for free.

The older ones for the P3a were BD139 & BD140 drivers with your choice of output (Rod used 2SA1302 2SC3281 - now obsolete & even 2955 3055 pairs I believe), but have a look at http://www.anidian.com/audio/construct/p3a_1.shtml for some alternatives

I'm building using the MJ15003/4 pair with MJE340/50 drivers & there are many other combinations that have been used on this amp with great success listed on this site.

My heatsinks will be internal with 2 chanels per 0.6C/W heatsink for a bi-amped setup

Cheers & good luck

Paul
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Old 29th September 2003, 10:53 AM   #13
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Default Re: Output Transistors

Quote:
Originally posted by Paulr
The older ones for the P3a were BD139 & BD140 drivers with your choice of output (Rod used 2SA1302 2SC3281 - now obsolete & even 2955 3055 pairs I believe), Paul

I believe the OnSemi version of those devices (MJL1302 and MJL3281) are still available (maybe in production as well).
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Old 29th September 2003, 11:07 AM   #14
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Default ON devices

For the P3A ROD suggest the MJL4281A (NPN) and MJL4302A (PNP) pair.

They are available as well as the MJL1302A/3281A from

www.onsemi.com

Good Luck

\Jens
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Old 30th September 2003, 07:55 AM   #15
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Well I made a four channel power amp that fits inside a 300*about 480* 75mm amp (w*l*h). This was using G Randy Slones amp design in his high power audio construction manual of design 11.4 "a low distortion amp" or summit like that.

I had to trim off a little bit of the boards and do like two point to point wires to fir them inside the case, heatsinks make the sides of the case and anodised silver alu the top and bottom with mahogany front and a ply back. I had to trim as I didnt check the size I just assumed that 300 (12" for you yankes) length would fit two in. Anyway these amps sound superb much better then a commercial amp costing 700.

I built these as a first power amp project (had done low level things and loudspeakers before tho) and had no difficulties in doing everything myself, from etching the PCB to making the case (but I had build speakers to knew my way around all the tools). I built these when I was 17 so it isnt too hard. Ok now for the last bit price.

OK Ill give a sum up of how much you can expect to spend on the power amp alone.

Power supply and boards all complete including connecty thingies for all channels = approx 300. This is sans case as I used a cheap old computer case that I didnt have to pay for as I already had it.

Ok the power supply I used has a 625VA from maplin which cost 40 and Ive got three 6800uf caps per rain for smoothing. This for me is fine under the light loads I stress the amp. If you want to run four of less then four ohm loads at loud levels, I would suggest a larger supply with summore caps.

The better case which is finished appart from some fancy looking LED's that I wanna add to make it better looking, was made from two conrad engineering heatsinks the 30-75 thing I think one per side ie one per two channels. The top and bottom cost 5 ebay A3 sheets and the front and back fom my dad he makes guitars as a hobby so I scavenged of him.


The book can be found in any good library.

Hope thats helpful Matt
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Old 30th September 2003, 10:12 AM   #16
Jennice is offline Jennice  Denmark
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Hi Belg,

Keeping the heat sinks inside will certainly limit their cooling efficiency, even with holes in the enclosure.
As nobody plays at peak level (full power) all the time, a lot of companies rate their heat sinks at 1/3 rated output power.
In your case, that would be 4 times 80 W = 320 W.
Total cooling ability should them be no less than approx. 100 W.
For comfortable operation, you will not want to calculate a temperature rise of more than 25 degree above ambient for the sinks. This leaves margin for the thermal resistance of the insulation when mounting the transistors, and the casing-to-die thermal resistance. (from the semi-conductive part of the transistor to its enclosure).
Effectively this gives an overall heat sink specification of 0.25 K/W which will be very difficult to obtain unless you place the heat sinks as the sides of the enclosure. Remember to mount the Vbe stage transistor on the heat sink for thermal compensation, or it'll melt down !

In stead of repeating myself over and over, I suggest you download my booklet from www.sylvest.dyndns.dk:8080 with the user name diyaudio and the password booklet.


As for the Cervin Wega speakers, my personal general oppinion is that they are great for partying, and can stand a lot of power. However, I would look for something like the british B&W speakers for something all-round, as I find them to be more musically and detailled.
As someone said, it depends on personal likings and preferred music taste.

Jennice
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Old 1st October 2003, 07:16 AM   #17
tcpip is offline tcpip  India
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Default Re: Re: Output Transistors

Quote:
Originally posted by millwood
I believe the OnSemi version of those devices (MJL1302 and MJL3281) are still available (maybe in production as well).
Why don't you just use 2SA1943/2SC5200, the "successors" of these transistors according to their original maker? They have a higher transition frequency. Do they oscillate in the P3A? The Aksa amp's maker has asked his customers to shift to this without any mods to the rest of the circuit, IIRC. If it oscillates, will increasing the value of the compensation cap or putting a gentle passive RC ultrasonic low-pass at the input (maybe 3dB at 60KHz or higher) stop it?

Tarun
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Old 1st October 2003, 07:54 AM   #18
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Im assuming that the heatsink requirements are half if only two of the channels are running. So as you quote 0.25 for the lot 0.5 for half. Finding two 0.5's for the sides of the case if indeed you take that route wont be too hard nor that expensive if you shop around (i got the two conrads for 38) that included shipping from Austrailia, these are 0.37 sinks so thats more then Jennice recommended, I will say that at 0.37 per channel (slone recommends 0.8 per amp) your not going to be in any danger of getting too hot as the thing runs cool even under hard duress. Altho this is active so the amps are not having to work as hard as they would under a full range pair of speakers. Altho the max SPL when using acitve increases so I can play it louder which will mean the amp heats up, but again its not hot just warm.
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