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Old 11th June 2006, 01:26 PM   #11
djk is offline djk
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It should also be pointed out that the Pass A40 board is still available for $6 from AudioXpress.com

The A40 used two pair of TO-3 darlington for 40W of class A power. With adequate heatsinking one pair will give 100W in lower bias class AB.

It should be pointed out that 1W of plastic does not equal 1W of metal when it comes to dissipation. The difference is the 150C vs the 200C maximum junction temperature ratings of the devices.

When pushing the minimum number of devices to their limits, the junctions are typically running around 100C. De-rating to maximum junction temperature for the respective types shows us that it takes 2W of 150C plastic to equal 1W of 200C metal. This would seem to indicate that two pair of TIP142/147 are not quite equal to one pair of 2N6284/87.

It all depends upon the MTBF you are willing to accept.
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Old 19th August 2006, 03:09 AM   #12
Marito is offline Marito  Argentina
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Default 100 watts amp

Hi guys, I find this schematic amplifier at http://europa.spaceports.com/~fishbake/index.html and i buid it but the tip 147 explode when use at 4 ohms and just deliver aprox. 40 watts.
Do you have any suggestion for this amp or is an horrible circuit or may be is a little joke of this guy? (I think, for example bc556 is the best option for the signal transistors).
Thank you for your help and comments
Greetings
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Old 19th August 2006, 05:32 AM   #13
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I have seen this circuit floating around here a bit. If I remember correctly, I believe it is supposed to work, it might not be the best, but it should work.

I can't see it putting out 100 or 150 watts. The device itself is rated for 125 watts. Could be an indication to why your amp blew up.
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Old 20th August 2006, 08:37 AM   #14
Marito is offline Marito  Argentina
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Hi, thank you for your answer, may be another cause of explosion be a counterfeit tip, principally those made for ON Semiconductors...
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Old 20th August 2006, 01:26 PM   #15
ilimzn is online now ilimzn  Croatia
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The schematic is a standard 3-stage amp paired down to the bare essentials, and not too well at that. It may be able to deliver 100W into a purely resistive load, as they say here, going down hill with the wind in it's back, for a short time. Don't expect sound quality from it, it has zero output stage bias so crossover distortion is going to be very high.
The reason why you get exploding transistors when driving a 4 ohm load, is because the ones used are woefully inadequate for the task - you simply violate the SOA curves, which in BJTs results in secondary breakdown - a fast and explosively spectacular failure on plastic cased devices.
I would strongly suggest you find a proper schematic and use proper parts... ultimately, you are going to save yourself some time and money, and learn a lot in the process.
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Old 21st August 2006, 05:41 PM   #16
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Might as well use something like this:

http://sound.westhost.com/project3a.htm
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Old 22nd August 2006, 02:43 AM   #17
Marito is offline Marito  Argentina
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Thank you ilimzn, you got the truth, this circuit is awful,
I want to find a circuit not too complex due I am so lonely a guitarist with no much knowledge of electronics(and english...,ja!), I build a combo guitar amp with 2 tda 7294 (2x12) and sound fine but i want to experiment another choice.
Please take a look at this other schematic that i found at http://users.swing.be/edwinpaij/ampli_mosfet_simple.htm and tell me your opinion(or anyone in this forum),if it can be work well, at least it seems to be a decent circuit, with more controls to adjust it (I dont want to explode mosfets because are more expensive that the BJTs).
Even in this page there is an upgrade version of this amp with some components but that.
Thanks to all
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Old 22nd August 2006, 06:22 AM   #18
Tim__x is offline Tim__x  Canada
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It will only work with lateral mosfets. Vertical mosfets will result in thermal runaway unless you add some temperature compensation. Get rid of C5, put a cap across P2, and consider replacing P2 with a Vbe multiplier or some other temperature compensating bias generator (even if you use laterals).
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Old 23rd September 2006, 11:43 AM   #19
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I made that amp using the TIP147 and TIP142 and burnt it out but i think i figured out what was wrong. I put a 1000uf capacitor from the speaker to ground and it stopped the spark but i still need another TIP147. I emailed the guy who disigned it but he aint replying. I'll surf around a bit and see what i can find.
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Old 23rd September 2006, 03:28 PM   #20
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1000uF from speaker to ground? Something very wrong there!
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