OT: amp design

Joe · June 11, 2009, 11:45:29 PM

Drew this circuit out from some simulator files. Can't afford to test it yet though.

http://www.diystompboxes.com/analogalchemy/sch/diodepwr.html

brett · June 12, 2009, 08:15:44 AM

Hi Joe
looks terrific. If you opt out of the short circuit protection section, it becomes extremely simple. (I figure that the 2955 and 3055 are very tough devices and would probably stand up to short short, and a fuse would protect anything more serious.)
How much output can this produce? 25W RMS? A little more?
If you were careful about thermal runaway, you could probably parallel 2 x 3055s and 2 x 2955s and run it at +/-30V. WooHoo. Or is that a recipe for a meltdown?
thanks

Joe · June 12, 2009, 10:49:48 PM

The transistors shown can handle 100V, so 40V rails will work. Doubling the outputs will be necessary with 40V @ 4 ohms. That would get 100W or so. With 25V @ 8 ohms, you're on target at 25W.

It's possible for the output transistors to burn up before the fuse blows, so the protection circuit is a good idea. Thermal runaway is kept into check with the Vbe multiplier and large amount of negative feedback. (Basically, the negative feedback loop stabilizes the output, while the positive feedback loop restores audio gain.)

wavenator · June 22, 2009, 09:05:32 AM

some questions
how much c/w should the heatsinks for the tips be?
how much for the 2n3055 and mn2955?
can i use a 50 volt 250 vat transformer? how much output would it give?
does this circuit need a preamp?

wavenator · June 22, 2009, 05:15:15 PM

bump
+1 question
would i have to add a supply circuit for filtering?

wavenator · June 23, 2009, 03:07:41 PM

bump again
1 more question ^^
does it a guitar amp or multi purpose amp

sean k · June 23, 2009, 03:59:58 PM

The tip's would most probably be alright with the little heatsinks you through on the back and the output trannies are in class AB so the heatsink wouldn't need to be too big. I've got a class A, which needs a far greater heat dissapation capability, (the hood)with two 3055's and the heatsink for that is about 100mm x 250mm and it does the job and I've never had any problems. The input sits on a 10k to ground so its low impedance I'd say, well line level. Hope this helps.

wavenator · June 23, 2009, 04:08:30 PM

oh thx for answers!
anyway, can you help me with the others?
looks like joe is not that active

about the 50-0-50 trans?
about the others if possible

thx!

wavenator · June 24, 2009, 03:55:51 AM

bump

wavenator · June 24, 2009, 12:18:26 PM

another bump

sorry for the bumps
i really wanna order the parts and build it
i've been looking for a build a lot of time

thx guys

wavenator · June 24, 2009, 08:27:40 PM

lol another bump with more questions (wanna be sure before the build)
well, the 2n3055 and the 2955 tabs are the emitter right?
you wrote :
Vbe multiplier and output transistors on same heatsink.

you meant that the tip31/32 ,just before the 3055 and 2955 , emitter should be connected to the tabs?

and about what you wrote about the negative and positive feedback
how can i choose either?

wavenator · June 26, 2009, 10:44:05 AM

somebody?

Joe · July 03, 2009, 11:26:27 AM

If you've never built a power amp, find an article that explains how to mount the transistors to the heatsinks, and how to adjust the Vbe multiplier. And also how to make the power supply and do the mains wiring. (Remember that although I've made similar amplifiers, this particular design is not tested yet.)

>> and about what you wrote about the negative and positive feedback
>> how can i choose either?

You don't choose.

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OT: amp design