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Old 26th February 2010, 05:49 AM   #1
db! is offline db!  Canada
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Default TIP3055/2N3055 based power amps

Hey guys,

I've noticed that I have amassed quite a few TIP3055, TIP2955, 2N3055, MJ2955 transistors throughout the years. These are the standard 60V/15A variety.

I would like to build a power amp that can put out approximately 300-500W into a 4 ohm load with +/- 30V rails. My main problem is the lack of a proven/suitable design to work off of.

Does anyone have any ideas?
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Old 26th February 2010, 06:09 AM   #2
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Originally Posted by db! View Post
Hey guys,

I've noticed that I have amassed quite a few TIP3055, TIP2955, 2N3055, MJ2955 transistors throughout the years. These are the standard 60V/15A variety.

I would like to build a power amp that can put out approximately 300-500W into a 4 ohm load with +/- 30V rails. My main problem is the lack of a proven/suitable design to work off of.

Does anyone have any ideas?
Hmmm. With 30V rails, your output will be some 28V peak which is 20V RMS, over 4 ohms that's 100W. So you will be needing two amps bridged to get to 300-400W. Each amp will 'see' 2 ohms load. To avoid 'gain droop' at high currents you probably want to have at least two output pairs in each amp.

Other than that, there's probably a ton of amp circuits around.

jd
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Old 26th February 2010, 07:09 AM   #3
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Not wishing to sound elitist or anything -- but arnt the ubiquitous old
2n3055/2955 (and the old chestnut - MJ802) a bit of a sluggish nail in the face of current epitaxy technology?
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Old 26th February 2010, 07:49 AM   #4
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You can put two 2n3055s in series to get higher rail voltages.

DC 300 sound as the 3055s are slow, but can be good for vintage bass sound

work great with a transformer drive for super stable amp

Look at a SS Vox or other older circuit where the outputs are driven by a transformer
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Old 26th February 2010, 08:27 AM   #5
godfrey is offline godfrey  South Africa
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You could look to some of the "golden oldies" commercial amps for inspiration.
There's a collection of them growing here: 2N3055 inside - commercial famous amplifier models, quasi complementary power output

There's probably schematics for some of them on Jan's site here: Welcome to Audio Circuit Denmark
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Old 26th February 2010, 09:44 AM   #6
djk is offline djk
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Build a multi-rail supply and you can use up all your 3055/2955 parts.

Use one pair of MJ21195/96 on 42V, use MJE15032/33 for drivers.

Use three pair of the plastic TIP3055/2955 in parallel, with another pair as drivers. They run on the 84V rail.

Use whatever front end you like, use the basic Carver circuit to drive the high-side outputs.

Should do 500W4R with a suitable transformer and heatsink, uses up 8pcs of 3055/2955 per channel.
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Last edited by djk; 26th February 2010 at 09:50 AM.
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Old 26th February 2010, 10:34 AM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
as suggested earlier, a pair of 150W into 2r0 amplifiers connected as bridged will give 300W into 4r0.
This can be achieved reliably with a 4pair output stage on +-30Vdc. That requires 16devices to get your 300W.
You will probably need another pair of devices as drivers due to the low gain of the 3055. Your total is now 18off 3055 and 2off 2955. There are better ways to do 300W.

Neither 400W nor 500W is possible from a +-30V supply.
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Old 26th February 2010, 01:23 PM   #8
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Default Famous Amplifier "Hadley 622" Schematic

I have start this thread:
2N3055 inside - commercial famous amplifier models, quasi complementary power output
look about post#22 and #23 for an interesting circuit topology for you.

I recommend highly to avoid true-complentary buffer topologies, because the
counterpart - the MJ2955/MJE2955/TIP2955 - have not mirror-symmetric behaviour !!!

Please note, that halving of output power means only a loss of 3db by max undistorted SPL !

Last edited by tiefbassuebertr; 26th February 2010 at 01:31 PM.
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Old 26th February 2010, 01:37 PM   #9
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Quote:
Originally Posted by AndrewT View Post
Hi,
as suggested earlier, a pair of 150W into 2r0 amplifiers connected as bridged will give 300W into 4r0.
This can be achieved reliably with a 4pair output stage on +-30Vdc. That requires 16devices to get your 300W.
You will probably need another pair of devices as drivers due to the low gain of the 3055. Your total is now 18off 3055 and 2off 2955. There are better ways to do 300W.

Neither 400W nor 500W is possible from a +-30V supply.
Bridged in 4 ohm, just about 400W. Only just with 28V out. Not sure it would work with 3055 on 30V, so you may be right.

jd
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Old 26th February 2010, 03:03 PM   #10
wg_ski is online now wg_ski  United States
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Originally Posted by AndrewT View Post
There are better ways to do 300W.
But are there better ways to use up a bunch of low voltage transistors? Unless you plan on building a dozen (or two) gel-cell chargers, they'll sit for years while working on more exciting things.

How 'bout this...

Cascode S-Leach style output using two series connected banks of 3x 2N3055driven by a TIP31 (and a 60V-selected 2N3904 predriver for a triple). PNP's would make the minus side easy, but of course you'd need an equal number of 2955's MJ802's, etc. Heck, mix-n-match them - just make sure parallel banks are the same type/date code. We're not looking at .00007% distortion anymore anyway. You could try an all-NPN but don't say I didn't warn you about sziklai's not tolerating non-zero rail impedance (the cascode will oscillate). They may work for the slaves, but not the masters! Use up that stash of old video outputs for the VAS's. Then bridge it. Three 24V high current surplus transformers in series to power it - 100 volt single rail. Even with the rail dropping to 65V under load you'll still get 400 watts at 4 ohms.
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