Can I use MANY MANY low power devices for 1 HIGH power amp? - diyAudio
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Old 29th January 2003, 11:50 AM   #1
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Default Can I use MANY MANY low power devices for 1 HIGH power amp?

Basically I wan to make a 150watt amplifier using any of the following parts...


MOSFETS:

IRFZ44 MOSFET: 60V / 50A (N channel, TO-220 package), 0.028ohm on resistance: (IRFZ44) $3 each

IRF820 MOSFET: 500V / 2.5A (N channel, TO-220 package), 3.0ohm on resistance: (IRF820) $3 each

SGSP239 MOSFET: (TO-126 package): (SGSP239) $1 each

MTP3055E MOSFET: 60V / 12A (N channel, TO-220 package), 0.15ohm on resistance: (MTP3055) $2.50 each

MTP2955E MOSFET: 60V / 12A (P channel, TO-220 package), 0.3ohm on resistance: (MTP2955) $3 each




--------------------------------------------------------------------------------

TRANSISTORS:

(NEW) POWER TRANSISTORS 2N3055: New TO3 package power transistor with metal case. Large but limited quantity: (2N3055) $1.20 each or 10 for $8.00

C8050 NPN Transistors: (2W 1.5A Hfe 120 - 200): (C8050) 20 for $5

C8550 PNP Transistors: (2W 1.5A Hfe 120 - 200): (C8550) 20 for $5

AD161 / AD162 TRANSISTORS: Obsolete germanium power transistors. These were once commonly used in the output of class B audio amplifiers. Max current 1A, Vce is 20V. AD161 is NPN, AD162 is PNP: (AD1612) $3 per pair



Some are failry low powered, but I have no money, and using more parts helps with heat disapation, so, basically, whats a safe number of what parts to use for a 150watt (into 8ohm) amplifier?? I am happy to use 10 or more devices, it makes the amplifier look more powerfull anyway.. lol.. I have searched for a few of these parts, but only found low power amps.. Please help.. I really need some ideas for my FIRST diy bi-amp / speaker system.. lol, perhaps I am aiming for too much in one go... ohh well..

ALSO ALSO ALSO ALSO!!! I don't want to brigde incase one day I want to use 4ohm speakers....
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Old 29th January 2003, 12:26 PM   #2
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Default Sounds like a rotten idea, sorry!

For 150 watts into 8 ohms you need at least +/ - 50v rails, so 100v devices minimum. For those prices you would be better of buying 1 big one rather than 10 little ones. If you are going to do that, then buy a kit because at least it will most likely work first time.
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Old 29th January 2003, 01:06 PM   #3
blmn is offline blmn  Brazil
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AD161/AD162!!!

These parts I remember from my childhood!!! Are they still in production??? thermally stable a lot!!!

If Yes, maybe a more powerfull AD149 could be used...

Regards
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Old 29th January 2003, 01:39 PM   #4
OliverD is offline OliverD  Germany
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Remember Jocko's "new law"? Don't use Germanium transistors in new designs.

You can always parallel a number of small devices instead of one big device as long as

1.) The small devices have the same or higher Vce (at least 2 x rail voltage)

2.) SOA of the n small devices is same or higher as 1 big device

3.) Care is taken to match the devices (or decrease the influence of differences by using higher emitter resistors)

4.) Ceb (or gate capacitance in case of a MOSFET) of n smaller devices is not too different from Ceb of one big device (lower is better than higher; in some applications this matters more, in others less)

5.) hfe is similar (higher is better than lower)
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Old 29th January 2003, 01:40 PM   #5
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AD161/AD162!!!


These are Germanium, right? Talk about retro-engineering...
I'm sure I have a couple of those somewhere, TO-66 package.
Great drivers!

Jan Didden
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Old 29th January 2003, 01:45 PM   #6
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Quote:
These are Germanium, right? Talk about retro-engineering...
Hey, the tube guys use antique active devices all the time . Maybe this will start a trend - anybody have any NOS 2N301s?
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Old 29th January 2003, 02:17 PM   #7
Werner is offline Werner  Europe
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For those who are into such trivia: in the eighties Belgian speaker company Synthese used to sell a big power amp using 256 (or so) signal transistors in its output stage.
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Old 29th January 2003, 02:36 PM   #8
joensd is offline joensd  Germany
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This is probably not what you´re looking for but a crazy amplifier with 35W and 44 opamps in the output stage working in class A.

What about a bridged amplifier using lower voltage and the given devices?

Regards
Jens
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Old 29th January 2003, 03:07 PM   #9
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Quote:
Originally posted by joensd
This is probably not what you´re looking for but a crazy amplifier with 35W and 44 opamps in the output stage working in class A.

What about a bridged amplifier using lower voltage and the given devices?
I think Dr Meier's idea is cool but otherwise I can't see any reason to be thinking of paralleling amps like he does. Save little money first and buy appropriate transistors.

http://home.t-online.de/home/meier-audio/preamp.htm

BTW: When AD161/162 I got flashbacks from my childhood and a little tear was seen in my eye My first amp, 8 W mono!
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Old 29th January 2003, 11:40 PM   #10
blmn is offline blmn  Brazil
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Peranders,

I know what you are feeling. I used it on my second design. My first was 1W using AC187/AC188k devices. After that, a less modern EL84 push-pull design. Lots of fun.
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