Can I use MANY MANY low power devices for 1 HIGH power amp?

[SkinnyBoy]

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....

 

[Circlotron]

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.

 

[blmn]

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

 

[OliverD]

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)

 

[jan.didden]

ad stuff

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

 

[mikewu99]

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?

 

[Werner]

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.

 

[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?

Regards
Jens

 

[peranders]

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!

 

[blmn]

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.

 

[Circlotron]

When a given generation of engineers that relied on a certain class of active device because there were none better, are all finally dead and gone, then those active devices have a big conference and decide to improve their sound because now people are only going to be playing with them and having fun. When people treat active devices seriously and lives etc. depend on them, active devices recognise this and act very proper and conservatively. So they sound very ordinary. But they like having fun and when they know their serious days are over they let their hair down and change their personality and help us to enjoy ourselves hifi-wise. Maybe germanium transistors have come of age? Same goes for old cars (excluding VW Beetles of course).

 

[SkinnyBoy]

riiiigggghhhhttt... anyway, I think I will NOT sure many many devices, too much trouble.. I am thinking of making either the Silicon Chip Ultra Low distortion 2 X 100watt stereo amp (which gives 100watts into 8ohms) or the 200watt mosfet amplifier module (which gives 150watts into 8 ohms) The 100watt one is in the Novermber 2001 Silicon Chip magazine (if you have it Circlotron) and the 150watt one is in the August 2001 mag. Both KITS are sold by Altronics. I am able to get the PCB design for the 100watt one, but not for the 150watt..

Here are the specs on both amps, are these any good?

Ultra Low Distortion 100W Stereo Amplifier Kit
Specifications:
Output power: 100W @ 8 Ohm
Signal to noise ratio: 109dB A weighted
Distortion: 0.002%
Frequency range: 20Hz-20KHz ±0.5dB
Dimensions: 422W x 400D x 88H
Weight: 12kg

200W MOSFET Amplifier Module
Specifications
Dimensions 300W x 82H x 225D
Output power 140W RMS into 8 Ohms, 200W RMS into 4 Ohms
Signal to noise more than 100dB below rated output
Distortion 0.007% @ 200W

So, which one should I waste my money on? If I was to design my own PCB for the 200watt MOSFET amp, chances are the design wouldn't be as good, and would result in noise... But I do have a PCB layout for it.... so I could do it just the same..

 

[AKSA]

Fine examples of designing for low spec.

Impressive though the specs are, these amps sound just like any other mass produced or kit power amp of the eighties. I've heard them all, and they are unsatisfying.......

Cheers,

Hugh

 

[SkinnyBoy]

Are you saying that the 200watt MOSFET amp will sound no better than a pair of bridged LM3886 ICs?? HERE IS THE SCHEMATIC!!!

 

[djk]

Given the transistor choices I would build a Hadley with doubled 2N3055 for the outputs.

http://home.kimo.com.tw/skychutw/Circuits/Hadley622.pdf

 

[SkinnyBoy]

LOL.. I have given up on the MANY MANY transistors idea, decided it was just as expensive, and impracticle.... I hate having to mount just one device... I say NO THANX to 20... lol

 

[joensd]

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.

Yes, it´s a crazy idea but he´s gone for it!
He must have a good deal with National Semiconductor.
I actually don´t have the knowledge to judge that but i doubt it´s an effective solution to get a good sounding amplifier.
And the trouble you probably end up in combining all those high-speed devices...
I just can´t believe he managed to make the PCB design work without oscillations.
At least he saved the money for the heatsinks

Jens

 

[SkinnyBoy]

Okay, I would LIKE to make the 200watt MOSFET amp... tell me why I shouldn't, and give me other options.... Okay, I think I found a big enough reason why not to make it.. THE COST OF THE MOSFETS!!!! Well, I can probably get them cheaper (haven't looked) BUT $15 EACH!!! thats $120 JUST for MOSFETS in a stereo amp..... PLUS about $150 for the 2 transformers, $40 for the heatsinks.... THATS $310!!!! AND I STILL NEED THE AMPLIFIERS FOR THE TWEETERS!!!!! bahh, I think I will finish my speakers, then put them in storage.. WHY ARE THINGS SO EXPENSIVE!!!! Perhaps I should just bridge LM3886s or somthing similar.. BUT ITS NOT THE SAME!!!

 

[hugobross]

what about using MANY MANY high power devices for 1 low power amp?

 

[peranders]

Okay, I would LIKE to make the 200watt MOSFET amp... tell me why I shouldn't, and give me other options.... Okay, I think I found a big enough reason why not to make it.. THE COST OF THE MOSFETS!!!! Well, I can probably get them cheaper (haven't looked) BUT $15 EACH!!! thats $120 JUST for MOSFETS in a stereo amp..... PLUS about $150 for the 2 transformers, $40 for the heatsinks.... THATS $310!!!! AND I STILL NEED THE AMPLIFIERS FOR THE TWEETERS!!!!! bahh, I think I will finish my speakers, then put them in storage.. WHY ARE THINGS SO EXPENSIVE!!!! Perhaps I should just bridge LM3886s or somthing similar.. BUT ITS NOT THE SAME!!!

Cool now! How many pairs do you really need and what type?

You need one or two pairs per channel and 15$ each seems much. You need 180-200 Volts, 10-15 A, 100-150 W, Rdson unimportant. If you lower your demand to 100 W = -3 dB! Think about that!