Transistor for Powerful Class A Amplifier

[mike7877]

https://www.ims-refacciones-industriales.com/datasheet/MG150Q2YS40.pdf

From what I've been able to piece together, transistors are usually best used at about 10% of their rated maximum for Class A amplification.

I didn't even know such beasts like Toshiba MG150Q2YS40 exist.

150A!!

So 150 watts should be a piece of cake!

Yes?

I've been looking into how amplifiers operate and looking at various schematics determining which parts do what. It's a process lol.
This coming summer I'd like to make an amplifier!
Not necessarily super high fidelity, but I've got the transformers and capacitors to support something huge, so I'm thinking why not a class A monstrosity?

 

[TurtlePaul]

A 150 watt per channel stereo class A design should pull about 500 watts from the wall at idle? Tjat is why nobody does it. A literal space heater. It either needs a few fans or 100 lbs of copper and heat pipes.

 

[Doodski]

I've got the transformers and capacitors to support something huge, so I'm thinking why not a class A monstrosity?

Class A is a beast to fabricate and assemble. Consumes the most power at idle and generates lots of heat. Generally speaking a waste of good energy and materials. Otherwise you would learn heaps and come out of this ahead of the curve if you do it right and learn what it is you are doing. To me this is like Op amp rolling. A waste of time, energy, materials and could produce less than what you expect or less than what can buy premade. Otherwise like I tell OP amp rollers you will learn to solder, in your case get good fabrication skills and learn some theory (hopefully.) What background do you have that you can transfer into this build and what parts do you have on hand?

 

[mike7877]

A 150 watt per channel stereo class A design should pull about 500 watts from the wall at idle? Tjat is why nobody does it. A literal space heater. It either needs a few fans or 100 lbs of copper and heat pipes.

My last 140WPC Class A amp only pulled 280W idle! It had a 120mm fan blowing maybe 20cfm, kept all the transistors between 80-90C (on purpose)

 

[Doodski]

My last 140WPC Class A amp only pulled 280W idle! It had a 120mm fan blowing maybe 20cfm, kept all the transistors between 80-90C (on purpose)

What is the make and model of that amp? My last class A was 70W@8R/ch and used ~8.5A at quiescent.

 

[mike7877]

Class A is a beast to fabricate and assemble. Consumes the most power at idle and generates lots of heat. Generally speaking a waste of good energy and materials. Otherwise you would learn heaps and come out of this ahead of the curve if you do it right and learn what it is you are doing. To me this is like Op amp rolling. A waste of time, energy, materials and could produce less than what you expect or less than what can buy premade. Otherwise like I tell OP amp rollers you will learn to solder, in your case get good fabrication skills and learn some theory (hopefully.) What background do you have that you can transfer into this build and what parts do you have on hand?

Ah, I see. Part of a first semester of Electrical Engineering. I know the essential basic electrical formulas and can figure things out I don't know (like sizing a capacitor to keep ripple under a maximum at a certain load).

I can solder decently and I've got a T12 soldering iron with digital temperature control.

For this project, so far I've got a 1kVA transformer for 50V (I think, it's around 50) and I've got 4x 33,000uf capacitors

 

[mike7877]

What is the make and model of that amp? My last class A was 70W@8R/ch and used ~8.5A at quiescent.

Kinergetics KBA-280. On startup it immediately drew 540, dropping 10W every 5-10 seconds or so. As it got closer to 280, the rate at which it dropped got slower and slower. The process took about 5-6 minutes

 

[Doodski]

Ah, I see. Part of a first semester of Electrical Engineering. I know the essential basic electrical formulas and can figure things out I don't know (like sizing a capacitor to keep ripple under a maximum at a certain load).

I can solder decently and I've got a T12 soldering iron with digital temperature control.

For this project, so far I've got a 1kVA transformer for 50V (I think, it's around 50) and I've got 4x 33,000uf capacitors

For the power supply you'll need a high rating for current as the bridge is constantly outputting power. Kinergetics amps have had issue when they became vintage of the bridge failing. So make sure you go heavy duty and heatsink the bridge. I am a electronic technician so I don't know what you study in the first semester. Is it principles of electricity as in Ohms law through reactance and associated circuitry analysis? (To really abbreviate the course structure.) I can size parts, service and calibrate but designing is not my forté.

 

[Doodski]

Kinergetics KBA-280. On startup it immediately drew 540, dropping 10W every 5-10 seconds or so. As it got closer to 280, the rate at which it dropped got slower and slower. The process took about 5-6 minutes

Nice. Very efficient for a true class A amp.

 

[mike7877]

What I think would be really helpful is an amplifier schematic with the purpose of each part described, and how changes to one affect the circuit. And a list of all the pertinent aspects of transistor specifications (which are important for amplifier design and why).
If there were maybe 4 different amplifiers, two different types - one more basic, one more complex. And then maybe descriptions of different things that are sometimes added, and their purpose.
Things I've come across... haven't been that lol. So it's been interesting.

Does anyone know of any learning materials for amplifiers for people with some electrical knowledge?
I once had a 600 page e-book which taught me literally EVERYTHING about designing speakers. Everything you could need to know was in there, explained so well. The math for ridiculous band-pass enclosures was not included, but everything else was... It was like the book was written for me! I have to find it - people here would love it. (I don't remember everything in that book now, 8 years later, but I still have a great understanding. I want to find and read it again lol)

 

[mike7877]

For the power supply you'll need a high rating for current as the bridge is constantly outputting power. Kinergetics amps have had issue when they became vintage of the bridge failing. So make sure you go heavy duty and heatsink the bridge. I am a electronic technician so I don't know what you study in the first semester. Is it principles of electricity as in Ohms law through reactance and associated circuitry analysis? (To really abbreviate the course structure.) I can size parts, service and calibrate but designing is not my forté.

One class was Electrical, it was all the laws and formulas, one was digital, it was PLCs, one was AutoCAD, one was "Communications" (basically english but with a bent towards emails and forms - I don't know why we had to take it. There was a lab for Digital and a lab for Electrical. The digital lab included soldering some stuff together and programming it. Last project was making a robot (from pretty low-level parts IMO, no Arduino etc.). Electrical's lab for the first semester was wiring a house panel and most of a 1500sq ft. house into a 6x8 foot cubby-room lol.

 

[Doodski]

What I think would be really helpful is an amplifier schematic with the purpose of each part described, and how changes to one affect the circuit. And a list of all the pertinent aspects of transistor specifications (which are important for amplifier design and why).
If there were maybe 4 different amplifiers, two different types - one more basic, one more complex. And then maybe descriptions of different things that are sometimes added, and their purpose.
Things I've come across... haven't been that lol. So it's been interesting.

Does anyone know of any learning materials for amplifiers for people with some electrical knowledge?
I once had a 600 page e-book which taught me literally EVERYTHING about designing speakers. Everything you could need to know was in there, explained so well. The math for ridiculous band-pass enclosures was not included, but everything else was... It was like the book was written for me! I have to find it - people here would love it. (I don't remember everything in that book now, 8 years later, but I still have a great understanding. I want to find and read it again lol)

A 600 page textbook detailing amplifier builds and construction would indeed be a great find. If you find one let us know. I would think ~4500 to ~6000 pages of textbook study would usually be required to approach the matter when going solo

 

[mike7877]

Nice. Very efficient for a true class A amp.

Mhmm. It sounded good, too. Good bass, good everything. I feel it could've been more revealing, but you can't have everything. Then you can't have nothin! I broke it! ...I didn't realise it was on and my soldering iron touched the positive output terminal. Blew up like 8 transistors :'(

It's in a small, local, electrical shop getting repaired. I kept calling the guy every two weeks and he never made much progress, so I bought some new amps and when he's done in 5-10 years he'll call me I'm sure

 

[Doodski]

One class was Electrical, it was all the laws and formulas, one was digital, it was PLCs, one was AutoCAD, one was "Communications" (basically english but with a bent towards emails and forms - I don't know why we had to take it. There was a lab for Digital and a lab for Electrical. The digital lab included soldering some stuff together and programming it. Last project was making a robot (from pretty low-level parts IMO, no Arduino etc.). Electrical's lab for the first semester was wiring a house panel and most of a 1500sq ft. house into a 6x8 foot cubby-room lol.

IC. Half a semester of that study would be a brief introduction to Ohms Law, reactance and all the theories and labs that relate the principles of electron flow. Your going to need to study a bit more and get a good book. I recommend The Principles of Electricity Electron Flow Version by Floyd. Most universities have it on hand.

 

[mike7877]

A 600 page textbook detailing amplifier builds and construction would indeed be a great find. If you find one let us know. I would think ~4500 to ~6000 pages of textbook study would usually be required to approach the matter when going solo

Well, for a complete understanding, yes, that sounds about right to me too...
I don't need to be a world-class amp builder though, I just want a foundation -I want to be able to build basic amplifiers and troubleshoot most common ones. Maybe improve common ones.

I don't need to be able to create new types of circuits, feedback types, amplifier categories (call it a Mike's class 9 amp!)

 

[GXAlan]

A 150 watt per channel stereo class A design should pull about 500 watts from the wall at idle? Tjat is why nobody does it. A literal space heater. It either needs a few fans or 100 lbs of copper and heat pipes.

Interesting part is that it is 500W at idle and a load. In the 1990s, it’s was pretty common for typical home floor lamps to run 300W halogen bulbs. Desktop gaming GPUs pull hundreds of watts.

So the idea of 150W Class A isn’t completely absurd as long as the owners are thoughtful about powering down the step when they aren’t listening. In the grand scheme of things, it’s not all that bad.

I say this as a Class A fan, having owned both Accuphase and Marantz pure Class A devices but running all Class D Meyer Sound active speakers nowadays…

 

[mike7877]

IC. Half a semester of that study would be a brief introduction to Ohms Law, reactance and all the theories and labs that relate the principles of electron flow. Your going to need to study a bit more and get a good book. I recommend The Principles of Electricity Electron Flow Version by Floyd. Most universities have it on hand.

Aight, I'll grab one from the uni library on Monday

 

[Doodski]

Mhmm. It sounded good, too. Good bass, good everything. I feel it could've been more revealing, but you can't have everything. Then you can't have nothin! I broke it! ...I didn't realise it was on and my soldering iron touched the positive output terminal. Blew up like 8 transistors :'(

It's in a small, local, electrical shop getting repaired. I kept calling the guy every two weeks and he never made much progress, so I bought some new amps and when he's done in 5-10 years he'll call me I'm sure

Yes, the Kinergetics amps are known for going to 2 Ohms in stereo without issue. Yours does not as it blows fuses at 2 Ohms stereo when under sine wave test. Don't let that fool you though it's a great amp for sure. I provided Kinergetic warranty service for Canada for years and it was a pretty lonely job...LoL. Very few breakdowns and most where a blown fuse and test or recalibration and a clean and test of the CD players. I did have service manuals at one time but they where returned to Kinergetics upon terminating the service agreement upon changing the business operations. Service manuals for Kinergetics are to my knowledge not available now. They have become unobtanium it seems.

 

[mike7877]

Interesting part is that it is 500W at idle and a load. In the 1990s, it’s was pretty common for typical home floor lamps to run 300W halogen bulbs. Desktop gaming GPUs pull hundreds of watts.

So the idea of 150W Class A isn’t completely absurd as long as the owners are thoughtful about powering down the step when they aren’t listening. In the grand scheme of things, it’s not all that bad.

I say this as a Class A fan, having owned both Accuphase and Marantz pure Class A devices but running all Class D Meyer Sound active speakers nowadays…

Yeah, my Kinergetics didn't take more power as the volume increased either! It did with lower impedance speakers though. Not right away, but with increased volume.

If you look up its review on stereophile, you'll see, the KBA-280 was 140W into 8 ohms, 280 into 4 ohms, 520 into 2 ohms, and over 1kW into 1 ohm. There's a 10A fuse in it, though, so you can only do one channel with a 1 ohm load. Obviously THD goes up as impedance goes down, but it's not too too bad if I remember correctly.

At 8 ohms, THD+n was somewhere around 100dB. 4 was maybe 90. I don't remember what 2 or 1 was for sure, but I think 1 was like -65 to -70dB THD+n.

 

[Doodski]

Yeah, my Kinergetics didn't take more power as the volume increased either! It did with lower impedance speakers though. Not right away, but with increased volume.

If you look up its review on stereophile, you'll see, the KBA-280 was 140W into 8 ohms, 280 into 4 ohms, 520 into 2 ohms, and over 1kW into 1 ohm. There's a 10A fuse in it, though, so you can only do one channel with a 1 ohm load. Obviously THD goes up as impedance goes down, but it's not too too bad if I remember correctly.

At 8 ohms, THD+n was somewhere around 100dB. 4 was maybe 90. I don't remember what 2 or 1 was for sure, but I think 1 was like -65 to -70dB THD+n.

Yes, it is a very nice amp. Hopefully your repair depot can get proper parts.