You need to measure the Idss of the 2sj74bl and select pairs as best you can.
You can use the P-channel measurement schematics shown here:
Transistor matching
Hope that helps.
You can use the P-channel measurement schematics shown here:
Transistor matching
Hope that helps.
I find this to be a very good description which mimics a lot of my own experience, albeit with the ACA, not the Aleph J.
Could I enquirer as to which is the Class D reference you are comparing it too?
For me, this added theatricallity made me keep both: the class A for intimate, small room acoustic rendition, and the class D on our living room... much larger space, and better suited for large orchestral works. Mine is a NuPrime ST-10.
Best regards,
Rafa.
"In a solid the heat will conduct omnidirectionally depending on the thermal resistance of the solid."
There's one less thing I don't know, thank you, Bfpca.
Thanks also to astromo and ThermalAlchemy for your comments on the subject.
I'm getting more curious about cooling these amps. If I ever manage to get a set of amp boards built and working in my 5U chassis, I'm going to do a survey of the exterior around and away from the point sources of heat with me trusty IR thermometer and see what is to be seen.
Actually in reality the heat Point is not Omnidirectional . You would think it is in a way where taught to think in some sense with what little little knowledge we are feel it sounds logical but in reality not. Anybody who welds or cast metal Will know this by experience . Example if you hold a solid copper bar in your hand half inch or 1 inch thick 2 feet long and you hold one hand at the bottom of the copper bar and another at the top of the copper bar and you have somebody put a blow torch at the center your hand at the top will get burnt really quickly well long after that your hand at the bottom can remain for a few more seconds. When you have a large ingot of metal and you attach a Thermalcouple to the top and taps a thermalcouple at the bottom with your heat source in the center you will clearly see how much of a difference there is between heat rising up words then there is down words in a solid piece of metal. That’s my daily job for my work is heat load calculations and using materials to cool items off . Unless you were in the vacuum of space with no heat load from radiation hitting your object like from a star. That’s why I have the ability to cool a transistor if I wanted to with 100 W output with a tiny cube of metal only 2 in.² by using hydronic’s or refrigerant to cool that tiny cube so heat sinks with large fins are actually not needed. That’s why I use the name Thermal Alchemy.
I can take and F5 turbo 150 W per channel and cool it with a three-quarter inch copper pipe with all the mOSFETs attached to it. It would be cool to the touch all day long.
Punkydawg on eBay has genuine Toshiba Jfets. I have a quad on the way now. Get them while you can.
Russellc
That sounds like very interesting work. With a torch, the flame will be causing large upward moving convection currents in the air next to the piece you are heating. This layer of hot moving air will certainly heat the top portion of a thin vertical rod faster than the bottom portion. Since you only need to heat the rod maybe 40c above ambient to get to hot to touch it really doesn’t take a high percentage of the torches applied heat to cause the effect you describe. Whatever mechanism is at work I don’t believe it is convection within the solid rod. That was the point I was making to the OP.
Liquid cooling or refrigerant cooling is certainly a valid cooling method for certain situations. I’ve seen it done many times using steel plates with cooling water flowing through the plate and a refrigerant based heat exchange system. Perhaps 20 rf mosfets mounted to the plate which is perhaps 10 x 18 inches. This was for 2000w plasma RF amplifiers.
The added complexity and issues with water leaks, pump issues, noise etc are enough to keep me from going there for audio.
Getting a wife to except your amplifiers in her living room
Noise with today’s equipment is no longer an issue water leaks are a thing of the past when one knows what they’re doing with the proper materials 15 to 20 years should be there expected life of your cooling system complexity extremely simple for those who have mastered it and cost no different than amount of large U5 chassis with all the bells and whistle’s . My significant other does not even like in barely excepts the size of the amp camp amp. Let alone I will eventually have for what would be a large amps trying to conceal and hide them down to the size of something less than an amp camp amp and make them look like art instead of square blocks with fins. I’m being forced to extremes to make my significant better half happy so she will allow me to continue on with my hobby and decorate the living room.
My quad just arrived 8 idss critters. I would suggest to all, get some for this amp, well worth it. Throw in a couple sets of matched pairs for the standard FirstWatt front end. Fet Audio supply is exhausted, when Punkydawg's are gone, there is one other supplier on ebay from Israel, name escapes me....that's all the legit matched sources I know of. Maybe a few members here that would let a set go?
There are a few sources for unmatched, buy, take a chance and see what matches. The LS are "available" but darn hard to find in stock.
Russellc
His name is Alexander, he’s a member of this forum and goes by the user name Alweit. I purchased my Toshiba matched pairs for my M2-x from him. He’s a good guy, polite and easy to communicate with, and his prices at the time that I purchased from him were very reasonable. He also has a vendor page on EBay. You can contact him through his DIY id, he usually responds quickly.
There's a fair bit of leeway with the gate resistor value. If you don't have
220 you might want to go a bit lower. ZM has a lot of experience with them
so I would wait for him to chime in.
One thing about using IRFP150 in place of pair of IRFP240 is that you will
be running the same current through a single device and it will get quite
hot. So it is important that you have properly sized heatsinks and that
your thermal interface between the mosfet and the heatsink be as efficient
as possible. Something like Keratherm Red will be a good choice.
220 you might want to go a bit lower. ZM has a lot of experience with them
so I would wait for him to chime in.
One thing about using IRFP150 in place of pair of IRFP240 is that you will
be running the same current through a single device and it will get quite
hot. So it is important that you have properly sized heatsinks and that
your thermal interface between the mosfet and the heatsink be as efficient
as possible. Something like Keratherm Red will be a good choice.