^ I pulled it from my dissipation calculations accidentally (2 devices per channel to calculate the dissipation per heatsink), then I caught it after posting. I should have had one more coffee.
So, yeah... I ooked that up. Nothing unusual for a dodo. I leave all my dodoness in the open for the world to see and get a giggle. Plus, too lazy too correct the full post... just add edit at the end.
So, yeah... I ooked that up. Nothing unusual for a dodo. I leave all my dodoness in the open for the world to see and get a giggle. Plus, too lazy too correct the full post... just add edit at the end.
39v rails and 32r load doable?meaning - you wrote Iq for 2 channels, which is somewhat uncommon
this amp with 33Vdc rails and for 16R load, doable
Rout - it's an Aleph, who cares what's Rout?!
if you care for Rout, build different amp
I haven't gotten around to building my boards yet. They are on deck after I finish my ZD-25 mini.
Just looking at the schematics, the front end is substantially different from the 'standard' Aleph J as sold by the store. This alone would suggest a different sound. The JFets are running in a quasi cascode environment, in some ways similar to what Nelson used in his early Threshold amps. I have a CAS-2 which sounds wonderful, and I expect some of the signature Pass sound to be present here.
I would anticipate that The Jzm boards are just fine with 26V up to 30V power supplies. I intend to use different FETs in the output stage. Either FQH44N10 (rare) or FQA28N15 (still avail). Bias current would start at 1.6A. I have been enjoying the Aleph J SS boards with 44N10, so I might do something different with the Jzm just for fun. The choice of output FETs plays an important role in the sound of an amp. To my ears the IRFP150 devices are better suited to current sources (the upper position) and higher transconductance devices in the lower position make the amp come alive. I have found that it may take a few days of experimenting with Gate stopper resistors to find a good voice for the amp. I ended up with 220 Ohm stoppers in my Aleph J SS.
Just looking at the schematics, the front end is substantially different from the 'standard' Aleph J as sold by the store. This alone would suggest a different sound. The JFets are running in a quasi cascode environment, in some ways similar to what Nelson used in his early Threshold amps. I have a CAS-2 which sounds wonderful, and I expect some of the signature Pass sound to be present here.
I would anticipate that The Jzm boards are just fine with 26V up to 30V power supplies. I intend to use different FETs in the output stage. Either FQH44N10 (rare) or FQA28N15 (still avail). Bias current would start at 1.6A. I have been enjoying the Aleph J SS boards with 44N10, so I might do something different with the Jzm just for fun. The choice of output FETs plays an important role in the sound of an amp. To my ears the IRFP150 devices are better suited to current sources (the upper position) and higher transconductance devices in the lower position make the amp come alive. I have found that it may take a few days of experimenting with Gate stopper resistors to find a good voice for the amp. I ended up with 220 Ohm stoppers in my Aleph J SS.
Fantastic work!!!
I know this thread is for the Jzm - but I started to build the original Aleph J almost 2 years ago, and got caught up in a new job, moving cross country, and it has been sitting. I have all the parts, the power supply is 100% done and tested, and I just need to do the amp boards. This has inspired me to get on it!
I'm tempted to buy the very well priced parts kit just to have it on hand for the future.
I know this thread is for the Jzm - but I started to build the original Aleph J almost 2 years ago, and got caught up in a new job, moving cross country, and it has been sitting. I have all the parts, the power supply is 100% done and tested, and I just need to do the amp boards. This has inspired me to get on it!
I'm tempted to buy the very well priced parts kit just to have it on hand for the future.
I usually don’t play with the value of the gatestopper resistors as much and I usually just use 100 ohm Takman metal film in my own builds. That being said, what subjective differences do you hear depending on if you increase or decrease the gatestopper resistance value?
Agree with your observations regarding the AlephJzm vs Aleph J. Subjectively they are like fraternal twins…not identical. Once hearing them you realize they came from the same mother.
Best,
Anand.
not really
just more of good things
if you really need controlled change of sound, for my ears better, think of implementing buffer in-between JFet drain and modulated mosfet
I'm blessed, my ears are not catching difference between various (sane) values of mosfet gate stoppers; will leave that to you guys with golden ears
I was listening to the character of the upper end. The high transconductance FETs can sound a bit too ‘hot’ in some situations. Some recordings seemed to have a hard edge to high frequency harmonics of percussion instruments. I started with 150 Ohms for the stoppers and finally used 220 Ohm Shinkoh Tantalum film for the lower device and 220 Ohm Vishay metal film for the upper device.
Thanks poseidonsvoice, I enjoy your evaluation. I'm running this Aleph J through a pair of Otis Scan1 MK11 4 way speaker system designed and built by Colin Wait RIP who was my wife's ex. It sounds excellent but it's eventually going into the house where we currently use a pair of two way bookshelf speakers also made by Colin, powered with a cheap hybrid Valve amp from WES components.
OK from what you suggest I imagine those bookshelf speakers may work very well in my workshop with the old Aleph J and a new AlephJZM could be the best option for the larger Otis Scan1 boxes.
So I guess I'll build a new AlephJZM and see for myself. Thanks Zen Mod, you are always a legend.
OK from what you suggest I imagine those bookshelf speakers may work very well in my workshop with the old Aleph J and a new AlephJZM could be the best option for the larger Otis Scan1 boxes.
So I guess I'll build a new AlephJZM and see for myself. Thanks Zen Mod, you are always a legend.
