read Babelfish J thread , you'll find several examples what's possible when input JFets are cascoded , to save them of excessive voltage
Aleph J itself , as made , I wouldn't go above 25V rails , without cascoding tiny JFets
not being fearless amp builder , as Pa ........ I'm Chicken
My rails are at 29 volts HA. Been over a year and all good though they could pop tomorrow hehe
you're probably good , if everything else is by the book
Pa sez several times that Toshibas are tiny little but tough buggers , enduring much higher voltages than I expected to read
again , I'm Chicken
I like to keep them at 12V bay , smaller ones - 2SK2145BL - the same 12V when regg-ed , and when cascoding , 9V is value of choice
Pa sez several times that Toshibas are tiny little but tough buggers , enduring much higher voltages than I expected to read
again , I'm Chicken
I like to keep them at 12V bay , smaller ones - 2SK2145BL - the same 12V when regg-ed , and when cascoding , 9V is value of choice
My BA3 has been @ 31 volts for years. They are Toshiba, don't know if LS are as robust in this department. Maybe more so for all I know?
Russellc
I'm running my Aleph J at 25 Volts, and chose to take a couple simple precautions to preserve the precious Toshibas. I changed D1 to a 10V Zener and adjusted the R8 resistance to maintain 10 mA through the diff pair. I also used a 200 Ohm resistor at R30, which drops another 2V. Very simple tweaks and good for peace of mind.
so , you guys are not Chickens
29 volt rails and running it @420mv bias and 55c on the sink all in a 4U chassis. Living dangerous my friend
1: The hum is gone is right channel with the input shorted (only one that has appreciable hum) The DC offset on the left channel (no hum) is stable. The DC offset is stable in left. The right channel (120hz hum), the DC offset jumps 200mv.
2: I'm not sure if I get exactly what you are asking here, but switching input jacks or even disconnecting the jacks has no influence on hum.
Yes, conventional bridge rectifiers will 'eat' from 2.8 to 3.5 Volts from the ideal. Using the recommended transformer with 18V secondaries, expect about 22.2V on the rails. I have found the LVB2650 bridge rectifiers to work well in my amp. They are running hot, and dropping their minimum Vf as a result. They need good heat sinks or good thermal connection to the base plate of the chassis. A set of FEP30 diodes on the diyAudio PSU board would also work with decent heat sinks.
A good PSU is a system that needs to be matched with the intended amplifier, rail voltage and quiescent current. It deserves every bit of attention as the main channel boards.
so , you guys are not Chickens
Well, I'm chicken, I just didn't know any better and followed 6L6 build guide including the rail voltage.
Russellc
Yeah, but some guys are more chancified than others, or use differing filter schemes, or just poke in what they've got on hand that's close enough to work.
I used the 2x18's myself with the DiyAudio store PS PCB's.
I was starting from scratch, went with the tried and true and it worked out very, very well.
Success! I narrowed it down to the JFETs. Replaced and the hum is gone. Offset is stable. Thanks for all your help everyone. Now all I have to make sure I don't cook another set
