I have a Sony VFET built using the boards from the Store. I'm using SK60/SJ18 instead of the originals. Bias is .5A (half the amount of the original version). All is well and it's been working fine for about a year. It runs extremely cool. I've read a couple times that the K60/J18 like a 16 ohm load better. Most recently Nelson mentions this in the article for the upcoming VFET kits for this who already have VFETS. Should I consider some sort of modification to this amp to take advantage of this load characteristic?
mu follower is main ingredient of new ones
taking ( as Pa said) 40% of work, it fools VFet of thinking that there is just half of load on it
now - either tweak existing circuit to that, or hop to Store for new pcbs
don't forget that PSU for this iteration is 36V and that Iq is in range of 1V2/0R94
you can alter that some, but not much, sweet spot etc.
taking ( as Pa said) 40% of work, it fools VFet of thinking that there is just half of load on it
now - either tweak existing circuit to that, or hop to Store for new pcbs
don't forget that PSU for this iteration is 36V and that Iq is in range of 1V2/0R94
you can alter that some, but not much, sweet spot etc.
Thanks for that information. I think I will try both suggestions. I'll get one of the new "VFET-les" kits and also see if I can modify the original push/pull circuit without ruining my Sony transistors.
It seems that modifying the original circuit might not be simple because of the power supply differences, but I need to spend some time pondering it.
Cheers.
It seems that modifying the original circuit might not be simple because of the power supply differences, but I need to spend some time pondering it.
Cheers.
I didn't realize that you have PP iteration
- in that case, no use of messing with existing pcbs ...... too much hassle and you can ruin them
- think - do you need SE or PP; if you think that you need SE, build it from scratch
- in that case, no use of messing with existing pcbs ...... too much hassle and you can ruin them
- think - do you need SE or PP; if you think that you need SE, build it from scratch
Thanks for this information. I certainly don't want to screw up the PP version. It's pleasant sounding, albeit I like the Aleph J (SemiSouth version) a bit better. I do have a set of K60 remaining so I'll order a kit from the Store when they are available.
Maybe this is an excuse to purchase a set of efficient 16 ohm speakers... (any suggestions?)
Maybe this is an excuse to purchase a set of efficient 16 ohm speakers... (any suggestions?)
sound advice. Can I quote it to my wife?you're already doomed, so just relax ..... and build and keep them all
OK, I've followed your advice to the letter...you're already doomed, so just relax ..... and build and keep them all
I just bought some genuine K82/J28s and will be able to compare the K60/J18. but I'm going to need a storage unit shortly if I keep listening to you...
Cheers.
I bought the new card 🙂 and have the 2SJ28.
Preparing:
Preparing:
- I need to change a bit the output-node/source resistor divider. Original for 2sj28 is 1,5//1.5ohm=0,75 ohm; new for 2sj18 is 0,5+0,5 ohm = 1 ohm total. So I need to lift the output, and insert the two 0,5 ohm resistors, and connect the output to the node in between. There will not be such a hole on the card probably.
- The 50k setting pot will work as well as the 25k trimmer.
redo after coffee helped me think:😕
Preparing:
Preparing:
- I need to change a bit the output-node/source resistor divider. Original for 2sj28 is 1,5//1.5ohm=0,75 ohm in one step (=pure CCS); new for 2sj18 is 0,5+0,5 ohm = 1 ohm total (=a MUfollower). So I need to linsert resistances in a different way, and insert the two 1,5 ohm resistors in parallel, and connect the output to the node in between with a short in the second hole. Then I have a CCS again.
- The 50k setting pot will work as good as the original 25k trimmer in the 2SJ28 design from last year.
- As my speaker is 6 ohms (mostly above 500Hz, because of shunted filter) might still need something in between, say 0,68 and 0,12 ohm or so, to still trick the 2SJ28 SIT into a thinking a higher load. Then I have a little bit of MuFollower; I can experiment a very little bit but lately I am not as effective any more. I have an analogue distortion meter.