Still at 20 volts and loving it.
At this voltage, I've had a bit of trouble getting my full 2 volts across the jfets while using the configuration in post #424. I couldn't get the drain of the jfet to hold 3 volts while keeping the source at 1 volt. The drain always stayed 1.75 volts, or less, over the source regardless of where I place the source voltage.
It's important to keep the source at 1 volt because of the 0R25 source resistor--I don't want more than 4 amps passing through the jfets.
The solution is to change the zener diode feeding the CCS from 9.1 volts to 5.1 volts. Now I have plenty of control over that 1 volt at the source of the jfet, and the two volt spread between source and drain.
I'm also coming to grips with the importance of adjusting the gates of the MOSFETs to control the 3 volts above the jfets--not to mention, the higher gate voltage on the MOSFETs seems to create a cleaner sound. I started at 6 volts and now have maxed P1 and P2 to get roughly 7 volts at the gates. I'll be adding more resistance above P1 and P2 in an attempt to raise the gate voltages of the MOSFETs further.
I'll keep anyone who's interested posted. What the hell, I'll post it whether anyone's interested or not...
At this voltage, I've had a bit of trouble getting my full 2 volts across the jfets while using the configuration in post #424. I couldn't get the drain of the jfet to hold 3 volts while keeping the source at 1 volt. The drain always stayed 1.75 volts, or less, over the source regardless of where I place the source voltage.
It's important to keep the source at 1 volt because of the 0R25 source resistor--I don't want more than 4 amps passing through the jfets.
The solution is to change the zener diode feeding the CCS from 9.1 volts to 5.1 volts. Now I have plenty of control over that 1 volt at the source of the jfet, and the two volt spread between source and drain.
I'm also coming to grips with the importance of adjusting the gates of the MOSFETs to control the 3 volts above the jfets--not to mention, the higher gate voltage on the MOSFETs seems to create a cleaner sound. I started at 6 volts and now have maxed P1 and P2 to get roughly 7 volts at the gates. I'll be adding more resistance above P1 and P2 in an attempt to raise the gate voltages of the MOSFETs further.
I'll keep anyone who's interested posted. What the hell, I'll post it whether anyone's interested or not...
Carpenter, I believe you are having trouble due to the cascode refrence circuit. Your R12, 13, C4 and RP1 should not be refrenced to ground for the best cascode operation of the JFET. The need to be connected to the Drain node of Q3. Then you are trully maintaining constant voltage across the JFET (and it's Source resisitor). The current source will force the Source 1 volt or so above the gate. But then, the gate Don't know what to do with that It might be O.K. that way but I'm thinking you need more of a refrence than a 220k to ground
Maybe a resistor to the supply rail above the 221k If your expecting the current source to use up 5 volts or so, then your JFET gates should be at about 4 Volts ... That would be an 884K to the + rail ...
Just some Idea's
Don't know what to do with that It might be O.K. that way but I'm thinking you need more of a refrence than a 220k to ground Maybe a resistor to the supply rail above the 221k
If your expecting the current source to use up 5 volts or so, then your JFET gates should be at about 4 Volts ... That would be an 884K to the + rail ...Just some Idea's
Last night I listened to beautiful music. "Migration" is the name of the CD. Peter Kater and Carlos Nakai are the primary musicians. Rich, well engineered--a perfect blend of flute, piano and standing bass describes their approach to quiet evening music with Native American overtones. I've never heard anything quite like this, and I've been listening to this CD for 15 years!
I listened for flaws and found none. The piano sounded perfect in the upper register where the ZV7-TJBC does it job. The jfets were operating smoothly, offering their particular, sweet, sonic signature. The flute's notes sent chills up my spine. The harmonics in the standing bass had me feeling more appreciative than at any other time in the past. Amazing.
To be perfectly candid, I have no complaints about this design. I only posted my suggestions regarding the switch in the CCS zener diode value in case someone attempted to copy my layout.
If this amp can be genuinely improved--not just changed--I'll be amazed. It's perfect as is.
I listened for flaws and found none. The piano sounded perfect in the upper register where the ZV7-TJBC does it job. The jfets were operating smoothly, offering their particular, sweet, sonic signature. The flute's notes sent chills up my spine. The harmonics in the standing bass had me feeling more appreciative than at any other time in the past. Amazing.
To be perfectly candid, I have no complaints about this design. I only posted my suggestions regarding the switch in the CCS zener diode value in case someone attempted to copy my layout.
If this amp can be genuinely improved--not just changed--I'll be amazed. It's perfect as is.
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