Was hoping so I could place the board at each amplifier. Even though I guess when the buffer is finished it might not be as important. Of course, I will be pleased with what you decide to do.
Hmmm... hadn't thought about that, Rick. I was going in the opposite direction by putting switching and volume pot on the PCB. Maybe you could take this opportunity to design it in KiCAD. If you drop the buffer, it could be pretty simple. The power supply PCB is going to be separate.
Yeah, it works really well with a power buffer, like the F4 or the Holy Grail output stage. Or even a simple lateral mosfet buffer, which would be my choice.
The latest iteration builds on those mods by replacing the input and gain transistors with JFETs. That is the biggest change. It can be done on the old PCB. In fact, I was using the old PCB to do all the testing. I can post what needs to be changed, if that would be helpful.
As you know I already have the circuit working on perfboard. Too lazy to learn KICAD, aka plenty of other things to do.
I guess with the buffers I could use interconnects - since I am not using a buffer I thought close proximity is important. My input load resistor is around 8K.
Not trying to influence. I will want two of the new boards when they become available.
I guess with the buffers I could use interconnects - since I am not using a buffer I thought close proximity is important. My input load resistor is around 8K.
Not trying to influence. I will want two of the new boards when they become available.
Update existing preamps to newest JFET version.
Here's the changes to make from the schematic in post 1193:
1. Set the CCS to 14-16 mA. Measured across Rlim or R107.
2. Short zeners Z13 and Z14 to ground. We are looking for a 70-80V supply at the top of Q103. You can take the two zeners out and put a shorting wire across the holes. Or you can create a string that hits 75-80V.
3. Short C102 to ground. It might be easier to short the C102 bypass cap. Either one works.
4. Replace Q101 with J111. The drain and source of JFETs are interchangeable. So, the hole pattern on the PCB will work if you put the JFET in reverse. Just make sure the gate pin of the JFET goes in the gate hole.
5. Replace Q102 with J175 or J74. Again, the PCB hole pattern works for these JFETs.
6. Turn RV103 until you get about 40V at drain of Q101, could be measured at either end of Rlim. Be sure to set the CCS current before replacing the two JFETs.
Here's the changes to make from the schematic in post 1193:
1. Set the CCS to 14-16 mA. Measured across Rlim or R107.
2. Short zeners Z13 and Z14 to ground. We are looking for a 70-80V supply at the top of Q103. You can take the two zeners out and put a shorting wire across the holes. Or you can create a string that hits 75-80V.
3. Short C102 to ground. It might be easier to short the C102 bypass cap. Either one works.
4. Replace Q101 with J111. The drain and source of JFETs are interchangeable. So, the hole pattern on the PCB will work if you put the JFET in reverse. Just make sure the gate pin of the JFET goes in the gate hole.
5. Replace Q102 with J175 or J74. Again, the PCB hole pattern works for these JFETs.
6. Turn RV103 until you get about 40V at drain of Q101, could be measured at either end of Rlim. Be sure to set the CCS current before replacing the two JFETs.
I have done the above - though I retained the original voltage - and it sounds very fine. I have had to use larger heatsinks for the current source. Makes a great compliment to the TDV amplifiers. I have been listening to the FET version for about four months so my happiness has not been fleeting
I will not change either until Rahul comes up with his next refinement. I want to use the boards to see if that makes a difference from what I get with the perf board. My layout is very compact. I look forward to what Rahul comes up for the pcb. Good to hear there will be room for large capacitors. Whether there will be enough room for my large capacitors I will have to wait and see.
Rahul has good ears. Rahul loves music. This is made plain with these circuits.
I will not change either until Rahul comes up with his next refinement. I want to use the boards to see if that makes a difference from what I get with the perf board. My layout is very compact. I look forward to what Rahul comes up for the pcb. Good to hear there will be room for large capacitors. Whether there will be enough room for my large capacitors I will have to wait and see.
Rahul has good ears. Rahul loves music. This is made plain with these circuits.
I am using DUELUNDs which, as you know, are round. Pin spacing is near 50mm though I use different ones on the tweeter boards which are slightly smaller.
Not expecting you to accommodate those monsters. There are ways around this by mounting them underneath if that turns out to be the best way.
Looked and nowhere can I find published specifications.
Nonetheless the larger the spacing the better within your constraints.
Already looking for the best way to use stereo boards. It should not be that difficult, especially with the buffer.
Thanks, Rahul
Not expecting you to accommodate those monsters. There are ways around this by mounting them underneath if that turns out to be the best way.
Looked and nowhere can I find published specifications.
Nonetheless the larger the spacing the better within your constraints.
Already looking for the best way to use stereo boards. It should not be that difficult, especially with the buffer.
Thanks, Rahul
I'll look into a 50mm pin spacing. The largest Wima are in the 37.5mm range, so maybe that could still be used for large caps with leads.
On the CCS, the current board uses the DN25XX series as the cascode for a JFET. I don't notice a big difference to the single DN25XX CCS. So, it could be deleted and we'd save one FET.
I still haven't resolved the buffer, otherwise this design is ready to go. Going to give it a few more days of trying various combinations with the buffer.
On the CCS, the current board uses the DN25XX series as the cascode for a JFET. I don't notice a big difference to the single DN25XX CCS. So, it could be deleted and we'd save one FET.
I still haven't resolved the buffer, otherwise this design is ready to go. Going to give it a few more days of trying various combinations with the buffer.
Those dimensions sound fine.
I know this will be worth the wait.
Another one of those questions - sometimes you have the 1M resistor as a load on the input and sometimes you do not.
Is this needed? I have used them but never mind getting rid of a component.
I know this will be worth the wait.
Another one of those questions - sometimes you have the 1M resistor as a load on the input and sometimes you do not.
Is this needed? I have used them but never mind getting rid of a component.
Another one of my questions this time concerning the buffer - if the board is close to the input of the amplifier are the two capacitors necessary? The line amp output and in the amplifier input - in my dilettante's understanding it would seem to me those two capacitors would be in series the resulting value would be one-half. There is about six inches between the output of the line stage and the input of the amplifier.
If this is required give me a short explanation why if you have the time and are feeling charitable!
Do the J113s need to be matched for the buffer? If so, what values do you recommend?
Thanks,
If this is required give me a short explanation why if you have the time and are feeling charitable!
Do the J113s need to be matched for the buffer? If so, what values do you recommend?
Thanks,
While I am no expert, certainly you are correct, two caps in series makes resulting one half the value. However, if they were selected large enough, say for below 2Hz cuttof, resulting change will be negligible.
But the question is it needed for this combination?
Thanks for the re-assurance, nonetheless.
Thanks for the re-assurance, nonetheless.