Regarding the proposed PSU wiring in post 1411:
I have a couple sets of those boards (both the synchronous rectifiers and the CRC). From what I can tell, the wiring diagram you have should work.
The CRC boards were obviously intended to be used with a different set of rectifiers in TO-220 packages. Those would make for a more compact installation, but the sync rectifiers work very well at maintaining a higher DC voltage relative to the secondary AC.
I have a couple sets of those boards (both the synchronous rectifiers and the CRC). From what I can tell, the wiring diagram you have should work.
The CRC boards were obviously intended to be used with a different set of rectifiers in TO-220 packages. Those would make for a more compact installation, but the sync rectifiers work very well at maintaining a higher DC voltage relative to the secondary AC.
I'm jealous... mine with the Tokin SIT has a habit of smoking R24 and a couple of things.
Pretty much the same temps. I tried a babysitter, it makes about a 5C difference.
But when it plays, it sounds really good. A bit stronger bass than the Sissy.
We're just waiting for ZM to tell us what to do.
Mine did the same smoking thing - opening C11 and C12. Long story short, I changed C11 and C12 to 16V caps and upped ZD3 and ZD4 to 6.2V out of an abundance of caution. Reason for R24 smoking was failure of Q1 - changed that as well after it left the world of transistors to become a lowly resistor!! Thus shorting the rails and causing R24 to attempt to act as a fuse. Used two 22R resistors as replacement for R24. All above changes seems to have done the trick.
Warning - Q1 measured fine in situ. But on changing C11, C12, ZD3 and ZD4 I opted to connect the board's power supply wires to the unpowered PS and quickly touched the positive rail wire to the PS board (with negative and 0V properly connected) while touching R24 with a finger - in case there was still a short. There was - the residual current in the PS was enough to cause instant heating of R24. So then I removed Q1 and Q2 and Q1 tested as a resistor once out of the circuit. Q2 tested fine but I replaced both. Good luck!
Warning - Q1 measured fine in situ. But on changing C11, C12, ZD3 and ZD4 I opted to connect the board's power supply wires to the unpowered PS and quickly touched the positive rail wire to the PS board (with negative and 0V properly connected) while touching R24 with a finger - in case there was still a short. There was - the residual current in the PS was enough to cause instant heating of R24. So then I removed Q1 and Q2 and Q1 tested as a resistor once out of the circuit. Q2 tested fine but I replaced both. Good luck!
^ Looking at the schematic for the XA252 SIT... C11 and C12 look to be 1000u/16V already, but ZD3 and ZD4 are spec'd as 5V6.
I guess I don't understand that part of the circuit but Randy does.
What is LS+ on the far right of the schematic?
My question is.. what's the root cause of Q1 failing?
In my amp, the right channel literally smoked, twice. The left channel did not but i noticed that its R24 showed heat discoloration so it was going for sure.
This happened twice. The 2nd time we had taken extreme steps to make sure the amp had plenty of cooling ( fans, larger heatsinks for the smaller components, new top/bottom covers fully ventilated -slots on the entire surface. I measure the temps on the internal and the heatsinks and nothing went over 51C.
We had the amp burning in for eight days with some music, not very loud. Then I decided to use it and played some music.... At some time I started to hear a "pfrrrt" sound on top of the music. If I turned down the volume it went away.... if I turned it back up it would come back after a while. Mind you, I had it playing no louder than the Sissy and I wasn't cranking "rock" music. Amp wasn't getting hotter.... For sure, I played no orchestral Can Can ...( the source of the FIRST smoke event ).
Amp was being run single ended.
I guess I don't understand that part of the circuit but Randy does.
What is LS+ on the far right of the schematic?
My question is.. what's the root cause of Q1 failing?
In my amp, the right channel literally smoked, twice. The left channel did not but i noticed that its R24 showed heat discoloration so it was going for sure.
This happened twice. The 2nd time we had taken extreme steps to make sure the amp had plenty of cooling ( fans, larger heatsinks for the smaller components, new top/bottom covers fully ventilated -slots on the entire surface. I measure the temps on the internal and the heatsinks and nothing went over 51C.
We had the amp burning in for eight days with some music, not very loud. Then I decided to use it and played some music.... At some time I started to hear a "pfrrrt" sound on top of the music. If I turned down the volume it went away.... if I turned it back up it would come back after a while. Mind you, I had it playing no louder than the Sissy and I wasn't cranking "rock" music. Amp wasn't getting hotter.... For sure, I played no orchestral Can Can ...( the source of the FIRST smoke event ).
Amp was being run single ended.
My kit came with C11 and C12 as 1000uF 6.3V. Which should be fine under normal circumstances. A friend, much smarter than me, had a look at the schematic remotely and said ZD3 and ZD4 were only there to catch excess drive to the output devices. His query was ‘where did all the current go when Q1 shorted?’ Probably into the Zeners. So change them was his recommendation although he noted going to 6.2 was still not a big margin. Tolerances on SITs may not be same as MOSFETS so maybe overdrive is possible - hence your smoking when you cranked the volume, the same thing happened to me, smoked when volume applied liberally (so not really a heat issue) - and interesting things might happen if those Zeners did their job. He has made some suggestions for putting scope probes on R24 and the output and keeping an eye on how closely they track as you crank the volume. I will try that next week.
LS+ is the positive loudspeaker output.
LS+ is the positive loudspeaker output.
My R24 was beyond melted... you should have seen the smoke... several things got melted...
Las time, per my notes, r21, r22, and r24 smoked.... plus some Q stuff and likely some caps. I didn't keep note on that.. shipped the amp back.
There's P1 to set some offset. If that's not set correctly, the current could really flow that way and drive Q1 and Q2?
How do you set P1?
I mean, I really wasn't playing it that loud. The Sissy plays louder on the same speakers with the same source...
Mostly, I'm afraid now of turning up this amp, I called it a "macho SIT" but it's turning out to be a "gigolo SIT"...
Las time, per my notes, r21, r22, and r24 smoked.... plus some Q stuff and likely some caps. I didn't keep note on that.. shipped the amp back.
There's P1 to set some offset. If that's not set correctly, the current could really flow that way and drive Q1 and Q2?
How do you set P1?
I mean, I really wasn't playing it that loud. The Sissy plays louder on the same speakers with the same source...
Mostly, I'm afraid now of turning up this amp, I called it a "macho SIT" but it's turning out to be a "gigolo SIT"...
BTW, what's the point of LT3092 and P2? Are they being set as a protection limit?
https://www.analog.com/media/en/technical-documentation/data-sheets/lt3092.pdf
https://www.analog.com/media/en/technical-documentation/data-sheets/lt3092.pdf
LT3092 helps set a constant current source, nothing to do with protection. P2 adjusts bias. It’s a fine design but I suspect that some tweaking for use with SITs may be required. My friend surmised that ZD3, supplying two gate-source voltages, might be running near its limit and, for SIT implementation, ZD3 and ZD4 might need differing values. All conjecture at this point and ZM will advise. Have faith in His Mightiness. I agree they sound very special with SITs.
good
important pcb measurements are in post #2
for both pucks mounted, no need for pcb mounting holes
for SIT at right side, two pcb mounting holes are needed
edit: post #1386 having even more measurement details
https://www.diyaudio.com/community/...2-sit-babelfish-xa252-set.373443/post-7543332
important pcb measurements are in post #2
for both pucks mounted, no need for pcb mounting holes
for SIT at right side, two pcb mounting holes are needed
edit: post #1386 having even more measurement details
https://www.diyaudio.com/community/...2-sit-babelfish-xa252-set.373443/post-7543332
Soren,
Looks like you got the right array of holes for both cases, as ZM confirmed.
Here's my method... put painter's tape / masking tape on the heatsinks. Put the unstuffed PCB where you will want it. Take a pen or marker and mark the hole locations using the PCB as your template. Once marked, have a look again to confirm the board didn't shift around while marking the various holes. In this case you'll be doing it with the MOSFETs mounted... You get the idea though.
If you're happy with the markings, then hit the marks with a punch. Confirm again. Then drill & tap. Repeat for SIT. This is a long way of saying that a paper template step is not necessary.
Looks like you got the right array of holes for both cases, as ZM confirmed.
Here's my method... put painter's tape / masking tape on the heatsinks. Put the unstuffed PCB where you will want it. Take a pen or marker and mark the hole locations using the PCB as your template. Once marked, have a look again to confirm the board didn't shift around while marking the various holes. In this case you'll be doing it with the MOSFETs mounted... You get the idea though.
If you're happy with the markings, then hit the marks with a punch. Confirm again. Then drill & tap. Repeat for SIT. This is a long way of saying that a paper template step is not necessary.
That's what I do, except I add an extra step. I tape the PCB down so that it does not shift while I mark the hole locations. It is extremely important to punch the drill locations accurately. Check, double check, even triple check. PCB mounting holes usually do not have much slop so slightly offset holes may cause standoffs to not align with the PCB holes. I know from experience.
Another thing I try for is to align holes between heatsink fins, if possible. I try to avoid blind holes and broken taps.
Another thing I try for is to align holes between heatsink fins, if possible. I try to avoid blind holes and broken taps.