Hi Terry,
You have found where the current entered T22 (the burnt collector track). Where did the current come out? Is there a burn mark where it passed through the non pink mask? Could it have gone into the emitter track that passes under the top mounted heatsinks?
I am suprised that the insulator gap allowed the mask to be scraped through to allow this short!! The fact that you had insulators under the sink means that there was a gap about 0.002inch between the mask and the sink. 64Vdc does not jump across this through a mask to ground. Can anyone explain the failure mode? Ahh was the back of the sink flat or gently radiused? Or did it have a burr on the back that would easily have punctured both the insulator & mask. You still need to find WHERE the current escaped to track down which semis have gone bad.
You have found where the current entered T22 (the burnt collector track). Where did the current come out? Is there a burn mark where it passed through the non pink mask? Could it have gone into the emitter track that passes under the top mounted heatsinks?
I am suprised that the insulator gap allowed the mask to be scraped through to allow this short!! The fact that you had insulators under the sink means that there was a gap about 0.002inch between the mask and the sink. 64Vdc does not jump across this through a mask to ground. Can anyone explain the failure mode? Ahh was the back of the sink flat or gently radiused? Or did it have a burr on the back that would easily have punctured both the insulator & mask. You still need to find WHERE the current escaped to track down which semis have gone bad.
AndrewT said:
Hi Andrew,
The current escaped at the very edge of the board. There is an ever so slight ground trace running along the edge of the board and evidently when I was bolting down the little heatsink the insulator got out of position enough for the heatsink to touch the board. I made the heatsinks out of some aluminum channel that I had, They are square on the back. I'm sure this was caused by poor building techniques on my part. I did a lot of drilling and threading of things as I was building the case, after I had assembled the boards. I tried to make sure that all metal shavings were cleaned out but I can't be sure I got all of it, even though I tried. I still find little flecks sometimes. That heatsink paste is bad for that. I should have disassembled everything and cleaned better I suppose. I'm doing it now.
I haven't had a chance to dig into it yet today but I'm hoping to have it going sometime today. I will report back as I progress.
Blessings, Terry
I think I have it sorted out. Haven't tried playing music through it yet but the voltages look good. I neet to know what value fuse I should use for the rails. I have a 5 amp slow blow in the main and 0.5 amp in each side of the regulator and they are holding fine. I just need to know what value will work for output and driver rails.
Thanks, Terry
Thanks, Terry
Hi Terry
Leach specifies a 5 A fast blow. Prehaps with your PS you should go with 4 Amp. These fuses are there to protect the transformer from meltdown more than anything else. You can even go lower if you like
It doesnt really matter if a fuse blows as this amp swings no volts when it has lost one of it's rails
Leach specifies a 5 A fast blow. Prehaps with your PS you should go with 4 Amp. These fuses are there to protect the transformer from meltdown more than anything else. You can even go lower if you like
It doesnt really matter if a fuse blows as this amp swings no volts when it has lost one of it's rails
Thanks guys.
I'll use the 5A fuses then.
I thought I had it sorted out but there is still something wrong. I'm getting weird readings from the 10R resistors for the bases of the output resistors. I may have hurt them somehow. I'm going to pull them and replace with new 1 % metal film. I had used some 2% 1W units that I had. I'll report back when I'm done.
Blessings, Terry
I'll use the 5A fuses then.
I thought I had it sorted out but there is still something wrong. I'm getting weird readings from the 10R resistors for the bases of the output resistors. I may have hurt them somehow. I'm going to pull them and replace with new 1 % metal film. I had used some 2% 1W units that I had. I'll report back when I'm done.
Blessings, Terry
Hi Terry & all,
I am reading http://www.angelfire.com/ab3/mjramp/index.html and the section dealing with rail fuses talks about F2A suppling 8A peak during continuous sine wave testing. He is using single rail PSU and capacitor coupled output but the rating should still apply to our topology.
On that basis and pro rata F5A should cope with upto 20A peak. That translates into 3ohm load. I was planning using F5A but will now experiment with F3.1A and F4A to see how long they last.
I am reading http://www.angelfire.com/ab3/mjramp/index.html and the section dealing with rail fuses talks about F2A suppling 8A peak during continuous sine wave testing. He is using single rail PSU and capacitor coupled output but the rating should still apply to our topology.
On that basis and pro rata F5A should cope with upto 20A peak. That translates into 3ohm load. I was planning using F5A but will now experiment with F3.1A and F4A to see how long they last.
Well, I replaced all of the outputs, the drivers, Checked for shorts to ground and between leads on all of the transistors, Replaced the resitors going to the output bases and now I have negative rail voltage on the output again.
I'm going to stop fooling around with it until Jens has a chance to make the schematic with the proper voltages on it. Every time I think I've made a step in the right direction, I take two steps backward.
Blessings, Terry
I'm going to stop fooling around with it until Jens has a chance to make the schematic with the proper voltages on it. Every time I think I've made a step in the right direction, I take two steps backward.
Blessings, Terry
still4given said:
I know the feeling. When I was making my pre, everytime I installed a new board something would go wrong with a prior board that I thought was working, its very frustrating, especially if you don't really understand the circuit. Heck I had a transformer go bad! After 2 years I got it working and now I'm going to rip it apart and replace all the perfboard with some group buy PC boards...assuming they show up. More problems ahead! Its never-ending I tell ya...
All I can say is hang in there.
JensRasmussen said:Terry,
I will try to get that schematic done tonight, after some more house DIY
I will generate a PDF and post it here and on my webpage... is that ok for you?
Good luck
\Jens
Hi Jens,
That would be excellent.
By the way, I was wondering if you ever found time to sork up the formulas for the "to be determined" resistors in the parts list.
I used the values that jacco had postd in post #820 for my amp but I still have R68 and R9 empty.
Thanks, Terry
Hi Jens,
I haven't had a chance to compare the voltages from my amp to your chart yet, but I did notice something. In your chart, in most cases the voltages are the same on the + side as on the - side. Does your amp read that way? I know that mine is slightly different from + to - though I don't remember exactly how much. Is the difference cause by mismatched transistors? I matched mine with the hfe circuit on my meter. Is this not a good method?
It would be good to be armed with this info before I start checking things tomorrow. Anyone else feel free to jump in here with suggestions if you care.
I checked my good channel against the bad one today with the VSS fuses pulled so I could just measure the front end. They measured almost exactly the same as each other but I noticed that neither of them measured exactly the same + to -. The good channel sounds fine but if getting the voltages closer to what Jens posted is better I would like to find out how to adjust this.
Thanks, Terry
I haven't had a chance to compare the voltages from my amp to your chart yet, but I did notice something. In your chart, in most cases the voltages are the same on the + side as on the - side. Does your amp read that way? I know that mine is slightly different from + to - though I don't remember exactly how much. Is the difference cause by mismatched transistors? I matched mine with the hfe circuit on my meter. Is this not a good method?
It would be good to be armed with this info before I start checking things tomorrow. Anyone else feel free to jump in here with suggestions if you care.
I checked my good channel against the bad one today with the VSS fuses pulled so I could just measure the front end. They measured almost exactly the same as each other but I noticed that neither of them measured exactly the same + to -. The good channel sounds fine but if getting the voltages closer to what Jens posted is better I would like to find out how to adjust this.
Thanks, Terry
The given voltages are based on a simulation in Pspice.
I have net yet build an amp with 1% resistors so I have no way of making an "ok DC" measurement.
For now you should compare your measurements and get something in the region of what I whote on the schematics.
I hope this helps you forward.
\Jens
I have net yet build an amp with 1% resistors so I have no way of making an "ok DC" measurement.
For now you should compare your measurements and get something in the region of what I whote on the schematics.
I hope this helps you forward.
\Jens
Thanks Jens,
i was worried there was something wrong with the good channel. A friend suggested getting the 20v diodes as closely matched as possible as a way of getting the two sides more closely matched. I think the - side read 39V and the + side 40V. That may be why I'm getting the descrepancies. I will check that tomorrow and see if I can get them more closely matched.
Thanks for your help.
Blessings, Terry
i was worried there was something wrong with the good channel. A friend suggested getting the 20v diodes as closely matched as possible as a way of getting the two sides more closely matched. I think the - side read 39V and the + side 40V. That may be why I'm getting the descrepancies. I will check that tomorrow and see if I can get them more closely matched.
Thanks for your help.
Blessings, Terry
Hi Terry,
I posted protection resistor values for you about 2 weeks ago. Did you see them?
I know the values are very different from Leach & Jens but I spent some time trimming values to get best out of the transistors without exceeding the SOAR anywhere and suit your operational conditions.
I posted protection resistor values for you about 2 weeks ago. Did you see them?
I know the values are very different from Leach & Jens but I spent some time trimming values to get best out of the transistors without exceeding the SOAR anywhere and suit your operational conditions.
RC timeconstant on protection?
Hi all,
Q1. How do you calculate the RC time constant on the protection resistors?
Q2. Where in the short term SOAR will you end up with a preselected time constant.
I would like to substantially increase the value of the caps across the bases but do not want to go too far.
Hi all,
Q1. How do you calculate the RC time constant on the protection resistors?
Q2. Where in the short term SOAR will you end up with a preselected time constant.
I would like to substantially increase the value of the caps across the bases but do not want to go too far.
AndrewT said:
Hi Andrew,
I did see them but I had already installed the values that jacco had suggested and was looking for the value for R68 and R69 that would work with those. If they need to be replaced I will but I was hoping to find some that would work with what I already used.
Blessings, Terry
Hi guys,
OK, I have a very weird thing going on here. If I power up the back end using 100ohm resistors it powers up fine with about 2mV drop over the 100 ohm resistors. If I power up only the front end using separate 100 ohm resistors, it powers up fine as well. However, when I have both the front end and the back end powered up at the same time, the back end will only come up to about 2VDC. The rest drops over the 100ohm resistors. Actually I am bringing it up with a variac and have only run it up to about 20VDC for fear of burning the resistors. (I'm using 100ohm 5V). At 20VDC I see 18VDC drop over the resistor and 2VDC on the rails.
If I disconnect one of the front end wires the voltage will come up on the back end, but with the front end energized the back end drops to 2V. Any ideas? I'm totally puzzled.
Thanks, Terry
OK, I have a very weird thing going on here. If I power up the back end using 100ohm resistors it powers up fine with about 2mV drop over the 100 ohm resistors. If I power up only the front end using separate 100 ohm resistors, it powers up fine as well. However, when I have both the front end and the back end powered up at the same time, the back end will only come up to about 2VDC. The rest drops over the 100ohm resistors. Actually I am bringing it up with a variac and have only run it up to about 20VDC for fear of burning the resistors. (I'm using 100ohm 5V). At 20VDC I see 18VDC drop over the resistor and 2VDC on the rails.
If I disconnect one of the front end wires the voltage will come up on the back end, but with the front end energized the back end drops to 2V. Any ideas? I'm totally puzzled.
Thanks, Terry
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