even more lateral fets
#16 Re: even more lateral fets
a bit more....
I don't like tapping blind holes, I have tried and failed in the past...so my M.O over the last 20 years has been to drill through heatsinks between the fins and attach circuit boards to the sinks with nuts and bolts and spacers.
this build was slightly different because I had the pcbs made by pcbway and the mounting holes didn't match the fin spacing on the heatsinks, which already had lots of blind holes already tapped......
so....I cut some 6mm Nylon which I drilled and screwed to the heatsinks using the tapped holes that were already on the sinks, the nylon shapes provided a base to screw the pcbs to.
the pics show the nylon sheet which I cut on the bandsaw...
I don't like tapping blind holes, I have tried and failed in the past...so my M.O over the last 20 years has been to drill through heatsinks between the fins and attach circuit boards to the sinks with nuts and bolts and spacers.
this build was slightly different because I had the pcbs made by pcbway and the mounting holes didn't match the fin spacing on the heatsinks, which already had lots of blind holes already tapped......
so....I cut some 6mm Nylon which I drilled and screwed to the heatsinks using the tapped holes that were already on the sinks, the nylon shapes provided a base to screw the pcbs to.
the pics show the nylon sheet which I cut on the bandsaw...
There's nowhere you can be that isn't where you're meant to be
- pre65
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#17 Re: even more lateral fets
If you are not requiring full thread strength, then using a drill a gnats bigger than specified can make things easier.
And/or, check the drill with a vernier (or micrometer) to make sure they are what you think they are, it's caught me out in the past.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#18 Re: even more lateral fets
moving on....
There's nowhere you can be that isn't where you're meant to be
- pre65
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#19 Re: even more lateral fets
Looks good.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
- IslandPink
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#20 Re: even more lateral fets
"Shiny shiny"
"Once you find out ... the Circumstances ; then you can go out"
#21 Re: even more lateral fets
bit more....
got it running in biased at 2 amps
here's the square wave at 10k.....
at this point it clips at 2.52v i/p - 6.74v o/p - 5.67 watts
got it running in biased at 2 amps
here's the square wave at 10k.....
at this point it clips at 2.52v i/p - 6.74v o/p - 5.67 watts
There's nowhere you can be that isn't where you're meant to be
#22 Re: even more lateral fets
waily waily.....
major disappointment......plugged into the main system and switched on.....serious buzz....
scratched head a bit...
took out the earth lift for the balanced supply to the audio circuit, bearing in mind that the meanwells only have chasis ground direct to the incoming earth point. So everything is connected to the incoming earth point.
even bigger buzz.
the volume masks the buzz but....we know it's there.
with hand on the chassis the buzz is ever so slightly reduced.
immediate thoughts suspect the smps, which is very close to the boards....in the last incarnation the smps was underneath the main amp so it was slightly further away from the bits that matter. In addition the wiring is a bit of a rat's nest.
back on the bench
major disappointment......plugged into the main system and switched on.....serious buzz....
scratched head a bit...
took out the earth lift for the balanced supply to the audio circuit, bearing in mind that the meanwells only have chasis ground direct to the incoming earth point. So everything is connected to the incoming earth point.
even bigger buzz.
the volume masks the buzz but....we know it's there.
with hand on the chassis the buzz is ever so slightly reduced.
immediate thoughts suspect the smps, which is very close to the boards....in the last incarnation the smps was underneath the main amp so it was slightly further away from the bits that matter. In addition the wiring is a bit of a rat's nest.
back on the bench
There's nowhere you can be that isn't where you're meant to be
#23 Re: even more lateral fets
a bit more..
I've taken the smps out of the chassis and I'm running one channel with the smps well away from the chassis.
This is a shot of the input and output on the scope with the input shorted. The input trace has me well curious.
If I put my hand on the chassis both traces go to a flat line for about 3 or 4 seconds and then resume the traces shown with my hand still on the chassis.
Anybody got any suggestions.....could I have excited the opamp? what about the output trace being inverted?
I've taken the smps out of the chassis and I'm running one channel with the smps well away from the chassis.
This is a shot of the input and output on the scope with the input shorted. The input trace has me well curious.
If I put my hand on the chassis both traces go to a flat line for about 3 or 4 seconds and then resume the traces shown with my hand still on the chassis.
Anybody got any suggestions.....could I have excited the opamp? what about the output trace being inverted?
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#24 Re: even more lateral fets
I doubt the SMPS runs at 9.1 MHz ... I'm suspecting parasitic oscillation? You've banged up the DC, and the chokes are different...? Are the amps working into a load?
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#25 Re: even more lateral fets
I spent a lot of time trying to understand what constitutes a capacitive load and thought I'd avoided it...but... I suspect that might be the problem...
I'm going to cut the capacitors out of the feedback loop to see if it makes any difference....any further suggestions would be gratefully received..
I'm going to cut the capacitors out of the feedback loop to see if it makes any difference....any further suggestions would be gratefully received..
There's nowhere you can be that isn't where you're meant to be
#26 Re: even more lateral fets
more head scratching
with respect to this circuit, same as the previous mofo except larger chokes and opa2134 instead of ltc1150...
here is the ouput from the opamp. With opamp powered but the fet unpowered with input shorted...this looks acceptable to me..
here is the output from the opamp. With opamp powered and fet powered with input shorted....
I've double checked and the sk1058 has input capacitance of 600pf..I didn't think this was much and it was the same device as the last version which had no problems.
there are reports on the web that the opa2134 show instability for no apparent reason..mmmm...
with respect to this circuit, same as the previous mofo except larger chokes and opa2134 instead of ltc1150...
here is the ouput from the opamp. With opamp powered but the fet unpowered with input shorted...this looks acceptable to me..
here is the output from the opamp. With opamp powered and fet powered with input shorted....
I've double checked and the sk1058 has input capacitance of 600pf..I didn't think this was much and it was the same device as the last version which had no problems.
there are reports on the web that the opa2134 show instability for no apparent reason..mmmm...
There's nowhere you can be that isn't where you're meant to be
#27 Re: even more lateral fets
What does the squarewave response look like on the output of the op amp? The general response you showed earlier looked a little rolled off on the leading edges. That may be the result of the 220R (r7) gate resistor OR the 15p (c3) compensation cap. Looking at the output of the op amp would hopefully show which is rolling that off.
My gut feeling is that its worth increasing the size of c3 and see if that helps the op amp to be stable. The mosfet gate capacitance is probably not going to be there when its not passing current.
Also, I have found that gate resistors can be double edged swords in that they will damp the HF response, but they can also allow the gate to do its thing less connected to the driver.
Not sure how it would work out, but my gut suggests that it would be nice to build the gate voltage from p2 into the op amp stage, so you could directly couple the op amp output to the mosfet avoiding C4.
My gut feeling is that its worth increasing the size of c3 and see if that helps the op amp to be stable. The mosfet gate capacitance is probably not going to be there when its not passing current.
Also, I have found that gate resistors can be double edged swords in that they will damp the HF response, but they can also allow the gate to do its thing less connected to the driver.
Not sure how it would work out, but my gut suggests that it would be nice to build the gate voltage from p2 into the op amp stage, so you could directly couple the op amp output to the mosfet avoiding C4.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#28 Re: even more lateral fets
I'm unable to reproduce the conditions at first switch on...something has popped/changed
here is the 10k square at the output of the opamp with no power to the fet...
and here with power to the fet...
here is the 10k square at the output of the opamp with no power to the fet...
and here with power to the fet...
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#29 Re: even more lateral fets
I would try increasing R7 and see if it makes it any better.
Also I would experiment with a 100R between the op amp output and C4.
Also I would experiment with a 100R between the op amp output and C4.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#30 Re: even more lateral fets
Thanks for looking
At the moment I don't think I'm going to acheive much because something fundamental has changed since first switching on. At first I had a buzz, but it produced a valid output, both sine and square, and it played music.....
now there is serious corruption. The output from the opamp looks valid as long as there is no power to the fet but the fet is now doing something it didn't do when first switched on....
I'm going to take the chassis apart and put 1 channel on a bread board and do some substitutions.....I think testing the fet might be first in line.
edit: got the lhs sink off the chassis and tested before taking the pcb off...and....the 220R gate stopper smoked..it's gone a lovely shade of brown but it still registers 219R. Not sure why so much current should run through the gate but the fet does look suspect...
onward
At the moment I don't think I'm going to acheive much because something fundamental has changed since first switching on. At first I had a buzz, but it produced a valid output, both sine and square, and it played music.....
now there is serious corruption. The output from the opamp looks valid as long as there is no power to the fet but the fet is now doing something it didn't do when first switched on....
I'm going to take the chassis apart and put 1 channel on a bread board and do some substitutions.....I think testing the fet might be first in line.
edit: got the lhs sink off the chassis and tested before taking the pcb off...and....the 220R gate stopper smoked..it's gone a lovely shade of brown but it still registers 219R. Not sure why so much current should run through the gate but the fet does look suspect...
onward
There's nowhere you can be that isn't where you're meant to be