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M³ amplifier build discussions thread - Page 16  

post #226 of 828
4/1/05 at 2:31pm
Thread Starter 
WSE819, how are you measuring the voltage (3V)? Between V+ and V-? Did you set all the BIAS and BIASOP trimpots to their initial setup positions (as documented on my site) before powering-up?
post #227 of 828
4/1/05 at 2:33pm
setup as per your instructions , 3v is at the power input.
post #228 of 828
4/1/05 at 2:44pm
Thread Starter 
Quote:
Originally Posted by WSE819
setup as per your instructions , 3v is at the power input.
If that's the case, it seems something is drawing too much current to cause the Elpac to "shutdown". Double check to make sure all parts are installed with proper polarity and pin-outs again. Are you using the specified BJTs, JFETs and MOSFETs? If not, what are you using and are the pin-outs compatible?

Also, when you got the 3V, are the opamps installed in their sockets?
post #229 of 828
4/1/05 at 3:14pm
All stock parts the ones I did not purchase from you came strait from your cook book, checked with and without ground opamp installed no diifeance. Led lights up and then dies as caps charge. It would seem logical to isolate power from opamps first , mosfets second, and then see if there is a problem with rails themself.
post #230 of 828
4/1/05 at 3:23pm

MMM/Parmetals Standoffs

What type of standoffs are people using (or will be using) to mount their MMM to a Par Metals or similar case?

From what I understand, my options are:
Quote:
1) Male-Female Threaded Hex Standoffs (Digikey 4314K-ND)

This would mean that I'd need to put threaded holes in the bottom of the case. Uses short screws to hold the board to the standoff.

2) Non-threaded Spacers (Digikey 1454CK-ND)

Again, I'd have to put threaded holes in the bottom of the case, only this time it'd be for the long screws going from the pcb through the spacers.

3) Plastic Clip type Standoffs (Mouse 534-1929A)

No threading holes... just drilling. No screws either.
Option #3 seems the best to me since it sounds like the least hassle and I can't see any disadvantages... but it is my first time building anything so I'm sure I'm overlooking something .

If I were to go with 1 or 2, how would I go about threading the holes I drill in the bottom of the case?
post #231 of 828
4/1/05 at 3:31pm
Thread Starter 
Quote:
Originally Posted by WSE819
All stock parts the ones I did not purchase from you came strait from your cook book, checked with and without ground opamp installed no diifeance. Led lights up and then dies as caps charge. It would seem logical to isolate power from opamps first , mosfets second, and then see if there is a problem with rails themself.
How much total C7 rail capacitance did you install? Maybe the initial charge-up current is too large for the Elpac.
post #232 of 828
4/1/05 at 3:33pm
It would depend on how high you want raise the board ( if you are mounting your pots on the board itself). I use the standoffs to mount computer motherboards it seems I always have bunch of them laying around. Another option, I buy aluminum spacers home depot and chuck in the drill to arrive at a custom hight and cut the screw to corispond.
post #233 of 828
4/1/05 at 3:35pm
I used 9 330uf caps,I could back a few out but I don't think that is top much.
post #234 of 828
4/1/05 at 3:38pm
Thread Starter 
Quote:
Originally Posted by Ob3ron
What type of standoffs are people using (or will be using) to mount their MMM to a Par Metals or similar case?
...
Don't bother threading the holes in the case. The case bottom is not thick enough to make any threading effective. Just drill standard round holes and:

1. Use spacers with machine screws and hex nuts, or,
2. Use female-female threaded standoffs and short machine screws on both ends.

Plastic clip-type standoffs are usually too flimsy, might pop-off or break over time.
post #235 of 828
4/1/05 at 3:44pm
Thread Starter 
Quote:
Originally Posted by WSE819
I used 9 330uf caps,I could back a few out but I don't think that is top much.
You'd be surprised at how much inrush current 3000uF can generate...

One other thing to check, are your BIAS trimpots installed the right way in? If not, fully-counterclockwise rotation would mean maximum bias on the MOSFETs.
post #236 of 828
4/1/05 at 4:04pm
Well I was using elpac in PPA with 2000uf , I will try backing off a few caps. Trim pots are installed correctly. I could power it off of steps from PPA but I would prefer to make sure there is not problem first.
post #237 of 828
4/2/05 at 9:04pm

M3 Initial Setup

I have one of my M3s up and running.....very cool! Need to make some casing decisions now.

A question however.....during initial setup I am reading only 15.0vdc across pins 4 and 7 of the opamps instead of the approx. 22vdc I should have there (my STEPS is putting out exactly 24vdc). I am able to adjust to .5vdc across the R5s, reading between .05 and 1.5mv dc between Is and Os, and I can easily adjust to 80mv dc across the R9s. The ac between Is and Os is running at .14mv instead of .10mv.

Is the low voltage at 4-7 OPAMPs a problem?
post #238 of 828
4/2/05 at 9:15pm
Thread Starter 
Quote:
Originally Posted by rjkdivin
A question however.....during initial setup I am reading only 15.0vdc across pins 4 and 7 of the opamps instead of the approx. 22vdc I should have there (my STEPS is putting out exactly 24vdc). I am able to adjust to .5vdc across the R5s, reading between .05 and 1.5mv dc between Is and Os, and I can easily adjust to 80mv dc across the R9s. The ac between Is and Os is running at .14mv instead of .10mv.

Is the low voltage at 4-7 OPAMPs a problem?
There should be about 0.8V drop on D1, and about 2.4V drop across Q5+ and Q5-. With a 24V input you should still have ~20.8V. So, yeah, 15V is definitely low. Are all three opamps installed when you made this measurement? If not, then check it again with all three opamps in place. If it's still low, check the voltage between the collector and emitter pins of the Q5+ and Q5- transistors to see what they are.
post #239 of 828
4/2/05 at 10:08pm

Pin 4-7 OPAMP Voltage

Quote:
Originally Posted by amb
There should be about 0.8V drop on D1, and about 2.4V drop across Q5+ and Q5-. With a 24V input you should still have ~20.8V. So, yeah, 15V is definitely low. Are all three opamps installed when you made this measurement? If not, then check it again with all three opamps in place. If it's still low, check the voltage between the collector and emitter pins of the Q5+ and Q5- transistors to see what they are.

With all the OPAMPS out, the resistance across the V+ and V- rails is 41Mohm, and the resistance across pins 4-7 on all three opamp sockets is 11.3Kohm. With the ground opamp in, and with all three opamps in and powered up, the voltage at pins 4-7 of all three opamps is 15.0vdc. The voltage across Q5+ and Q5- is .788vdc.
post #240 of 828
4/2/05 at 11:09pm
Thread Starter 
Quote:
Originally Posted by rjkdivin
With all the OPAMPS out, the resistance across the V+ and V- rails is 41Mohm
The 41M ohm reading is not real meaningful except to indicate that there is no short circuit. You're essentially reading whatever small residual charge there is in the C7 capacitors interacting with your meter.

Quote:
the resistance across pins 4-7 on all three opamp sockets is 11.3Kohm.
This is a bit interesting. Does it measure 11.3K ohm both ways (i.e., does it read the same if you reverse the meter leads)? The only resistance shunted across the opamp supply rails is the TLE2426's internal resistor divider, although the 11.3K ohm seem too low to be from that. Are all your C5+ and C5- capacitors installed in the proper polarity? Maybe one or more of these are backwards.

Quote:
With the ground opamp in, and with all three opamps in and powered up, the voltage at pins 4-7 of all three opamps is 15.0vdc. The voltage across Q5+ and Q5- is .788vdc.
0.788V is in fact about right for the drop across each of the Q5s, but then if you're only measuring 15VDC across the opamp rails, then the MOSFET rails must be at 15V + (0.788V * 2) = ~16.6V. Add the 0.8V drop across D1 and the voltage across V+ and V- should be at most ~17.4V, far short of the 24V. Something is not adding up... Check the output voltage of the STEPS again while everything is powered up and connected.

Also, what do you get if you measure the voltage across the drain leads of the N and P channel MOSFET? You could simply put the test probe on the metal tabs of each pair of the MOSFETs for this measurement.
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