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Old 20th October 2013, 12:55 AM   #681
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Quote:
Originally Posted by mattmcl View Post
How important is it to heat sink Q11&12? Can I leave them on the current heatsink I made, or should those too be mounted to the chassis heatsink?
Both scenario's will work , but having the drivers on the main heatsink will be
superior for high current use.

With the drivers on a small separate HS , the amp will be a slightly overcompensated thermally , as well. (This would require a small change in
R28 ...)

OS
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Old 20th October 2013, 06:23 PM   #682
pthep is offline pthep  Canada
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Having a dilemma concerning the power supply.
Transformer has 2 secondarys (Antec8445), I have 2 35 amp bridges.
Monoblock type supply, having one bridge per amp? Or have one bridge
provide + and one provide - and split the output to the two amp boards?
What if any, differences could be expected from the two differing scenerio's?
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Old 20th October 2013, 08:51 PM   #683
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Quote:
Originally Posted by pthep View Post
Having a dilemma concerning the power supply.
Transformer has 2 secondarys (Antec8445), I have 2 35 amp bridges.
Monoblock type supply, having one bridge per amp? Or have one bridge
provide + and one provide - and split the output to the two amp boards?
What if any, differences could be expected from the two differing scenerio's?
An-8445 has two separate 45V secondaries , but you will be using both for
a 90V secondary with a center tap. That would be green/blue together = centertap (CT) , the other green and blue are the 2 AC inputs to your bridge(s).

The ideal is to have the two bridges output 60-0-60VDC separately to each amp
with each amp having it's own separate + and - rail capacitors.

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Old 21st October 2013, 06:05 PM   #684
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How would 2 bridges give you 60-0-60VDC? Each would give 60-0VDC; one 60 and the other 0 would be combined to give the effective zero.
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Old 21st October 2013, 06:30 PM   #685
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Both bridges are fed by the transformer in parallel. Each will produce a +/-60VDC output after filtering. The 0 is referring to the center tap.
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Old 21st October 2013, 07:24 PM   #686
PJN is offline PJN  United States
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Hi Guys,

I'm running into a problem firing up my amp boards and hope you can point me in the right direction. I've got my chassis built and dual mono PSU installed and working correctly. I've got 63 VDC rails out of the PSU's. I've adjusted R7, R17, and R30 on accordance with the build guide, R7 set to 85R, R17 to 500R, and R30 to 500R. I have checked all of the transistors on the heat sink to make sure there is no continuity, all are properly insulated. I'm seeing the same exact issue with both boards so I must be a symetrical screw up. When I hook up V+ and V- to the amp board, the V+ led lights, but the V- led doesn't. and I'm reading 2.7 VDC across each of the two temporary 10R resistors across the fuses on both boards. The fuses get warm but haven't burn't up yet since I quickly disconnected everything. I've attached a picture of my board. Any Ideas would be greatly appreciated.

Thanks,

PJN
Attached Images
File Type: jpg HB board.jpg (194.1 KB, 388 views)
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Old 22nd October 2013, 03:42 AM   #687
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Sounds like you may have inserted the V- LED backwards.

You are getting about 270 mA draw. As the guide says, check your work. To me that says you haven't got output transistors in the wrong spots (it would be instant smoke with 63V rails), but check anyway. You may have the wrong values in the Vbe multiplier, R28 and R29. That might be turning your outputs on too hard.

A way to check the front end without pulling the output transistors is to connect test leads from the bases of Q14 and Q15 to the end of R43 and R46 closest to the bottom of the board. That prevents the output from turning on and closes the feedback loop. If you do that and still see any significant voltage across the fuse resistors, you have a front end issue. If you can set up the front end with the jumpers your issue is the output stage or Vbe multiplier.
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Old 22nd October 2013, 05:33 AM   #688
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Quote:
Originally Posted by PJN View Post
Hi Guys,

I'm running into a problem firing up my amp boards and hope you can point me in the right direction. I've got my chassis built and dual mono PSU installed and working correctly. I've got 63 VDC rails out of the PSU's. I've adjusted R7, R17, and R30 on accordance with the build guide, R7 set to 85R, R17 to 500R, and R30 to 500R. I have checked all of the transistors on the heat sink to make sure there is no continuity, all are properly insulated. I'm seeing the same exact issue with both boards so I must be a symetrical screw up. When I hook up V+ and V- to the amp board, the V+ led lights, but the V- led doesn't. and I'm reading 2.7 VDC across each of the two temporary 10R resistors across the fuses on both boards. The fuses get warm but haven't burn't up yet since I quickly disconnected everything. I've attached a picture of my board. Any Ideas would be greatly appreciated.

Thanks,

PJN
I looked ... are the drivers isolated ? I see large washers on them ??

The VAS heatsink looks like it is "ON" the V+ rail . This could be my angle on the photo.

OS
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Old 23rd October 2013, 03:51 AM   #689
mattmcl is offline mattmcl  United States
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Quote:
Originally Posted by ostripper View Post
I looked ... are the drivers isolated ? I see large washers on them ?

OS
Pretty sure those are soft plastic washers.

PJN were the leads long enough on those small drivers to mount to the heatsink as you did, with enough for standoffs?

Also OS, I think you recommended grounding the heatsinks. The ones with the 5U Deluxe Chassis are anodized. Should I sand off the finish and ground to that, leave it unfinished...?

Last edited by mattmcl; 23rd October 2013 at 03:57 AM.
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Old 23rd October 2013, 04:13 AM   #690
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Quote:
Originally Posted by mattmcl View Post
Pretty sure those are soft plastic washers.

PJN were the leads long enough on those small drivers to mount to the heatsink as you did, with enough for standoffs?

Also OS, I think you recommended grounding the heatsinks. The ones with the 5U Deluxe Chassis are anodized. Should I sand off the finish and ground to that, leave it unfinished...?
Never saw a "5u deluxe chassis" ..... a star washer lug (below) should dig through
the anodization with enough torque.
Semi-tighten it .... move it around with pliers - then fully tighten it.

BTW - (below 2).. are the correct driver washers.

OS
Attached Images
File Type: jpg star washer lug.jpg (10.0 KB, 313 views)
File Type: jpg to-220 washer.jpg (8.2 KB, 308 views)
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Last edited by ostripper; 23rd October 2013 at 04:17 AM.
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