SX-1980 power supply problems
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SolderIron
Addicted Member
>I would appreciate any comments or suggestions.
A suggestion is to see if it is possible for an aluminum band going around the board for heat sink. That should give you enough surface area.
A suggestion is to see if it is possible for an aluminum band going around the board for heat sink. That should give you enough surface area.
tramtrist
Slug Salter
I've often wondered if the techs here could do something like this to create a "new" vintage box. Could all new parts be sourced/printed to do something like that? This person is doing just one circuit board but would it be possible to do a whole unit? Fancy thinking but you techs have so much experience at basically rebuilding these things from scratch what would be the biggest hurdle to do it?
Maybe this deserves its own thread ;p
Maybe this deserves its own thread ;p
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No it wouldn't, plus there are heat considerations for crowding most of the other components together.
There are SO many things (blind avenues, sub par results, difficult to manufacture etc) I have done for the SX-1980 and SX-1010 power supplies that I haven't had time to document well enough to do write ups.
PLUS You have those honking big, tall relays to contend with that come perilously close to the bottom cover.
I have to get my car to the point where the rear suspension isn't going to punch itself into the trunk, get one other amplifier squared away, and then I get BACK into the SX-1980 power supply board, getting a well heat sunk one working on the NEXT SX-1980 that crosses the bench - after which I set up an assembly line to rebuild SX-1980 amplifier driver cards and test them in that chassis...
So maybe by that time, I can put in some time critiquing (or pointing directions) for these revised PS boards. Right now? No way...
Good point on the relays! I will probably make some small daughter cards for the relays and mount them sideways.
I would have to say, from what I have read over these last few years, that many of the AK tech's have never designed themselves a pcb before, so it will be a challenge for them.
The mechanical design (chassis/heatsinks) would be the toughest part to sort out, next sourcing a multi-tap transformer as used on the 1980. I still think the market is very small verses the NRE costs.
Good luck on your pcb power supply design.
Hint, if you want to save some space you may want to consider doing some of it in smt.
Why, are you unable to find an equivalent relay?, I know they are out there.
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The only drop-in replacement is the Omron MY2-02-DC48, and it's rated for less than 1/2 the current of the original.
If I was going to re-design this section of the 1980, I'd use two Omron LY2-DC24 relays (coils wired in series, contacts on each in parallel), one for each channel. Might also consider using a socket to make relay swapping easy.
LY2-DC24 -> solder-tab/socket style
LY2-0-DC24 -> PCB mount
It does not have to be a Omron relay. I am using TE and Panasonic 16A relays for speakers and soft-starts these days. I do agree using two 24V coiled relays in series is a good option.
Nix the sockets, it is just more contact resistance and a place for oxidization.
655-RT314048 is a good economical part to use. It is being used on the Elektor Q-watt power amplifier design. The specs are very good. One 2 pole relay per channel which gives a 32A contact rating = should be good enough for your application.
Take a look at the Spec4 protection circuit as well.
Nix the sockets, it is just more contact resistance and a place for oxidization.
655-RT314048 is a good economical part to use. It is being used on the Elektor Q-watt power amplifier design. The specs are very good. One 2 pole relay per channel which gives a 32A contact rating = should be good enough for your application.
Take a look at the Spec4 protection circuit as well.
The LY and MY series Omron stuff has been around for 40+ years, and will probably be around for 40 more, which is why I chose them. Easily recognizable and an industry standard (several mfgr's make identical parts), they are tough, future-proof, and easy to source.
One LY relay with paralleled contacts is set for 20A. The 655-RT314048 SPDT relay is rated for 16A.
Spent a good deal of time in semiconductor wets where some benches used 100+ socketed relays. Oxidation is not an issue. And contact resistance is generally higher at the speaker-wire/speaker terminal connection than anywhere else. We'll have to agree to disagree on this one, but if I was going to redesign a 1980 PS and protection, I'd socket the relays.
One LY relay with paralleled contacts is set for 20A. The 655-RT314048 SPDT relay is rated for 16A.
Spent a good deal of time in semiconductor wets where some benches used 100+ socketed relays. Oxidation is not an issue. And contact resistance is generally higher at the speaker-wire/speaker terminal connection than anywhere else. We'll have to agree to disagree on this one, but if I was going to redesign a 1980 PS and protection, I'd socket the relays.
SolderIron
Addicted Member
>No it wouldn't, plus there are heat considerations for crowding most of the other components together. There are SO many things (blind avenues, sub par results, difficult to manufacture etc)
In many cases people just add heat sink to the original layout. The added on is limited by space available around the device. It is better than before and not necessary the best for the device. Here is a chance to do a new board, it just seems reasonable to make the heat dissipation more efficient with some thought. I would think the best place to put the heat sinks would be on an edge/edges and leave the rest of the board free for normal dissipation components. It is only a case to lay the board out to have more heat dissipation area.
In many cases people just add heat sink to the original layout. The added on is limited by space available around the device. It is better than before and not necessary the best for the device. Here is a chance to do a new board, it just seems reasonable to make the heat dissipation more efficient with some thought. I would think the best place to put the heat sinks would be on an edge/edges and leave the rest of the board free for normal dissipation components. It is only a case to lay the board out to have more heat dissipation area.
There's just too much heat to be dissipated in too small of an area with inadequate ventilation - that's the key - inadequate ventilation...
I was thinking to use 2 of 655-RT314048 instead of LY4, LY4-O has pcb terminations. Obviously both relays will work in the application, it is the designers choice what to use.
I guess we shall see what they come up with.
I agree with Mark, it is thermal design issues to be resolved.
I guess we shall see what they come up with.
I agree with Mark, it is thermal design issues to be resolved.
Thanks for all of the suggestions...
I think for the relays it just comes down to space. Since the board is being laid out from scratch the components can be moved around a bit. Also the board can be double sided to save space. I really don't want to stray too much from the original design.
Heat is a concern.... I think that moving the 80V stuff to the big heat sinks cures most of the problem. New, slightly larger heat sinks could be used for the other regs.
I should have a schematic and layout done in the next few days, I'll post it up.
I think for the relays it just comes down to space. Since the board is being laid out from scratch the components can be moved around a bit. Also the board can be double sided to save space. I really don't want to stray too much from the original design.
Heat is a concern.... I think that moving the 80V stuff to the big heat sinks cures most of the problem. New, slightly larger heat sinks could be used for the other regs.
I should have a schematic and layout done in the next few days, I'll post it up.
FYI, a while back I provided a ltspice simulation of the +/- 80V reg, re-designed to add tracking and over-current protection. You might want to at least consider OCP, (it is only a few bjts) instead of relying on the fuse or worst, smoke.
I will search/post for what thread it was put into.
http://www.audiokarma.org/forums/showthread.php?p=6879128&highlight=ltspice#post6879128
I will search/post for what thread it was put into.
http://www.audiokarma.org/forums/showthread.php?p=6879128&highlight=ltspice#post6879128
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I experimented with a number of fans. While they cured the heat problem, even a big fan (a nice Noctua 140mm) with a low speed was not anywhere close to silent. And anytime you're moving air, you're moving dirt, which would necessitate periodic disassembly and cleaning.
Edit: What I failed to make clear about Kramden's post was that small fans tend to turn at high RPM to move any appreciable amount of air, and are noisy by default. The quiet fans are large and spin slowly. Noctua has been instrumental in quiet fan design, and they have helped many computer users like me to build a tolerably quiet PC. But even with one of their biggest and quietest fans (the 140mm), the fan can be heard during quiet music passages, taking you 'out of the moment', so to speak. I put a link in Post #4 to the method I use now...moving the 80V pass transistors to the big heatsinks, installing the tallest heatsinks I can squeeze in there for the 13V and 8 & 5V supplies, removing the stock 80V heatsink altogether, and changing R202 to a 22 ohm 3W job. Both the 13V and the 8V pass transistors still get plenty toasty, but with the 80V transistors and heatsink out of the way there's tons more airflow around them and lifespan should be much better.
Edit: What I failed to make clear about Kramden's post was that small fans tend to turn at high RPM to move any appreciable amount of air, and are noisy by default. The quiet fans are large and spin slowly. Noctua has been instrumental in quiet fan design, and they have helped many computer users like me to build a tolerably quiet PC. But even with one of their biggest and quietest fans (the 140mm), the fan can be heard during quiet music passages, taking you 'out of the moment', so to speak. I put a link in Post #4 to the method I use now...moving the 80V pass transistors to the big heatsinks, installing the tallest heatsinks I can squeeze in there for the 13V and 8 & 5V supplies, removing the stock 80V heatsink altogether, and changing R202 to a 22 ohm 3W job. Both the 13V and the 8V pass transistors still get plenty toasty, but with the 80V transistors and heatsink out of the way there's tons more airflow around them and lifespan should be much better.
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SolderIron
Addicted Member
>I think that moving the 80V stuff to the big heat sinks cures most of the problem. New, slightly larger heat sinks could be used for the other regs.
The max surface area out of the way is the edge of the board. A band of Aluminum around one or two edges share by all the power devices will make thermal management the simplest.... just a thought.
The max surface area out of the way is the edge of the board. A band of Aluminum around one or two edges share by all the power devices will make thermal management the simplest.... just a thought.