I have been tasked with rebuilding a PSU for an early 1970s Auditronics Grandson 110 for a friend. Service manual power requirements state "bipolar +/-15 VDC 2A regulated for Amplifier Circuits" and "bipolar +/-24 VDC 4A unregulated for LED's, Logic, Lamps, and Relays" The 15v supply also has a "sense" circuit. Everything goes to the console via a barrier strip on the back.
Anyone who knows about Auditronics knows the stock power supplies are weak and crap out. Tons of documentation of owners replacing them with beefier Acopians, Power One / International Power linear modules, etc. It is a very old design using an opamp regulating scheme with LM709s (predecessor to LM741...) and 2N3055 (or later, 2N3771) for current boosting. Attached schematics for the original Grandson 110 PSU and the later, slightly improved & updated "Son of Grand" 501 PSU.
Instead throwing money at recapping or rebuilding the stock supply (again), I got a really great deal on a brand new huge Power One HDD-15-5-A linear PSU module (+/-15vdc at 5A and has the built-in sense circuit). My initial plan was to keep using the old PSU rack for the +/-24v and disregard the 15v supply, but my friend would like to house the whole PSU in one enclosure for convenience sake.
Since there is no audio on the +/-24v Logic rails, I figure SMPS would be adequate for that purpose -- I plan to "daisy chain" two Meanwell LRS-100-24 modules (rated 4.5A each) with a CLC scheme I have successfully used with other, albeit smaller, projects. Based on Auditronics ancient and prob inaccurate data of 4A draw for the 24v rails, LRS-100-24 seems to be a good fit.
I've attached a schematic of how I *think* everything should get hooked up in one box. Any thoughts before I move forward? Is the R.GND / C.GND scheme to tie the 24v and 15v rails to the chassis "star" ground necessary? Or is there a better way to connect all of the common/grounds/0v etc. etc.
Should note that the console does not have a direct connection to the PSU chassis ground. See attached “interconnects” doc for a diagram.
Also regarding external fuses on the VAC lines, Meanwell has a note about external fuses on their site: https://meanwellpowersupplies.com/f...-suggestion-for-using-an-external-input-fuse/ came up with the 2A value based on the AC current being rated 1.9A but I’m assuming should prob go a little higher value…
SOME NOTES:
On the original PSU scheme, the respective “common” for both the 24V and 15V rails were tied together on the PSU’s barrier strip and also meet at the power xformer center tap.
On the functional physical PSU’s barrier strip, all respective “common” ref pins have jumper wire linking them all together to Chassis ground. Both the 24V and 15V rails (pin 2 and pin 8) have been jumped to Chassis Ground (pin 17 and/or 18 on the barrier strip), but someone ALSO jumped the “sense” common (pin 5) to these other ground connections, but shouldn't the "sense" common NOT connect to anything other than the "sense" circuit?
Also: The board never had the phantom power option operational, so the owner does not care to add phantom power at this point. If he ever wants to add phantom, I'd probably just get one of the little Meanwell RS-15-48 modules as other people have done here on the forum.
Anyone who knows about Auditronics knows the stock power supplies are weak and crap out. Tons of documentation of owners replacing them with beefier Acopians, Power One / International Power linear modules, etc. It is a very old design using an opamp regulating scheme with LM709s (predecessor to LM741...) and 2N3055 (or later, 2N3771) for current boosting. Attached schematics for the original Grandson 110 PSU and the later, slightly improved & updated "Son of Grand" 501 PSU.
Instead throwing money at recapping or rebuilding the stock supply (again), I got a really great deal on a brand new huge Power One HDD-15-5-A linear PSU module (+/-15vdc at 5A and has the built-in sense circuit). My initial plan was to keep using the old PSU rack for the +/-24v and disregard the 15v supply, but my friend would like to house the whole PSU in one enclosure for convenience sake.
Since there is no audio on the +/-24v Logic rails, I figure SMPS would be adequate for that purpose -- I plan to "daisy chain" two Meanwell LRS-100-24 modules (rated 4.5A each) with a CLC scheme I have successfully used with other, albeit smaller, projects. Based on Auditronics ancient and prob inaccurate data of 4A draw for the 24v rails, LRS-100-24 seems to be a good fit.
I've attached a schematic of how I *think* everything should get hooked up in one box. Any thoughts before I move forward? Is the R.GND / C.GND scheme to tie the 24v and 15v rails to the chassis "star" ground necessary? Or is there a better way to connect all of the common/grounds/0v etc. etc.
Should note that the console does not have a direct connection to the PSU chassis ground. See attached “interconnects” doc for a diagram.
Also regarding external fuses on the VAC lines, Meanwell has a note about external fuses on their site: https://meanwellpowersupplies.com/f...-suggestion-for-using-an-external-input-fuse/ came up with the 2A value based on the AC current being rated 1.9A but I’m assuming should prob go a little higher value…
SOME NOTES:
On the original PSU scheme, the respective “common” for both the 24V and 15V rails were tied together on the PSU’s barrier strip and also meet at the power xformer center tap.
On the functional physical PSU’s barrier strip, all respective “common” ref pins have jumper wire linking them all together to Chassis ground. Both the 24V and 15V rails (pin 2 and pin 8) have been jumped to Chassis Ground (pin 17 and/or 18 on the barrier strip), but someone ALSO jumped the “sense” common (pin 5) to these other ground connections, but shouldn't the "sense" common NOT connect to anything other than the "sense" circuit?
Also: The board never had the phantom power option operational, so the owner does not care to add phantom power at this point. If he ever wants to add phantom, I'd probably just get one of the little Meanwell RS-15-48 modules as other people have done here on the forum.
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