48V Relay issue...

[Svart]

actually now that I think about it, it will be hard to do exactly what I said.. when you rectify to 48v you lose your mid point ground reference. you would then need to switch mode the setup to get it back.

 

[guavatone]

Maybe you could change the resistor ratio to yield 46-47V which should give you some headroom, but then a heatsink is even more important.

 

[Guest]

Did you consider powering your relays by unregulated voltage?

 

[Flatpicker]

[quote author="drpat"]...Once again it reads 18.6VAC on each leg of the secondary. That's 37.2VAC... Probably the issue, as earlier suspected...[/quote]
Yes, that's the issue. Keith's power supply will not make 48V with much less than 20VAC on each leg. It just doesn't multiply the voltage enough.

What you are seeing (voltage drop when relay is engaged) is the result of a much bigger problem, which is your 48V isn't being regulated properly to begin with. To fix it, you have to use at least a 20V-0-20V power transformer like the schematic says. The toroidals from Digi-Key come in 22V-0-22V flavors - that's what I would use.

 

[drpat]

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[Flatpicker]

Most condensers will run just fine on less than 48V. If you are not using some of the picky few that won’t (like Neumanns), why not just adjust the regulator down to 46~47V? I can’t quite make out the resistor colors in the picture, but R1 and R2 doesn’t look like 8.2K and a 240 to me. It's either running lower than 48V, it's driving a very small load, or the line voltage there is really high (~130VAC).

If you end up running 24VAC-0-24VAC using +/-15V regs, I’d be sure and heat-sink them with something. (Aluminum stand-offs work real nice for a quick ‘n dirty heat-sink.) Also, you might consider using +/-18V regs if your preamp will take it.

 

[drpat]

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[Flatpicker]

Having said all that, I just noticed that my board (the silk-screened version) has "18VAC" printed on the input pads. I've haven't tried an 18VAC source myself, but have sim'd it with loads from 500 ohms up to 10K on EW and that's just cutting it too close, if you ask me. But then, I'm an over-kill kind of guy (all my food ends up burnt when I cook :wink: ).

Edit: Oh, I see you have it going - good deal! I think +/-18V is a better choice anyway. Have fun. :thumb:

 

[drpat]

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