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Switching DC side of o22

post #1 of 13
3/25/10 at 3:39pm
Thread Starter 
So I am looking to build a pair of o22 in dual-mono to power a B22 and EHHA. I am trying to figure out a feasible way to switch the DC side of the o22's between the two amps. There would be two 8 pole speakOn connecters (one running between each of the amps) so you could do the switching from the front panel. I've read that using a relay in this configuration could cause damage to the o22 due to momentary short behavior (loose the sigma's soft start behavior). Perhaps I could run a couple of soft-start type circuits between the DC side and the Amps? Any ideas or advice is much appreciated.

Thanks.
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post #2 of 13
3/25/10 at 3:48pm
Why spend so much effort switching the DC side when you could build the amps with umbilical cables and just disconnect?
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post #3 of 13
3/25/10 at 4:28pm
Thread Starter 
I am planning to use umbilical power cables, but I am exploring the other option to see how difficult it really is.
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post #4 of 13
3/25/10 at 7:13pm
You risk damaging the σ22 if you switch its output. The σ22 website has warnings against this.
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post #5 of 13
3/25/10 at 8:04pm
Thread Starter 
Quote:
Originally Posted by amb View Post
You risk damaging the σ22 if you switch its output. The σ22 website has warnings against this.
I've read this in other threads as well, but I was wondering if there was a way around this such as implementing some sort of soft-start circuit between the DC out of the o22 and the amp boards.

Perhaps this is just not a real feasible option...
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post #6 of 13
3/25/10 at 8:41pm
I'm having a hard time understanding this (the problem and the proposed solution).

Why can you not switch the DC outputs of the Sigma22? Just power the Sigma22 down before doing so and you won't have a problem correct?
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post #7 of 13
3/25/10 at 9:00pm
Quote:
Originally Posted by FallenAngel View Post
I'm having a hard time understanding this (the problem and the proposed solution).

Why can you not switch the DC outputs of the Sigma22?
By design, σ22 has no output current limit protection in order to allow very large output current peaks. If the σ22 is already powered up, connecting it to a load that has rail capacitance (as most amp boards have) will cause a current surge that looks to the σ22 like a momentary short circuit. Depending on the amount of capacitance this might be enough to blow out the σ22's MOSFETs or output resistors.

This is not a problem when switching the AC mains side, because σ22 itself has a nice soft-start characteristic and will charge any load capacitance gracefully.

Quote:
Just power the Sigma22 down before doing so and you won't have a problem correct?
Correct, but user error could easily make this a less-than-desirable solution.
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post #8 of 13
3/25/10 at 9:02pm
Quote:
Originally Posted by Horio View Post
I've read this in other threads as well, but I was wondering if there was a way around this such as implementing some sort of soft-start circuit between the DC out of the o22 and the amp boards.

Perhaps this is just not a real feasible option...
The very act of "adding" anything between the σ22 and its load will adversely affect the performance of the power supply. Even a little bit of resistance will degrade the load regulation.
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post #9 of 13
3/25/10 at 9:14pm
So effectively the only viable switching solution is powering down and reconnecting the umbilicals to the new load. Is there a certain amount of time the σ22 must be left in it’s power down state?
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post #10 of 13
3/25/10 at 9:18pm
Thread Starter 
Sounds like I may need to concede to manually switching the umbilicals...
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post #11 of 13
3/25/10 at 9:26pm
If you want to get really fancy, you can design a time-delayed relay switch that will first power down the S22, then switch DC outputs, and power the S22 back up.
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post #12 of 13
3/25/10 at 11:22pm
Quote:
Originally Posted by amb View Post
The very act of "adding" anything between the σ22 and its load will adversely affect the performance of the power supply. Even a little bit of resistance will degrade the load regulation.
... including an umbilical cable?

I've convinced myself on this subject I suppose, but couldn't resist the comment
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post #13 of 13
3/26/10 at 12:39am
Yes, the umbilical cable resistance could degrade load regulation, and that is why I recommend thick cables for long runs. But here we're typically talking about milli-ohms range, whereas any sort of "soft start" circuit in series with the PSU's DC output would be quite a bit more than that.
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