Ok, we know that you can't use a relay between the caps and the amp...why? because its DC and you can't switch DC (DC over 32v can't be switched easily). Ok, so lets say you cut main power w/ a relay....then the PS caps still have enough charge to blow the speakers. DOH. Rod Elliot also incorporated a "mute" circuit that would trip the relays as soon as AC was detected...ie...switch on ...and switch off BOTH throw the relays for a couple of seconds. If DC is detected, it throws the relays also. Knowing this, I see one solution. Use 2 DPDT relays per channel (i'm doing monoblocks w/ these ideas). 1 relay will switch the power coming out of the transformer. But it won't switch it completely off...it'll switch it (since its still AC) to a couple of big resistors that won't let too much power in, but will still help charge the caps a little on startup. When the time limit (2-3 seconds) is up after startup, the relay goes back, and full power goes to the caps...perhaps through a thermistor as well to help prevent current inrush. Thats besides the point. Ok, so now we know that it'll limit the current in by quite a bit at startup. In a fault, DC on the output, the relay also gets thrown and drastically cuts down the power that goes to the capacitors. Ok, thats relay #1. For relay #2, you also need a DPDT relay. Some *genius* came up w/ an idea for a "crowbar" circuit years ago. Rod Elliot told me about this. Basically the circuit detects DC and then drops a "crowbar" across the capacitors to rapidly discharge them...but unfortunately that didn't work because it also ruined the amp and arcked other caps. My idea is this, use relay #2 to do a modified crowbar circuit, only instead of a dead short across the ps caps, maybe a high wattage low resistance resistor. Maybe 200 ohms at 40 watts. I'll discharge the caps FAST...and can be done both at startup, shutdown, AND during a fault. It doesn't allow much charge during startup, shuts the amp down FAST during shutdown and fault. I have NO CLUE if it'll work or not, but was up all night one night a while ago figuring it out. Feedback would be great. Later!
-Matthew K. Olson
ps...a seperate little power supply would be fine to power the relays...but it'd be best not to...why? because Rod Elliots circuit detects its own turn on and off (AC on and off) and uses that to determine when to switch the relays. Think about it and let me know.
later!
-Matthew K. Olson
ps...a seperate little power supply would be fine to power the relays...but it'd be best not to...why? because Rod Elliots circuit detects its own turn on and off (AC on and off) and uses that to determine when to switch the relays. Think about it and let me know.
later!
I'm not worried that power is not cut & blead down in an instant, my, and most speakers for this kind of power, can stand a few minutes before melt-down. So I think a 10-30W 3-500ohm from rail-rail would bleed quick enough, and be safe enough, so you can turn your back to the amp (or find a new cold-one in the fridge).
Arne K
Arne K
Does my general idea sound good? Sounds to me like it'd work...but I haven't tried it yet. My next set of amps will have it though. I have a bunch of 20 watt wirewound resistors that I'll use in parallel for the fast bleeders...oh...also attached to the relay will be slow bleeders. Basically when the amp is powered up, I'll have 5k bleeders on ...when the amp is powering down (or just starting up), I'll have 200ohm bleeders. Powering the amp down fast I think is a good idea. Later!
-Matthew K. Olson
-Matthew K. Olson
I recently came across an EB-TA0103A Evaluation Board and am planning ot build an amplifier based on it.
For the power supply - I was thinking of using two of these SMPS:
For a volume control I thought one of these might be nice:
Stereo Stepped Attenuator
Would the 50K value be appropriate?
And this seems like good value for a chassis to put it all into:
Black Metal Chassis
Any thought's, ideas, warnings or other advice would be appreciated.
For the power supply - I was thinking of using two of these SMPS:
For a volume control I thought one of these might be nice:
Stereo Stepped Attenuator
Would the 50K value be appropriate?
And this seems like good value for a chassis to put it all into:
Black Metal Chassis
Any thought's, ideas, warnings or other advice would be appreciated.
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