almikel Posted May 15, 2013 Posted May 15, 2013 Hi guys, After reading the discussion regarding turn on/turn off thumps relating to the MiniDSP, and I'm about to head down a path of needing a MiniDSP I had a think about what the issues are. There appears to be 3 problems to solve: staged turn on/turn off under normal circumstances to avoid thumps through expensive drivers unexpected power outage - this would require a circuit that detected a loss of 230V and disconnected the speakers via relays quick enough to avoid clicks/thumps DC to the speakers caused by a fault in a power amp If you did a Likelihood vs Impact assessment they all need to be dealt with as 1 is annoying with potential damage but happens often vs 2 happens less often but could casue more damage, and 3 is the least likely but the most catastrophic. With active crossovers, and power amps connected directly to drivers things become more critical. I'm keen to come up with a total solution and welcome some discussion. Part of a total solution will likely need to have drivers connected via relays, so I'd like to exclude discussion on "relays degrade sound" and accept where relays are concerned some people consider them to be an issue in the signal path. If there's a solution that meets all the issues above without relays, bring it on. Issue 1 - Staged Turn On/Turn off The ability to have equipment turned on and off in specific order (eg pre-amp turned on first followed by power amps, Power amps turned off first followed be pre-amp) This could be accomplished by using a circuit such as the MiniDSP Isolator circuit to drive AC relays (Contactors in 240V AC speak). I haven't done much research yet to determine if the current driving ability of the Isolator circuit is sufficient to drive 1 or more AC relays, but it can drive 100mA on its REM Out, which on a lightning Google scan should be enough to drive at least 1 relay. The miniDSP isolator board provides 3 seconds of delay for turn on and turn off, non-programmable - prob enough for turn on, prob not enough for turn off for big amps and big caps. A similar effect could be gained by a muting circuit (eg part of Rod Elliot's project 33 "Loudspeaker Protection and Muting") but driving AC relays instead of relays on the speakers Lots of commercial options exist for this issue also - please provide info on cost effective options. Issue 2 - Power outage The ability to protect speakers from thumps during an unexpected power outage This issue seems to need a muting circuit connected directly to the speakers (via relays) that detects loss of 240V and disconnects as fast as possible. Rod Elliot's project 33 "Loudspeaker Protection and Muting" incorporates this capability but may require an additional implementation to solving staged turn on/off (ie an additional board) Issue 3 - Power amp failure sending a DC rail voltage to a driver I've never had a power amp fail like this (touch wood), but the outcome would be catastrophic. Based on limited (nearly no) research a DC detector circuit would be required per amp stage and driving relays for each speaker as per Rod Elliot's project 33 "Loudspeaker Protection and Muting" Note I have no affiliation with Rod - I just go to his site first when looking at these types of challenges, and usually find he's got a solution. Rod's link to his project 33 "Loudspeaker Protection and Muting" project http://sound.westhost.com/project33.htm Issue 2 and 3 appear to need the drivers connected by relays Issue 3 needs a detector per amp stage Issue 2 could be solved by a single circuit operating multiple relays issue 1 could be solved without any relays connecting directly to drivers Over to discussion... cheers Mike
davewantsmoore Posted May 15, 2013 Posted May 15, 2013 Timely! My biggest issue is "accidental disconnection of power to minidsp" (stupid humans). Leaving MiniDSP on permanently solves issue #1 #2 is extremely rare .... and can be solved with a battery/UPS on MiniDSP #3 is extremely rare On my 10x10 .... I get an extremely small transient at turn on .... but quite a loud bang on turn off (disconnect power). I have amplifiers with large caps and no mute/relay which are the worst. I need to do some more "testing" (with some expendable speaker) ..... I haven't harmed any drivers yet ... and even though (most) drivers are quite robust, my luck won't hold forever. I'm not keen to run my signal through relays. There has been some very fleeting discussion re: modding the minidsp (remove or change output cap) ... which may remove the turn off thump issue. Hopefully this turns out to be workable.... I just haven't had time to follow up. (Busy with speakers, no time for electrons)
almikel Posted May 16, 2013 Author Posted May 16, 2013 I don't have a problem with signals running through relays if they protect the drivers, but then I also have an MKT cap in series with my tweaters (56 or 68 uF can't remember which) I'm not sure of the signal paths in the DEQX, but on turn on and off there's all sorts of relay clicking going on inside it, and my stereo is much better behaved for turn on/off with the DEQX than it was with a dbx 2/3/4 pro crossover, which was so bad dbx didn't include an on/off switch. Maybe I'm inventing a solution to a problem that doesn't exist, but it was the threads on MiniDSP turn on/off that made me think, as I'm about to add a miniDSP to get a 4 way setup - maybe the battery and trickle charger is the best option for the MiniDSP. I can't recall an occasion where my stereo was going full tilt and we had a power outage. I just did a low volume power outage on my current setup (everything off at once excluding the laptop source), and the music stopped instantly, and I had the same click through the tweeter I get on a normal shutdown with no music playing - on turning everything back on, the DEQX stayed muted until I stopped and started the music. If I had the cash I'd buy the DEQX HDP4 and run it and my HDP3 as a 4 way DEQX solution. I'm still keen on others input on options such as turn on sequencers and UPS solutions that are cost effective Mike
hochopeper Posted May 16, 2013 Posted May 16, 2013 (edited) I don't have a problem with signals running through relays if they protect the drivers, but then I also have an MKT cap in series with my tweaters (56 or 68 uF can't remember which) I'm not sure of the signal paths in the DEQX, but on turn on and off there's all sorts of relay clicking going on inside it, and my stereo is much better behaved for turn on/off with the DEQX than it was with a dbx 2/3/4 pro crossover, which was so bad dbx didn't include an on/off switch. Maybe I'm inventing a solution to a problem that doesn't exist, but it was the threads on MiniDSP turn on/off that made me think, as I'm about to add a miniDSP to get a 4 way setup - maybe the battery and trickle charger is the best option for the MiniDSP. I can't recall an occasion where my stereo was going full tilt and we had a power outage. I just did a low volume power outage on my current setup (everything off at once excluding the laptop source), and the music stopped instantly, and I had the same click through the tweeter I get on a normal shutdown with no music playing - on turning everything back on, the DEQX stayed muted until I stopped and started the music. If I had the cash I'd buy the DEQX HDP4 and run it and my HDP3 as a 4 way DEQX solution. I'm still keen on others input on options such as turn on sequencers and UPS solutions that are cost effective Mike If you're keen on a battery supply, I'm about to design a little pcb for an NiMH trickle charge while the system is off and DPDT relay to disconnect charger while system is on. It'll be taking form over next few weeks as my minisharc addons progress a bit, I have a schematic and know what it needs to look like, just need to work on the PCB ... Edited May 16, 2013 by hochopeper
almikel Posted May 16, 2013 Author Posted May 16, 2013 cheers Hochopeper, Rod Elliot's views on the same topic if you haven't seen them already - they may assist http://sound.westhost.com/project98.htm If you had a board that had been tested and came with some doco - not necessarily like Rod provides, but enough to understand how it works/troubleshoot I'd be interested. cheers Mike
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