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Peavey CS800 fan behaviour

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studio45 View Drop Down
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    Posted: 19 April 2013 at 1:55pm
I'm just running some 20hz signal through a new bass bin to get the woofer loosened up and I'm using a Peavey CS800 in bridge mode. The driver is 8 ohms. The amp is pretty warm to the touch near the vent on the front, and every now and then the fan is spooling up and then almost immediately spooling down again - like a 2 second burst of full speed. I normally use this amp for live music bridged into two paralleled 8 ohm bass bins for a load of two ohms per channel, and it sometimes overheats on me and stops playing for 30 seconds or so, then carries on. I don't run it with the DDT light even flashing. Is this normal behaviour for the fan in one of these amps, or has it got some kind of a fault? And is it supposed to be able to play continuously at full power into 2 ohms or what?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbinks-v2 Quote  Post ReplyReply Direct Link To This Post Posted: 19 April 2013 at 2:49pm
CS800 is 4ohm/channel minimum

CS800X is 2ohm/channel minimum

I'm guessing the fan control isn't working properly due to the load impedance. Test by running with 4 ohms load at high power for an hour or so.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 19 April 2013 at 2:58pm
the old CS range were triac controlled and continuously variable, I think the modern ones either run at tickover or flat out with nothing in between??
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 20 April 2013 at 10:15am
It is normal for the three-rack space CS 800 to operate warm even at idle. The fan cycling back in forth is common as it is responding to the impedance dip of the driver. There is a great chance that the loudspeaker is offering an impedance below 4 ohms (Which is the minimum in bridged mode) to the amplifier. This is why the amplifier is resetting itself. There is no need to operate the amplifier in bridged mode for what you are doing. Just feed the driver 10 Hz or below if you want to loosen up the suspension in stereo mode.

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Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote taurusty Quote  Post ReplyReply Direct Link To This Post Posted: 20 April 2013 at 12:22pm
Need a pic to see which version CS U have. I'd go w JBINKs tho...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 20 April 2013 at 12:39pm
It is the X version actually. Says "600w x2" under the name. I think it is due for a clean out there may be some Hamsters living in there. If that doesn't work I'm going to try glomming another fan onto the front, I have a suitable one in the cupboard. Love the sound, but can't have it cutting out on me.
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 20 April 2013 at 12:41pm
Oh and I don't specifically use bridged amps to loosen drivers up, this was just the easiest one to reach in the workshop at the time and it happens to be wired up that way :)
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 20 April 2013 at 3:13pm

Originally posted by studio45 studio45 wrote:

It is the X version actually. Says "600w x2" under the name. I think it is due for a clean out there may be some Hamsters living in there. If that doesn't work I'm going to try glomming another fan onto the front, I have a suitable one in the cupboard. Love the sound, but can't have it cutting out on me.


You seem to be overlooking that the loudspeaker is dipping below 2 ohms at the given frequency. So the amplifier is protecting itself by resetting itself. I can assure you if the amplifier were overheated, you would not be able to touch it with your hands. The fan would be operating at high speed at all times.

I own close to a dozen CS 800s and your dillema tells me that the impedance is dipping below the amplifier’s minimum load for a long duration. Bear in mind a loudspeaker’s impedance rating is nominal load. The fluctuations of a loudspeaker impedance is proportional to the frequencies the loudspeaker needs to reproduce.

Best Regards,
Elliot Thompson
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 21 April 2013 at 11:37am
Ah I see. So this is over current protection operating, not over temperature? It only seems to happen after the amp has been playing for about an hour and once it has got warm to the touch. Hence why I assumed it was heat related. I've only been using it for a few months, not quite got used to its "personality" yet :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 21 April 2013 at 11:57am
Originally posted by Elliot Thompson Elliot Thompson wrote:




I own close to a dozen CS 800s and your dillema tells me that the impedance is dipping below the amplifier’s minimum load for a long duration. Bear in mind a loudspeaker’s impedance rating is nominal load. The fluctuations of a loudspeaker impedance is proportional to the frequencies the loudspeaker needs to reproduce.

Best Regards,


This is very true Elliot,i wish people would realise this, just because they are running a pair of 4 ohm cabinets parralleled to "give 2 ohms",doesnt mean the amplifier is receiving a 2ohm load at its terminals...the actual load may be well below 2 ohms,hence all the problems with failing amps we get reported on here.
Be seeing you.
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studio45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 21 April 2013 at 2:19pm
Erk. I'll get my impedance analyser out then! I'll post the graph if it's interesting.
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