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Is it safe to run this amp with this speaker setup?


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#1 mikehende

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Posted 14 January 2014 - 08:08 AM

Hey guys, I have a Crown MA 3600, I am using one channel to run a Double 18" Sonic Subwoofer and the other channel for my Peavey Tops which I run Parallel, first thing I'd like to confirm please is if both speakers are running this amp in 4 ohms mode as the sub's both 18" woofers are not run parallel [I think] since the wires from both woofers are connected to one connector?

#2 Stephane

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Posted 15 January 2014 - 08:13 AM

Safe for the amplifier or speakers? could you please list your speakers (brand and model), that would help to figure out stuff.

#3 mikehende

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Posted 15 January 2014 - 09:58 AM

Safe for the amp? This is the Sonic Speaker:

www.sonicspeaker.com/r218sub.htm

and these are the biampable tops like what I have, as mentioned they are run full range with one speaker connected to the other then that goes back to the amp so I am guessing this is 4 ohms mode? If so, is the Sonic sub running at 8 or 4 ohms please?

http://www.ebay.com/...=p2047675.l2557

#4 Stephane

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Posted 16 January 2014 - 12:24 AM

So according to the spec sheet your sub is 4 ohms. for your peavey speakers they are good for about 300 watts each, so would be careful to not push the amp too much because chance are you will burn some voice coil. Yoursub i'm not familar with the brand and by looking at the spec sheet they are not concistent with their spec on one page they say 1200watts  rms and the other 1600 watts rms. I would make sure to have a hipass set around 40 or 45 hz to avoid damage again. For your other question your amp is running at 4 ohms on but side so no big deal for the amp, it is rated for 2 ohms.

#5 mikehende

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Posted 16 January 2014 - 07:46 AM

Thanks for the advice on the speakers, I am not concerned about them really as I use a general rule when playing music, if I hear any distortion or see the clipping lights going off I cut back on the volume, my main concern with this is running the amp with "mis-matched" ohms per channel, since you've confirmed that with my current speaker usage, both channels on the amp amps are running in 4 ohms mode [thanks again] then this is safe for the amp so far so good. Let me throw one more issue at you if you won't mind please? I am thinking of adding one single 15" sub to the sonic meaning I plug the 15" sub directly into the Sonic's connector so would this mean that amp channel which runs the sonic will be now running at 2ohms? If yes, then would it be ok [for the amp] to run speakers in mis-matched mode so as in this case 4 ohms on one side for the Peavey tops and 2 ohms on the other channel for the sonci and the 15" subs?

#6 joust

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Posted 16 January 2014 - 09:07 AM

The 3600 will run hot at two ohms but if not cranked up, should be good. As you mention, if clipping occurs bring down the levels!
On the issue of running at different ohmages, there should be no issues with the 3600: It has two independant power supplies!
Note: In Parallel mode, the amp could run at 1 ohm, in mono mind you.
Note 2 : For better thermal management, especially at high levels, refurbish the output stages at a regular intervals. It will make the amp run better!

Alain

#7 mikehende

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Posted 16 January 2014 - 09:31 AM

View Postjoust, on 16 January 2014 - 09:07 AM, said:

Note 2 : For better thermal management, especially at high levels, refurbish the output stages at a regular intervals. It will make the amp run better!
Alain

Thanks, can you explain the above please as I am not understanding what you mean by "refurbish the output stages at a regular intervals"?

#8 joust

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Posted 16 January 2014 - 10:41 AM

Amplifiers generate heat. Heat is generated by current passing through the [internal rsistance of the] output devices. An unfortunate property of bi-polar transistors is thermal runaway : current passing through a transistor generates heat; Heat lowers the internal resistance of the transistor and thus, passes more current; Passing more current, generates more heat which lowers the internal resistance of the transistor... until the current level destroys the device. To alleviate and cool down the output devices, engineers use 'heatsinks'.
Transistors, especially output devices, are clamped down on heatsinks. To transfer the heat adequately, a thin layer of thermal compound is applied on the output device and heatsink before the transistor is clamped down. After time and multiple heat-cooling cycles, the paste looses coherence and becomes dust. Dust transfers very badly heat and the output device suffers from lack of cooling. This is where I come in!
A refurbishment entails the removal of all output devices, removal and cleaning of all surfaces and application of new thermal compound to both the output devices and heatsinks. A thin layer please! Then a reinstallation of the output devices. Then, try to locate and also refurbish drivers, pre-drivers, the bias transistor and thermal sensor, where applicable.
Once the refurb is done, you will need to verify and adjust the bias levels. For Crown amps, look into the owners manual for correct location and adjustment of these bias levels. I usually adjust between 325mV and 350mV. If necessary, the owner manual states that the ODEP can also need adjustments. I use an IR thermometer for thermal measurements.
Using sine @ 1KHz : At 8 ohms, I can run an amplifier output into soft clipping for hours.
At 4 ohms, I can run the amp at clipping and then draw back a notch under clipping. ODEP may click in after some time.
At 2 ohms, I run the amp below clipping, before ODEP clicks in.
I've never tried at 1 ohm :) Beware of your AC supply! The amp will run as well as it can as long as it gets all the energy from the wall. Don't run an amp under-powered.

I hope this helps!

Alain

#9 mikehende

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Posted 16 January 2014 - 10:47 AM

well, that's a lot of technical knowledge, really appreciate you taking the time to explain all of this and I thank both you and Stephane for your help and advice!

#10 dakos

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Posted 17 January 2014 - 01:55 PM

Thank you for the educative post J :)