Hi I have a pair of Mackie SRM450s. When applying power I get a high pitch squeal whether I have speaker leads connected or not. After flicking the low cut or contour buttons on and off it then goes away. It seems pretty random as to which button will clear the noise. Very puzzling and pretty annoying. Any help would be gratefully received. Thanks John.S

I think you mean No Lows, but if you don't have the solid lows your issue may be a blown sub speaker. check the large speaker with a direct signal if it does nothing that's your issue if it is working then your main amplifier board needs a check. with these separate components your best bet is finding the defective part, one of my Mackie's went silent once I replaced the speaker, Hope this helps.

Sounds like a problem with the horn amp in that cabinet. This is not a user fixable problem and needs to go to the shop. Here is a link to the Mackie support page where you can find a link to the repair shop list.
Mackie Tech Support

Whether you are experienced in electronics repair?
if not, try this simply way:
1: Test whether the power amplifier is still working. See figure 1.
Power OFF,adjust the EQ settings as shown in the picture.
Minimize LEVEL.Switch ON Power. Touch pin 3 at the INPUT socket by using a small screwdriver or piece of wire / cable.
Slowly raise the LEVEL,a little bit only (as the clock showed 7-8) until
sound is heard in speaker. If not heard, slowly raise again LEVEL.
If audio input signal is heard,it can simply be taken to mean
that the amplifier is working.
If LEVEL at 9 o'clock position,and the audio is not heard,
the possibility of the amplifier is damaged.
Switch OFF the power. Take it to a repair place.


2: When the Power LED is lit, but no sound,
There are many possible causes, one of which is:
I have been getting 3 times similar cases, and all are caused by
two Rectifier-Diode (either or both.) damage on the power-supply-unit.
Remove/desolder,measure, if damaged replace it with a new one.
See figure 2-3.




Hope it helps. Regards.

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Make sure you are using BALANCED interconnection cables to the speakers, either XLR or TRS connections. ALSO make sure all interconnected equipment such as the speakers AND the mixer are powered from the SAME receptacle at the venue... yes you have to run extension cords... the pro's do it so they don't have hum and other noise and don't damage their equipment.

Well, you aren't going to like this... You have a system that can deliver 250 Watts maximum RMS BECAUSE that is ALL the input power there is from the power cord. All these numbers like 800 watts a side are BS... those are PEAK power and not sustained power... More basically fake advertising that we are so accustomed to lately. The good thing is you won't blow your speakers.

The clipping is the internal protection that limits the amp from saturating.

I know you aren't going to like to hear this after spending that much... If you want more power you will need to buy another amp to get the higher sound level and use this as a mixer... One side of this should be able to drive 125 watts which SHOULD be enough to use for monitors. You should procure a sound level meter and make sure you are staying within the sound level guidelines now to protect your hearing... I know of several musicians that now are near deaf due to exposure to high sound levels...

The best way is to use a two-way crossover between the mixer and the amplifiers. In your case, the low output from teh crossover would go to the powered subs, the highs to the QSC. Use the crossover adjustment to set the frequency crossover point to get the sound quality you require.

Dan

Mackie 1604 ---> Crossover --- Highs ---> QSC --->Speakers
'
-----> Crossover --- Lows ---> Powered Subs.

You can probably trace which colors go to the smaller of the amps... Yellow is often used for tweeter but there really is no standard. Striped wire is probably the minus lead. If a pair is heavier, that would be the pair for the woofer... and red is often positive for woofer and black the minus. Searching the Mackie schematics doesn't really show colors. You could call their service dept.

DO NOT FACE THE GUITAR TOWARDS YOUR AMP. IT WILL MAKE IT SQUEAL.

Usually you attach a pair of POWERED monitor speakers to the Control Room outputs to use as monitors.

First thing is to run a known signal from a simple device like a small CD player to verify the problem.

If these are driven from a mixer, the EQ could be set to kill the highs.

Assuming it isn, something simple like an EQ setting, probably the units will have to be serviced. I know you would already have checked the EQ on the back of these things as a first step.

Remember to ALWAYS power these from the same source as the devices connected to them to avoid ground loops and damage.

Supersonic feedback can fry these. Oscillations higher pitch than you can hear can put too much power into the tweeters of these.