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Alto mac 2.3 hipass filter issue

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Tonskulus View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tonskulus Quote  Post ReplyReply Direct Link To This Post Topic: Alto mac 2.3 hipass filter issue
    Posted: 10 October 2017 at 7:20pm
This thing is weird. In stereomode, hipass 30hz (switchable) is working properly, cutting down the low freqs for both channels.  But if i switch this amp to a bridge mode, something weird is happening: hipass filter makes bass boost for ch2,  ch1 stays unaffected. I noticed that while watching signal leds, ch2 channel blinks more than ch1.  So I tested speaker for both channels and noticed that indeed there is much more bass in ch2. 
As far as I know, both channels should give exactly the same signal in bridge mode (only polarity should be changed for another channel and this part is working properly).

What is that? :D 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote njw Quote  Post ReplyReply Direct Link To This Post Posted: 11 October 2017 at 10:00pm
 I have noticed that the signal leds do weird things on my 2.4's when in bridge mode and hi pass filter enabled, I've never actually tried connecting a speaker to each channel when in bridge to see what's going on, I just leave the hi pass switched off as the amps are always ran off an lms anyway. 

 I would also be quite interested to know what's going on here...Confused
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Post Options Post Options   Thanks (0) Thanks(0)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 11 October 2017 at 11:15pm
Is it to do.with negative feedback being done differently while in bridge mode? Just a thought....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tonskulus Quote  Post ReplyReply Direct Link To This Post Posted: 12 October 2017 at 6:24am
I don't know... should look for schematics to see how did they do that hi-pass..thing, but could not find any.  I see this amp is definitely copied from QSC rmx somehow, but the input stage might be different. There is no DIP switch array like in QSC. 
Maybe they missed something while copying the input stage, so it is just a bug :D

I always test both channels separately @ bridge mode to make sure everything is ok.  






Edited by Tonskulus - 12 October 2017 at 6:26am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote njw Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2017 at 9:41pm
I know that on the QSC RMX and the Berry EP (RMX copy) that if the dip switches aren't set correctly then some very weird things can occur. I can only assume that Alto (or whoever the oem is!) missed a trick when they 'copied' the circuit but opted to use the three way mode switch rather than the dip switches.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2017 at 9:49pm
What does the owners manual say is the correct way to implement bridged operation? Should one or the other filters be disengaged? Should one of the gain controls be zero'd?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tonskulus Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2017 at 3:53pm
Originally posted by Conanski Conanski wrote:

What does the owners manual say is the correct way to implement bridged operation? Should one or the other filters be disengaged? Should one of the gain controls be zero'd?

From manual
"Operate MAC 2 series in Bridged Mode In this mode, the channel 1 input signal will be output from the bridge output connectors. ( The 2 RED binding post ) In this case, use the channel 1 volume control to adjust the volume, keep the volume control of channel 2 turned completely down ( counter clockwise ). Bridged mode is intended for driving loads with a total impedance of 4 ohms or greater. In Bridge Mode you will combine the power of both channels into one speaker. You will have available massive amount of power so check carefully the power handling of your speaker before operation."

And that's how I did.. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2017 at 5:26am
I suspect the ch2 filter should be disengaged too, if it doesn't mention that in the bridged section maybe it does elsewhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote njw Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2017 at 9:07pm
There is only one filter switch which operates on both channels....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2017 at 10:20pm
Ok.. well you didn't mention it yet but what does the bridged output look like?


Edited by Conanski - 17 October 2017 at 10:21pm
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