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Matrix amps with JBL718s subs

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fishsound View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fishsound Quote  Post ReplyReply Direct Link To This Post Topic: Matrix amps with JBL718s subs
    Posted: 20 May 2021 at 5:54pm
For a number of years now I have been using a Matrix UKP2100 SMPS amp and a Matrix Quantum P2100 SMPS amp, each driving one 8ohm JBL718s sub in bridge mode.  Each was supplied by Andy Hunt - one was even hand delivered by him.

With one QSC HPR122i per side, this set up has done what I've needed it to do for live bands mainly although in the last few years I've only used/needed one amp and one sub.

I've noticed that the Quantum amp output is quieter than the UKP amp with the respective volume controls set at the same position with both amps being fed the same balanced input signal.  This is also true for both channels with the amps set to stereo mode.

Any thoughts on why this might be?  Are the Quantum amp inputs less sensitive and therefore require a bigger input signal to achieve the same output volume with the controls set similarly?

Also, are these amps "good enough" to drive the SRX718s subs at higher levels if/when I need that when live events pick up again.

Many thanks
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simonp1100 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote simonp1100 Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2021 at 7:00pm
Sounds like the input sensitivity for each amplifier is different, do you know what they are ? or can you look up the specs for each amplifier. Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fishsound Quote  Post ReplyReply Direct Link To This Post Posted: 21 May 2021 at 11:51am
Thanks for the reply.

I don't have any specs for input sensitivity or overall gain.

I have checked the input DIL switch settings and the quieter amp is set to 0.7v on both channels and the louder amp is set to 1.2v on both, which makes it even stranger. 

Changing the settings confirmed the PCB labels are correct and in any case the volume level differences were nowhere near as much as the level differences between the two amps.

I've compared the two internals by eye but I can see no difference.  The DC output rails from both SMPS are the same at +97.5v and -97.5v.

Many thanks


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Post Options Post Options   Thanks (0) Thanks(0)   Quote fishsound Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 2021 at 4:57pm
I reckon I've solved the conundrum.

With the same 100Hz sine wave feeding each amp, I measured the unloaded AC output voltage of each channel for each amp with the volume controls set to maximum and both amps gave 24v (sensitivity DIL switches set to 0.7v on both amps).

Repeating this with the volume controls set at halfway, the UKP2100 gave 12v per channel but the P2100 gave 2v per channel.

Checking the volume control pots, the UKP2100 is fitted with lin pots whereas the P2100 is fitted with log pots so the UKP2100 would appear louder at low volume control settings.

This would explain why I did not notice any difference in the field as I ran the amps with the volume controls set to max.

I always understood volume controls should be log but I see no reason the change them on the UKP2100 as I will continue to use the max volume settings.

Thanks
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