crown macrotech parallel mono mode questions

[monekh]

was just asked about parallel mono mode by a friend which led me to this diagram on the back of a macrotech (on the far right next to the binding posts) and made me question if I've been using this mode incorrectly myself...



I've been running 4x T60s off a macrotech 3600 in parallel mono mode, using a single input to channel 1, but using both output channels - 2x T60s on each, 4 ohms per channel. obviously the 2 sub outputs from the DSP are already in mono, so I could just connect them both to the amp and leave it in stereo mode, but only using 1 or them means I can use the other for a 2nd 3600 powering another 4x T60s the same way, which occasionally happens. I set it up like this without checking, as it was clear that the single input was being sent to both channels, and apart from that I assumed the amp would function the same as in stereo.

but after seeing this diagram and trying to find more information, it seems like maybe there's more to it than that with certain crown amps, and that parallel mono is designed to enable loads down to 1 ohm, runnning off output channel 1 only with a jumper across the channel 1 and 2 positive terminals. Setting it up like this would still allow me to run 4x T60s off the same amp, with the advantage of only having to run a single cable to the stack, but some instinct is telling me that 2 channels at 4 ohms is better and safer than 1 channel at 2 ohms, despite the clear instructions on the back of the amp...

my questions are:
1. am I doing any damage to amp or drivers, or increasing the risk of anything bad happening, by using both channels in parallel mono mode?
2. would there be any advantage, beyond saving cable, to switching to the 'correct' jumper cable / single channel parallel mono wiring?
3. is my instinct right or is 1 channel at 2 ohms all the same to the amp / drivers in this case?

thanks!

[himhimself]

Interesting question, monekh. Made me do a little exploring, so thanks for that - always good to learn something new. As you've found, Crown's version of parallel mono is very different than other amps "parallel" meaning just an internal Y connecting input A to B. Found this thread, maybe you've already seen it, but it has some good info about the Crown micro/macrotech amps and the use of parallel-mono mode: https://forums.prosoundweb.com/index.php?topic=74724.0

[Bruce Weldy]

You didn't mention which model you have.....600,1200,2400?

If it's the 2400, I'd run it in stereo mode (4ohms per side) - BUT - you can still just parallel the inputs so that you are sending the mono sub out from your DSP via one cable. The input connectors on the amp are in parallel, so you could plug into channel one with an XLR from your DSP, then use a TRS 1/4" jumper from channel 1 to 2. That would allow you to still use the Channel 2 XLR to feed another amp wired the same way for two more channels of 4 ohm power.

Make sense? If not, I can go into more detail. My sub amps are all wired this way.....(except that they are newer and have an internal setting that lets you Y the input to both channels without having to use a jumper). I use a jumper to go to the next amp and then from that one to the next.

[Bill Fitzmaurice]

Compared to one channel parallel bridging gives the same voltage into a halved impedance load, series bridging gives double the voltage into twice the impedance load. Which to use depends on the impedance load. If it's lower than the single channel rating use parallel, if it's higher use series.

[monekh]

Interesting question, monekh. Made me do a little exploring, so thanks for that - always good to learn something new. As you've found, Crown's version of parallel mono is very different than other amps "parallel" meaning just an internal Y connecting input A to B. Found this thread, maybe you've already seen it, but it has some good info about the Crown micro/macrotech amps and the use of parallel-mono mode: https://forums.prosoundweb.com/index.php?topic=74724.0

yes I came across that thread, I've never had any issues or 'crunchiness' while using both channels with the amp set on parallel mono, but reading that scared me that something bad like that might happen at some point, or already be happening without me noticing!

You didn't mention which model you have.....600,1200,2400?

If it's the 2400, I'd run it in stereo mode (4ohms per side) - BUT - you can still just parallel the inputs so that you are sending the mono sub out from your DSP via one cable. The input connectors on the amp are in parallel, so you could plug into channel one with an XLR from your DSP, then use a TRS 1/4" jumper from channel 1 to 2. That would allow you to still use the Channel 2 XLR to feed another amp wired the same way for two more channels of 4 ohm power.

Make sense? If not, I can go into more detail. My sub amps are all wired this way.....(except that they are newer and have an internal setting that lets you Y the input to both channels without having to use a jumper). I use a jumper to go to the next amp and then from that one to the next.

using 3600s for subs - thanks for the tip, I didn't realise you could jump the input signal from channel 1 to 2 using the TRS sockets.

Compared to one channel parallel bridging gives the same voltage into a halved impedance load, series bridging gives double the voltage into twice the impedance load. Which to use depends on the impedance load. If it's lower than the single channel rating use parallel, if it's higher use series.

I think in this case, 4x T60s on a single channel means 2 ohms impedance; the reference manual for the amp has power ratings for parallel mono mode into 1 and 2 ohms, which would imply that a single channel into 2 ohms in parallel mono mode is ok.
My question is whether running a single parallel bridged channel into 2 ohms (even if it is within the rating) is worse for the amp or drivers than running 2 channels into 4 ohms?
And also whether anyone can see any logical reason why running both channels while the amp is in parallel mono mode, rather than the bridged single channel specified in the instructions, would be harmful to anything?

[Bill Fitzmaurice]

My question is whether running a single parallel bridged channel into 2 ohms (even if it is within the rating) is worse for the amp or drivers than running 2 channels into 4 ohms?

Electrically it's the same thing. The reason to parallel bridge is so you can use a single output cable for all four cabs. But then you have to make sure it's of sufficient gauge.

[monekh]

My question is whether running a single parallel bridged channel into 2 ohms (even if it is within the rating) is worse for the amp or drivers than running 2 channels into 4 ohms?

Electrically it's the same thing. The reason to parallel bridge is so you can use a single output cable for all four cabs. But then you have to make sure it's of sufficient gauge.

thanks Bill. my cables are 2.5mm which I believe is 14AWG, usually only a 10m run - is this a sufficient gauge for a 2 ohm load? I'm finding conflicting information online but I suspect it might be too narrow...

[Bill Fitzmaurice]

Cable capacity requirement is determined by the ampere draw. Calculate that with this. https://ohmslawcalculator.com/ohms-law-calculator

You know the voltage from your limiter setting. 2.5mm cable is safe with a 15 ampere load. If you're limited to 50v then a 2 ohm load is 25 amps, which I wouldn't do with less than 4mm.