Poweramp on bridge mode question

[Ghost_Bass]

Hi, i just got a brand new poweramp to use with my Yamaha PB-1 preamp. It's a KMT DC5. I want to use this amp in bridge mode so it can feed 1kW to my Barefaced Super12T but here's the deal:

On the poweramp manual it says that on bridge operation both channels A and B must have the volume knob on full. I'm usin a Ken Smith who has a very hot output and the Yamaha isn't much cooler. I'm finding myself setting the preamps volume at 1/10 because past that the volume is simply insane (insane in a good way but some venue owners might not think like me).

I would like to know if there's a valid reason for having the poweramp's volume on full in bridge mode or if its safe to turn both of them to 50% so i can get more control through the preamps volume.

Thanks in advance
Marco

[brensabre79]

I can't help but think you're missing something there... Why not just use one side, un-bridged?
You've clearly got an over-powered rig there

[Ghost_Bass]

I could but then i had to cart one poweramp channel and not use it. And, believe me, there's a lot of difference in headroom

I'm more than happy with the power available, i'm never going to use it flat out, but i do like the extra headroom. I just want to know if i'll damage the amp in any way if i run the bridge mode with the channel's volume at 50%

[dincz]

I've used various power amps in bridge mode and none of them required both volume controls full on. Usually only one volume control is active in bridge mode and it can be set anywhere you like. No offence meant, but are you sure you read the manual correctly? Using both volume controls would be more applicable to dual-channel mono operation.

[brensabre79]

[quote name='Ghost_Bass' timestamp='1385745297' post='2291815']
I'm more than happy with the power available, i'm never going to use it flat out, but i do like the extra headroom.
[/quote]

I think you might find that if you run the amp in bridged mode at half power, you'll have the same or less headroom as running one channel on full power. But the attenuator on the power amp is going to affect the sound in some way too. IMO power amps shouldn't even have a volume control, the Preamp should take care of the level being sent to the power amp. If you're having to turn EVERYTHING down to run the power amp at 0dB, then the power amp is too loud.

Plus, 1Kw into a Barefaced S12??? Are you trying to cause an earthquake?
I played a 300 capacity dance hall last night, with a rock band, no PA support, with a 500w amp into my Barefaced S12. The master volume was on 3, and believe me I wasn't sitting under the mix!

All that said, if you really want to run bridged mode I can't see why this amp would work differently to any other. I'd check with the manufacturer / manual to be sure, but it should be ok to attenuate the input of the power amp - as said though, you won't be getting the full 1kW out of the amp if you do this.

Alternatively, if your bass is too hot for the pre-amp you could attenuate at this stage to let the preamp have some headroom (where you really need it) a simple pedal can do this - like an EH Signal Pad...

[Ghost_Bass]

I got a reply from the manufacturer today. Yes, both volume controls on this amp have to to be turned on when in bridge mode (it's a class-H poweramp, if that mathers). The manufacturer replied that i can, in fact, use the volume at 50% but i must set both volumes equal.
Yesterday i was at a bass bash and the amp preformed very well, i'm leaving the volume set at about 75% and that is enough to give me some control over the PB-1's volume so i can run it low for home practise. With tho poweramp's volumes on full that rig only had two volumes: loud and louder

Here's a pic of my current setup:


and what it was up against on yesterday's bash

[Phil Starr]

In bridge mode you are connecting the output of the two amps together pushing in the opposite direction to each other with the speakers connected in between. If one were turned right up and the other not then you are directly applying an electrical potential across the output of the amp which is turned down, which in turn could cause it to fail or trip some of the protection circuitry depending upon the exact design of the amp. The problem with setting volumes half way is that the potentiometers in the volume controls may be a poor match and combined with any inaccuracies you introduce this may cause a mismatch. the afest thing is to turn both up full and put up with the high sensitivity or to buy a little mixer or pedal to cut the volume somewhere earlier in the chain such as in the fx loop.

[Ghost_Bass]

[quote name='Phil Starr' timestamp='1386143822' post='2296247']
In bridge mode you are connecting the output of the two amps together pushing in the opposite direction to each other with the speakers connected in between. If one were turned right up and the other not then you are directly applying an electrical potential across the output of the amp which is turned down, which in turn could cause it to fail or trip some of the protection circuitry depending upon the exact design of the amp. The problem with setting volumes half way is that the potentiometers in the volume controls may be a poor match and combined with any inaccuracies you introduce this may cause a mismatch. the afest thing is to turn both up full and put up with the high sensitivity or to buy a little mixer or pedal to cut the volume somewhere earlier in the chain such as in the fx loop.
[/quote]

Yep Phil, your reply makes perfect sense. I'm not thinking about opening up the amp and measure the pots but i know that there will always be a slight difference between the two amps, every pot has an error tolerance.

The cool thing is that i know i can get very close with the values because the pots are step-by-step detented and i'm putting myself to the trouble of counting the amount of steps i turn down on each pot.

I'm hoping that the difference in potential between both power amps will be minimal doing things like i'm doing and this will reduce the risk of harming the amp.

Cheers