Parallel Mono Amp Operation

[KevinE]

Hello, I was called out to a couple of amps today which are overheating unless a desk fan is pointed at them by the user, they've run them like this since they were installed a few years ago.

 

The amps are RCF DCA1050 units and each one supplies a pair of parallel-connected 8-ohm cabs rated 1000W RMS each.

 

The amps are each fed with a mono signal to ch1 input only, and the input switch set to parallel-mono.

 

The query is that the speaker leads are connected only to one (left) speakon socket on each amp, to pins 1+ and 1- thus giving this side a 4-ohm load, with nothing on the right channel speakon in each case. Can anyone tell me if the DCA1050 internally connects the amp outputs together when the parallel-mono switch is set, (via relay, like the Camco) or do we physically have to bind the L & R outputs together (like the Crown Macrotechs)?

 

If they are already paralleled internally, then I need to look elsewhere for the fault, or if they arent..then the sound system has been running with only 1 channel on each amp supplying the whole 4-ohm load since installed and may be the reason for their overheating. I can't remove the amps from the rack just yet as the venue will need to hire in a replacement whilst the amps are out as they're in almost constant use.

 

RCF cant help and Audio Workshop have never heard of Parallel Mono being used like this so I'm stuck!

 

 

Cheers

 

Kev

[Simon Lewis]

Kev

 

I'm confused here... usually, parallel mono implies that both amp channels get the same input signal (thus saving on an XLR jump lead between inputs on the back panel).

 

However, you seem to be describing bridging?

 

Some amps require the bridged output to be connected across the two channels "red" speaker terminals, others provide a third Speakon outlet wired appropriately to the +ve of each amp.

 

I can't find any details on the amp to check!

 

Simon

[drsound]

Simon, he's right about the Macrotechs. When you put them in parallel mono (as opposed to bridge mode) you have to bridge across the positive terminals of both outputs. In bridge mode it's more conventional in running from 1+ and 2- or the other way around (can't remember hwich it is now).

 

Strange but true. Perhaps it's to avoid having too much current flow from each terminal or some other practical reason. The Crowns will also drive 1 ohm happily in this parallel mode so it's almost like they treat bridge as a serial mode and parallel as just that.

 

Kev, most amps do tend to just stick with using both outputs and bridging the input signal internally as Simon says.

[boswell]

Some limited info on the amp

 

http://www.noretron.fi/sendfile.php?site_i...ba050cac79a5b33

[Solstace]

Hiya

 

If the NL4 with the speakers dangling off it is wired pins 1+/1- like you say, then the channel 1 will see the presenting 4-ohm load (two 8-ohm speakers in parallel, yes?) and you'll get about 500W out according to the spec-sheet. If it's wired 2+/2- then the 4-ohm load is split across the two sides, so each side sees 2-ohms. That's rather too low according to the amp spec - and would explain the hot running.

 

If they can't afford more amps, I think they'll do better to put the amps in dual-mono mode and drive each sub individually from each output channel. At least that way the amp load is in spec and each sub still gets half its max RMS. They'll also need to stop driving them so hard!!!!

 

Sheet I'm looking at is here:

 

http://www.noretron.fi/sendfile.php?site_i...ba050cac79a5b33

 

EDIT Darnit! Beaten to the punch on the datasheet - hope the rest makes sense at this end of the day...

[MarkPAman]

That helps a bit. It does look as though parallel is expecting only one speaker line to be plugged in.

 

No figure for 4 ohm running in parallel mode, so we can't tell if you could squeeze a little more headroom by running as stereo 310W each at 8 ohm. My guess would be probably not.

[upsuEnts]

Why not just run the amp in bridged mode?

Then it wouldn't be running as hard and (hopefully) not getting as hot.

[MarkPAman]

Bridged mode is 8 ohms minimum, so you only be able to run one speaker per amp :D

[themadhippy]

Or 2 in series

[KevinE]

If it's wired 2+/2-

 

No it's wired 1+ 1- . The no2 pair are for bridge (series bridge) mode only.

 

drive each sub individually

One amp runs a stereo left mid-high and the other a stereo right mid-high.

 

if you could squeeze a little more headroom by running as stereo

 

Yep I would like to do this ideally but the venue is wired with speaker pairs in daisy chain and it would mean re-cabling the place and floors up and I'd like to avoid it!

 

The spec sheet for the amp (I'd found it thanks to google!) does mention 'parallel mode output' being 2 ohms 1000W..this does suggest to me that the L&R channels can be parallelled for double current. I'd just like it confirmed by someone who knows the amp!!!

 

:D

[mal421]

Just a thought . Are both channels on Ch1 speakon . What I mean is this , some amplifiers have Ch1 on 1+ & 1- and Ch2 on 2+ & 2- . If this is the case then there should be a 4 core cable to the speakers . This may explain why there is only one speaker cable .

[MarkPAman]

Just a thought . Are both channels on Ch1 speakon

 

Read the first post & the one before yours!