Power Amp Users

[la bam]

Just a quick question for those of you using power amps to power preamps for live gigging...

What type of amp are you using (class D, class A/B etc) and wake make?

Also, and here is the main question - with most power amps being stereo and having a L and R input, and most preamps having one output - how are you connecting/using them?

[Dood]

When I have used power amplifiers in the past I have tried to go for trustworthy brands that are known for producing decent hardware. Powersoft and QSC are great as an example. D Class is obviously light but there's some 'lead-sleds' which can be picked up really cheap that some PA companies still really love for their ability "in the lows".

Connection depends on the amplifier, but most will have a switch marked Parallel/Stereo.

Switch to Stereo and connect your preamp to channel A and a cabinet to output A and you will have a nice single cabinet set up. Abiding by the lowest impedance allowable on the output will give you a certain amount of flexibility with connecting more cabinets to that socket. E.g, two 8 Ohm cabinets on output A will give you a minimum load of 4 Ohms

Switch to Parallel and (usually) input A will feed the same signal to both amplifier A and amplifier B. This is handy if you want to run more cabinets (to a minimum load specified by the manufacturer, usually 4 ohms) - so you could run in this case two 8 ohm cabinets on output A and another two on the output B. Usually both channel's volume controls will still work the separate outputs.

Switch to Stereo and plug in a preamp like the Line 6 Helix and you can run full stereo sounds using a cabinet plugged in to each output and the Left and Right Helix outputs plugged in to Channels A and B respectively.

Finally, you may have an amplifier that can run BRIDGED. This essentially uses the power of both channels to make one big amplifier. You'll need to read the instructions, but usually Channel A input will be where you connect your preamplifier and sometimes there will be an additional output socket marked 'bridge'. There will probably be a switch that puts the amp in to that mode too. Treat it as one mono amplifier and don't connect to any other outputs. You will also probably find that if each channel has a minimum load of 4 ohms allowable, the bridge mode will be double with a minimum permissible load of 8 Ohms.

[drake]

1st reply says it all really. I use a QSC PLX2402 which is class H. Plenty of power, not too heavy. Just check that you pre-amp has enough output to drive your power amp, which my SRW Grand Prix does with no problem in this set up.

[la bam]

thanks, i'll be using either a tech 21 rbi or vtrm to drive them.

ive gone this route so i can have my 'sound' in one rack (x2 preamps - x1 for spare - tuner etc) and then can choose what powered set up to take - either heavy duty amps for big gigs and my sealed markbass 610, or smaller backline where i can take a lesser amp and something like a 1x15.

In the past ive tried a bass flyrig into a crown lightweight XLS amp into a barefaced super compact and it didnt have half the power that my markbass evo had, but that could have been down to either the flyrig not being power enough to drive the amp properly or the amp running on one single side. I asked about bridging but you need a different type of cable.

[NancyJohnson]

Doesn't seem a week goes past without a, 'What power amp are you using...' thread.

Here you go.  Just buy a Matrix GT1000FX.  It weights next to nothing, goes loud, looks good, it's reliable and (tempting fate here) has never failed.  I feed it copious quantities of Tech21 gear, GED2112, the DP-3X or when I'm feeling old school, a BDDI.  It's done thousands of hours since I bought it. 

http://uk.matrixamplification.com/gt-1000-fx-2u.html

You're welcome.

[NancyJohnson]

Oh, concerning connections, the GED is hacked to mono output and goes into the power amp on one side (I'm looking to go 2 x 1x12" at some point), the DP-3X into the other and I just decide what I want to use.  Simple really.  It's currently running bridged.  1000w into 8ohms.

[BassManGraham]

Hi I have a Tech 21 Sansamp RBI in a rack with a Crown XLS 1002 Drive Core class D stereo power amp. (about £246 on Thomann at the moment) . I choose this power amp as it has a choice of input sensitivities. I use in bridged mode i.e. 700 W into 8 ohm or 1100 W into 4 ohm. Plenty of power. Easy to operate with really useful built in crossover with choice of high pass, low pass or  bandwidth selection. I use bandwidth selection to limit sub bass rumble and excessive high end. A great combination and nice and light too.

[la bam]

38 minutes ago, BassManGraham said:

Hi I have a Tech 21 Sansamp RBI in a rack with a Crown XLS 1002 Drive Core class D stereo power amp. (about £246 on Thomann at the moment) . I choose this power amp as it has a choice of input sensitivities. I use in bridged mode i.e. 700 W into 8 ohm or 1100 W into 4 ohm. Plenty of power. Easy to operate with really useful built in crossover with choice of high pass, low pass or  bandwidth selection. I use bandwidth selection to limit sub bass rumble and excessive high end. A great combination and nice and light too.

did you buy a different cable to run in bridged mode?

thats the bit i fell for - itll let you set up bridged mode, but wont actually be operating in bridge mode unless youre using the correct modified cable as in the instructions.

[BassManGraham]

There are two simple options for connecting speakers to the power amp in bridged mode. This is explained in the online  manual. But briefly

1. You connect a standard speakon cable or Jack plug on one end (speaker cab connection) with bare wires to amp connection to the pair of bridged +ve and -ve red terminal posts. 

2. I also got a special speakon cable made up by Dave (obbm) on this very forum. It's just different connection to terminals on the speak on plug. This then connects to speak on output on power amp. 

[BassManGraham]

58 minutes ago, la bam said:

did you buy a different cable to run in bridged mode?

thats the bit i fell for - itll let you set up bridged mode, but wont actually be operating in bridge mode unless youre using the correct modified cable as in the instructions.

Hope pic helps, cheers Graham 

[paul_5]

Ampeg SVP’s preamp our into a Behringer deHummer box and then into my Laney SP300. I used to bridge the power amp to 300w at 8 ohms, but as my new cab is 4 ohms then I’m having to use it set to stereo and just use one channel. Still plenty loud enough at 150w at 4ohms though.

[Jus Lukin]

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Edited March 1, 2022 by Jus Lukin

[NancyJohnson]

I'll just weigh in here on the bridged/parallel thing on the Matrix.  I'm not point-scoring, but the solution is a bit more elegant than the Crown.

If you look at the Matrix below, you have an area to the bottom left that's your INPUTS (confusingly marked B & A, but I suppose this is the reverse of the facia controls) AND output type selection toggle switch (Stereo, Parallel and Bridged).  In the middle, there's three Speakon outputs left to right channel A, Bridged, Channel B.

Flipping the output toggle to BRIDGE activates the centre Speakon output and the unit delivers 1000w into 8ohms.  There's no wiring up to terminals.  Obviously you can only use a single source input (into B or A on the left) in bridged mode.

You can run the amp in switched parallel mode (single input, B or A), switch to Parallel, single or pair of speakers attached to channel A&B or A or B, same signal to both OR switched stereo mode (different input sources to B & A), switch to STEREO, two enclosures individually attached to channels A & B.

Longterm I'm looking to run a pair of 1x12" cabinets to utilise the switched stereo mode to take full advantage of the GED2112 pre-stage.  The ease of switching/outputs just makes it easy to run a single input into bridges as well.

 

 

[jimbartlett]

You need a different wiring in the speakon for running in bridged mode. It’s Speakon(4p) to Speakon(2p). Check out OBBMs website, he sells them (link below). You won’t get the correct power output using a normal speakon in bridged mode.

http://www.rock-wire.co.uk

[NancyJohnson]

1 hour ago, jimbartlett said:

You need a different wiring in the speakon for running in bridged mode. It’s Speakon(4p) to Speakon(2p). Check out OBBMs website, he sells them (link below). You won’t get the correct power output using a normal speakon in bridged mode.

 

Dave made mine...maybe all his are 4-pole from the outset.  Never had an issue, parallel or bridged.

[la bam]

3 hours ago, Jus Lukin said:

Can’t you just run a speakon-speakon from CH1 in bridge mode? That’s how I interpreted the manual, and how I’ve been doing it!

Not that I’m ever likely to need the full 1500w from the 1502, but be good know if I’m doing something wrong!

No, you need a differently wired speaking cable. Like you, I assumed you could just see it to 'bridged' on the menu, but that doesn't work.

[la bam]

5 hours ago, BassManGraham said:

Hope pic helps, cheers Graham 

Pics are a great help. That's going to be pretty similar to my final rig. Thanks.

[BassManGraham]

14 hours ago, NancyJohnson said:

I'll just weigh in here on the bridged/parallel thing on the Matrix.  I'm not point-scoring, but the solution is a bit more elegant than the Crown.

If you look at the Matrix below, you have an area to the bottom left that's your INPUTS (confusingly marked B & A, but I suppose this is the reverse of the facia controls) AND output type selection toggle switch (Stereo, Parallel and Bridged).  In the middle, there's three Speakon outputs left to right channel A, Bridged, Channel B.

Flipping the output toggle to BRIDGE activates the centre Speakon output and the unit delivers 1000w into 8ohms.  There's no wiring up to terminals.  Obviously you can only use a single source input (into B or A on the left) in bridged mode.

You can run the amp in switched parallel mode (single input, B or A), switch to Parallel, single or pair of speakers attached to channel A&B or A or B, same signal to both OR switched stereo mode (different input sources to B & A), switch to STEREO, two enclosures individually attached to channels A & B.

Longterm I'm looking to run a pair of 1x12" cabinets to utilise the switched stereo mode to take full advantage of the GED2112 pre-stage.  The ease of switching/outputs just makes it easy to run a single input into bridges as well.

 

 

 

Just for the record (and to satisfy my pedantic OCD) a more elegant and aesthetic option is possible for the Crown . Channel 1 is wired for both channels so it can be used for BRIDGE mode wiring (or stereo wiring of two speakers using one 4 pin speakon plug) I use the rock-wire Speak-on to Speak--on with bridged terminals 1+/2+ and white sheath to avoid incorrect connection. The Crown is very flexible and excellent crossover allows bi-amping if you want to be reallly flash! 

[la bam]

How do you find the sound with the crown running the pre amp (with it being class d)? Is it just ok? Good, or as good as a quality A/B style amp?

Edited September 2, 2018 by la bam

[BassManGraham]

3 hours ago, la bam said:

How do you find the sound with the crown running the pre amp (with it being class d)? Is it just ok? Good, or as good as a quality A/B style amp?

Hi the Crown it is good, clean, loud and powerful and very good value for money.. The Sansamp ceates the tone, and sound engineers love them . I can't honestly compare the Crown with many A/B style amps as I have been using Class D stuff pretty much exclusively for 12 or more years and I am always DI'd through a PA so the power sections of all my amps are there to provide on stage sound. The bass and preamp are key in shaping sound/tone , the power amp and speakers deliver volume and 'heft'. With the right speaker cab this Sansamp/ Crown set-up is plenty powerful for most venues without going thru PA if you want a deafening sound on stage! 

I did try my Sansamp with a friends A/B style t.amp power amp before buying the Crown. The t-amp sounded OK, but to me the Crown sound was much better, and had far greater flexibility with high pass, low pass, bandwidth selection etc. Unable to compare with a high quality A/B amp.I sometimes wonder if the finer nuances are lost when a full band and drummer kick in?

Personally I like class D amps. I have had valve heavyweights but even back in the day I preferred my solid state Acoustic 220 to my valve Fender Bassman 135 for cutting thru the mix,. I dare say you could get marginally better results by spending a lot more money. Demeter spring to mind. You just have to let your own ears judge what's best for you.

Edited September 2, 2018 by BassManGraham

[jazzyvee]

On 01/09/2018 at 11:59, drake said:

1st reply says it all really. I use a QSC PLX2402 which is class H. Plenty of power, not too heavy. Just check that you pre-amp has enough output to drive your power amp, which my SRW Grand Prix does with no problem in this set up.

Yes I agree i had one of those QSC PLX2402 amps and sold it due to it being too heavy in my 6u rack with the rest of my gear. The weight meant it didnt get used much so i recently replaced it with a crown Xls1502 which is also a good amp but to my ears the qsc wins hands down seems to have more power in the low end and more density in the sound overall. Maybe i should have kept it and bulked up at the gym🤔😂. 

But we live and learn and now i use the crown in my big rig and have a smaller 3u shallow rack with a Synq 1k0 1U class D amp in  with a F1-x preamp for travelling light to gigs with a backline provided as the heads usually are raspy. 

I generally use one cab on gigs but where there are two i use one on each side of the power amp in the mode where one input drives both channels. My pre amp has a crossover so i could bi amp but not at the moment. 

 

[BassManGraham]

17 hours ago, jazzyvee said:

Yes I agree i had one of those QSC PLX2402 amps and sold it due to it being too heavy in my 6u rack with the rest of my gear. The weight meant it didnt get used much so i recently replaced it with a crown Xls1502 which is also a good amp but to my ears the qsc wins hands down seems to have more power in the low end and more density in the sound overall. Maybe i should have kept it and bulked up at the gym🤔😂. 

But we live and learn and now i use the crown in my big rig and have a smaller 3u shallow rack with a Synq 1k0 1U class D amp in  with a F1-x preamp for travelling light to gigs with a backline provided as the heads usually are raspy. 

I generally use one cab on gigs but where there are two i use one on each side of the power amp in the mode where one input drives both channels. My pre amp has a crossover so i could bi amp but not at the moment. 

 

 

QSC power amps are great,.

In fact I use my Quilter Bass Block 800 (from Patrick Quilter, the Q in QSC) far more often than my Sansamp/ Crown rack unit these days, it just so handy!

[Leonard Smalls]

I've been so excited by this power amp stuff and the relief it'll provide to my poor back that I've just ordered a Crown XLS 1502, complete with flightcase and rack power strip...

[WinterMute]

I used the Crown XLS1500 for 4 years with a Line6 Pod XT Pro into a BF Big Twin, ran it bridged to output 1500w into 4 Ohms using a 4p to 2p Speakon, coded with red tape to indicate the end that went into the amp.

Never had a moments problem, fed the PA from the second Effected output so the FoH got exactly what I was hearing onstage. Tons of clean power, all tone control at the bass and the Pod.

The 1502 is a better amp.

Edited September 3, 2018 by WinterMute
added pic for extra zip...

[jazzyvee]

 I drove mine XLS1502 directly from my bass recently without a pre-amp and it worked a treat. A great option if you want the completely clean unadulterated sound from your bass. I can't imagine doing it on a gig though but it's good to know that if my pre-amp ever went down I could carry on the gig using the power amp. The fact my bass runs at 36v (+/-18vdc)  might have something to do with it.