Which amp for mains and subs

[chickbird]

OK....quick question.

Trying to decide which amp should run mains and which amp for sub.

Current set up is single GX5 running mains parallel mono (yam s115v) and sub (tuba 60 w/ lab15)

I want to run mains in stereo so a buddy sold me a yamaha P2500s. This amp can be configured a bunch of different ways including bridge mono that the GX5 can not. So I don't know if I should run p2500 in bridge mono and dial in the low pass dial for sub or use it for mains and set up the low cut. I believe p2500 would be a good choice for sub since bridge puts out 620watts and lab 15 is rated for 600 continuous.

Would love to hear comments, thoughts, recommendations and feedback. Thanks in advance!

[DJPhatman]

If it were me, I would use the Yamaha bridged on the T60, but not with any of the other settings on. Do all of your processing outside of the amp, where you have control. You are using an active crossover and limiter, right?

[chickbird]

If it were me, I would use the Yamaha bridged on the T60, but not with any of the other settings on. Do all of your processing outside of the amp, where you have control. You are using an active crossover and limiter, right?

Phatman.........I wish I could say i have a driverac or dcx.....but i don't. I rely on the built in 100Hz crossover in the gx5

on a side note......I do measure voltage to driver and never go over 50 volts.

[DJPhatman]

If it were me, I would use the Yamaha bridged on the T60, but not with any of the other settings on. Do all of your processing outside of the amp, where you have control. You are using an active crossover and limiter, right?

Phatman.........I wish I could say i have a driverac or dcx.....but i don't. I rely on the built in 100Hz crossover in the gx5

on a side note......I do measure voltage to driver and never go over 50 volts.

Then spend the money and get one. Can you afford to lose a Lab15? DCX2496 can be found for US$150 used, sometimes less. Does everything you need. There are no limiters in either amp, nor are the built-in filters better than 12 to 18dB/octave, making them pretty much useless. GX3 has a 3rd order (18dB/oct) to the sub, and a 2nd order (12dB/oct) to the highs. The Yamaha has only a 12dB/octave filter. Either amp has enough crest power to make your lab15 toast.

1 Lab 15 will cost you around US$250 or more. You can spend some now, on a proper crossover and limiter, or you can spend a lot more later on another driver.

My other question is... why are you bothering with stereo tops? If they are more than 25-30 feet apart, the effect is lost and each side of the audience (the reason you are even there) does not hear what the other side hears. I doubt that you are doing any shows that stereo imaging would be useful and not detrimental to the overall sound. My advice to you would be to forget running in stereo, but still get at least a proper crossover and a proper limiter. These are must haves, no matter how you run.

[BrentEvans]

on a side note......I do measure voltage to driver and never go over 50 volts.

How can you guarantee this? What happens if someone drops a mic or unplugs a cable, and you get a surge of power?

Gotta get a limiter, man.

[chickbird]

I think we are getting a little off topic. All I asked was for thoughts on which amp should drive which speakers. This rig is set up for DJ use in a small 1500 sq ft room 99% of the time. So ya....listening to half of AC/DC really sucks.

I understand the need for active crossovers and limiters but its just not in the budget right now. So I guess i'll take BFM advice and NOT bridge unless its absolutely necessary.

When should I bridge?
The answer is almost never. Forget about the silly power ratings that manufacturers post for bridged output, that's just advertising piffle aimed at the unwashed masses. Bridging isn't about power, it's about voltage swing. You use it when your amp doesn't have enough voltage swing to drive the speaker to its displacement limit. Nine times out of ten that's because the speaker has a high impedance, say 16 ohms. The tenth time is when your amp is rated at less than a quarter the power output that your speaker is.
If you do bridge when you don't need to the doubled voltage swing quadruples your chances of blowing drivers.

[Grant Bunter]

Hi chickbird,

I don't want to add to any impression that we are having a go at you if that's what you're thinking, but honestly, if you can't afford the required equipment now, then you shouldn't run your system as a DJ until you can!

The reason I say this is because there is nothing worse for your business than blowing your sub driver up on your first night, halfway through the show.

It's all right there in the plans for the T60 under "protecting your driver":
"You must limit the output voltage of your amp to the driver voice coil rating or the displacement limited power rating, whichever is less."
Not just look at output levels, you have to limit that level.

"The Lab 15 power and displacement ratings are both 600 watts, so 60 volts is the maximum allowable."
ie 60V is what you have to limit to.

"The signal to the amp must be high-pass filtered at 25 to 30Hz, to prevent excessive power and/or excursion below the cab pass band. High pass filters are contained in many active crossovers, in loudspeaker management systems like the Behringer DCX 2496 and DBX Drive Rack series, and in many modern amps with on-board DSP."
You haven't mentioned high passing, and you can't with either of the amps you have.

We're just trying to make sure your system will act as it should, we really don't want to have you come back to the forum and say "hey, what's up with my T60, I was playing Hells Bells through it and it stopped working".

While it may seem that we're going off topic, we're not.
If you had come to the forum before you bought the Yammy off your mate, you probably would have been asked what DSP etc you were using, and, if you had said "none", a viable alternative at that time would have been to suggest buying an amp with on board DSP for your T60...

[chickbird]

Hi chickbird,

I don't want to add to any impression that we are having a go at you if that's what you're thinking, but honestly, if you can't afford the required equipment now, then you shouldn't run your system as a DJ until you can!

Grant bunter...........i understand you guys are not doggin me and talkin the truth. its just my buddy was in dire need of cash and i picked the amp up very cheap. Couldn't pass it up.

i'm not a DJ i'm a bar owner in a small town and have this system set up in the corner for when we get crowded and the bose speakers attached to the jukebox just don't cut it. So i turn on my system to give it more oomph. I've been running this system for over a year prolly closer to year and a half and have not had any issues. Even had some bands play thru it.

So on the yammy amp there are some controls that filter some. IE. sub, low cut and i believe high pass. now are they as good as dcx / driverack.... obviously not but that is what I have to work with. So have to make do.

I'll just keep using gx5 as usual and yammys for tops

[DJPhatman]

i'm a bar owner

This also makes you a business man. Do you allow customers to come in the bar and mix their own drinks? They are doing the same job as the bartender, but eventually, there will be something that will come back and bite you in the ass. Running your T60, with pretty much any amp, without proper limiting and high pass filtering, is going to come back and bite you in the wallet.

It's your rig, and you have control over it. This forum is dedicated to the proper support for bill Fitzmaurice Loudspeaker DIY designs. If you choose not to follow the advice of the forum, it is your choice. I will only advise you to run a properly deployed and protected system. Good luck with your venture.

[Grant Bunter]

Grant bunter...........i understand you guys are not doggin me and talkin the truth. its just my buddy was in dire need of cash and i picked the amp up very cheap. Couldn't pass it up.

i'm not a DJ i'm a bar owner in a small town and have this system set up in the corner for when we get crowded and the bose speakers attached to the jukebox just don't cut it. So i turn on my system to give it more oomph. I've been running this system for over a year prolly closer to year and a half and have not had any issues. Even had some bands play thru it.

So on the yammy amp there are some controls that filter some. IE. sub, low cut and i believe high pass. now are they as good as dcx / driverack.... obviously not but that is what I have to work with. So have to make do.

I'll just keep using gx5 as usual and yammys for tops

No worries about helping a buddy. We do what we do.

While not having a DSP is far from ideal, if you're going to persist without DSP there are some ways to utilise both amps and get some semblance of crossover etc.

As you've said, the GX5 for subs and the yammy for tops. But set it up like this:
GX5 manual:
http://qsc.com/files/9713/4625/5907/QSC ... vD.pdf.pdf
Under specs it says one channel driven outputs 600W/8ohms, or 69V.
More than enough to blow the Lab15 at full tilt!

If you can do this:
Signals in to channel A and B, set switch on rear upwards to crossover. Use channel A (only) for output for T60 (Nothing in channel B). This will give the T60 a HP and LP of 20Hz and 100Hz respectively. Manual says it's a third order filter for sub output (channel A) but defines no parameters. Even though the HP is lower than that in the plans, better than no HP at all, I hope.

Yammy Manual:
http://download.yamaha.com/api/asset/fi ... et_id=3028
Then 1/4" to 1/4" leads out of the GX5 channels A and B into the Yammy A and B input channels.
Set each switch on each Yammy input Channel to Lowpass and turn both dials to 100Hz (which is really going to make it a 100Hz HP) and since you're using Yammy tops, set switch "Y processing" to ON and stereo/bridge/parallel switch to "stereo".

Should work.

And please, get some DSP as soon as you can. At least that way you protect your T60 driver properly, and get some EQ to boot...