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To daisychain or not?

#21
wcriley said:
Very common spec for power amps.
The power supply is more heavily taxed when both channels are driven; less taxed when just one is in use. Hence the different power rtaings.
Click to expand...

That I get... just a strange way of presenting those specs.

So, he has two options if I'm understanding this:

Each 8ohm cab out of each side of the amp, resulting in 1000 watts (500 watts per cab), or the two 8ohm cabs daisy chained out of one side of the amp running at 4ohms, resulting in 850 watts.

If I finally have that right, then the former option is better in every way (i.e., running each cab out of each side of the amp).
 
#22
KJung said:
That I get... just a strange way of presenting those specs.

So, he has two options if I'm understanding this:

Each 8ohm cab out of each side of the amp, resulting in 1000 watts (500 watts per cab), or the two 8ohm cabs daisy chained out of one side of the amp running at 4ohms, resulting in 850 watts.

If I finally have that right, then the former option is better in every way (i.e., running each cab out of each side of the amp).
Click to expand...

welcome to the world of power amps, Ken. BTW, I think I said this back in post # 6. :D
 
#23
Actually, QSC's way of presenting the power specs is less confusing than Peavey's before they added the phrase "both channels driven".

Rated Power (2 x 2 ohms) - 800 watts per channel @ 1 kHz at <0.1% T.H.D. both channels driven.
Rated Power (2 x 4 ohms) - 530 watts per channel @ 1 kHz at <0.1% T.H.D. both channels driven.
Rated Power (2 x 8 ohms) - 300 watts per channel @ 1 kHz at <0.1% T.H.D. both channels driven.
Rated Power (1 x 2 ohms) - 1000 watts @ 1 kHz at <0.1% T.H.D.
Rated Power (1 x 4 ohms) - 600 watts @ 1 kHz at <0.1% T.H.D.
Rated Power (1 x 8 ohms) - 320 watts @ 1 kHz at <0.1% T.H.D.
 
#24
jnewmark said:
welcome to the world of power amps, Ken. BTW, I think I said this back in post # 6. :D
Click to expand...

Ah, didn't see your post before. Again, just kind of a strange way of posting those specs. I guess they went into all the 'one side versus two sides' thing since this particular amp can't be bridged.

Still not sure what that 2ohm spec is about, since I believe the text on the site says the amp cannot be run at 2ohms, but that is a moot point.

So, again, daisy chaining would not be the optimal way to run the OP's cabs.
 
#25
What seems even odder to me is a power amp that can't be bridged, but I have'nt bought one in a few years, at least one of the lighter weight ones !
 
#27
1958Bassman said:
That would be great if you were sending signals to the amp at 1KHz, but you're not. The low end is where you play and that usually means the amp puts out less than the spec. Personally, any amp company that uses 1KHz as the specified frequency won't get my money if they don't show full frequency range power specs.
Click to expand...

The difference between the 1kHz and the full range spec is going to be <5% typ. The difference is insignificant in the real world.

1958Bassman said:
Running it at 2 Ohms, both channels driven is worthless. It will make the amp run hot and that means failure is inevitable.
Click to expand...

Not accurate on this (and some other multi-raoil amps) because at 2 ohms, under operating conditions the high voltage rail is essentially disabled reducing the SOA stress on the power transistors as well as the power supply to normal levels. It's part of how the "guardrail" circuit operates at 2 ohms.
 
#28
Regarding the SVT, I was under the impression the original '70s ones were wired so the 2ohm tap from the OT is used only when the second speaker jack has a plug in it, automatically switching over.

If I'm correct about this you shouldn't daisy chain two 4ohm cabs to it without at least using a dummy plug.

I hope I've remembered this correctly.
 
#29
i think you're right on the old SVT thing, plugging the second cab into the head switched the transformer to 2&#937;. (new ones just have impedance selector switches.)

as far as the power amp thing, yes, technically running one cab into each side of the amp will net a little more power, but the difference may not be all that.

i run a pair of LDS single 15s into one side of a crest LT1500, which gets me about 750 watts. running one cab into each side might get a little more power (since with power amps, 4&#937; never brings out exactly twice as much power as 8&#937;), but as it is i've yet to ever have to turn it up loud enough to clip the amp (and i play aggressive rock with some loud drummers).

running one side makes it easy to adjust my stage volume (the amp channel's volume knob serves to tweak stage level without affecting my preamp's level into the house), and frees up the other side of the amp for other duties, like the occasional extra monitor mix.
 
#31
Hi.

KJung said:
Here is what I'm not giving with this very strange spec sheet:

8&#937; / both channels driven / 1 kHz: 500 W
8&#937; / single channel driven / 1 kHz; 600 W

I don't get this.
Click to expand...


wcriley said:
Very common spec for power amps.
The power supply is more heavily taxed when both channels are driven; less taxed when just one is in use. Hence the different power rtaings.
Click to expand...

^This.

Well, I don't know how common it is to publish it outside pro circles, but that's how it goes in any case. Not a problem, since for most it goes without saying.

OTOH some manufacturers publish the average of those two, some publish the lower one.

BTW, I'm just a hobbyist (without an AF distortion meter), but even the crappiest of power amps have delivered roughly the same wattage on 50Hz as they do on 1K before clipping. Most deliver about 10% more than advertised, but that's well within' the measurement error limits of the basic method I use, and is most likely the result of observing the distortion visually by comparing waveforms.

Regards
Sam
 

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