dincz

[quote name='tauzero' post='1095522' date='Jan 19 2011, 08:17 PM']Surely the output power will be limited by the power supply rail voltage rather than the current?[/quote] Amounts to much the same thing. As you approach the power supply's maximum current capacity, the rail voltage will drop. So if you run only one side, the power supply will be loafing and giving full rail voltage.

[quote name='cocco' post='1088999' date='Jan 14 2011, 11:01 AM']I fear this may be pointless, but then the best things in life are.[/quote] But they're supposed to be free

[quote name='Mr. Foxen' post='1088229' date='Jan 13 2011, 05:10 PM']I think that is the lack of vertical bit, like you need two lines to make a right angle, and it ain't a square without one. So it is just a flat topped wave, not a square one like you can do with synths.[/quote] OK, not perfect square waves with infinitely short risetimes, but definitely squarISH. A synth (or anything else) won't produce a perfect square wave either but an amp with good HF response and slew rate would surely produce as good an approximation as a synth, no?

[quote name='alexclaber' post='1087959' date='Jan 13 2011, 02:42 PM']But if you run a Fourier Transform on that square wave you'll see that the additional energy is entirely made up of higher frequency overtones.[/quote] OK the fog is clearing. Of course it makes sense that there's nothing below the fundamental. It's just so tempting to see "alternating DC" in a square wave. But what about this: "Clipping does not cause square waves" Can't quite get my head around that.

"Clipping only increases the power output at higher frequencies" But the RMS voltage of a sine wave is about 0.7 of its peak value, whereas the RMS voltage of a square wave is the same as its peak value. So a square wave of a given peak voltage has an RMS value 1.4 times that of a sine wave of the same peak value. Surely that results in a doubling of power (I^2 x R)? At least in an ideal world with an ideal power supply. OK, I'm talking pretty severe clipping here - bags of level into a sensitive input - and an amp running into a purely resistive load. I've only ever tested this into a dummy load as I've always had intolerant neighbours

[quote name='Soliloquy' post='1087467' date='Jan 13 2011, 01:26 AM']Is this any good ? [url="http://www.dv247.com/search/3071/1527/ProductQuantity/Descending/-/1/"]http://www.dv247.com/search/3071/1527/Prod...Descending/-/1/[/url][/quote] Who knows if it's any good, but the output power is 900 watts peak. RMS output power is 580 watts bridged into 8 ohms. Apart fom that, if you can get around the anti-Behringer sentiments, it may well be a good, lightweight, 600 wattish solution. Have a look here too: [url="http://basschat.co.uk/index.php?showtopic=109387&hl=epq900"]http://basschat.co.uk/index.php?showtopic=...7&hl=epq900[/url]

[quote name='TimR' post='1087458' date='Jan 13 2011, 01:12 AM']Are you saying that the power rails don't sag at all at 8ohms full power?[/quote] The power supply (particularly the transformer) has resistance. The more current you draw from it, the more voltage is dropped in that resistance. If you double the current through say, a 1 ohm resistor, you double the voltage dropped by that resistor. Changing the load impedance from 8 to 4 ohms would result in double the output current, all things being equal. Yes, the output current increases, but it has to come from somewhere - the power supply. Because of the power supply's resistance, the supply voltage drops and so the output current is determined by the new lower rail voltage and the load impedance. So you don't get double the current and you don't get double the power. At 8 ohms, less current is drawn from the output stage and therefore from the power supply, so the drop in rail voltage is less at full power than it is with a 4 ohm load.

10 amp mains fuse would indicate they're talking VSPWRFF (very short peak with random fudge factor)

[quote name='thinman' post='1087261' date='Jan 12 2011, 10:19 PM']That being the case, is some of the variance in ratings into different loads due to the duration over which output is measured? I'd imagine that with sufficient capacitors in the power supply high peaks could be achieved, but not sustained. I'd like TimR to elaborate on what he was saying about looking at things the other way round, i.e. output is not halved by doubling the speaker impedance - just for education purposes.[/quote] Don't know about peak ratings but I expect it could have managed brief bursts of higher power. The figures I mentioned were for continuous (i.e. several minutes) operation.

[quote name='grayn' post='1087052' date='Jan 12 2011, 08:00 PM']As the amp output says, MAXIMUM 8 ohms, I can't see why it should fry, with 4. I guess you were attempting humour but this is a decent, small combo.[/quote] From the manual: Impedance: 8 ohms maximum Allowable power input: 100 watts minimum Looks like they mixed up the max and min

[quote name='ThomBassmonkey' post='1082161' date='Jan 8 2011, 03:57 PM']As WH says, 4 Ohms is MORE than 8 Ohms. It's weird, but that's how it works.[/quote] 4 ohms is less impedance than 8 ohms - it impedes current less so it allows more to flow.

I once had a power amp that put out 280W into 4 ohms. At maximum power (onset of clipping), the supply rail voltages dropped significantly (about 15% from memory). I added a second (identical) power transformer in parallel and the amp then managed 318W. Not that significant and hardly worth the effort or the added weight, but it did at least show that the transformer is a major factor.

Or this with headphone out plus all the other useful goodies: [url="http://www.thomann.de/gb/behringer_xenyx_502.htm"]http://www.thomann.de/gb/behringer_xenyx_502.htm[/url]

[quote name='Bill Fitzmaurice' post='1078727' date='Jan 5 2011, 05:09 PM']It's not a shortcoming, merely the reality of how amps work. At low signal levels current does double into a halved impedance load, so power doubles as well. But at full power the actual current delivery increase, and therefore power increase, averages only 70%. That translates into an actual full power level increase of only 2dB. That small figure, combined with the fact that few speakers can actually make use of more than half their rated power before reaching their mechanical limits, makes the oft seen "I want a 4 ohm speaker to get all the watts out of my amp" a generally fruitless quest.[/quote] "Shortcoming" was probably the wrong word. Ideal worlds and zero-impedance power supplies don't and can't exist, and I'd say that a manufacturer who achieves a 70% increase in maximum power with a halving of load impedance is doing a brilliant job. Most don't reach 70%. Regarding the impedance of the output stage - it certainly has an effect but is typically only tenths of an ohm. Sagging power rails are the major culprits.

[quote name='thinman' post='1077818' date='Jan 4 2011, 09:25 PM']Isn't it often to do with the amp's power supply not being able to deliver enough current to deliver double the current when the impedance is halved? To reach double the quoted 8ohm power at 4 ohms and double again at 2 ohms would mean much beefier, and expensive power supplies. There's probably other reasons too![/quote] Exactly. That's what I meant about "an ideal world" and "a perfect power supply". So I'm wondering how valid it is to look at the percentage increase as an indicator of how well engineered an amp is. For class A/B, I'd expect weight (big transformer) to be an indicator as well (unless it's a switch mode supply of course).

[quote name='warwickhunt' post='1077733' date='Jan 4 2011, 08:32 PM']In fact I can't think of a single amp that I've tried or owned that does the near double.[/quote] Agreed and I wouldn't expect to find one. My amp is pretty much the same as yours - halving impedance gives 50% more power. Even a Crown XLS1000 gives only 57% more into 4 ohms than into 8.

I've noticed quite a bit of variation in various heads and power amps in terms of how much more power they will deliver when speaker impedance is halved. In an ideal world, an amp with a perfect power supply would deliver twice as much power into a 4 ohm load as into an 8 ohm. The degree to which an amp falls short of this ideal seems to me to be an indication of the shortcomings of its power supply. Any thoughts?

[quote name='Steve_nottm' post='1075549' date='Jan 2 2011, 07:15 PM']cheers erm..... Is this a solvable problem or just a "feature" that I'll have to live with and work around?[/quote] Easily solved - just plug in a new valve! A quick check might be in order first. Unplug your bass from the amp, turn the volume up almost to the point where the noise happened, and give the amp a firm tap. If you hear noises from the cab when you tap the amp then it's very likely a dud valve.

[quote name='citymariner' post='1073040' date='Dec 30 2010, 08:32 PM']Checked the wiring and they are wired correctly[/quote] Ignore me if I've got the wrong end of the stick, but you can't actually tell if the cabs are in phase by checking the wiring unless you're comparing two identical cabinets. You really need to do it by trial and error or by connecting a battery to the speakers to check that all cones move in the same direction at the same time.

From your description, it sounds like you might have a microphonic preamp valve - i.e. it's picking up and amplifying the sound from your speakers. If you turn it up far enough, the result will be feedback.

[quote name='Musky' post='1075030' date='Jan 2 2011, 10:03 AM']Behringer don't provide RMS figures for the power of their amps, so the actual RMS is likely to be about half of the figure they're stating.[/quote] They do provide it but choose to market their amps using the peak figure. The EPQ2000 does 700W per side (RMS) according to the PDF brochure on their web site. The MIC2200 is not a good choice for a bass preamp. It's designed as a microphone preamp and the input impedance is way too low for a bass. You might get away with it with an active bass but definitely not good for a passive.

Combo and 15 out of phase?

[quote name='charic' post='1063588' date='Dec 19 2010, 04:07 PM']Thanks for the info, don't really want to replace the headphones as they are an xmas prezzie from the gf (wireless) these are the headphones in question [url="http://www.dv247.com/headphones/sennheiser-rs110-open-supra-aural-wireless-rf-headphone-system--33902"]Headphones[/url] I was thinking something like this might have fixed the problem: [url="http://www.dv247.com/studio-equipment/behringer-ha400-microamp-ultra-compact-stereo-headphone-amplifier--33860"]Headphone mixer[/url] or using the di [url="http://www.dv247.com/studio-equipment/behringer-ma400-micromon-ultra-compact-monitor-headphone-amplifier--38127"]More me[/url][/quote] If you're using wireless headphones, then the 32 ohm impedance is not a problem as your amp is not driving them directly anyway. I couldn't find the specs but I'd guess the input to the base unit is pretty high - 10Kohm or thereabouts. Low batteries in the base or in the headphones could cause distortion. Do you get distorted sound with wired headphones? The mixer and DI you linked to are for use with wired headphones.

[quote name='charic' post='1063300' date='Dec 19 2010, 11:40 AM']The ones I want to use are 32ohms [/quote] A headphone amp would be overkill and probably more expensive than another pair of headphones. A resistor in series with your existing headphones would fix it as the power level is only a few hundred milliwatts. I'd suggest you borrow a higher impedance pair or try the resistor before you spend any money.

[quote name='charic' post='1063214' date='Dec 19 2010, 08:25 AM']The headphone out on my rh450 sounds a little fuzzy. I know the headphones are fine (and I've tried a few pairs) has anyone else experienced this? It's the first time I've tested it and It's a tad annoying[/quote] Headphones should be 40 - 600 ohms.