Measuring Amplifiers - Page 61

Couldn't you just check your subwoofer output nearfield connected to each channel with full voltage/max gain?? That will atleast show if there is a dB or more difference??

Not easily without a dummy load. Using an SPL meter might find obvious problems but as it's taking a broadband measurement could easily give misleading results, especially with drivers in different parts of the room.

A quick method I've used is to use a high impedance resistive divider on the output of the amp. If your S/C is rated for a max of 2Vrms (say) and your amp capable of 1000W/4R or 63Vrms make a resistive divider of 40:1 and 5kR or so. I use whatever I have to hand as it can be calculated out at the end. Using resistors of only a couple of watts will do.

Connect RD across output of amp, and lower half to S/C input, apply test tone to amp input at low level and bring up slowly watching waveform on monitor, even better of you have something that will display the spectrum.

With the amp set to parallel output, both channels will be getting the same signal and should be identical at the point where they begin to clip. Power is V^2/R where R is the total resistance of the resistive divider and V is the RMS voltage or Vpeak-peak/2.828 for a sine.

Considering the love affair AVS forum members have with Emotiva, I am surprised that none has ever been tested here. I would love to see that.

Is there a formula available to determine/estimate how much an amp can output while in bridged mode for 4ohms, given the 1khz and 8ohm spec?

Reason being, I want to get an idea of how much my Yamaha p2500s can output under this load. I currently have a Fi Q18 sealed and will be adding another for ht purpose. The 2500 seems to drive the sub ok and my pioneer supplies Enough voltage to clip the amp if played loud enough but i'm just curious since Yamaha doesn't give a 20-20khz spec when in 4ohm bridge mode.

The reason they don't give the spec is that they don't rate their amplifiers for 2ohm continuous use, which is what 4 ohm bridged is.

interestingly enough I just called Yamaha today and spoke to Ed in technical support. i asked him a couple of questions and he basically told me the Yamaha PxxxxS amps are not designed to be used for 2ohm subwoofer load. There is a huge difference on sound between my EP4000 out of the box and a P3500S out of the box. The EP4000 is about 6dB hotter at max attenuater settings and seemingly has more umpf down low. Here is my post on this -
http://www.avsforum.com/avs-vb/showthread.php?t=1357457

Well actually they do, but only the 1khz rating. But the manual, at the same time advises against running 4ohm bridged all together. I plan to get a different amp soon anyway that is specifically rated for bridged 4ohm loads. I actually spoke with yammy in regards to why they list bridged ratings but advise against it, i was basically told it is only a 20ms burst rating not really a spec to consider for daily use.

Great thread. Its good to see a comparison. I dont doubt the yammy ability but at the same time, i dont wanna continue using it against the oem specs. Im on the hunt for a new amp so i got some searching to do lol

They don't rate it continuously at 2 ohm (which is what I said before), but only give a 20ms burst rating. These are two different things. Continuous means you can run 2R or 4R bridged as a long term load, and the burst to indicate it can handle odd loads where the impedance dips at come frequencies because of xovers etc and won't be damaged not have the protection step in and shut it down. It does not mean it is rated only at 1kHz, rather that is the frequency they tested it at. Bit pointless doing it at 20hz as the cycle time there is 2.5x the burst capability.

Can you break this last part down into layman terms for me? -- just the last part about the cycle time - I don't get understand what you said.

From what I've read if an amp is rated at only 1KHz at an ohm rating, it is usually a "read between the lines way" of hiding the fact that the amp doesn't put out even wattage at that particular ohm rating through the whole audible frequency range typically defined as 20hz - 20khz. Does that seem to be a true assumption?

One single cycle of 20Hz is 50ms. Rated burst period is 20ms.


No. What they are saying is that it can exceed it's continuous ratings under transients of 20ms into lower than rated loads without obvious clipping. This is useful in many situations such as I described in the previous post.
It is not hiding anything, but stating clearly under what situations it can output given amounts of power. If you don't know how to read the specs, that is not Yamaha's fault. It was probably written by an engineer for engineers.

Thanks for the explanation that makes sense. So at full gain attenuation, the amp would likely clip with ~30ms remaining on a single 20hz note cycle.

The peak portion of a 20Hz sine-way cycle doesn't last 20mS.

It is not rated for continuous duty into 2R/4R bridged. If that is what you need, buy something else.

Yes, you should go and sit in the corner - it has already been explained but you haven't understood. My life has a finite amount of time and I have wasted all I'm going to on you.

Only if YOU push it that hard. The gain/level control setting is not a power control/power limiter per se. The amp can and will put out full power and or clip at any position (except perhaps fully CCW) of the gain control if fed sufficient input signal.

I have a behringer inuke DSP 3000 I'd like to have tested if the op is still doing testing? Ill pay for shipping both ways.

Send a nice personal message (PM) to chasw98 and ask if he still has time to do an amp test. Explain the shipping costs to him.

done

i dont think amps have been actually tested here since 1981!!! whats going on??

chasw98 was only volunteering his time to test amps and this thread is stickied more as a reference than for further testing I believe. chasw98 is probably just busy enjoying life and the testing he did helped a lot of us out which I am grateful for.

I don't know if anymore testing will take place on this thread, I doubt it. It's a good reference though and I appreciate the time chasw98 took to test out the amps.

I've just re-read all of this thread for the N th time!

Still undecided which amp to get for my subs. Need about 2 X 800 watts onto 4 ohms, mostly silent operation and great efficiency a plus! Want to buy used.

Crown K2, out of production for a long time and may need overhauling to continue service in the future. Silent, great damping factor, must leave open space above and below in the rack for the passive cooling.

Crown CE4000 also out of production. Powerhouse! Loudest fan of the bunch.

Crown CTs 2000, have funny "install" connectors, should be fairly silent and have that superior damping factor Crown is renowned for.

Crown XLS 2500, just a tad underpowered, rated at 1 kHz only, dead silent and efficiency over 90%. They converts the signal to digital for processing, but that may not be an issue.

Yamaha p7000s have provided great service in pro use at my work, very efficient and silent, 100% analog and I like them a lot!

Peavey IPR 3000, the light show they put out on their own is a deal breaker for me. I wonder if one could obscure the LEDs with black paint?

I have no actual question, I just wanted to vent!

PS, I curently run a Bryston 4B which unfortunately double up as a space heater! 2.5A on iddle, ouch!

Your best bet is probably a Behringer EP2500 or 4000 if your looking to keep costs low with a proven amp.

If you want to step up then I was incredibly impressed with the Face Audio F1150TX which beat out a EP4000, QSC PLX3402 and PL 9.0 I had at the time running a pair of sealed LMS Ultra 18's. The F1150TX has been discontinued though so you would have to step up to the F1600TX but they are not cheap.

I know the F1200TS got some flack on this thread for it's 4ohm bridged performance and I happen to have one of those as well. I can tell you for sure that the F1150TX is in a different league all together. I have never had a problem with my F1200TS and sold my QSC PLX3402's because I felt the F1200TS was just better. I actually sold all of my QSC amps and now just have the Face and a single EP4000 which is gathering dust at the moment waiting for a project.

You won't have a problem running dual 4 ohm loads on the Face F1200TS and there is one on ebay right now. Face audio has excellent customer service as well, one of my F1200TS amps was running a little hot and even though I bought it used the 5 year warranty is on the amp, not the original owner. They fixed my amp under warranty and it works like new.

I just looked up those face audio amps and they seem very nice but good looord they are expensive!

There much more reasonably priced on the used market, if you can find them

In what way did the Face 1150TX beat out the PL9.0?

Considering they are passively cooled home theater amps, with the features aimed at that market (12v triggers, unbalanced inputs, nice looking case with heavy weight due to the passive heatsinking) I doubt they would fair very well on a simple price-per-watt comparison with the pro-amps tested in this thread. Different markets.

For someone like me, with my amps out of sight and hearing range in another room, the EP4000 was a no brainer. Cheap, clean, AB(H?) power... nothing really comes close for price/performance.

If I had to have my amps in-room, in listening and visual range, the Emotivias would have definitely been in the running. However, there is still a good chance I would have bought EP4000s and done a fan mod.

As far as I can see, the load resistors are water heater elements or something like them. The obvious and serious problem with these parts like these is their temperature coefficient which is usually very large, even for modest temperature changes.

I'd be happy to recant on this comment were I answered with actual tests of their resistance versus temperature from room temperature to the boiling point of water.

After playing around with the alternatives for over 50 years, I now use a load resistor bank composed of a dozen forced-air-cooled 250 watt precision non-inductive resistors.

Having enough bench power to actually test modern amplifiers is another usually unmet challenge. I pulled a 30 amp (per leg) 230 volt line to the room where I test amplifiers.

I have 2 Xti-2000s and an Xti-1000 in service. I've tried to do measurements that expose their alleged difficulties below 20 Hz, and have been unable to do so. The XTi's internal 20 amp power line fuse blows before it clips.

I've done a fair amount of work that involved exploiting the internal DSP's equalizers. A very powerful tool - very complex systems can be devised with zero external active hardware.