Measuring Amplifiers - Page 57

Yes, here they are! 4 way programmable active and balanced.



These are before I mounted the power switch and summing switch. Obviously it is before I had the panels silkscreened. It works very well.

Chuck

You didn't miss it at all. When I asked the folks at Peavey about a 'bridged mono' setting, I was told this. (And this is why it is a unique amplifier!)

"Peavey does not advertise or list bridge specs. The amplifier can be externally bridged. This is because the B channel is already inverted on the output (and again on the input). That in effect puts the amp in bridge mode when it is in stereo mode. To externally bridge, all that is required is to connect the inputs in parallel via the rear panel patch jacks. The combined output consists of pin 1+ of channel A and 1- of channel B. Alternately, if using the phone plug outputs (which you shouldn't due to their power limitations) the tip of the plug on channel A is + and the sleeve of channel B is the -. The eight ohm bridge spec then simply becomes twice the four ohm stereo spec."

And no, you should not try testing this with a 4 ohm load which essentially puts the unit into a dual 2 ohm load. The amplifier will run a 2 ohm load when playing music. (Probably all day and into the night. It did on my pair of sealed subs.) But when you try and measure the unit with sine waves for power output and distortion, etc. it will trip the breaker. It will only run in 2 ohm stereo for a minute or so with sine waves at full power. But with music, it will run all day.

So, no, I did not test it in bridge mode.

Chuck

Oh, it is absolutely the burst vs. RMS discussion. Digitals, Class D, Class A, Class A/B, etc. are not per se any better at burst than any other. And it is not really a burst vs. RMS because you are measuring RMS watts in both cases. You should properly call it a "Burst vs. Steady State" discussion. What determines how many watts an amplifier can put out in a given 'burst' of time is more determined by its slew rate. Back in prehistoric days when I went to school at Crown we were told that anything over 10V per microsecond slew rate didn't matter and you could not hear the difference. Now you are talking about a 10 volt change in a microsecond! That would interpolate out to a 100 volt difference in 10 micro seconds. 100 volts at 8 ohms = 1,250 watts RMS. So in 10 microseconds you can have a difference of 1,250 watts in any amplifier of any topology that can attain a slew rate above 10 uV per second. Obvioulsy the discussion comes down to..... can you maintain that 1,250 watts for more than 60 seconds? That is what the older generation of amps can do. Work out the numbers for a 60 ms burst time with 20 ms down time. Now we are talking about milliseconds. .06 seconds on, .02 seconds off and so forth. And then you need the test gear that is fast enough to measure at that short an interval. You will hear the argument that measuring by using a burst of power is more like "real world" usage. Let me know when you put on Slayer and crank it up as to whether or not there is any let up in the music that resembles 60 ms on, 20 ms off. Some would argue that most of Slayer's music is a bazillion ms on, NO seconds off! That may be an extreme example but if you are listeniong to a concert DVD of a fairly intense rock group at a loud volume, you are asking your amplifiers to put out continuous watts, not a burst here and there. And, yes, you can argue that a subwoofer amp will only need to supply megawatts for a short duration when called on so that burst testing is appropriate in that situation or is it? And then you come full circle to argue about what would be a fair cycle for burst testing or what would be a fair amount of time for steady state sine waves. And the arguments go on and on.

More long windedness.....

Chuck

Under normal conditions of playing music and movies it should do 4 ohm bridged or 2 ohm stereo (which are essentially the same to this amp).

Chuck

Look here at Par-Metal. They come with a blank front panel that you can then machine or drill, whatever. They are available in different rack mount heights and depths. A reasonable price for a one off custom project.

Chuck

Ahh, but will you take it to the next level? Build it so it is true balanced from input to output, then use a 46 position Shallco stepped attenuator with remote control option, matched pair fets all around (since you are building balanced you will need 2 sets of PC boards), and finally a low noise, low ripple, external DC power supply. Then you will have a preamp!

Oh, and don't forget the custom milled 1/2" aluminum faceplate instead of the faceplates that come with the Par-metal units

Chuck

Not that I have ever thought about building one of those...........