spectrum analyze an amp..dyno test

jim milewski · Post by **jim milewski** » 28 Sep 2004 4:03 am

I read a lot of motorcycle tests, they dyno test the bikes engine to let you know the HP, torque at an RPM etc. It would be informative to put a pink noise generator into an amp and get a graphic illustration of the tonal characteristics of the amp, what frequencies it is strongest at. An example would be to have the readout of a Session 400, then use that to compare to an amp you may be interested in. Of course tone settings, cabinet, and speaker being used, room acoustic characteristics, etc., would come into play

John Daugherty · Post by **John Daugherty** » 28 Sep 2004 4:14 am

Jim, the NV400 has enough EQ control that you you can vary the response curve any way you like. Response curves would be useful for power amps w/o EQ controls but all good amps have a flat response and the speaker is the controlling factor.

jim milewski · Post by **jim milewski** » 28 Sep 2004 4:25 am

John, I agree, the power amp does have it's own tone characteristics, I think that's why MusicMan and some Peaveys were hybrid, using SS preamps and power tube poweramps. But I have an early Session 500 that has that "honk" no matter where I set the eq, I can minimize it, but it's still there. My Session 400 is (to my ears) a better sounding amp, and the schematic of the two power amps are not all that much different. I would think a power amp should be linear.[This message was edited by jim milewski on 28 September 2004 at 05:26 AM.]

Mike Brown · Post by **Mike Brown** » 28 Sep 2004 4:56 am

Jim, ever considered our Session 500 mod kit for the eq circuit. Here is a link to the kit from our website; http://www.peavey.com/media/pdf/steelguitar/Session500mod.pdf

The U.S.MSRP of this kit is $36.35 and the part number is #90500050. You may purchase it through your local Peavey dealer or direct from the factory by calling toll free in North America at 1-877-732-8391.

Mike Brown
Peavey Electronics Corporation

Ray Minich · Post by **Ray Minich** » 28 Sep 2004 7:52 am

I would think a power amp should be linear.

And therein lies a controversy that has existed since the beginning of electronic audio reproduction and amplification. How linear? Exact linearity is best left to transmitter boosters for radio communications. It's the subtle non-linearities that give each amp circuit/system it's own characteristics (as in warmth, hardness, softness, crispiness, etc.

Ricky Littleton · Post by **Ricky Littleton** » 29 Sep 2004 4:28 pm

When I had my electronics shop in Texarkana, I ALWAYS did a pink noise/spectrum test before it went on the "READY FOR PICK-UP".

Ricky...

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Emmons LeGrande - 8x4
Session 400 Ltd, Peterson VS-II Tuner
Dan-Echo, E-Bow, Ibanez Distortion, Boss Comp./Sustain, Ibanez Auto-Wah, PX4 Pandoras Box

T. C. Furlong · Post by **T. C. Furlong** » 6 Oct 2004 5:56 pm

Measuring a preamp/equalizer/power amplifier/speaker (like a steel guitar amp) is pretty easy to do if you have the right equipment. I do it in my business with sound systems etc. several times per week. Interperetting the results of the tests is not such an easy task. There are a few things other than frequency response to consider. Two things that come to mind are phase response and subtle distortion. Phase is a basically when frequencies arrive at slightly different times. When they do they create sort of acoustic filters called "comb filters" (named because the response looks like the teeth of a comb)This has a huge impact on how we hear the tonality of complex signals (as compared to pure tones)Think of the sound a phase shifter makes with a guitar. Imagine one of those stuck during it's shifting cycle. That is what a shift in phase can do to your sound. BTW all equalizers, or tone controls introduce phase shift into the signal when they boosting or cutting frequencies. Subtle types of distortion can also influence the way we perceive tone. I refer to subtle distortion as compared to obvious distortion (amp breaking up, fuzz tone, amp models, etc.)Tubes have a different type of subtle distortion than transistors and I think that's the main difference between the two "sounds".

If anyone is interested in learning more about measuring frequency response and phase response, the equipment etc., shoot me an email.

TC Furlong