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asr_jon

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I have some 100W 8ohm resistors, a multimeter, a couple of laptops, a good firewire audio interface, a cheap (Audiogram) USB interface which I don't mind if I blow up, and a desire to play with REW.

I believe my new BT20A pro is pushing out distortion at levels it oughtn't - or at least I'd prefer it didn't, but I'd like to establish:

1. am I really getting distortion or am i imagining it
2. am I driving the input too hard
3. is the distortion coming from my speakers

Plus I feel like if I start measuring I'll get a better handle on what the equipment is doing.

Can I learn anything useful with the resources I have? Where to start?
 

fpitas

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I have some 100W 8ohm resistors, a multimeter, a couple of laptops, a good firewire audio interface, a cheap (Audiogram) USB interface which I don't mind if I blow up, and a desire to play with REW.

I believe my new BT20A pro is pushing out distortion at levels it oughtn't - or at least I'd prefer it didn't, but I'd like to establish:

1. am I really getting distortion or am i imagining it
2. am I driving the input too hard
3. is the distortion coming from my speakers

Plus I feel like if I start measuring I'll get a better handle on what the equipment is doing.

Can I learn anything useful with the resources I have? Where to start?
I'd start by using a measurement mic. Most programs (REW, Holm Impulse etc) will show distortion.
 
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A

asr_jon

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I'd start by using a measurement mic. Most programs (REW, Holm Impulse etc) will show distortion.
I have one, post now edited. let me check my measurements, I saved them.

So other than the actual distortion measurement, can I run spectrum analyser, then pump a sine wave through it and wait for harmonics to pop up?
 

RayDunzl

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fpitas

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I have one, post now edited. let me check my measurements, I saved them.
If you really are hearing distortion, that should be relatively easy to spot.
 

Gruesome

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To answer the question, yes, you can measure distortion both from the amplifier output using your USB (or firewire) input/output interface, or from the speakers, feeding the microphone into your audio input (ADC) gizmo.
Feeding the amp output into an audio interface one has to be a bit careful, because of a) levels, and b) not accidentally/unknowingly shorting bridge-tied amp output lines to ground.
Maybe best to start with a headphone output, or indeed with the speaker-microphone route.

REW takes a bit of playing around to become aware of the settings and options. There is an REW support forum at https://www.avnirvana.com/forums/official-rew-room-eq-wizard-support-forum.10/ .
It's probably best to read up a bit first, but in a nutshell, after firing up REW and selecting your audio in and out devices in preferences/soundcard, you can hit the 'RTA' and the 'generator' buttons at the top of the main REW window, hit the green 'play' button in the generator window, and the red 'record' button at the top right of the RTA window, and if you cabled things just right, the main frequency peak and beautiful harmonic distortion peaks will pop right up.
 
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