Harmonics

[audioguru]

You added a second harmonic with resistors but the phases were not the same to show compression or expansion of half the waveform. You might be able to use an all-pass filter to adjust the phase of one of them.

 

[linguist]

Merv,
Thanks for your time & explanation, it is very helpful indeed, a good explanation as well.

audioguru,

Yes I see, I will try a few things.

Thanks to everyone for the help with this!

Cheers

 

[linguist]

I have posted a youtube link of a JJ Cale song & in particular the guitar audio from 3 Minutes on.

YouTube - JJ Cale ... Guitar Man

From 3 minutes on in the clip you hear the valve amp working nicely--well to some!

What makes up this sound.

Is this just an overdriven valve amp with a good share of 2nd Harmonic or is their more to this sound besides maybe some voltage sag?

My appologise Merv if you read this & the audio is difficult!

Cheers

 

[audioguru]

I have posted a youtube link of a JJ Cale song & in particular the guitar audio from 3 Minutes on.

YouTube - JJ Cale ... Guitar Man

From 3 minutes on in the clip you hear the valve amp working nicely--well to some!

What makes up this sound?

Is this just an overdriven valve amp with a good share of 2nd Harmonic or is their more to this sound besides maybe some voltage sag?

Many guitar pickups and guitar speakers have a peak in the response at a fairly high frequency that I heard.
I also heard a lot of overdrive of a single valve causing even harmonics distortion which caused the sustain type of sound.
Valve amplifiers and speakers made for playing guitars have poor very high frequency response that cuts off the very high harmonics.

 

[linguist]

Thanks audioguru,

I see what you mean with the sound, learning about & studiying harmonics is one thing but knowing what your listening to is I think an important part of it.

So if I have things correct, besides the overdriven valve creating the even harmonics etc , it is the frequency response of the pickups, amp & speakers as a combination that gives the final sound.

Is it best to try to design an amp that closely duplicates the frequency response of the speakers instead of having an amp & speakers with differing frequency responses?

Cheers

 

[audioguru]

A single 8" to 12" speaker has a peak in its response at 3kHz to 6kHz unless it is made very heavy to be a woofer only for bass frequencies.
The pickup coil for an electric guitar resonates with cable capacitance to make a peak in its rersponse.

Since the electronics for a guitar are overdriven and have awful distortion (called fuzz) then the poor high frequency response cuts the highest harmonics so the sound is not too shrill.

 

[linguist]

Thanks audioguru,

I can see what your saying, you have made things a lot easier to understand.
Yes, their is a lot of awful distortion sometimes, it needs to be tamed.

Is a "resistive" load really the correct way to test an amplifier considering they normally have an inductive load when operating.
This would have to give a variation in results.

What's the best load for testing an amplifier besides the speakers themselves?

I have been reading about people who test amps with square waves to look for distortion, which is most suitable in your opinion, a sine or square wave for testing?

Cheers

 

[linguist]

Sorry for the double post again!

I have attached an FFT of a circuit.

How to analyse this correctly, as you will see their are odd & even harmonics.

It was mentioned that 1% (-60db) is audible, I understand that but from the picture attached what "won't you hear" or will all these harmonics be audible?


Cheers

 

[audioguru]

Yes, there is a lot of awful distortion sometimes, it needs to be tamed.

Rock "music" is full of distortion.

Is a "resistive" load really the correct way to test an amplifier considering they normally have an inductive load when operating.
This would have to give a variation in results.

A solid state power amplifier has an extremely low output impedance so the inductasnce of a speaker does not make any difference to the response or to the distortion. Amplifiers are tested with a non-inductive resistor for a load.

I have been reading about people who test amps with square waves to look for distortion, which is most suitable in your opinion, a sine or square wave for testing?

A square-wave is full of odd-harmonics distortion.
The distortion of an amplifier is measured with a pure sine-wave at the input. The sine-wave has only one frequency which is the fundamental frequency. At the output of the amplifier the fundamental is notched out in a distortion analyser then anything remaining is distortion and noise of the amplifier being tested.

It was mentioned that 1% (-60db) is audible

No.
1% is -40dB and is audible to almost everybody. 0.1% is -60dB. Odd harmonics sound "awful" but even harmonics are musical and don't sound too bad.

 

[linguist]

Thanks again audioguru,

Yes I should have written 1% is -40db, like to say it was a typo but it wasn't.

Now armed with all this wonderful information, it's time to get the soldering iron out & then make some noise, or smoke?

Cheers

 

[linguist]

I finished designing a guitar amp circuit idea i've had, the idea was to add or take away particular harmonics as needed.
I read on Rod Elliots site where he said that basically this can't be done in real world conditions, with the FFT attached I have added just a second harmonic.

I can adjust things to get the fundamental frequency only etc.

With the components selected carefully is it possible to come close to the results that LTspice shows.
I know I have to build it to see for myself but how close is LTspice?

Cheers

 

[audioguru]

I have never heard music that is a fundamental sine-wave plus only the second harmonic. Maybe it sounds something like a flute.

Most musical instruments (except a flute) produce many harmonics. An amplifier with distortion adds many harmonics. Even harmonics are the 2nd, 4th, 6th, 8th, 10th and maybe 12th harmonic and are added to all the sounds that are produced. The amplifier and speaker might not be able to produce the highest harmonics.

 

[linguist]

audioguru,

Yes, especially a guitar has many harmonics-overtones, I am attempting to change a few things around so I can just add in or take out what harmonics I want & be selective about it.

My reasoning is that a particular sound is made up of certain harmonics so to get those harmonics for a particular sound it should be made easier if one can add or take away what is or what is not wanted.

May be silly, but for chasing particular sounds surely being able to select the harmonics to a degree will make for some interesting tones.

The FFT posted is from my valve amp design, I can add in & or take away many harmonics with the circuit.

I find it interesting

How can I add noise into the LTspice sim?

Cheers