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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Nov 07, 2012 3:58 pm
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Aspiring Musician
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Posts: 824
If I play single notes on the 6th string, from 5 to 15 th fret and let them ring a second or so, and particularly with bassy or clean blackface presets I can hear some fizz in the back, probably 6dB less than the main harmonic for half a second or so. And that is if the speaker is pointing directly at my ear, otherwise the directionality of the mustang speaker will mask it anyway.

I can totally live with it and is more of a curiosity than anything else in my case. If it degenerates to the point it gets annoying I wil replace the power amp with another one and forget about it.

I'm not worried about loosing the warranty as it's not very useful anyway (all the problems I know about the Mustang line so far are either the fizz or broken audio connectors and those are not covered so who cares about the warranty) and that combined with the fact I should pay for the shipping in case of a return takes the warranty out of my mind completelly.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Nov 07, 2012 4:27 pm
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Joined: Mon Nov 10, 2008 7:44 pm
Posts: 136
Location: Dayton, Ohio
Well, it's down in my basement in a Sweetwater box. As I said, I bought this device with open eyes. If it doesn't work out, the only person to blame will be the one I see in the mirror each morning.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Mon Nov 12, 2012 11:35 am
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Aspiring Musician
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Okay, I think I discovered a way of making any M3-4-5 fizz, In case you want to check yours. This is not pure masochism, it actually tells me a lot about the issue at hand if I'm right. I tried with 3 different amps and got possitive results (meaning I can make the amp fizz)

I will appreciatte any feedback of people either confirming or not a not-fizzing amp becoming fizz-enabled :) this way:

On your guitar
-select your bridge pickup, preferably a humbucker in this case
-put guitar volume at 10 or max
-lower tone of the bridge pickup to 1 or min

On your M3-4-5
-Select preset 92 (basic deluxe 65)
-lower treble to minimum
-lower mid to minimum
-increase bass to maximum
-put master volume to around 2.5

Now, on your guitar, fret the 12th fret 6th string and gently pluck the the 6th string with the tip of two fingers, if you do it very hard it could mask the fizz, as the fizz is usually 3dB lower tha the actual guitar sound

so fizz or no-fizz? (is the scitar modulated high pitched sound in the back)

Techie talk warning
if the answer is that this makes fizz in all amps, I think the source is either a bad quality operational amplifier used for power amp or that the negative feedback circuit for the power amp is badly designed and the frequencies one octave(?) higher than the signal get too amplified. Particularly the second possibility could be potentially solved without even changing the power amp.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Mon Nov 12, 2012 11:44 am
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Joined: Sat Apr 21, 2012 6:39 pm
Posts: 154
I'll try this tonight when I get home. Have you verified that the resulting fizz is NOT also present on the USB output, and the FX send?



jedi2b wrote:
Okay, I think I discovered a way of making any M3-4-5 fizz, In case you want to check yours. This is not pure masochism, it actually tells me a lot about the issue at hand if I'm right. I tried with 3 different amps and got possitive results (meaning I can make the amp fizz)

I will appreciatte any feedback of people either confirming or not a not-fizzing amp becoming fizz-enabled :) this way:

On your guitar
-select your bridge pickup, preferably a humbucker in this case
-put guitar volume at 10 or max
-lower tone of the bridge pickup to 1 or min

On your M3-4-5
-Select preset 92 (basic deluxe 65)
-lower treble to minimum
-lower mid to minimum
-increase bass to maximum
-put master volume to around 2.5

Now, on your guitar, fret the 12th fret 6th string and gently pluck the the 6th string with the tip of two fingers, if you do it very hard it could mask the fizz, as the fizz is usually 3dB lower tha the actual guitar sound

so fizz or no-fizz? (is the scitar modulated high pitched sound in the back)

Techie talk warning
if the answer is that this makes fizz in all amps, I think the source is either a bad quality operational amplifier used for power amp or that the negative feedback circuit for the power amp is badly designed and the frequencies one octave(?) higher than the signal get too amplified. Particularly the second possibility could be potentially solved without even changing the power amp.

_________________
1963 Princeton
1965 Twin Reverb
1968 Bandmaster
1970 Champ
1983 (?) Musicmaster
2012 Mustang III
West Grande (x2)
Acoustic G60-T
Marshall JTM 60


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Mon Nov 12, 2012 1:26 pm
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Aspiring Musician
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Posts: 824
Very good point Thompal, with that setup there is no fizz on:
-fx-send
-phones
-USB out

More tech talk warning
Particularly in the case of fx-send, if we had fizz, that would point to a wiring or PCB track to track feedback that would be much more difficult to solve

I did a spectral analysis of the fizz vs the original signal and it appears to be 3 octaves higher than the base note, the timbre is different because some of the harmonics are more excacerbated than others, but for example for our case of a note in 165 Hz (12th fret 6th string) if you filtyer out above 1500 hz the fizz is gone.

This would explain also why the fizz is only audible mostly on the 6th and 5th string, because if the fizz is always 3 octaves higher, at some point the mustang speaker is simply not able to reproduce it anymore (around 5Khz according to Celestion site). In fact using my setup, I just can not hear the fizz anymore above the 2 string 12th fret, and in general is difficult to hear above 4th string.

Again guys, please let me know if your non-fizzing amp fizzes using this setup


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Mon Nov 12, 2012 1:38 pm
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Amateur
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Joined: Sat Apr 21, 2012 6:39 pm
Posts: 154
jedi2b wrote:
Very good point Thompal, with that setup there is no fizz on:
-fx-send
-phones
-USB out

More tech talk warning
Particularly in the case of fx-send, if we had fizz, that would point to a wiring or PCB track to track feedback that would be much more difficult to solve


Since it does not exist on the headphones, USB, or FX send, it also eliminates any DSP or converter error (digital realm distortion, aliasing, etc), and places the problem firmly in the analog output section (power amp). Good job (and good news)!

_________________
1963 Princeton
1965 Twin Reverb
1968 Bandmaster
1970 Champ
1983 (?) Musicmaster
2012 Mustang III
West Grande (x2)
Acoustic G60-T
Marshall JTM 60


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 3:19 am
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Hobbyist
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Joined: Sun Nov 18, 2012 4:23 pm
Posts: 98
Anyone managed to see what part in the poweramp is making this fizz? Maybe change an IC? I am okay with the soldering-iron but not good good with experimenting with electronic components, if I have a schematic or know what to replace I can test it at home.

That phaser-like effect is even worse than the distortion itself.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 3:57 am
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Professional Musician
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Joined: Sun Jun 17, 2012 11:37 am
Posts: 1315
Location: England
My 2p / 2c - not because I'm an expert, and not because I want to get involved in the speculation and debate in this topic, but I'd hate to see someone chop-up their amp for the wrong reason.

I don't think the power amp itself is at fault. The only explanation that (to me) is consistent with *all* the reported evidence, is noise being introduced into the power amp from the DSP section, by a means other than the audio signal. The most likely such means would be the power supply line, if this is shared by the power amp and digital sections of the amp, and not adequately isolated between the two.

So, fitting a new power amp with its own power supply will probably fix the problem - not because of the new power amp, but because of the separate power supply.

Also, fitting a new power supply for the existing power amp (and isolating the power amp from the power supply to the DSP section) would probably achieve the same and may be simpler. Again, not because of the power supply per se, but rather the isolation that gives from the original power supply being polluted by noise fed back into it from other parts of the amp.

Another route would be working out how to shield the existing power supply to the power amp from the power supply to the DSP section. This sort of thing is typically only a couple of capacitors and resistors, but the necessary connection points may not be accessible (if internal to one of the chips, for example).

Conversely, fitting a new power amp that uses the existing power supply, without adding any additional isolation/shielding, probably won't fix the problem.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 8:56 am
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Aspiring Musician
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Joined: Fri Aug 03, 2012 8:08 am
Posts: 824
Hi Scott,

a couple of observations:
-I don't think the fizz has anything to do in any way with the pre-amplifier itself or the connection between pre-amplifier and power amp, and this is the reason: if you connect your guitar directly through the fx-return, with enough volume on your guitar you will be able to hear the fizz, and AFAICT the fx-return gets directly in the power amp and actually cuts out the pre-amp connection to it while anything is plugged into it.

-the PS interference theory is possible but unlikely in my opinion, and this is why: i discovered the fizz is a two harmonic overtone that is 10x and 15x the fundamental note you play. I'm not aware of any kind of PS interference that is so dynamic in nature

-Now this is what I think is happening on the power amp module: pretty much all power amp chips have either internally to the chip or externally some sort of negative feedback network (capacitors, resistors and sometimes active components) to avoid the power amp to distort or oscillate. If the feedback network is badly designed, or has some bad quality component, some frequencies will be more cancelled than others by the feedback network or will have a tendency to exacerbate some oscillation on some particular frequencies (which is the fizz itself on my opinion)

Unfortunately I wan unable to find anywhere a electronic schematic of the mustang power amp so I can not analyse the root cause.

In the meantime if anybody can post the results with the fizzy-setup I posted before that would give us mounting evidence against the power amp design, if we van prove than all mustangs will fizz more or less. This will lead us to the path of creating a simple mod to correct the issue.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 1:37 pm
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Roadie
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Joined: Tue Oct 19, 2010 7:26 am
Posts: 238
Quote:
-the PS interference theory is possible but unlikely in my opinion, and this is why: i discovered the fizz is a two harmonic overtone that is 10x and 15x the fundamental note you play. I'm not aware of any kind of PS interference that is so dynamic in nature


The fizz I saw didn't look anything like a two harmonic overtone. The fizz is not a stable frequency. It moves. It's like a flanging effect.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 1:48 pm
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Aspiring Musician
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Joined: Fri Aug 03, 2012 8:08 am
Posts: 824
Hi,

that is correct. the phaser effect you talk about is the effect of the two overtones going up and down in amplitude in alternance which creates the feeling of a modulation.

One interesting fact is that the mustang speaker is no good for frequencies greater than 5khz, 6khz if you are lucky, which means, if i'm correct that the fizz should diminish and then disappear for notes above 400-500 hz (somewhere in the middle of the 2nd string I think) that is pretty much what I can hear in my case.

Obviously if the preset you use has a lot of overtones they will mask the fizz (any overdrive for example), but if you choose a clean preset with a lot of bass you will get it right away, particularly if you roll off your treble on your guitar, as the overtones I'm talking about will really contrast with the guitar tone.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 1:57 pm
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Roadie
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Joined: Tue Oct 19, 2010 7:26 am
Posts: 238
jedi2b wrote:
Hi,

that is correct. the phaser effect you talk about is the effect of the two overtones going up and down in amplitude in alternance which creates the feeling of a modulation.
...


I don't see two overtones going up and down in amplitude.

I see some tones sweeping in frequency. It's a frequency modultion effect not an amplitude modulation effect. It's phase distortion.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 2:02 pm
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Aspiring Musician
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Joined: Fri Aug 03, 2012 8:08 am
Posts: 824
I will try to go again through the spectrum plots I got and posts the results but I can tell you that definitely there is an harmonic bloom at 10x-15x the fundamental.

How did you get your results? I could try to imitate your setup.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 2:53 pm
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Roadie
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Joined: Tue Oct 19, 2010 7:26 am
Posts: 238
jedi2b wrote:
I will try to go again through the spectrum plots I got and posts the results but I can tell you that definitely there is an harmonic bloom at 10x-15x the fundamental.

How did you get your results? I could try to imitate your setup.


The fizz in NOT harmonic. It's a frequency sweep that has no business being part of a clean guitar signal, which is (ignoring things not worth talking about here) harmonic.
To take a guitar signal and get something like the fizz you need to mess with the phase.

The fizz is also not somthing you go out of your way to try to recreate with extreme settings on the guitar or amp. To have the fizz means that you can't get a clean sustaining
guitar signal.

Instead of trying to reproduce fizz, why not take one of the posted clips and analyze that.


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Post subject: Re: Mustang III - Digital Aliasing (Strange Fizz Sound)
Posted: Wed Dec 05, 2012 3:34 pm
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Amateur
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Joined: Sat Apr 21, 2012 6:39 pm
Posts: 154
jedi2b wrote:
Hi,

that is correct. the phaser effect you talk about is the effect of the two overtones going up and down in amplitude in alternance which creates the feeling of a modulation.


Does the changing amplitude of the overtones seem to be related in any way to the LFO frequency?

_________________
1963 Princeton
1965 Twin Reverb
1968 Bandmaster
1970 Champ
1983 (?) Musicmaster
2012 Mustang III
West Grande (x2)
Acoustic G60-T
Marshall JTM 60


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