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Post subject: Mustang IV: Hiss from Power Amp: Acceptable or Problem?
Posted: Mon Jul 02, 2012 6:36 am
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I'm wondering how much hiss is reasonable from the power amp section of a Mustang IV?

Note I don't mean 'fizz' nor am I referring to deliberately-introduced noise to emulate the original amps being modelled. Also it isn't interference picked up by the guitar lead, or anything else like that. And it's not mains hum. I've done enough tests to eliminate all those. [EDIT] Firmware is 1.10.

With all volume controls set to minimum, especially the master volume, there is an audible background hiss from the speakers. It's the same on all presets. It isn't present on the headphone output (well, if I turn the master volume up high, there's a bit of hiss through the headphones, but they're completely quiet otherwise). Also, when I plug the headphones in, the hiss from the speakers stops, as one would expect.

Surely there's no reason for the analogue amp parts of the Mustang to be anything other than whisper-quiet, hifi quality, FRFR (cf the cheapest of cheap hifis these days doesn't hiss). So I'm a bit surprised by this.

The hiss isn't loud, but it's definitely there, and is still audible in an otherwise quiet room when playing. It's loud enough to be irritating and distracting. It's probably comparable to the volume and type of sound you get when blowing (not whistling) air forcibly through pursed lips. Not an exact analogy but I hope that gives the idea. It's not as loud as the background noise from my other amp - but that's an old, small, cheap, solid-state amp that I wouldn't expect to be good. I was hoping for better from the Mustang.

My question is whether I'm being too fussy and this is an acceptable level of hiss for a guitar amp, and a Mustang in particular? Or if my amp has a problem I can take it back to the shop, but wanted others' views first as that's a bit of a trek and I don't want to make a fuss if it's normal. I don't recall hearing it on the demo model I tried, but probably it was masked by the background noise in the shop.

Thanks for any opinions/comments.
Scott


Last edited by scott-uk on Mon Jul 02, 2012 8:38 am, edited 1 time in total.

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Post subject: Re: Mustang IV: Hiss from Power Amp: Acceptable or Problem?
Posted: Mon Jul 02, 2012 8:34 am
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Scott, just to rule out the basics ... did you update the amp firmware to v1.10? My MIII is very quiet ... maybe an MIV owner can verify what kind of hiss you can expect.

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Post subject: Re: Mustang IV: Hiss from Power Amp: Acceptable or Problem?
Posted: Mon Jul 02, 2012 8:43 am
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Hi, always good to check the basics, but yes, the firmware is 1.10.

Also worth pointing out that, because it's a high-frequency hiss, it's quite directional. It's most noticeable if I'm sitting right in front of the amp. If I'm standing a few feet to one side, it's much less audible. That may explain why I didn't hear it in the shop, and perhaps why different owners report different amounts of hiss? (I found a few old topics talking about hiss to greater or lesser extents)


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Post subject: Re: Mustang IV: Hiss from Power Amp: Acceptable or Problem?
Posted: Fri Jul 06, 2012 7:18 am
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I was also somewhat disappointed with background hiss on the M3. The amp modeling stage contributes quite a lot of the hiss, but it's there to a lesser degree also when bypassing everything digital and going directly to the power amp through the FX return. Like that it's still there, but much less objectionable.


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Post subject: Re: Mustang IV: Hiss from Power Amp: Acceptable or Problem?
Posted: Fri Jul 06, 2012 6:16 pm
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I have been trying to find this problem and so far can't. My Mustang 3 is quiet, no hiss or fizz. I will look into the schematics and see what I can find.
ABS :D


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Post subject: Re: Mustang IV: Hiss from Power Amp: Acceptable or Problem?
Posted: Sat Jul 07, 2012 3:47 am
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I've had a couple of modeling pedals in addition to my MIII, and they've all had hiss. The crisper and more trebly the model, the more hiss there is since the upper frequencies are being boosted, and that includes any hiss inherent in the processor.

This is why noise gates were invented, and I have them included in all my working presets to one degree or another. The Mustang noise gate is pretty good. The only model that has so much hiss that I find it unacceptable is the Princeton.

You can also experiment with changing the cab on the preset, since each one of those is EQ'd differently. Also, some models have a presence control and/or a bright switch, adjustable on Fuse, and that can affect hiss.

In the final analysis, these are mass-produced, solid-state modeling amps, not tube amps--which BTW have their own set of headaches. Pick your poison.


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Post subject: Re: Mustang IV: Hiss from Power Amp: Acceptable or Problem?
Posted: Sun Jul 08, 2012 6:55 pm
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Quote:
amp modeling stage contributes quite a lot of the hiss

Quote:
hiss inherent in the processor ... noise gates ... changing the cab

As per original post, this isn't hiss introduced in the modelling stage, and it isn't amplified noise. If it were, I'd hear it through the headphones. But it isn't there on the headphone output, only on the amp's speakers - ie the power amp output.

Also, the hiss is still there when all volume controls are set to minimum, and with noise gates turned fully on, and with master volume set to minimum. That is, there's still hiss in the power amp when all signal (including noise) to the power amp has been cut off.

NB Yes I've checked that the headphones (and the headphone circuit in the amp) aren't just attenuating the noise: if I select a noisy model (and turn off the noise gate, etc), I get the same noise type and level through both headphones and speakers.

Quote:
these are mass-produced, solid-state modeling amps ... Pick your poison

Indeed. I didn't say I was looking for perfection. I was asking whether others had this hiss and whether it's considered acceptable for this type of amp. If the answer is that it's expected/acceptable, that's fine. If the answer is that the power amp, in its quiescent state, should be hi-fi-quality silent, then I'll know mine has a fault. I was just asking for others' experiences to help ascertain that. Thank you to everyone who's replied for your comments.

Quote:
will look into the schematics and see what I can find

Thank you, that will be interesting.


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Post subject: Re: Mustang IV: Hiss from Power Amp: Acceptable or Problem?
Posted: Tue Jul 10, 2012 11:25 am
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New guy on the block here, just bought a MIV and its very quiet and also fizz free! The noise gate work nicely on the high gain models!


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