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Topic: Will too hot a signal damage an amp? |
Cliff Kane
From:
the late great golden state
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Posted 13 Oct 2008 1:59 pm |
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Hi,
lately I've been using an old DOD FET Preamp pedal with my six-strings to drive my Fender Twin Reverb tube amp. I don't think this pedal was designed as a guitar overdrive pedal as it has no on/off switch (it's on all the time); I'm guessing that it was made to be a general purpose preamp for raising signal levels. However, it makes my Twin sound great! It pumps out a lot of gain: is there any damage that I will cause to either my amp or tubes by hitting it with a high-gain preamp? It seems that I recall hearing that the Zvex Super Hard On preamp pedal was named for it being so hard on amps. As I said, this pedal makes my Twin sing, but I love my Twin and I sure don't want to hurt it at all!
Thank you,
Cliff
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Michael Douchette
From:
Gallatin, TN (deceased)
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Cliff Kane
From:
the late great golden state
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Posted 13 Oct 2008 2:59 pm
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Hi Mike,
yes, it's a cute name. |
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John Bresler R.I.P.
From:
Thornton, Colorado
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Posted 13 Oct 2008 3:22 pm
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| If it lasts more than 4 hours, call Michael!!! |
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Michael Douchette
From:
Gallatin, TN (deceased)
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Jonathan Cullifer
From:
Gallatin, TN
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Posted 13 Oct 2008 8:35 pm
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| I think you can hit Twins pretty hard without hurting them. At least I see a lot of people who do and seem to get by with it... |
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Jim Sliff
From:
Lawndale California, USA
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Posted 13 Oct 2008 9:34 pm
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The DOD pedal is similar in principle to the MXR Micro Amp - which will drive a set of headphones but not hurt the input stage of an amp. Both the Dod and the MXR make great clean-boost pedals; less distorted signal than the ZVex, but if you are running your amp at a middle-level volume you'll get a nice solo boost with any of them.
You essentially need an output stage plugged into an amp input to cause damage; a preamp is simply an additional gain stage (or more than one), and many modern guitar amps have multiple gain stages for metal-style playing. You can string several boost and overdrive pedals together and run them all at once, but you don't want to take a speaker output and plug it into an amp's input.
It's fine.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 14 Oct 2008 4:22 am
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| Distortion raises average power levels, so what's okay for low-to-moderate playing can be a problem at high levels. Too much signal can kill a speaker or weaken output tubes if the volume's run very high for long periods. |
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Jim Sliff
From:
Lawndale California, USA
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Posted 14 Oct 2008 4:53 am
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Well, distortion itself doesn't raise power at all - but raising power CAN create distortion.
However, distorted signals at volume levels equal to clean signals are much harder on a speaker; it's a much more complex signal requiring far more voice coil travel in short bursts, creating heat. Some players (mainly on 6-string) are surprised when they blow a 50-watt speaker in a 40-watt amp, but if you play with heavy distortion all the time it can happen.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 14 Oct 2008 8:08 am
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| Jim Sliff wrote: |
| Well, distortion itself doesn't raise power at all... |
Wrong. Distortion raises average power significantly! That's what I said, and that's what let's you burn out 100-watt speakers with an amp rated at 40 watts. Look up "programming", "duty-cycle", and "underpowering" in an audio engineering textbook - or even on google. |
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Cliff Kane
From:
the late great golden state
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Posted 14 Oct 2008 5:28 pm
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Thanks so much for the help and good info!
Cliff |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 14 Oct 2008 6:40 pm
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I wouldn't worry about blowing the tube input section of a Twin Reverb with a pedal like this. Tubes are pretty hardy.
However, it is possible to fry the input section of some solid state amps by feeding too large an input voltage - I have witnessed it. Such a signal would have to be pretty bloody hot - probably much hotter than a signal hot enough to make the amp sound absolutely terrible.
I agree with Donny that square-wave type distortion definitely increases the duty cycle and RMS power, and can definitely do damage to output transformers, speakers, and so on. Jim's also correct to point out that the impulsive on-off bursts of square-waves certainly also raise yet even more havoc with speakers. Twin Reverb transformers are generally pretty over-designed, but I would want to have some pretty unbelievably tough speakers if I was cranking a Twin Reverb with high distortion levels. Of course, that would also be pretty tough on power tubes - a Twin Reverb runs quite a bit higher than the 6L6 plate-voltage design center, so I'd want to have some pretty awesome NOS tubes in there if I was really cranking it. |
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Jim Sliff
From:
Lawndale California, USA
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Posted 16 Oct 2008 2:23 pm
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Haven't been able to get time to return to this for a couple of days, but I wanted to clarify and explain what looked like a set of conflicting facts; instead, everyone is right in a certain context.
Donny and Dave are correct about more distortion=more power in an absolute sense - but I was trying to ride the fine line between the guys who know waveforms and audio engineering and players with just practical electronics knowledge (r NO electronics knowledge); this subject has come up before on other forums and suddenly guys were touting their "modified" 200-watt Twin Reverbs (by sticking a distortion circuit in the preamp) and confusing the hell out of everyone...especially unsuspecting amp buyers.
It's absolutely true that when you take that square wave and lay it out flat it's a LOT longer than a comparable-amplitude sine wave, hence you DO have more power. It's the total length of the wave over a period of time that, in a simplistic sense, defines power - the longer the wave, the higher the power, and straight up, over a distance, then straight down, then over again and up again makes a much longer line than a "wavy" line over an equal distance.
These "lines" are what you see with a pure signal on an oscilloscope (like a pure 1kz signal from a signal generator - a guitar sends multiple waves even with one note due to the multiple harmonic content of a vibrating string.)
So - If you have a distorted signal with sharp edges it technically means you have more power.
But from a *practical* standpoint - you don't. The reality is, you still have a 100-watt RMS amp when measured at something like 2-3% total harmonic distortion and this is where it gets VERY confusing - and why I try to stay away from telling folks distortion means more power. It's a statement that's technically true, but is so easily misinterpreted I've found it MUCH wiser to just talk about practical (and non-inflated) power levels of amps as advertised.
This whole distortion/power increase technicality is where amp companies (cheesy ones) distorted (pun intended) claims back in the 60's with "300 watt" guitar amps - that were 300 watts only at some ungodly ear shredding distortion level that was totally useless, even for modern metal players. We are talking about distortion so intense there is zero articulation and all you hear is unidentifiable mush.
So yes - distortion DOES increase power...but it doesn't increase PRACTICAL power - in most playing circumstances.
And really, it's not the fact you have a square wave hitting a speaker that fries it - it's the increased power of the square wave...again, there's more of that "line" on a scope over a given length of time.
I hope that explains it in fairly simple terms - it's a LOT more complex than that, but it sorta shows that we were all correct and incorrect at the same time - depending on practical vs theoretical analysis.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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