#1
I tried asking this on the Vox forums but didn't get an answer. I have a Vox VT30 amp and I recently changed out the stock speaker with a Celestion G10 Vintage. I noticed though in my Vox owners manual that the stock speaker was 4 ohm and the Celestion I put in is 7.47 ohms. Is this safe for both the amp and speaker or am I taking a risk of blowing something out?
#2
ted weber has addressed this in his faq
Quote by TedWeber
I have heard various views on impedance mismatches between the amp and the speakers. One is that you should always match the impedance (4 ohm amp = 4 ohm speaker or two 8 ohm speakers in parallel), or you can blow your transformer. The other is that it is fine to mismatch, but you may lose power. Should the impedence match? If yes, then how quickly could you damage your amp when you have a mismatched impedence?

Chuck, technically, you should always provide a load that is recommended by the manufacturer of the amp. The designer of the amp chose a particular output device (tube) and specified all of the operating voltages for the output stage so the tube would work at its optimum efficiency while delivering maximum power to the load with minimum distortion. Ok, so let's discuss the problems associated with mismatches. When you use a load that is lower than the intended load, the output has to drive the load (speaker) with more current because it is a lower impedance than is expected. Two inherent problems associated with transformers are flux leakage and regulation. Flux leakage is also referred to as leakage inductance. It is related to the current in the secondary, and these problems increase as the current increases. As the current draw in the secondary increases, the primary has a more difficult time transferring the signal to the secondary, so the secondary signal to the load gets squashed, or 'soft-clipped'. This soft clipping is called regulation. While regulation is desireable in a power supply, it is undesireable in a transformer. In other words, in a power supply, if the input voltage or the output load current changes, we don't want the output voltage to change. In a transformer, we want the output voltage to follow the input voltage and not regulate at all. When you put a heavier load on the output than was intended, it will pull the output voltage down, hence regulation. The leakage inductance problem arises because the current from the heavier load causing the regulation to occur reduces the efficiency of the transformer by not allowing the output to follow the input. Transformer designers simulate or view this problem as having extra inductance in series with the primary. The extension of this idea then, is that with the heavier load, you could affect the efficiency of the transformer, alter the frequency response (due to the extra leakage inductance in series with the primary), and cause other distortions to occur. OK, on to mismatching the other way. A speaker is a current operated device in that it responds to the current through it to generate a magnetic field that works against the magnetic field of the speaker magnet to make the cone move in and out. Thinking in very short amounts of time, when the output charges up the voice coil with current, then the signal goes away or gets reduced, the cone system moves the voice coil back to its home or resting position. As it is moving back, it generates a voltage that is fed back up the line into the transformer and appears in the output circuit of the amp. This generated voltage is often referred to as flyback voltage, because we are charging up an inductor, then when we disconnect or stop charging the inductor, the magnetic field in the inductor collapses and induces this big voltage into itself. This big voltage then 'flies back' to the source of the charging current. There is a mathematical formula to determine how big the voltage is and it is related to the inductance of the voice coil, the amount of time it was fed current, and how much current it was charged with. The bottom line is that the voltage fed back to the output circuit is oftentimes much higher than the voltage that was used to drive or charge up the voice coil initially. This voltage gets transformed up by the turns ratio of the output transformer, and in many cases can be over 1,000 volts. What happens then is that arcing can occur between the pins on the output tube socket. Once this has occured, a carbon path forms on the tube socket between the pins. The carbon path allows a steady current to flow between the pins and eventually burns up the socket due to the heat that is generated. For example, it wouldn't be too uncommon to see a transformer turns ratio of 30:1. If we had a voltage fed back from the voice coil that was around 50 volts, 30 times 50 would be a 1,500 volt spike at the plate of the output tube. This is why you often see designers connect diodes in a string between the output tube plates and ground. They are trying to suppress these spikes and dissipate the energy in the diodes rather than allowing an arc to occur at the tube socket. So, when you use a higher impedance load on a lower impedance tap, the turns ratio is higher and resulting fed-back (flyback) voltage gets multiplied up higher than what it would have been with the correct impedance load.
It's just about impossible for me to answer how long an amp would last under these conditions. It all depends on how the designer took these potential problems into account in his or her design with regards to the quality of the tube sockets, the use of stringed diodes, the output circuit operating voltages, etc.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
#3
Thanks for the wall of text, can I get a more solid answer from someone?
#4
damn dude it's all right there, that is a more solid answer than you can get just about anywhere on this forum.

it says it's bad. not only does it say it's bad, but it says no one can tell you how bad it is without knowing the engineering of the amp. but you are running a higher impedance speaker, this is causing an astoundingly higher flyback voltage to your transformer, eventually the transformer will be ruined. thats major bad.

if the above is too much then just read: ITS BAD, THAT MEANS IT'S NOT GOOD.

really that is a complicated question, and deserves an actual answer. this speaks volumes on how much you really care about your gear if you are unwilling to read a couple of dense paragraphs.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
Last edited by gumbilicious at Oct 1, 2009,
#5
Quote by gumbilicious
this speaks volumes on how much you really care about your gear if you are unwilling to read a couple of dense paragraphs.


And this is coming from someone that calls himself "a prick with no good equipment, no musical talent, and bad advice"?
#6
exactly, you were forwarned.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
#7
Seriously TS, this guy took the time to not only give you the answer, but find a paragraph that was exceptionally detailed and provided all kinds of explanations to back up the answer, and you've done nothing but be ungrateful and flame him. Classy...
Gear:
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2012 Babicz Identity Dreadnaught
2015 Gibson Les Paul Traditional SR
Line 6 POD HD500
Peavey XXX 112
Fender Blues Jr
#8
Looks like I found my answer on Celestion's site:

"Speakers must be capable of taking at least as much power as the amp puts out, or you risk damaging them. So, for a single speaker, pick one with a power rating the same or higher than the amp itself"

Looks like I'm good according to Celestion...
#9
Quote by Musicman48858
Seriously TS, this guy took the time to not only give you the answer, but find a paragraph that was exceptionally detailed and provided all kinds of explanations to back up the answer, and you've done nothing but be ungrateful and flame him. Classy...


No he took the time to copy & paste a bunch of bull**** that didn't help me with my question. And with a sig such as his I'm not going to take him seriously.
#10
power rating is watts, not ohms.

So for a 60 watt amp, have at least a 60 watt speaker. Not the same as impedance.


edit: He didn't copy and paste stuff that wasn't helpful, it was quite helpful, it did answer your question, and you just didn't bother to read it. And seriously, because of a sig that's clearly in jest you're ignoring his advice?
Gear:
2003 Fender Standard Strat w/ Texas Specials
2010 EBMM BFR JP6
2012 Babicz Identity Dreadnaught
2015 Gibson Les Paul Traditional SR
Line 6 POD HD500
Peavey XXX 112
Fender Blues Jr
Last edited by Musicman48858 at Oct 1, 2009,
#11
Quote by Musicman48858
Seriously TS, this guy took the time to not only give you the answer, but find a paragraph that was exceptionally detailed and provided all kinds of explanations to back up the answer, and you've done nothing but be ungrateful and flame him. Classy...


HS, thanks music man. i thought i might just be going crazy, thank god you gave me a little parity. is that name after music man amps? or just kinda a musical guy thing. i love MM amps man.

Quote by tpcrisis

Looks like I found my answer on Celestion's site:

"Speakers must be capable of taking at least as much power as the amp puts out, or you risk damaging them. So, for a single speaker, pick one with a power rating the same or higher than the amp itself"

Looks like I'm good according to Celestion...


this would be correct... if you were indeed talking about power handling to begin with. instead the name of the game is impedance. this basically translates into how much back pressure your plumbing is expecting(using a hydraulic analogy). Ted Weber went into the more fine details and are actually discussed in the first post better than i could ever do it. thats why i am the prick and Ted Weber was the man.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
Last edited by gumbilicious at Oct 1, 2009,
#13
O.o

amazing.

would it help if i changed my sig to 'The King of All Answer Electrical"?
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
#14
Quote by tpcrisis
Thanks I'll just take my question elsewhere


Dude, we've ALL said that doing this will A. sound bad and B. wreck your amps output transformer (arguably the most expensive part of the amp.)
Get a different speaker.

Plain and simple.
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#15
damn, i guess i scared another one off. now i'll never be on the gg&a who to listen to list.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
#16
I.Am.Astonished.

Gum, I read through your first post and thought, "man! what a great discussion!" only to next find TS's "thanks for nuthin', anybody want to dumb it down for me?"

TS, choke on my sig while I tell you that Gum knows his s***.

This is why I flame people, because they're ingrateful oxygen stealing idiots.

...think I might spend awhile in "asshole mode" thanks to this.
#17
Holy piss lol.

What was his problem, did he refuse to believe he wasted his money on that speaker, well I hope he blows the power transformer and posts another thread called "Help my amp won't work anymore!!!"
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#18
frankly i don't know what his problem was, i thought grisky would get a kick out of this though. really i a dumbfounded at it all.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
#19
wow
just
wow
holy crap
talk about ungrateful

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My rig is simple
Haha. UG's Chuck just said chuck. haha
You're not truly playing guitar unless you know theory.