Removing a Speaker

[starbuck26]

Hey fellas,

I have a Hughes and Kettner 1x12... not sure of the model number (but will provide in a later post), and I have a matching speaker (12" celestion) in a closed back extension cabinet. I was recording last night and both the producer and I liked the sound of the closed back cabinet much more than the tone coming off the original speaker. So we get the brilliant idea of isolating the cabinet and putting the amp in the control room so we can twist away while doubling up guitar lines.

He thought to desolder the original speaker, and leave the extension cabinet connected. Of course the whole time I moaning "don't blow up my amp, please don't blow up my amp" and he's convinced that it will work until he goes silent with his hands on his forehead.

He's staring at a big bold warning sign on the back of the amp that says:

WARNING. NEVER USE AMPLIFIER WITHOUT SPEAKERS CONNECTED!

Now, it's all capital letters, and includes an exclamation point. BUT it also pluralizes 'speakers...'

Any thoughts? We're probably going to open up the extension cabinet and wire the speaker in place of the original, but it sure as hell would save us a lot of time (which I'm certainly paying for) if we could just use a speaker cable to the ext cab and desolder the main speaker....

 

[ocnor]

That waning just means don't run the amp without a speaker load. As long as you have at least one speaker of the correct ohms hooked up you are fine.

 

[starbuck26]

That waning just means don't run the amp without a speaker load. As long as you have at least one speaker of the correct ohms hooked up you are fine.

That was our thinking. But we were worried that the main speaker is wired in permanently, and that without 'seeing' the first speaker, it wouldn't send the load to the external speaker.

 

[ggunn]

That was our thinking. But we were worried that the main speaker is wired in permanently, and that without 'seeing' the first speaker, it wouldn't send the load to the external speaker.

If one speaker is hard wired and there is an external speaker jack, then the external speaker will most likely still get signal if the internal speaker is disconnected. That said, in the unlikely case that the external speaker gets inserted in series, then you will have a problem, though it is easily solved.

Disconnect the internal speaker (making sure that the wires that went to the internal speaker are not touching), connect the external speaker, and power the amp up with the volume all the way down. Plug into the amp and start playing and have someone start to bring up the volume very slowly. If the external speaker works, then you are good to go. If the external speaker does not come on, then turn the amp back down and short the wires that went to the internal speaker together and repeat the procedure.

If the external speaker does not come on in either configuration, then something else is wrong; get someone who understands this stuff to look at it.

 

[ocnor]

If the external speaker does not come on, then turn the amp back down and short the wires that went to the internal speaker together and repeat the procedure.

 

[starbuck26]

Care to elaborate?

 

[ocnor]

Care to elaborate?

Connecting the positive and negative leads together will most likely smoke the transformer. It would be similar to stripping the ends of an electrical cord, connecting the leads, and plugging it into a wall socket.

 

[starbuck26]

Connecting the positive and negative leads together will most likely smoke the transformer. It would be similar to stripping the ends of an electrical cord, connecting the leads, and plugging it into a wall socket.

Gotcha. But what of ggun's first method...

Disconnect the internal speaker (making sure that the wires that went to the internal speaker are not touching), connect the external speaker, and power the amp up with the volume all the way down. Plug into the amp and start playing and have someone start to bring up the volume very slowly. If the external speaker works, then you are good to go.

 

[ocnor]

Gotcha. But what of ggun's first method...

I agree with the first part. The ext jack is probably wired parallel to the hard wires.

 

[starbuck26]

I agree with the first part. The ext jack is probably wired parallel to the hard wires.

Good enough. Thanks guys.

 

[ggunn]

Connecting the positive and negative leads together will most likely smoke the transformer. It would be similar to stripping the ends of an electrical cord, connecting the leads, and plugging it into a wall socket.

Actually, it won't, at least not at low volume. The main speaker jack on my Super Reverb is a shorting jack; it shorts the output transformer if nothing is plugged into it. If you plug a speaker only into the external speaker jack, the amp plays into a short. I've done it by accident, and other than barely a squeak coming from the speakers when I tried to play, there were no ill effects.

Shorting the output transformer is safer for a tube amp than open circuiting it. Sure, I guess you could blow an output transformer by shorting it, turning the amp up all the way, and pounding power chords, but raising the volume slowly from all the way off and not taking it very high is pretty safe. The resistance of the secondary of the power transformer limits the current through the short.

Solid state amps, however, are a different animal; playing into a short with a SS amp is a lot more dangerous, but since this amp has a warning against playing into an open circuit, it's got to be a tube amp since a SS amp wouldn't care.

But actually, this is all beside the point; if he gets no sound by separating the leads and plugging into the external jack, his amp is trying to put the speakers in series and shorting the primary speaker leads will not be shorting the output transformer.

To the OP: If your external speaker jack is a shorting jack wired to put the speaker in series with the primary speaker (not very likely, but possible), then disconnecting the primary speaker and plugging a speaker into the external jack will put the amp playing into an open circuit and you'll get no sound. Shorting the primary speaker leads will correct this; that was the point of the second procedure. With both trials, keep the volume very low and back off immediately if you get no sound from the external speaker. But don't worry too much about it; 5'll getcha 10 that the first trial (disconnecting the internal speaker, keeping the leads isolated, and plugging the other speaker into the external jack) will give you what you want.

 

[MajorTom]

Actually, it won't, at least not at low volume. The main speaker jack on my Super Reverb is a shorting jack; it shorts the output transformer if nothing is plugged into it. If you plug a speaker only into the external speaker jack, the amp plays into a short. I've done it by accident, and other than barely a squeak coming from the speakers when I tried to play, there were no ill effects.

+1

Some tube amps are wired that way, (for all I know, maybe most of them...) I guess the thinking is that if the end user unplugs the main speaker, that shorting the speaker output to ground is the lesser of 2 evils; the only other choice would be no load at all. Fender Hot Rod series are also like that, as an example. Personally, I would not short a tube amp's output on purpose...I'm just not brave that way, but yeah, I have done it accidentally when I plugged the internal speaker plug into the wrong (external) jack - no damage occurred. I guess if you ran it that way for an extended period, with the volume up high enough, it may damage the output tubes or circuitry...?

You did not mention if your amp is tube or not, that makes a big difference. If it is solid state, the load is not critical like it is on a tube amp. The main thing would be for it to have a load that is greater than its lowest rating. If it is rated @ 4 ohms minimum, anything greater than 4 ohms will be ok, including no load at all. Never short the speaker output on a SS amp.

If it is a tube amp - if it has an impedance selector, like Marshall, you set that for the total impedance that is connected to the amp, regardless of how they are physically connected. The way the external speaker jacks function (for amps without an impedance selector switch ), is when a plug is inserted into the ext. speaker jack, a switch in the speaker jack engages some extra windings on the output transformer, to match the amp output to the lower total speaker load.

You will not hurt anything by disconnecting the internal speaker. The amp does not "see" or sense that speaker per se, it is just part of the total load. If it is a ss amp, that won't matter at all. If it is a tube amp, with no impedance selector switch, more than likely, plugging your external speaker into the ext. spkr jack will engage windings on the tranny to where the total load is set for 4 ohms. With only the ext speaker connected, if it is 8 ohm, your total load will be 8 ohm - the amp's output will be set for 4 ohm (again if it is a tube amp). That is a slight mismatch, but it won't hurt anything. Some guys will tell you that the speaker load must be exactly what the amp's output impedance is, or else catastrophe (or at least bad tone) will result. It won't, at least not in this instance.

If if is a tube amp -You would not have hurt anything as long as you heard sound coming out of a speaker.

Think in terms of total load - the amp doesn't know or care how that is achieved.

 

[starbuck26]

ggunn, ocnor:

worked just fine last night. brilliant, actually. thanks a million.

 

[ggunn]

+1


You did not mention if your amp is tube or not, that makes a big difference. If it is solid state, the load is not critical like it is on a tube amp.

It's a tube amp. It would not have had the warning about operating it without a speaker if it were a SS amp. Besides, I looked it up.

 

[ocnor]

I guess the thinking is that if the end user unplugs the main speaker, that shorting the speaker output to ground is the lesser of 2 evils; the only other choice would be no load at all.

If you have zero resistance between the positive and negative terminals then it is the same as no load at all. I don't doubt that some amps are wired that way but to me it seems like an unsafe way to do it. Having an impedance selector switch seems like a no brainer.

 

[MajorTom]

If you have zero resistance between the positive and negative terminals then it is the same as no load at all. I don't doubt that some amps are wired that way but to me it seems like an unsafe way to do it. Having an impedance selector switch seems like a no brainer.

No, zero resistance is a dead short, zero ohms, just like a piece of metal - shorting the OT's one secondary lead to the other. No load at all would be infinite resistance, the OT's secondary leads are not connected at all.

No load (infinite resistance) on a tube amp when it is operating can cause flyback voltage in the OT - like the Tesla coil in high school science class. That much-higher-than-normal voltage can cause arcing in the OT, which can break down the enamel on the windings, which will lead to failure.

Impedance selectors will not protect anything. If there is no speaker plugged into the amp, it still has no load, no matter where an impedance selector would be set.