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Author Topic:  X spkr volume?
George McLellan


From:
Duluth, MN/Mesa, AZ USA
Post Posted 8 Jul 2018 5:46 pm     Reply with quote

Is it possible to put a volume control for the
speaker? I'd like to be able to adjust the volume of the extension speaker so is it possible to just put a pot in line between the amp and speaker?
Geo
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post Posted 8 Jul 2018 7:32 pm     Reply with quote

In practice: no, as a regular potentiometer will be blown to pieces the moment you turn the amp on because it cannot handle the power. Your amp may not survive either.

In theory – and technically: maybe, but only if you can get hold of a "pot" or variable resistor that can handle the output of your power amp. Even those "monster" pots that can handle the power your amp can deliver (whatever that is), are unlikely to be frequency-linear enough to be of much use for audio – most are coiled, and those that are good enough will cost you a small fortune.
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Donny Hinson


From:
Glen Burnie, Md. U.S.A.
Post Posted 9 Jul 2018 6:12 am     Reply with quote

As Georg said, you can't use a regular pot. But you can use an L-pad, which is a special rheostat designed for just such a purpose. They allow you to change the speaker volume while maintaining a constant load for the amp. They're much larger than a pot (hockey-puck sized), but you can mount one easily in the extension speaker cabinet. They're easily available rated up to 100 watts for about $12-$15.

(Be sure to get one that matches the impedance of the extension speaker.)
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Dave Mudgett


From:
Central Pennsylvania
Post Posted 9 Jul 2018 8:16 am     Reply with quote

Definitely don't use a regular potentiometer! They are not designed to handle power signals.

An attenuator using an L-pad will work in the sense that it will safely drop the volume if chosen correctly for the amp/speaker combination. The Weber speaker website has a calculator to figure out what you need here - http://www.tedweber.com/webervst/lpad.htm

Most L-pads and attenuators based on them are purely resistive (made from power resistors of some sort), and don't well simulate the load of a real speaker, whose complex impedance is dominantly inductive at low-midrange frequencies where most of the signal content is. I've tried several commercially available resistive attenuators, and made a couple myself - but they all change the load frequency response too much for me. If I want anything more than a tiny amount of attenuation, they thin out the sound too much for me. But it might work in your application to cut the extension speaker volume down a little bit, and a simple L-pad is cheap enough to try out.

It is possible to more closely approximate a real speaker load using just the motor from a speaker. One can make one from a speaker of the right power handling and impedance - Gerald Weber (Kendrick Amplifers, not Weber speakers) wrote an article on doing this about 20 years ago in Vintage Guitar magazine, but I can't find it now. It involves carefully cutting out the speaker cone without disabling the motor. But to make it practically small, you'd have to also cut out the frame. Too much of a pain, IMO.

Weber speakers (webervst referenced above) and some other companies make speaker motor-based or other attenuators that closely match a speaker's complex impedance. Weber's are here - https://www.tedweber.com/gadgets/attenuators/speaker-motor-models. Their FAQ on attenuators is here - https://www.tedweber.com/attenuator-faq. Not cheap like a simple L-pad, but in the $100-250 range, depending on how much power attenuation needed.

I finally gave in and got a Fryette Power Station, which is a complex-impedance speaker attenuator coupled with a 50-watt tube re-amplifier. I use it to tame a Twin Reverb for use with both guitar (attenuator in circuit) and steel (attenuator bypassed), and also to amplify a little amp (like a Tweed Champ, Princeton Reverb, or something like that) to a more useful gig volume. Definitely not cheap, but worth it to me.
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Erv Niehaus


From:
Litchfield, MN, USA
Post Posted 9 Jul 2018 8:37 am     Reply with quote

I don't know how they do it, but I have a couple of Peavey extension speakers that have volume controls.
I find it real handy to balance the sound on a PA system. Very Happy
Erv
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George McLellan


From:
Duluth, MN/Mesa, AZ USA
Post Posted 9 Jul 2018 11:30 am     Reply with quote

Many thanks to all of you for your advice. I use a Fender Deluxe Reverb (I have two). I've been using an extension speaker, but not often enough to warrant hunting down the parts to upgrade it. If I run into it again where volume is a problem I'll just use my second amp on the other side of the stage and they can set it to their liking. (Some of the gigs don't mic amps - that is where the problem can happen some times).
Geo
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Rick Contino


From:
Brattleboro, Vermont
Post Posted 9 Jul 2018 4:04 pm     Reply with quote

This one works great for me. And at a good price! https://www.amazon.com/Ohm-Speaker-Soak-Guitar-Attenuator/dp/B00A6VON2Y
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Dave Mudgett


From:
Central Pennsylvania
Post Posted 10 Jul 2018 7:07 am     Reply with quote

George - I didn't realize this was for a Fender tube amp. If you just want to cut the volume of the extension speaker some, you could put a 16 Ohm speaker in it. This has two useful benefits:

1. Assuming the 16 Ohm speaker isn't a lot more efficient than the 8 Ohm speaker in the amp, the extension speaker should be somewhat lower in volume. The power should split about 2:1 (main:extension) - it's actually more complicated than that because of the variation in impedance with frequency.

2. The overall speaker load would be closer to the correct 8 Ohm load - nominally 5-1/3 Ohms instead of 4 Ohms for an 8 Ohm extension speaker. Again, it's more complex than that because of the variation in impedance with frequency.

Simple enough to try if you have a 16 Ohm speaker handy.
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Jim Sliff


From:
Lawndale California, USA
Post Posted 18 Jul 2018 11:35 am     Reply with quote

Quote:
I don't know how they do it, but I have a couple of Peavey extension speakers that have volume controls.
I find it real handy to balance the sound on a PA system.


Those are not "volume controls"

The are built-in attenuators.

An attenuator could be used just in front of the extension - but in all likelihood it will not only cut the output going to the extension speaker, it will shunt that output to the internal speaker, *increasing* its level.

What you need for this purpose is something I have not seen on the market - a balanced attenuator that reduces the output feeding one speaker while maintaining the existing level to the internal speaker.

I just don't think there's much demand for such a thing.
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Erv Niehaus


From:
Litchfield, MN, USA
Post Posted 18 Jul 2018 12:50 pm     Reply with quote

All I know is when I crank the knob on the speaker, the volume either goes up or down depending on the direction of the crank!
Why does somebody always has to make a mountain out of a molehill, geez!
Erv Whoa!
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Donny Hinson


From:
Glen Burnie, Md. U.S.A.
Post Posted 28 Jul 2018 5:33 am     Don't overlook the obvious! Reply with quote

It's not rocket science, guys. Extension speaker too loud? Face it in another direction; towards a wall, towards the ceiling, or even angle it face down. You can also put something in front of it, like a coat, curtain, amp cover, or blanket.

On one gig, a certain female singer had a terribly piercing voice. To keep the screaming in check, I simply folded my amp cover in half and laid it over my monitor speaker when that singer got on stage. (It was far easier than plugging and unplugging the monitor.)

Problem solved! Mr. Green
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Nathan Guilford


From:
Oklahoma City
Post Posted 28 Jul 2018 9:59 am     Reply with quote

Same principal here, but for some reason Singers seem to always put their set lists over the horn end of the monitor. Then complain that they can't hear. well....duh? (and I capitalized "Singers" on purpose to signify the type of self-important singer that I'm talking about)

I've used this trick with inattentive sound guys in the past to keep me from getting blown off the stage by the monitor volume.
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Lane Gray


From:
Topeka, KS
Post Posted 28 Jul 2018 2:27 pm     Reply with quote

Erv Niehaus wrote:
All I know is when I crank the knob on the speaker, the volume either goes up or down depending on the direction of the crank!
Why does somebody always has to make a mountain out of a molehill, geez!
Erv Whoa!


In this case, Erv, you're thinking a giant complex subterranean boulder is just a molehill. Reducing the volume from a speaker under power means doing something with the excess power.
If you always want it quieter, I like the 16ohm speaker in the extension cab. If you want different volumes, I like the idea of bringing a second amp (just run a cable from the other input of the amp behind you over to the other amp).
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Donny Hinson


From:
Glen Burnie, Md. U.S.A.
Post Posted 28 Jul 2018 5:02 pm     Reply with quote

Lane Gray wrote:
Reducing the volume from a speaker under power means doing something with the excess power...


That's what an L-pad or a power-soak dingus does. The excess power is converted into heat. They may change the tone somewhat, due to the resistive load in parallel with an inductive load, and it may not please the purists like the unbuffered speaker. But it's usually acceptable for someone else on the stage to hear what you're doing (which is the reason that most players use a remote speaker, anyway).

Even a single amp/speaker can have a different tone at higher or lower volume levels, so it's not like we've never encountered that issue before.
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post Posted 29 Jul 2018 1:30 am     Reply with quote

A high-power rheostat like this example connected in series with an external speaker-element that is connected in parallel with the main speaker, will allow the signal to the external speaker-element to be attenuated over a wide range – from fully on to less than about 1/10th of the wattage. Should cover the OP's case and most other cases where some control over volume for external speakers is needed.

Not a perfect solution soundwise, as the external speaker will behave as if connected to the amp via an extremely long and thin cable when attenuated via a variable series resistor like the one I have used as an example, but with the high-power pot fully on (zero resistance in series with the speaker) there won't be any losses – heat or otherwise – caused by it.


For amps designed for an ideal speaker-load it is important that the main speaker is always connected, while for most SS amps this doesn't matter as long as the connected speakers together have a combined impedance that is larger than the smallest impedance / heaviest load the amp can handle.
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George McLellan


From:
Duluth, MN/Mesa, AZ USA
Post Posted 29 Jul 2018 4:58 am     thanks again Reply with quote

Thanks again for all the input from everyone. This is way over the top for me - a non electronic person.
For the few times when I'm not mic'd and used an extension speaker, since I use my Fender Deluxe Reverb (I have two of them), I'll just bring my second one instead of my extension speaker and place it on the other side of the stage and they can set the volume to their liking.
Geo
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ajm


From:
Los Angeles
Post Posted 29 Jul 2018 11:15 am     Reply with quote

A lot of good technical info in here, but.....

Stop.
A lot of comments were made without knowing some of the facts.

We initially did not know any specifics about George's set up, including the type of amp being used. In that regard.....

Resistive loads and resistive attenuators: Be very careful when using them with solid state amps. Careful to the point of probably not using them at all. The THD Hot Plate and the Scholz Power Soak, both resistive designs, for starters say specifically NOT to use them with solid state amps.

Weber attenuators: The several schematics that I've seen for the MASS series do have a speaker motor in them, BUT in reality they are resistive attenuators. More than likely meaning that they are not meant for solid state amps. In fact, I have not seen an attenuator schematic yet that has me convinced that it's nothing more than resistive.

Erv: What model of Peavey speaker are you referring to that has the volume knob? It sounds like it may be a powered PA speaker with a built in amp, but I/we don't know.

About half way through, and at the end, George posted what I believe is the ideal solution for his problem. Use two Deluxe Reverbs, one on the other side, and let the guys over there set it however they want. This will also let you get the benefits of stereo if you happen to be using an appropriate effects device.
Make sure that your AC power connections are OK for hum and grounding/shock issues. Also, make sure that your signal connections are OK so that there is not excessive loading. However, at least you won't need to worry about speaker loading being messed up and blowing up an output stage.
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post Posted 29 Jul 2018 3:31 pm     Reply with quote

ajm wrote:
About half way through, and at the end, George posted what I believe is the ideal solution for his problem. Use two Deluxe Reverbs, one on the other side, and let the guys over there set it however they want.
George is right of course … that is indeed always the best, and definitely the safest, solution.


However, allow me to address some seemingly unclear issues related to alternative solutions more in line with George's original question…
ajm wrote:
Resistive loads and resistive attenuators: Be very careful when using them with solid state amps. Careful to the point of probably not using them at all. The THD Hot Plate and the Scholz Power Soak, both resistive designs, for starters say specifically NOT to use them with solid state amps.

Weber attenuators: The several schematics that I've seen for the MASS series do have a speaker motor in them, BUT in reality they are resistive attenuators. More than likely meaning that they are not meant for solid state amps. In fact, I have not seen an attenuator schematic yet that has me convinced that it's nothing more than resistive.
I agree that there are many "solutions" on the market that may do more harm than good – let the buyer beware.
However, that resistive loads and attenuators are in themselves problematic, especially in connection with SS-amps, doesn't make sense to me. Can you expand on what's so bad/wrong with resistive loads?


All SS-amps will behave perfectly well with purely resistive loads, and it is in fact a pity that no speaker set-up ever made will provide such a perfect load. That's why we have to deal with "impedance", which takes resistive, capacitive and inductive components of whatever load into account over the relevant frequency range, and beyond. Pretty hopeless to calculate in details – especially when cables and cabinets are thrown into the equations, so all speakers' written impedance are safe estimates.

For SS-amps figuring out the safe range is rather simple: don't go below the lowest load-impedance (in ohm) the amp is designed to handle, as doing so is likely to overload that amp when the speaker(s) and/or other load draw power.
Some SS-amps don't tolerate well to be without a load, but a couple of hundred ohm of resistive load will keep even the worst SS-design in check – make it settle and prevent drift.
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ajm


From:
Los Angeles
Post Posted 30 Jul 2018 2:32 pm     Reply with quote

Well, here comes a rather unclear response to the topic of SS amps and resistive attenuators.

Like I said, both the Scholz Power Soak (make a note of this for later) and the THD Hot Plate instructions say to not use them with a SS amp. It could be due to technical reasons, or it could be due to liability. I did some research on the internet and it's really not clear (quel surprise).

From personal experience: Years ago I built a resistive attenuator to use with one of my tube amps. For the checkout process, so as not to possibly damage my tube amp, I hooked it up to an old ancient 1974 Peavey Standard I have laying around. I don't remember the specifics, but what I do remember is that even with no signal applied, I touched either the amp back panel (power section) or the attenuator, and it was extremely hot after only a few seconds. That convinced me that there might be something to this SS with an attenuator phobia thing, and I never did it again. The attenuator was not mis-wired. I never went back and researched why all of this heat from a technical point. I have used that attenuator for over 10 years on my tube amp and have never had a problem and never felt any heat like when using the SS Peavey.

So based upon personal experience, and what a couple of manufacturers have said, I'm sticking with the "attenuators with tube amps only" modus operandi......for now. As Georg said, let the buyer beware.

Maybe the Peavey (1974) design is much different than SS amps of today, and there is something that it doesn't like about a resistive load.
Also, there are probably many different ways to design a SS power stage. Some of them might not like resistive loads for whatever reason.
Maybe it's because SS amps are usually direct coupled to their loads, I don't know.

All that said, I have always wondered why this exists. After all, from a common sense standpoint, how are you supposed to bench check a SS amp if you don't use a resistive load? Yes, I know there are other ways to do it, but practically, what is the average bench tech going to do? They're probably going to hook it up to a load resistor. If SS amps really didn't like resistive loads, they'd be frying on benches all over the world.

So back to the Scholz Power Soak and not using it with a SS amp........
Doing research I found out something that I didn't know, or had forgotten. It seems that Scholz made a later version that CAN be used with SS amps. Below is text from a Rockman forum:

An updated version of the original Power-Soak, known as "Model II", was issued in the end of 1981: it has an extra switch made to adapt the Power-Soak to the solid-state amps (though its primary target is the tube amps market). The resistors network was tweaked a little, for a more precise attenuation control (?). No audible sonic difference with Model I.
Discontinued in 1982 when the Rockman headphones amp was created, the Power-Soak was re-issued in 1992 as a PS-III model: the difference is in the jack positions (rear panel on the re-issue, front panel on the original). The solid-state switch has disappeared, and the manual says that the PS-3 can be used both with solid-state and tubes amps. The impedance selector has two positions only (4 & 8 ohms), but 16 ohms amps can be used at the 8 ohms setting.


So there you have what I've been able to uncover so far. Maybe someone can shed some light on this topic.

However, like I said, based upon personal experience and a couple of owners manuals, until I see better evidence I'm shying away from using an attenuator with a SS amp. Or at least, one of MY solid state amps.
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post Posted 30 Jul 2018 3:51 pm     Reply with quote

ajm wrote:
From personal experience: Years ago I built a resistive attenuator to use with one of my tube amps. For the checkout process, so as not to possibly damage my tube amp, I hooked it up to an old ancient 1974 Peavey Standard I have laying around. I don't remember the specifics, but what I do remember is that even with no signal applied, I touched either the amp back panel (power section) or the attenuator, and it was extremely hot after only a few seconds. That convinced me that there might be something to this SS with an attenuator phobia thing, and I never did it again. The attenuator was not mis-wired. I never went back and researched why all of this heat from a technical point. I have used that attenuator for over 10 years on my tube amp and have never had a problem and never felt any heat like when using the SS Peavey.

Bad experience … explains why you are skeptical to using such attenuators with SS-amps.

The reason for overheating was most likely instability – tendencies to self-swing (oscillation) – in that particular amp, that kicked in with that particular load. But, I have no way of knowing for sure since I wasn't there to measure.

Fact is that with no signal out of the amp, a regular speaker is also a purely resistive load and the amp should put out zero, or next-to-zero for a bad one, voltage, as DC. Thus, no heat should be generated.
It is only when a signal (AC) is sent to it that the speaker-coil presents its "frequency dependent impedance" to the amp. The "rated impedance" of the speaker is always higher than its DC resistance. A 4ohm speaker will show about 3ohm DC resistance, an 8ohm speaker about 6ohm DC resistance, and so on.

Anyway, your explanation is a good one, and better safe than sorry Smile
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