Would the schematic for the Weber Mass work if i replaced the speaker dummy coil with an equivalent resistor?

itsGiusto

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The designs look pretty simple. Here's one:


WeberMASS100.gif


I could probably make one for myself for pretty cheap, except that I don't know where to source the "Voice Coil Motor Assembly 16 ohm 100w". Could I just use an equivalent 16ohm 100w resistor without risking damage to my amp and speakers?
 

schmee

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It will need to be a very large resistor! But... hmmm, I guess I dont see why not.
But maybe the variation of a 'speaker motor assembly' is needed to sound right? A speakers impedance varies in use....?
 

itsGiusto

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It will need to be a very large resistor! But... hmmm, I guess I dont see why not.
Cool. Yeah, I think I could maybe make a 200w attenuator by using two of these in series.
And I'd also use this 200w rheostat.

But maybe the variation of a 'speaker motor assembly' is needed to sound right? A speakers impedance varies in use....?
Maybe, though really, I'm not convinced that the speaker coil is pulling much weight in the weber schematic above. So much of the power is burned through the rheostat. Not to mention, I've made L-pad attenuators that are purely resistive that sound fine, especially with the bright switch (bypass capacitor) engaged.
But I guess I'd like to hear what other people think about it, so I'm not asserting too much and then ultimately making a bad decision.
 

King Fan

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Weber seem to think the motor makes a difference.

“Our MASS attenuators use an actual moving speaker motor for the load, and our Load Dumps are purely resistive like all of the other attenuators on the market. All MASS products use an actual moving speaker motor for the load and are more interactive with the output circuit of the amp, thus providing a more realistic load to the amp.”

Smart folks here may be able to support or downplay that. I'm just quoting it. OTOH, it seems like a lot of trouble — and a poor business plan — if that claim isn't logical.
 

NTC

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OTOH, it seems like a lot of trouble — and a poor business plan — if that claim isn't logical.

Not much trouble for them since the already make speakers. A resistor is a resistor and will remain constant with frequency (for the most part). A speaker, or even just the motor of the speaker, has inductance and resistance. The argument that the Mass is different is logical, though what it sounds like may or may not warrant the difference.
 

itsGiusto

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Weber seem to think the motor makes a difference.

“Our MASS attenuators use an actual moving speaker motor for the load, and our Load Dumps are purely resistive like all of the other attenuators on the market. All MASS products use an actual moving speaker motor for the load and are more interactive with the output circuit of the amp, thus providing a more realistic load to the amp.”

Smart folks here may be able to support or downplay that. I'm just quoting it. OTOH, it seems like a lot of trouble — and a poor business plan — if that claim isn't logical.
It's a poor business plan if it sounds feasible to tens of thousands of guitarists, who know jack all about the technical details of their gear, that a reactive load might make a difference? And you're the only or the biggest company selling a reactive load attenuator? And then you can charge upwards of $300 for each attenuator unit you sell? I feel like that describes the entire music industry. So I don't think it'd be a poor business strategy. Placebo effect is what makes this industry go round.

It's a lot of trouble for companies to source Brazilian rosewood, and I'm pretty sure it makes no difference to a solid body electric guitar sound. Have you ever seen those youtube videos where a guy builds a strat out of colored pencils, or carboard, or even jawbreaker candies, and it sounds exactly like a normal strat? Or this one, where another guy makes a guitar with no body whatsoever:


And then there's Vox who swear that their amps are class A, so that guitarists will go around saying "I just had to get a vox AC30 so I could get that chimey class A tone!" But then it turns out that you can only really call an AC30 a class A amp if you really really stretch the definition of class A, and the only mass produced amps that are actually class A are really small ones like the Champ, which may or may not be chimey at all.
See this great article on vox and class A:



To be clear, I'm not saying that I know one way or the other if the speaker dummy motor matters in a Weber attenuator. But I think it's entirely plausible that it doesn't and it's all just marketing. Guitarists will shell out for anything if they think it'll get them that tone they need. I'm very very guilty of it too. And then, on top of it, I just find it suspicious that the reactive motor doesn't seem to be shouldering that much of the load in the schematic. Much of the power is burned through the rheostat. The motor could play a large role. It could play a small role that makes some really small impact on the sound. Or it could play no role at all.

But mostly I want to know if the design would even work if I used a resistor instead of the motor, not necessarily if it'll sound identical to a Mass attenuator
 
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King Fan

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OK OP. I've found Weber a decent company. Ted Weber was famously honest. So I gotta choose:

1. They might be telling the truth
2. You might have grounds for doubting what they say

....
 
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itsGiusto

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I've found Weber a decent company. Ted Weber was famously honest. So I gotta choose:

1. They might be telling the truth
2. You might have grounds for doubting what they say

OK....
I don't know much about Ted Weber, but I know that almost all music gear is based on hype, myth, and gullible people. I'm not even saying Weber's necessarily lying, for several reasons. Placebo effect is a big thing and you can't even always tell. Weber could truly believe it themselves that it really matters, so they could be being honest, even if they're not correct.

Besides, like I said, the coil could have an effect, but a really small one that doesn't really matter that much in the grand scheme of things. Like if it had a very mild increase of the high frequencies, that may entirely not matter at all when you compare it to the effect of switching in a bright-cap into the circuit anyway. There are a lot of non-reactive attenuators out there that sound much the same to me as the Weber ones.

I'm not here to debate whether we think Weber is an honest company. I want someone who understands electrical engineering to weigh in on this particular schematic to indicate if it matters, and if the schematic would work with a resistor instead of a speaker coil. I don't take "well, Weber pinky swore to me that it mattered" as scientific evidence.
 

tubeswell

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I don't know where to source the "Voice Coil Motor Assembly 16 ohm 100w".
Try emailing the speaker parts guy at Weber (used to be Brian Spane, and it could be still). You'll probably find its almost as expensive as a speaker (seeing as how it's essentially a substitute speaker). Sure, you could use a 16R 100W resistor, but a resistor will present more of a linear* response to the amp's output transformer, as it's just a straightforward resistance - whereas speaker impedance is different at different frequencies - and you can see from the schematic that they have a switchable conjunctive filter in parallel with the speaker/'voice coil motor assembly' (and conjunctive filters are designed to flatten the frequency response, so that should indicate that it does sound different from a straightforward resistor). But as to how much of a difference a straight resistance will make to what YOU hear - only you can say that, YMMV.

*A resistive load on the OT secondary won't mean the whole signal output is totally linear, because the tube that is driving the OT doesn't have a totally linear signal output (although pentodes and tetrodes are more linear than triodes - because the screen grid flattens and evens-out spacing between the signal grid curves over the central part of the load line where the signal spends most of its time - whereas a triode skews/flattens its output signal more on one side than the other as the signal swing gets larger). But the way a signal responds across a fixed resistance is linear due to ohms law. So we can expect the response with a fixed resistive load to be 'more linear' than a speaker.
 
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archetype

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I'm no EE, definitely. My layperson's circuit analysis is that all those power resistors and Rh1 are doing the heavy lifting for attenuation. The speaker motor may be there to add what a speaker brings to the party: impedance that varies with frequency. The coil bypasses Rh1 and R6 so unless attenuation is bypassed by switch, the speaker motor is providing the likely small tonal changes that come with changes in impedance, plus some reactance from the inductive load. That's part of what makes a speaker sound one way at 800 kHZ and another way at 4000kHZ. It's not a purely linear reproduction of the fundamental note

That's my guess, at least. The circuit is intended to mimic the electrical characteristics of a physical speaker while attenuating. There are several other companies producing "reactive" attenuators, AFAIK all with proprietary circuits intended to mimic the electrical characteristics of a speaker motor. Weber does this at around half the cost by simply incorporating a speaker motor. Voice coils and magnets are commodity items that can be ordered and incorporated by those other companies, so they may feel they've built a better mousetrap, or they're enjoying greater revenue per unit, or both.

I received a Weber Mini-Mass last Friday. I bought it for the feature set: it can match a 4, 8, or 16 Ohm OT, has two tiers of treble bypass, and is compact. I needed an attenuator for my Tremolux and Deluxe Reverb and Weber's 10% off sale helped me finally make a decision. Speaker cables arrived today, so I haven't given it a test drive.

Here's a plain language Understanding Attenuators:

To the OP's original question, in my layperson's view it looks like one could simply eliminate the speaker motor from the circuit and get resistive attenuation. Applying a bit of Ohm's law would tell you if the power handling would remain the same, or if you'd need to increase the power rating of the Rh1 to compensate for the lack of the coil.
 
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itsGiusto

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and you can see from the schematic that they have a switchable conjunctive filter in parallel with the speaker/'voice coil motor assembly' (and conjunctive filters are designed to flatten the frequency response, so that should indicate that it does sound different from a straightforward resistor). But as to how much of a difference a straight resistance will make to what YOU hear - only you can say that, YMMV.
That's an interesting viewpoint. For the switch at the top with the capacitors, I was not viewing it as a conjunctive filter (which I know very little about), and more akin to a switchable bypass bright cap, much like we'd see in a Fender AB763 amp.

The biggest complaint that attenuators get is "it kills the tone, and makes it sound too dark/dull". As we know from amps design, this effect happens because the volume pot resistor/rheostat more easily lets bass frequencies through than high frequencies. Weber markets this capacitor switch as a mechanism to combat that. So I wasn't really thinking that the capacitor circuit is proof that it sounds different than resistive circuits, since these sorts of treble-bypass bright caps are also used in resistive circuits

Come to think of it though, and slightly tangential, but the fact that resistors impede high frequencies more than low frequencies makes it not purely resistive, but reactive, right? Why is that? I thought resistors were supposed to only be resistive.
 

itsGiusto

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I received a Weber Mini-Mass last Friday. I bought it for the feature set: it can match a 4, 8, or 16 Ohm OT, has two tiers of treble bypass, and is compact. I needed an attenuator for my Tremolux and Deluxe Reverb and Weber's 10% off sale helped me finally make a decision. Speaker cables arrived today, so I haven't given it a test drive.

Here's a plain language Understanding Attenuators:

To the OP's original question, in my layperson's view it looks like one could simply eliminate the speaker motor from the circuit and get resistive attenuation. Applying a bit of Ohm's law would tell you if the power handling would remain the same, or if you'd need to increase the power rating of the Rh1 to compensate for the lack of the coil.
The mini mass was the first attenuator I owned, and then years later I bought the mass 200. Both are really excellent and so useful, the 200 allows me to play my 50w Marshall in my house without getting evicted, and it really sounds good despite the bad rep that attenuators get. The trick is to not turn down too low. Your amp should still sound loud, just not painfully loud.

I've previously built a purely resistive L-pad attenuator which also sounded good, but was rated for much less volume, and only worked with 8 ohm loads. The fact that it sounded much the same as the Weber Mini mass is what got me thinking that maybe the reactive coil doesn't matter much, despite the fact that I like the mini mass quite a bit.

If I were to emit the coil entirely instead of replacing it with a resistor, it'd probably make sense for me to instead just replace the whole thing with an L-pad, so the load it presents is constant. I think that just removing the voice coil without replacing would vary the load too much across the sweep of the rheostat.
However, I can't find an L-pad rated at 200w. So that's why I'd rather just replace the voice coil with a 200w resistor instead.

BTW, if you're interested in the load the attenuator may present under different conditions, check out this post I did many years ago where I made a python program to graph the load that the weber attenuator presents, assuming that the voice coil is resistive (simply because I don't know how to graph a reactive load, nor do I know the reactance of the voice coil):
 

archetype

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The mini mass was the first attenuator I owned, and then years later I bought the mass 200. Both are really excellent and so useful, the 200 allows me to play my 50w Marshall in my house without getting evicted, and it really sounds good despite the bad rep that attenuators get. The trick is to not turn down too low. Your amp should still sound loud, just not painfully loud.

I've previously built a purely resistive L-pad attenuator which also sounded good, but was rated for much less volume, and only worked with 8 ohm loads. The fact that it sounded much the same as the Weber Mini mass is what got me thinking that maybe the reactive coil doesn't matter much, despite the fact that I like the mini mass quite a bit.

If I were to emit the coil entirely instead of replacing it with a resistor, it'd probably make sense for me to instead just replace the whole thing with an L-pad, so the load it presents is constant. I think that just removing the voice coil without replacing would vary the load too much across the sweep of the rheostat.
However, I can't find an L-pad rated at 200w. So that's why I'd rather just replace the voice coil with a 200w resistor instead.

BTW, if you're interested in the load the attenuator may present under different conditions, check out this post I did many years ago where I made a python program to graph the load that the weber attenuator presents, assuming that the voice coil is resistive (simply because I don't know how to graph a reactive load, nor do I know the reactance of the voice coil):

Thanks for that link. This whole thing has been pondered multiple times, it seems.
 

Alex_C

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The designs look pretty simple. Here's one:


WeberMASS100.gif


I could probably make one for myself for pretty cheap, except that I don't know where to source the "Voice Coil Motor Assembly 16 ohm 100w". Could I just use an equivalent 16ohm 100w resistor without risking damage to my amp and speakers?
Yes, but a resistor won't sound the same. An eq can help but it'll be a different sound.
 

_Steve

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The speaker motor makes a significant difference electrically here. But instead of taking my (or other internet expert's) word for it why not just do a basic simulation in LTSpice? It's pretty quick and easy to knock up. If you run an AC analysis on it you will see a speaker-like response-curve vs a flat one with a resistor.

FYI other manufacturers do more or less the same thing using one or multiple inductors. In my mind it's debatable whether there's a benefit using a moving motor vs a basic inductor.

You might also be interested in the excellent DIY attenuator by JohnH over at the marshallforum. I have built a couple and also own the Weber Mass 200 and Mini Mass. But basic L-Pads also do a good job IMHO if you are not fussy.
 
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itsGiusto

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The speaker motor makes a significant difference electrically here. But instead of taking my (or other internet expert's) word for it why not just do a basic simulation in LTSpice? It's pretty quick and easy to knock up. If you run an AC analysis on it you will see a speaker-like response-curve vs a flat one with a resistor.

FYI other manufacturers do more or less the same thing using one or multiple inductors. In my mind it's debatable whether there's a benefit using a moving motor vs a basic inductor.

You might also be interested in the excellent DIY attenuator by JohnH over at the marshallforum. I have built a couple and also own the Weber Mass 200 and Mini Mass. But basic L-Pads also do a good job IMHO if you are not fussy.
I should probably learn LT Spice, but my quick attempt to last year wasn't great. I found it somewhat excruciating to use, with poor user interface, and it doesn't even have native support for potentiometers! Maybe someday I'll learn it.
 

Len058

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I do believe a reactive attenuator sounds better than a pure resistive one.

I have a Koch dummybox home. It has a line out. I tested the recorded tone through the line out. So no Fletcher Munson effect, all levels the same.

As a loadbox, without speaker it sounded like crap. No reactive load
With a speaker at high attenuation, it got better. Some reactive load
With a speaker at low attenuation, it was tolerable. A bit more reactive load

Now I've built the JohnH reactive attenuator. It sounds better than the Koch and at the lowest attenuation setting, it's quite nice. But the more resistors you add to the signal, the more unwanted compression you get. You can lower the gain to get a better tone, and have enough overdrive but straight to a speaker sounds best.

The diy attenuator
https://www.marshallforum.com/media/attenuator-m-190110.10430/

https://www.marshallforum.com/threads/simple-attenuators-design-and-testing.98285/
 

itsGiusto

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I do believe a reactive attenuator sounds better than a pure resistive one.

I have a Koch dummybox home. It has a line out. I tested the recorded tone through the line out. So no Fletcher Munson effect, all levels the same.

As a loadbox, without speaker it sounded like crap. No reactive load
With a speaker at high attenuation, it got better. Some reactive load
With a speaker at low attenuation, it was tolerable. A bit more reactive load

Now I've built the JohnH reactive attenuator. It sounds better than the Koch and at the lowest attenuation setting, it's quite nice. But the more resistors you add to the signal, the more unwanted compression you get. You can lower the gain to get a better tone, and have enough overdrive but straight to a speaker sounds best.

The diy attenuator
https://www.marshallforum.com/media/attenuator-m-190110.10430/

https://www.marshallforum.com/threads/simple-attenuators-design-and-testing.98285/
I've seen that John H attenuator before, but I'd much prefer to make one continuously adjustable, with a rheostat, not just with discrete switches for discrete attenuation levels. I find with the attenuators I own, I do a significant amount of tweaking of the dial to get it just right. I'm not sure discrete switches will allow me that flexibility and the fine-grained control I want.
 

Timbresmith1

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The designs look pretty simple. Here's one:


WeberMASS100.gif


I could probably make one for myself for pretty cheap, except that I don't know where to source the "Voice Coil Motor Assembly 16 ohm 100w". Could I just use an equivalent 16ohm 100w resistor without risking damage to my amp and speakers?
A resistor is not a reactive load. Technically you COULD just run a resistor as a load, but it doesn’t simulate a speaker.
 

itsGiusto

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A resistor is not a reactive load. Technically you COULD just run a resistor as a load, but it doesn’t simulate a speaker.
Yes, I'm very aware that a resistor is not a reactive load. I just want to know if it'd work and not damage anything, not if it'd sound exactly the same. And I'm not convinced that having just a small portion of the load be reactive (look at the schematic to see how small. It can be pretty small, especially with the impedance selector on!) would necessarily matter that much. I wouldn't mind quantifying how much it matters.

FWIW, I've seen people just run an 16ohm output amp directly into a 16ohm resistor as a dummy load, so I think that it doesn't seem like it's an absolute necessity to always be running a reactive load on an amp. L-pad attenuators seem to do just fine, but I can't find a 200w L-pad. I can find a 200w rheostat, however, which is why I want to build this schematic.
 
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