Weber MASS Attenuators

Tube or solid-state, this section goes to eleven!

Re: Weber MASS Attenuators

Postby dai h. » 27 Sep 2010, 04:35

The LOAD R needs to be about 3 to 4 times the speaker Impeadance otherwise it's going to be very lifeless. 8 Ohm Loads on 8 Ohm tap will just turn your favorite tube amp into a limiter (a valve version of a TS9)
i.e. An 8 Ohm speaker out needs more like 30 Ohm Resistive Load. A Huge improvement will be immeadiately apparent.


I thought such a drastic change in load could be dangerous for some outputs (such as Marshalls). If less lifelessness, or liveliness comes from the increase in L, how about a more matched load in series with an inductor? My Palmer PDI-03 has such a load (about 6.5ohms if memory serves plus what looks to be an 0.3mH-ish inductor in series for an 8 ohm load). Then maybe an additional R across the L to control the impedance rise towards the high freqs.
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Re: Weber MASS Attenuators

Postby phatt » 27 Sep 2010, 15:18

Hello dai H,
If not already obvious I'm not the chief guru on all this insanely complex stuff.
But I do have a brain that can think outside the well worn attenuation game and from all I've read and the experience gained from building a lot of different ideas has proved attenuation has limitations.

Some attenuators work ok,,, but HEy I wanted Fantasticly Stunning Sonic Heaven.

If attenuators work for you then great but obviously you are already inside the guts of the Palmer wondering how to improve it? :? If you where truly happy with the Palmer you would not be asking.
I wish you luck trying to work out all the maths. BTDT,,Meantime I'm off playin my guitar and having far more fun than sitting over a hot soldering iron.

I admit I fell for the tecky game and started chewing all the attenuator maths inducky stuff but once I heard and also understood the Guytron GT 100 was just a simple resitive load on a small Amp into a second BIG amp. WOW DING!!! :idea: :idea:
A little bell rung in my guitarded brain that said hang on a mo,, if a simple resistor can pull such a fantastic tone why waste time on these attenuators.
Plan B materialized in a short space of time. Probably not quite as slick as the Guytron sound but still I'm miles ahead of attenuators. 8)

Except for a dud socket in the load box I've never had any issues in 5 years and I play every 2 weeks for 6 hours at a local club. When I built that little Amp I ran it through an 8 Ohm soak test for 3 days flatout. I hardly ever touch it or worry about it as it gives me no sign of problems.

I run a Derated well setup but simple PP cathode biased 10 watt Amp.
Signal path thus;
Small tone box of tricks> 10 watt tube amp> Load box/Lineout > GraphicEQ > 120 Watt SSamp.

As to the Marshall load;
Well I've read more than once that *The Ultimate Attenuator* uses a 30 Ohm Load.
So your best bet is to ask folks that own the UA and a big Marshall?

An 8 Ohm resistive load is a very different animal when compared to an 8 Ohm speaker.
An 8 Ohm Resistive load puts a fair amount of stress on an Amplifier output,, much more than the speaker does.

Remember one is R and the other is Z.
R is the same load at ALL Freq whereas the speaker is a constantly changing load at different frequencies.
My best guess is 30 Ohms is a compromise between the two extremes.

There is nothing new under the sun :) Heck if you search Tube schematics for long enough you will find that some old stuff used a *Safety resistor*. Maybe 50 Ohms across the speaker out socket.
This is there as a backup load so if the speaker is unplugged the amp won't run open circuit and try to push an infintite R causing major damage.
(A very smart idea,, some Amp builders could learn a lot by checking the real old stuff)
****Point being that R load can be higher than Z load and be quite safe.****

Marshall's have had problems over the years because they don't protect the *screen grids* enough. (King TUT gives a very indepth explanation of the old Marshall meltdown problems covered in his book TUT 2)

It's just that under stress for long enough (i.e. like running flat out through an attenuator) will show up the flaw in the Amps design. **This has absolutely Nothing to do with the attenuator**,,, but of course the ignorant will blame the attenuator,, not the sacred Marshall,, Winky.

My advice is get your BIG Amp checked out by one who knows how to derate for such use.
Frankly you will be far better served by using a $small tube $Amp and $soak that. $ cheaper :idea:
**Then** use the Marshall as the second Amp. (a couple of hot wire tricks can bypass V1 in the Marshall as you will likely have to much signal now)
Remember you have to carry 2 amps now!! Do you really wish to carry a great big heavy 100 Watt Amp when a small one does the same job?
Of course if you Are EVH you can have it all done for you while you sit back in your Limo. :)
Cheers, Phil.
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Re: Weber MASS Attenuators

Postby DougH » 27 Sep 2010, 20:24

I agree with you 100% Phil and I've said similar things in similar threads before.

Look at a typical speaker impedance curve and the load varies all over the place at different frequencies. If you just intuitively look at the average over the useful frequency range, it will be several times the rated impedance of the speaker. This is why a higher *resistive* impedance a) will sound better, and b) won't hurt anything. And as you say, running it low (i.e. 8 ohm) could be more harmful, esp to a vintage amp with vintage output transformer, by stressing it with too high of a current demand.

I know- I built an Airbrake that uses this principal and my ears don't lie. It sounds very good. It's not a perfect facsimile of my "cranked tone" but close enough and easy on the ears. It works with 4/8/16 ohm speakers and up to 100W amps. I'm set...

I also agree that the very best way of doing this kind of thing is by re-amping: load/line-out/second amp/guitar speaker. I've done that before and the results are very satisfying. It's a lot of stuff to wire up, but you could build it into a box using a simple SS chip amp for your second power amp. This is basically what the newest generation of pricey boutique attenuator builders are doing.

In any case, the principles are pretty simple and it ain't rocket science to do this sort of thing and have it sound good.
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Re: Weber MASS Attenuators

Postby dai h. » 27 Sep 2010, 21:36

I've heard sound clips and was already aware of things like Guytron, the U.A., etc., so I've already come to the conclusion that the sort of setup described can sound good, just wondered whether "3 to 4 times" spk. Z would be safe universally (since as I understand it would stress the insulation--while the other way round going to/working into a lower Z as Doug mentioned increases power so can stress the power tubes and the OT from heat I gather). I don't know, maybe x3 to x4 is fine, but wondered if there was a safer compromise (if unsafe).

re: The U.A.'s 30ohm load, if the Marshall output was set on 16ohms, then I would think 30ohms(R) wouldn't be too far off (I understood 8ohms AC would be about 11ohms, so x2 that = 22ohms--not far from 30ohms). Also, IIRC the company offered an option to insert an inductor (maybe this was called the "Marshall mod" or something like that.
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Re: Weber MASS Attenuators

Postby DougH » 30 Sep 2010, 16:16

going to/working into a lower Z as Doug mentioned increases power so can stress the power tubes and the OT from heat I gather


It's not a matter of increasing the power, it's a matter of lowering the load and increasing the current (V=I*R). Older vintage transformers may not have high enough current capacity in the windings. Newer gear and especially some mfr's (e.g. Hammond) tend to have higher safety factors built in.

Yes, there are certainly limits to how high you can increase the load before back EMF starts output tube pin arcing and etc. But if you look at speaker impedance curves, 2 or 3 times the rated impedance of *resistive* impedance is not a problem. The key is to look at the curves to convince yourself and to understand it's not complex impedance we're talking about. If you have an inductive load (or a speaker) you should try to match as close as possible although with most amps 1/2 to 2 times is usually not a problem.
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Re: Weber MASS Attenuators

Postby dai h. » 30 Sep 2010, 22:29

DougH wrote:
going to/working into a lower Z as Doug mentioned increases power so can stress the power tubes and the OT from heat I gather


It's not a matter of increasing the power, it's a matter of lowering the load and increasing the current (V=I*R). Older vintage transformers may not have high enough current capacity in the windings. Newer gear and especially some mfr's (e.g. Hammond) tend to have higher safety factors built in.


I was thinking working into a lower impedance = higher current draw (and vice a versa), so I suppose I should've said "current" instead of power (as in "power output")?

Yes, there are certainly limits to how high you can increase the load before back EMF starts output tube pin arcing and etc. But if you look at speaker impedance curves, 2 or 3 times the rated impedance of *resistive* impedance is not a problem. The key is to look at the curves to convince yourself and to understand it's not complex impedance we're talking about. If you have an inductive load (or a speaker) you should try to match as close as possible although with most amps 1/2 to 2 times is usually not a problem.


maybe I'm being overly finicky but the recommendation was 3 to 4, and not 2 to 3 times. I do understand that it can depend on the amp how sensitive it is to mismatched impedances (for example, I have a Boogie .22+, and in the instructions, it basically suggests to set it where it sounds good (4/8/16, stock spk. is 8ohms)).
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Re: Weber MASS Attenuators

Postby DougH » 01 Oct 2010, 15:12

dai h. wrote:maybe I'm being overly finicky but the recommendation was 3 to 4, and not 2 to 3 times.


Okay, 3 to 4 then. The key is to look at the speaker curves and understand it's not really a "mismatch" to begin with. The term "mismatch" only really makes sense if you are comparing one complex impedance to another complex impedance . In this case you are comparing a complex impedance to a purely resistive impedance- apples to oranges, similar only in the sense that they present a load to the output section of the amp. The resistive value serves as an average approximation of the complex impedance.

There's a lot of misinformation flying around about this kind of stuff. The reason people burn out output tubes with attenuators is usually because they are doing their best Eddie Van Halen impression- running the amp at max all the time, and with or without an attenuator that's going to wear out tubes more quickly. Too low of a load can stress the windings on a vintage output transformer, etc.
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Re: Weber MASS Attenuators

Postby phatt » 01 Oct 2010, 15:46

Hi again,
Dough H, you certainly have a better handle on this than some comments I've read :thumbsup
One thing I'd like to add is some of these amps have a rather high working voltage.
There maybe merit in dropping the HT if you want to stay below the flashover issues and also the punch through in the OTr windings.

Dai h, The .22 Amp schematic shows 390Volts HT which is highish. To Messa's credit they have at least lowered the screens by a good 100 volts or so, that will help as the higher the supply the more you have to drop the screen voltage,, if you want it to survive for a long time.

Remember the Voltage potential between the 2 ends of the primary are 2x HT !!!
With big amps running 600VDC the signal can swing way past 1,000volts AC easy :shock:
I don't know the specs but there is a voltage punch through limit for enamaled wire used in OT's

Maybe look into the Dana kit idea if it all worries you,, can't hurt.
My little Amp runs at 250 VDC ,,safe as it gets,,so It will likely out live me 8)
Just thowing ideas around.
Phil.
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Re: Weber MASS Attenuators

Postby DougH » 01 Oct 2010, 17:01

phatt wrote:One thing I'd like to add is some of these amps have a rather high working voltage.
There maybe merit in dropping the HT if you want to stay below the flashover issues and also the punch through in the OTr windings.

Dai h, The .22 Amp schematic shows 390Volts HT which is highish. To Messa's credit they have at least lowered the screens by a good 100 volts or so, that will help as the higher the supply the more you have to drop the screen voltage,, if you want it to survive for a long time.



Those are good points. Matchless does (did?) the same thing- lowered the screen voltage to keep the out-of-spec voltage-wise EL84's from going up in flames. My Peavey Windsor has 450V B+ but IIRC the screen supply voltage was reasonable. Then they only put 400 ohm screen resistors on them (?). I changed those to 1.5K's I had lying around. But then, they connect the EL34 supressors to the negative bias voltage and also put diode protection on the output transformer. They engineered a lot of smart stuff into that amp to keep it durable. Off topic, but another misconception I always found funny was the thing about Marshall having bad output transformers when it was actually poor screen regulation that was killing those amps. Something that could have been fixed by a four 25 cent resistors...;-)
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Re: Weber MASS Attenuators

Postby dai h. » 01 Oct 2010, 22:10

DougH wrote:
dai h. wrote:maybe I'm being overly finicky but the recommendation was 3 to 4, and not 2 to 3 times.


Okay, 3 to 4 then. The key is to look at the speaker curves and understand it's not really a "mismatch" to begin with. The term "mismatch" only really makes
sense if you are comparing one complex impedance to another complex impedance . In this case you are comparing a complex impedance to a purely resistive
impedance- apples to oranges, similar only in the sense that they present a load to the output section of the amp.


to be clear I'm not talking about a speaker but a resistor (the recommended x3 to x4 the load).

The resistive value serves as an average approximation of the complex impedance.


*I think* I comprehend this (my 8ohms AC = 11ohms DC example--though I gather this could be diff. though depending on the specific spk. being equated to DC ohms).

There's a lot of misinformation flying around about this kind of stuff. The reason people burn out output tubes with attenuators is usually because
they are doing their best Eddie Van Halen impression- running the amp at max all the time, and with or without an attenuator that's going to wear out tubes
more quickly. Too low of a load can stress the windings on a vintage output transformer, etc.


I think I do understand some of the issues (maxing a vintage amp that was maybe never designed to be used on full power, design flaws in some attenuators,
possible prior damage to amp OT), but I guess my concern is this:

phatt wrote:One thing I'd like to add is some of these amps have a rather high working voltage.
There maybe merit in dropping the HT if you want to stay below the flashover issues and also the punch through in the OTr windings.

Remember the Voltage potential between the 2 ends of the primary are 2x HT !!!
With big amps running 600VDC the signal can swing way past 1,000volts AC easy :shock:
I don't know the specs but there is a voltage punch through limit for enamaled wire used in OT's


and if a blanket recommendation of x3 to x4 is safe for every amp? Or is it more a case of "it depends"? In case it isn't (in every amp), hence the suggestion to try the series inductance(to raise the impedance towards the highs).

And another thing (my question) is (assuming the higher load sounds better) WHY does the higher (R only) load sound better? Is the amp output less loaded and more "free" (damped) or something?

re: the M/B .22+, yes I know the B+ is high (but the screens are low). Haven't used it in years. Just stating an example where the maker clearly says it's okay to play with the impedance.
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Re: Weber MASS Attenuators

Postby phatt » 07 Oct 2010, 15:53

Hi Dai H,

I think you sort of answered this one yourself :lol:
"and if a blanket recommendation of x3 to x4 is safe for every amp? Or is it more a case of "it depends"? In case it isn't (in every amp), hence the suggestion to try the series inductance(to raise the impedance towards the highs)."

Yes so many Amps with so many variations you just don't know for sure which is why I say Test with a load box and take some measurements.

If you care to give us the *name and schematic* of amp you wish to use I'm sure there is enough talant on these pages to give you an idea of how well it will work.

As to the inductance;
I assume you are talking Attenuator straight to amp type circuit?
In which case *Soulsonic* has already commented early on that he found the simple resistive idea more rewarding.
Truth is you can go in circles working out the maths but just like racing cars;
maths although useful,,is all heresay.
Lets see what happens on race day :wink:
Phil.
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Re: Weber MASS Attenuators

Postby sparkeyjames » 08 Oct 2010, 05:30

airfox wrote:I've had great success with Weber attenuators and would like a 2-channel version--something they don't make. Specifically, I'm looking to build an attenuator with two different volume levels that are foot-switchable. Anyone have any idea what this requires? Thanks.



Weber does indeed make an attenuator with a boost switch unfortunately it is an optional circuit to the 200 watt attenuator kit. You would have to purchase the parts separately and install them into the kit yourself. Kinda like what this website is all about.
The schematic is here....

https://taweber.powweb.com/store/attensch.jpg

I love how attenuator threads always degenerate into either "tone sucking" or "resistance/impedance mismatch" arguments.
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Re: Weber MASS Attenuators

Postby phatt » 08 Oct 2010, 08:55

OK Sparky J,
Re this:
""I love how attenuator threads always degenerate into either "tone sucking" or "resistance/impedance mismatch" arguments.""

I'll Be a mug. :roll: So your point is ???
Phil.
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Re: Weber MASS Attenuators

Postby dai h. » 09 Oct 2010, 02:22

phatt wrote:As to the inductance;
I assume you are talking Attenuator straight to amp type circuit? .


hi phatt,

what I specifically have in mind is (one) "real world example" where a certain Swede heavily into the Van Halen thing (the old sound) made some very compelling clips using a modded Marshall Power Brake followed by a resistor only L-Pad to knock the output down even further. (The starting point was that he could REALLY play, but) what I found interesting was the load he was using, plus the extra low volume he claimed to be getting his sound at. Basically what I found out was that he had shorted out the "LC tank" part of the PB load (which is there to emulate the rise in low freq. impedance you get from a spk.), which meant that most of the load the amp was "seeing" was a 10ohm R in series with a 1mH inductor. Also, I've experimented with putting a resistance across the 1mH L(in my own PB), and going towards the completely shorted (i.e. not in circuit) direction seems to deaden the high end excitement. I'm not really looking at this as only having to do the x3 or x4 with a resistor, or having to do it with an R and L, etc., but thinking there are various approaches that are valid. (Plus the other examples, the UA additional inductor option and the Palmer load which is an R+L--although I haven't listened to this with the line lvl. output running into another gtr. amp, in a way it was similar except that the signal eventually arrived at a headphone amp inside the mixer circuit I was listening through.) I've also heard (sound clips) of resistive loaded amps that sounded good (to me) using (IIRC) a load not particularly high. The Trainwreck Air Brake attenuator (the one Doug H mentions)--if memory serves, I recall reading something about the inductance of the wirewound Rs used being a factor in their choice also (though I'd guess the L isn't very much--I've measured an 8ohm alu clad 50W wirewound, and I forget the exact value but it wasn't very much at all).
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Re: Weber MASS Attenuators

Postby phatt » 09 Oct 2010, 13:54

Hello dai h,
OK to much data to deal with at once. LOL

OK, So all this complexity to emulate Speakers,,,But what has not been metioned in all of these posts (unless I missed one?) is What type of Speakers are being emulated???? Sorry but guitar speakers can be WORLDS Apart in sonic effects.

In the case you mention here I'll Assume 80's EVH type sound which implies the ever-lovin Marshall midrange honk signiture.
But that's a lot to do with Greenback response and Quad box resonance.

So you could do everything the *Swede* does but through a 112 combo Amp it may well sound very very different.
Sorry mate but there are just to many varying viariables :shock: in that post for me say anything constructive.

May I suggest a schematic or even a mud map of the signal path (including speakers used) that you wish to use.

If you are asking for tecknical exacts I'm not the man.
It should be clear by now that I'm a rule of thumb kinda guy who places no great importance on teckno exact drivlle.
You know the,,,""hand made by Robots or wound by Virgins thing"".
my ears tell me all I need to know.

I personally went to a lot of trouble setting up different ideas to prove for my own sanity what works and what is only a marginal difference. What some will say is *Better* another will say *just different*

What I can say with great certainty is that Att/Lpad relies heavily on the Speakers used,,,
whereas reAmping is less dependant on speakers.
That is the reason I have access to a lot of quite different sounds.

Pays to stick to simple observations when things get tecky.
i.e. no matter how complex it's just **tone shaping**.
The hardest most expensive tone stack is a PB or similar circuit as it forces you to use big massive heavy chunks of metal and copper and big watt resistors.

As I said before do you want to spend your life trying to deduct the inducktance of the square root of the holy grail,,,,
or spend ten bucks on a second hand Graphic EQ and then reamp it?

Somewhere you are going to have to bite the bullet and try something until you test ideas it's just shooting Arrows into the Air.
Cheers Phil.
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Re: Weber MASS Attenuators

Postby DougH » 15 Oct 2010, 14:46

As far as the "x3 x4" thing is concerned, what you have to do is look at some typical speaker curves and convince yourself that a resistive impedance that is a few multiples of a reactive impedance rating is not necessarily a bad thing. Only you can do that yourself.
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Re: Weber MASS Attenuators

Postby Rogue » 16 Oct 2010, 05:25

What are the pitfalls of using just the mass motor as the load? Nothing else, just the motor. Is this a proper load seen by the amp while operating?
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Re: Weber MASS Attenuators

Postby dai h. » 16 Oct 2010, 10:02

DougH wrote:As far as the "x3 x4" thing is concerned, what you have to do is look at some typical speaker curves and convince yourself that a resistive impedance that is a few multiples of a reactive impedance rating is not necessarily a bad thing. Only you can do that yourself.


yes you are right. This is something I don't understand and need to look at (in order to comprehend fully what that is doing). Something I remember about this is Randall Aiken having an issue with someone suggesting R loading w/a higher value on a very old alt.guitar.amps discussion thread.

Phil/phatt,

to be clear I'm not asking for advice on how to get a sound or anything (not that I know everything or am some sort of expert).
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Re: Weber MASS Attenuators

Postby phatt » 16 Oct 2010, 15:22

Rogue wrote:What are the pitfalls of using just the mass motor as the load? Nothing else, just the motor. Is this a proper load seen by the amp while operating?


Hi Rouge,
I assume you mean just drive the mass motor like a speaker?
Then it would be the same as a normal speaker,,,,but (oh there is always a but with electronics)

The driver in the Mass unit is used *in series* with the output hence it's only used for it's inductive qualities.
The resistors across the output take most of the load so your problem then becomes how much can the mass motor handle when used as a speaker load.
My guess is a lot less, I would not push my luck.

If you are interested?
In real world experiments I have done tapping a signal from a real speaker and then switching to a resistive load makes no audible difference that my ears can hear, Ziltch.
A scope may pick up something the old ears can't hear but I'm not much interested in playing to a crowded room full of scopes! :lol:

I do understand the conundrum that most find themselves in.
Example;
Go pickup a mass motor (or real speaker for that matter)
Now put it right beside a Ceramic Resistor.
Now ask yourself a quick Q?
Which one holds the *most* magic smoke?
The speaker will most often win hands down simply because it looks and it IS more high teck.

In reality the diff maybe neither here nor there.

If tapping signal from a resistor load was good enough to elevate EVHalen to the very top of the pile,, why on earth would you wish to waste time on hi teck when a simple resistor is all that is needed.
Now all you need to do is price a Resistor and a $Mass motor$ :)

If you wish to capture the speaker in all its glory then an ISO Box with speaker of your choise and a the best$$$ Mic and recording gear known to exist and you will get what you want$$$$.

I did once hear a recording of a little tube amp driving a speaker inside a cardboard box with a cheap mic and it sounded every bit as pro as the top line stuff.
You would be amazed at how easy these things are to achieve when you are prepaired to think out side the box (unintended pun) 8)
Cheers Phil.
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Re: Weber MASS Attenuators

Postby Rogue » 16 Oct 2010, 16:57

Thanks phatt. That is exactly my concern. I am curious as to whether the speaker motor itself is an adequate load.

I'm a not convinced (just yet anyways) that a resistive load is better than a reactive load.

Allow me to explain my experience....

I have a setup for recording direct....amp->direct box->weber mass lite->speaker cabinet. The direct box kicks out a line signal that goes into the DAW and I use convolution plugins and cabinet/mic impulse responses.

This works ok, but the signal going to the DAW is very mid heavy, stuffy, and dirty sounding. A good dosing of EQ helps, but I simply can't dial it out. I did a test the other day where the only difference was the weber at full load and the weber bypassed. The signal into the DAW when bypassed was much, MUCH better. It was much cleaner, open, and more balanced EQ wise.

So I know the weber negatively affects the tone. I don't know if it's the resistive elements or not. BUT, I am going to find out. :D

At some point today, if fate is on my side, I'm going to try it out. I'm going to try the weber normally with load, try it with just the motor as the load, and with it bypassed and compare all three signals from the direct box. I think if I don't push the volume too much it should be ok for a quick test. If the signal is better with just the speaker motor as a load, then I hope to figure out a way to make this a safe solution.

If there is no safe solution, then I'm going to build a iso box that's only purpose is to knock down the noise level and record with the direct out and use the IRs. They sound pretty good as long as you can get a good signal to them. They don't sound as good as a well miced cab (key words being well miced), but they are very convenient and there are tons of mics, positions, and speakers to choose from. And I only have one mic and not a very good environment for micing it. So the IRs are a very good alternative if I can get a good signal to them. :thumbsup
Rogue
 
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