Weber MASS Attenuators

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

Re: Weber MASS Attenuators

Postby soulsonic » 29 Apr 2008, 20:53

bancika wrote:Weber motors seem to have some sort of a weight (that black thing on the top) that simulates cone resistance using gravity. Provided I'm right that also means you can mount them only one way - weight facing up.
Cheers

No, they do not have a weight. The black thing you're seeing is most likely the pole piece. The only possible added mechanical resistance is the second "damper" spider which is mounted on top of the main spider; but I believe that is more to keep the voice coil straight in its assembly than anything else. The Weber motors do not have the same mechanical resistance as a regular speaker, and due to being either weakly magnetized or not magnetized at all, the motors do not exhibit anywhere near the same motion as a regular speaker.

They just sit there and get hot - very hot. I am sure if you tried to put a continuous 100 watts through the 100 watt motor it would likely burn up. Despite that, I've never seen a Weber attenuator returned with a burned up motor. The failures of the MASS units are almost always either due to failures of the junky rheostats (they tend to fall apart) and sometimes failure of the impedance matching resistors (from gross overheating, probably due to overpowering). With the resistors, more often it's the contact glue they use to hold them in place which often fails and emits a noxious odor and sometimes even begins smoking. On numerous occasions I suggested using proper thermal epoxy to make this bond, but I was always ignored - obviously epoxy is too expensive for them, though it only requires a small amount to get a good bond, as opposed to the gallons of contact cement and super glue they go through and still get a crappy bond. The only failures I've ever seen in the motors are on a couple units in which the tinsel lead wires (located underneath the spider on the interior of the assembly) were improperly insulated and were shorting against the metal chassis. Those lead wires should be entirely coated with black insulated glue, but a couple of the former contract builders didn't do so, and if the uninsulated wires have too much slack they may short as described. I've only seen that happen a couple times.

To address the other points; yes, rotary L-Pads differ from standard rheostats because they have two resistance tracks of different value which are intended to provide the correct impedance match with the given load throughout its sweep. A rheostat doesn't keep a constant resistance with the load in parallel with it the way that an L-Pad does, that's why I prefer the L-Pads. And yes, I believe those are intended for lower-current things like tweeters, though 100 watts into 8 ohms is still 100 watts into 8 ohms... but at what nominal frequency is that measured - I assume the current through the load would be the same at a given power level and frequency? Even though that resistance would change depending on its AC impedance, I'm going to assume that the given resistance of an L-Pad is specific to the nominal AC impedance of the load for which it is intended. But yeah, anyway, that 100 watt one I tried started smoking, though it didn't actually burn up or fail - maybe it was just some stuff on it that started smoking from the heat even though the device itself was still fine. I'll need to experiment with it some more and observe closely what happens when it is adjusted to a heavy amount of attenuation with a large amount of power through it. I think I should do this experiment with a cheap solid state amp. :wink: :lol:
They have those stereo ones; you could use both halves wired in parallel for more power handling at a different impedance.
And if you used some series/parallel resistors with the L-Pad to match to different resistances, this would also divide the power dissipation duties to take some of the heat off the rotary L-Pad (literally!).
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Re: Weber MASS Attenuators

Postby dai h. » 29 Apr 2008, 23:17

thanks! Tried searching for a bit and found this:

http://colomar.com/Shavano/lpad.html

scratching my head for a bit it sort of looks like (for an 8ohm L-Pad) the first VR would be 8ohms and the second (must be the one on the inside in the pic above) would be higher (since it ends up in parallel with the output, i.e. spk--haven't figured out what value it would be though)?

this is the highest rated one I could find (200W) :

http://www.madisound.com/catalog/produc ... cts_id=263

price is not listed but fwiw here(japan) it's priced around USD$35.

Also, (since it's two internally ganged) rheostats) I think it'd be possible to get higher rated ones if you had a ganged rheostat custom made. (The limitation on wwnd. rheostats as I understand is the current rating with generally higher ohm rheostats having a lower current rating--the higher the resistance the thinner the wire on the substrate(?)--the ceramic "body" portion).
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Re: Weber MASS Attenuators

Postby dai h. » 30 Apr 2008, 13:38

found this which shows a value for the 2nd VR:

http://www.bcae1.com/lpad.htm

and 120 and 8(using DC) in parallel is 7.5ohms, so seems not quite perfect. Looking at the diagram, one can see that you could also use a rotary sw. and indiv. resistors for fixed attenuation steps.
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Re: Weber MASS Attenuators

Postby floris » 01 May 2008, 09:39

bancika wrote:I also canibalized some small speakers for speaker motors...

@bancika: What are your experiences with this, did it work ok? How much power can such a "canibalized" speaker motor without cone dissipate before giving up, 10% of its RMS power rating or something?
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Re: Weber MASS Attenuators

Postby bancika » 01 May 2008, 16:00

floris wrote:@bancika: What are your experiences with this, did it work ok? How much power can such a "canibalized" speaker motor without cone dissipate before giving up, 10% of its RMS power rating or something?

Actually, I didn't do anything with them yet because I found about about "the catch" after cutting the cones out (even more, I prepared everything to make something like weber mass rated at 5-10W). I made two motors from speakers that are 4ohm 5w each but I don't want to risk damaging my amp in case motor dies.
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Re: Weber MASS Attenuators

Postby vanessa » 02 May 2008, 20:45

Anyone have a Weber Z-Matcher schematic? I've read these work pretty well. If not is it just resistors?
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Re: Weber MASS Attenuators

Postby soulsonic » 03 May 2008, 05:46

Z-Matcher is just an autotransformer. That's all. You can purchase the Z-Matcher autotransformer by itself from Weber if you want to make your own. It's simple to wire, and fairly intuitive to figure out from the wiring diagram of the autotransformer which can be found on the page listing all the Weber transformers. The part numbers are WZC-50 and WZC-100 for the 50 and 100 watt versions, respectively.
The only additional circuitry are the ubiquitous line out jacks which are done with the usual bare bones voltage divider resistor arrangement, and also includes a "balanced" XLR out which is realized with a shitty telephone transformer which I would never consider attempting to duplicate.
My personal experience with the Z-Matcher is that it does it's job fairly well with a minimal amount of coloration. I could detect a slight leanness in the low-end when using it, but it wasn't anything I'd consider deleterious to subjective tone.
I suppose you could maybe try using a Z-Matcher transformer as an autotransformer attenuator. :hmmm: I mean that's basically what it's doing; shifting the voltage levels to match with whatever impedance.

A little update to the MiniMASS: They are currently using 47uF (!) caps for the Treble Boost circuit. I have a feeling that's probably going to change pretty soon when people start complaining about it being way too bright...
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Re: Weber MASS Attenuators

Postby daniel_pt » 12 May 2008, 00:29

Hey everyone... I just found freestompboxes.org and I really want to build a minimass attenuator!

I'm reading this thread as if there's no tomorrow!! :mrgreen: and so far, I really liked it...

Today I just have a couple of questions for you.

I have a Peavey Valveking 50w and I want to attenuate using, as I said, the minimass... Do I have to change more parts or just the rheostat (btw, 100w L-pad should be the way to go?) and voice motor coil to 100w (I think leaving it at 50w can be tricky when crank the amp to the max)?

I live at Europe... Can you point me where can I find these couple of parts? The L-pad (or rheostat) and voice motor coil? I don't have old speakers where I could "steal" it! :mrgreen:

Thanks in advance for any help, suggestion, comment! :)

Cya
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Re: Weber MASS Attenuators

Postby floris » 12 May 2008, 12:15

daniel_pt wrote:Hey everyone... I just found freestompboxes.org and I really want to build a minimass attenuator!
Can you point me where can I find these couple of parts? The L-pad (or rheostat) and voice motor coil?


Please read the above thread because some links were already posted...

http://www.freestompboxes.org/posting.p ... 94#pr27000
Weber MASS speaker motors: (at bottom of page)
https://amptechtools.powweb.com/truload.htm

L-pad in europe:
I've searched Conrad in the Netherlands, found this one: http://www1.nl2.conrad.com/scripts/wgat ... results=10
In Dutch they are called "Luidspreker niveauregelaar" not L-Pad. So try also to search for "loudspeaker attenuator" or something. Makes it hard to find one... :slap:
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Re: Weber MASS Attenuators

Postby dai h. » 15 May 2008, 21:54

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Re: Weber MASS Attenuators

Postby daniel_pt » 10 Jun 2008, 02:17

Is it safe to use a Mass Lite 100 with a peavey valveking 50w?

MASS Lite with 50 or 100 watt rating. 8 ohms. May be used on 4, 8, and 16 ohm amplifiers.


I don't quite get the meaning of this in the attenuator characteristics.

This attenuator is supposed to be connected to an 8ohm speaker and can be connected to any amplifier with those outputs?

This valveking has an 16ohm speaker, so I suppose the output is also 16ohm...

Can I use this device with no problems with this amp?

Cheers!
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Re: Weber MASS Attenuators

Postby soulsonic » 10 Jun 2008, 09:13

daniel_pt wrote:Is it safe to use a Mass Lite 100 with a peavey valveking 50w?

MASS Lite with 50 or 100 watt rating. 8 ohms. May be used on 4, 8, and 16 ohm amplifiers.


I don't quite get the meaning of this in the attenuator characteristics.

This attenuator is supposed to be connected to an 8ohm speaker and can be connected to any amplifier with those outputs?

This valveking has an 16ohm speaker, so I suppose the output is also 16ohm...

Can I use this device with no problems with this amp?

Cheers!


You can use the 100watt Mass Lite with a 50w amp no problem.
The impedance thing isn't exact with these kinds of attenuators. The "8 ohm" rating means that when the attenuator is turned all the way down it will give something sort of like an 8 ohm load to the amp. At different levels of attenuation, you will get different impedances depending on the ratio of the impedance of the attenuator in tandem with the impedance of the speaker plugged into it. This sort of attenuator will never give you an exact impedance match. They say that you can use it with 4, 8, or 16 ohm amps because most tube amps can tolerate impedance mismatches as long as they're not too far off. Using a 16 ohm speaker with the Mass Lite could potentially get you a range of impedances anywhere from 8 to 24 ohms, depending on the level of attenuation and the setting of the "Range" switch. This should be okay for a 16 ohm amp, but you have to be aware that mismatching the impedance will change the tone and response of the amp from its "normal" sound.
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Re: Weber MASS Attenuators

Postby daniel_pt » 10 Jun 2008, 11:35

soulsonic wrote:
daniel_pt wrote:Is it safe to use a Mass Lite 100 with a peavey valveking 50w?

MASS Lite with 50 or 100 watt rating. 8 ohms. May be used on 4, 8, and 16 ohm amplifiers.


I don't quite get the meaning of this in the attenuator characteristics.

This attenuator is supposed to be connected to an 8ohm speaker and can be connected to any amplifier with those outputs?

This valveking has an 16ohm speaker, so I suppose the output is also 16ohm...

Can I use this device with no problems with this amp?

Cheers!


You can use the 100watt Mass Lite with a 50w amp no problem.
The impedance thing isn't exact with these kinds of attenuators. The "8 ohm" rating means that when the attenuator is turned all the way down it will give something sort of like an 8 ohm load to the amp. At different levels of attenuation, you will get different impedances depending on the ratio of the impedance of the attenuator in tandem with the impedance of the speaker plugged into it. This sort of attenuator will never give you an exact impedance match. They say that you can use it with 4, 8, or 16 ohm amps because most tube amps can tolerate impedance mismatches as long as they're not too far off. Using a 16 ohm speaker with the Mass Lite could potentially get you a range of impedances anywhere from 8 to 24 ohms, depending on the level of attenuation and the setting of the "Range" switch. This should be okay for a 16 ohm amp, but you have to be aware that mismatching the impedance will change the tone and response of the amp from its "normal" sound.



Thank you for this explanation!

Anyway, the bold sentence worries me a bit, because at the back of the amplifier, the output to connect it to a cabinet says "16 ohms minimum". I dunno why they say minimum, but if I get a window between 8 and 24, I wonder what the reason can be. I mean, should only be as you say a tone and response change or can it put the amp in jeopardy? :hmmm:

Using the Mass 100 would be more suitable that the Mass Lite 100?

once again, thanks a lot for every answer! :)
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Re: Weber MASS Attenuators

Postby soulsonic » 10 Jun 2008, 17:05

daniel_pt wrote:I mean, should only be as you say a tone and response change or can it put the amp in jeopardy?

I'm not familiar with the specifics of that amp, but most amps can tolerate a 2:1 mismatch without being damaged.
Using the Mass 100 would be more suitable that the Mass Lite 100?

The Mass 100 has the same general impedance mismatch characteristics. It has that switch that makes an attempt to match impedances, but like all the Mass attenuators, you only get a close match when it is turned all the way down to maximum attenuation.
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Re: Weber MASS Attenuators

Postby noelgrassy » 14 Jun 2008, 13:43

Learning about the Weber firm through Martin, sheds some light on the choice nickname some other folks use.

"Barbeque Boy"

:oops: LULz
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Re: Weber MASS Attenuators

Postby mora_di2 » 05 Nov 2008, 23:49

Hi.
I'm wondering, if I wanted to build me a dummy speaker load (don't need adjustable attenuation), could I just substitute my normal guitar speaker with one of these weber speaker motors? I wouldn't need any rheostat/L-pad/resistor?
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Re: Weber MASS Attenuators

Postby SirElwood » 06 Nov 2008, 05:03

mora_di2 wrote:Hi.
I'm wondering, if I wanted to build me a dummy speaker load (don't need adjustable attenuation), could I just substitute my normal guitar speaker with one of these weber speaker motors? I wouldn't need any rheostat/L-pad/resistor?


You can do dummy load with just a normal power resistor.
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Re: Weber MASS Attenuators

Postby mora_di2 » 06 Nov 2008, 15:48

SirElwood wrote:
You can do dummy load with just a normal power resistor.


Thank you for the answer, I already knew that, but I wanted a reactive load with a impedance closer to a real speaker. This is for using the line-out/slave out of tube amp's, and since this is post power-amp I believe a simple resistive load messes with the line-out sound as well (it surely does with my THD Univalve), that's why I was thinking a speaker-motor could match the ordinary speaker load quite well since I won't be needing a rheostat or resistors for making the load adjustable, I just need a speaker-like load that doesn't make any acoustic noise.

So could I use just the weber speaker-motor and not any other parts substituting a real speaker, or do the speaker-motor have different characteristics causing the need for added resistors?

If the speaker motor mimics a real speaker, it could in combination with a Crate Powerblock create a very nice reamp setup.

regards
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Re: Weber MASS Attenuators

Postby floris » 06 Nov 2008, 22:41

Well, Weber sells these speaker-motors. You could send them an email and ask them?
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Re: Weber MASS Attenuators

Postby seniorLoco » 07 Nov 2008, 03:01

Thanks for your kind effort Soul...appreciate it.

:wink:
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