Weber MASS Attenuators

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

Weber MASS Attenuators

Postby soulsonic » 10 Apr 2008, 04:05

I've been meaning to post these up for awhile, but never got around to it. I was packing stuff up today for the big move this weekend and I found my old notes I used for building these when I worked at Weber. So I figured I'd formally draw up the schematics to share.
Now, you have to keep in mind, Weber has changed the design of these things numerous times already, so these might not match exactly with any random one you may find and it's not necessarily like the current ones (though I'm not aware of any major changes during the past year). Despite the inconsistency you will find with various "eras" of Weber attenuators, I can assure you that these schematics are correct for the hundreds of ones I built personally.

I will likely add the regular MASS100 soon, I just didn't feel like drawing it up yet - it's very similar to the MiniMASS, except it has the tone controls added to line out circuit.
You wanna talk about inconsistent...? The values of the line out tone stack in MASS100 sometimes changed on a monthly basis! :slap: Though I'll do my best to provide accurate values for the MASS100 tone stack, I personally advise removing it entirely or designing something else if you're looking to build your own. It always sounded terrible to my ears (and most customer's!).

Layouts to follow!

MiniMass
Mass Lite
Mass150

Personally, I've always thought the MASS Lite is the best sounding one.
Another thing to note is that the more recent attenuators, since late 2006/early 2007, have had small magnets glued to the pole pieces of the motor assemblies. The earlier versions in that style box didn't have any magnets, and the very earliest ones (large, heavy slant-front box) actually had full small speakers (with magnet and frame, but without a cone) inside.

P.S.
I misspelled "Freestompboxes" in the phrase, "To be hosted only on Freestomboxes.org" - LOL!

For this message the author soulsonic has received thanks:
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Re: Weber MASS Attenuators

Postby noelgrassy » 10 Apr 2008, 04:26

Freakin' beautiful gesture soulsonic! If anyone should draw up the plans it should someone who has
first hand experience with unit in question.
Again, very cool of you.
thanks, NG





PS: If I never move again, it'll be too soon! :wink:
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Re: Weber MASS Attenuators

Postby soulsonic » 10 Apr 2008, 12:22

MASS100 added!

MASS100

I really hope I got the Tone Stack right. I only had a partial drawing to work from. I know all the cap and resistor values are right, I'm just not 100% on how it's all connected. I'll say I'm 95% sure because I remember the circuit being really screwy like that. It really sounded bad. I'd recommend ignoring it and maybe trying just a simple hi-cut filter to give some basic cab sim. The rest of the attenuator sounds fine - either you like it or you don't. I still prefer the MASS Lite.
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Re: Weber MASS Attenuators

Postby AL » 10 Apr 2008, 16:56

:applause: Thanks !!

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Re: Weber MASS Attenuators

Postby beerbunny » 11 Apr 2008, 20:02

:hug: Thanks from me, too.

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Re: Weber MASS Attenuators

Postby super velcroboy » 13 Apr 2008, 05:47

I've had 2 masses in the past. To be honest, i think it is a waste and a huge tone sucker. I sold them off. You can't attenuate your amp and still expect good tone. There is always some level of tone change, and usually all bad.
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Re: Weber MASS Attenuators

Postby floris » 13 Apr 2008, 13:12

Does anybody know where to get a "voice coil motor assembly 8ohm 100Watt" part like for the Weber Mass Lite?
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Re: Weber MASS Attenuators

Postby Torchy » 13 Apr 2008, 16:24

Those rheostats are available from RS Online but NOT cheap - example part number 220-2494 (47R 25W) is £24.46+VAT and delivery !!!
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Re: Weber MASS Attenuators

Postby floris » 13 Apr 2008, 17:18

That a lot of money for these rheostats! Not very practical to DIY a Weber Mass like attenuator then, right? Unless the rheostats are replaced with a simple switching setup for the EQ or get rid of the EQ completely. But were to get these power voice coils, use some old speaker or something?
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Re: Weber MASS Attenuators

Postby bancika » 14 Apr 2008, 17:46

I'll try to use a rotary switch instead. With 12 position switch you'd need 11 ~5ohm resistors, 10W each (for 100W version). you wouldn't have a continuous sweep, but it's much cheaper. Cheers
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Re: Weber MASS Attenuators

Postby soulsonic » 16 Apr 2008, 00:46

Weber purchases their rheostats for about $5-$10 each. They get them shipped directly from their factory distributor in China.
I still have an original factory catalog which features these rheostats and includes contact information for sales. I try and dig it up to share. I don't know what kinds of quantities you'd need to purchase

Having personally handled hundreds of those rheostats, I'd have to say that you'll be better off spending the extra money on a quality Ohmite one - those Chinese ones seem to range from okay quality to absolutely dismal quality, and it's hard to predict . I remember that we had to put glue on the back of the wiper contacts on all of the 25 watt ones because the contact would come loose and fall apart from the wiper... etc, etc. Though, if you're on a budget, they can be a good deal if you don't mind potentially having to rework them a bit and clean them up.

There are some other ways to reduce costs as well; for example - in the MASS Lite and MASS150, you don't have to use 100 watt rheostats for the "Mids-Highs" control. There's no way that you're going to have 100 watts worth of high-frequency energy flowing through there, so you can easily substitute a 25 watt, possibly even a 12 watt, rheostat in that position. When those were designed, I don't think they bothered to take into account the fact that the vast majority of the power being transferred to a speaker is in low-frequency energy; it's a shame, because I'd think they could save alot of money by not having to use two big 100 watt rheostats on each one of those things.

For the speaker motors, you could just use any old speaker with the correct impedance and power rating. Here's how I would do it: I'd cut the cone out - be careful not to damage the voice coil or spider. Then, I'd cut the bulk of the frame away from the motor, so you'd be left with just the magnet/voice coil assembly. Then you'd have something that wouldn't be too difficult to mount in a box with the rest of the attenuator. You have to be careful not to damage the lead wires coming from the voice coil when you cut the cone off, and you want the voice coil to still be able to move freely in the motor - don't glue the voice coil in place (like it says to do in the Kendrick book - stupid!). The coil has to be able to move, otherwise it won't behave correctly in the circuit and it will run a higher risk of overheating and burning up. To dampen any noises the motor may make, you could try using some insulation over the motor, though you should take care to use something that can withstand heat without catching fire because the motor will definitely get hot in use.

You can order speaker recone parts directly from Weber and build your own motors from scratch if you wish. It's really not that difficult. If anyone is interested, I may be able to do a tutorial on how the motors are assembled. It kinda depends... it's not necessarily easy for me to get those parts from Weber; I'm thinking they might not be too keen on selling me parts so I can do a tutorial on how to clone their products. :lol:
I know they used to sell the motors by themselves for people to build attenuators and loads with, so maybe they'll still do that if you ask 'em. Hell, they may sell you some of those cheap rheostats too. Basically, as long as they're making sales of some kind, they're happy, so go ahead and ask. Trust me, they would much rather sell you parts than have to deal with actually building things themselves.
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Re: Weber MASS Attenuators

Postby floris » 17 Apr 2008, 23:18

@soulsonic: Thanks for the very interesting follow-up post!
I guess it would be easy to make a reactive attenuator for a 5W single ended tube amp then, right? No large power to dissapate. Like a "Weber UltraLite". :)
Do you agree that using resistors and switching would be a more cost effective solution instead of the Rheostats but of course less flexable? Rheostats seem very expensive for something you probably dail in once and be done with it.
(Or just hardwire an EQ...)
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Re: Weber MASS Attenuators

Postby soulsonic » 20 Apr 2008, 08:27

You don't even have to use a rheostat; you can use a standard L-Pad and probably get a much better impedance match anyway. I've used L-Pads with good results, though they don't seem to be able to handle high powered amps very well. I think you could do a low-powered one with a common L-Pad just fine.
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Re: Weber MASS Attenuators

Postby floris » 22 Apr 2008, 00:44

L-pad instead of rheostat, good idea thanks!
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Re: Weber MASS Attenuators

Postby soulsonic » 24 Apr 2008, 00:21

These are the ones I've tried:
http://www.partsexpress.com/pe/showdetl ... er=260-261
http://www.partsexpress.com/pe/showdetl ... er=260-262
They work great and, unlike a rheostat, they keep a constant correct impedance.
Only caveat is that you should not trust the 100 watt rating. I tried one with 100 watt amp that was turned up about halfway and it started smoking! :shock:
I think it should be just fine with lower powered amps, especially those under 50 watts, and you could probably adapt it to work nicer with high-powered amps by having a fixed L-Pad resistor network in front of it to knock down the power so the rotary L-Pad doesn't have to do all the work.
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Re: Weber MASS Attenuators

Postby stratotrasto » 24 Apr 2008, 10:28

There are photos of inside?
It is to see the disposition of the components.

Thank!!

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Re: Weber MASS Attenuators

Postby dai h. » 24 Apr 2008, 21:41

hey thanks for putting up the schemos, soulsonic. Interesting stuff.

(if you don't mind me asking) what's the difference between those L-Pads and a rheostat? Taper (and otherwise the same innards, i.e. wirewound rheostat?)? Also, why do you think is the reason the "100-watt" L-Pad started smoking? Is it not actually capable of handling 100-watts in some way, or?

FWIW, I've done a bit of websearching on attenuators, and from what I could gather using a reactive load together with a resistive (L-Pad) might be a good option for low volume playing. There's a very old post by Randall Aiken relating that he did this to get good sounds at apartment-dweller levels. In one of his amps also, there is an on-board attenuator and as far as could be surmised from mediocre resolution pics, it's basically some sort of variable L-Pad (a group of power wirewounds are clearly visible, plus a pot for the lowest continuously variable setting). Also if anyone has heard the Swede "Ralle" and his van halen "brown sound" clips, so far as I could gather he was also using a reactive load followed by an L-Pad (Marshall Power Brake followed by a fixed resistive L-Pad).

also, re: the Weber MASS motor units I do believe they have been avail. separately (again) for a little while now (6mos.??)
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Re: Weber MASS Attenuators

Postby dai h. » 25 Apr 2008, 06:33

(spent a few mins. searching, and apparently *I think*) those are meant for use in-line with tweeters, so if I'm seeing it correctly the wattage rating will go down when used w/lower frequencies. Not sure about the other stuff though.
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Re: Weber MASS Attenuators

Postby floris » 25 Apr 2008, 09:39

Weber MASS speaker motors: (at bottom of page)
https://amptechtools.powweb.com/truload.htm
"These are the motors from our MASS attenuators. Many techs like to use them to quietly test an amp with an authentic load so they can look for instabilities. These are speaker motors, they will blow up just like a speaker. So, don't think they are indestructible. We have 4, 8, and 16 ohm units available in power ratings of 50 and 100 watts. The red and black leads are 18" long. I would say the power ratings are conservative, RMS ratings, but I don't want to give the idea the motors are invincible. Be careful when using these and keep an eye on them if you are cranking an amp into them with heavy distortion.
We prefer to sell these only to amp builders and those who understand their proper use.
50 watt motor - $30
100 watt motor - $45"

Price is not too bad but I think I'll just try to DIY one from an old crappy 8Ohm 40W speaker.
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Re: Weber MASS Attenuators

Postby bancika » 29 Apr 2008, 14:40

I also canibalized some small speakers for speaker motors but have in mind the following:
Original speaker rating assumes that speaker has a cone which dissipates the power (by moving the air), but if you just remove the cone you don't have anything to dissipate the power, coil won't have any resistance on the way. I've heard (didn't test though) that speaker without a cone will be able to handle just a fraction of specified power, i.e. will die much easier. 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.
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