Weber Mass Lite Attenuator / Peavey Classic 100 application

[tbonuss]

Hello all--

I just happened upon a Weber Mass Lite (100 Watt) attenuator and am interested in using it on a Peavey Classic 100 (Watt) head.

Before I start messing around with this, and make some kind of boneheaded irreversible error, I thought I'd get ask the good people here for some guidance.

1. Communicating with Weber and they caution agains using the 100 watt rated attenuator on a 100 watt head above half volume. Evidently, I need the 200 watt version to do that as they advise the amp can put out 50% over rated power when overdriven (?).

2. The amp has 3 output impedances (16, 8, 4) and the Weber will adjust accordingly (however it does that).

3. I keep the preamp gain moderate as I'm trying to get a balance with power amp distortion.

So...

The first thing that occurs to me is that I should buy the 200 watt version. However, based on what I read, I like the way this one has one rheostat for low-mid and one for mid-high. That configuration really makes a lot of sense to me. Guess I could buy a second one and run on the parallel amp outs...oy.

The second thing that occurs to me is that I should get an estimate of maximum output power based on my settings. I don't know the best way to do that.

Third, not sure if impedance mis-matching can help here, and may be a bit risky as I'm trying to dime the power amp (well actually, trying to figure out the reasonable limit and see how that sounds).

Fourth, *eventually* maybe I need to put a half power switch on this thing. Look at me, trying to lead my own thread off topic.

I dunno...help, thoughts, harassment? Any additional information I should provide?

Thanks in advance!

[Chuck H]

It's true that your 100W amp will put out bursts beyond that when overdriving. And you mention dialing the amp in for "a balance with power amp distortion". Well, if your power amp is distorting it's clipping the output tubes. Ideally you should have the 200W attenuator. Since Weber makes those attenuators with a speaker motor it may be that their caution against using a 100W amp with the mini is due in part to that speaker motors limitations. That's something I can't comment on. Otherwise, an attenuators limitation is heat. The speaker motor not withstanding you can ordinarily run any attenuator with any amp as long as or until the attenuator becomes too hot. So, it's just as you knew it was. Iffy enough to skirt an endorsement. Proceed at your own risk with the amp at 100W. But...

You mentioned that the Mass handles a range of impedances. This is likely because guitar speakers actually only present their rated impedance in a limited frequency range. All other frequencies typically being MUCH higher impedance. As a result many attenuators use something like a 25ohm or 32ohm load to sort of average what the amp sees compared to an actual speaker. Some such attenuators claim to work fine for all impedances. I don't entirely agree with this practice.

You can always pull two power tubes. The two inside or outside is typical but I'm not familiar with that amp. It's common practice when pulling two power tubes to set the amps impedance switch one load setting lower. ie: if the amp is typically run into an 8ohm load and the impedance switch is set for 8ohms, if you pull two tubes, set the impedance switch to 4ohms and continue using the 8ohm load. Let's assume the MiniMass has a nominal load for 8ohms, so pull two tubes and set the amps impedance switch to 4ohms. This should provide a safe margin for the MiniMass.

[olddawg]

I'm assuming the intention is to saturate the amp and bring the volume down with the attenuator. If you have to use that amp and have to use that attenuator..... do as stated above and pull 2 power tubes. Just make sure the impedance setting on the attenuator and the load match up. Just a thought. I use a mini mass gigging all of the time. They work best just taking the edge off of a screaming saturated amp. My mini mass 50 watt has a the footswitch option so I can turn it on and off. I use a 2 channel 20 watt amp with a master volume. I set the amp up and use the attenuator as a volume boost for leads usually hitting the sweet spot for most clubs. IMHO. If you are pulling tubes, you don't really need a 100 watt amp. You might consider a lower wattage amp to begin with.

[tbonuss]

Thank you all for the responses. The Classic 100 has 8 el84's...maybe I should pull 4 for now? I'm trying to get it at a volume where I can mess with it in the house without too much volume.

Sorry I didn't make it clear about what I was trying to say with balancing the power. What I mean is that I'm ASSUMING that since I don't run very clipped / saturated preamp the RMS values when the p/a starts to clip will be lower than if it was starting with more squared waves. I know that would be true of other gear in theory and practice, and I don't happen to know why it would be different for guitar amps. But it very well could be...or maybe I'm just thinking about this wrong.

I really don't get the impedance thing with this. If the impedance is that high, can't it damage the o/p transformer?

Can I safely pull 4? I think that if that works maybe put a switch in to idle either set of 4 or run all 8 (I do have opportunities to play at that volume).

Again, thanks for your help. Standing by to learn.

Steve

[Chuck H]

Well it sounds like you ARE pushing the power tubes and prefer their compression over preamp distortion. In reality I have a hard time believing that even eight EL84's is ACTUALLY producing 100W so you're probably safe ignoring the issue and just using your MiniMass. But if anyone can do it, Peavey can And you absolutely CAN pull out four of the tubes and follow the same instruction as for pulling two big bottles from a four big bottle amp. The exceptions being that Peavey has been known to do what works rather than what is common. So make sure you're pulling two tubes from either side of the push/pull circuit. And make sure the amp is fixed bias (like most Peavey el84 amps) because if it's cathode biased there may be a bias issue with just pulling tubes out. I couldn't find a schematic for that amp (where's JPB? ).

[Justin Thomas]

Isn't Peavey also notorious for the series heater strings???
As in, pull a power tube or two or four and, in AOL-Guy voice, "goodbye!"
Yeah, a schematic would he awesome...

Justin

[tbonuss]

Thanks Chuck!

I am cautiously "cranking" it bit by bit...well was, my youngest is now asleep...and the attenuator isn't getting hot.

http://music-electronics-forum.com/a...-schematic.pdf

[Chuck H]

Isn't Peavey also notorious for the series heater strings???

Justin

OOooo.!. Good call! Ok, tbonuss, if the filaments go out when you pull tubes, don't do it

No harm will occur to the amp by trying, but if the filaments happen to be in series then pulling tubes, straight up, won't work.

[tbonuss]

Isn't Peavey also notorious for the series heater strings???
As in, pull a power tube or two or four and, in AOL-Guy voice, "goodbye!"
Yeah, a schematic would he awesome...

Justin

THANKS!!! I was thinking about the p/s and didn't even think / know about that. Thanks!

*LATER* Nope--looked at the schematic. They aren't in series.

http://music-electronics-forum.com/a...-schematic.pdf

[lowell]

Maximum power based on your settings: Measure RMS voltage on the speaker. Square that and divide by speaker ohms. P=V^2/R. Weber is saying that once clipping starts to occur, RMS power increases exponentially... or rather a lot more.

I can't comment on if there are occasional SPIKES over that reading.

[tbonuss]

Thanks Lowell. That's really what I was trying to figure out. I guess If I simply test the RMS voltage on the speaker out using a sampled banged out chord, and keep it at or less than 50 watts calculated that would effectively be following the Weber guidance (?).

[J M Fahey]

Thanks Lowell. That's really what I was trying to figure out. I guess If I simply test the RMS voltage on the speaker out using a sampled banged out chord, and keep it at or less than 50 watts calculated that would effectively be following the Weber guidance (?).

Nice idea but it does not work that way.
You won´t be feeding that amp a sampled chord loop or any other "mechanical player" but a human guitar player, whose signal output can and does vary +/- 20dB within the same song.

ONLY way to play safe is to physically limit power out by physical , not human means:

* attenuator (MASS is NOT an attenuator but a silent speaker, not the same by a country mile)

* pulling tubes

* lowering +B (power something using HV MosFets

or the REAL solution: buy a 5W amp.

As a side note: can you post a couple MASS pictures?

Never saw them in detail or closeup and guess nobody in Argentina owns one.
Thanks.

[bob p]

I wouldn't say that it's not an attenuator. Take a look inside.

[tbonuss]

Nice idea but it does not work that way.
You won´t be feeding that amp a sampled chord loop or any other "mechanical player" but a human guitar player, whose signal output can and does vary +/- 20dB within the same song.

ONLY way to play safe is to physically limit power out by physical , not human means:

* attenuator (MASS is NOT an attenuator but a silent speaker, not the same by a country mile)

* pulling tubes

* lowering +B (power something using HV MosFets

or the REAL solution: buy a 5W amp.

As a side note: can you post a couple MASS pictures?

Never saw them in detail or closeup and guess nobody in Argentina owns one.
Thanks.

Thanks for the response J. M. Fahey

1. I meant sampling a long loop on a digital pedal and using an o-scope that would register max transient--doesn't that work. I don't know why that would be any different electrically / physically.
2. I don't know why it wouldn't be an attenuator...not sure what the two "big" (for a guitar application) rheostats are for then...
3. I want to mess with this amp. I could have a billion 5 (or 1 watt amps) and I'd still be goofing around with this one. I'm not claiming this makes sense. I'm just trying to get back into electronics after a 25 year hiatus, and I sort of have a laissez fair approach to hobbies...for example, last night I had to remember what fixed vs. cathode biasing is. If I were just using a 5 watt amp, I wouldn't have learned / remembered that last night.

I sincerely appreciate all of the help here. You guys are beyond awesome.

I'm assuming you want me to open it up and take pictures. I will plan on doing that tonight.

[lowell]

IMO you could put some signal in, with a generator, or any audio source and dial in about 1v peak to peak or .7Vac RMS if that's what your meter reads. Then, crank your amp up all the way briefly while your meter gets a reading ON THE SPEAKER. You may want to use your speaker and wear some headphones so as to not risk blowing the attenuator. If you do it fast hopefully, hopefully, you won't create enough heat to hurt anything. This will give you some idea of the real RMS wattage on 11. At least that's what I'd do... and ideally into a suitably rated speaker cabinet. At least it will get you an idea of it. Most pickups are a few hundred millivolts, I THINK, and this varies obviously a lot from pickup to pickup and depending on strings and strength of strumming and pickup height etc... This is all ballpark.

All this said, I agree with others in that I tend to go with twice the rated power for speaker loads... especially being I like overdrive.