Weber Mass Lite Attenuator / Peavey Classic 100 application

[tbonuss]

It's been my experience that a shorting jack is the best and easiest safeguard. I use an attenuator and do some bench testing with amps out of their cabinets so it HAS come up that I have failed to have a correct load on an amp accidentally. I've never lost an OT that was shorted. Another example would be a poster here some years ago asking questions about how he was operating his stock Bassman head. He was using it as a preamp by plugging a cable from the "ext" speaker jack to another amps input. With NOTHING plugged into the "speaker" jack!!! Apparently, due to the low impedance there was enough signal bleeding onto the ext jack to be useful in driving another amp. And he had been doing this for years with no failures.

Sorry if I'm being obtuse here, but am I right that this is a little less practical with two parallel output jacks? Maybe I'm not thinking about it right.

[J M Fahey]

Two speaker jacks with one of them shorted has been the standard fender configuration for decades.

usicians are expected to plug into the main jack, which is shorted,and only use the clearly labelled extension one if they have another cabinet.

So in practice it works.

[tbonuss]

Two speaker jacks with one of them shorted has been the standard fender configuration for decades.

usicians are expected to plug into the main jack, which is shorted,and only use the clearly labelled extension one if they have another cabinet.

So in practice it works.

Ok. Got it--thanks Juan.

[Chuck H]

This is the back of a Fender clone build. The jacks are clearly marked SPEAKER and EXT.SPEAKER but musicians occasionally get it wrong anyway. Probably assuming Fender just marked them that way so users would know they could use another cabinet, but still thinking the jacks are simply parallel. They're not. The SPEAKER jack is a shorting jack but the EXT.SPEAKER jack is not. So if, for example, one wanted to use an extension cabinet but not use the amps own speakers they would need to plug it into the SPEAKER jack and not the EXT.SPEAKER jack. A little confusing. Probably why practical thinkers don't warm up to it right away. But it's worked out pretty well overall and the worst that can happen is the amp will run into a short. Which is much preferable to an open load.

[olddawg]

This is the back of a Fender clone build. The jacks are clearly marked SPEAKER and EXT.SPEAKER but musicians occasionally get it wrong anyway. Probably assuming Fender just marked them that way so users would know they could use another cabinet, but still thinking the jacks are simply parallel. They're not. The SPEAKER jack is a shorting jack but the EXT.SPEAKER jack is not. So if, for example, one wanted to use an extension cabinet but not use the amps own speakers they would need to plug it into the SPEAKER jack and not the EXT.SPEAKER jack. A little confusing. Probably why practical thinkers don't warm up to it right away. But it's worked out pretty well overall and the worst that can happen is the amp will run into a short. Which is much preferable to an open load.

Symptom: Older Fender tube amp has very low output. Solution: Musician has a single speaker load plugged into the Ex Speaker jack. The Speaker Jack shorting leaf has oxidized. Enough over time to allow some signal through.

[tbonuss]

This is the back of a Fender clone build. The jacks are clearly marked SPEAKER and EXT.SPEAKER but musicians occasionally get it wrong anyway. Probably assuming Fender just marked them that way so users would know they could use another cabinet, but still thinking the jacks are simply parallel. They're not. The SPEAKER jack is a shorting jack but the EXT.SPEAKER jack is not. So if, for example, one wanted to use an extension cabinet but not use the amps own speakers they would need to plug it into the SPEAKER jack and not the EXT.SPEAKER jack. A little confusing. Probably why practical thinkers don't warm up to it right away. But it's worked out pretty well overall and the worst that can happen is the amp will run into a short. Which is much preferable to an open load.

Thanks Chuck. The truth is at first I thought (for whatever reason) that you meant both shorting jacks--requiring a load to be plugged into each all the time. Then when I thought about Fenders ala Juan's comments I thought that it would drive me crazy not remembering which one to plug into and that I'd have to label the TOP of the head (not the back) or keep it in front of a mirror

Also, as far as I can tell, there isn't any problem with the Weber or the Power Soak handling the power output of this amp. I can't get more the 100 watts out of it with everything dimed and BANGING the $#@#$ continuously out of the guitar. I'm using a couple of clamp-meters, one the reads true RMS and one that seems to just multiply by .707. Anyhow, neither attenuator gets hot under full attenuation, also the Power Soak attenuates more than the Weber. Interestingly, the Peavey puts out more from the clean channel on 12 (eat that Spinal Tap) than the lead channel with both pre and post on 12. Maybe that makes sense to you guys??? I dunno.

[Chuck H]

That's the way most modern amps that have "distortion" channels are set up. The "normal" channel is just an amp, but the distortion channel is a signal processor that adds clipping. A square wave sounds louder (to your brain) than a more rounded wave form (even though there are fewer watts). Also, the amp will clip inconsistently if the clipped wave form is further clipped by the power amp making for inconsistent performance at maximum volume. In this light the "distortion channel" is typically set up to be capable of the amps rated power but NOT clip the power tubes. The "normal" channel can though. And since tubes can continue to amplify some transients when near clipping the normal channel will be capable of more measured power (but not necessarily perceived loudness) than the distortion channel.

[tbonuss]

Quick update. I'm still messing with this. To me, the Tom Scholz Power Soak works the best. It can tame this thing down to headphone levels. The Weber sounds good too, but its just not as straightforward, nor can it attenuate as far down as the Power Soak. Pulling the tubes doesn't sound / feel as good to me as dime-ing it on either of the attenuators. I think its probably because I'm not loading down the p/s with the tubes pulled. No point in putting in a half power switch at this point, since I can just dime it on the attenuators.

As always, thank you all for the help and conversation!