Bizarre Schroeder problem - found and solved!

[busmandan]

I've had a Schroeder 412R for some time now. I don't always use it since it's frequently more than necessary for a given gig, but when I know I'm going to need volume, well...

It recently crapped out on me at a St. Patrick's day gig. Turned the head on and got nothing but fuzz at anything above a whisper, plus it kept throwing the amp into protect mode. Now, this was a private party gig where the entire stage and PA were powered from a single 120 outlet, so figured that power sag was the culprit. I wound up busting out the BDDI and running the bass into the PA and monitors.

The next time I used it was at a rehearsal for a sub gig and it worked fine. That said, a few days later at a pre-gig rehearsal(!) it crapped out again. Same symptoms - every time I turned it up, the amp went into protect. I also noticed the voltage meter on my Furman would dip every time the protect engaged. I had to run home and grab my backup cab (SWR Goliath III) for the gig that night.

Last night, I decided it was time to find out what the problem was. Tried different heads and cords with no change. I pulled the jackplate out to check the wiring, thinking that maybe something had come loose and was shorting.

As I'm looking through the hole the jackplate came out of, I discovered I was right - only it wasn't the wiring that was shorting. Rather, the cover had come off the back of the rheostat that controls the tweeter - and had wedged itself between the magnets of the upper two speakers. One edge of it was resting on the speaker terminals of one of the speakers, creating a dead short to the other speaker.

The rheostat cover has four tabs that bend around the ceramic edge of the rheostat to hold it on. How it got sprung enough to come off, I'll never know - the cab has been in a live-in road case since I got it. I couldn't get it tightened up enough to feel secure about it staying on, so I took a strip of rubber, punched two holes in it, looped it around the cover, and slipped the ends over the shaft through the holes.

A bizarre problem, but an easy fix. Curious to know if anyone else has had this problem.

[wideyes]

Thanks for sharing!

[twinfallsbass]

I had the same issue with a Shroeder cab putting my head into protect mode as well ( at two seperate shows ), but it was not the same problem you had. I had to send mine back to Shroeder twice, they said it was bad drivers. After the cab came back the second time, I just sold it, lost faith in the product.

[BassmanPaul]

Very poor quality control by the manufacturer. BTW it's an L-Pad not a rheostat.

Paul

[wideyes]

FWIW, I found Schroeder to have excellent customer service when I had an issue with a damaged cab. You might try contacting them (him, Jorg Schroeder himself) if you want further resolution.

[WingKL]

Rubber can eventually degrade and break. You may want to find more permanent solutions.