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SurfGuitar101 Forums » Gear »

Permalink Blown amp using reverb unit

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Hello! I recently purchased (used) a Fender Frontman 212R, a very LOUD amp--100 watts. I've had pretty good experiences with the smaller Fender solid state amps in the past, so I picked this one up. Anyway, about two weeks after getting it, I was using it at practice with my Fender Reverb unit. I had to unplug the cord running from the reverb to the amp when suddenly there was a loud POP and a humming noise from the amp. Anyway, long story short, all the output transistors were completely blown Fender is sending me another one since it was still under warranty. I really like this amp, but I've got concerns about the reliability of this particular model now, especially as I'm gigging frequently. What I'm wondering is this: what could have caused the problem? How could simply unplugging the cord from the amp have blown all the transistors? Also, how can I make sure it doesn't happen again? Has anyone else had experiences with the Frontman 212r?
Thanks for any input you may have!

hangtenhangman wrote:

Also, how can I make sure it doesn't happen again?>

Switch to standby before unplugging cords.

The Hicadoolas

Last edited: Aug 14, 2013 02:25:36

Turn the amp down before plugging or unplugging anything. Transistor amps don't have standby switches.

http://thewaterboarders.bandcamp.com/

The stock Fender reverb unit can built up a relatively high voltage on the output. The both the Tone and Mixer pots are connected to the circuit through capacitors, so they have no DC reference to ground. If you put a guitar cable into the output and place a voltmeter across the cord plug, you'll see something like 60 volts on the output when it is warming up. Of course, if a cap has gone leaky there will be a significant amount of DC voltage on the output. I've seen this only on old reverb units, though, the ones with the Astron caps.

I modded my Fender Reverb with a 1M pulldown resistor to keep DC from getting out of the reverb unit, but if you don't want this to happen, make sure the reverb unit is plugged into your amp or an effect before you turn it on. This will load the output and drain off the charge.

If it ain't broke, fix it until it is.

Just like high power PA amps/systems:

Power amp on last at start up and power amp off first at shut down.

Keep it Drippy Brothers and Sisters!

Last edited: Aug 14, 2013 13:43:21

Wow, thanks for all the great advice. I'm not a technical kind of guy, so some of the information about DC reference and voltage and so forth is a little out of my league. However, the advice about turning on the power on the amp last and turning the volume down before turning off is easy enough.
Thanks again!

One more question: would using input number 2 minimize the chances of problems? I've read that the second input is for plugging in high-output effects such as pedals as things.
Thanks!

According to Fender here - you have to select Specs , Input 2 takes 6dB out of the signal. This is normally used for guitars with active pickups.

This is Noel. Reverb's at maximum an' I'm givin' 'er all she's got.

Last edited: Aug 14, 2013 17:46:03

I'm not convinced the amp was damaged by it being turned on and plugging a reverb unit into it. If it ate the power transistors as suspected DC would have most likely been applied to the output stage. This would usually let the smoke out of the voice coils of the speakers prior to the power transistor failures. The amp should be protected against this by coupling caps between the input and output stages. My best guess is that something went wrong in the the power supply that brought the amp down.

You most likely will not like the sound of the amp plugged into the #2 input. A 6 db loss in gain will make the guitar sound weak and lifeless with no "feel". You would compensate for this by turing up the volume and be right back where you started unless you play it dimed all the time. Not a likely senario.

The #2 input is used for high gain inputs as Noel says and for guitars with huge output. Steel guitars for example that have so much output that you can't get a clean undistorted sound from the amp.

Keep it Drippy Brothers and Sisters!

also and somewhat relatedly... i LOVE and SWEAR by my 212r.. One time i had a gig at a larger venue, so i grabbed a long shielded guitar cord for the stock footswitch. BIG HUGE NO-NO!

the footswitch needs a 2 conductor cable -like a speaker cable. were you using something other than the stock cable?

I got my amp replaced under warranty, but that's what blew it. Just like using a guitar cord for a speaker cab. Nope..

otherwise, the amp is great.

I also love the 212r (even though I only got to use it for a short time!). I wasn't using the footswitch at all as I don't use the drive channel. It's possible that being technically ignorant as I am that I was using the footswitch cable as a guitar cord, but my memory is hazy on this. Could this have caused the problem?
Fender apparently has discontinued the 212r and only had the "limited edition" cobalt blue amp in stock as a replacement for the warranty, which they're sending me. The guy at the music store has agreed to swap out the chassis for my original black one, which I prefer.
I'm really hoping this replacement amp doesn't have any problems, as I've read rave reviews about this amp and really liked it myself! I'm just baffled that something as simple as unplugging the cord from the input could bring the whole amp crashing down the way it did.

I reread your original post and saw you said you were unplugging the cord from the amp. No way is this the cause of your failure. As you unplug the cord, the jack in the amp shorts the input to prevent signal from getting to the input stage of the preamp section. Unplugging cords part way from the amp input jack is a long accepted method, a poor mans standby if you will, to keep things quiet while changing guitars, tuning etc.

Somthing went south in the amp all on its own and you were not at fault. I think Fender may be aware of an issue as they seemed to readily replace the amp.

BTW, I noticed Joe Walsh playing an FM212 when he did his gig on Daryl's House. His tone was superb.

Keep it Drippy Brothers and Sisters!

da-ron wrote:

Transistor amps don't have standby switches.

Whoops, you're right, of course Cool

The Hicadoolas

If this amp crapped out all by itself it's still strange that it happened right at the moment I unplugged. I can't help but think that Fender took a big chance putting a 5-year warranty on an amp like this!

if you were using the footswitch cord for a guitar cord, i don't know if that would cause a problem. it's a speaker cord that's not shielded... just more noise.

It is a great amp. get a good set of cords. The stock reverb aint bad.

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