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Post subject: fender Bassman 250/210 Problem
Posted: Wed Apr 18, 2012 12:53 pm
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Hey everyone I was looking for some help with my bass amp. I have a Fender Bassman combo amp, and while I love it's tone, it's rendered useless by the fact that I get little to no volume out of it at times.

For context, I use an active Ibanez bass, as well as a passive Spector, both of which are high output and require the use of the -6 dB switch on the amp. I also use a MXR Bass Octave, SansAmp BassDI (for grit), and a Boss ME-25B in my effect loop, in that order.

This combo comes equipped with two volume knobs, one of which acts as a gain, setting the maximum volume the other knob, the master knob, can go up to. I was told by the dealer that when I plugged in my bass to have both knobs set at 0, then slowly turn up the first knob until an indicator light beside the first knob flashed yellow, and then that would be my optimal playing volume from that knob without overloading the amp. At first the amp was fine, it wouldn't clip the amp no matter which of my basses I used, and I would hear no distortion. Now every time I do this, the yellow light comes on, but my bass signal gets an unwanted distortion that sometimes shuts down the amplifier in the middle of my gig/practice session/recording take/what-have-you and brings volume down to nothing. I'm left to bring my amp down to low volumes and turn my master knob to full to prevent the amp shutdown, and I'm left with a sound that's too quiet for what I need (and want).

Do you guys have any idea what's making my amp do this? I've tried turning down my horn volume and I've tightened the screws around my speaker to try and prevent vibration creating distortion, to no fruition.

The manual for my amp is here, if it helps diagnosis: Manual

Thanks.


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Post subject: Re: fender Bassman 250/210 Problem
Posted: Wed Apr 18, 2012 10:51 pm
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Joined: Thu Aug 07, 2008 3:12 pm
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Location: Albemarle, NC
It could be any number of things. Of course you've tried different instrument cables right?

A couple of things to narrow down the source of the problem follow.

Patch from the XLR output to a mixer input using a microphone cable. Plug in quality headphones to the mixer. Turn down the master on the amp. Listen through the headphones and see if you are hearing the same problem in the headphones. If you are hearing the same problem it is likely to be a problem in the preamp electronics and you can stop right here.

If you do NOT hear the same problem in the headphones, next try a different bass speaker cabinet. With the amp unplugged from the AC, unplug the built in speakers and plug in an external bass cab. Plug the amp into the AC, turn on the amp and compare the sound of the external cab to the internal speakers. If you hear the same distortion now it is something in the power amp section. If you do not hear the same distortion with the external cabinet then you either have one or more problem speakers or something is loose inside the speaker cabinet area of the combo.

Once you know where the problem is then you'll know how to proceed. If the problem lies in either the preamp or the power amp then you will need to take it to a qualified amp tech. If it turns out to be the speakers that are at fault, they often can be re-coned by a speaker specialist. Or of course you could just buy new speakers instead of repairing them. The cost to re-cone is often less than new speakers though. Very often something gets loose in the cabinet itself and causes vibration.

However I must say from your description of the issue it sounds electronic and heat related. Usually cabinet vibration noise will only happen on certain notes and you didn't specify that it is only certain notes so I'm guessing it is every note. If an amp has a fan the first thing to look at for heat issues is the fan. However as I recall the Bassman 250 doesn't have a fan. So that leaves the electronics. Sometimes there is a bad or weak solder joint. Everything works fine until the unit heats, the board expands and the contact breaks or becomes intermittent. It could also be a faulty input jack or jack contacts to the printed circuit board. It also could be a faulty electronic component that works ok cold but when it warms up it malfunctions. If that is the case it needs to be fixed ASAP because depending on what it is, it can actually cause other components to fail eventually like one domino falling will cause a chain reaction. It is easier to replace one bad part than a bunch of them.


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Post subject: Re: fender Bassman 250/210 Problem
Posted: Wed Apr 18, 2012 11:11 pm
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Rock Star
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Joined: Thu Aug 07, 2008 3:12 pm
Posts: 6355
Location: Albemarle, NC
It could be any number of things. Of course you've tried different instrument cables right?

A couple of things to narrow down the source of the problem follow.

Patch from the XLR output to a mixer input using a microphone cable. Plug in quality headphones to the mixer. Turn down the master on the amp. Listen through the headphones and see if you are hearing the same problem in the headphones. If you are hearing the same problem it is likely to be a problem in the preamp electronics and you can stop right here.

If you do NOT hear the same problem in the headphones, next try a different bass speaker cabinet. With the amp unplugged from the AC, unplug the built in speakers and plug in an external bass cab. Plug the amp into the AC, turn on the amp and compare the sound of the external cab to the internal speakers. If you hear the same distortion now it is something in the power amp section. If you do not hear the same distortion with the external cabinet then you either have one or more problem speakers or something is loose inside the speaker cabinet area of the combo.

Once you know where the problem is then you'll know how to proceed. If the problem lies in either the preamp or the power amp then you will need to take it to a qualified amp tech. If it turns out to be the speakers that are at fault, they often can be re-coned by a speaker specialist. Or of course you could just buy new speakers instead of repairing them. The cost to re-cone is often less than new speakers though. Very often something gets loose in the cabinet itself and causes vibration.

However I must say from your description of the issue it sounds electronic and heat related. Usually cabinet vibration noise will only happen on certain notes and you didn't specify that it is only certain notes so I'm guessing it is every note. If an amp has a fan the first thing to look at for heat issues is the fan. However as I recall the Bassman 250 doesn't have a fan. So that leaves the electronics. Sometimes there is a bad or weak solder joint. Everything works fine until the unit heats, the board expands and the contact breaks or becomes intermittent. It could also be a faulty input jack or jack contacts to the printed circuit board. It also could be a faulty electronic component that works ok cold but when it warms up it malfunctions. If that is the case it needs to be fixed ASAP because depending on what it is, it can actually cause other components to fail eventually like one domino falling will cause a chain reaction. It is easier to replace one bad part than a bunch of them.


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Post subject: Re: fender Bassman 250/210 Problem
Posted: Thu Apr 19, 2012 12:55 pm
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Joined: Wed Apr 18, 2012 12:50 pm
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It actually used to happen on certain notes, now that you mention it, now it's spread to everywhere really.

I'll check that stuff out, thanks!


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Post subject: Re: fender Bassman 250/210 Problem
Posted: Fri Apr 20, 2012 9:49 am
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Joined: Wed Jan 14, 2009 10:54 am
Posts: 438
Location: Alabama, Michigan, Florida, Wisconsin, Mississippi and Tennessee seasonally
From personal experience, let me make two suggestions...

First, unplug the amp from the wall outlet. There is one speaker feed plug coming out of the rear panel on most 250-210's made after 2002 and two speaker jacks. Only one jack is used for the combo configuration and the other sits empty. Unplug the speaker feed plug from it's speaker jack. Take some 400 grit sandpaper and gently clean the plug surfaces and then wipe it down with rubbing alcohol. Let it air dry for 15 minutes. If you have a couple Q-TIPs available in your bathroom cabinet, twist the cotton end with your fingers as tight as you can make it, with it dry. Soak the compressed cotton tip in rubbing alcohol and carefully clean the surfaces inside both of the speaker feed jacks. Look at the cotton Q-Tip ends to see if you are removing any dust or residue. If so, clean inside the jacks again with new Q-TIPs and do this until the cotton tips come out clean. Any crud built up in the jacks or on the speaker plug can introduce 'resistance' into the speaker circuit. Let that air dry as well for 15 minutes. Plug the speaker feed plug back into one of the jacks and plug the amp back into a wall outlet BUT do not turn it on yet.

Secondly, a good starting point for the right hand MASTER Volume control would be at the 12 o'clock position. The left hand Input Volume control can start at the 9 o'clock position and make sure that if you are using PASSIVE pickups on your guitar, that the -6 db push button is in the OUT position. The Horn control on the center of the back panel can start at 9 o'clock. Set the front panel Compressor Ratio control to full CCW. The Room Balance control also at full CCW. The Contour control set to full CW. Bass control at full CW. The four Low Mid and High Mid frequency and level controls all set to 12 o'clock. Treble control at full CW. The FX blend and Line Level controls at full CCW. The Pre-Post and Ground Lift push buttons should be in the Out position.

Try these settings initially to test. Connect your guitar to the front panel input jack, turn on the amp and use the volume control on your guitar for a pleasant level initially for TESTING. Run it through it's paces that way and let us know how things turn out.

Once you have tested this way and if things work well, experiment a little one step at a time. Write down your settings and what the outcome was at each step so you know what works for you and what doesn't. That set of paper notes that you write down can also help you to do setups at gigs and save you a bunch of time.

Keep us posted.


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Post subject: Re: fender Bassman 250/210 Problem
Posted: Sun Apr 22, 2012 3:24 pm
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Joined: Wed Apr 18, 2012 12:50 pm
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Thanks everyone! I haven't had a chance to look at the amps, it's exam season for me, but I'll be looking at it on a week or so. I'll keep you posted.


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