Amp tone changing

[Dirthill]

Hello again Talkbass people! I am having a problem with my amp. I have a Fender Bassman Pro 1200 head. I don’t think this next part matters but I’m running it into 2 Eden cabs (4x10 & 2x15) at 8ohm each. The 2x15 is a newer addition to my rig. No issues before I got the 2x15. It might be a coincidence. So when I’m playing the tone suddenly drops off like I rolled back the tone knob all the way. After a minute or so it return's to normal then after a bit it does it again. Any suggestions would be greatly appreciated. Thanks.

 

[fdeck]

I know you say it's not the cabs, but the first step is ruling things out, since there could be problems anywhere in your signal chain: Bad connections in your bass, cabling, amp, and the new 2x15. For instance if one of the two drivers were kicking in and out. Trying different bass, cabling, and cab arrangements might be the start to diagnosing this. Sadly, once you isolate it to a specific piece, it might still require a trip to the tech.

 

[Dirthill]

Ok, makes sense. I’ll start with disconnecting the 2x15 and going from there. I’ll let you know what happens. Thanks.

 

[agedhorse]

On that amp, you might try bypassing the effects loop with a short 1/4" patch cord, this is an easy thing to do to rule out something that's common with amps of this era.

Like Francis says above, can you try it with one cabinet at at time to rule out a speaker cabinet as the root cause?

 

[Dirthill]

Sorry, I’m not familiar with bypassing the effects loop. Would I just use a patch cable in the send and return?

 

[agedhorse]

Sorry, I’m not familiar with bypassing the effects loop. Would I just use a patch cable in the send and return?

Yes

 

[Dirthill]

That being said I am running pedals in front of the amp.

 

[fdeck]

Did you step on one?

I'd get those out of there until the root cause is found.

 

[Chris_will_do]

Sounds like it's the effects loop. Try that first.

 

[agedhorse]

Sounds like it's the effects loop. Try that first.

It's a possibility, but far from the only possibility.

 

[Stylee Mousse]

Definitely pull your pedals. Any one of them or their cables could cause dropouts or tone changes.

 

[Dirthill]

Sounds like it's the effects loop. Try that first

 

[Dirthill]

Well, I bypassed the effect loop and so far so good. Why would the effect loop do that and does that mean there is a problem with it?

 

[fdeck]

You're on the path towards "differential diagnosis." Now you could try different arrangements of the FX loop, starting with just a jumper cable from send to return, and then adding one piece at a time.

It's annoying, but less annoying than paying a bench fee for diagnosing a perfectly good X when the problem is Y.

 

[agedhorse]

There is an internal switch inside the effects return jack that handles the bypass signal path. They can become intermittent but about 90% of the time just cycling a plug into the return jack will clear the fault for good.

 

[Dirthill]

Thank you for everyone’s help.

 

[vvvmmm]

I have that very problem (on of all things, a VT60) - plugging and unplugging the FX loop fixes it until next time.

 

[Dirthill]

Can I just leave the patch cable plugged into the effect loop? Maybe I’ll run a couple of pedals through it if that will prevent it from happening again.

 

[agedhorse]

Can I just leave the patch cable plugged into the effect loop? Maybe I’ll run a couple of pedals through it if that will prevent it from happening again.

Yes.