I changed the rca speaker jack on my Bronco (Vibro Champ) to a 1/4" jack so I could plug it into my 2x12 and for some reason when I plug it into a different speaker cabinet it causes squealing. It works totally fine with the internal speaker but screams like a banshee plugged into something else. Any ideas what could be causing this?
Vibro Champ external cab mystery squeal
- Thread starter Cvoxdog
- Start date
Guardians of the analog
Well-known member
What's the impedance on the 2x12. In stock form the champ wants to see 4 ohms. I'm not sure what you're 2x12 has in it and how it's wired up. That would be where I start. Got a pic of the output jack wired in the champ chassis?
chris.knudson
Well-known member
Check the impedance of the speakers. Also, are you using a 1/4" speaker cable or a 1/4" instrument cable?
chris.knudson
Well-known member
Are you disconnecting your internal speaker when you plug in to that jack? If you are running 4 ohms on the internal speaker and 4 ohms on the external speaker simultaneously (in parallel) the amp is only seeing 2 ohms of impedance. My recommendation would be to replace that 1/4" mono jack with a 1/4" stereo jack and have the connection to the internal speaker be broken when you insert the speaker cable.
It's just one shared speaker output jack so I unplugged the main speaker and plugged the cab direct to the that same jack. It's weird but I'm sure I'll figure it out eventually. I've been going back and forth with doing mods on this thing. I found that it either sounds good clean at low volume but crappy at higher volumes or crappy at low volume but better turned up. As I was taking out the 2nd input jack to put in a raw knob my soldering iron broke so I have to wait for a new one before I mess around some more.
Problem solved. I had to flip the secondary wires from the output transformer and now I can plug into other cabs with no issues. What boggles my mind is that it never squealed with the internal speaker so I figured everything was fine. Apparently it's been injecting positive feedback instead of negative feedback this whole time. Now it sounds completely different too.
