ryema22 Posted June 11, 2007 Report Share Posted June 11, 2007 I've done some googling but I can't seem to find what I have in mind. I have a Blues Junior amp. I love it, but one of the shortcomings is that it only has a single 8 Ohm speaker output. I'd like to know if there are any available schematics for an impedance selector? Ideally I'd like to put something in a seperate box (rather than modding the amp's board) and mount it to the bottom of the cabinet next to the reverb tank. Headphone output would be awesome too. Does anything like this exist? Quote Link to comment Share on other sites More sharing options...
mikhailgtrski Posted June 11, 2007 Report Share Posted June 11, 2007 I believe you'd have to replace the output transformer with one that has multiple secondary taps. Unless the Blues Jr. OT already has them and Fender decided to just cap them off. A headphone out could be tapped off the speaker output jack - a resistor feeding a potentiometer, wired to a jack. Quote Link to comment Share on other sites More sharing options...
ryema22 Posted June 12, 2007 Author Report Share Posted June 12, 2007 Thanks for the response. I'm in no way qualified to replace the output transformer on a tube amp but I might try the headphone output. Quote Link to comment Share on other sites More sharing options...
Geo Posted June 12, 2007 Report Share Posted June 12, 2007 I believe you'd have to replace the output transformer with one that has multiple secondary taps. Unless the Blues Jr. OT already has them and Fender decided to just cap them off. A headphone out could be tapped off the speaker output jack - a resistor feeding a potentiometer, wired to a jack. Correct. You could probably get a replacement output transformer for $50 for that amp. FYI, most tube amps can handle a "wrong load" 100% in either direction--i.e., your amp should be okay with a 4ohm load or a 16ohm load (but not 2ohm or 32ohm). E.g., I have a 3w amp that should run 4ohm, but I use it with an 8ohm speaker. Also, I believe that impedance changes with frequency, so an exact match isn't important. If you use a different load, you'll probably get slightly less power output and maybe slightly different tone (not sure). With the headphone output, I don't think it's that simple. You want to wire in something that switches the speaker OFF and switches on a resistance in place of the speaker (something like a 10 ohm 20w resistor). The amp's power section needs to see some kind of load similar to what it's designed to see. With that set up, I think you could then do the pot and headphone jack. Quote Link to comment Share on other sites More sharing options...
mikhailgtrski Posted June 12, 2007 Report Share Posted June 12, 2007 With the headphone output, I don't think it's that simple. You want to wire in something that switches the speaker OFF and switches on a resistance in place of the speaker (something like a 10 ohm 20w resistor). The amp's power section needs to see some kind of load similar to what it's designed to see. With that set up, I think you could then do the pot and headphone jack. Good call - I was thinking of a line out. If you want to silence the amp while using headphones, yes, you'd need a switching jack and a resistor load in there someplace. Quote Link to comment Share on other sites More sharing options...
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