dwell USA Aug 31st, 2001 10:55 PM Edit Profile Noticed a lot of you guys have hum and/or hiss with your reverbs. Here's what I found: Mine came from the factory humming, and I discovered that the reverb send and return wires were reversed on mine. I switched the red and black plugs on the reverb tank, and the problem went away. Hope this works for others. Please post if it does. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * rholloman Sep 1st, 2001 12:03 AM Edit Profile I found a "fix" for the reverb problem, but it involves changing several resistors and capacitors in the reverb circuit. It also gives the amp more reverb than my DRRI. That's 'more' - not the same. The DRRI's longer delay still sounds richer, but I don't know how to change the delay of the BJr pan - yet. Anyway ... If anyone is interested, here is a list of the changes to the Blues Junior reverb circuit that helped mine; C20 = 820pf R43 = jumper R44 = 1meg ohm R47 = 100K ohm C22 = remove R49 = 2.7K ohm R50 = 220K ohm C24 = 47pf C12 = .47uF C26 = remove R56 = 270K ohm R51 = 240pf cap across the pot to ground It works for me!! Oh ... also, after quieting the reverb down, I found and "fixed" a very slight hiss in the preamp (and made a few minor tweaks to the tone - more useable bass) Changes to preamp; R7 (volume pot) = 1000pf cap across pot to ground R6 = 50K ohm C25 = 330pf (treble cap) C11 = .1uF (bass cap) C16 = .0033uF R40 = 220K ohm The only other changes I found, that helped (tried many) were in the feedback and presence; R27 = 42k ohm R26 = remove resister and wire in a 25k ohm pot for presence control. I mounted the pot beside the jack for the "FAT" footswitch up under the back cover. Tubes; #10 Groove Tube EL84s & 12AX7LPS preamp Speaker; stock Eminence (very well broken in) I've played the amp every day for over a month with all these changes and everything is still working great! Maybe this will help someone else. Hope so. This message was last edited by rholloman at 07:38 AM, Sep 1st, 2001) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * hatton3 USA Sep 2nd, 2001 07:29 PM Edit Profile I switched the wires on mine as above, and the hum went completely away. This needs to be tagged for the archives. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * dwell USA Sep 2nd, 2001 07:53 PM Edit Profile Great! Hopefully this will solve much heartache. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * electro-cute USA/North Texas Sep 2nd, 2001 10:16 PM Edit Profile Yep, had the same problem and fix as Dwell...works well now with little noise. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Chuck Eads CT Posse,MBJ,TRRI,LS Sep 3rd, 2001 06:56 PM Edit Profile OK guys, I'm very curious about this. When looking in from the back, my black connection is on the right and the red is on the left. Is that the way your's were before you switched them? Thanks, ce * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * dwell USA Sep 4th, 2001 01:09 AM Edit Profile No, they were the other way around. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * lew USA Sep 4th, 2001 11:17 AM Edit Profile rholloman- I like your thinking. I've changed out the TL072 opamp for a 4560 which has better current drive capability, since the reverb pan is being current driven! Also, be careful that you are not violating the common mode input range of the opamp since you've dramatically increased the signal level there. It might sound bad! A pair of diodes (opposite polarity) across the input pins could help. Sorry non-techie folks! Another tone suggestion: Swap the 250k Treble and Bass pots. Make the Bass 250k10A and Treble 250kB. With a 10A taper on the treble, the amp is very dark until knob gets above 9 or so and the amp begins to open up. Changing to B taper is more like traditional Fender tone stacks. Good luck! * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * electro-cute USA/North Texas Sep 4th, 2001 06:13 PM Edit Profile Lew, can you give me more info on your chip change? I am assuming you have a solid state amp since you are talking TL072, correct? What did it do for the tone, hiss, hum..etc? Please email your answer unless you just want to post here. Gary * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * reedbuster usa Sep 4th, 2001 09:41 PM Edit Profile Mine aren't reversed and the hum just comes and goes at will. I'm quite sure it has something to do with roll off voltage in what Rholloman has so eloquently explained above. Just today as I was finishing building my new airtight PVC crystal element mic with harp slot for maximum airtight one-handed wailing (had to mention it because it's never been done before) anyway, as I was sitting right next to the amp, testing different sounds setting the reverb from 0-12 numerous times I finally stopped it at 4 and was tinkering with a potentiometer for several minutes with no mic plugged in, it started to hum right out of the blue. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * [end of file]