Potato Cakes
Well-known member
Hello, everyone,
In a previous thread I mentioned that I finished building a Vibro Champ and had the joy of troubleshooting what was a bad output transformer. Now it's done and it sounds really great. It does have a couple of small things that make my OCD flare up. One is the foot switch sometimes pop. It's infrequent, but does occasionally happen when disengaging the tremolo. I've gone through all of the things one might do to fix a switch that pops and even found a thread on another forum where the guy said he got it to completely go away by soldering the ground side of the switch to the chassis of the switch and then add a 47k resistor to the tremolo switch and heatsink it so it stays together. That part didn't make too much sense to me but I think this pertains to a two channel foot switch. (The ultimate Fender style footswitch - The Amp Garage). There is kind of an explanation at the bottom of the thread but it also didn't make too much sense what was the purpose of the 47k resistor. I don't know of another way to bleed DC to ground without altering the function of the tremolo itself unless I can strap something like a 1n4004 across the contacts. Not a big deal but a mystery to me nonetheless and I don't like mysteries.
The other thing is that there is a slight amount of distortion when using the tremolo. At the height of the amplitude wave there is audible breakup. Nothing too crazy but enough to want to investigate the cause. I tried pulling the cathode bypass cap on V2 of the tremolo circuit thinking the gain on that tube needed to be brought down but it did not fix the issue. I even tried different speakers as I saw that solved a similar distortion issue for someone else. It just sounds like the second gain stage of V1 is breaking up because the tremolo is hitting it with too much signal at the peaks. This happens even at lower intensity levels. I also tried turning down the bass to see if minimizing the low frequencies would help but it was to no effect. I did go through a fun tube swapping exercise for both of the 12AX7s.
This may but just the way the circuit is. I have a friend who as a Vibro Champ reissue (solid state rectifier and possible tremolo section as well) and his amp does not have this break up characteristic so he even noticed the slight break up on the tremolo of the amp I built. This may just be normal for an amp built with the original circuit, but I can't stop thinking that there must be a way to fix this without completely changing the schematic.
Thanks!
Paul
In a previous thread I mentioned that I finished building a Vibro Champ and had the joy of troubleshooting what was a bad output transformer. Now it's done and it sounds really great. It does have a couple of small things that make my OCD flare up. One is the foot switch sometimes pop. It's infrequent, but does occasionally happen when disengaging the tremolo. I've gone through all of the things one might do to fix a switch that pops and even found a thread on another forum where the guy said he got it to completely go away by soldering the ground side of the switch to the chassis of the switch and then add a 47k resistor to the tremolo switch and heatsink it so it stays together. That part didn't make too much sense to me but I think this pertains to a two channel foot switch. (The ultimate Fender style footswitch - The Amp Garage). There is kind of an explanation at the bottom of the thread but it also didn't make too much sense what was the purpose of the 47k resistor. I don't know of another way to bleed DC to ground without altering the function of the tremolo itself unless I can strap something like a 1n4004 across the contacts. Not a big deal but a mystery to me nonetheless and I don't like mysteries.
The other thing is that there is a slight amount of distortion when using the tremolo. At the height of the amplitude wave there is audible breakup. Nothing too crazy but enough to want to investigate the cause. I tried pulling the cathode bypass cap on V2 of the tremolo circuit thinking the gain on that tube needed to be brought down but it did not fix the issue. I even tried different speakers as I saw that solved a similar distortion issue for someone else. It just sounds like the second gain stage of V1 is breaking up because the tremolo is hitting it with too much signal at the peaks. This happens even at lower intensity levels. I also tried turning down the bass to see if minimizing the low frequencies would help but it was to no effect. I did go through a fun tube swapping exercise for both of the 12AX7s.
This may but just the way the circuit is. I have a friend who as a Vibro Champ reissue (solid state rectifier and possible tremolo section as well) and his amp does not have this break up characteristic so he even noticed the slight break up on the tremolo of the amp I built. This may just be normal for an amp built with the original circuit, but I can't stop thinking that there must be a way to fix this without completely changing the schematic.
Thanks!
Paul
