How much hum is acceptable for a Liverpool? I have completed my RJ Guitars Liverpool kit (very nice I might add) and have been playing it for a couple of weeks now. So far I have diddled with the preamp area wiring and have gotten rid of any high pitched squeally feedback sounds when all controls are maxed out and I am happy with the results. The 60 cycle hum on this thing is a little more than I would like to hear. Past the noon setting on the volume control the hum gets pretty noticable. I play pedal steel and use a Pod XT for effects (I can feel the Pod hate ). The hum and hiss really increase with the Pod as a preamp before the input jack. If I dial the output for the Pod to a low level the hum gets reduced but is still there. I have played the amp with just the guitar/cord/amp and still notice the hum. It's somewhat less with this setup but still annoying to me. I use the same setup with my Express and get an acceptable hum level to me. All these observations are at living room volume to give an idea of how the amps behave.
I have some pix of the Liverpool and would welcome any suggestions on how to reduce the hum. This Trainwreck thing is somewhat addictive I might add!
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I'll try to start this. 60Hz hum is rare. It's below the low E on your guitar. 120Hz is rectified and is in between A and B on the A string. There is a bit more hiss to these than some amps.
There are questions like:
1) any fluorescent lights? (turn 'em off)
2) any dimmers in the house?
3) do you have a metal plate covering the bottom of the chassis? (required)
4) single coils, humbuckers, or with no input connnected?
5) have you swapped tubes?
6) have you verified that all the el-84s are biased appropriately? (no lite redplating)
Grounding scheme
Signal path leads in relation to filament leads, 90 degrees is what you want
Did you elevate the filaments from ground?
How well are your power tubes matched?
How is your input grounded?
Try removing preamp tubes one at time to locate the source
Thanks guys for the info. I will use the info and get back to y'all. It never occurred to me to match the output tubes or worry about that. I have a quad of RFT's right now in the amp. I will try my Polem's, Reflektors and slum it with my JJ's next. Swapping preamp tubes with my Express didn't occur to me either. Time to fiddle and diddle now!
1. Power tube swap-no change
2. preamp tube swap- no change
3. I pulled the first preamp tube-hum 95% gone!
4. When I max out the treble the hum seems to reduce. Can't say for sure because the hiss level greatly increases and may mask the problem.
5. Mid and bass pots at zero-hum decreases slightly
6. Mid and bass pots maxed-hum greatly increases
7. The input is grounded at the chassis where it enters. I used a Swithcraft jack.
8. I have a ground buss bar going to a connection on the chassis a couple of inched away form the input jack. I didn't use the wire on the back of the pots for a ground buss like most people do.
Preamp section problem?
More chop-stickery needed?
Problem with C1 at the first preamp tube? (cathode capacitor)
Isolate the input jack and ground to my preamp buss?
Any opinions welcome!
Hey, I was checking out your pics and your comment on the ground buss being grounded to chassis on one end, it also appears to ground to chassis on the other end with the filter caps. This may produce a ground loop! try lifting the input end.
). The hum and hiss really increase with the Pod as a preamp before the input jack. If I dial the output for the Pod to a low level the hum gets reduced but is still there. I have played the amp with just the guitar/cord/amp and still notice the hum. It's somewhat less with this setup but still annoying to me. I use the same setup with my Express and get an acceptable hum level to me. All these observations are at living room volume to give an idea of how the amps behave.
