Guitar Gear Forum

I know this isn’t quite the place anymore for such things and generally I’m good about diagnosing issues. And I’m sure there’s not just a single reason this would happen, but it’s specific enough maybe someone has had it happen and had it fixed.

So my 6505. I’ve been in and out of that thing dozens of times. Lol. So it could be I MESSED it up, but I actually doubt it. Since the original reason I went in there was to track down a loud hum that was pretty bad. I found a bad filter cap. Replaced it, I’ve put a choke and replaced the OT. All that helped a bit but the hum was basically tracked down to one of these connecting ribbon cables. So I soldered that shit to the board and problem gone.

BUT, I have noticed I still get hum when ANY effect is turned on in the effects loop, and the more effects in the effect loop on, the more it hums! So 2 effects and it’s twice as loud. Clearly this feels like some sort of ground issue. And I do think there is sumthin off with the ground in this amp. But I would think the issue would persist even with the effects OFF, since the loop is still on. It’s just when I activate the pedals, the hum starts. Turn em off and it goes away.

Any ideas?

Does the hum go away if you touch anything? (metal part of cable end, metal part of fx unit, the amp chassis? etc.)

The 6505 schematic is a real fuck to read
Here: https://elektrotanya.com/peavey_6505_sc ... ad.html#dl

The loop is tube buffered (V3) and switchable. How does the loop behave with the loop switched out? Does it still get fucky with a patch cable jumping it? It uses switching jacks, which can get gunked up, so try contact cleaner. They aren't isolating jacks and should ground though the chassis though? Non-isolating jacks are a pain in the ass and there is good reason nobody uses them anymore

Last ditch is try a new tube in the loop position.

You can try to eliminate the possibility of grounding issues by using batteries on the pedals as a test. If the hum goes away with the batteries, it's ground related.

broslinger wrote: ↑Wed Aug 28, 2024 6:26 pm Does the hum go away if you touch anything? (metal part of cable end, metal part of fx unit, the amp chassis? etc.)

I have to specifically check this. But yeah I would say that DOES effect it. At least when using this Zuul gate which runs in the loop but has a “trigger” input taken from the input of the guitar. And that’s when I really noticed I have a problem. I thought for sure it was a ground loop cause it has a trigger taken from the “front” of the amp. But then I read this pedal has a problem and it was fixed later on. But for sure this amp had the worst issue. The hum with that pedal made it unusable. And I swear when I touched metal that got better but I need to specifically check that again cause I ditched the Zuul cause of this issue for now.

zozobra wrote: ↑Wed Aug 28, 2024 6:41 pm The 6505 schematic is a real fuck to read
Here: https://elektrotanya.com/peavey_6505_sc ... ad.html#dl

The loop is tube buffered (V3) and switchable. How does the loop behave with the loop switched out? Does it still get fucky with a patch cable jumping it? It uses switching jacks, which can get gunked up, so try contact cleaner. They aren't isolating jacks and should ground though the chassis though? Non-isolating jacks are a pain in the ass and there is good reason nobody uses them anymore

Last ditch is try a new tube in the loop position.

I want to say I ve tried numerous tubes. And I definitely cleaned em thoroughly. I’ll try the patch cable. Altho like I said with the pedals all hooked up there is no hum. Even when the loop is on. It’s literally when I kick the pedals on. Maybe I’ll make a quick vid. But I’ll look into some of this.

Guitarbilly wrote: ↑Wed Aug 28, 2024 7:35 pm You can try to eliminate the possibility of grounding issues by using batteries on the pedals as a test. If the hum goes away with the batteries, it's ground related.

I’ve tried it with batteries cause I was certain it was prolly coming from my pedal power supply since it powers shit thru the front AND the back. But I will just run guitar into amp and see if the loop changes. Hell i won’t even plug in my guitar and just turn the pedals on and off in the loop

Thanks dudes. I’ll report back tonight!!

Have you chosen a different gate? I would recommend the GupTech SUN. Similar function to the Zuul, but the key and through jacks are both built into the pedal. I find it to work better than the Zuul, and was half the price.

Yeah I ditched the Zuul from my board. These are other pedals having issues. In the end, Zuul works great on most of my amps but live I didn’t like it cause I have to have the loop always on, and I prefer to have my lead stuff in the loop so it’s all kicked on just by activating the loop on the foot switch . So I lost that with the Zuul on the board. If I want to use the Zuul for home and for recording it works fine. I remedied the ground loop by lifting the ground off the patch cable I used to trigger the input. The 6505 tho hummed badly still. What sucks is I finally have the amp that I always wanted it to be! Not long ago, cause I felt the mids were just too forward even when I totally was scooping it. So I put back in the 25k pot for the mid control and voila! Now I have em around noon! Can even do the 6-6-6 setting that I remember being able to do on the old 5150 heads. So I don’t believe the 25k did that alone but I think the mid pot I had put back in there was bad or simply wasn’t soldered In correct or sumthin. So it was like mids were running wild in that amp! Hah. Now it’s way more tonally what I like but this loop hum isn’t bad enough I couldn’t use it, but it’s definitely audible and it can come Thru my playing especially if I’m hanging on a high note, that hum will be heard. Luckily In Slayer shit I don’t hang on any solos and just go nuts and fucking whammy it up. So what’s a little hum gonna hurt. Lol.

I had to lift ground on a cable with the Zuul at some point, too. Maybe when I was using the Synergy stuff briefly. Interesting that the gate itself had a problem that they addressed. I didn't realize that.

I get that about the lead stuff in the loop. I don't play a ton of leads, so that was never really a thing I cared about.

It’s not even that I can’t hit 2 pedals to click on my lead volume boost and then my Delay. But I sue a pretty small board for this and the way the pedals are situated there are really close and my lead boost is actually situated different than the rest so I could get to the other pedals output jack and it was just difficult to consistently hit the pedals without hitting others or kicking the knobs. With a bigger board I’d prolly use a gate in the loop, but I prefer the littler board for live and it’s just easier to hit the foot switch loop

Yeah, makes sense.

I have recently started playing a few solos, and my solution is also a small pedalboard with only 3 pedals. Wireless/tuner, gate, and a Dispatch Master, which takes care of my delay and reverb. So I just hit the dispatch master, and it's on!! lol

There's always little particular reasons why we each have things set up the way we do, and it always seems to affect stuff like this.