Using my amp's loop sounds like crap; Tube or tech problem?

[p4vl]

I've got an Ampeg VL503 (supposedly even Lee Jackson didn't want to put loops in the VL series). Whenever I turn on the Loop, the tone becomes much 'weaker'. If I press the 'bypass loop' button, the tone is much thicker and aggressive.

This amp's loop a +4/-10 switch (no send/return knobs) and the tone is unquestionably strongest when the loop is bypassed.

Some of my cables are old but I don't use anything over 3ft. (and 6" Dimarzio jumpers) so it's not an issue with 20ft cables that people run into.

The v8 slot in the preamp is for the loop. I've tried a Sino 12at7, chinese 12ax7. It doesn't seem to make much difference.

I'm not a guy that relies on effects at all but I just spent $100 on a really nice Phaser and I love my MXR 10-band EQ and the pedals themselves sound better through the loop, even though my tone with the loop on is crap (kind of a Pyrrhic victory).

Any of youse know what the hell I could do about this?

 

[cardinal]

Maybe try cleaning the sockets with something like deoxit? If you just run a patch cable between send and return, is it still bad? Any difference between pedal and line level?

Some loops just suck, unfortunately.

 

[p4vl]

Maybe try cleaning the sockets with something like deoxit? If you just run a patch cable between send and return, is it still bad? Any difference between pedal and line level?

I ran a 6" patch cable through the loop, still just not acceptable. I have some compressed air but that didn't do anything.

Would something like the ISP Decimator G string work as like an alternative loop?

 

[glpg80]

The schematic shows the amplifier's tube for handling buffering of the loop return is V8, not V7.

Make sure V4 is a 12AU7 or 12AT7 and make sure it's also balanced. It's a cathode follower long tail pair design for more gain to drive the tonestack. I'd make sure V8 is a 12AX7 of some variety, but a tube of higher quality as it's feeding the PI stages.

Technically speaking the effects loop return does not feed directly into V8, the effects loop impedance buffering is actually completely solid-state for send and return both before it even touches V8.

I'd consider checking those tubes first. Another thing that can possibly be done is upgrading the opamps that are used for the effects loop. I've seen similar op-amps used in laney amplifiers in the past and there are better more efficient ones out there that are hot-swappable for better performance.

 

[p4vl]

The schematic shows the amplifier's tube for handling buffering of the loop return is V8, not V7.

Make sure V4 is a 12AU7 or 12AT7 and make sure it's also balanced. It's a cathode follower long tail pair design for more gain to drive the tonestack. I'd make sure V8 is a 12AX7 of some variety, but a tube of higher quality as it's feeding the PI stages.

I said V8, not V7. V4 (and V3) are for the 3rd channel. Those slots are for high gain and really high gain tubes, if I can afford them. The purpose of buying this amp was to get something like a modded JCM800 thrash/death/black metal tone with an adjustable bias that would allow me to use 6550's (also it was $400).

I find I'm having to use hotter pickups in addition to a OD pedal to get the tone I want from the 3rd channel (then again, I'm used to my XXX which has a idiotic amount of gain, so I think I should look). I'll give it a shot but unless using an AU7 or AT7 in V4 is a miracle cure. I'm used to amps where I can get by with simply filling the preamp slots with JJ 12ax7's, so this is new to me.

I'd consider checking those tubes first. Another thing that can possibly be done is upgrading the opamps that are used for the effects loop. I've seen similar op-amps used in laney amplifiers in the past and there are better more efficient ones out there that are hot-swappable for better performance.

Any idea where I might find these opamps? I know I could sift through Mouser Electronics until I go blind, but are there any sites that offer opamps specifically for amps/loop-related purposes?

Oh and thanks for your post.

 

[neoclassical]

Some loops do suck, but I would have a tech take a look at what glpg80 said. There are also some molex connector and overheating issues with those amps at least in the head form IIRC.

 

[cwhitey2]

...

Some loops just suck, unfortunately.

Nailed it.


You can probably get the loop modded though