HELP: Signal dropping on Ampeg SVT 3 Pro and EBMM Stingray

[the baint]

Occasionally over the past year, while playing my Stingray through my Ampeg SVT 3 Pro and 210HE, my signal has dropped quickly (sort of like turning down the volume on the bass quickly, but not instantly), and then when it comes back (I can't establish why it comes back, I shake cables, turn pots, etc… it sounds sort of scratchy or low-fi until it finally returns to full strength and fidelity.

This happens every once and a while - a few times a month maybe - so I have a hard time replicating it or even reducing the variables. Earlier in the year I thought it was the amp input jack, so I started using a light-weight patch cable from my tuner so it wouldn't have as much sag weight from a thick instrument cable going directly to it. Finally hoping to fix the problem, I spent a chunk of change having an authorized tech open it up and resolder several cold solder joints that _could_ have been compromised.

However, a few weeks later the problem showed itself again.

I have also checked the battery of the bass, though I don't believe I've replaced it as it still read "good" on my analog battery tester.

Sometimes I have a 1 Spot powering a Boss TU2, and further sometimes the daisy chain will be powering a 3Leaf Doom and Line 6 DL4. There are uncovered and unused caps on this chain.

Also, I have put a short patch on the rear of the SVT 3 from the effects send/return as I had read somewhere that was a common issue (maybe a fuse?).

So, here I am. A bass that annoyingly sometimes cuts out, but without enough replication to figure out which variables aren't effecting it.

Does anyone have ideas? Have you experienced this? Thanks in advance!





(BTW, the tech guy is NOT close to my house, not cheep, and not the most confidence exuding, so I don't really want to drop off the amp again for weeks without hope my $ will actually solve the issue.)

 

[JimmyM]

Sounding like a tube to me, but it's hard to say without having it in front of me. If you have a known good tube of each kind, see if replacing each tube one at a time helps.

 

[the baint]

@JimmyM Thanks for the suggestion! Is that really similar to how tubes going bad present themselves? I've never had to change them before. Could I just purchase one of each type (2 kinds in this model, I think) and plug and play? I know I've heard about tube biasing, but don't have any experience in this stuff.

 

[beans-on-toast]

Yes, the tubes can cause that when they are nearing the end of their service life. Here are some symptoms of a failing tube.

Tubes | TalkBass.com

 

[the baint]

Would you guys suggest I get 1 tube of both types to diagnose, or that is a waste of time and I should just get an entire kit. I've had this amp 15 years and never replaced the tubes. I was thinking of going with the JJs from Tube Depot, mostly because I'm not sure what the differences are or why one would pay for more expensive ones.

Thoughts on the JJs or Tung-Sols?

 

[Wood and Wire]

Would you guys suggest I get 1 tube of both types to diagnose, or that is a waste of time and I should just get an entire kit. I've had this amp 15 years and never replaced the tubes. I was thinking of going with the JJs from Tube Depot, mostly because I'm not sure what the differences are or why one would pay for more expensive ones.

Thoughts on the JJs or Tung-Sols?

If you have another preamp, or a preamp pedal, plug that into the F/X loop return - if it still exhibits the problem, it's most likely the power tubes (or remotely possibly a dodgy connection between amp output, and loudspeaker).

If it no longer exhibits the problem in the above scenario, plug your bass into the amp, and go from the F/X loop send, into a different amp, or recording device - if the problem persists, it's most likely a preamp tube.


This assumes you've already torture tested your bass (and cables, pedals etc) with another amp / DI recording, and not encountered the problem.

 

[ihixulu]

Have you tried the bass through another amp? One possible cause may be that the battery on the bass is not seated snugly in the battery box so when you move the bass around it breaks the contact momentarily. Had that happen to me recently on my StingRay - I changed battery brands and the new one was slighty shorter. I bent the contacts back into place and the problem went away.

Just a thought.

 

[the baint]

@JimmyM I'm just now circling back to this, and am about to order a 12AX7 and 12AU7 for the power-amp section. Is there any reason to replace ALL of the tubes instead of the affected power tubes? Any reason to choose the Tung-Sol's over the JJs? Thanks in advance!

 

[JimmyM]

@JimmyM I'm just now circling back to this, and am about to order a 12AX7 and 12AU7 for the power-amp section. Is there any reason to replace ALL of the tubes instead of the affected power tubes? Any reason to choose the Tung-Sol's over the JJs? Thanks in advance!

I never replace any tubes but the broken ones, so no, no reason for replacing all of them unless you like spending money on things that aren't broken. And I'm not sure about for driver tubes, but the only reason I'd get a Tung Sol over the JJ is if I liked a really bright and trebly tube in V1. Which I don't. I have a Tung Sol and was surprised at how very bright it is. Too bright for my tastes in an Ampeg.

 

[the baint]

@JimmyM This is invaluable - thanks! I don't do "very bright" anything in my tone, so this is not only saving me some cash but helping me avoid a disappointing result. Kudos!

 

[BassmanPaul]

Put a brand spanking new battery into your bass to eliminate that as a cause.

 

[rickdog]

So many things it could be... but there are some easy things to check, especially if you have a spare 12AX7 handy.

This was a good suggestion:

If you have another preamp, or a preamp pedal, plug that into the F/X loop return - if it still exhibits the problem, it's most likely the power tubes (or remotely possibly a dodgy connection between amp output, and loudspeaker).

If it no longer exhibits the problem in the above scenario, plug your bass into the amp, and go from the F/X loop send, into a different amp, or recording device - if the problem persists, it's most likely a preamp tube.

Try simply reseating all of the tubes, there could simply be some slight corrosion on the pins. For best results, use a good contact cleaner like Deoxit when doing this. (If you don't have any, you should get some!)

Replace the 12AU7, and replace V1 with your new 12AX7. If the problem persists, put the old V1 in place of V2, and so on.

One more long shot: the Stingray is active, with a pretty hot output, right? A really hot signal applied to the input could drive the first gain stage in V1 (which is before the Gain control) into "blocking distortion", which could cause symptoms similar to what you described. Does the "Peak" light come on a lot even with the gain knob turned down? If so, try either turning down the volume knob on the bass, or engaging the input pad switch.

Good luck, the 3 Pro is a great amp when everything is working right!

 

[acostaa]

Pardon the necromancy, but I am experiencing similar volume drops with my svt-3. Did OP resolve his issue? and if so what was the culprit? There's five tubes in there, would like to be able to narrow it down some. Thanks,

 

[the baint]

@acostaa Thanks for reviving this. I bought a single tube from TubeDepot to replace the most likely culprit. Unfortunately I’m still having the drop outs, and have been meaning to go ahead and get the rest of the set.

Quarantine has actually been killing me with work from home and 4 kids and a puppy, etc, so I’m hardly a person with hobbies and dreams these days.

I’ll update here if that fixes things.

 

[the baint]

Alrighty, I'm taking delivery of the remaining tubes from TubeDepot today. I'll install them this weekend and report back if the problem persists or appears fixed.