Distortion issue - SVT 4 Pro

[Smite]

Hey All, new here and could use some of your knowledge on my head. I did a search and have found nothing with the same symptoms that I'm experiencing. If there is a thread and i missed it I do apologize:

SVT 4 PRO head with Ampeg 8x10e cab - Running Mono with XLR wired +1 +2 on head side. Plenty of power*

I run no affects, just plug in and go with a korg rack tuner running through the tuner out input.

Basses-
Warwick Standard Corvette 5 with passive pups/ active aguilar preamp.

Corvette Proline 4 active MEC.

I've had this rig for a year now, purchased used, and had it dialed in and sounding amazing. In the last month I've had a issues with faint noises and distortion coming through. It suddenly sounds "farty" and clippy, at times much like a blown speaker but not constant and not as bad. I removed the cloth grill and tried to locate the speaker(s) but it is faintly in all, and all the same. This leads me to think its a issue with the head.

I tried swapping out the preamp tubes with 12ax7s (new) my guitarist had on hand, the sound was the same.

I have tried running a cord in the return/send (mono) effects loop as I've heard dirt and grime can get in there causing unwanted noise. No change in sound.

One thing that I believe is new that I've noticed on my head (if you have a pro 4 and active bass maybe you can plug in and help me out here) is that the gain light flashes at all times no matter the level of gain. Gain on 0 and light flashes when picking with my active controls on, on my bass at full volume. If i turn down the bass/treble active controls it won't do this.

I believe this may be the cause of my unwanted distortion, but don't have enough knowledge about amps to know what this means, if anything (as i know that light functions more as a signal light rather than a clipping light).

It could be that I never noticed it before, but I doubt it as I set my gain to flash solidly when I accent riffs with heavy picking, then adjust my master volume for desired output.

The previous owner took the head into a tech complaining about low output levels. All voltages tested correctly and soldering points were sound, as i suspected he did not have the cable wired +1 +2.

Due to this I got a good price on the rig, but now I wonder if he may have done some damage to the head by not having the speaker cable wired properly.

Any input would be greatly appreciated. Or any trouble shooting tips I may have overlooked/failed to find.

This is the second time I've posted about this. I didn't recieve a reply last time, but I'm hoping I explained my situation better in this post.

Thanks,

Matt

[Jerrold Tiers]

have you got it set to mono? If not, it will do what you say, aside from the peak light....

The peak light flashing could indicate a problem in that circuit, which would also give an effect such as you describe.

A mute circuit issue can do it also

[Smite]

Thanks for the reply.

To see if the light flashes normally as i described i went to guitar center, brought my bass. I played through the same set up and sure enough it sound exactly the same as mine. I'm thinking my pups may just be to hot, or too close to the strings picking up my pick.


The mute button seems to function properly, I'm now wondering if its a problem with my bass. Swapped out my monster bass cables so I'll see if that could be the issue tomorrow.

I appreciate the help.

[joelb79]

Sounds like really hot pickups. Turn the gain down and turn up the master.

That is if a tube is not the culprit. If another head is working the same way I'd change your gain structure. Run the input gain lower and master lower, and push that graphic EQ volume slider past the middle point of +0db to higher or full. That usually helps with the clean volume (did on my SVT-3 Pro. I always ran that slider at max so my master was closer to 9 o'clock or noon. On the 3-Pro if you don't do that you will think the head has no power, but it has gobs and a different gain structure before the preamp.)