Weird crackling from speakers when preamp connected

Do you have a spare set of tubes for the preamp? Swap those in. 

I assume it is both channels. If only one then swapping tubes between channels would help verify. 

I've swapped tubes & confirmed they're good.

Sorry, that sucks.  What maintenance did you have done?  The times I’ve heard something like that was from dirty connections between components and interconnects, so if you haven’t I’d try cleaning those connections especially on the VTL with Deoxit or something similar if you haven’t already.  Pray you don’t need repairs from VTL because their reputation for service, especially if you bought used, is awful.  Best of luck in finding a solution. 

I had it looked at by a professional, they ran tests & checked the tubes, no issues when they had it hooked up and couldn't reproduce the issue. I haven't tried to clean the terminals, but may give that a shot.

That has got to be frustrating. 

Perhaps it needs to go off to VTL.

I remember giving a tape deck to a professional electronics repair a long time ago and having it never sound good again. They can be good for replacing and capacitor or resister... but sometimes not for nuanced stuff. VTL, shoud  have an engineer that knows were something like that can happen and find and fix it. Hopefully 

I’d be going back to that service guy and politely ask WTF???  It was working before he got it and doesn’t work fine when you got it back.  Pretty damn simple math there, and I’d be right pissed off if I was you. 

+1 @soix 

I would contact VTL and also try to talk to the person that actually worked on your preamp. 

If there were new parts involved, perhaps find out if the replacement parts were the same specifications, the same manufacturer and that they were new.

The service person and I talked extensively about the preamp, he ran tests on the device, tested tubes, no parts were replaced. They also hooked it up to a system and couldn't reproduce the issue.

Again it doesn't happen when I run my DAC directly to the amp, only when the pre is in the chain.

Are you using the RCA terminals on the Vega and the 275? (Just to confirm you are checking the same inputs and the XLR isn't bypassing an RCA input connection problem at the amp).

Crackling can be a bad connection on the RCA ground. But if the problem only occurs after warm up the first thing I check is the soldering at the tube pins. Then I check the volume pot, and the plate and cathode resistors by putting pressure on them with a chop stick. Things move when heated and a bad solder joint can lose contact, especially if the volume pot and sockets are circuit board mounted. If I was looking at it and could not reproduce the problem I would at least reflow all those solder joints.

This could be a factory lemon or it was dropped in transit. Ask the tech to take another (careful) look.

@gs5556 I’m using only RCA connections and not XLR. I’ll try your suggestions and have them look again. 

How old is the MC275?  I had a similar issue with a pair of Ohm speakers and a Sansui receiver that a qualified technician could not replicate in his shop.  Turned out to be the receiver.  It was 30+ years old and needed to be recapped.

failing capacitors (electrolytic) or tubes 

If tubes you could have a bad tube or needs to be reseated in the preamp 

if SS check all your connections with it completely Off reinstall all cables to make sure everything is in place , and check all wires going to the preamp as well as going to the Amplifier.

Sir,

Is the Vega DAC an S1?

If S1 does it have the Purer Power supply?

If no, to either or both disregard this post.

If yes to both, post and I can provide the work around.

@shxmd

The DAC isn't an S1, nor does it have the Purer PS, that said what would be the workaround, I'm willing to give it a shot.

Is there any pattern to the crackling sound, or rather does it appear kind of random / intermittent?

@maddog66blue OP - I had a similar issue with a tube preamp;  I was getting intermittent static noise in one of the channels. It turned out to be a bad capacitor. The technician discovered the problem by nudging the capacitor with a wooden chopstick while the preamp was on.

@classic8 I'll take your suggestion. I'm surprised they didn't find anything wrong with it, but it's like taking your car to the mechanic.

I sent the preamp to the manufacturer and he couldn’t figure it out (he retouched some solder joints, replaced a few resistors, and declared victory); luckily the local technician did.

@OP Assuming the VTL has a non-captive mains, try a different mains cable. Also, try plugging into a different mains socket.

Check if any new source of RF could be present since you sent the pre for service.

Those are long shots as crackling is almost always a bad joint, cap or tube - but they are worth a shot on the basis of ruling things out.

I remember Davy O’Brian telling me that at  McIntosh they cleaned contacts until they got tired of cleaning them. Then they used sealed rotary switches. Then then had to drill holes in sealed rotary switches to clean the contacts. I have a similar problem on my c28 preamp. I turn the rotary switches all the way in one direction and then all the way in the other 4-5 times. My problem may not be your problem but it is cheap and easy. 🙄🖖

https://forum.audiogon.com/discussions/crackle-from-tube-preamp?highlight=speaker%2Bcrackling%2Bbad%2Bpreamp%2Bcapacitor