[kingdeezie]

I have a VAC Ren Mk3, that I am currently having some issues with. I have heard that sending the unit back to VAC can be a long process, since they are such a small crew. I also purchased it used, so its not covered by any sort of warranty.

Out of one of the channels, there is an intermittent "crackling" noise. It comes in spurts. It is independent of the volume control.

At first I thought it was bad tubes, so I purchased an entire new set, and the problem remained.

Then I thought it might be oxidized tube sockets, so I purchased some Deoxit, and sprayed it on an old tube. I inserted and removed the tube 6-7 times per socket, reapplying the Deoxit each socket.

I let the Deoxit air dry for an hour, reinserted the new tubes, and it seemed to get better. The next day however, the sound was back.

So, then I thought that maybe I had gotten unlucky with two sets of bad tubes. So I swapped the tube sides, and the sound remained in the same channel.

So then I thought it might be the cables, or amp, so I swapped cables and amps, and the sound remained on the same side of the preamp.

I tried both sets of outputs on the preamp, and the sound remained unchanged.

So, at this point, I am 100 percent sure that its the preamp, but I am unsure of what could be the problem. The sound is not different out of the channel, nor is the output level. I tried moving the tubes around with the sound playing, thinking it might be a tube socket or something, but noticed no change.

It just crackles. At best its just annoying, but at worst, I am unsure if it could be something catastrophic.

Anyone ever experience something similar?



 

[sfox7076]

Does it happen on all sources? 

[kingdeezie]

Does it happen on all sources?

Yes.

[sfox7076]

I would swap the cables on the amp to see if the other speaker does it after that swap.  That will rule out the speakers.  Seems odd, but could be a bad capacitor.  When you switched tubes did any appear to be bulging?

Shawn

[kingdeezie]

I would swap the cables on the amp to see if the other speaker does it after that swap.  That will rule out the speakers.  Seems odd, but could be a bad capacitor.  When you switched tubes did any appear to be bulging?

Shawn

I already tried this. I swapped around the cables and channels. Its definitely isolated to the same side on the preamp.

I didn't see any caps bulging. The preamp is only three years old, seems unlikely a cap would go bad that quick.

Could it be a resistor or something?

[BobM]

I would bet you have a bad solder join somewhere, maybe to a ground plane. Hard to find unless it is obvious.

[G Georgopoulos]

sounds like a bad joint,,,

[sfox7076]

I would concur with a bad solder joint, but IMHO, that would have shown up in the intervening 3 years.  Just my thought.  Could be a resistor, but in my experience, the resistors last for years and caps are usually more suspect unless it is a resistor directly connected to the tubes and the tube has redplated. Once the resistor is cooked, it's cooked.  It would be odd in a preamp to lose a tube to redplating, but it could happen I guess.  I don't know what the inside looks like, but you can test resistors in circuit (unless they are paralleled with others), so you might want to do that.  It will be a PITA without a schematic.  Is there a warranty?  Any fix you do will void it. 

[kingdeezie]

I did have a set of tubes go bad, but they just stopped working one day when I turned the preamp on.

This was also a few months ago, and everything was working fine after that time.

This just started getting progressively worse and worse out of no where.

[Hugh]

Are all the tubes you used within VAC specs?

We recently got something akin to your situation with somebody's Melody M845 and it turned out they used 845C tubes instead of 845Bs.
We opened it up and found the capacitor leading to the 845 tube on the verge of opened up (swollen).

In your case, it might be just a resistor (as the least), a capacitor (as the next serious), or the power supply is going out (as the worst case scenario).
I think it's best you try to contact VAC to get it fixed.

Good luck.

Hugh

I did have a set of tubes go bad, but they just stopped working one day when I turned the preamp on.

This was also a few months ago, and everything was working fine after that time.

This just started getting progressively worse and worse out of no where.

[kingdeezie]

Are all the tubes you used within VAC specs?

We recently got something akin to your situation with somebody's Melody M845 and it turned out they used 845C tubes instead of 845Bs.
We opened it up and found the capacitor leading to the 845 tube on the verge of opened up (swollen).

In your case, it might be just a resistor (as the least), a capacitor (as the next serious), or the power supply is going out (as the worst case scenario).
I think it's best you try to contact VAC to get it fixed.

Good luck.

Hugh

I called VAC when I got the unit. They said any tube that was a 12AU7 and 12AX7 ( in their respective positions) was acceptable. They said the unit wasn't picky.

I've heard horror stories of VAC taking 6-12 months to repair equipment. I was hoping to avoid that. Guess I'll have to find someone local.

[sfox7076]

Where are you?

[kingdeezie]

Where are you?

PM sent.

[Hugh]

Then it might be something else.

I called VAC when I got the unit. They said any tube that was a 12AU7 and 12AX7 ( in their respective positions) was acceptable. They said the unit wasn't picky.

I've heard horror stories of VAC taking 6-12 months to repair equipment. I was hoping to avoid that. Guess I'll have to find someone local.

[G Georgopoulos]

point to point wiring is notorious of bad joints if used with solder alone...

[DaveC113]

This recently happened to me and it was a tube, but the problem was intermittent... I'd tap on the tube and the crackle would go away for a while. No doubt other things could cause a similar problem... if you have a schematic I'd start measuring voltages, even without one you can get a tube pinout and make sure it's operating to spec. Beyond that, or finding a bad part or solder joint through inspection you'd need to follow the signal through with an o-scope and find where the noise is being introduced.

[Steve]

I have a VAC Ren Mk3, that I am currently having some issues with. I have heard that sending the unit back to VAC can be a long process, since they are such a small crew. I also purchased it used, so its not covered by any sort of warranty.

Out of one of the channels, there is an intermittent "crackling" noise. It comes in spurts. It is independent of the volume control.

At first I thought it was bad tubes, so I purchased an entire new set, and the problem remained.

Then I thought it might be oxidized tube sockets, so I purchased some Deoxit, and sprayed it on an old tube. I inserted and removed the tube 6-7 times per socket, reapplying the Deoxit each socket.

I let the Deoxit air dry for an hour, reinserted the new tubes, and it seemed to get better. The next day however, the sound was back.

So, then I thought that maybe I had gotten unlucky with two sets of bad tubes. So I swapped the tube sides, and the sound remained in the same channel.

So then I thought it might be the cables, or amp, so I swapped cables and amps, and the sound remained on the same side of the preamp.

I tried both sets of outputs on the preamp, and the sound remained unchanged.

So, at this point, I am 100 percent sure that its the preamp, but I am unsure of what could be the problem. The sound is not different out of the channel, nor is the output level. I tried moving the tubes around with the sound playing, thinking it might be a tube socket or something, but noticed no change.

It just crackles. At best its just annoying, but at worst, I am unsure if it could be something catastrophic.

Anyone ever experience something similar?

Hi King,

Most likely one of two problems, after the volume control.

1) Noisy resistor. Have preamplifier on, and spray cool individual resistors until the crackling stops or gets worse. Be careful you do not shock yourself.
One can purchase cooling spray from R Shack or Parts Express.

2) What is often called a cold solder joint.

My first bet is a noisy resistor, but hopefully just a cold solder connection.

Cheers
Steve