Preamp Deal of the Century

Crackling sound from speaker due to 6SN7 tubes. Overall the sound of my Chardonnay(60hrs)is very nice except for the occational crackling sound I hear on the speaker. I have narrowed down the problem to the 6SN7 tubes.

With the stock EH 6SN7 tubes the crackling is constant even when swoping the tubes. The crackling follows the tube

With a pair of 6SN7 Mullards the sound is distincly better but the occational crackle does still exsist.

The crackle at any given time occurs only on one speaker
Also, when I tap the amp chassis with my finger(not the power section) I hear the tap (amplified)from the speaker...is this a grounding issue?
Your input is much appreciated.

Tapping the amp and hearing it in the speakers is a microphonics issue. How hard are you tapping? Don't know about the crackling, but I did have a problem with the power umbilical. When you move tubes around, you could be jiggling it. Make sure it is secure and fully in place, and then try moving it around to see if it makes the crackle.

Swampwalker thanks. Just a light tap nothing serious. I have been very careful with the insertion and removal of the tubes and making double sure everything is the way it should be.

Did your umbical effect the sound quality also do you play the pre with gain swith (just behind the 6SN7 tubes) in the on or of position?

I have mine set to of.

Jay- Mine Syrah does not have a gain switch. It was custom-configured with a mono-stereo blend switch. The umbilical can affect sound quality if it picks up some emi or rf noise, but what I was thinking of was in intermittent short/open connection. There are multiple very small solder joints at each end of the connector, all of which are vulnerable due to cord movement. BTW light tap on chassis audible does indicate a microphonic tube, as well.

Jay461 - As swampwalker said you are having problems with tube microphonics. By their nature all tubes are microphonic to some degree. Some more so than others. There are a lot of things to do. You should replace the tubes till you get a more acceptable pair. You can try isolating your preamp. I use a combination of brightstar airmass and symposium rollerblocks and hal-o tube dampers. There are many other isolation products out there also. Some use small innertubes from children's bikes. Under-inflated works better than fully-inflated. Considering the prices of some of these you should probably try the innertubes first to see if it helps. You also might want to consider the placement of you system rack relative to your speakers.