resonance/micro phonic sound when tapping on the unit

[Mike B]

The guy that built that thing is suspect.

I see an LED propped way up from the board right next to one that is flush.  I see lots of unclipped leads.  I see a lack of solder.  I see a resistor connection that was clipped too short.  I see transistors that are too low.

Yup, I suspect the age old assembly problems.

I can tell you that mine does not ring even if I tap the tubes let alone the plate or the base.

Good luck!

 

[xcoolhandx]

Everyone, chill.

If you are certain that it isn't a tube, then the next step is to turn the amp over in its base, carefully plug it in, turn it on and take a non conductive implement like a chopstick or plastic pen and tap the components near the area where you noticed the sound coming when you tapped the top. Listen over your headphones for the ringing, you may find a part that is loose and vibrating when you tap it, that is transmitted into your headphone cable or into a tube.

I did what you suggested with no avail ,can't find the source , still pulling to the left (hear more in the left channel)
EDIT; if you want I can take close-up pics of all the soldering ,I also noticed that one of the square PCBs (I think it's called LED and that's what the MikeB was referring ) is tilted-there is little to much solder on  one of the heatsink posts ,don't know if it's this would be the problem

 

[xcoolhandx]

I was going through the manual today just looking for my culprit ,here is the first thing that didn't look right quote from manual  ;
"Attach the 1/4” stripped end to terminal
13U. Thread the 1” stripped end
through terminal B5, then through
terminal B2. Solder 13L, solder B5"

comparison manual and my crack

 

[Paul Birkeland]

I will again say that this is most likely a microphonic 12AU7, have you tried a substitute?

In my opinion, the amp looks well built. 

In my experience, I haven't had microphonics in tube equipment come from anything but the tubes themselves. 

 

[xcoolhandx]

I will again say that this is most likely a microphonic 12AU7, have you tried a substitute?

In my opinion, the amp looks well built. 

In my experience, I haven't had microphonics in tube equipment come from anything but the tubes themselves.

I understand what you saying and wouldn't bother posting here ,I'm well aware of all the ins and outs of the valve tube in general ,..let me repeat my self again ..there is imbalance-> I can here more in the left channel then I can here in the right one (no matter what tube I use-TS 7236,5998,GEC 6AS7G,Haltron 6AS7G A1834  and for driver -new JJ ECC82,NOS 1952  Lansdale 12AU7 Black Plate,GE 12AU7 and two other tubes)  that was the main reason for me to investigate what was causing it  ,the tapping was just a tale tale of the right channel being noisy-lack off proper balance between both channels and an example of something not being right  that's why I mention it ,left channel is dead silent
I'm waiting for some 20 gauge wire and will disassemble this thing myself ..half blind ,will give some more slack for some wires especially around 9 pin socket and trim
excess leads

 

[Paul Birkeland]

Is the channel imbalance present regardless of volume control position?

 

[xcoolhandx]

no it's not ( I did read the FAQ ) ,sorry I edited my last post

 

[Paul Birkeland]

OK, if you have an imbalance at low volumes, you can pad the input of the Crack, or decrease the amount of signal coming out of your source.

 

[xcoolhandx]

NO I don't have imbalance at low volume just like I mention it in my last post
as for imbalance it's not a big difference but you can tell

 

[xcoolhandx]

there is at list two or three threads in the last two pages mentioning bad right channel ..co-incidents ? 

 

[Paul Birkeland]

The next thing to do would be to take voltage measurements. 

 

[Paul Birkeland]

thanks Jamie ,finally someone that actually trying to help ,yeah Crack seems to be very vulnerable to anything and everything ,just noticed very similar thread here with dead end as well
http://bottlehead.com/smf/index.php/topic,5806.0.html

right channel is barely audible

I'm not sure how this has a dead end?  There was an issue present in this thread that would show up on voltage checks (and probably resistance checks), and once the error was remedied, the amplifier performed to its specifications.

 

[xcoolhandx]

The next thing to do would be to take voltage measurements.

I have to look in manual since I'm not sure where you take the measurements,also

It took some time, but I found what was causing the buzzing noise in the right channel. I had previously swapped speedball boards left to right, but this had no effect. Eventually I noticed that the red wire coming from the pot was running right beside the heater wires toward the input tube. I rerouted the red (signal) wire to approach the socket terminal from another direction and this completely fixed the problem.

here is my 9 pin socket

 

[Doc B]

Did you change the output coupling capacitors?

 

[xcoolhandx]

yes I did but nothing changed


,here is the weird part ..when I have the unit on it's side everything is nice and even and no noise

 

[Doc B]

A change by laying the unit on its side would tend to indicate that gravity is changing the contact of something. The first thing that comes to mind is that the headphone plug might be making better contact inside the jack. That might be supported by your earlier mention of some kind of microphony when tapping near the jack. Perhaps the plug was overheated a bit and distorted a little when soldered.

 

[xcoolhandx]

I already ordered new phone and RCA jacks from this place
https://www.parts-express.com/ShoppingCart.aspx
and Blue velvet arrived today as well

EDIT; were there any socket complains in the past and what would be good socket replacement ?..just in case 

 

[Paul Birkeland]

EDIT; were there any socket complains in the past and what would be good socket replacement ?..just in case

Yes, we have had at least one customer remove a teflon upgrade socket because it was defective. 

 

[xcoolhandx]

little update on this issue..
impedance no more rerouted few wires ,swapped phone jack ,RCA jack and I'm back in the game (the tapping noise is almost gone )

P.S. I recently noticed this thread (probable cause of my dead HE400s ..I think I connected my cans to early -loud pop=only one channel active)
http://bottlehead.com/smf/index.php/topic,2946.0.html