Finished my first Shaka tube but things are strange

[mrfirstime]

HI Guys

I finally finished my first shaka tube pedal but have stumbled again. I am using the layout I found herehttp://www.diyguitarist.com/DIYStompboxes/ST1590BB.htmand have not (to my knowledge) deviated from that scheme.  My first attempt I wired the board in a hardwire fashion.  Quite a mess but I was proud.  Until I fired it up.  I had an intermidend signal.  I then decided to build the main board using the pc layout.  I ironed on the photostat and etched it in ferry chloride.  It only took ten tries to get it right.  I connected up my new board with great confidence but I have landed up with more or less the same problem.  The signal seems to come and go.  At first I thought it was a loose wire and I found by toughing some wire it went on and off.  Then that wire seemed fine and the problem seemed to be triggered by another random wire.  Then it happed by jiggling the pot.  Everynow and then it suddenly boomed louder and then back.  I noticed that when I turned the distortion pot down fully that about 5 seconds later it died.  The only way to get it back was to turn it back up to full and then turn the bias trim pot abit to one side and bam there it was.  At times it sounded really great and then the distorion got weaker.  I think I have a misunderstanding about the earth issue.  Does the input neutral connect to the earth on the jacks. (not that I have done that as it doesnt seem to make sense as there would be a current running through it).  I have read the debugging section but again I dont know if im measuring the signals correclty.

Here is what I have recorded.

incoming ac black wire to v+ = 14v
"                         "          v- = -11
     "       "                       bias = -1.9

tube pins

pin1=-10
pin2=-9.1
pin3=-9.8
pin4=12v ac
pin5=12v ac
pin6=3.7v
pin7=-8.8
pin8=-9.6

TL071:

pin1=-10.5
pin2=-10.7
pin3=0
pin4=-10.7
pin5=-10.5
pin6=-0.6
pin7=-13.9

Any Ideas

thanks

[GibsonGM]

"Input neutral"??  As I understand it, you have a hot signal at the tip of your input plug, and the barrel of the connector is GROUND, not neutral. No signal goes thru the outside conductor of a guitar cable; it acts like a shield and is simply grounded.  Same with the output jack. 

Yes, the grounds should all be connected together, and tied to the power supply ground as well (AFTER THE TRANSFORMER). 
Sounds like the major issue might be that, plus some loose wiring.  AND, whenever you're working with tubes, wires floating around have stray capacitance between them - they can couple signal back and forth and cause 'fading' type effects.   Wires that make noise when moved usually indicate a bad solder joint on the other side of the board!  Check those carefully.     A 'fading pot' might be mis-wired or (much less common) a bad pot.  Are those electrolytic caps oriented properly ("-" to ground)?

Try cleaning up the layout; it's not bad but could use some 'stability'  - wiring ties, etc.  Power supply wires in 1 bundle, signal wires in another kept away from power.  All ground wires to 1 point, at the power board ground, using SEPARATE WIRES (to start with).  Good news is that you're hearing a signal, so you are getting close!
Keep at it while being safe, and you'll clean it up and having it working right!
Ask ?'s, there are no dumb ones, and we've all been there....

~MJP

[mrfirstime]

Hi

Thanks for those words of wisdom and encouragement.  I appreciate it.

At first I just used wires cut off an old dvd player and some from telephone cable.  When I built my second proper board I bought some decent wire but left the ones on the tube pins because when I first put them on it seemed that the heat made them soft and loose and I didnt want to do it too often.  I wanted to leave them on until I was ready to put it into the pedal but I can see now that that was a bad idea.  Yes I do have the caps in the right direction so it cant be that.  I am going to clean it up and also use the new board I made for the power supply instead of the perf board one.  Then the moment of truth.

Just a quick question about the forum.  If I take two days to work on my pedal and then later I want to continue with this discussion do I have to submit a new thread or is there a way to get everyones attention back to this one for more advice.

Thanks
Linton

[MikeH]

Replying to this thread will "bump" it back up to the top in the main forum.  Good luck!

[mrfirstime]

Thanks.  It all makes sense now.

[Paul Marossy]

Very important: connect ALL grounds together, or it will not work properly. A lot of people with no tube building experience seem to make this mistake for some reason. That or they get the pinout on the 12AX7 backwards.

[mrfirstime]

Hi Paul

I am using your pcb layout.  Im not sure what grounds  are left to be tied.  Is at the power board with the diodes or are there more.   I mean besides the ground to the one pin on the tube.

[mrfirstime]

Is this correcthttp://www.undercoverband.co.za/images2/shaka3.jpg

[mrfirstime]

sorry I meant this

[Paul Marossy]

That looks right as far as the grounds are concerned. And you have all of the other things connected together? (ie V+ & V+, V- & V-, Bias & Bias, 12VAC & 12VAC)

[mrfirstime]

Yea I did have all the V+ etc but not the grounds.  However when I attach the grounds in the way it is in this diagramme above,  the cirute just shorts out and the sound disappears.  I think Im having a real misunderstanding of this ground issue. ( Even with all the information you guys have given me.)  Wouldnt the ground that comes from the transformer be half the cylcle of ac 12 v. 

[Paul Marossy]

Yea I did have all the V+ etc but not the grounds.  However when I attach the grounds in the way it is in this diagramme above,  the cirute just shorts out and the sound disappears.  I think Im having a real misunderstanding of this ground issue. ( Even with all the information you guys have given me.)  Wouldnt the ground that comes from the transformer be half the cylcle of ac 12 v.  

Yes, transformer ground would be 1/2 cycle of your 12VAC. The "positive" leg of the 12VAC then goes thru a voltage doubler circuit. You must have done something wrong because your transformer shouldn't be shorting out when you connect all of the grounds together.

Here is the schematic: http://www.diystompboxes.com/pedals/schems/shakatube.gif - maybe that will help.

[mrfirstime]

Ok.

Does it matter which wire I pick from the transformer to be the ground.  I have 3 outputs one in the middle = 12 volts and the two outer = 24.  I am using the first and the middle.

Also I wanted to ask could I stick in the 072 op amp into that circuite.  I only had one of the 071's and I have used it twice.(once for the first hardwired and then for the etched one.)  maybe i I burned it out abit. Not sure how sensitive they are.

[Paul Marossy]

Don't use the middle connection of the secondary of your transformer. Use the two outer connections. Also, you do have a 12VAC transformer, right? If you have a 24V-0V-24V transformer, that's not going to work right. You need a 12VAC transformer.

Also, a TL071 and a TL072 are not interchangeable. One is a single opamp and the other is a dual opamp.

[mrfirstime]

The transformer has output printed on it as 12-0-12vac.  I asked the guy at the shop for a 12v transformer and thats what he gave me. It has 2 black outer wires and if you mesure accross that you get 24v.  If you use the first black with the middle blue you get 12ac.  I took this as being right and disregarded the last lead from the equation altogether.  You can see it going off into the distance on the pic of the board.  Is it wrong?

[Paul Marossy]

Well, that seems to be your problem. You need a transformer that is 12VAC from peak to peak. He gave you one that is a center tapped 24VAC transformer, which is not the same thing.

[mrfirstime]

Ok took it back to the shop and after abit of  hooha I managed to get a straight 12 ac.  Connected it up but all is the same.  if I put earth from in or output jack onto the power board marked ground in, the signal gets cut.  However if I put the pin to ground it doesnt dissapear?   Just want to check, at no stage here are we talking about the earth on the transformer.( in other words the 3rd wire that goes to the wall socket)?

[Paul Marossy]

You don't need a ground connection of the primary side of your transformer, a regular two prong power cord is fine. I used a 13VAC 800mA wall wart to power mine. Works great with a small series resistor to lower the voltage to about 12.6VAC before going to the circuit board.

Anyway, maybe you need to put it aside for a few days and come back to it. You must have miswired something. I know that my PCB layout works, I built my own Shaka Tube from it.

Just a thought, are you sure that your input & output jacks are wired correctly? Ring should be ground and tip is your signal.

[mrfirstime]

ok great.  My transformer is like yours.  I have checked the wiring over and over again.  The pedal works great but it seems like the signal is hanging on a thread.  if I turn down the gain it starts to cut out.  If I really hit the guitar strings hard then it kinda peeks through and then dies. Also if I knock the posts in a certain way it suddenly gets like twice as loud.  I keep looking for a bad solder but they all look strong.  I am peterbed that I cant put the ground from the jacks to the ground of the 12v in but I can do it the other way round (input signal to ground) and it doesnt cut out? Go figure.  I will take it to the old man down the road and see if he can help.  Maybe he will see something obvious.

[Paul Marossy]

Yeah, sometimes a second set of eyes will immediately see something that you don't. I hope you get it figured out.