Sparkle Boost. We have to get to the bottom of this!

[milkwasabadchoice]

Ok so a while ago i built 3 SB's. I bias the J201 and 2 min later it goes out way off bias wise and sounds horrible. When it works it sounds great.

I set them aside since then because I was just so sick of messin with all three of them I just needed a break.

The other day I got them back out and they did the same thing. I cannot figure out why at first i can bias them to 4.5v then a couple of mins later they are like at 1.2v.

Could it be three messed up trimmers?

Really guys, Thanks for your help,

Jason

[petemoore]

  Yupp, could be anything.
  Checking everything [except caps and transistor], counting node connections etc. w/DMM may help locate the problems.

[davec69]

Hi. I just finished a build of the Sparkle Boost Deluxe, which is working except for the reversed led on the boost side.  I'm wondering.  When you bias your, where do set the knobs? Do you turn them all the way down then bias, or all the way up.  Does it even matter?

[milkwasabadchoice]

i didnt think it mattered. what do you mean the node connections?

thanks guys.

[Barcode80]

a node is a point on a schematic where connection is made. for example, ground would be a node. each junction where parts connect together is a node. when someone says check the nodes, they mean to make sure that the right components are connected to the right other components, including ensuring that each component is connected to the right side of each other component.

[milkwasabadchoice]

gotcha i just cant see how i could have messed the same thing up on every pedal.

[JonFrum]

Just a thought from a relative beginner around here. Ohm's Law tells all, so let's get down to basics. you start with 9V, and a given current passes through a given resistance to give you a voltage drop, which is changing over time. So how can this happen? Either the current or the resistance is changing over time. The resistance should be fixed, as should be the current draw. The only other thing involved is the batteries. Supply voltage, resistors, transistors. If there was a mis-wiring, I wouldn't think the voltage could move over time like that. Do the parts in the builds all come from the same batch? Have you replaced each part? Rhetorical questions, I expect you already did. But Ohm's Law does not lie. Can you breadboard one?

[Barcode80]

you might remove a couple of those trimpots and check them with a meter. sounds like they might be faulty

[petemoore]

  Probably dont' even have to remove the pots to check them.
  Test and see what they are, if the R value moves when adjusted [hook to the middle and correct outside lug..
  Look for alternate DC path through the circuit across the trimpot as connected, this'll throw the reading off.
  Do the math, or then pull the dern thing and test it, if you're 1/2 sure it's open, very small chance of a shorted one I think.
  I bet 9 to 99x9 that all three trimpots aren't faulty.
  Put one of them through the 'what to do when it doesn't work' tests.

[Paul Perry (Frostwave)]

When a circuit slowly goes off bias over a minute or so, there are two possibilities:

1. something is wrong (resistor value ) and a semiconductor is overheating & drifting away.
Or, more likely here,
2. there is a wiring problem so that a cap is gradually discharging or charging & the bias point is moving.

The fact that you have made three circuits with exactly the same fault, means that you havn't made the circuit that you think you have made!
This is the absolute cornerstone of troubleshooting - converting the circuit that you HAVE, to the circuit that you WISH you had.

[milkwasabadchoice]

I'm thinkin Mr. Perry is right. I just need to start over fresh. I think and at this point hope I just read something wrong all three times. Deff. wouldnt doubt it. haha

Thanks again guys, I 'll let you know what I find.

-Jason

[milkwasabadchoice]

Can someone point me to a layout of the Sparkle Boost using the J201. I dont want to have to bend the leads of the tranny.

Thannks,

Jason

[petemoore]

  Just hand-drawing-freestyle the layout a few times might show you the problem.
  J201 is same as 2n5457/Mpf102 pinout, see data sheet, GSD, legs down print toward you.
  All connections are as on the schematic for both layouts, but the G/S assignments have been swapped.
  Count the number of connections at each node, prior to populating any parts to that node.
  Measure every resistor prior to installing it.
  Make sure the - of the cap is at Gnd. side.
  Draw the transistor pinout right on the printed sheet you're going to build by.
  I think there at least 3x as many tests [+other debug tasks] you can perform per part count on most of these circuits.
  Apply the DMM
  Every way possible using it in R mode
  Same for V mode
  and continuity beep mode.
  test that the supply +/- are not shorted
  Test all ground connections, including the ones to guitar and amp.
  Consider using a breadboard.

[Dragonfly]

Torchy has a J201 layout in his folder.

Weird that you had the same problem 3 times. My layout has been verified TONS of times with no issues.  The "cap" idea might be a possibility, or i seem to remember marty had some bad trimpots a while back that were messing up his builds....

AC

[markm]

Can someone point me to a layout of the Sparkle Boost using the J201. I dont want to have to bend the leads of the tranny.

Thannks,

Jason

I have both PCB and Perfboard layouts for this circuit right here>>http://aronnelson.com/gallery/album15

[David]

Can someone point me to a layout of the Sparkle Boost using the J201. I dont want to have to bend the leads of the tranny.

Thannks,

Jason

I have both PCB and Perfboard layouts for this circuit right here>>http://aronnelson.com/gallery/album15

And they're verified, right?

[markm]

And they're verified, right?

Yes Sir, that is correct.

[squidsquad]

One more thought.  Sometimes a wiring error will cause the battery to discharge at a high rate...and the bias will move.  Big clue= warm (or hot) battery.  And check it's voltage before & then after playing a few minutes.