Beginner question - Has to be simple

[Axis29]

Cause I'm a simpleton!

I'm trying to build the CB1 (LPB replica) from http://www.generalguitargadgets.com/index.php?%20option=content&task=view&id=72&Itemid=103

I'ts my first build.  I know my solders are good.....  I have run over everything it seems like 40 times.  I have made a few substitutions:

I used a perfboard instead of the PCB.
Component     Planned      Used
R1                   430k            470k
R2                   43k              47k
R3                   10k              SAME
R4                   390 Ohm      330 Ohm
R5                   POT             SAME
R6                   1M5 (1.5 M)  SAME
R7                   1k                 2.7k
C1                    .1uF Film      SAME
C2                    .1uF Film      SAME
D1                     LED             SAME
Q1                    NPN Bipolar Junction Transistor   2N3904JP
J1                     Stereo ¼ Jack      SAME
J2                     Mono ¼ Jack        SAME

I have a couple of problems.  The first is that if I hook up the lead from R3 and R1 to the LED/Power/Jack, I get a horrible hum and nothing from the guitar.  But the LED still works, etc.
If I disconnect that lead, my problem is that when I step on the switch, the pedal works like a defeat rather than a boost.  The pot works, and works in the correct direction (ie. I turn it down the volume goes down to nothing).  The LED works (and doesn't fluctuate with the pot).  The switch works as a true bypass.  Without a plug in the input there is no power, like it's supposed to be.

I have tried several transistors (I also used a IC socket, cut up and soldered to the board to keep from heating up the transistors).  I have tried turning them around...

I swear I've tried everything I can think of, but then as stated earlier I am a simpleton...

Can anybody point me in the right direction? Being an absolute electronic moron, are my resistor values too far off?  I used the closest ones I could find at the shack....

Thanks in advance,


John F.

[pjwhite]

Your resistor substitutions should be OK.  Check your wiring (again).  Are all the grounds connected together?  Are the jacks wired properly?  Look especially at the input jack -- with the plug from your guitar inserted, the minus (-) side of the battery should get connected through the plug shank to the ground connection on the jack.  Check the switch wiring as well.  Use a continuity checker.  With the switch in the active position, you should have continuity from the cathode of D1 to ground, from the tip of the input jack to the R6/C1 junction and from the wiper of R5 to the tip of J2.

[Barcode80]

R7's substitution is a little bit suspect to me, you are subbing double the value, can be problematic in low tolerance builds, though the lpb is not a low tolerance build. the "Defeat" effect you get when you disconnect the resistors is not surprising, as you are removing the power from the circuit, so when you switch to the circuit no signal can pass as it is unpowered. the loud hum is likely a grounding issue. make sure EVERYTHING that is marked to connect to ground is connected firmly to the ground. also, the lpb is a booster, so it boosts noise too. you should switch back and forth between different pickups and see if the noise persists at all switch settings. if it gets significantly quieter at any position, you need to check the guitar wiring and also you might want to shield the guitar cavity.

[choklitlove]

R7's substitution is a little bit suspect to me, you are subbing double the value, can be problematic in low tolerance builds, though the lpb is not a low tolerance build.

i doubt it.  R7 is the LED's current limiter.  2.7K should be okay.

[jrem]

are you sure that you have the transistor in the right way?  without any power the signal is going through R1 and R3, so yeah, it's going to be reduced.  You are using a battery, and not a wall wart, right?  Triple check your wiring, you should have some gain off of that circuit.

[Axis29]

Your resistor substitutions should be OK.  Check your wiring (again).  Are all the grounds connected together?  Are the jacks wired properly?  Look especially at the input jack -- with the plug from your guitar inserted, the minus (-) side of the battery should get connected through the plug shank to the ground connection on the jack.  Check the switch wiring as well.  Use a continuity checker.  With the switch in the active position, you should have continuity from the cathode of D1 to ground, from the tip of the input jack to the R6/C1 junction and from the wiper of R5 to the tip of J2.

First, thanks for the quick response!

Okay, let's try it all...  I'm using a FLuke 79 digital multimeter.  I've got it set on continuity:

All grounds are connected together - check
Jacks wired properly, sleeve to ground, Input tip to switch, output tip to switch (and the proper locations according to the simple schematic/layout) - check

Switch in active position
Continuity between cathode of D1 and ground - check
Continuity between wiper of R5 to tip of J2 - check

Between ground and R6/C1 junction - No!  But, I have continuity on the negative side of R6 and the resistance reading across R6 is 1.49....  Meg

While I was typing the reply, I got notification of a couple other replies and so I have checked my grounds and everything seems fine.  I have re-soldered again and nothing but hummmmmmmmm.... 

Now, I also see (now, that I've actually really explored this circuit a painful amount of times!  LOL) that in fact, the piece I have disconnected (the lead from the junction of R3 and R1) is the piece that supplies power to the effect...  interesting to me, but still not helping me much...  Like I said, a simpleton, but trying to learn!


Not sure what to try now?  Maybe it's the switch?  I'm gonna walk away from it for a few hours at least.  If anybody else has any ideas, I'd sure appreciate them!

[Axis29]

are you sure that you have the transistor in the right way?  without any power the signal is going through R1 and R3, so yeah, it's going to be reduced.  You are using a battery, and not a wall wart, right?  Triple check your wiring, you should have some gain off of that circuit.

Came up as I hit post...  Thanks.

I've installed several different transistors in both orientations.

I am using a 9 volt power supply, the kind that snaps onto the battery snap.  If it turns out that I've wasted this much of mine and everyone ele's time because of a battery I'm going to go hang my head in shame....  I checked the voltage on the adapter too, while I was at it, came in at just over 10 volts.  But, please don't yell at me if it turns out this is it!  I will feel like a complete A$$

[Axis29]

Tried a 9 volt battery... no more hum.    Still no sound.   I'll trya gain tomorrow...  I've given up for tonight!

I'll pull the IC socket and resolder it.  Then try several other tranissitors....  Oye, shouldn't be this hard, I know it shouldn't.

[sfx1999]

Some older Japanese transistors have an ECB pinout instead of CBE. Also, the 2N5088's pinout is reversed of a 2n3904.

[Axis29]

Some older Japanese transistors have an ECB pinout instead of CBE. Also, the 2N5088's pinout is reversed of a 2n3904.

Hmmm, I cannot figure out what brand I have purchased and the datasheets I've found at: http://www.datasheetcatalog.com/datasheets_pdf/2/N/3/9/2N3904.shtml don't give me any clue and seem to be inconsistent...

I bought it at Arcade Electronics and their website says that they are NTE .  The datasheet for this brand says EBC.

I went to: http://www.kpsec.freeuk.com/components/tran.htm and tried to test a brand new transistor out of the pack (I bought a 30 pack in case I screwed a few up!  See I did try something intelligent in this escapade of mine)  here are my results (pardon my horiible ASCII drawing):

_____________________
|  1          2           3     |
|  0          0           0    |
\                               /
   \________________/

Negative lead on 1, positive on 2 - .553 VDC
Negative on 3, positive on 2 - .557 VDC

Nothing on any others.

Does this mean that 2 is Base, 1 is collect and 3 is emit?  Which would make it CBE?  Or is that EBC?  I think after I get this one done, I'm gonna go back to studying music theory....  LOL


Thanks again for everyone's imput and patience!

[petemoore]

  Not sure how to read...take a look at the debugging thread for how to format circuit information.
  Maybe I'm backstepping too far, but if you can clip the black DMM lead to a ground point, then use that as a reference [0.0 Volts] to measure the voltage potentials by...ie all voltages measured using ground, 0v as reference voltage.
  include battery or supply voltage, this is the V+ reference...all the other points measured'll be between Gnd. and V+.
  then the transistor type..say 2n5088
  Battery voltage is 8.47v
  C  should be around 1/2v or 4.2v
  B  Base needs to be a diode drop above emitter
  E  Should be at near ground voltage
  Post the voltages thusly...

[squidsquad]

Yo bro,

When all else fails...try new/different in-out jacks.  Sometimes ya get a bogus one...that shorts everything from the get-go.  Also....use a probe to follow your signal.