Dr. Boogey doesnt boogey... yet. Litte help?

[joelap]

Hey all, got this Dr. Boogey pedal build here.  The bypass works, the LED works.  Turn it on, and there's no sound.  Here's some voltage readings:

Q1
D: 5.3
S: .1
G: .00


Q2
D: 4.9
S: 4.6
G: 4.6


Q3
D: 5.5
S:4.3
G: 3.8


Q4
D: 6.2
S: 5.8
G: 5.7


Q5
D: 8.95
S: 6.12
G: 6.17

Also I should mention everytime I set the bias and check, they revert back.  For instance, I set the bias and checked the voltages here, and when I went back to check Q1 after Q5, it was back in the 1 volt + range.  Its not staying unless I bias them at 8+ volts.

Any help?

[George Giblet]

Q1 looks OK but the other are wrong.

Given there are so many wrong I suspect you have put the JFET in the wrong way.  My guess if flip then around the other way better still check your pinouts against your circuit and make sure D is going to D.  Pay attention to bottom view and top view of the JFET in the datasheet and on the circuit.

[petemoore]

  IIRC we're talking about a string of gain stages
  Q1
D: 5.3
S: .1
G: .00 [looks pretty good if 5.3 is 1/2v of supply v.


Q2
D: 4.9
S: 4.6
G: 4.6 is the G connected to the S ?...shouldn't be


Q3
D: 5.5
S:4.3   should be a relatively lower V, and above G voltage
G: 3.8 Pinout is the first thing to triple check W/data sheet/schematic


Q4
D: 6.2
S: 5.8 
G: 5.7


Q5
D: 8.95
S: 6.12
G: 6.17
  pinout...
  you can also put a DMM probe on a transistor pin, then measure bias Resistors from there....thing is if you get a 'funny', lower than marked color code R reading on a resistor, you may have to 'calculate or eliminate' an alternate path through the circuit...if one exists.
 

[joelap]

But how can it be possible that I get the drain of Q1 set for 5.5 volts, then measure the Drain of Q2, then measure the drain at Q1 again and its at 4.5 volts?  Then a minute later its at 2 volts.  I'm not touching anything or adjusting anything.  I'm using a Dunlop DC adaptor rated 9V and 200mA output, not a battery.  This is absolutely crazy and I cant even begin to understand what the problem is.  I double checked every connection: all my wiring is precise and there are no touching solder connections that shouldnt be.  How can the drain shift like that?

EDIT: Also, when biasing the Jfets, not even a 1 degree turn of the trimpot is changing the voltage at the drain from 8.94 down to 1.45 volts.  Somehow.  I honeslty cant make a movement minute enough to get it between that range for some reason right now.

[mojotron]

But how can it be possible that I get the drain of Q1 set for 5.5 volts, then measure the Drain of Q2, then measure the drain at Q1 again and its at 4.5 volts?  Then a minute later its at 2 volts.  I'm not touching anything or adjusting anything.  I'm using a Dunlop DC adaptor rated 9V and 200mA output, not a battery.  This is absolutely crazy and I cant even begin to understand what the problem is.  I double checked every connection: all my wiring is precise and there are no touching solder connections that shouldnt be.  How can the drain shift like that?

EDIT: Also, when biasing the Jfets, not even a 1 degree turn of the trimpot is changing the voltage at the drain from 8.94 down to 1.45 volts.  Somehow.  I honeslty cant make a movement minute enough to get it between that range for some reason right now.

It seems like you have a problem with solder joints. When I have problems like this I go through and re-heat all of the solder joints - making sure that the copper and component lead are heated and the older flows on both.

Also, you might want to make sure that the solder is not making a short between components while your re-heat the other connections.

Hope this helps.

[John Lyons]

You most likely have a single turn trimpot. They are hard to get a precise adjustment. What you want is a multi-turn trimpot. You get about 15 turns + or- with them much easier to bias and tune in things with them.

John

[joelap]

You most likely have a single turn trimpot. They are hard to get a precise adjustment. What you want is a multi-turn trimpot. You get about 15 turns + or- with them much easier to bias and tune in things with them.

John

Thanks, I'll grab some of those now.  Also, would having the JFets not biased correctly cause the no sound that I'm experiencing?  Or do you think theres another problem in addition to the bias problem?\

[petemoore]

Q1would having the JFets not biased correctly cause the no sound that I'm experiencing?
Or do you think theres another problem in addition to the bias problem?\ Getting the transistors biased will make it easier to answer this one...
  Using an audio probe...
D: 5.3
S: .1
G: .00
  This one should be passing signal and amplifying.
Q2
D: 4.9
S: 4.6
G: 4.6  This one source/gate is same, and both are close to the 1/2v, doubtful even a sputter would get to the gate w/big input
Q3
D: 5.5
S:4.3
G: 3.8  Not much room to swing signal on this one..\
Q4
D: 6.2
S: 5.8
G: 5.7  Not biased/ no sound
Q5
D: 8.95
S: 6.12
G: 6.17 Source lower than gate, no sound.
  Use an audio probe into powered circuit with an input source and you'll probably get an amplified version of that out of Q1 [everything else being wired correctly],
  After that I'd start on Q2, and get it to bias/pass signal/amplify...

[mojotron]

You most likely have a single turn trimpot. They are hard to get a precise adjustment. What you want is a multi-turn trimpot. You get about 15 turns + or- with them much easier to bias and tune in things with them.

John

Thanks, I'll grab some of those now.  Also, would having the JFets not biased correctly cause the no sound that I'm experiencing?  Or do you think theres another problem in addition to the bias problem?\

IMO, single turn trimmer pots are fine for this kind of circuit, and are generally the standard around here. I would say that your biasing issues are a symptom of a wiring/soldering issue somewhere.

It would be good to do spot checks with a meter at this point. This is what I would do first:

1) remove Q2, then check the resistance at the Q2 source and Gate pads to ground (first on the board, then to the ring on the output/input connectors - these should reflect the resistance as in the schematic. (You should have less than 2k ohms at Q2's source pad to ground, and 1.5M to .5M ohms to ground at the gate pad of Q2...)

2) then, if this seems all correct, put Q2 back in and do the same for Q5.

Once those are correct, then try to bias the circuit. You may end up doing this for Q3 and Q4 if they don't bias correctly after resolving the issues with Q2 and Q5, but it seems like Q2 and Q5 are the places to start.