Dr. Boogey help!

[had_hc]

Hi, i build a dr boogey pedal on perfboard using the layout created by Chris Brown which is based on Gaussmarkov's revised schem. wired everything up already but only got sound when bypassed! when switched on, the LED does lights up but got no sound AT ALL out of it. checked back the continuity of all that supposed to be and all seems to be good/correct.

tried the audio probe, but the sound stopped after the 'Gate' foot of Q1 (the first j201). There's still sound at the 'Gate' foot but nothing after that ('Source', 'Drain' and following components). first i suspected the C17 cap is not good coz i had quite a hard time soldering especially for that cap (got some problem with my iron). but according to gaussmakorv schem, http://gaussmarkov.net/layouts/drboo/drboo-schem.png, wouldn't the circuit still be working even without C17?

Or is it may be coz my j201 has failed? I already tried checking the voltage of the feet of the Q1 and all shows readings.

btw, here's the perf layout i followed.



thanks in advance!

[Auke Haarsma]

post the voltages on the Q's. You should have sound on the drains.

Have you biased the the Q's?

[frokost]

Double check the pinouts.

[petemoore]

  Not sure if I saw trimpots there.
  Sometimes a trimpot and a fixed stop resistor helped me to find a range that the sensativity of the pot would allow nice 'fine tuning' to discover the needed value for the drain resistor for stable bias, for say, each J201 transistor, swapping the transistor sometimes made it easier to get a biased stage.
  50k pot and a 47k resistor, with and without the resistor divides a 100k range in two parts, allowing the pot to have a smaller, hence less 'coarse' adjustment sensativity.
  I decided that anything over about 100k to just get another transistor which doesn't require such a large value resistance to achieve drain bias.
  You can open between the drain and drain resistor [or between the resistor and V+] to insert more resistance [try a pot with wiper and outside lugs wired in series.
  To reduce resistance, jumper across the drain resistor. 
 

[jimosity]

Without the trimpots, I'd be wondering just how accurate those JFETs are biased.
Put your DMM probes on each of the outside legs of the JFETs and if they are around half of your supply voltage, it should give sound.
If not, you'll need to adjust the resistor near the JFET (which is why the trimpots are a good idea).
Or just use a trimpot to adjust it, then measure the trimpot when it's set accurately and then replace the pot with a resistor of that same value.

[had_hc]

These are the Q readings
Q1
D : 8.6
S : 8.6
G : 8.18

Q2
D : 8.1
S : 0
G : 7.7

Q3
D : 4.74
S : 0.55
G : 0

Q4
D : 4.5
S : 0.56
G : 0

So... what should i check? pinout are where it supposed to be and connected to what is supposed to connect with.

anyhow, how to check whether a capacitor is still ok or not?

[had_hc]

Those yellow 'VR1/2/3/4' are trimpots. i somehow couldn't bias the drain of Q1 and Q2 low enough nearing 4.5v

[jimosity]

Where's a larger version of the layout that you used?
Can't seem to find it and can't read the one you posted.

[had_hc]

Try and click the link below to see a bigger of the perf layout.

http://2.bp.blogspot.com/_2mvQNIEjC7g/Sk-gDo0ixwI/AAAAAAAAAFA/WAFpG9qT5QE/s1600-h/boogie+layout+2.gif

[frokost]

i somehow couldn't bias the drain of Q1 and Q2 low enough nearing 4.5v

Well, there you have it. Start looking around those, especially look for shorts around Q1, try other trannies etc.

[jimosity]

Might be dumb to say, but make sure you have C14 and C20 polarity correct.
The layout looks the same as the Gaussmarkov layout.
Since you're not able to get the bias down to the right range on Q1/Q2, check for solder bridges in that area.
If you have another JFET to test in those spots, that might be worth trying too.

EDIT: DOH! Sorry to previous poster, I was typing when you posted that!

[had_hc]

i managed to get drain voltage of Q1 to around 4.5v but still couldn't figure out why can't i bias Q2 to 4.5v. the lowest was around 7.1v. all components seems to be in their respective places. 

and still however, i got no sound at either source or drain of Q1, as before, last trace of sound is at Q1's gate. help me!! where should i look more?? there seem to be no short circuit or bridges wutsoever....

[kristoffereide]

This may sound stupid, but what I did wrong with the Dr. was the offboard wiring. I put my guitarsignal to the output of the perf and vise versa... A week of troubleshooting, 2 minutes to fix

[frokost]

i managed to get drain voltage of Q1 to around 4.5v but still couldn't figure out why can't i bias Q2 to 4.5v. the lowest was around 7.1v. all components seems to be in their respective places. 

and still however, i got no sound at either source or drain of Q1, as before, last trace of sound is at Q1's gate. help me!! where should i look more?? there seem to be no short circuit or bridges wutsoever....

Well, it sure looks like you've got a short between Q1's source and drain. Does your meter measure continuity between source and drain? Do you use sockets, so that you easily can swap the transistor?

[had_hc]

Thanx all! i don't know what i did wrong but i got sound when enganged! only tuning needed now!

[had_hc]

somehow i feel that there's not enough gain in my Dr. Boogey and the distortion is kinda.... fizzy/fuzzy i might say. very little bass present and really loose sound at palm-muting.

any reason's why it might be?

[petemoore]

  I kind of remember DB as being a number of seriesed Jfet Stages, no schematic limits the dialogue and accuracy for me.
D : 8.6
S : 8.6
G : 8.18
  Source should be kinda near Gnd., Source above gate, check them' resistances to ground around the S/G, also check the R value between D and V+, all these pins are around V+, and should be D in the middle of the supply, S and G nearish ground voltage.
Q2
D : 8.1
S : 0
G : 7.7
  I would start checking the ground connections, is the source grounded?
Q3
D : 4.74
S : 0.55
G : 0
   This is the kind of voltage I'm talking about ... see if you can make the other stages resemble this one more, use the DMM to compare anything / everything possible with the DMM to see how the offbias stages compare, especially resistance wise.
Q4
D : 4.5
S : 0.56
G : 0
  Here...source above gate, 4.5v would be spot on with a 9v battery, but I'd still check sound and bias by ear, this stage should be working fine.

[dschwartz]

just forget about the 4.5v bias now..and start tuning it by ear..this is my technique
- Set the dr B gain really low, with the guitar connected.
- Set the volume of the guitar so you get the cleanest sound...
- Pay attention to the background hum/hiss and move r4´s trim
- set the trim where the noise is louder
- Pay attention to the background hum/hiss and move r3´s trim
- set the trim where the noise is louder
- repeat for Q1 & Q2..

- Now.. pluck the strings gently, trying to get a clean sound (there will allways be distortion), and re-fine tune the trims to taste based on sound, touch response and clipping..by fine tune i mean microscopic turns!
- try different j201´s on Q1, Q2...you´d be surprised how much the selection of fets improves the sound.

[petemoore]

  With the gates that are above source, I'm thinking there's a problem with the bias unrelated to, and not affected much by the trimpot settings.
  Where's the schemati

[budjb]

http://gaussmarkov.net/layouts/drboo/drboo-schem.png