Just built a Dr. Boogey (and my perf layout is verified now). Whoa.

[PaulC]

On Q1's source, I used a .47uF + 47k resistor for the AC bypass (in place of the 1uF cap)

Hey Mojo,

    Having the 47k in series with the cap will remove the cap from the circuit.  It's there to lift the cap out of the circuit when you're in the clean mode.  When you're in the overdrive mode the LDR shorts it out bringing the cap in for a hotter front end.  This is used on all three high gain stages to tame them down for the clean channel.  If you're going for the gain stuff you'd leave off the 47k.

   Also if you don't get splats try to set up the drain voltage on Q3 to around 7 or 8 volts.  This will give you the hard asym saturation clip that the tube stage does instead of the cut off clip. 

   I keep going back to the SLO when thinking about this circuit, but I did dig out my schematics for this amp the other day (I used to be an authorized service guy for boogie).  I'd forgotten about that 20pf cap on the second stage.  So really that would push the value of the miller cap closer to 170pf or so for an even greater roll off than the 100pf you used will do.  The 100pf will give a -3db at about 3400Hz while the 170pf will be at about 2kHz

 
Later, PaulC

[mojotron]

... Having the 47k in series with the cap will remove the cap from the circuit.  It's there to lift the cap out of the circuit when you're in the clean mode....

Yikes!  what was I thinking - of course.... that's one of those 'can't see the forest for the trees' things...
Although, I do like the sound the way it is - that would be - without the cap... 

Also if you don't get splats try to set up the drain voltage on Q3 to around 7 or 8 volts.  This will give you the hard asym saturation clip that the tube stage does instead of the cut off clip. 

   I keep going back to the SLO when thinking about this circuit, but I did dig out my schematics for this amp the other day (I used to be an authorized service guy for boogie).  I'd forgotten about that 20pf cap on the second stage.  So really that would push the value of the miller cap closer to 170pf or so for an even greater roll off than the 100pf you used will do.  The 100pf will give a -3db at about 3400Hz while the 170pf will be at about 2kHz

Yep - I will try these - THanks!

Earlier, I was going for exactly what others had tried. As there's a 470pF cap not in the Dr Boogie (between Q2 and Q3) - that's in the DR between stage 2 and stage 3 - I was taking things iteratively working my way through several changes - one at a time. Bumping up the Miller Caps is on the list of things to try.

[Xavier]

Hi guys, building my THIRD boogey board so far . This time with the Miller caps in Q1, Q2 and Q3.

Just one question. These caps are from gate to ground, or from gate to source? I've seen both things when searching through the forum.

When I finish this damn circuit I'll call it quits for a while......

[mojotron]

Hi guys, building my THIRD boogey board so far . This time with the Miller caps in Q1, Q2 and Q3.

Just one question. These caps are from gate to ground, or from gate to source? I've seen both things when searching through the forum.

When I finish this damn circuit I'll call it quits for a while......

On Q1 and Q2 - you can go from gate to source as you have a source bypass that is much larger then the 200-100pF Miller cap. I would not worry about Q3, from my experience it's not going to produce that much gain. But, on Q3 if you wanted to put a cap in there I would make it a smaller one (<100pf) and make it gate to ground, because the Miller cap is really 1-3pF multiplied by the gain of that stage. I had planned on doing more homework on this but from what my simulating/experimenting with this leads me to think is that if you always go gate to source with a small cap, on a circuit like this, in a common-source stage with 150-200pF you can cover the parasitic loss (normally in a triode as grid to plate) by coupling some hi-end signal to the source and achieve the marginal parasitic loss via degenerative effects of reducing the V_gs voltage difference for hi-freq signals that are shunted from gate-source; which reduces the gain for that part of the signal. So, I have been going gate to source on this and I think works best because by doing that you scale the affect of the Miller cap with the gain of the circuit - even if it is not a lot of gain. Someone (and be nice please  ) set me straight if that's not the case.

[Xavier]

Hey Mojo, thanks for the explanation. I'm building it from scratch (again) but this time I'll check every step with both the oscilloscope and the tester. I'm using 100pF's throughout.

I hope this time it works.

[mojotron]

Hey Mojo, thanks for the explanation. I'm building it from scratch (again) but this time I'll check every step with both the oscilloscope and the tester. I'm using 100pF's throughout.

I hope this time it works.

Let me know how that works, I went with 220pF caps (all gate to source) on the Dr B and it sounded great and still had plenty of high end. It helped with some of the squeal, but I still have some issues after doing a fairly good job at isolating leads from eachother. I was going to try a choke on the supply voltage as well as redo my leads a bit. On the other hand, I can get it up to about 70% of the max gain without any oscillation and that's more than enough for me anyway - the Dr B sounds awesome!

What layout are you using?

[Xavier]

Hey Mojo, thanks for the explanation. I'm building it from scratch (again) but this time I'll check every step with both the oscilloscope and the tester. I'm using 100pF's throughout.

I hope this time it works.

Let me know how that works, I went with 220pF caps (all gate to source) on the Dr B and it sounded great and still had plenty of high end. It helped with some of the squeal, but I still have some issues after doing a fairly good job at isolating leads from eachother. I was going to try a choke on the supply voltage as well as redo my leads a bit. On the other hand, I can get it up to about 70% of the max gain without any oscillation and that's more than enough for me anyway - the Dr B sounds awesome!

What layout are you using?

My own perf layout again. I tried the small 22x7 stripboard but everything was so packed that was very hard to find the bugs. This build needs a bigger board.

[Xavier]

OK, built it again and now it works. I've been testing every step so now I know where the problems come from. Basically the wiring is the problem, I'll explain.

I have been following the signal with the oscilloscope and a probe, everything is OK. I have a very clean sinus wave at the input, and an almost perfect square-ish wave at the source of the last J201

Then I have wired the final eq section and voilá!! oscillations and what's worse, it even appears at the input jack (how can that happen?).

This means new wiring for sure, so now I have to particular questions about the wiring.

- What is the correct way for wiring it? Should I use shielded cable throughout? Should they be arranged in a certain way?
- The high frequency content varies A LOT depending on how the 1M master volume is set. At 25% the treble content is perfect, but it gets muddier as you turn it up. At 50% sure you have output, but even with both the treble and presence pots maxxed, all I have is high mids. Any trick in order to solve this?

[Xavier]

UPDATE:

I have just built the voltage regulator that a forumite has suggested some threads below, and it works woohoo !!

The noise when the effect was bypassed has disappeared, along with the hum. I have rebiased again now that I had a clean 9,2V and it sounds even better.

The only problem I have now is that it still oscillates BUT only when there's nothing connected at the input. As soon as I plug the guitar in all oscillations disappear, even with everything maxxed. As this is meant to be played it's going to stay like this.

Worth the build, but what a challenge !!!!!

[Bucksears]

I gotta tell you, other than noise when the effect is engaged (and the gain is at 50% or higher), my Dr. Boogey works fine. It's the original one that I built over a year ago, but all the knobs work correctly, no excessive squealing or anything. I may try shielded leads to/from the board, but that's about it.

[mojotron]

UPDATE:

I have just built the voltage regulator that a forumite has suggested some threads below, and it works woohoo !!

The noise when the effect was bypassed has disappeared, along with the hum. I have rebiased again now that I had a clean 9,2V and it sounds even better.

The only problem I have now is that it still oscillates BUT only when there's nothing connected at the input. As soon as I plug the guitar in all oscillations disappear, even with everything maxxed. As this is meant to be played it's going to stay like this.

Worth the build, but what a challenge !!!!!

You mean the choke idea worked, I had not tried that yet. So, if I understand this, you had immense squealing at higher gain settings, you put a choke in series with the supply voltage, and then the squealing went away?

If so, what kind of choke did you use?
   
Or can you point me to the voltage regulator thread.

Also, you can ground the input in situations where the plug is not plugged in the connector... Are you using the 3 connector switchcrafts for the input?

[mojotron]

UPDATE:

I have just built the voltage regulator that a forumite has suggested some threads below, and it works woohoo !!

The noise when the effect was bypassed has disappeared, along with the hum. I have rebiased again now that I had a clean 9,2V and it sounds even better.

The only problem I have now is that it still oscillates BUT only when there's nothing connected at the input. As soon as I plug the guitar in all oscillations disappear, even with everything maxxed. As this is meant to be played it's going to stay like this.

Worth the build, but what a challenge !!!!!

You mean the choke idea worked...
Also, you can ground the input in situations where the plug is not plugged in the connector... Are you using the 3 connector switchcrafts for the input?

Ahh, I see - you were refering to the 'Topic: Power supply filtering, some advice please.....' thread.

Thanks!

[Xavier]

UPDATE:

I have just built the voltage regulator that a forumite has suggested some threads below, and it works woohoo !!

The noise when the effect was bypassed has disappeared, along with the hum. I have rebiased again now that I had a clean 9,2V and it sounds even better.

The only problem I have now is that it still oscillates BUT only when there's nothing connected at the input. As soon as I plug the guitar in all oscillations disappear, even with everything maxxed. As this is meant to be played it's going to stay like this.

Worth the build, but what a challenge !!!!!

You mean the choke idea worked, I had not tried that yet. So, if I understand this, you had immense squealing at higher gain settings, you put a choke in series with the supply voltage, and then the squealing went away?

If so, what kind of choke did you use?
   
Or can you point me to the voltage regulator thread.

Also, you can ground the input in situations where the plug is not plugged in the connector... Are you using the 3 connector switchcrafts for the input?

No, I'm using a two connector Switchcraft since I'm not using a battery, but I could try your suggestion. How do I wire it?

Regarding this matter I also built a small buffer and placed it between the footswitch and the board input, but it didn't solve the problem.

Your idea seems stupidly simple but effective.