proposed dr. boogey layout -- seeking comments

[gaussmarkov]

i have learned some new layout ideas from several threads, Marty Marts Tornado built, but has a small problem, guidelines for laying out high gain circuits?, and PCB layout tips for high gain FET circuits?. there are probably other places where the ideas found there are explained, and references to them are welcome.  what really brought the ideas home for me was applying them to a particular case.  so here is another application, dr. boogey, where folks have had some difficulty taming the circuit.

i am hoping to learn more/better by having this layout critiqued here.  and i hope others will learn, too.

what you see below is my attempt to apply of 4 principles: (1) a simple signal path, (2) +9v trace next to a ground trace, (3) star grounding, and (4) grounded guard traces.  i learned them from a bunch of folks, including Basicaudio, MartyMart, puretube, and R.G.

the signal path is marked off in darkish blue.  i hope that you can followi it going up the left side, down the middle, and back up the right side.  i tried to avoid twisting back and forth in tight little zigzags, something that often happens if i am just trying to get a tight layout because of the way components get lined up in rows.  what you see is piece-wise linear.  still there are a couple of tight spots.  the upper left-hand corner where the gain pot hooks up and the upper right-hand corner where the tone section hooks up.  i am guessing that these are o.k.  any thoughts?

the +9v rail is marked in red.  several different ground regions are marked in two shades of green.  notice that i have ground on either side of the +9v rail, wherever it goes.

star-grounding, as i understand it, brings several branches of ground together at the ground lead of the big supply filter cap, C14 in this layout.  i have taken sections separated by coupling caps and connected their grounds indivdually to the location of C12 (roughly speaking).  the input section has its own branch (the light green patch on the lower left.  gain and Q2 have the next dark green patch, and so on.  using the coupling caps as demarcations was my idea.  is there a better approach?

finally, you will see that ground fill or traces also surround most of the signal path.

after comment, i will revise this and post it as a new dr. boogey layout.  the schematic is the same one as for my most recent dr. boogey layout: schematic.  here is the layout:

[Ardric]

ii am hoping to learn more/better by having this layout critiqued here.  and i hope others will learn, too.

What a great idea!  I wish more of this went on.  It's easier to learn from practical examples, and a better layout for this popular circuit would be a great help to all.

still there are a couple of tight spots.  the upper left-hand corner where the gain pot hooks up and the upper right-hand corner where the tone section hooks up.  i am guessing that these are o.k.  any thoughts?

Well, I'm no expert, but I'll blab away anyways....

You've used vertical (standing) resistors throughout, yet there's still a fair bit of empty space on the board.  It could probably be shrunk a lot further.  But that's not important right now.

C14, the PS filter cap, looks to be falling off the layout.  R2 is pretty close to the edge too.  May cause mechanical problems.  Oh, and how about some mounting holes?

I wish R5 was closer to Q2's gate.  The blue signal wire from Q2 goes through C18 and C5 before hooking up with R5.  This wire is very high impedence and sensitive, so I'd try to get R5 closer.  The other Q's gate resistors are tucked up against the JFETs except for Q1.  Q1 doesn't have a series gate resistor, just R1 for bias.  I'd put a little resistance in series with it to help C17 work properly, a la fetzer valve.

The presence network, R15/C13, carries strong HF content and is awfully close to Q2's gate.  Even worse, the presence pot is right up against the gain pot.  It might help a lot if the knobs were re-ordered:  gain, bass, mid, treble, presence, volume?  The bass pot is less likely to leak to it's neighbours.  Good that you gave the gain pot it's own ground.

I'm personally dubious of the +9 rail for everything.  My preference is... battery though a small series resistor, cap to ground, protection diode to ground, and we have +9 for Q5, Q4 and Q3.  Another series resistor and cap to ground from that rail, and we have the rail for Q1/Q2.  Is this pointless?

using the coupling caps as demarcations was my idea.  is there a better approach?

Seems reasonable to me.  Q1 and Q2 are in opposite phase, so hopefully anything they do to the gnd and power rails will cancel somewhat.  Same for Q3, Q4 and the follower Q5, which is the same phase as Q4.

[markm]

Just as an aside from this topic I have to say gm your website has gone from excellent to Outstanding!
Nice work indeed.
BTW, I had thought about taking on this circuit and making a layout for it as a "fun" project but, it truly frightened me too much! 

[John Lyons]

Very nice Gauss, I like this open layout ideas thread.

There should be a 68K resistor before the gate of Q1 as Ardric mentioned (pretty sure it's on the original schematic) what this does is work in conjunction with C17 to guards against RF pick up and also creates the Miller Capacitance for the FETs that tube have by nature. Sets a similar capacitance curve...rolls of some of the super high frequencies.

R5 could be closer, just a matter of shuffling around C5 and C18. Maybe moving C15 and moving the left side of the board closer as well. The only thing that would really get too close are the first two trimmers and that's not a big deal.

The Cap and resistor that are off the board a little are no big deal. The board won't stop at the trace anyway.

The presence and Eq components are a bit close to Q2. This gets into the "Linear" layout area that we want to strive for. The EQ section is at the end of the line and is sensitive anyway. Lots of gain here. Wrapping it around to an earlier Stage (Q2) is "oscillationville".
I would try to swing those components to the right and you'll probably have the widen the board a bit to get it to work.
Maybe lowering the Last trimmer and laying out the pots so the presence is just before the volume. That way you don't have to put the presence components all the way over to the top left and close to the earlier stages.
In marshal amps this is the place they go anyway. The presence control in amps comes off the Output transformer and is the last thing in the line. Lots of gain and current here.

The point about a small series resistor and adding another cap and resistor to power Q1 and 2 sounds good. More capacitance is fine and the resistor would be more along the lines of RC filters in amps.

Adding theprotection Diode is aways good as well.

I pretty much go along with all of Ardric's post don't I ?

Looks like a good start. Just shuffle around the EQ section to get away from the input stages and were close...

John

[gaussmarkov]

thank you all!  i will give this another crack tomorrow.  regarding the 68K resistor on Q1, i missed that somehow.  it isn't on the schematic that i found here and that i worked from: http://geocities.com/electrictabs/dr.boogey.png.  can someone point me to the right version?  or perhaps there is a thread where that got added?

again, thanks!  i'm sure that others are learning from this as well.  and  we'll get a better dr. boogie layout out of it to boot.  who says nothing gets done by committee? 

cheers, gm

[Pushtone]

regarding the 68K resistor on Q1, i missed that somehow.  it isn't on the schematic that i found here and that i worked from: http://geocities.com/electrictabs/dr.boogey.png.  can someone point me to the right version?  or perhaps there is a thread where that got added?

I just finished a hissy but otherwise well behaved Dr Boogey and there is no 68k anywhere in it??

After reading all the DB threads I could find, I'm under the impression the "Miller Cap" was achieved solely by adding the 220pf cap between the transistors gate and drain. I was planning on adding this using Gaussmarkov's schematic as a guide. So, is there more to adding Miller Caps than just a cap?

Yes please, someone post a link to the thread where this comes to light.


Nice work on your layout.
Why did you not connect the two ground traces just to the left of C1?
I see a jumper that does the same. Whats the reason for it not to be connected?

[John Lyons]

I guess I just added the 68K myself, sorry about that....I think on the layout it's a jumper. It help with the miller effect  to set a roll off in conjuction with the 220pf from gate to source.
This explains it: http://www.aikenamps.com/ look under tech info > advanced > miller capacitance Also see the grid/gate resistor article

Pushtone: Gaussmarkov is using satrt grounding on this layout. Each section is connected to the central grounding point. This was each section gets a clean ground reference. This way dirty or poluted ground areas do not impart noise to sensitive areas. Also explaind in the above link.



John

[mojotron]

...I'm under the impression the "Miller Cap" was achieved solely by adding the 220pf cap between the transistors gate and drain. ...

That would be 2-3pF from gate to drain, or approximating this with a 220pF cap from gate to source.

The parasitic loss is multiplied by the gain when you go from gate to drain.

The 220pF G-S "Miller-Caps" do help with getting a more amp-like sound rather than sounding like just another pedal.

[mojotron]

I guess I just added the 68K myself, sorry about that....I think on the layout it's a jumper. It help with the miller effect  to set a roll off in conjuction with the 220pf from gate to source.
...

Yep, I did the same thing and that's what I thought too. I also added input/ouput coupling caps - along with a rev-volt protecting diode - it's something I try to always do.

[MartyMart]

I guess I just added the 68K myself, sorry about that....I think on the layout it's a jumper. It help with the miller effect  to set a roll off in conjuction with the 220pf from gate to source.
...

Yep, I did the same thing and that's what I thought too. I also added input/ouput coupling caps - along with a rev-volt protecting diode - it's something I try to always do.

Yup +1 on all that, also I think that I stuck a 33k or 47k where the 68k is being used, a bit like the fetzer valve
input choice.
MM

[Nashtir]

Just a little suggestion for avoiding the beast from screaming..and what about pcb mounting jacks?

[gaussmarkov]

After reading all the DB threads I could find, I'm under the impression the "Miller Cap" was achieved solely by adding the 220pf cap between the transistors gate and drain. I was planning on adding this using Gaussmarkov's schematic as a guide. So, is there more to adding Miller Caps than just a cap?

the miller caps are in there.    i did catch that part of the wave. 

[Pushtone]

I guess I just added the 68K myself, sorry about that....I think on the layout it's a jumper. It help with the miller effect  to set a roll off in conjuction with the 220pf from gate to source.
This explains it: http://www.aikenamps.com/ look under tech info > advanced > miller capacitance Also see the grid/gate resistor article

Thanks John for explaining that.
I see the jumper you speak of in Buck's layout.
I'll socket it and try different values after I add the Miller caps.

Thanks for posting the Aikenamps link, I think thats the second time you pointed to it in reference to the DB.
Made more sence this read through.

And thanks Mojotron for correcting my error. Gate to Source on the Miller cap, got it. Thanks

[Pushtone]

I took the liberty to scale your layout. I wanted to see what enclosure it fits in.
I matched the trimer pads to scale it but didn't look if the right value caps would fit.

I'm I close?


1590BB bottom outline shown.

If so...

Its a super nice fit in a 1590BB sideways. Plenty of room for the battery and FS.

Nice work!  Its still about the size of Bucks layout I'm using, maybe even a little smaller.

[John Lyons]

Looks like a good fit but sure tight on the pots. Not sure if those are scaled 100% accurate but They are touching in the mock up there. Too tight for my comfort. Hopefully they are actually smaller so there is a little slop room in between.

Did you make that Hammond template pushtone or was that a data sheet thing from hammond?

John

[gaussmarkov]

the layout is on a .1" grid.  25 x 16.  i cannot tell whether your scaled version is bigger or smaller, pushtone.  waddya think?

i just finished a revised version, same size and i will post it shortly.  i think my original layout was 22 x 16, so i haven't added many columns.  everything fit on the last one, caps and all.  i use the datasheets to make my component outlines and so far those have been reliable. 

[gaussmarkov]

new schem and new layout.  i hope i incorporated all of the suggestions.  there are now two +9v rails, both with RC filters.  the polarity reversal diode is there.  i moved all the tone section to the upper right-hand corner--is it too tight?  and the presence pot is beside the bass pot now.  i left bass, mids, treble in the original order because flipped over they are in the order one expects.  i suppose that one does not have to put all of the pots in a straigth row.  and if necessary the presence pot could be shielded.

also R5 is now much closer to Q2's gate.  will that do?  it could be closer still, no problem.

everyone, thanks for the help.  please feel free to critique this version also.  as soon as it passes consensus, i will post all files:  eagle, graphics, and pdf project file.

[John Lyons]

Looks like a winner Gauss
One thing that I do is to have the pots layed out like this:

Looking at the finished pedal with the shafts face up in two rows of three knobs each.

Volume  Presence  Gain

Treble    Middle      Bass

This way you can have the volume directly above the "out" pad on the board, the gain pot above the gain pot pads and the treble mid and bass controls in a row on the bottom with short wires . This is good because the treble wiring is right next to the gain wiring otherwise. Which is like having the end of the circuit next to the input of the circuit and will cause oscillation. I use shielded wire from the gain to the board and from board in/out and in/out jack to the switch. Some people have had success without doing that but better safe than sorry.

John

[Pushtone]

Looks like a good fit but sure tight on the pots. Not sure if those are scaled 100% accurate but They are touching in the mock up there. Too tight for my comfort. Hopefully they are actually smaller so there is a little slop room in between.

Did you make that Hammond template pushtone or was that a data sheet thing from hammond?

John

Basicaudio, thats the pdf from www.hammondmfg.com, scaled and edited in Adobe Illustrator.

The scale was just for the layout part. I know six 16mm pots will fit cause I just did it for a "Bucksears" version.
I  took Buck's layout literally and put all six pots in a row even though I would have preferred a different order to the controls.

I was expecting your (Gussmarkov) layout to be bigger, ya know with more space between parts and all.
I was expecting a 1790NS size enclosure would be required. Like what Basic posted in the Pictures thread the other day.
It's great that you kept it small. You got skills Guss! I'm blown away that you totally moved the PRESENCE pot to the other side so quickly.

Your schematic is just what this project needed.
Documentation of the evolved Dr Boogey. For the little pepole.

Thanks in advance Gussmarkov! 

I would be honored to build on your (finalized) layout.
Then I could make a direct comparison between Electrictabs original schematic and Bucks original layout (just finished) with your improved schematic and layout.
And I'll be able to do it in the same enclosure with the same parts layout to boot!

[John Lyons]

Ok, cool. I didn't mean to say that the scaling was wrong.
Just that I didn't know how close it was as pictured verses in real life.
I admire being able to get tolerances that close.
I er on the side of larger enclosures so I have some room to work.

Thanks for all the work again here gauss and to those who gave their input.

Here's a different pic of mine with the two row spacing.



1790NS size box in Red Texture powdercoat from Pedal Parts Plus

John