REQUEST: component values for Brownface vibrato layout

[Mark Hammer]

Trying to finish a harmonic tremolo for a buddy.  The layout provides for some parts that I don't have component value information for. 

Here's the Morocotopo layout I'm working with:


Here's the parts placement:


I thought I had a corresponding file with all the values, but it was this one below. It corresponds to RG Keen's schematic and to the above layout, but it kind of stops a few components short. presumably because the layout above include an additional gain recovery stage.  Possible the sought-after information is here in the gallery, but I couldn't find it.  If you know the values of the 3 or 4 highest numbered resistances and caps, it would really help me out if you could fill in those blanks.

Thanks for any help you can provide.

[R.G.]

I did a look in the archives, but I don't have that variant. I can probably come up with workable values for the stage, though. Do you have a schematic for that board? I guess I could trace it for a schematic, but I thought I'd ask first.

[Mark Hammer]

Here's your original Pro-in-a-box schematic.  I've left off the LFO because it's the same in every variant I have on my drive.  It's the output that is in question.


And here is the closest thing I have to the layout, with an additional gain stage on the output.  But you can see that the trimmer on the layout attenuates the fixed output of that gain stage, whereas this schematic shows a trimmer for adjusting the gain of that additional stage, and no adjustable attenuation of the output.  That's what has me wanting to know what the values of those last highest-numbered components are.  I thought I was okay for info and etched, drilled and stuffed the board, until I got to those last few parts, and realized I didn't know what was supposed to go there.  If anybody has a parts legend for this layout, I'd be obliged.

[Morocotopo]

Oh my lord! You´re using one of my layouts!
Hi everyone, long time since I've been here.
Mark, let me search through my files to see if I have the corresponding schem.

[Morocotopo]

Is this the schem you need? I think I made that layout using this. But It's been a long time.

[Mark Hammer]

Thanks, Ariel.  This schem corresponds to the layout about 95%, but the output gain-recovery stage is different.  Fortunately, brother RG generously dug around and found a layout that corresponded, electronically, AND had the component values listed.  The trimmer in the schem you show is used to adjust the gain of the BJT output stage.  In the layout I initially posted, that trimmer is for adjusting the output level of a fixed gain stage.  So, a little different.  But all good.  Thanks for chiming in, though.  Much appreciated.  Keep well.

[Morocotopo]

Oh, OK. Glad you could work it out.

I made this into a pedal using that layout when it was published, loved it. But later remade a new layout (much smaller) to fit it in a smaller box, and reused the original box for something else, so it doesn´t exist anymore.  So if you ever need to make another one I can provide a better PCB. And corresponding schem.

The file you used was made with Photoshop, it was one of my early attempts at making layouts. Around 2007 maybe? Those were the days.
Glad my little work was useful to you, albeit with a few snags.

Cheers.

[Mark Hammer]

I should learn to follow my own advice.  After trying for the better part of a month to get the Brownface harmonic tremolo working that RG kindly drew up, and Ariel generously made a layout for, I was getting nowhere in my troubleshooting.  I thought it might be a bad electro, cannibalized from another board.  I thought it might be a fried FET, a cold solder joint, solder bridge, or fractured trace.

Then, just for the hell of it, I decided to look up the pinout of the 2N5484 FETs I was using instead of 2N5952s.  Wouldn't you know it, their pinouts were opposite.  5484 gates and drains were on the pins where 5952 drains and gates were.  I desoldered and reinstalled the FETs, and the thing came to life.

      

[PRR]

5484 gates and drains were on the pins where 5952 drains and gates were.

Not sure how that comes out, but.... wouldn't the DC voltages be whacko?

[Mark Hammer]

Those I measured certainly were.  Being a rank amateur, I kept checking solder joints, and looking for "bad components".  Turned out I was the worst component of all.

[PRR]

Being a rank amateur

DEBUGGING - What to do when it doesn't work
"...list the voltage on each pin of every transistor"

I know where you are. I have been there, much deeper.

[R.G.]

At least you had components in there. I still have vivid memories of debugging for a looooong time on the bottom of a board with IC sockets that I didn't fill. Couldn't figure out for the longest time why nothing had the right voltages. 8-|

[Mark Hammer]

What messed me up was that, using an audio probe, I was getting signal at what I thought was the drain of Q1.  Of course, as I eventually found it, it was the gate and not the drain.  Signal at the gate of Q1, but nothing further down the line?  That should have been my clue, but I assumed it was the drain, hence okay, implying the bottleneck was further along the circuit.  Insert face palm here.