Mini Sample Hold - Transfer Layout

[Kevin Mitchell]

I find myself dinking around with DIYLC when things are quiet. So I'll be sharing the circuits I come up with in means to archive and develop/improve them.

If you've ever played a Maestro FSH before you'll quickly learn why the sample hold half is sought after. The quick blips of the OTA based filter is mesmerizing to say the least. This effect is used in quite a few popular rock songs. Off the top of my head I can list RHCP, Audio Slave and The Mars Volta as a few of my favorites that had utilized such an effect (though lets be real, they were likely digital modelers such as the L6 FM4). Well here's the real deal adapted to a more modern design - using the most of the LM13700.

MSH - Mini Sample Hold
My transfer layout here
BOM and build notes here
My revised schematic here (origional by nocentelli)
Original discussions here



Please chime in with any questions or concerns. I'll be etching the first one to verify the layout some time this week.
-KM

[rankot]

Is there a demo for this somewhere?

[Kevin Mitchell]

Is there a demo for this somewhere?

I had put up a video of it on a breadboard in the original thread - almost two years ago  I gave my old veroboard proto to a friend. Maybe I can dig up a track.

I'll put up something of "quality" after I build it up. I'll look things over tonight and maybe I can bang it out tomorrow night.

-KM

[Kevin Mitchell]

Was having trouble getting a satisfactory toner transfer. I might leave the clothes iron behind and try out some alternatives tonight. I've made some changes to the layout. There were a few components that I wasn't comfortable with the ground routing. Price to pay when you cheat with ground fill 



-KM

[rankot]

Lovely PCB!

[snk]

Is there a demo for this somewhere?

Nice PCB, thank you for sharing !

[EBK]

The sound at the beginning of that video reminded me a lot of my Creaky Floor with an envelope filter in the fx loop:
https://www.diystompboxes.com/smfforum/index.php?topic=121805.msg1146642#msg1146642 (first video)

[Kevin Mitchell]

Just pointing this out in case it was overlooked 
Though they are in theory the same circuit this Mini Sample Hold has that small change "using the most of the LM13700" - replacing the JFET buffer with the unused darlington buffer on the LM13700. So we can hold onto one of our discontinued JFETs 

Trying to get it done before I'm off for a backpacking trip out in NY.

-KM

[Mark Hammer]

I'll put in a plug for what I've termed the "droop function".  The idea is that one provides a less-than-perfect "hold" by having a high-ish value resistance to ground from the storage cap.  It's illustrated here: https://www.youtube.com/watch?v=YbWtreDE7tM although I get the droop/step switch positions confused.

[Kevin Mitchell]

Taking this project from the back burner and to the foreground. I still need this thing on my pedal board



Will be back soon 

-KM

[Mark Hammer]

Just finished drilling and tinning the PCBs.  Looking forward to firing one up later today.  I will be incorporating a "droop" option, which would be something like a 1M-2M2 resistor in parallel with the 47nf "hold" capacitor.

I retouched your PnP layout a bit.  As much as I understand the rationale for fill-in-the-gaps layout software, I'm not a huge fan of that approach, as it tends to result in unintended solder bridges when I use it.  So here's my retouched version that creates as much reasonable space between pads as possible.  Use whatever you feel comfortable with.

[Kevin Mitchell]

Cool! 

Yeah as I've said - I cheated with the ground fill. Sadly when it comes to DIYLC you can't apply fill rules. But I don't mind the results since it precautions me to be careful and also to run continuity checks before attaching any wires. In that respect - I'll be using legitimate solder masks for my projects moving forward which will make the fill easier to work around.

Trying to step up my home-brew game 

-KM

[Marcos - Munky]

Just saw this one! I have a half populated board for a fsh just because of the sample hold part. This one looks more interesting, since it's more compact.

I noticed the noise transistor is wired as the original fsh schematic. I recall I saw this connection when I was searching for some fsh info before etching my fsh board, so maybe it's something to try on this circuit too.

Btw, Kevin, which software did you used to draw that layout? It looks beautiful.

[Kevin Mitchell]

Btw, Kevin, which software did you used to draw that layout? It looks beautiful.

Thank ya 
I used DIYLC with a few custom touches.

Regarding the noise transistor pin swap - that was discussed in the original thread (last link on my first post). It's been a while but I recall having better luck getting a nice musical range with the original configuration. But then again it's likely about luck of the draw when it comes to noise transistors. Whatever get's you there 

-KM

[Mark Hammer]

Which is why I installed a socket, in order to audition transistors.
The boards are stuffed.  Wiring them up (I made two) will have to wait until tomorrow.

[Marcos - Munky]

Just another question. Are those fet pins correct? I mean, the D S G in red doesn't match the jfet symbol. Which one is the correct one?

[Kevin Mitchell]

Just another question. Are those fet pins correct? I mean, the D S G in red doesn't match the jfet symbol. Which one is the correct one?

Had to wrap my brain around this. Thought I had it cleared up when I did the layout 

Sorry guys. The mistake is the jfet label. My main go-to jfet is the 2N5457 which is what they should have been labeled. The tonepad layout labeled pin 3 as "G" when it's actually D! So that mixed me up. But after looking at everything - my schematic is OK - it's just the jfet choice that was wrong.

-Tonepad layout is oriented right - but mislabeled the 3rd pin.
-My layout is oriented right - but mislabeled my jfet choice!
-The schematic checks out - just didn't jive with the way the BF245 were facing - which are now 2N5457

So if you're using the BF245, flip them around. I've updated the jfet names to what they should have been.

-KM

[Mark Hammer]

And if using a 2N5457, orient the transistor as graphically depicted on the drawing?

[Kevin Mitchell]

And if using a 2N5457, orient the transistor as graphically depicted on the drawing?

Yes! I've changed the jfet choice to accommodate this. BF245A is the substitute you'd have to flip around to use.

-KM

[Marcos - Munky]

Thanks for the reply. I'll have to look at it again later when I'm home, since I'll give a try on drawing a 1590A layout for it and all my files are on my pc. So basically I'll follow your layout for the pinout, using a 2N5457 as it is also my go-to jfet rn. Hope I can do a 1590A layout, I think 1590A is pretty mini