Doubling up the MN3008 as an MN3005

[aballen]

I decided to make a board for this.  I based this on the schematic from smallbear.  Mine is a little different in that it connects to an 8pin header on the edge, hopefully making a smaller board.

I wasn't sure, but I think that VEE, and VPP are supposed to all be connected to each other.  I think these are chip generated voltages.  I'm hoping someone can spot check it, and if its good I'm going to order a few.  If they work I'll see if there is interest enough to order a larger batch.

smallbear schematic
https://www.smallbearelec.com/HowTos/MN3005/3005_to_2x3008_SCH.pdf

Here is my schematic


here is the layout

[madbean]

You've got some mistakes in there. For an MN3005, negative ground supply, pin1 goes to 15v and pin 5 (or 8 in your schematic) goes to ground. The 100k resistor should be a pull-up (connect to 15v) not connected to ground. Pin8 on both BBDs (or pin14 in your case) should both be connected to Vgg.

Use this schematic as a reference. It's from the Aquaboy 2012 documentation. It's slightly different than the DMM way which your is based on but both varieties work.

Here A and C would be connected to 15v, and B and D connect to ground for MN3005/MN3008.

[aballen]

Is there an eagle part for the MN3005?

[aballen]

I'm totally confused here, when I look at the schematic up on small bear, pin1 is clearly GND.. how am I misinterpreting this?

[madbean]

I'm totally confused here, when I look at the schematic up on small bear, pin1 is clearly GND.. how am I misinterpreting this?

Because he's showing you how it is set up for a -15v supply, not a negative ground supply. MN3008/3005 were designed to run at -15v (check any Deluxe Memory Man schematic and you will see what I am talking about). This is pretty inconvenient by modern pedal standards so when we use our regular neg. ground supplies, the ground and power pins are flipped so the chips can run off a positive voltage.

http://www.alldatasheet.com/datasheet-pdf/pdf/87983/PANASONIC/MN3005.html

[aballen]

oh wow.  Ok, I'll try to put together another schematic based on your layout tonight.

After looking at the datasheet, I'm curious if a BBD reverb sounds good.

[madbean]

Actually, looking at that schem again on SB- it shows +15v (I did not notice that before). This is confusing to me. His schematic appears to be wrong for +15v operation.

[aballen]

Ok, here is another attempt.  This is based on your schematic Brian, mine is cluttered because I could not seem to get eagle to rename the supplies, so to be safe I drew the wires.  I also changed the header to properly match the 1-8 pinout on the board it will be plugged in to, to make it clearer.  This one look better?

Schematic


layout


Also, really appreciate your feedback, and the explanations so far.

[madbean]

Looks good! You know, here's what would make it better; move R7 back a bit so it is between C1 and R5. This way, you get the signal limiting (if it's needed) without it throwing off the bias voltage delivered through R5. Other than that you are good to go.

For some more reference about the apparent mistake on the smallbear schem, take a look at both the DOD FX-90 and DM-2 schems for the MN3005. You'll see that the negative ground setup follows just as I described (although these are for 9v, not 15v).

http://www.freeinfosociety.com/electronics/schematics/audio/pictures/dodfx90.jpg
http://www.freeinfosociety.com/electronics/schemview.php?id=128

[aballen]

thank Brian I just made that change too.  I also routed it by hand with fatter traces, and tried for a single sided, but did not quite make it.




What do you think?  Ready for an OSH park proto?

[aballen]

This is what the board will look like.  I wish I could move the 8 and shrink it a little more.   You think its ready to order?

[pickdropper]

Have you thought about the 8 connections going to properly spaced pin headers so that it could be directly soldered to the board (or inserted into a socket below).  If you used longer headers, one could use a deeper enclosure and just have this daughter-board hover above the main PCB.  It might save some wiring hassle and clean up the interior of the pedal.

[midwayfair]

Have you thought about the 8 connections going to properly spaced pin headers so that it could be directly soldered to the board (or inserted into a socket below).  If you used longer headers, one could use a deeper enclosure and just have this daughter-board hover above the main PCB.  It might save some wiring hassle and clean up the interior of the pedal.

+10^16

[Stomptown]

Have you thought about the 8 connections going to properly spaced pin headers so that it could be directly soldered to the board (or inserted into a socket below).  If you used longer headers, one could use a deeper enclosure and just have this daughter-board hover above the main PCB.  It might save some wiring hassle and clean up the interior of the pedal.

I was thinking about that too! If it weren't for all of the PCb mounted pots you could mount it on the underside, but that would work with a deeper enclosure...

[aballen]

I did consider that, originally I had an IC1 for that purpose.  I think this is more versatile since I might want to put two of these in a DBD or an aqua puss.  Depending on where this is being used two of these might not fit if they need to be attached like a daughterboard.  

For example, in the DBD and Aquaboy the BBDs are right on top of each other, trying to mount two of these would create overlap... I could modify it to work in this configuration... but then it would not work side by side.

The board mounted pots(which I love) might get in the way, so your stuck with offboard wiring pots or this, or hovering this board 11-12mm above some caps.  

I don't know, seems messy no matter how you slice it.  I'm thinking the smallest board give you more options for placement.... maybe I'll wait to see what the new DBD layout looks like.

Also bigger board means more $$.

I hear what you are saying about less off board wiring though, I do hate that.

Have you thought about the 8 connections going to properly spaced pin headers so that it could be directly soldered to the board (or inserted into a socket below).  If you used longer headers, one could use a deeper enclosure and just have this daughter-board hover above the main PCB.  It might save some wiring hassle and clean up the interior of the pedal.