Geofex - Transformer Coupled Splitter

hourglass · Jun 19, 2008

I'd like to build one of these but I generally fall flat on my face when it comes to translating a schematic into a PCB layout.

This time, I've tried to let the computer help me by putting the schematic into ExcpressSCH and doing a board design in ExpressPCB.

I've had a bit of trouble just getting all the traces to route without wanting to crisscross, but I think I've finally got all the connections in place.

If anyone could take a look at this and let me know if it's all connected properly I'd really appreciate it.

I'm sure there are better ways to do it, too, so if you have suggestions on what to do differently please feel free to post them.

Here is the original GEOFEX schematic:

My version of the schematic:

http://www.ryanadam.com/splitter/SplitterSchem.jpg

My PCB:

http://www.ryanadam.com/splitter/SplitterPCB.jpg

I've also placed the schematic and pcb files for the ExpressPCB programs in the folder with my images.

ExpressSCH file:
http://www.ryanadam.com/splitter/Transformer Coupled Splitter.sch

ExpressPCB file:
http://www.ryanadam.com/splitter/Splitter.pcb

EZ81 · Jun 20, 2008

Hi Hourglass,

adding one cap in series with R3 and connecting the bottom of R2 to a bypassed voltage divider would allow the circuit the circuit to work in single supply configuration (negative supply pin of opamp grounded, positive pin to 9V, 18V (or 27V, 36V if you want to go crazy with batteries) like Telefunken, ANT, Lawo, Siemens, V672 and would render that kludgy supply switching circuit obsolete.

You might also want to use a real opamp (5534, TL071, $$$ OPA***) instead of the 741.

HTH
Matthias

Bryson · Jun 20, 2008

Yes..as with the MXR Micro Amp. PC and schem here:

http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=70&Itemid=26

An LF351 can make a decent (fet) guitar buffer.

hourglass · Jun 21, 2008

Maybe something like this?

If so, that's a whole lot cleaner and easier to arrange on the PCB.

Ryan

New Schematic:
http://www.ryanadam.com/splitter/SplitterSchem-SingleEnded.jpg

New PCB Layout:
http://www.ryanadam.com/splitter/SplitterPCB-SingleEnded.jpg

ExpressSCH file for new schematic:
http://www.ryanadam.com/splitter/Transformer Coupled Splitter - Single Ended.sch

ExpressPCB file for new PCB layout:
http://www.ryanadam.com/splitter/Splitter-Single Ended.pcb

Denyle Guitars · Jun 21, 2008

Another way to do it is to use a Max1044 IC, as per the Geofex article. Either configure it for dual rails or keep you're current arrangement and double the voltage.

EZ81 · Jun 22, 2008

Hi Ryan,

The output jack without transformer needs to be dc-decoupled as well (I missed that in the original schematic). It would be easiest to move C2/C3 between the opamp output and R6/R7. One pin of C1 seems not to be connected to anything in the layout. I would also add a bypass cap to the power supply.

HTH
Matthias