GEO Polarity reverser and buffer question

[Pushtone]

I'm working on the PCB for another parallel effect mixer like in JD's Parallizer article.

My question is:

Do I need to stick a buffer stage in front of the GEO polarity reverse circuit?

Can it do the work of a unity gain buffer and polarity reverse?

Thanks, Dave

[R.G.]

The input signal source drives Rbias, R1, and R3 in parallel.

What's your signal source impedance?


If it's raw guitar, yes, you need a buffer in front of it as a practical matter.

[bent]

Hello pushtone,

do you have a complete schematic of the reverse polarity circuit with all the detail of parts...?

I want to build the JD's Parallizer... but i dont have all the info....

i have test the mini-mixer and it's working perfectly, but missing the reverse polarity....

if you have it , can you send it to me....or post it here....

thank you in advance...

bent

[Pushtone]

I want to build the JD's Parallizer... but i dont have all the info....

Then we are in the same place because I want to build one too. 

do you have a complete schematic of the reverse polarity circuit with all the detail of parts...?

Just what is already noted in JD's article (the GGG simple mixer and GEOFEX.com polarity reverse).

Whats missing? The values and voltage divider for Vbias. Anything else missing from R.G.'s schem?

i have test the mini-mixer and it's working perfectly, but missing the reverse polarity....

Same here.
Did you see my other thread?
I'm actually quite impressed with JD's simple mixer for parallel effects mixing.
Seems to work great! I did up the pot value to 100k but didn't touch other values.
I see no reason to add additional buffers to the inputs.

if you have it , can you send it to me....or post it here....

Well, that's the idea.
I started working on a layout, but I need some help and I'm not exactly fast at this stuff.


BTW:
I'm designing the layout to fit a 125B Wildmouse box.
This parallel effect mixer will have TWO effects loops and TWO mixer channels plus a bypass footswitch.

[Pushtone]

First layout question...

I have decided to base the buffer and polarity section on the TL072 opamp.

Should I combine the buffer and polarity circuits on one TL072...

Or should I group two buffers on one TL072 and two polarity circuits on another TL072?

Or maybe it dosen't matter? Let see how it shapes up.

Dave

[Pushtone]

Grouping the buffers on one IC is working out better for me in DIYLC.

Dave

[R.G.]

Should I combine the buffer and polarity circuits on one TL072...

Or should I group two buffers on one TL072 and two polarity circuits on another TL072?

Or maybe it dosen't matter? Let see how it shapes up.

1. Signal flow
2. You

[Pushtone]

1. Signal flow
2. You

OK I get the signal flow point.
I started with buffers grouped on one IC.
I've trashed that and am working on a new layout with the buffer and polarity on one TL072.
Seems to be working better.

Thanks RG

[Pushtone]

UN-verified layout for a guitar buffer with polarity reverse switch.

**EDIT: I uploaded a new pic with a more compact layout but with the same file name.
You may have to hit the refresh button to see it. **

C2 is the output cap on the GGG IC buffer schematic.
Do I need a decoupler between the buffer and the polarity circuits?
Do you guys think it should be an electro or film?

Schematics:
GGG IC BUffer
Geo Polarity Reverse


This layout is meant to be modular to create as many buffers as needed. Duplicate layouts would be joined at the gnd trace on the right side.
Now its time to breadboard this and fill in the missing values for the polarity reverse section.
Bent? Are you there? Got a breadboard?

[bent]

Bent?

Hello....

Are you there?

Yes... 

Got a breadboard?

Yes....

need to test something ? 

one problem.... working 12h a day , next day off-tuesday 

bent

[MadMac]

C2 is the output cap on the GGG IC buffer schematic.
Do you guys think it should be an electro or film?

C2 is electro.  The polarity is shown in the circuit.

This circuit looks awesome.  Can't wait until its finished.

[Pushtone]

Bent: It needs to be breadboarded to find the missing values for R5 thru R9.
Any suggestions for resistor values?


MadMac: The question about C2 is about weather or not a decoupler is needed between the output of the buffer and the input of the polarity reverse.
The whole circuit has 0.1uf decoupling caps at either end. Is C2 needed in the middle between circuit snippets?

In the layout I included extra pads so C2 could be either an electro or film.




There are a few things about the layout I don't like so much if using it to make a 2, 3 or 4-way splitter.
1. Input cap C1 would be redundant with multiple buffers. Should be redrawn so C1 feeds the input of all buffers.
2. The layout will need separate  INPUT and 9V leads going to each buffer and the mixer sections.


Here is a sample layout of two buffers and JD's simple mixer (less two channels to make a 2-way splitter/mixer).
It shows the problem of multiple off-board leads that would be needed for this layout.
I suppose I could throw a few more pads in for a "kluge" type solution with wires running under the board.




Anyway thats where I'm at with it. Can't really go any further until the missing values have be breadboarded.
I won't be able to do that for awhile so DIY.