Fraverb Question

[KazooMan]

I built the Spinsemi FV-1 based Fraverb from the Tonepad site a while back.  It took quite a bit of troubleshooting to get it to work and I documented all of the issues I uncovered in a build report over there.

Yesterday I got an email from someone who is going to build the pedal.  He asked me about some mods that are shown on the schematic (here:  http://www.tonepad.com/getFile.asp?id=122) that are intended to provide for mixing the dry and wet signals.  There is NO documentation about these modes (cutting some traces and adding a few connections and components).  The pcb transfer and component layouts do not incorporate the mods.

I can see what they are trying to do, but I don't think the indicated mods will accomplish the job.  They are running the input into both channels on the chip.  Spin semi says you can do that for a mono setup, but they tell you to only use one of the outputs.  The mods as shown have the two output channels going to a stereo jack.  The hookup of the dry/wet mix pot is what seems strange. 

Do you think that this would work as intended?

[slacker]

It should work. The Q1 buffer takes a mono input and sends it to both the FV-1 inputs, you need to do this for mono use because some of the patches are stereo with a different effect on each channel.
The dry level pot then takes the signal from the Q1 buffer and sends it into the Q2 buffer. That part is a bit confusing as the schematic shows a trace cut before Q2, this shouldn't be there, it's for if you're not using a dry mix pot, the green mod. There should also be no connection back to the input jack. I think the idea behind this is to stop the output being fed back to the input.
The dry and wet signals are then mixed at the output jack tip. This will give a mix of the left channel and dry. For mono use you probably want to connect the right output to the tip as well, otherwise you only hear the left channel. Don't connect the left and right outputs together at the FV-1, build it as shown but connect both outputs to the tip.
A better way to do this would probably be to use the second buffer as an output buffer, connecting the dry mix and the wet outputs to it.
I'm not sure how useful this mod is though. Most of the effects already have dry signal in them, this is slightly delayed because it's gone through the FV-1. If you try and mix in dry signal you'll probably get weird phasing issues.

[KazooMan]

Thanks for the quick response.

You know, I didn't realize that this was supposed to be two different mods!    Than's why I couldn't see how it could possibly work.  The layout has traced highlighted in three colors and I assumed that both the green and purple connections were intended for use.

You are correct.  If you omit the green connection, and restore the cut connection to the cap then I can see how the signal path works.  

However, if one were to use the green signal path into Q2 where should the output of Q2 go?  I assume it was intended for the right input of the chip (reconnect the connection from the 1k resistor).  If that is what is intended shouldn't the input signal for Q2 be coming upstream of Q1?  That is, basically having a single input running through the two parallel circuits and into the two inputs on the chip.  As the green path is drawn (with the cut traces restored) the right hand chip input is going through both stages.

They could sure use some documentation on this one.  

[slacker]

I'm not sure what the green mod is supposed to do, it could be to give a separate dry out.

[MusicianMark]

You guys rock.  Thanks for clearing-up the confusion on that schematic.  I'll have a go at this with the original layout, leaving options on the PCB for the dry mix if I want to test it later.