questions regarding th-custom effects pro-cessor build

[schmolmo]

hey there,

i hope i'm asking this question in the right place, if you don't think so, please feel free to move it! (and btw, what a nice forum! already found a lot of useful information just by reading...)

i'm looking into building a loop switch with the following spec:

1. true bypass stomp switch w/ latch mode
2. one or two fx loops
3. filters on the fx sends
4. phase invert on the fx sends/returns

for points two and three, the th-custom pro-cessor v4 seems just about right, i've been wondering how i could achieve points 1 and 4... so here are my questions:

1. does anybody here know how the dry/wet potentiometer on the pro-cessor works? it has two fx loops, so is it like this (clockwise): wet a - clean - wet b ? 
2. does anybody know of a true bypass (relay based?) switch that also has a latch mode?
3. how would i easily implement the phase invert? sadly i don't have experience with circuit design, although i've built quite some pedals...

if you have any other idea about a diy build that would be more fitting, i'd be happy to hear about your recommendations!
thanks in advance for your help!

all the best from berlin,
moritz

[Mark Hammer]

First, willkómmen.  It's a terrible forum....which is why I've been here for over 20 years. 

The TH-V4 circuit is interesting.  All stages in the circuit are non-inverting so there is nowhere to tap a phase-reversed signal from.

Since there are two send-return loops, any need for phase-inversion is really only for one of those loops.

But before leaping into any modifications, one has to ask what the phase relationship is for whatever you want to put into the send/return loops.  If the goal is to handle anything in future, then a phase-inversion stage makes sense.

I think the simplest fix is to add a unity-gain inverting op-amp stage like this one between the common of one of the switches used to select filter-type/no-filter and its respective output jack.  Happily, the DC-blocking 10uf cap and terminating resistor are already in place.

[iainpunk]

welcome to the forum

the mix pot doesn't allow to blend clean if both FX loops are in use.
not using the return on one of the FX loops normalizes it to the filtered input, so if you want to clean blend, you should detach one loop.

you need 2 phase inverters if you want to mix 3-way

if you want to add a 3-way blend, i'd use 3 pots to determine each blend's level individually, instead of the crossfade the original has.

if you don't mind omitting the filters, here is a schematic of a build i did for a friend, it has the switches in blue to make it clearer.
its not true bypass, since its filled with buffers, but the switches can be whatever you want. you can just graft on a relay bypass with the toggle/latch functionality.





the 4 opamps in the main part are a TL074 and the power part is a TL072, of which one opamp is unused.
the diodes are 1N4007, but others from the 400x series will work too

hope this helps
cheers, Iain

[BJM]

I thought the Pro-cessor already had a 24dB Highpass filter and Lowpass filter before the Effects loop? I built the simpler version (Mad Box), without the filters and as Iainpunk wrote, the blend pot only blends the two loops, so not what you're looking for.

I'll leave the phase inversion and relays to the experts here but I did have some succses adding a switchable TRS jack to the pot and controlling the blend with a slighty modfied expression pedal (M-audio, also very cheap). So if you're looking to change the design that may be a fun thing too  .

I suppose you buy from Musikding? They also have a four-way splitter, maybe that togheter with the GGG mini mixer?