FX loop A/B... feasible idea?

[tommycataus]

Hey guys,

I came up with an idea and have no clue as to whether it exists yet. I have seen A/B boxes for switching amps, but I realised that I could make use of switching effects loops since it enables me to focus one loop on rhythm and one on lead:



This was my idea (although rather than having a buffered on-off footswitch I am planning on using true bypass). I was also going to put a couple of pedals like the ditto looper and a phase 90 between this and the amp for use with both rhythm and lead where required.

Any reason why this shouldn't work if wired similarly to an ordinary A/B box?

Cheers

[nick d]

      I've built two of these , using a schematic from BYOC , one as an A/B box , one built into a dual-channel Muff . Works a treat !

[tubegeek]

Any reason why this shouldn't work if wired similarly to an ordinary A/B box?

First: what a useful idea, and second: what a great picture!

No reason it should not work, I think your biggest worry may be the possibility of noisy grounds with the two sets of pedals connected to two different sections of the same device (the A/B box.)

I THINK - this might require a trial and error phase - you will want to switch the grounds as well as the hots when switching the two loops, so that the ground for loop A is not able to affect the ground for loop B when B is active, and vice versa. Or you may get away with switching only the hots.

If you do get hum/buzz, I think the uberslick way to do this would be with some relays that could delay the hot switching just a tiny instant until after the grounds switch, to avoid a "pop." But there's no reason to start there - a simple setup for proof of concept without relays is certainly worth doing.

If it were me, I would keep the buffer active at all times and just be sure to build in a clean and neutral buffer, but whatever.

[blackieNYC]

Shouldn't have hum problems.  RG answered my question about my very similar pedal and ground loops. Basically, watch out for multiple grounds on multiple circuits when plugging in your rig.

"In most circumstances, no, you won't have an issue.

In some cases, yes. The cases usually involve more than one amp, or an effect that is self powered from AC power. Some wall warts have ... um, less than perfect    AC isolation and can cause this issue. Some wall warts are more carefully designed and generally have no issues."
Take a look at my hand scrawled schematic, which your drawing does indeed put to shame.
http://www.diystompboxes.com/smfforum/index.php?topic=105154.0
If your buffer is off, you are passive.  Might keep it on and add a 2nd one for boost. On that switch there. I chose to turn mine into a 3 ch mixer- dry, loop A, and loop B.  A 3-way splitter follows the input buffer. I can have A,B, or dry together or by themselves.
There are a lot of things in my schematic that you don't need. The 3-way FET splitter (AMZ) works- unity gain only.  Brighter folks than I may differ, but I tried this with FETs and got (nice) distortion every time I tried to have a little gain.  It's the 9v battery limitation. Go TL072 if you want any gain at all.  This is a pedal you want clean and neutral.  If the boost feature is added to the pedal's output, then and sound/pedal string you bring up can be "lead".  Or boost off for unity. I blend distortions together, you can but simple RC filters on your sends- highs for one loop blended with lows for another. 
Your pedal is exactly where I started out with mine, it will do what you want as is, and now I'm throwing all this crap at you. Sorry. Too many options are what caused me to spend months on my splitter/blender.  But there are some fun circuits to incorporate.

[tommycataus]

Thanks for the responses guys. I've been undecided on whether to include the buffer so I'll probably just add a toggle switch. I'm glad you guys have built similar switching boxes with positive results, that's encouraging.

Tubegeek, I appreciate your kind words and will investigate switching grounds. Any suggestions on the clean and neutral sounding buffer?

Blackie, your feedback looper contraption looks amazing... I can hardly agree that my little diagram made with MS paint rivals the work you have done!

Thanks for all your help with this. I'll keep you updated...

Cheers

[duck_arse]

if yr going to have the buffer, you might investigate adding a "pickup simulator" as well. check amz for details.

[tommycataus]

Thanks Duck, that's a cool idea. Is there a reason why I've never seen this before? Does it make a dramatic difference sonically, or does it depend on effects in the loop... or is it all tonally subjective?

I guess I thought it would be a good idea in the event that all pedals in the chain are true bypass and some tone was being lost...

[duck_arse]

as far as I know, it makes fuzzing things like fuzz faces think they are looking at a proper pickup, instead of the arse-end of a boss, which they object to. and it's so simple to include.

[tommycataus]

Thanks Duck, I've built the box but not got to the buffer yet. The basic idea works, I've tested it with a couple of successful builds, although it seems to sap a little tone... I'll have to get the buffer sorted and fit the pickup simulator and report back. Hopefully I've done it right:

[duck_arse]

tell me your wiring is neater than that, please. I hate looking at wiring/vero/perf diagrams, they are too abstract for me. whereas a circuit diagram isn't (?).

are you using the case to earth all your jacks? and what type of leds are you using, dull diffused coloured lens types, or high efficiency/intensity types? if HE, those 390R will mean you'll be blinded, and they'll burn holes in the ceiling. I use 15k to 22k with he's but I don't like them bright or wasting battery power.

and I always use millenium 2's and dpdt footswitches.

[tommycataus]

No... I started drawing a pretty picture and it got out of hand so I added the switches diagram to the right which I guess is equally crap!
I should have mentioned that I am using the case to ground on this one since it is a prototype. I'm using diffused leds here but for the builds with super brights I tend to go between 10k and 20k otherwise it's painful!
I've never used millennium 2 before simply because I have a decent supply of 3pdt switches. Would you recommend it here or is it much of a muchness?

[duck_arse]

use what you have, as they say. go with the 3p. I'm thinking of doing a 3V Ge boost, and trying to think of a way to work the millenium from pos ground.

lucky for me, I have 1 only 3pdt, pulled from something that really needed 3 poles.

[Kipper4]

there is a pos millenium on the rg site i'm sure i've seen it.


here

http://www.geofex.com/article_folders/millenium/milckt.gif

[duck_arse]

I found it, but .....