PedalPCB 5-Loop True Bypass Switcher

[CR0SSBL4DE]

I'm wondering if they're using a combination of mechanical and solid state switching...

Relays to bypass, but solid state switching to route the order when a loop is active. That'd still technically be true bypass ...

I might have to crack one open just to see...

True by pass implies no buffers, but a direct cable from input to output, when the effect is off.
That said, it would not surprise me if marketing would coin the term even when it does not apply. (there has been Class AB amps marketed as Class A, because of the term "Class A" thought to mean higher quality than B or AB)

 

[Giorfida]

True by pass implies no buffers, but a direct cable from input to output, when the effect is off.
That said, it would not surprise me if marketing would coin the term even when it does not apply. (there has been Class AB amps marketed as Class A, because of the term "Class A" thought to mean higher quality than B or AB)

I’ve also seen MXR/DOD style SPDT “output bypass” switching (where the input is always connected) called “true bypass” since it used a click switch.

And don’t get me started on folks calling eyelet/turret/strip board “point to point” amps!

 

[Robert]

True by pass implies no buffers, but a direct cable from input to output, when the effect is off.

Right, what I'm suggesting is additional solid state switching when the effect is on.

For example, let's say we have five relays, the relays never change order, they're always hardwired in direct sequence.

When Relay 1 is switched off it is indeed true-bypass, a straight wire connection across it's contacts passing on to the next relay in the chain.
If they're all off it's a straight shot from the Input to the Output... True-bypass.

However, when Relay 1 is switched ON it doesn't connect directly to Loop 1, instead it goes to a matrix of switching ICs that can route that relay to Loop 1, Loop 2, etc.

Still technically true-bypass, but only requires 5 relays.

 

[CR0SSBL4DE]

Right, what I'm suggesting is additional solid state switching when the effect is on.

You mean like when all the effects are off? One effect off still means to route the signal from the effect before to the effect after. It still goes through the routing.

 

[Robert]

When any given relay is off it would bypass that channels switching matrix entirely.

I'll draw a diagram of what I'm describing when I switch off my soldering iron for the day.

 

[juice886]

I guess most likely in this case when the channel is on it needs a buffer to support such an electronic switching. So it is 'true bypass' only when the channel is off but involves additional components in the signal path when the channel is on. I guess that's what Robert means.

 

[Robert]

Exactly. I'm not saying that's how the Fender switcher works, just that it's a possibility.


This is extremely simplified, but this is what I'm describing:

One relay for each spot in the signal chain. When that block is active the relay is on and the digital controlled switching routes the signal to the appropriate effect.

When that block is bypassed the relay is off and that entire block of circuitry is true-bypassed.

If the desired order is [Loop 1] > [Loop 2] we (by way of the microcontroller) enable U1.1 and U2.1, and U3.2 and U4.2, then turn on both relays.

If the desired order is [Loop 2] > [Loop 1] we enable U1.2 and U2.2, and U3.1 and U4.1, then turn on both relays.

True-bypass doesn't necessarily mean "True-active".

This similar scheme could be used to add switchable buffers before and/or after each effect, a movable volume control, etc.






It's also entirely possible that Fender has a matrix of relays in there, I'm fairly sure that's how the GigRig G3 works.

 

[benny_profane]

Wild speculation is so unlike you, @Robert

True-bypass doesn't necessarily mean "True-active".

The hiccup there is that the copy makes a point to discuss the switchable input/output buffers. Any transistor switch will amount to a buffer of sorts.

 

[Robert]

We live in a world where diodes can be magical.

 

[benny_profane]

Silly me, I forgot. And a buffer is not a buffer.

 

[benny_profane]

What impact on impedance does CMOS multiplexing have?

 

[Giorfida]

What impact on impedance does CMOS multiplexing have?

Say goodbye to your high end. That was one of the big problems with the Craig Anderton electronic (CMOS) switch

 

[Robert]

The hiccup there is that the copy makes a point to discuss the switchable input/output buffers. Any transistor switch will amount to a buffer of sorts.

Yep, like I said, I'm not suggesting this is what's happening in the Fender gadget. I was just describing a method of switching that could be technically still considered true-bypass.

 

[giovanni]

Daniel from the GigRig discussed the fact that he wanted his switcher to never be buffered (unless you want to turn a buffer on) so I assume he has some sort of relay matrix in there? He didn’t go into details but I’m very curious.

 

[Robert]

Yep, I haven't seen one personally but I'm fairly sure GigRig states that the G3 uses a relay matrix.

 

[PapaBear]

I've only ever wanted to switch the order of my Wah to be honest, from first in line to AFTER the dirt.

I have a GuitarPcb board that has a double throw 4 pole switch, that you could make that easily. Be happy to send you one, I probably have the switch here too.

 

[CR0SSBL4DE]

My calculations are that for 100% mechanical routing and switching one would need:

[X = No. of loops]
No. of SPDT relays = 2 * X * (X-1) + X

1 loop --> 2 relays
2 loop --> 6 relays
3 loop --> 15 relays
4 loop --> 28 relays
5 loop --> 45 relays

I doubt that's what they are doing on the fender switcher. I wonder if jumping all the loops and measuring with input/output with a DMM would give you continuity. That's what I would assume for "true by pass switching". (also it has a volume control integrated)

I though of a way to do it with less relays:


(Sorry for the horrible quality, I don't have my phone around so I used my webcam)

This way the amount of SPDTs needed is a lot less. I didn't decompose the function, but it's basically L squared (5loops is 25 spdt relays. 8 loops is 64 spdt relays).

 

[Feral Feline]

I knew this thing was coming from a few posts elsewhere, but somehow missed there was this entire thread for it.


Only read first page, gotta hit the hay, but Carl Martin Octaswitch was mentioned as having dipswitches — it wasn't the only one!
Early GigRig switchers and Flex Reaction series switchers (4 loop, 6 loop, etc)...

I'll read the rest of the thread tomorrow and post something inane then.

 

[Feral Feline]

I once silently watched the big lebowski on a trumpet players IPad in the pit during a professional performance of West Side Story. Using it on a book isn't actually that far fetched.

Low brass gets a lot of rests and tacets in the theater world. Pay per note was off the charts.

Did you at least have captions/subtitles?

Or are you not only a good sight-reader but a good lip-reader, too?

---

Switcher-Looper options in the DIY realm beyond a bunch of 3PDT footswitches that I've looked at...

BYOC Super8, though Jimilee was not keen on it, I have one, too, and think it's cool in theory; there's also...
THCustom's "EFFECT CONTROL" 5-loop switcher. (been meaning to get this, but Robert's version would be preferred)
JMK's "EPIC BYPASS LOOPER", a project developed with THCustom above (and available there, too. (I have this one).
UK-Electronic's "8-WAY LOOPER", which has some minimal MIDI functionability. Been meaning to order this one, too.


So... yeah. There's only so many features you can pack into a 1032L enclosure or Hammond BX2...


IN / OUT order is important to get right (ie how I want it) — scoff at that statement but there's a number of smaller DIY loopers I've passed on because of the way the in/out jacks were configured....

 

[jimilee]

We're 8 pages in, I'm really chomping at the bit.