Selecting the right Multiplexor - Pedal order switching

[lukatosh]

Hi Everyone!

Best Regards from Chile!

This last days i've talking with Tom (@ElectricDruid) about switching pedals using the AD75019 and other arrangements like the one proposed by RG about using smaller multiplexor's like the CD4051. I would like to touch some points here and ask for your help and guidance.

We agree that very few guitarists would fully use the "16x16" possibilities of ordering pedals offered by the AD75019 ... Then, a good starting point, as DSM suggest Here, would be separate the loops in two blocks. One fixed and the oder with the order change capabilities, offcourse, taking the design proposed by R.G.

While i was looking for alternatives to the CD4051, i've came across several alternatives. But looking at datasheets, a lot of terms come through:

- On Resistance (ohms)
- Different types of current leakage (uA, nA, mA)
- Different types of capacitance (pF)
- Chage injecition (pC)
- Off isolatión (-db)
- TTL control lines
- Voltage supply

Some candidates  may be de DG508, ADG5048 or the MAX308 but i dont really know what value of those parametters tells me that the chip is a good candidate. Their datasheet says that they are improved replacements for the classic industry CD4051. As far i know, a good voltage amplitude will allow to manage propperly audio signals and a TTL logic compatible will allow me to controll it whith arduino or 5v logical...

In between designs they claim to have "the lower on resistance" but is this a good thing?... for instance, how do I know if buffers are needed? and so on...

if someone could helpe to understand, in practical terms, what those parametters mean or how interpret their values, it'll be so much helpfully.

Here are the datasheets :
AD75019
ADG5408
MAX308
DG508

After that..the thing is about costs...for an N loops, R.G design uses N+1 Multiplexor. For 4 loops, 5 chips are needed and with that you almost reach the cost of the AD75019...

Well... any help will be appreciated. thanks so much!

[ElectricDruid]

Hi Lukas,

Let's see what everyone has to add to our little conversation! After all, I'm sure plenty of other people here have considered doing what you're thinking about. Maybe they've got experience to offer.

[Mark Hammer]

One of the ways to simplify matters is to think in terms of "nested loops".  So, one loop could be A->B or B->A, but be treated by whatever master controller as a single loop with the added flipping feature.  A second choice would be a  combination of loops C and D, that can be C->D or D->C.  That first pair, and second pair, could be treated as flippable, the same way that the two loops within each pair are.  Of course, the big consideration is just how much order flipping one wishes or needs to do.  The configuration I just pitched - pair 1 (loops A and B), pair 2 (loops C and D) - provides for an extensive range of possibilities.  Is it "enough"?  I can't say.  But I think that breaking the entire goal into "modules" might make it more achievable, and maybe even expandable.

[Ripthorn]

If you are okay with using a microcontroller, I think using a cross point chip would be easier. I've had a design on the back burner fir a while that does this. You could then do up to 8 stereo loops switched or arranged in any order. Of course, those chips only come in smd packages, but are rather straightforward top control using i2c.

[digi2t]

Don't know if this will help, but you're welcome to it.

I have a couple of 360 Systems AM16 16x16 Audio Matrix units. I also have the manual for them, which includes the schematic at the end. Perhaps it might help with the design. It's old kit, but maybe it can contribute some ideas. Here you go;

https://drive.google.com/open?id=1eqZryUnMMUImtaaYtHgbffGRytDIM0mi

[lukatosh]

Thanks so much for all your replies!

It is interesting to analyze the way in which the thing of "changing the order of the pedals" could be treated... There are many valid options but as Mark points, well never know if it is enough.

I like the idea of design a modular arrangement... But as I said, in costs this could be too expensive vs the alternative of using a 8x8 or 16x16 crosspoint switch.

If you are okay with using a microcontroller, I think using a cross point chip would be easier. I've had a design on the back burner fir a while that does this. You could then do up to 8 stereo loops switched or arranged in any order. Of course, those chips only come in smd packages, but are rather straightforward top control using i2c.

What chip did you used? Did you ever tried it?

Don't know if this will help, but you're welcome to it.

I have a couple of 360 Systems AM16 16x16 Audio Matrix units. I also have the manual for them, which includes the schematic at the end. Perhaps it might help with the design. It's old kit, but maybe it can contribute some ideas. Here you go;

https://drive.google.com/open?id=1eqZryUnMMUImtaaYtHgbffGRytDIM0mi

Thanks so much! Very usefull info!! The system employes input and output buffers and uses a couple of 8x8 crosspoint switches. Nothing more than that.


I still have a couple of questions... hope you can help me.

1.- Since on most chips the supply voltage limits the signal amplitude that can be processed, What could be a good powering option? The easiest would be to use a MAX1044 / LT1054 to get +/- 9V but ... would this be enough?

The A360 powers the chips widh +/-5V. So then...Wich are the common amplitude values of a guitar/effects signal?

2.- Loking for the right chip: Wich parameters do i need to compare or to loo for? (Ron, Charge Injection, etc) and their values considered as "good".since there is no ideal chip, it's a trade off thing...

3.- Buffers... the need of them is related to Ron, Capacitance or other parameters of the chip? To determine if i really need them or not.


Well... I've ordered a couple of DG408, the cheapest mux that i could find. TTL levels compatible

- Ron: 100 Ohms
- Cs(off): 3pF
- Cd(off)26pF
- Cd(on): 37pF
- Charge Injection: 20pC
- Off Isolation: -75db (it's labeled pF)

But don't know if it's a good candidate. I will try it on and post the progress. Thanks so much!!

[merlinb]

FWIW we use DG411 at work.

[digi2t]

Don't know if this will help, but you're welcome to it.

I have a couple of 360 Systems AM16 16x16 Audio Matrix units. I also have the manual for them, which includes the schematic at the end. Perhaps it might help with the design. It's old kit, but maybe it can contribute some ideas. Here you go;

https://drive.google.com/open?id=1eqZryUnMMUImtaaYtHgbffGRytDIM0mi

Oh, I forgot to mention, I also have the .bin file for the EPROM for these units, if ever you need it. I know I said that I had a couple of units, in reality, I have three. One of them had an older version software, so I pulled an EPROM out of one of the more recent units, read it, and updated it. I saved both versions for posterity. I can't remember what the difference was between the two versions. Some functionality differences in how the patch chains could be built and saved I believe. It was long ago, and many brain cells have past on since.