Help please! A/B/Y wiring

[flateric]

Somethings wrong - I wired up a passive A/B/Y box this evening according to this schematic:

I'm plugging in
but the Y (A+B) switch just gives me a scary loud hum and the LED doesn't come on. I've rechecked all the soldering and corrected one error. Can you see any flwas in the schematic?
Cheers!

[JohnH]

Those switches with 3x3 lugs could be rotated 90 degrees. The ones that I buy would have the lugs horiz instead of vertical. LED polarity is another item that is easy to get back to front. I like the LLECARUD battery - horray for positrons!

John

[flateric]

The 3pdt switches I've used come from more than one source so it is possible the Y-switch is rotationally challenged. The LEDs are correct polarity, or as I like to say, ytiralop. I'll get the multimeter out when I've drained me beer. Cheers.

Just one stupid Q though: are A/B/Y switches intended to be used where the Y can be either an input or an output?
So you have a choice of feeding 2 instruments into one amp, or either one or the other, OR having a guitar plugged into the box and use it as a splitter to feed into either amp 1, or amp 2 or both?

[JohnH]

The box would do its simple job of connecting the O/I to A or B or both.
I think it would be OK for selecting one or other guitar input for example, but not both.

But two inputs feeding one output at once is prone to lots of problems in many scenariios. Two active inputs will fight each other and degrade sound and maybe damaged. Two passive guitars, will not give a balanced combination unless they are identical output impedances, and set the same volume. It seems to me that mixing inputs to a common output needs a mixer.

John

[flateric]

It would seem from this that when A+B is selected the signals from a fet inverted compared to B, so wouldn't this short them out? = big scary hum ?
I know there are A/B/Y pedals commercially available that allow for operation 'both ways' so the I/O (Y) can act as an input or an output, maybe their circuitry is far more complex than just a couple of switches?
For me, the main use will be for either having 2 guitars used separately into one amp, or for having one guitar and a tuner out. Ideally 2 guitars into 1 amp and a tuner out/amp mute would be best on stage. This should be relatively straightforward even for me to figure out.

[ashcatlt]

I'm not sure about the FET thing. I don't think you'll cause any damaging "shorting" type scenarios by mixing through this thing.

IF you had one guitar split to two effects AND one of these had an inverted output THEN you'd expect to get a certain amount of cancellation of the parts of the signal which were unaltered by the respective effects.

What will happen is that the two outputs which you're mixing will tend to load each other, and create a sort of voltage divider which could cause unpredictable volume/tone performance. The normal configuration for a passive mixer includes a resistor in series with each of the inputs. This helps to isolate and mix the two inputs some. You'll probably still have issues if the out-Z of the two input are significantly different.

Splitting the other direction (actually using it as a Y) also presents issues in that the 2 outputs will be in parallel with one another and will necessarily present a lower overall input-Z to your pickups. At best - when the two inputs are equal Z - your guitar will "see" half. It will never see more than the smaller input-Z. This is not something I'd worry much about with active/line-level inputs, but could equal tone suck where passive guitar pickups are concerned.

You could definitely get away with using the A/B function to switch between 2 seperate guitars. You don't need the Y for that.

[flateric]

Been looking at schematics for some other A/B/Y passive boxes, theres a Morley one where theres a 100k resistor across the A and B jacks.
What function would this serve?
Any way of eliminating the loud popping when I use the switches?

[allmektig]

Sorry about performing necromancy on this old thread, but I have a similar question.

A friend of mine wants to run his guitar trough two parralell effect series, plugged into two separate inputs on his amp, and he wants to be able to switch each channel on and off.

This is what I've come up with:

Would this cause any problems?
How can it be improved?

[JohnH]

I had a stare at that, and I think its good. Obviously you have thought carefully about it, since it avoids pitfalls such as having an off channel short out the guitar, and you have the off channels nicely grounded to keep them quiet, instead of just hanging.

I think it would switch quietly, but youd have to confirm hat by building it.

How about using another pole on each switch with a battery and a couple of LEDs and resistors to indicate status?

John

[allmektig]

Yeah, that was the plan all along, I just didn't put it in the drawing.
Anyways. I've put it together, and it works.
There are two minor problems though.
I hooked one output to my computer soundcard and the other to my amp.
When I was using the distortion channel on my amp, I would hear some noise that I believe came from my computer, since it disapeared when I switched off that channel.
But I guess that without using some elaborate scheme with transformers and active electronics, there's no way to get rid of that problem?

The other problem was an audible pop when I turned a channel on or off. Is there some way to eliminate that?

[JohnH]

Jan 18, 2013 20:46:53 GMT -5 allmektig said:

Yeah, that was the plan all along, I just didn't put it in the drawing.
Anyways. I've put it together, and it works.
There are two minor problems though.
I hooked one output to my computer soundcard and the other to my amp.
When I was using the distortion channel on my amp, I would hear some noise that I believe came from my computer, since it disapeared when I switched off that channel.
But I guess that without using some elaborate scheme with transformers and active electronics, there's no way to get rid of that problem?

The other problem was an audible pop when I turned a channel on or off. Is there some way to eliminate that?

I'd say that was a fair check on whether the basics work, but there could be a few reasons for those problems when plugged into two such different devices, instead of two inputs on the same guitar amp.

I would hold off worrying further about the pc noise coming through the amp distortion channel unless you find such issues when using it as intended. It will never be a good idea to connect a guitar direct to a pc anyway, an active buffer is needed. Probably, if you tested that, say by putting a switched-off non-true-bypass pedal (such as any Boss) between the box and the pc, it should fix it.

With the pops, does it happen if if you only connect to the amp and use just one channel of the the box to switch on and off? A capacitor between box output and amp input may help, with a high value resistor to ground on the box side.

Also, try it with the pedal between box and amp.

[allmektig]

I connected it to the instrument input on my soundcard, wich is designed for plugging in a guitar.
But there is a LOT of electric noise going on around my pc, with powered usb hubs, LED ligthing connected to the same power supply as the PC, powered speakers etc etc.


The pops occur when I have my guitar connected to the box, and one output connected to the amp.
I tried it with the guitar connected to the box connected to my floorpod connected to the amp, and I still got pops.
They're not very loud, so I'm not very concerned.
My friend plays in a jazz band, so high gain distortion isn't really his thing anyways.

I'll try the capacitor thing tomorrow.