Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jonas on February 22, 2024, 07:18:17 pm
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this time I'm looking at building a passive or tube buffered ABY pedal :think1: leaning toward tube buffered. My application is to use the ABY to switch between 2 channels on the same amp. My initial thoughts are to use a single 12A_7 by splitting the plates using a common cathode; also envisioning a side chain loop for one of the channels to patch in a volume / expression pedal.
looking for a few suggestions on the following.....
more than likely I will experiment with a passive ABY first. What should I keep my cable lengths under?
I have used hammond 261C in the past for a couple pedal builds. Can anyone suggest similar in torroidal design?
I also want to experiment with transformer isolating one of the channels to feed 2 different amps. Does anyone have a good isolation transformer suggestion?
Any other considerations I'm missing?
Thanks
Jonas
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My application is to use the ABY to switch between 2 channels on the same amp
You can use a proven quiet effective relay switching approach for this that doesn't require a tube.
Relay circuit & layout board & ft switch (el34world.com) (https://el34world.com/Forum/index.php?topic=14348.0)
I also want to experiment with transformer isolating one of the channels to feed 2 different amps. Does anyone have a good isolation transformer suggestion?
I don't understand what this means? Or why you would wish to do this?
with respect, Tubenit
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You can use a proven quiet effective relay switching approach for this that doesn't require a tube.
No tube, what fun would that be?
I don't understand what this means? Or why you would wish to do this?
Maybe for ground loop isolation, but interested to hear his response.
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No tube, what fun would that be?
What is it about using a "tube buffered ABY pedal" that makes it more fun than relay switching?
I am interested in seeing a schematic of the tube buffered ABY pedal used in channel switching. I'm not understanding what is being advocated here?
With respect, Tubenit
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tubenit thanks for sharing the post and tutorial on relay switching - there is some great information in there! Relay switching might be inevitable near future, but plan to start with a simple passive passive ABY box as the amp already has an input for each channel.
As things progress (or if noise starts to creeps in), I might need to buffer the signals. No schematic yet, but would plan on using a dual triode to split the single in two, then do ABY switching after the split. This way I can run one channel through an expression pedal without effecting the other.
Then possibly try to isolate one channel (break ground loop) via transformer coupled output to use with 2 different amps at the same time.
Just checking to see if anyone has built an ABY pedal before and had some thoughts on the subjuect
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An ABY does NOT want voltage gain. It really should be transparent.
A tube working below unity-gain and signal levels under a Volt won't have enuff "toan" to notice.
ABY is a mechanical function, not an artistic spice. Do it any simple clean way, then find your "flavor" somewhere else.
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No tube, what fun would that be?
What is it about using a "tube buffered ABY pedal" that makes it more fun than relay switching?
I am interested in seeing a schematic of the tube buffered ABY pedal used in channel switching. I'm not understanding what is being advocated here?
With respect, Tubenit
First, it has a tube! Sometimes we tube just to tube.
There are ABY pedals with buffers and adjustable gain. Lots of companies like to promote "true bypass" marketing, because it sells and then they can sell you a buffer too.
Buffers help with longer cable runs and when spitting the signal to 2 or more amps. I don't think I'm telling you anything you don't know here.
This pedal could be made to have 2 inputs/outputs and be used as a dual buffer, phase inversion, gain, line isolation, ground lift, and a kitchen sink. Or you could buy a standard ABY off Temu for $14, but that wouldn't do what the OP is wanting.
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thanks PRR - I will plan to keep it mechanical and simple and see if it pass the sniff test.
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ABY pedal turned out great, thanks for the help! it is basic and mechanical with battery powered LED. (I am using it switch between 2 channels on the same amplifier)
I honestly cannot tell the difference when "in the signal chain" compared to guitar cable plugged straight in to amp. If I can minimize the popping when switching channels, I think I will be happy with it.
I going to tack in a few resistors and start trials shortly (values ranging from 2M to 10M)