Switching guitar and accordion inputs with ABY pedal on vintage '66 Reverberocket 2

[mrzdb]

Hi.

I like the tone of both the guitar and accordion inputs.

Is it possible to switch between the two inputs with an ABY pedal.

I'm getting a volume/gain drop when I plug into both inputs - it sounds like it's defaulting to the guitar input.
ABY output A(guitar) seems to work, but when I select output B (accordion) there is no change in tone or volume.
However when I select Y(both) the amps volume increases.

I've checked/reversed the ABY switches outputs and the same thing happens.

Thanks for your help.

[mrzdb]

hmm, after a bit of googling it looks like if plug into both inputs of a channel, the signal is attenuated to the the lowest inputs level,
and/or the higher input (accordion) signal is passed to the guitar input.

Is there a way to mod this?

Seems a shame that we can't switch between the two inputs on single channel amps.

[patlaw]

You are more likely to get help if you post a schematic.

[mrzdb]

AmpegGS-12R.jpg Photo by Travst | Photobucket

[Chuck H]

The link doesn't provide a legible schematic and downloading it results in a distorted image. But...

It's obvious to see that both inputs are mixed directly into a single input triode. This being the case it's almost certainly similar to a hi/low input arrangement found on many amps. So when you plug into both inputs the input of both defaults to the low gain circuit. Sorry, there is no way to ABY the amp as it is. Any mods to change this are fairly extensive.

[mrzdb]

Thanks for clarifying Chuck

[patlaw]

Sorry, there is no way to ABY the amp as it is.

What does ABY mean?

[pdf64]

Schematic of the ABY pedal?
It may be that one of the switch poles is used to short the unused output to ground.
If that ground to the switch is disconnected then all conditions may be unattenuated, and so at a similar volume.

[mrzdb]

Hi patlaw
This is the ABY pedal it allows routing of guitar signal to different or two outputs.
ABY Pedals - Loopi Pedals

[mrzdb]

Hey pdf64

Can you clarify this a bit.
Do you mean that it may be the ABY pedals circuit that is preventing the use of the two inputs.
I don't have a schematic for the pedal, but here is the pedal in question. ABY Pedal - Loopi Pedals

Also here's a better schematic of the Reverberocket 2

[pdf64]

'Do you mean that it may be the ABY pedals circuit that is preventing the use of the two inputs'
I don't see that it's preventing the use of both inputs?
Rather that in your particular application, it may be better to leave an unused input open circuit, as opposed to shorted to ground.
In the more normal application of a full 2 channel or 2 amp set up, leaving an unused amp input open circuit may result in hum pick up.

As I understand it, your issue is that as it is, there's a volume change when switching from A/B to Y? If so then removing the ground from the switch may help; but it may still change a bit, especially if the instrument output impedances are widely dissimilar (which may occur over a certain range of an instrument's volume control adjustment).

[Jazz P Bass]

What does ABY mean?

A, B or Both.

[g1]

Maybe it would be easier to consider the design objectives and start from scratch.
It seems to me you are not interested in using both inputs at the same time, rather, you want hi and low level with a footswitch to choose between.
Forget the aby for now. In the factory drawing, if you are plugged into the upper jack, it is higher gain. Now if you add an extra 150K from grid to ground, you are the equivalent of using the lower jack (lower gain). If I've missed something someone please correct me.
So the trick is to switch in 150K from grid to ground via a footswitch without adding noise.

[mrzdb]

Maybe it would be easier to consider the design objectives and start from scratch.
you want hi and low level with a footswitch to choose between.
Forget the aby for now. In the factory drawing, if you are plugged into the upper jack, it is higher gain. Now if you add an extra 150K from grid to ground, you are the equivalent of using the lower jack (lower gain). If I've missed something someone please correct me.
So the trick is to switch in 150K from grid to ground via a footswitch without adding noise.

Yes g1 that's what I want to do. Because the hi input (accordion) has a different 'tone' to the lo input.

In an ideal world I'd like to use both inputs at the same time (tho I'm not sure this will make a positive contribution to the sound), but if your solution of only plugging into the hi input and changing the gain by switching to the 150k resistor works, i'd definitely settle for that.

Thanks for the insight.

[Leo_Gnardo]

Yes g1 that's what I want to do. Because the hi input (accordion) has a different 'tone' to the lo input.

In an ideal world I'd like to use both inputs at the same time (tho I'm not sure this will make a positive contribution to the sound), but if your solution of only plugging into the hi input and changing the gain by switching to the 150k resistor works, i'd definitely settle for that.

Thanks for the insight.

That 150K resistor also loads down the output of your guitar. Instead of an AB box you could construct a "brown tone box", I've done it for some customers. Simply enough, one switch position, signal passes straight thru. Other position, wire a 150K resistor across the signal line. You could put in a pot instead & dial in a "sweet spot" other than exactly 150K, that's what I do in my brown boxes - dial & smile.

Fender amps' similar, #2 input loads the input 134K to ground, near as dammit to 150K. Sounds terrific for motown/stax style rythm chunk parts, sorta boxes up the tone. Brown n bake, enjoy!