Question re: rig signal paths

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alund

alund

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Pondering while trying to fall asleep last night. I have been thinking about different signal paths. I am assuming the specific amp schematic will determine this possibility..
1) Can one plug a preamp (for ex..ADA mp1) into the return of an amps fx loop (for ex..slo/EVH) (not using the amp fx send at all)? This would bypass the preamp stage of the main amp obviously BUT the real question is; Does the amp fx send have any requirements here or can it be unplugged and allow me to do the second question below?
2) can one at the same time have an A/B pedal switcher coming from the guitar going into that A)preamp and to the B)front of the amp at the same time and A/B toggle which preamp is being used from the A/B controller. ie can the signal from the a/b box control which preamp is isolated in use without damage to amp or preamp?
 
You can do that without damaging the amp. Using one of those programable loop/routing devices, like the Mini Fx Gizmo, to route the signal to the amps input, to add or remove the preamp from the amps fx loop, and to turn the amps fx loop on or off.
Output of the loop 1 of the Gizmo into input of the amp with the amps FX loop off = amplifiers preamp being used + rack bypassed
Output of the loop 2 of the Gizmo into return of the amps fx send with FX loop on = amplifiers preamp bypassed + rack used as main preamp
Use another output of the Gizmo as a function switch to turn on/off the amps FX loop. On then Rack is used, and off when the amps pre is used.
What will probably be more concerning is:
-Will ground loop occur, and how to get rid of that.
-You might need a amp fx loop bypass in order to have the rack in or 100% out of the chain?
 
Certainly not an amp building expert, but I would think having a on/off switchable effects loop would be a good start. If you turn off the loop, the external preamp isn't in the signal path.

you can use an ABY pedal to send one cable to the front of the amp, the other cable to the front of the preamp that's also in the loop, and use the ABY and loop on/off switch - so the signal either goes 1) through the amp with the loop off or 2) through the external preamp into the loop on
 
rsm said:
you can use an ABY pedal to send one cable to the front of the amp, the other cable to the front of the preamp that's also in the loop, and use the ABY and loop on/off switch - so the signal either goes 1) through the amp with the loop off or 2) through the external preamp into the loop on
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This is what I’m thinking. I have the Lehle ABY which has isolated transformers to prevent ground loops. I had that battle years ago and this unit corrected it.

So; when the signal is strictly on the amp input, is there any risk to the inserted preamp?
 
alund said:
This is what I’m thinking. I have the Lehle ABY which has isolated transformers to prevent ground loops. I had that battle years ago and this unit corrected it.

So; when the signal is strictly on the amp input, is there any risk to the inserted preamp?
Click to expand...
Not 100% sure, but I don't think so; I'm pretty sure preamps don't need any output load vs power amps that need speaker load.

And if there's no signal into the preamp there's no load on it either...and if there is a signal, the preamp will process it with or without any output connected.

That said, there may be preamps that are exceptions
 
if you have the amp's preamp going into the loop then into your external preamp, it will probably not sound good, but not sure if the loop is expecting instrument or line level which could put more or less load on the preamp's input

edit

Path 1: guitar --> ABY - A --> amp input --> loop off --> power amp

Path 2: guitar --> ABY - B --> preamp input --> preamp output --> (loop on) loop return --> power amp

just need to be sure the loop is off for Path 1; and on for Path 2; and the ABY is set to the correct path.
 
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rsm said:
if you have the amp's preamp going into the loop then into your external preamp, it will probably not sound good, but not sure if the loop is expecting instrument or line level which could put more or less load on the preamp's input

edit

Path 1: guitar --> ABY - A --> amp input --> loop off --> power amp

Path 2: guitar --> ABY - B --> preamp input --> preamp output --> (loop on) loop return --> power amp

just need to be sure the loop is off for Path 1; and on for Path 2; and the ABY is set to the correct path.
Click to expand...
Good info. Exactly what I think… but the on off fx loop is key. What if the fx loop left on and running through the A path (in your schematic). What does the B path fx loop being left on do? Why does it have to toggle on and off if the signal is not a passing through the external preamp at all? Does the “left on” fx loop add something (noise) unwanted ?
 
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alund said:
Good info. Exactly what I think… but the on off fx loop is key. What if the fx loop left on and running through the A path (in your schematic). What does the B path fx loop being left on do? Why does it have to toggle on and off if the signal is not a passing through the external preamp at all? Does the “left on” fx loop add something (noise) unwanted ?
Click to expand...

If you use the ABY for the amp input path, then no signal will be coming into the loop return (or into the external preamp).

however, the amp preamp will go through the amp's loop circuit which may impact the tone or noise (vs the loop off = loop is bypassed, not in the signal path).

edit; also even though the external preamp is not receiving an input signal, it will still be sending output (with noise, if any) into the loop return. turning the loop off avoids this. My DSL40CR has a loop, the footswtich has a switch to change amp channel, and to turn the effects loop on/off.
 
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T
rsm said:
If you use the ABY for the amp input path, then no signal will be coming into the loop return (or into the external preamp).

however, the amp preamp will go through the amp's loop circuit which may impact the tone or noise (vs the loop off = loop is bypassed, not in the signal path).

edit; also even though the external preamp is not receiving an input signal, it will still be sending output (with noise, if any) into the loop return. turning the loop off avoids this. My DSL40CR has a loop, the footswtich has a switch to change amp channel, and to turn the effects loop on/off.
Click to expand...
That edit is key.
 
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I haven't tried this, so my comments are 'theoretical" at best, just thinking through the signal paths...I like to write out the path(s) I want, then see how I can do it...

I had a strange signal path when I got my Boss SY-300; it did guitar synth well, but the regular guitar sounds were limited. I added a Boss GT-1 for standard guitar tones, then had to figure out a way to send a stereo output, and balance the GT-1 and SY-300 signals. So I wrote out the paths...and came up with this:

Guitar --> SY-300 Input;
SY-300 thru ---> GT-1 input;
SY-300 headphone out (1/4" TRS) --> GT-1 Aux Input (1/8" TRS);
GT-1 out to FRFR/PA in stereo

This let me have GT-1 guitar only, SY-300 guitar synth only, and using the expression pedal control the amount of SY-300 level in the mixed stereo output.

really helped visualize what I needed and how I could do it with the options in the rig components
 
rsm said:
I haven't tried this, so my comments are 'theoretical" at best, just thinking through the signal paths...I like to write out the path(s) I want, then see how I can do it...

I had a strange signal path when I got my Boss SY-300; it did guitar synth well, but the regular guitar sounds were limited. I added a Boss GT-1 for standard guitar tones, then had to figure out a way to send a stereo output, and balance the GT-1 and SY-300 signals. So I wrote out the paths...and came up with this:

Guitar --> SY-300 Input;
SY-300 thru ---> GT-1 input;
SY-300 headphone out (1/4" TRS) --> GT-1 Aux Input (1/8" TRS);
GT-1 out to FRFR/PA in stereo

This let me have GT-1 guitar only, SY-300 guitar synth only, and using the expression pedal control the amount of SY-300 level in the mixed stereo output.

really helped visualize what I needed and how I could do it with the options in the rig components
Click to expand...
I’m on a drinking binge in Destin Fla so I cannot connect anything and confirm. Just thinking.
 
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Yes and yes. I do this, switch between the amp's preamp or a preamp pedal to feed the FX return. You can use a passive splitter or Y-cable to send the guitar to the amp input and the preamp input. Then put the amp FX send and the preamp output to an A/B switch (I get them from Saturnworkspedals.com). The A/B switch will decide which preamp you hear thru the power amp.
BUT, you need to put a buffer just before the A/B switch on one of the lines going into it. Because the A/B switch is passive, it sends the bypassed signal to ground, but since both signals come from the same guitar signal being split, then it grounds the entire chain, unless you put a buffer on one side of the split.
Or just use an active splitter and switch.
 
something like this help?

https://www.sweetwater.com/store/detail/TriParMix--electro-harmonix-tri-parallel-mixer

I came upon this looking for a solution to do a similar thing with my amp and tonex pedal without multiple a/b switches.

Plug your guitar into the pedals input.

First loop send would go through your pedal board + amp input with the return on that loop coming from your amps fx loop send.

Second loop would go through the preamp for both send and return

Third loop would be your post time fx that would allow you to add reverb and delay to both via the mix.

Then the pedal output would go into your power amp via the amps fx loop return.

Idk the quality of this and I may have screwed up the routing but I think it will work in and be all in one + its a cheaper option. There are other boxes that do this too if you search for parallel looper pedal. I watched it a while ago but I think you can set it up to mix and combine channels with one press.
 
tjnx said:
something like this help?

https://www.sweetwater.com/store/detail/TriParMix--electro-harmonix-tri-parallel-mixer

I came upon this looking for a solution to do a similar thing with my amp and tonex pedal without multiple a/b switches.

Plug your guitar into the pedals input.

First loop send would go through your pedal board + amp input with the return on that loop coming from your amps fx loop send.

Second loop would go through the preamp for both send and return

Third loop would be your post time fx that would allow you to add reverb and delay to both via the mix.

Then the pedal output would go into your power amp via the amps fx loop return.

Idk the quality of this and I may have screwed up the routing but I think it will work in and be all in one + its a cheaper option. There are other boxes that do this too if you search for parallel looper pedal. I watched it a while ago but I think you can set it up to mix and combine channels with one press.
Click to expand...
The 3rd loop being for delay/reverb wouldn't work because they're parallel loops. It would skip both preamps and just do gtr->delay->FX return. Delay/reverb would have to be between the TPMixer output and the FX return.
My previous post gives the simplest/cheapest way to do what OP wants, with a splitter adapter, an A/B switch, and a buffer.
Your idea should work for the first 2 loops between amp & preamp, but the 3rd loop won't work like you said.
 
DECEMBER said:
The 3rd loop being for delay/reverb wouldn't work because they're parallel loops. It would skip both preamps and just do gtr->delay->FX return. Delay/reverb would have to be between the TPMixer output and the FX return.
My previous post gives the simplest/cheapest way to do what OP wants, with a splitter adapter, an A/B switch, and a buffer.
Your idea should work for the first 2 loops between amp & preamp, but the 3rd loop won't work like you said.
Click to expand...
Ah ok, yes output > verb / delay > power amp was the way to do it.

I think I remember looking at a buffered splitter + a/b box. Wouldn't your first Y split cause tone suck? I looked at the jhs buffered splitter but some people didn't like the tone.

Are you saying it would be the same problem and you need both a buffer and an active switch, or would just a buffer before the Y suffice? I have a good buffer so if I just need a Y and their cheapest AB that would be cool.

I looked at things like the klein bottle too but at that point I figured why not get a boss switcher for the same $$. I guess if you wanted to blend the 2 pre's then that's where something like the EH would come in.

I last ended up on the boss or equivalent if I was going to do this and putting some pedals in their own loop. Main reason being tonex midi control. But at that point I'd have to be playing covers and making money somehow to justify it so meh
 
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tjnx said:
Ah ok, yes output > verb / delay > power amp was the way to do it.

I think I remember looking at a buffered splitter + a/b box. Wouldn't your first Y split cause tone suck? I looked at the jhs buffered splitter but some people didn't like the tone.

Are you saying it would be the same problem and you need both a buffer and an active switch, or would just a buffer before the Y suffice? I have a good buffer so if I just need a Y and their cheapest AB that would be cool.

I looked at things like the klein bottle too but at that point I figured why not get a boss switcher for the same $$. I guess if you wanted to blend the 2 pre's then that's where something like the EH would come in.

I last ended up on the boss or equivalent if I was going to do this and putting some pedals in their own loop. Main reason being tonex midi control. But at that point I'd have to be playing covers and making money somehow to justify it so meh
Click to expand...
If using a passive splitter and A/B switch, you need a buffer after the split/before the A/B switch on at least one side of the split. Being passive, the A/B switch selects A by sending B to ground. Since the same signal is the source of A & B, grounding B also grounds A, so you get silence from A & B.
I put the buffer just before the A/B switch input B, after the preamp pedal.
A passive A/B switch from Saturnworks is $29. An active switch already has buffers in it, but costs more and needs to be plugged in.
I just use Pig Hog y-splitter adapters and there's no noticable signal loss.
A buffered splitter from Saturnworks would have the necessary buffers in it already, and a passive A/B switch would work without adding another buffer.
As long as a buffer is somewhere after the split and before the switch. Saturnworks stuff is buffered on the inputs and outputs, so you'd only need an active splitter OR switch. Or if you already have a buffer, then a $29 passive switch and a $10 y-splitter is sufficient.
 
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