A/B TESTS WITH MOD50

[peter_traj]

Hi guys,
I am a nutter for A/B testing gear. Until know, i would just unplug and replug the gear to test it. I now want to do this without unpluging. I have attached a diagram of what i think will work to A/B the MOD50 pre amp with a rack based pre amp, and A/B the MOD50 power amp with a rack based one. Also, this set up should allow me to run the MOD50 pre into the rack amp and the rack pre into the MOD50 power amp. But, i am not completely sure if it would work--thas why i am asking you guys for advice.
The diagram shows the guitar signal going into a 2 channel looper. Channel 1 goes to the input of the MOD50 and out of its "send" socket. Channel 2 goes out to a rack pre amp and back. Then the signal then goes to an A/B box which sends the signal to the "return" of the MOD50 or the the input of a rack power amp.
I am a bit scared to try it out in case i cook something. Can anyone see anything wrong with this routing?

Thanks

 

[RockStarNick]

Diagrams on monday morning... let me down this coffee first and take another look after my brain has woken up.

 

[peter_traj]

Make it a double espresso over-caffeinated and take your time!!!

 

[RockStarNick]

OK I took a closer look this time. And yes I'm drinking some coffee. haha.

Lets break this down into 2 seperate sections: Preamps and Poweramps.

Switching between 2 preamps is no big deal, because you're only dealing with a guitar signal; there's no "juice" in it like a speaker level signal. So when you have it routed to the Mod50, it's as if there's just nothing plugged into the Rack Pre.

The possible problem that *I* see is with your power amp A/B setup. You just need to make sure that the 1922 Cab is acting as TWO SEPERATE SPEAKERS, to ensure that each power amp is seeing a load at all times. Lack of speaker load will cause a power amp to fry itself.

 

[muudrock]

OK I took a closer look this time. And yes I'm drinking some coffee. haha.

Lets break this down into 2 seperate sections: Preamps and Poweramps.

Switching between 2 preamps is no big deal, because you're only dealing with a guitar signal; there's no "juice" in it like a speaker level signal. So when you have it routed to the Mod50, it's as if there's just nothing plugged into the Rack Pre.

The possible problem that *I* see is with your power amp A/B setup. You just need to make sure that the 1922 Cab is acting as TWO SEPERATE SPEAKERS, to ensure that each power amp is seeing a load at all times. Lack of speaker load will cause a power amp to fry itself.

+1
I would also add that you would want speakers that were rated to handle the load of the respective amps. What are the speakers in the 1922 rated at?

If this were me, I would get a speaker cab switcher like the Radial CabBone and just switch the power sections that way. This lets you run multiple amps into one speaker cab and would keep a load on both power amps at all times. You have several options for switching the preamps in and out and back/forth.

Good luck with this. I'm interested to see what you come up with.

 

[aeroic]

OK I took a closer look this time. And yes I'm drinking some coffee. haha.

Lets break this down into 2 seperate sections: Preamps and Poweramps.

Switching between 2 preamps is no big deal, because you're only dealing with a guitar signal; there's no "juice" in it like a speaker level signal. So when you have it routed to the Mod50, it's as if there's just nothing plugged into the Rack Pre.

The possible problem that *I* see is with your power amp A/B setup. You just need to make sure that the 1922 Cab is acting as TWO SEPERATE SPEAKERS, to ensure that each power amp is seeing a load at all times. Lack of speaker load will cause a power amp to fry itself.

+1
I would also add that you would want speakers that were rated to handle the load of the respective amps. What are the speakers in the 1922 rated at?

If this were me, I would get a speaker cab switcher like the Radial CabBone and just switch the power sections that way. This lets you run multiple amps into one speaker cab and would keep a load on both power amps at all times. You have several options for switching the preamps in and out and back/forth.

Good luck with this. I'm interested to see what you come up with.

Back in the day the 1922 I had had G12T75s in it. So it should be enough to handle the Mod50. Depends on your rack amp though. My 1922 was mono / stereo, with a switch go between the two.

 

[peter_traj]

Thanks guys,
Ill give you some more info.The speakers are the GT1275 at 75watts a piece. The rack amp will be a Rocktron Velocity 250 in mono and the preamp will be a Rocktron Voodu Valve.(i love comparing valve to solid state and mixing them round). The cab takes a stereo input at 16ohms and a mono at 8 ohms on the right jack only.
So, i figure that if i have 2 guitar leeds going into the cab and select 16ohm out on both power amps all should be fine as the two leeds should select the stereo circuit in the cab to feed each speaker independently. I realize though, that only one speaker will have power on it at any one time which shouldn't be a problem, at least i cant see why it would be, because the A/B switch is switching the signal between the input of the rack amp and the return of the MOD50. The outputs, therefore, should always see a load, even when no signal is at their inputs
The only thing that i am worried about is if the send/return (serial) does not COMPLETELY separate the MOD pre amp from the power amp--can anyone clarify this? As far as i know, the "return" of the MOD50 is the same as an "input" of any rack-based power amp and completely separates the pre's from the power stage (in serial loop only of course).
Anyway, thanks again for your comments. I am still waiting for the looper to arrive and i think ill just give it a go.

Cheers

 

[RockStarNick]

Just curious, what looper did you go with? Loooper, LoopMaster, etc?

 

[peter_traj]

Just curious, what looper did you go with? Loooper, LoopMaster, etc?

I have ordered a loopmaster looper, but only to crack it open to see what parts they use, as i want to make a custom one myself. However, the 2 channel looper that i have ordered for the A/B tests has no brand name. A guy on eBAY was selling it and i only bought it because it had an "inversion" switch which is brilliant (i need to know how they did this so i can incorporate it into my own custom one).
The inversion switch works as follows: If ch.1 and ch.2 are on--it turns them both off: if ch.1 is on and ch.2 is off--it turns 1 off and 2 on etc etc. So, if you want to A/B a pre amp or stomp box for example, you can switch between them with "one" switch and not have to push "both" channel switches simultaneously--awesome idea.
It also does away with having to use 2 A/B switches when comparing 2 stomp boxes that have to terminate to a common amp input (you need 1 A/B switch to divide between 2 stomp box inputs and another to divide the 2 outputs to a single input on the amp.
I will email the guy that i bought it off and try to get more info on it, and i will also post the schematics of the pedal that i will be building--which will be at least a few months away.

Thanks guys