Helping a friend connecting pres to an amp

[Ghost_Bass]

Hello, a friend of mine phoned me today with a question that i'm not sure about the correct answer. He's got some gigs comming up where he'll be using both electric and double bass. He wants to use two preamps, one for the electric and another for the upright but he wants to use only one power amp and a single cab. Here's the problem, the power amp only has one input so he asked me if it was safe to link the two outs from the pres to the amps input using a Y adaptor.
I know that you can't connect the out of two amps together (like hooking two amps to a cab) but i honestly don't know if there's any kind of crosstalk between the signal from the pres. If he can't use the Y what would be the cheapest/easyest way to solve this (if told him about using an A-B pedal but he would need to buy one)?

Can someone shed some light on this? Thanks!

[subrob]

I'd take the pedal every time - in principle the low levels here arent much different from amp speaker outputs. at worst you'd want to replicate the precautions you'd take if you were playing two alternate amp heads into one cab, to be sure of its reliable and safe operation. the pedal is almost certainly going to be less faff on stage, and there's no danger or at best, oddity, between two directly connected preamp outs.

HTH

[icastle]

I wouldn't go for the Y cable solution.

The pre-amps are going to be able to see each other and will present the input on the power amplifier with twice the voltage that it's expecting to see.

A-B switch every time for me.

[Ghost_Bass]

Thanks for the replies, you're confirming my fears. The voltage explanation makes some sense even though he wont be using both basses at the same time. Keep posting other alternatives to the pedal.

Cheers

[icastle]

[quote name='Ghost_Bass' timestamp='1332715688' post='1592151']
Thanks for the replies, you're confirming my fears. The voltage explanation makes some sense even though he wont be using both basses at the same time. Keep posting other alternatives to the pedal.
[/quote]

It doesn't matter if he's actually using both the basses simultaneously or not, if both pre-amps are switched on then they'll both be supplying a voltage to the input of the amp, even though there may not be a signal present.

If the power amp is a stereo one then he could perhaps feed one pre-amp into the LH channel and the other into the RH channel but that's just starting to get messy and complicated (and 'simple' always works best IME).

Seriously, the AB pedal is the safest way forward and, as they're generally a passive device, it doesn't have to cost a fortune - you can get a perfectly adequate Behringer one for about £20 and a Boss one for around £30.

Edited March 25, 2012 by icastle

[Ghost_Bass]

[quote name='icastle' timestamp='1332717161' post='1592163']
It doesn't matter if he's actually using both the basses simultaneously or not, if both pre-amps are switched on then they'll both be supplying a voltage to the input of the amp, even though there may not be a signal present.

If the power amp is a stereo one then he could perhaps feed one pre-amp into the LH channel and the other into the RH channel but that's just starting to get messy and complicated (and 'simple' always works best IME).

Seriously, the AB pedal is the safest way forward and, as they're generally a passive device, it doesn't have to cost a fortune - you can get a perfectly adequate Behringer one for about £20 and a Boss one for around £30.
[/quote]

I understand what you're saying and it makes sense. My first answer to him was in fact to get a boss AB-2 pedal to do this but i wanted some confirmation about this subject. Thank you for your replies.

Cheers