I'd like to switch 5 different pre-amps in and out of a single power amp. It doesn't necessarily need to be a foot pedal type deal. Would a mixer work for this? What do I need?
Enjoy the benefits of a premium membership!
Upgrade Account
-
TalkBass has been independent since 1998. Add your voice.
Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
Join free Log in
Want zero display ads or expanded classifieds tools? Compare plans.
Switching pedals
- Thread starter GreyBeard
- Start date
I'm assuming that you only want to use one pre-amp at a time, yes? (Sorry if that sounds obvious, but you never know...)
I can't really suggest any known pieces of commercial hardware to do the job - I imagine you'll be getting out the soldering iron and making something up yourself - if so, there's one technical aspect of which you need to be aware (if you're not already).
Whatever kind of switching device you end up using/making, it should be designed to dump the signal input of the power amp to ground as you switch out of one pre-amp choice and into the next. If it doesn't do this, the input to the power amp will be left briefly open-circuit between choices, resulting in a lot of nasty noise (loud hum...RF interference...possible squealing etc) and one hell of a thud when the next pre-amp is connected.
Here's one way to achieve this:
1) Purchase a really good quality heavy-duty multi-position rotary selector switch. The switch should be a single-pole, ten-throw and will have to be an M-B-B type ("Make-Before-Break") - i.e. it makes contact with the next stud on the rotation before it breaks contact with the previous one.
2) Wire the switch studs as follows:
1: Pre-amp A
2: Ground
3: Pre-amp B
4: Ground
5: Pre-amp C
6: Ground
7: Pre-Amp D
8: Ground
9: Pre-amp E
10: Ground
This way, it will always ground the power amp input between pre-amp selections.
Depending on the mechanical construction of the switch, you may even be able to set it up so that it rotates endlessly - i.e. switching beyond stud 10 would bring you back to Pre-amp A.
The only major downside to a rotary design is that you can't jump between pre-amps that aren't adjacent to each other on the switch!
3) Finally, mount the switch into a suitably sturdy die-cast box or rack-mount unit and fit the rear of the housing with five input sockets for your pre-amps and one output socket for the feed to the power amp.
In choosing the type of wiring to go from the switch terminals to the sockets, you can either use screened wire (with the screening grounded at one end only to avoid earthloops) or, if you can ensure that your housing is a good screen by itself, it would be a lot simpler to use unscreened wires. Just keep them as short as practically possible.
The above method assumes that all of your pre-amps and your power-amp input are of the unbalanced type. It's quite easy to make a similar device for balanced line as well.
I hope this has been of some use. Feel free to PM me if you want more detailed input on this idea. I may be able to suggest a possible source for the right type of rotary switch.
I can't really suggest any known pieces of commercial hardware to do the job - I imagine you'll be getting out the soldering iron and making something up yourself - if so, there's one technical aspect of which you need to be aware (if you're not already).
Whatever kind of switching device you end up using/making, it should be designed to dump the signal input of the power amp to ground as you switch out of one pre-amp choice and into the next. If it doesn't do this, the input to the power amp will be left briefly open-circuit between choices, resulting in a lot of nasty noise (loud hum...RF interference...possible squealing etc) and one hell of a thud when the next pre-amp is connected.
Here's one way to achieve this:
1) Purchase a really good quality heavy-duty multi-position rotary selector switch. The switch should be a single-pole, ten-throw and will have to be an M-B-B type ("Make-Before-Break") - i.e. it makes contact with the next stud on the rotation before it breaks contact with the previous one.
2) Wire the switch studs as follows:
1: Pre-amp A
2: Ground
3: Pre-amp B
4: Ground
5: Pre-amp C
6: Ground
7: Pre-Amp D
8: Ground
9: Pre-amp E
10: Ground
This way, it will always ground the power amp input between pre-amp selections.
Depending on the mechanical construction of the switch, you may even be able to set it up so that it rotates endlessly - i.e. switching beyond stud 10 would bring you back to Pre-amp A.
The only major downside to a rotary design is that you can't jump between pre-amps that aren't adjacent to each other on the switch!
3) Finally, mount the switch into a suitably sturdy die-cast box or rack-mount unit and fit the rear of the housing with five input sockets for your pre-amps and one output socket for the feed to the power amp.
In choosing the type of wiring to go from the switch terminals to the sockets, you can either use screened wire (with the screening grounded at one end only to avoid earthloops) or, if you can ensure that your housing is a good screen by itself, it would be a lot simpler to use unscreened wires. Just keep them as short as practically possible.
The above method assumes that all of your pre-amps and your power-amp input are of the unbalanced type. It's quite easy to make a similar device for balanced line as well.
I hope this has been of some use. Feel free to PM me if you want more detailed input on this idea. I may be able to suggest a possible source for the right type of rotary switch.
I'm no authority, but would an AB box or three do the job?
More importantly, WHY would you want 5 different pre-amps?
More importantly, WHY would you want 5 different pre-amps?
bongomania
Commercial User
Switching devices exactly like this are commonly used in Guitar Centers and other large instrument/PA stores. They can be bought directly from certain manufacturers of rack gear- for instance, I have seen these switchers with Ampeg and Rane logos. I've even seen them on Ebay for cheap when these stores close up or slough off old fixtures.
Oh, and yes a mixer will work if you have one lying around and don't want to go to any further trouble finding a switcher box. Just pan all of the input channels 100% to one side (L or R), and then send the main output for that side to your power amp. Using the input level faders instead of switches will help avert some of the noise problems Espidog mentioned.
Oh, and yes a mixer will work if you have one lying around and don't want to go to any further trouble finding a switcher box. Just pan all of the input channels 100% to one side (L or R), and then send the main output for that side to your power amp. Using the input level faders instead of switches will help avert some of the noise problems Espidog mentioned.
