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Multi preamp switch box project - wiring help!


Walker
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[b]Multi preamp switch box project - wiring help![/b]

I would like to have a quick and simple way to switch between 3 preamps that all go into the same power amp.

I don't want a footswitch, as I'll be switching between songs (one for blues harp, one for bass and another for guitar), so I was thinking about rotary chickenhead knobs mounted on a panel on my rack.

Before I research the switches, wiring diagram and hardware I'll need for the project, looking at the diagram below, is this the best way to do it?

Two 4 way patch panels, each with a rotary knob. The first panel has the 3 inputs into the preamps, the second panel takes the outputs from the preamp into a single poweramp.

Thanks very much!

Chris

Edited by Walker
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I'm not quite sure what you're doing. Is it:

3 sources, each into its own pre-amp, then select which preamp connects to power amp

?

If so all you need is the switch between pre outs and power amp in. I don't see why you need patch panels, or to switch the inputs to the pres.

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Assuming that you change the instrument connected you your wireless transmitter, and you want to switch the receiver to feed the correct preamp for that instrument, I think you only need one switch - a rotary switch with three positions (four if you want a 'mute' position), and two poles, one for the preamp inputs and one for the preamp outputs.

I would also aviod the use of a patch panel - it will cost you for the plugs and sockets, and give you more places where you could get a faulty contact. A metal box containing the switch, connected to 8 cables which end in jack plugs, would be cheaper and more robust.

David

Edited by Mottlefeeder
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[quote name='Mottlefeeder' timestamp='1352205339' post='1859988']
Assuming that you change the instrument connected you your wireless transmitter, and you want to switch the receiver to feed the correct preamp for that instrument, I think you only need one switch - a rotary switch with three positions (four if you want a 'mute' position), and two poles, one for the preamp inputs and one for the preamp outputs.

I would also aviod the use of a patch panel - it will cost you for the plugs and sockets, and give you more places where you could get a faulty contact. A metal box containing the switch, connected to 8 cables which end in jack plugs, would be cheaper and more robust.

David
[/quote]

How much do you want paying for a wiring diagram!!!

Seriously, this sounds great and thanks for the idea (you and paul 5) about the mute switch too - I would never had thought of that until I got that first big 'thump'!

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[quote name='zero9' timestamp='1352206069' post='1860008']
Why not get a 4-channel mini mixer?
[/quote]

Another great idea I hadn't considered. Thank you. May well go down that route.

The thing is, now it's getting cold and dark, my soldering iron keeps me warm! I fancy the project and my kids like to watch!

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[quote name='bremen' timestamp='1352207529' post='1860060']
Yeah, I'd do as Mr Mottlefeeder suggests.

You could guard against thumps with a bunch of caps and bleeder resistors; I could draw you a diagram but if you want to keep it simple then yes a mute switch might be easier.
[/quote]

I would prefer to do it this way to be honest, as I'm trying to learn basic electronics with my eldest son, so if you did find time to do a quick drawing for me, that would be appreciated. As long as you don't mind me asking a few questions!

At least I can then read up about the components and find out why the are stopping the thumps.

Many thanks bremen.

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Thanks very much David, will that diagram be with a mute switch or [i]'a bunch of caps and bleeder resistors'[/i]?

I'm happy to go the more complicated route for the learning experience, but whatever is easiest and quickest for you.

I really appreciate this - thank you everyone.

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I've drawn the basic switching circuit, and how you connect the cable cores and earthed screens. If others chip in with click suppression, I can add that (assuming I understand what they suggest...

First problem - my scanner at work produces PDFs, which Photobucket ignores. I'll photograph the page when I get home.

David

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Crikey, I can actually follow this! Brilliant job, thank you very much indeed. When you talk about screened cable, doesnt that have 3 cores?

Also, what gauge cable should I use for the internal stuff?

I'm planning on have the box in the back of my rack and the two switches mounted on a panel on the front for quick access when playing. That shouldn't be aproblem should it?

Thanks again, this is perfect!

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The screened cable is single core - instrument cable rather than microphone cable, and if you bring it into the box through a grommet, you can wire it directly to the switch. for other internal wirng I suggest 7/0.2 (seven strands of 0.2mm each), or you can use any wires stripped out of a mains cable - colour is not important ans size is not important. By the way, there is only one switch, but it contains both sections.

When you build it, I suggest using a box that is not as high as your rack panel, and using screws and/or the switch mounting bush to mount the box on the back of the panel. That way, all the unscreened cables and ends of cables are contained in a metal box and will not pick up hum.

If you do not have the gear to drill large holes in metal, you could use a plastic box and then line the inside with copper foil - you can get it in sheet from from guitar-spares shops on-line, or you can use slug-repelling copper tape from your local garden centre - garden centres are expensive, but so is postage on a small mail order.

David

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sorry, I've not been keeping up with this. the click reduction, should it prove necessary, is a 1uF film cap in series with each preamp output, then a 1 Meg resistor to ground from the switch end of each cap. this makes sure that any dc offset on the output of a preamp is eliminated.

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Thanks David,
So you are suggesting that I take cables out of the box with plugs on the end rather than have sockets in the box? Would you use zip ties around the cables inside the box for strain relief?

I think I'll understand the switch once I get my hands on one!

I have tools, so the metal box attached to the panel should be fine. Looking forward to getting started.

Thanks again for your help on this.

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Yes, each socket and plug is an extra joint that could become noisy, and will cost you to buy. You can use cheap grommets and cable ties to anchor the cables inside the box, or use a cable gland that includes a cable clamp. e.g. Maplins UP95D or JH23A or equivalent, to suit your cable diameter.

Maplins switch FF75S is a 3 pole 4 way, which would do, as would their FF74R 2 pole 6 way. You can restrict the 6 way so that it cannot go past position 4.

David

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[quote name='zero9' timestamp='1352206069' post='1860008']
Why not get a 4-channel mini mixer?
[/quote]

I did this, initially as a stop gap, but I found the pre-stages so clean that I stuck with it.
It's been great when other bassists share the rig (Phonic mixer into QSC PLX1202 power)
Set up one channel each. [b]MUTE[/b] the ones you're not using, and off you go!

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Thats really interesting.

I've been wanting a way to switch between channels on my rack compressor (ideally ch1 or ch2 or ch1 into ch2) in my fx loop to allow me some more options re compression in between toons.

Looking at this it may be exactly what I need for at least ch1 or ch2. Now if I could figure out how to do ch1 -> ch2 as well....

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