Switcher box

[mike1127]

Hello DIY guys, I hope you can clue me into good part sources. I want to build a switcher box. I have two sources and three destinations. (My two sources are my CD player and my computer; three destinations are two headphones amps and a speaker amp.) So I want to build a 2-in 3-out switcher. I want to switch ground as well as the signal so that the grounds of my sources do not have to be connected together at all times.

A friend of mine is Don North, who is an experienced designer and builder of equipment, and could probably give me all the help I need, but he's a busy guy! I'm going to get info from this forum if I can. Don did give me just a bit of info. He said I could use a 4PDT (4-pole double throw) switch for the two inputs. It has to be 4-pole because I'm switching grounds. For the output he recommended a high quality rotary switch. Okay, my issue with that is it's expensive! Why not use three DPST (double-pole single throw) switches which each connect one destination to the common signal and ground? I could engage one at a time. Engaging two or three would mean my sources see a lower impedance but it wouldn't destroy them. This seems completely safe to me.

So what places sell quality parts? I need the switches and I want good ones. I need RCAs (5 pairs). I need a case and I need hookup wire. Don favors silver-coated copper. Where can I get stuff like that? I also need a case for the project and quality solder.

I have a temperature-controlled soldering iron already.

Thanks,

Mike

[Pars]

Almost all commercial audio equipment has left and right signal ground shorted together internally, so you could get away with a 3PDT switch. The Electroswitch C4 series is supposed to be quite good:

http://www.mouser.com/catalog/catalogUSD/639/1674.pdf

Take a look at Nate's post #8 inthis thread.

Decent rotary switches? - Head-Fi: Covering Headphones, Earphones and Portable Audio

For switching between sources, you could certainly use a DPDT or 3- 4PDT toggle switch if you are certain that 2 inputs is the most you would ever need.

Rotary Switches - Head-Fi: Covering Headphones, Earphones and Portable Audio

Another good thread on rotary switches. Note that many of the quality switches will have a high rotational effort, so a large knob will be needed to make turning these easy.

[mike1127]

Thanks, Pars.

I was hoping to get a comment on the wisdom of using single-throw switches instead of a rotary switch to select the three output destinations. Instead of selecting on via a rotary switch, instead you would have three single-throw switches which "engage" the outputs. The primary reason is to save money (I'm assuming good rotary switches are $$$).

Also, this way you could have multiple outputs engaged at one time, but that would cause my source to see a drop in impedance, so I would probably never do that.

Does this seem like an okay idea?

Thanks,

Mike

[Pars]

I didn't like that idea personally because of the ability to select multiple outputs at once. so I didn't comment on it. Rotary switches are $30 or less for a really good one; dig thru the links I posted, but Lorlin switches are ~$8 or so each; Grayhills a bit more. Look at Digikey or Mouser as your main suppliers for the switches. RCA jacks I would go elsewhere (partsexpress, Cardas CTFA from Soniccraft or handmade electronics, etc.).

[CarlSeibert]

A good rule of diy-ing (followed mostly by people smarter than I am) is don't skimp on the parts or functionality because by the time you've put the thing together and built or bought a case for it you will have so much time and money in you will have forgotten how much the parts cost in the first place.

That said, a quick look on DigiKey suggests that you could do two Grayhill rotaries of decent-looking quality for less than $50.

Then there's always Elmas from Goldpoint.

-Carl

[mike1127]

Thanks for the help everyone. I agree it is classier (at least) to go with rotaries. Also it would be nice to have three inputs rather than two for future flexibility. In fact I could get a 4 or 5 position rotary and just not put more than two input RCAs in the box for now.

Remember these have to be at least three poles rotaries because I am switching ground. Are those the prices you are quoting? How many positions?

Also, can someone explain what "decks" are? What is the difference between a 3-pole 1-deck rotary and a 1-pole 3-deck rotary?

Thanks,

Mike

[mike1127]

Okay, here's my plan so far. Any comments welcome.

My big question right now is: what case to use? Can anyone suggest a type of case (aluminum, steel, plastic?) and a source? What size is good? Is it always good to have it large, so it's easy to work inside? Or is smaller better?

I've decided to make it a 3-input 3-output box with option to expand. So I'm going to get two 6-position 4-pole rotary switches from Percy Audio. Part 04-2261. Costs about $60 each.

I'm also getting six sets of RCAs from Percy Audio. Relatively inexpensive Vampire brand. ($10.50 per set). Initially I'll only install 3 inputs, but leave room for more.

For hookup wire and solder, Don is just going to give me some excess he has.

Thanks,

Mike

[bperboy]

One thing to watch out for is interference. I experimented with a switchbox several years ago that had many in/outputs, and I used plain hookup wire. There were all sorts of grounding and interference issues, so I would suggest using shielded cabling on the internals of the switchbox.

[mike1127]

One thing to watch out for is interference. I experimented with a switchbox several years ago that had many in/outputs, and I used plain hookup wire. There were all sorts of grounding and interference issues, so I would suggest using shielded cabling on the internals of the switchbox.

What were you getting interference from?

-Mike

[bperboy]

What were you getting interference from?

-Mike

Poor choice of words on my part.. I'm pretty sure it was crosstalk from all the hookup wire crossing inside the case. The wiring wasn't the neatest to begin with, but I had something like 6 inputs and 6 outputs, so there were quite a few wires inside.

[The Monkey]

Slightly OT, but here goes. Let's say you build a switch box. All RCA in/out. Assume balanced source and amp. What happens if you take the balanced source and use an XLR-to-RCA cable to go in to the switch box and an RCA-to-XLR to go from the switch box to the amp? Is that still properly considered balanced?

[n_maher]

No, you'd have lost half the information going through the switchbox so it would not be a simple feat to recreate the lost half. It really wouldn't be hard to build a balanced switch box though.

[penger]

Quick! Get Nate to build you one before he says he's retired.

[The Monkey]

heh. Even I could probably do it; Nate's got enough on his plate with me.

When comparing the DACs I have in-house, I have been using the Manley SkipJack to compare single-ended. What I'm now wondering is whether I would be able to do a fair comparison of the DACs' balanced outs using the SkipJack, but it seems like it really wouldn't work.

[The Monkey]

Here's what the manual has to say about switching balanced:

Using the Skipjack with balanced sources and destinations:

This one is usually pretty easy. All you need is appropriate adapters because the Skipjack switches both the signal and grounds

on the RCA jacks.

XLR pin 1 = not used, Ground & shield will generally be connected at the other end of the XLR cable. Occasionally a simple

“alligator clip lead might be needed to connect the chassis of one unit to another if it hums because it is floating.

XLR pin 2 = RCA phono center pin signal.

XLR pin 3 = RCA phono shell.

If the destination (usually a preamp) is balanced, then it will almost always be happy being driven by either balanced or

unbalanced sources. Balanced inputs tend to be very forgiving and tolerant. Use the adapter wiring described above.

[n_maher]

That might work, sure. You'd need a bunch of fairly specific cables but otherwise what it means is that the skipjack keeps all grounds separate throughout the switching process. That's pretty unique in my experience.

[Dusty Chalk]

Actually, if you're talking completely passive, it depends on the two components being switched, and the adapters you use. If they both result in using the "hot" and "inverted" signals (I.E. not ground/shield), then it's just like having two switches, and floating the ground. (And if they ground-ground [i.E. if they connect "ground" to ground], then you're not even floating the ground [well, you are, but who cares?]). Similarly, if they both use "hot" and ground (I.E. only one side of the balanced), then again, it's just like having two switches in the signal path, and you lose the balanced-ness of it.

I wouldn't mix the two, is all.

[The Monkey]

Stupid balanced/unbalanced world.

[screaming oranges]

Is it doable, then, to make a switchbox that has a mix of balanced and SE ins/outs?

I ask this because it'd be nice to have the ability to select a balanced source to balanced amp or balanced source to SE amp at will.

I'm doing a lot of research everywhere as I intend to work on my 1st DIY project, a switchbox. If it turns out too difficult to do I'll just ass out and buy one. But I don't wanna be a punk!

[spritzer]

By using transformers to perform phase splitting then it should work.