[gitarretyp]

I've recently purchased a RWA squeezebox 3 and it sounds best run directly to my amp. Currently, i have it in the home theater bypass of my pre (see system link), which sounds slightly better than through one of its regular inputs. I'm considering building a simple switchbox that would sit between the pre/squeezebox and amp that would allow me to switch between the pre and the squeezebox. The switcher would have two pair of switchable inputs to two pair of non-switched outputs (amp and subwoofer eq). I'm wondering if anyone else has built something like this or if anyone has any thoughts on the efficacy of such a switcher (ie, would it likely be more transparent than running through my pre)? I'm not a big fan of having a switch in the signal path, so i'm curious to hear other's input. By the way, the best "audio grade" switches i've seen for this would be either the 4pdt offered by percy or a pair of dpdt offered by welbourne.

[jonwb]

You might want to take a look at this thread.  A couple different ideas were thrown around.

I recently purchased one of these at my local hifi shop (they had it in the demo section cheap).  



Its made up of a fairly heavy metal box w/ a crinkle finish.  I haven't opened it up yet, but the switch feels fairly robust w/ very positive detents.  Its not the ultimate switch box, but I figured it'd be a good stop-gap until I either buy something fancier or make my own.  I figured if I wend the DIY route I could always use this box for the enclosure.

I like the simplicity of having the switch box.  Makes it straight forward for the family (1 - for movies, 2 - for the SB2).  I'm sure there is a bit of a sonic penalty w/ the box in line, but I'm not complaining, my system sounds better than ever.

[gitarretyp]

Thanks for the link to that thread, i hadn't seen it before.

So, even your non-audiophile approved (no insult meant) niles switcher is an improvement over your pre? If so, it would seem building a nice switcher would probably be a good idea for me.

[gitarretyp]

While i'm asking, is it advantageous to use two dpdt (one for each channel) rather than a single 4pdt?

[JoshK]

While i'm asking, is it advantageous to use two dpdt (one for each channel) rather than a single 4pdt?

Good question...but I don't know the answer.  With small signals, I can't imagine the magnetic fields coupling, so I can only imagine that by using one switch rather than two you are tying the channel signal grounds together.  Does this create a loss in channel seperation? Don't know.

[gitarretyp]

Good question...but I don't know the answer.  With small signals, I can't imagine the magnetic fields coupling, so I can only imagine that by using one switch rather than two you are tying the channel signal grounds together.  Does this create a loss in channel seperation? Don't know.

Since i'd be using a single 4pdt, the grounds would not be coupled. But that raises another question: How much, if any, would be lost tying all the grounds together and using a single dpdt? I doubt i'd do this simply to avoid ground loop problems, just curious.

[mgalusha]

While i'm asking, is it advantageous to use two dpdt (one for each channel) rather than a single 4pdt?

Maybe. It's possible there will be some capacitive coupling between the channels at higher frequencies. How much? No way to know without measuring. Since a large percentage of gear uses standard rotary selectors I doubt it's much of a problem. (even though you are not using a rotary switch, it too has adjacent connections)

However...

I did some work once on Melos SHA-1 that used a 4P3T switch for input selection. In the case of that unit you could hear a signal from an input that was not selected.

[Dan Banquer]

For you DIY guys building a selector switch box, it's really not that tough. I use an Elma rotary switch (Elma #04-2121) because the spacing between the right and left channels is far enough away so that coupling is not an issue. I use a coax through out the unit to insure low coupling between each channel. The grounding is such that all the right channel grounds are tied together with a 1/8 inch flat braid at the RCA connectors, and the same for the left channel. The flat braid is connectd to the solder tabs of the RCA Jacks. The coax that goes to the rotary switch does NOT have a ground connection at the rotary switch.
If anyone is interested maybe I can get Nathan to do a photo or two of the inside of the SB1.
               d.b.

[Occam]

Dan,

So this is (if you've a mind to implement Banquer's Rational Grounding (tm)  ) where the signal grounds are tied together, including the output obviously, and fed to the linestage proper in which those singnal grounds are tied to its chassis, which is of course tied to the mains ground?

Or in the case of the SqueezeBox where you might digitally control volume and therefore not have a linestage, it still could provide that signal ground/mains ground connection via the fed poweramp, which would require the amp to have signal and mains ground tied together.

Or one could simply view your technique as the proper way to implement single point signal to mains grounding in the switching section of a pre.....

And iff'n you really want a transparent single ended switcher, you've really got to do it this way to avoid gound loops/noise, unless you're very lucky.

[Dan Banquer]

The chassis ground on the  SB1 switch box is NOT connected to the audio ground. I would connect the switchbox chassis to to the chassis of the pre amp, or another chassis you are using in the chain or just earth it.
Hope this helps;
               d.b.
P.S. I hope Chair Dude reads this thread, he might learn how to do customer support and how to approach technical issues from a technical standpoint. Either that or I must be smoking crack:    

[ryno]

This is a relavent thread for me, I'm just finishing a ucd amp where I want two inputs. one for a pre/preo, and one for a two channel pre.  I was planning on using a pair of dpdt's, switching both the signal and the ground. Am I asking for problems?
Thanks, Ryan

[Occam]

This is a relavent thread for me, I'm just finishing a ucd amp where I want two inputs. one for a pre/preo, and one for a two channel pre.  I was planning on using a pair of dpdt's, switching both the signal and the ground. Am I asking for problems?
Thanks, Ryan

Inevitably , because there are no stadards for grounding in consumer audio. I'll refer you to a previous thread and a post made by Dan -
http://www.audiocircle.com/index.php?topic=19860.msg177365#177365&highlight=grounding#177365
and becuase there is no standard, whenever we slot in a new component  with a 3 prong plug we run a substantial risk of ground loop/noise. Inevitably we run have the mandatory finger pointing as to which component is at fault. Usually the new one. After all, it worked fine until that new component was add to the mix.
And we even see vendors advocation 'solutions' which really aren't much different than using a cheater plug ( but with a proviso to avoid advocating a clear violation of code(s) ) -
http://www.hypex.nl/docs/wiring.pdf
HTF is a DIYer going to 'Build according to double insulation safety standards'?

Ryan - first you've got to suss out the grounding scheme of the components you're going to hook together. This is why the good Lord gave us multimeters with ohm settings. With this arcane instrument one can divine whether the grounds are switched, signal ground connected to mains ground, mains to chassis..... That is going to determine what is required to make the whole shebang work.

And if both of those preamps have their signal grounds connected to their power grounds/chassis you might find that swithing the poweramp input signal ground is required to avoid leakage currents and the resulting hum/noise, even if you use Hypex's curious method. Nor does this consider the grounding schemes of the source components your feeding to those individual preamps. With no standards, the opportunities for problems are limitless.    But this is really Dan's bailywick.

[gitarretyp]

I'm a bit confused and would appreciate anyone's input.

It seems to me that switching the hot and ground would help obviate potential ground loops; however, it's been suggested here that tying all of the grounds together is better. This practice seems counterintuitive to me. Is it simply a way of insuring that all components are at the same ground potential? What if one component is improperly grounded?

Also, since i'll only be switching between two components, i don't need a multi-way switch, such as the elma. However, i was wondering if the elma might be higher quality than a dpdt, such as the tocos toggles percy sells.

[Dan Banquer]

I'm a bit confused and would appreciate anyone's input.

It seems to me that switching the hot and ground would help obviate potential ground loops; however, it's been suggested here that tying all of the grounds together is better. This practice seems counterintuitive to me. Is it simply a way of insuring that all components are at the same ground potential? What if one component is improperly grounded?

Also, since i'll only be switching between two components, i don't need a multi-way switch, such as ...

All of your grounds are going to meet at the pre amp right? and if you have an improperly grounded unit I think the best idea is to repair the unit.  Just my 2 cents here. The Elma rotary switch will give you more space between the channels giving less coupling. If that's not important to you than by all means use a DPDT.
The following is part of a post  I put up a few years back. I think this is relevant to the subject at hand.

Typical stereo separation at the listening position is usually somewhere around 8db to 10db or so I have read. This alone would appear to nullify further investigation of electronics and stereo separation, but over the years I have made some interesting observations that I would like to share with all of you.
     In designing and building a few line level units I have observed that the coupled signal when doing stereo separation testing has been 90 degrees out of phase from the input signal. It also appears that it is capacitively coupled and decreases as the frequency drops, and typically 6 db per octave. In reducing this coupling I have also observed better noise immunity. For Example: If I use an “unshielded” wire to go from the back panel input to the board I will degrade stereo separation and at the same time, due to the high input impedance of the input I am connecting to I will have more noise due to pick up. If I use a piece of coax for the same connection I get an increase in stereo separation and lower noise pick up.  It would appear that a higher level of stereo separation could well be more indicative of better noise immunity in this application. My own personal observation is that reducing the 90 degree out of phase coupling gives a better “image” along with reduced noise. At present I generally shoot for close to 70 db of separation at 20 kHz, I find audibility is very difficult above this.  The above makes me ask the question; Is it stereo separation, or noise immunity, or both?
 
         Dan Banquer