Switch Box for Two Turntables into Eros

[adeep42]

Would like to build a simple, passive switch between two turntables and my Eros. Need to know what kind of switch to buy and best way to accommodate the grounds. Do you think adding these additional components in the signal path would have any negative effects? Any thoughts welcome. Thanks,

Alan

 

[Paul Birkeland]

I would get a 4P2T switch so you can switch both signal hot and signal cold.  The grounding connections from both turntables should be happy enough being connected at the same time.

 

[Adrian]

This should work.
The center row goes to the EROS and the outside rows from the turntables.

https://www.parts-express.com/4pdt-mini-toggle-switch--060-524

 

[adeep42]

Thanks Adrian,

Really appreciate the help. Have been looking at PartsExpress, PartsConexion, Mouser and elsewhere trying to find the right switch. RCAs should not be a problem. Still looking for the right type of ground connector and am still trying to work out how to wire the grounds. Thinking about just wiring them straigt through and the connecting to the Eros.

Btw, this is all still early in the process. My goal is a new rack with some more room for a second turntable. Then I'll have one for stereo and one for mono.

 

[Paul Joppa]

Are you planning to put the switch in a separate box? If so, then here are some thoughts on grounding:

First off, distinguish between shield and signal grounds. The turntable ground wires should connect to the box, which should then connect with another separate wire to the ground post on the Eros. This puts all the signal components inside a metal shield. The signal and signal ground should both be switched, as PB explained. The signal ground should should have no connection to the shield ground, except for the connection inside the Eros (at T20 and T26, which are wired to T23 which is bolted to the chassis; T23 is also connected directly to the ground post).

 

[adeep42]

Thank you Paul. Yes the plan is to put the switch in a separate box. Could be a plastic or metal project box. Wood would be more esthetically pleasing if I could find the right box. My thoughts definitely were to have two sets of inputs (including grounds), then one set out to the Eros (including the ground).

 

[Paul Joppa]

To provide shielding, the box must be electrically conductive - that means a metal box. You could of course wrap it in wood, or line a wooden box with sheet metal.

Eros itself relies on the "ground plane" effect, which provides some shielding as long as the components and wires are close to the chassis plate relative to the size of the plate, and not close to the edges of the chassis plate. This is good enough in most cases, but adding wiring and switches in the input lines creates so much additional potential exposure to interfering electrical fields that I would still recommend the metal box for your addition.

 

[John Swenson]

For the input to a phono preamp I would recommend gold contacts, the signals are very low level, the gold contacts will keep the contacts from corroding over time.

Most of the toggle switches use silver contacts, but I did find one 4PDT toggle switch with gold contacts:

NKK  M2042SS1G01

These are in stock at Digikey and Mouser.

This is the switch I would use.

John S.

 

[adeep42]

Paul, Thanks for your ongoing interest. What about a box like this from PartsExpress, Hammond 1590BB Aluminum Diecast Case 4.7" x 3.7" x 1.34"? Would I ground the RCAs to the box and then pass the tonearm grounds through the toggle switch?

John S., Thanks for your input as well. Really greatly appreciated. That toggle really looks good.

Alan

 

[Paul Birkeland]

Signal and signal grounds are switched.  You do not want to ground the RCA jacks to the box (the box is part of the shield ground, not the signal ground).

 

[adeep42]

Thanks Paul, I've ordered the parts. will report progress and hopefully success.

A

 

[adeep42]

Finally got around to building the switch box over this past weekend. Thanks to all for the input and suggestions. Will test within the next few days. Keep your fingers crossed!!! Meanwhile a few pics.

Alan

 

[Paul Birkeland]

All of your signal grounds are floating;no signal will flow. 

You do not need to switch the shield grounds.  Each of these is already connected through the chassis anyway.

You do need to switch the signal grounds.  Your RCA jacks should've come with washers that have integrated solder lugs, you'll want to use those. 

 

[adeep42]

Thank you Paul. Yes I have the ground lugs. I had a feeling this was were there might be a mistake. When I put the ground lugs back on the RCA's, How do I wire them?

 

[Paul Birkeland]

Image attached.

 

[adeep42]

Thanks Paul. Thats great. Back to work.

 

[adeep42]

Paul, just rewired as per your diagram. Your green is my blue. Busy schedule for the next couple of days. Will try to test during the weekend. Again, keep your fingers crossed. Thanks for the help.

Alan

 

[adeep42]

PB, Help. Started testing and before I knew it, no signal. Thought it might be a tube and as I was pulling one out to replace, realized that as the top plate was flexing, I had a signal. Since it's both channels, do you have a thought as to where I should start with the chopstick?

 

[Doc B]

Visually inspect all solder joints. If you don't find the bad one, do all voltage measurements.

 

[adeep42]

Doc, Thanks for the guidance. Found that the 6" STP red wire where it is attached to T6U had broken. Repaired and resoldered. Did the resistance checks for that terminal and all the voltage checks. Back to sounding great. Will test the switch box in a couple of days. Btw, I found during the original build and now that the wires in the STP are very brittle, one little nick and they'll break. Think it would be good to amend the Eros manual with a warning to future builders.

Alan