Radiospares OT/Electroswitch placement

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Radiospares OT/Electroswitch placement

Postby bigtomrodney » Tue May 03, 2011 4:37 pm

Howerya!

I'm looking forward to installing an RS OT with rotary switch to allow proper impedance switching. It's the Electroswitch rotary layout as seen on the JTM45 Yahoo Group.

The switch has a large diameter and would normally be right over or between the output valve sockets. I'd be a bit concerned about the proximity of the solder lugs of the octal socket and the switch perimeter. I was considering moving it elsewhere and the most obvious place is to swap the order at the back so that the speaker outputs move closer to the power socket side and the rotary switch ends up at the phase inverter socket.

Here's my question: Is this a terrible idea? Should I expect to increase noise by having the OT secondary leads hovering near a preamp stage?

Any better suggestions?


Anyway, cheers for getting this far dudes.

Take it easy,
Tom.
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Re: Radiospares OT/Electroswitch placement

Postby dai h. » Wed May 04, 2011 8:00 pm

It's not generally a good idea to move stuff backwards, that is, place signals backwards after they've been amplified. Mentally, I picture more signal radiation, plus if you place lower impedance signals near high impedance areas, they are liable to be picked up. There are examples I've seen where it's possible to accomplish this through careful placement and shielding, such as when the OT is placed near the preamp area, and the wiring is crossed at a right angle and shielded relative to other wires. Easy experiments to check out how bad (unstable, noisy) things can be are putting the pickup near the output transformer, or running the cable from the guitar to amp input in parallel with the speaker cable (so they are paralleled). I would think about what is running through the wires in mind, then distance, orientation, shielding.
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Re: Radiospares OT/Electroswitch placement

Postby bigtomrodney » Thu May 05, 2011 6:28 am

That pretty much confirms my suspicions, thanks for that Dai.

I'll see if I can work it in the current impedance selector position. At worst it'll move towards the IEC socket or I'll settle for only 8/16Ohms through the DPDT setup.

Cheers again,
Tom.
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Re: Radiospares OT/Electroswitch placement

Postby bigtomrodney » Wed Dec 07, 2011 4:36 pm

I just wanted to update this thread, seeing as how I've found it a few times in Google searches!

I wired the rotary switch and all looked well, I had it sitting just above the Phase Inverter. During some troubleshooting I decided I wasn't happy with my wiring, particularly for something like an output so I pulled it and went for the DPDT solution. Anyway, the amp is working great and even with this directly above the PI the amp is dead quiet. This puts my two year old Bluesbreaker Reissue to shame in terms of the noise-floor.
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