Building a 3 Deck Grayhill from two 2 decks

[corgan4321]

I need a couple of the 3 deck 12 position Grayhill switches for a pair of the EZ1290 preamps. Unfortunately it looks like nobody has stocked these in over a year, I'm sure the pandemic has affected Grayhill's production as it has for everyone. I see that Allied has the 2 deck version in stock here. I've never dismantled a Grayhill, is it possible like it is on other switches to add decks? Can I buy 3 of these 2 decks and build 2 triple deckers?

Thanks!

 

[Bo Deadly]

I don't think so. The shaft and the bolts will not be long enough. The bolts you might find replacements for. But the shaft is a cast and milled piece that is also maybe pressed into the bushing. Your best bet is going to be elma maybe. I used relays but that's a whole 'nother process.

You could just use a conventional switch for "line" vs "mic" that engages / disengages the extra amp and then use two decks for the rest. Something like that.

 

[corgan4321]

okay thanks for that info. The EZ1290 is actually only mic input so it’s even simpler.
Interesting, would you be willing to share your solution either relays? What PSU are you using to run the relays?

 

[Bo Deadly]

okay thanks for that info. The EZ1290 is actually only mic input so it’s even simpler.
Interesting, would you be willing to share your solution either relays? What PSU are you using to run the relays?

I would have to do some hard digging to recall enough to fully answer that but it was something like this:

Neve 1073 Relay Gain Control

I'm pretty sure the secondary load impedance using this is correct but not sure about the source impedance seen by the amps. I would have to put some real thought into it but I'm supposed to be writing code right now.

Then I used an Arduino but my code is wound a little too tight to just dump it on some website. Supply was just 5V.

Glancing at the 1290 schem, it seems to me you could just leave the first stage in, adjust things a little (attenuate a little more on the low steps) and do 40db and up with just two decks. Then you could do 3dB steps or just use 7 positions for 5dB steps. The 3 deck switch is really a serious impediment. Adjusting the design for 2 decks would make things worlds easier. No doubt it has been done before. If you're not a pro-builder, then you should really find a proven 2 deck schem and just follow that.