Roberts/AKAI Preamps New Mod/Layout (pic)

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fmhurst
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Roberts/AKAI Preamps New Mod/Layout (pic)

Post by fmhurst » Fri May 21, 2010 1:05 pm

I am developing my own take on the Roberts/AKAI Preamps.

This would be a combination of Rod C's original mod and his Boris mod.

This is the faceplate design:
http://i131.photobucket.com/albums/p290 ... ESTver.jpg

I plan to use the mic input trannies from a Shure M68 mixer - one each - to feed the 12AX7 and the EF86 mic inputs. The two line input jacks to each input are downstream from the trannies.

The power switch on the preamp will be a triple pole double throw. Down will be preamps only, up will be preamps plus amp.

I?m planning on using male XLRs in the panel because female to female cords are mostly what I have around. I noted that Rod uses male, so that?s got me thinking? Am I missing something and should be using female panel connectors?

Does my approach make sense to those of you have completed the mods? Am I missing anything?

Image

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tubetapexfmr
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Post by tubetapexfmr » Mon Jun 07, 2010 11:35 pm

Well female XLR connectors have been the universal input standard for about 30+ years now. I would say stick with what is a universally accepted standard and get some new cables or new tips for one end of your cables. I always found it nutty early on in my gear building adventures to get something from the early XLR days that had male sockets for an input. I've even had old Altec mics that had female outputs on attached cables. All inputs and outputs used to be male and all cables were female. I was told they decided to standardize XLR cables with male on one end and female on the other so they could be daisy-chained if needed, can't do that with male/male without a pain-in-the-A coupler. I mean it is logical now for female to be INPUT and male to be OUTPUT, right?

Also, be sure to wire the socket for pin 2 hot, going to the yellow wire on that Shure transformer, pin 3 going to the green wire, then on the secondary the white wire going to the grid (or in this case DI input switch or tip shunt), and the black wire going to ground. Shure originally had the transformers wired with pin 3 hot on these old mixers. Heck the original 60's models had male inputs as well so go figure.

Don't forget to replace all those electrolytic caps and KEEP the oil caps. The oil caps are usually marked as .01 or .02, some as high as .1 on some models. Anything over .1 is more than likely an electrolytic that needs replacement.

By the way I keep meaning to finish up my tutorial blog but probably won't have it ready until at least August now, so I'll update you guys when its ready, I'll have some of this Shure iron on some of those projects as well. Good luck!

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