Ultra-high performance low-buck phono preamp (DIY project!)

[laatsch55]

What she actually said was " My, what big nuts he has"....
Yeah, she's a trip, definitely a keeper..

 

[laatsch55]

We have some that measure 4-1/2" across, the go on wrist pins on a pumping unit, torqued to 5500ft/lbs.

 

[J!m]

5500 ft/lb is serious.

Breaking 1” drive torque multipliers serious.

Approved.

 

[laatsch55]

3' long hammer wrench, as far as you can go with a 20 lb sledge, then go to the next hole for the 3/8' cotter key...with the crane usually..

 

[J!m]

Today my enclosure came in so I started roughing it out.

it has more RCA holes than I need, so I adapted two for turntable grounds.



Since they didn’t fit, I made some adapter bushings for them.


Put some clear coat on them after I verified they fit.


Had to make an adapter for power. It’s set up to have everything in one box but I’m running the power supply remote. Filter board is in here but what started as an adapter plate turned into a steel box to control RF.

 

[J!m]

I had this bit sticking out I figured I’d extend to the front to isolate the power but the board is so small it evolved into an enclosure.


I blasted and painted it. Now to work out the front panel…

 

[mlucitt]

Nice work on the bushings and the enclosure. Don't forget to drive a Dremel around and inside the phono grounding hole, that anodizing is a fairly good insulator and may act as a capacitor dielectric!

 

[J!m]

There's a washer with a spade terminal on it for running a ground.

 

[J!m]

I’ve not updated here in a while!

Bunch o photos inbound!

 

[J!m]

More:

 

[laatsch55]

That's a lot of work there Jim...

 

[J!m]

Plenty of time when you get the wrong relays.

Twice.

 

[laatsch55]

Twice?? That's nice...

 

[J!m]

Yep.

 

[mlucitt]

Power supply?

 

[J!m]

Got one.

 

[J!m]

Believe it or not, it’s a cheap switching power supply. And although apparently not necessary, I am mounting it external.

The small board in the steel box is a filter board.

 

[J!m]

Minor progress today.

Some of the caps are 1% tolerance, and they are back ordered u til December. I found nearly identical ( brand etc) at 2% tolerance because I figured they would be the only thing I’d be waiting on.

Today I measured them with my Fluke (not the best tool for the job) and they all measure within 1% of value. Three were right on.

So I took two that were right on and put them in the MM board, so it would be finished. I also added the cartridge “loading” caps. So that board is now done. I already had the output wires in place but added the input wires today too. Small victory as I placed another Mouser order…

The muting relays are also back ordered until December. Two “replacement” relays are well spec’d but larger form factor. Today I found the SMD version of the exact relay and orders those. I’ll have to straighten the legs out and through hole solder them. Wish I figured that out a couple weeks ago…

 

[J!m]

A little more wiring today. The box is starting to not look so big…

 

[J!m]

Another update.

Again with the wrong relays… these are/were the same relay, just with bent legs for SM. I straightened them carefully and found:

They don’t fit.

After three failed attempts to get a fucking pair of relays, I MADE them fit.


One side I got through the board; the other side is surface mount. I flowed enough solder to see it in the holes on the other side so, DONE.