AML ez1073 modification: Can a knob be built in the kit in place of the "Trim" dial?

[Troisi]

I just completed the new DIYRE 1073 clone and I really enjoyed the build.

I really want to try one of Colin's kits, and obviously the 1073 makes the most sense.

Compared to the ez1081, I like to have two "gain stages" for lack of a better term, which is somewhat universal and the absence of one on the 1081 seems odd.

MY QUESTION:

Has anyone successfully implemented a KNOB in place of the "Trim" screwdriver slot on the AML EZ1073PRE?

Like, literally just did whatever it took to have a potentiometer sticking out the front panel, presumably the exact size to fit the smaller grey marconi knob?

Would this be a futile effort? Or a nightmare?

Should I try a 1081 instead and see what it's like to only have a gain switch?

Thank you very much for any information.

 

[TwentyTrees]

Yep, both my ez1073pre units have pots with longer shafts in the output trim position, which is R73 (dual 10k linear) in the version of the build manual I have. Unfortunately I don't have a note of which pots I used, but apart from the shaft length they will need to have exactly the same dimensions as the originals (Sfernice P9A) in order to fit - it's a very full and mechanically relatively complex module, so it's not going to be possible to just shove any old pot in. I may have had to ream the holes slightly for the shaft as well, I can't remember.

In my view it's definitely worth doing. The gain switches are well matched regardless, but it does allow for "pushing" the preamp more easily. You can also reduce the value of R71 to allow a greater range of attenuation from this trim pot. 0 ohms = full attenuation counterclockwise.

 

[Troisi]

Thank you for your reply.

I will definitely do some research with the colourbook and what exactly goes in and around that trim knob. While I do have quite a large amount of those sweet 70's - 80's precision scientific pots (inherited from my late father), I know I can't just pull one out of the pile and shove it in.

But if I'm reading you right, and what my research will probably tell me - is that I need a Dual Gang 10kohm Linear Taper pot with a shaft (and bushel) thin/narrow enough to fit.

If this is all there is to it then that's wonderful news.

Thanks again.

 

[TwentyTrees]

If this is all there is to it then that's wonderful news.

Pretty much, yes. You could also use a single gang 5k (or 4k7) pot, as the two gangs of the 10k are paralleled, though if you can find a two gang 10k then it will be marginally stronger and more stable, mechanically speaking. Though if you use one with a long enough bushing to secure to the front panel with a nut, you'll be fine with a single gang.

On the pot itself, I think the Sfernice P9A range has been discontinued but the datasheet is still out there so you should be able to get the key dimensions from that.

 

[Troisi]

I haven't looked through my bins of hundreds of old Clarostat pots my father left behind, and whether or not I will find something in there is a question to be answered another time.

I did get the old Vishay Sfernice P9A datasheet, and compared it against the design spec/instuctions in the AML pdf.

Suppose I cannot find anything in my current NOS potentiometers "pile", and purchase something from Digikey or Mouser.

This is a slow process, and I don't want to waste your time (Thank you for all of your great help so far), I'm hoping maybe someone sees this thread and has an exact part number for the "best pot for the job" on this modification.

So far, I have only found the "worst-case scenario" pot, which is this: https://www.digikey.com/en/products/detail/cts-electrocomponents/270X232A502B1A1/203785

That is a single gang 5K with a long (and thin) enough shaft to protrude far enough through the front panel. But it is only one gang, and not "mechanically stable" as you mentioned.

I don't like how the placement on the PCB is so far back.

What I really want to find is a 1/8 shaft or thinner diameter, with a 1/4" bushing (or thinner), where the bushing extends BEYOND the faceplate - far enough to fit a washer/nut onto the faceplate itself, But still solder dual gang into the correct PCB positioning.

Is this asking for the moon? Maybe so.

At worst, I think I could live without a nut on the faceplate and just have the shaft extend long enough to fit a knob on. However, I would like to find something similar to the part I linked above, but dual-gang 10K instead, for stability.

If/when I finally figure this out, I will post an update here for anyone else trying to do this modification.

Thanks again.