more about home brewed prefixes...?

[chrisbathory]

Hi Gents,

I was lurking in the old forum and started to follow a thread about a DIY prefix based on Naim phono 323 stages and a hicap, however beyond a few messages that it was easy, the thread petered out quickly...

I'd love to have crack at this - I'm sure at least half the 'tuning' problems I have on my LP12 are due to the complications to suspension bounce caused by the existing arm cable....!

As a trained solderer, but having little experience beyond once having worked in an electronics production unit, I was wondering if anyone could explain a little more about what would be involved?

I have both spare 323 S boards and a hicap available. Clearly I need to get an SME type connector to attach into my Ittock arm pillar, and I need to fake up a mount for the PCB's underneath my LP12, but what else would need to be done? Any advice on cabling e.g type of wires, terminations etc all gratefully recieved.

Thanks very much for any advice offered!
Chris

 

[LesW]

As I said, a piece of cake:

Locate the cards away from the motor and wire them according to the format within the NAC series pre-amps ie. Both 0V (pin 2)together for a common ground, the 2 X +24V (pin 4) to the relevant supplies from the HiCap. Signals in to pin 1 with screen to pin 2. Output from pin 3 with screen again to pin 2 (0V).

Should work like good 'un.

 

[chrisbathory]

Hi Les,

Thanks hugely for the help, the board connections are clear for me now...

Do you have any advice on connecting to the arm pillar?

- I've been hunting around but can't find SME type plugs listed anywhere! - maybe they are really called something else? Or can you recommend another way to connect up to the arm/cartridge...?

Thanks!!!
Chris

 

[Martin]

Chris,

I hope you are sitting down (likely, if you're reading your computer monitor). SME plugs cost about £65 each. You can buy them direct from SME.

BTW, note the lovely (70's?) picture on the front page of the SME web site.

cheers, Martin

 

[chrisbathory]

Good job I was seated when I read your reply Martin!!!

Do you think some push-on connectors (like headshell ones) would work OK here? It looks like I could push 'em on with some fine needle-nose pliers...

And any suggestions for the type of wire to use would be gratefully received... seems like very fine so as not to impede suspension has to be balanced with electrical characteristics...?

Thanks!
Chris

 

[Andrew L Weekes]

Chris,

Since the SME plug is a form of DIN, IIRC, it might be possible to hack a DIN connector to do the job.

I'll take a closer look at my redundant Linn arm cable - in fact why not visit a Linn dealer and ask to buy an old second hand arm cable for a few quid?

My dealer always had loads kicking around, it seemed, you may be able to persaude a dealer to part with an old one?

Andy.

 

[chrisbathory]

Thanks Andy,

I'll certainly try this next time I visit a Linn dealer... Of course I do have an SME plug on my existing cable but an irrational fear of irreversible changes sets in when I look at it!

So this morning I decided to head for my nearest Maplins armed with a fiver, a little knowledge from Les (and some supplementary info gleaned from a posting by Mr Ron the Mon).

I had already decided to transplant a chord cobra 2 phono - din from my NAD 512, and butcher my old grey Snaic 5 (redundant from a black snaic upgrade 2 years ago). So I needed something like cartridge push connectors (to replace the SME plug), some suitably flexible wire and a couple of phono sockets - so that my cobra 2 can go back onto the NAD as required.

Bad news at Maplins, no stock of the flexible 1mm cable in any colour, no cartridge tags either... So brow furrowed I started browsing the shelves... 10 mins later I headed for the checkout with a couple of meters of screened audio cable (not the thinnest they had 'cos it just looked too thin!) a pair of phono sockets, and a 'D' socket (computer-type connector with many holes - and therefore many individual miniature sockets inside !). Total bill £3.60...

Several hours later I had a piece of thin MDF with 2 tie wraps holding my 323/4 boards, another tie wrap holding a butchered plastic tray - now housing the phono sockets, and a maze of screened and unscreened where it seemed sensible (I stripped the screen off).

My old grey snaic had an end chopped off and the D connector sockets (which fell out when I drilled the assembly rivets from the casework) proved very versatile being not only the right sort of size to fit the SME pins, but also were a tight fit inside the connectors on the 323 boards (trying to be both easily reversible and upgradable - if it was worthwhile I wanted to be able to transfer in my 323/5-K boards from my 62 smart-ish).

The Hicap was ceremoniously set up and plugged in, the 'DIY-fix' I screwed into the Sondek, Grey Snaic '3' (not signal carrying in this implementation) plugged in, the cobra yanked from the NAD and eased into the DIY-fix phono sockets...

Switching on and putting on a handy REM record, I turned the ligts down, grabbed a G&T, and settled onto the sofa... From cold it was all immediately better, more space, more tune, more detail, and by the time 3 or 4 tracks had flowed by it was sounding very nice indeed.

Hmmm, next step is to pull the 323/5 boards from my 62, I couldn't resist listening again before doing the 323 upgrade, and it was really excellent !!! board pulling the 323/5's from the 62 really snapped things into a much tighter focus, the music really started to bounce along... I ran and dug out my old Peter Gabriel 4 (Mask), got another G&T and sat transfixed with all the hairs on the back of my neck standing up - It was just like hearing it for the first time again!!!!

Cooooo-ol stuff!!!

I guess I need to make it all more professional now, plug the hicap into my hydra, do the proper SME plug (the D sockets work, but aren't really tight enough) and solder in the wiring to the boards... I should also be able to hard-wire the cobra 2 to the DIY-fix (I have a plan to acquire a Naim CDP soon - I hope!)

So thanks for all your assistance chaps - hugely worthwhile mods which have really transformed my LP12 - it even seems to 'bounce' cleaner!!!

Chris