DIY Audio General - stuff you're making, tips, advice sought, etc

[Mrs_Maureen_OPinion]

The last few days I’ve been spending an hour here and there on the pre in-between hacking-down mighty swathes of assorted trees and hedges in the garden before da boids start nesting.

And its throwing-up more challenges as we go along. I know this can happen, but in nigh on 20 years fannying-about with PCBs I’ve never actually experienced it -

We all lift pads at some point - too much heat, too much graunch… But these pads have not lifted, they are not on the upper side of the board where that’s likeliest to happen, instead they have dissolved away to nothing in molten solder!

These are for the smoothing caps, and those inevitably need a bit of heat to free them, but they were no more difficult than any similar I’ve shifted, so this was not the outcome I anticipated. Rather thin copper layer it seems.

Not a problem per se - it’s only a few of them, and I can hardwire point-to-point instead. Irksome, just the same.

[Valvebloke]

Wow ! If it had just been the isolated ‘rail’ pad that was missing then I’d have bet money that it had lifted and got lost somewhere/sometime/somehow. But there’s a neat disc missing from the ground plane too. Any idea what the solder alloy might have been ?

[Mrs_Maureen_OPinion]

You may well have got to the nub of that - all I know is it’s a Pb-free solder that now has a high copper content! I’d guess that it had a very acidic flux content, and since nothing on the board had been hot long enough to expel the flux when it was assembled, that, plus the highish temp (380C) plus the time needed to get the caps up to temp worked together to eat the pads.

Thankfully there’s nothing else that’s going to take so much heating to shift - and, though I usually like to save components by pulling rather than cutting, I’ll err on the safe side with what remains and cut and desolder.

[Mrs_Maureen_OPinion]

So, resistor colour band whizzkids - what value are these two? The colour render in the pic is nearly spot on FWIW, and for @edd9000 what you see is red - brown - brown - gold:

If you’ve answered “210R 5%” give yourself a pat on the back. I can never remember the values and always have to go and look it up…

Anyway… they’re actually 27K…

They’re rather well-cooked 27K carbon films - half watt at most.

They should be these colours (big brown job):

i.e. red - violet - orange - gold

This came to light thanks to needing somewhere to tie the + tabs of the smoothing caps back to now the solder pads are history, so the opportunity to put some 3W rated metal film resistors in should be good for long-term reliability at least.

Obviously that link will have to be hard-wired so I’ve carefully traced the now useless track’s route out onto the underside, so hopefully no unwanted noise pickup/loops.

I’ll tack the wire in place with small dabs of hot melt once everything’s tested, and cut the defunct tracks of course.

[Mrs_Maureen_OPinion]

First of the Fat Bastard Resistors - 220K, now with suitably skinny silver leads.
Knew that reel of silver would come in handy one day (purch’d 2007…)!

I used a high melting point solder for the lead-to-lead connection, and then a LMP solder for the lead-to-board joints, adjusting iron temp accordingly!

Two down, about thirty to go…

[Valvebloke]

@Mrs_Maureen_OPinion

First of the Fat Bastard Resistors

What make and model ?

[Mrs_Maureen_OPinion]

Standard 2W ANUK Tants - AKA “Wobbly Bobby”.

[Mrs_Maureen_OPinion]

This is certainly taking longer than I feel it should! Mind, not been feeling great these last few months. Anyway - 48 resistors later, some sense of progress…

Also got some new valve bases in to replace the horrid, rattly alumina things the pre came with - with their nasty, sketchy contacts. Replaced (after two entirely different styles of Teflon bases refused to fit), with some nicely-made Belton B9A bases with fibreglass insulators and gold plated contacts - hopefully no-more bad connections…

Most of the chonky 2W ANUK Tants needed slimmer, silver leads bending-on, as the thru-holes in the PCB were all sorts of random sizes (but almost always too-small) - often varying as you went from one channel to the other (never mind that the solder-pads on the left channel were almost all fucking tiny! … WHY!? GAH!)…

Not a faff at-all, that…

I hadn’t originally intended-to, but I also pulled and replaced the resistors in the PSU. Some of those fitted were somewhat underspecified for current and/or voltage, and ‘cooked’, and some were carbon film - which is fine, but in time they’re going to get noisy and eventually drift as they were being run harder than they were meant to be.

I had most of the values in 1W, 2W or 3W Welwyn or Vishay metal films in the parts drawers - need-2-buy-20 has certainly paid-off as the years grind-by and prices increase exponentially…

Now if the resistor faff looks egregious (and I admit, it is), then this has rubber-room potential…

The front-panel LEDs - I mean, look at them! Yuck! And they were starting to suffer from the amount of handling this PCB has now received. Steel leads do get brittle fast…

So, with an eye to the inevitability of me putting this all back together only to find I’ve fucked-up and need to dismantle - multiple times… I’ve decided to ease that process by doing a load of work now… So out they all came…

And now they all have nice flexi silicone kit-wire leads.

When I have some more, the little green 2.5mm pitch PCB terminals will populate the board.

Next to do will be the smoothing caps and their attendant hard-wiring: I don’t relish bodging fuck-ups…

Then I have some quieter 12V voltage regs to fit. Those will be interesting as the heat-sinks can’t be removed, and need drilling to ensure really good thermal contact, while making sure no shorts are introduced. They’re being asked to handle close to their maximum current (I think, they certainly run hot as hell even on the big sinks - indeed, I’ve never encountered VRs run so hard in anything, ever!), but they’re also mechanically frail, so much care needed…

With that lot done, it’ll be a rat’s-nest of oversized axial film caps to add, which can only be stood well off the board. Need to figure out how to make some kind of supports for them - gonna feel Rong just zip-tying/hot-melting them all together…

[Gyroscope]

I don’t really understand any of this really, but this amp (it’s an amp, right?) seems to have more than a hint of Trigger’s broom about it

[Mrs_Maureen_OPinion]

Pre-amp, FWIW. Yeah, I’ve got a little carried-away TBH, I started with more conservative intentions. It’s quite the gamble, as I like how it sounds out-of-the-box, but wanted more insight without losing its tender touch with tonality (which is partly why I’ve gone for the insultingly overpriced ANUK resistors…).

Even DIYing-it, this won’t leave change from £1K, so the rational, logical thing to do would have been to buy a different pre, but there’s a lot I like - the sound, look and overall functionality all beat anything else that I could afford at the time, so the dice are rolled…

There were issues with how this example had been put together, too, and those would have needed fixing sooner-or-later…

I also picked it up cheap, and it is now both near worthless AND impossible to service since Herr Becker died and AudioValve is no more.

Still mad: don’t do this at home kids.

[spacehopper]

Maybe but I bet there won’t be much that will better it once you’ve put all back together - a labour of love.

I wish I was good at something other than drinking beer.

[Mrs_Maureen_OPinion]

@spacehopper

I wish I was good at something other than drinking beer.

1. I am NOT good at this - I couldn’t design a circuit to join a battery to a lightbulb. I just bodge other people’s stuff.
2. You have single-handedly breathed life into this forum’s musical awareness for years.
3. Modesty’s fine, but too much of a good thing, isn’t.
4. Drinking beer is one of the Top One life-skills! Cheers!

[spacehopper]

1 - Clearly you are - if I tried anything like that I’d have electrocuted myself within 10 seconds.
2 - Not true - as I’ve said umpteen times we (collectively) have an incredible breadth of musical taste and a lot of my favourite albums have been recommendation from fellow meatmen.
3 - You can never have too much of a good thing
4 - I’'ll give you that one.

[Gyroscope]

This

@Mrs_Maureen_OPinion

You have single-handedly breathed life into this forum’s musical awareness for years

And these days I’m rubbish at this

@Mrs_Maureen_OPinion

Drinking beer is one of the Top One life-skills

too

[spacehopper]

[Waxy]

Get a room you lot.

[Mrs_Maureen_OPinion]

No forum is Compleat without a Belgium / Norn Iron / Barbican correspondant

[Mrs_Maureen_OPinion]

It’s the drink talking…

The thread prune is gonna be hilarious…

[Gyroscope]

I rather saw myself as the 80s hair metal SME

[Mrs_Maureen_OPinion]

This could very well be so, but I so rarely recognise your musical choices that I couldn’t begin to pigeonhole it…Clearly this has to be self-certifying thing…

All moot of course, because Pete and Mark get to decide who we are… “Rolex Curious” indeed! And me, openly bimetalsexual!