hellr8zr wire-wrapped randall 80es 100es red channel aka "preamp from hell"

[quackhead]

This is the red channel from the randall 80es 100es preamp or “preamp from hell”
except wire-wrap is used instead of a pcb.

Wire-wrap is a technique to make electrical connections. It is very reliable and has even been used by NASA. It's also easier and quicker than soldering for me. Super begginer friendly. It's like electronic chrochet or knitting haha
https://www.nutsvolts.com/magazine/article/wire_wrap_is_alive_and_well
Introduction to wire wrap
https://www.youtube.com/watch?v=IXvEDM-m9CE

here is one I made














Want to make one?

You are going to need some wire-wrap pins or sockets. I used 8 wire-wrap sockets with 14 pins per piece.

I also used 8 x 14 pin ic sockets for the components. The components are inserted into ic sockets and then the ic sockets are later inserted into the wire-wrap sockets. You could just insert the components directly into the wire-wrap sockets but putting them into ic sockets allows ease of repair and to swap out components quickly. You can test all the components, out of circuit, by just pulling the ic sockets out. If you want to try carbon comp resistors instead of metal film you can just pull out a ic socket with the metal film resistors and put a new ic socket in with carbon comp resistors. Or switch out capacitors quickly etc...



Amazon or ebay has cheap wire-wrap tools. I have found that after a lot of wrapping 28 gauge wire the cheap blue tool doesn't work as well.. Also the strippers on those are nearly useless for 28 gauge. The 28 gauge wire strips better with a blue handle wire stripper that is”pro tools” brand. The 28 strips in the 30 gauge slot...
I got lucky and found an old ok machine electric wire-wrap tool on ebay for cheap.

Wrap the wires

I used 28 gauge solid core silver plated kynar ul422. There is another kynar in the same gauge but with a different ul number. I don't like it as much because it seems harder to strip. There are 60 or 70 wires to wrap.

Start stripping, follow this order, and then you should have a circuit to insert your components into 

B28 – Input
A28 – D24
D22 – B26
D22 – C19
B26 – C22
C20 – B22
B22 – D25
C10 – C21
C21 – D14
D12 – B21
D12 – Gain Vref
A21 – C27
C28 – A19
A19 – 50k Wiper
B19 – C14
B19 – C16
C18 – C12
C12 – D8
C17 – B23
C17 – C7
C18 – D21
B15 – D20
D20 – C3
C4 – A11
A11 – A9
A9 – A10
B9 – Sustain +
B10 – B9
C 4 – B1
B1 – Vol. Vref
B2 – Vol. Wiper
B2 – B13
A12 – B11
A13 – B6
A13 – A14
B14 – A2
B14 -B5
B3 – Mid. Wiper
A1 – Treble Ground
A1 – Bass Vref
A3 – Mid. Vref
A3 – Bass Wiper
A3 – Bass Ground
B7 – Treble Vref
D6 – Treble Wiper
D1 – D1
D15 – D1
D7 – D18
B16 – D17
D17 – D4
D3 – B18
A18 – Prez Vref
A18 – A24
B24 – Out
A7 – Prez Ground
A7 – Prez Wiper
A6 – D19
A6 – 24v +
A6 – D16
D16 – C15
D19 – D10
D10 – C8
C25 – A26
C25 – Input Ground
A26 – A22
A22 – D28
D28 -D26
D26 – Gain Ground
D26 – A23
A23 – C6
C6 – A15
A15 – B12
B12 – C13
C13 – Vol. Ground
C13 – C11
C11 – Sustain Ground
C11 – D5
D5 – Mid. Ground
D5 – C1
C1 – A16
A16 – A4
A4 – Out Ground
D8 – D9
C9 – C10
A4 – Stomp Switch

Stomp Switch Layout




Here is the randall red channel schematic that I cut up and printed out. It made it easier to make the wrap order.




With a large wire-wrap bit you can even wrap the the pot leads. I put a  little tack of solder on those for extra reliability.

For the power supply I tried several different power supplies. I found the jameco 500ma 24v linear regulated power supply to be the quietest. Most Switch mode power supplies will make a very horrible noise. I also tried 24v batteries meant for garage remotes and they had a whine to them. I did not like how it sounded with two 9 volt batteries. You may be able to do the 9v to 24v boost that was on geofx...seems to have taken it down for some reason and is telling people not to use it without permission or something weird... also with the 9v to 24v I'm not sure what kind of ripple noise will be heard or “sag” you might feel with gain maxed.

If anyone doesn't want to make one but wants one. Email me hellr8zr@protonmail.com  $120 usd equivalent in bitcoin. Comes with 24v power adapter.

edit: I swapped the values of the volume and gain pot from the randall schematic and it seems to work better...

[idy]

It's different.

[strungout]

I'll stick with my iron XD

But good on you for doing stuff differently and showing it off. I'd never heard of wire wrapping before. Always wondered what those sockets with long pins were used for... Learned something today!

Any soundclips?

[quackhead]

I would but I don't have a mic 

They seem to all have a little different tone. I guess cause of the transistor value and capacitors value randomness

Some info on attaching the components to the ic sockets:

I tried conductive silver expoxy. Basically it is put in the oven at 150c for 15 minutes and it hardens. Pretty cool but some components like polysterene 250pf capacitors will melts. If you use all high temp components it might be fine.

Then there is solder paste.
most through hole components do not allow temps high enough for putting into a reflow oven. I tried to use the reflow skillet method but the capacitors will start bulging before reflow temp is reached.

If you get the right diameter lead it will fit snugly into the gold plated socket then put some nasty hot glue on it or maybe dip the whole thing in some resin. I've been using my personal one without glue or solder and it hasn't broken in a few months and i've dropped it with just the bare board clipped to a "third hand"

I guess I could hand solder 96 points plus the stomp swithes and jacks but that's not fun for me. I always seem to accidently inhale fumes. Maybe I need fume hood or I'm burning the flux.

Most of  the boards in those "butiquie pedals" you see on reverb are soldered all at once in a solder pot then sold for 260 dollars lol....