Rosamp SLO 30 build diary: a noob perspective

Asdrael

Well-known member
Hey,

So since I have been building a few pedals (and confidence), I thought I would tackle building something I always loved the sound of: a SLO. And since I am in the EU, there is a reasonable option pricewise in Rosamp. The few thread in here also convinced me it was within reach, provided I take my time and double/triple check my steps. I thought I could open a "build thread" here as it's my first amp build and might help people decide if they want to attempt it, and so you can all shit on my routing/soldering skills :ROFLMAO: (advice welcome obviously!).

So queue up waiting anxiously for the Rosamp shop to open again over summer, and this showed up (home made pedal for scale):

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I went over it with the help of @TillMack (thanks again for the hand holding!) and we agree a few electrolytic caps needed an upgrade (25€ or so). Queue up an order of Nichicons/Panasonic/Vishay later, and a quick exchange with Rosamp because I somehow was missing the tube sockets, and I was ready to start.

Day one in the workshop, starting with a clean desk:

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Putting some sockets in:

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Some more hardware goes in - the standers were not that easy, as the threads with not perfect/dirty and the screws are pretty soft metal. Had to be careful not to strip the heads:

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Some wiring done for the first day, inspired by some clean builds from @jjjimi84 @KindCanuck :

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And my my first flying ground bus - I didn't trust myself to bend and twist all the pots though so I went with links. If you all tell me it's shit I'll redo it:

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Queue a lot of continuity tests, all seems good and ready to go for the next stages (only once a week though, sad).
 
Yesterday evening was PCB day. Rather straightforward except that I learned that the leg length of axial electrolytic capacitors has nothing to do with their polarity.

Went from this:

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To this:
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And from this:
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To this:
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I am pleased with how it went, seems I got better at soldering:
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I also redid the ground bus for the pots. I was ashamed of my first attempt:
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I also did a bit of random soldering in the chassis. I tried to tackle the "switch harness" but broke one resistor while bending it so I decided to delay it till the next session. I will then solder the harness mounted on cardboard and dump it in. Funny how a chassis looks big until you actually have a soldering iron in hand.

Then I spent one hour trying to figure out why my heater buses were shorting (the lamp was in...) and why my input jack was shorting (a neutrik shorts without a jack in...). That's when I realized it was midnight, way passed my bed time, and that my brain fog was London fog worthy.

Till next time.
 
Nothing major for the diary, but I had a good hour tonight so I decided it was enough to install the transformers and do a bit of preventive cable management. For some reason I dreaded cutting the cables coming from the transformers, but I had a clear mind (ie no beer in me) so went for it.

Pop the irons!
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After a bit of routing, figuring out that diarrhea green on the layout is actually yellow, and a transformer having "mixed" cables (wrong color, wrong hole but hey):
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Should be good for next time I have the soldering iron in hand. I still have to cut the feeds I don't need (ie 120 and 240V) and isolate them. No idea how to do it smartly. Cut short, heatshrink, isolating tape is my plan (and then tuck them with a cable holder somewhere).
 
Yesterday was one of those days where it does not look like much but I actually made quite some progress. The offboard wiring is almost complete and it's turning out just fine. I just have some issues with the 12AX7 soldering as they are narrow slits and it feels like I have to put quite a lot of solder for the joint to feel good between the eyelet and a narrow wire/resistor wire, almost to the point where it's running down the pin. So I killed to birds with one stone and decided to put heatshrink on the pins. Maybe not industry standard but it both looks and feels better.

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Kinda happy with my harness. I decided to use quite a bit of pretinned stranded cloth wire as it felt like a good compromise between rigidity/flexibility, diameter and workability (you can see it on the pots as well). I use it in my guitar wiring and was always pleased with it. Note the solder lob on pin 2, that's what I meant by sometimes having troubles soldering those pins. I found a better way though so the next ones should be good looking.

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Effect loop and output jack are all neat and tidy. Note: the rotator switch is really heat sensitive, but the pins are thick. Almost impossible to solder, even with a good iron at 350°, without a tiny bit of plastic deforming. Shouldn't affect function tho.

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Also holy cow the soldering on the power tube socket sucked was really cramped. And having only 2 holes to put 2x 1mm leads + a bus was not fun.

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Last but not least, I had to spend an hour with a tiny 2.2nF ceramic cap in hand playing "where is Waldo" as I could not locate where it should be. Found it hiding on the preamp board...

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Take you time
That's the name of the game right now ;)
 
Couple of days ago, I had some time at home so I did a complete check of what I had done so far (looked good) and prepared the next steps: a ton of flying wires. So yesterday I did the mating between PCBs and the rest, which started by preparing the chassis thoroughly:

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and then soldering said wires to the preamp PCB.


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Also noticed I had completely missed the bridge under the PCB (J1-J2), so I started with that. Opted for a silver plated thick wire with some transparent shrink tube on it.

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Well that looked fun. Also that made the soldering iron look massive in comparison to tube sockets.

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Went through everything. The V1 wires were a tad short and not fun but from BV2 on I had a good rythm. I only made one mistake with the side of the iron connecting to a wire coming from a pot. I replaced it to be on the safe side. Rest was smooth, but holy rat's nest.

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Did the same on the poweramp PCB side, which completed the wiring and soldering part of the build.

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I wasn't ultra happy with the looks and I had just gotten hold of a bunch of cable binders to I went to town.

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Much better.

Overall, a pretty fun project and some good experience. There were no troubles, except some of the soldering for the ground of the coaxial wire on the PCB were on a bit of bare plate at the back of the PCB, which may be standard practice but was a bit of a struggle. On the kit itself, everything was fine but the plastic of the wires were not of the best quality. Pretty low melting point. I could/should have started with something better.

Now before you ask: no, I haven't fired it up yet. I know myself, if I do and something doesn't work I will completely forget I have a family and a job until I figure out what to do. So I am keeping it as is until I am done with the shell (I'll do it myself) and my workshop buddy brings his variac and light bulb limiter (can't find incandescent lightbulbs in Europe anymore).

I'll do a triple check of the wiring this week and grab the plywood for the headshell (like 18mm birch but I'll see what they have left). I have the tolex, handle etc already. It shouldn't be a big deal doing it, I think we have a box joint jig at the workshop too.
 
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