Rosamp SLO 30 build diary: a noob perspective

[Asdrael]

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 (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):



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:



Putting some sockets in:



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:



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



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:



Queue a lot of continuity tests, all seems good and ready to go for the next stages (only once a week though, sad).

 

[Asdrael]

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:



To this:


And from this:


To this:


I am pleased with how it went, seems I got better at soldering:


I also redid the ground bus for the pots. I was ashamed of my first attempt:


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.

 

[Asdrael]

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!


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):


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).

 

[Gordo]

Looking very nice!

 

[TillMack]

@Asdrael
Really clean build so far !!!
Really good work !
Take you time and it will turn out awesome.

 

[Asdrael]

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.



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.



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.



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.



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...

Take you time

That's the name of the game right now

 

[Asdrael]

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:



and then soldering said wires to the preamp PCB.




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.





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



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.



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


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.



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.

 

[Asdrael]

I need to vent so here goes

Still waiting on the light bulb limiter and Variac from a friend so started on the headshell. I wanted to do Box joints, but we don't have a Datto blade, plus I was scared of doing something with a table saw and too lazy to do something with a saw and chisels. I thought about doing a jig with the laser cutter, but I found an old jig in the workshop:

So I'm not sure how to explain it. You have an adapter that you have to put into a drill (no, not a router), onto which you clip the black handle thing, which has a hole in which you screw the router bit. The template is what you camp on your boards, and the handle slides into it to guide the drill to route out half-blind dovetails. It's the most unlogical thing I have seen. Fun fact: it's so shit that we have three of those because the fucking router bit is ass to unscrew and gets stuck. Plus, because it rotates so slow (remember, a drill, not a router) that it will not stay sharp more than 5 minutes. Icing on the cake? You still have to round off the dovetails by hand so they fit. Why we have those and not a regular router template for box joints? Beats me.

Anyway, I did it, and I tried to make the most of it. The good thing is, with a bit of glue and a lot of hammering, it went it very tight. And looks rather nice, beside some small alignment issue that I have to sand out. This is likely due to the fact that you have to align the board on the side of the template which has rounded off edges. My god.

Part one drying, everything is 90° (miracle I tell you) and tight. Need to hammer in the top now.



Hoh and I build a pedal for the channel switch but only had a momentary footswitch left, so a latching in on the way.

 

[Zanshin]

I was wondering how your power up went.

The joints look strong regardless of the frustration involved! I’ve thinking about this process too. The best solution I have on hand is a Kreg pocket hole jig, maybe I’ll just get a box made haha.

 

[Asdrael]

I was wondering how your power up went.

The joints look strong regardless of the frustration involved! I’ve thinking about this process too. The best solution I have on hand is a Kreg pocket hole jig, maybe I’ll just get a box made haha.

Thanks! Yeah the joints are actually way stronger than I though. I had to use the wooden mallet and a bit of force to slide everything in place. With Titebond in the slots, and considering it's 18mm birch multiplex, I am fairly sure it won't fail.

And for the power up: I will post an update at least every two weeks until the amp works. If I don't, send a search and rescue team

 

[Asdrael]

Hey the case turned out better than I thought it would!

Rounding off the edges was fast and smooth, thanks to a brand new router bit.




Putting the Tolex on was messy. Also, the instruction of the glue asked for 30min minimum of resting time (apply on both Tolex and wood, wait 30+ min, put the two together) but that was way too much. 15 was plenty. It's my first Tolex job so there are imperfections where you expect them (yes, the corners) but overall I am happy with the results. The corner mistakes are mostly hidden by the metallic corner protections. I am not that happy with the handle that seems a bit cheap but I am a bedroom player so no big deal. The worse mistake is that some of the screws holding the actual chassis are too close to said protections so I had to file some metal to make it fit well. Not a big deal as it's on the underside but hey, it's there.



Yeah, snakeskin, it's a Soldano kit in the end! Sue me.

With the chassis in, there is 2mm at most on each side. That was my safety net.It's a bit more than on commercial amp that tend to have 1mm but given the jig I used and my amateur hour Tolex job I take it as a win:





Also did a pedal for channel switching:





I need to finish putting together the light bulb limiter (I still have 2 filament light bulbs in my stash... you know, the ones the EU banned 20 years ago?) and order/put a finish on the grill plates and I will be done with the construction part and ready to zap myself!

 

[TillMack]

@Asdrael
Awesome job !
Just fire up the amp and rock the hell out of it.

 

[Asdrael]

@Asdrael
Awesome job !
Just fire up the amp and rock the hell out of it.

Cheers! I have family visiting but I have done this yesterday:

And I received my front and back panel grills so I have to paint those. Hoping to fire it up tomorrow...

 

[Asdrael]

Well well well... Got busy today.



Took my time to follow Rob Robinette's recommended startup procedure with my current limiter and new multimeter. Happy to report it went very well!

It even fits great into the housing I made.



Even my pedal to switch channels works (!). I have to say I am very, very pleased with how it sounds. The overdrive channel both has presence and great definition while punching you in the chest on every palm mute. The clean isn't that amazing but more than decent. And the crunch is in between and it's actually pretty silent even with quite a lot of gain. I still need to mess around with boosts etc but I am ecstatic now, it sounds even better than I thought. Also surprised that it worked on the first startup and that I didn't hurt myself.

Overall, I can recommend the kit if you like complex projects and taking your time. The layout is well made and beside soldering the 12ax7 sockets there was no real technical challenge.

Head shell and high end transistors included, I think I am at around 1200€ total for this. Worth it.

Also obligatory tube pic:


I will paint and label the front and back grill that I received yesterday at the end of the week, post a final update and call the project done then.

 

[fontoponto]

It looks fabulous! Especially the powder coated chassis gets me everytime I see the Rosamp kit.
And thanks for the link to Robs startup page. I need this. Last week I was so out of my mind that I fired up my first tube amp without a load and measured for like 15 minutes until I noticed... All is fine.

 

[Asdrael]

So yesterday evening, I completed the build by adding some support plates inside for the front and back grills and painted everything. I am very happy with the results!

Amp now officially done, a great experience, can recommend, five stars, etc. Happy to say I did everything myself start to finish. Thanks again @TillMack for the initial guidance on capacitors!

 

[lowpitch]

So yesterday evening, I completed the build by adding some support plates inside for the front and back grills and painted everything. I am very happy with the results!

Amp now officially done, a great experience, can recommend, five stars, etc. Happy to say I did everything myself start to finish. Thanks again @TillMack for the initial guidance on capacitors!

View attachment 85432

Turned out beautifully. Gotta be honest, I'm a little jealous

 

[drgonzo1969]

Congrats on the killer build and thanks for posting the whole process! I’m torn between building a SLO and buying one of the new X-88ir’s.

 

[fontoponto]

sir this is a diy forum! the answer is clear
Edit: another slo choice if it has to be a preamp
https://www.musikding.de/High-Gain-Tube-Preamp-Kit