High gain SLO/Ubershall: 1 Intro

The machine, this is the main amp I play and the platform I most try to optimize. Origins in Sloclone, It can be switched between key components of an Ubershall, tastes of a Rectifier, controls of a Larry(Fortin), Friedman and lots and lots of modifications and circuit choices and ideas of my own, and select ideas from the sloclone forums. In total I have implemented 28 switchable mods, as seen in the image, and while the rear and top certainly has a lot less in terms of switching going on, except for some 50/100W, pentode/triode, and parallel/serial loop arrangement, the circuit have a lot more going on that is not switchable as well.

Note the Logo of a real Soldano amp, this may be frowned upon but I really only use it in respect of the origins of the circuit not to pretend it is something it’s not, rather have that there than some made up logo as a badge. Since in the 80’s the core soldano amp inspired so many others that where to come, sadly the Mesa Rectifier just straight out copied the preamp, before it went to dominate the 90’s and 00’s. For my reinterpretation and extension of all these Metal amps I’ve taken what I wanted expermented and made a very very tweakable amp, not actually seen anything like it on any of the builder forum’s I’m on.

The Circuit can be gleaned in this blurred image, I’ll add the full clear one at the end of the series, but before that Ill walk through most if not all of the mods, in batches, including their parts in the circuit, for now all colored blocks in that image is deviations and additions from a soldano SLO 100 circuit, basically not a lot left that is a SLO however many edits can be switched out so that much of the core SLO sound can be retained.

So the parts count of this is fairly challenging, close to triple the original parts count, so I had to be creative, building the circuit in layers, and on vertical arrangements,  using standoffs and posts.

First I guess I can mention something that isn’t a mod but very much improved the sound of it. Parts selection, I have during the years tried so many different parts in this, rebuilt it many times, changing all the parts except for a few resistors and the tube sockets.

I Found that there is are reason for selecting carefully the coupling caps, the capacitors that carry the signal one stage to another, the usually used polyester caps actually is not the best ones used in a hifi setup, it has some distortion, but we humans when playing a guitar amp don’t want the perfect clean sound this makes the amp more alive-feeling with some nice sweet distortion, most of the time. I so used the best of the best for this, old sprague 6PS and 10PS capacitors, the importance is that they are FILM capacitors, and also they are somewhat directional being more noisy (in a bad way) picking up noise when oriented the wrong way. Also I have a mod that switches all of them at once, to a set of mica and teflon caps, old russian USSR ones, new would cost an arm and 10 legs as in hundreds of euros. when selecting these there is a more complicated high end spectrum, very nice crispness.

For resistors, those that carry the signal needs to be carbon type, carbon film for noise, since their distortion, when they are close to the power rating of the signal, tooo high wattage won’t have the effect, is a very good thing bringing a distortion to the sound that most describe as a ‘sweetening’. these are old known selection, but I even recently heard mr Friedman himself in a podcast explain how he tried the new very cool looking and hifi, PRP resistors, but the amp turned out sterile and lifeless, so switched back to carbon composits. I do use PRP though but they are good when not directly carrying the signal, bypass resistors etc. and then for power the military grade DALE RN70 is a stable etc. Key is be aware of selecting grid resistors and caps. and lastly the Filtering of an amp impacts its sound, this is true for guitar amps and hifi amps. in a Soldano it has very stiff filtered power section, big caps, not much to do there select great big caps. But in the preamp here using paralleling and serialing of caps using great WIMA polycarbonate caps the preamp power section is supremely clear and direct, where otherwise ppl would put in can caps, electrolytics never as good as films, and I manage to track down metal shielded wimas, those are also seen throughout the circuit in select places superb high end response and very shielded. In all this makes for a LOT of changes below see what’s typical of a regular Sloclone and soldano, next to a shot of mine work in progress

This Series of posts will have to be an extended one due to the plethora of  mods done here, as it’s pretty much all possible ways I can think of coaxing nice sound out of a high-gain amp, It has gone through at least 50revisions/ mods over the years, started in 2012, but I have continuously attempted to only keep the ones I like most. Next I’ll cover a set of posts on mods, parts selection etc. And of course I aim to eventually upload a video with some audio as well, re-amping and capturing with Captor-X, though this is way to many mods to spend time to do a complete inventory. In all this amp covers everything metal, for other types of music I have other amps, this is to do everything I want in that genre, without spending 4.000 euro each on a real SLO, Uberschall, or Larry/Fortin, and though it’s a 6l6GC amp it has some Friedman feeling mods in it as well.