January 24, 2020 at 10:52 am #10046
One of the industry and hobbyist standard builds is the basic Tube Screamer circuit. Many different mods and tweaks have been used on this fundamental circuit for as long as it has existed. Barry’s “Tube Screaming Ultra” build is one way of exploring many of those available mod options. In this “Tube Screaming Ultra” build, I went down the same road as many others with this build and added a couple twists. First, this build is using 2 x “Tube Screaming Ultra” PCBs in series; each is switchable and combinable. The second ‘twist’ is that the builds are NOT identical – one uses the standard TS-808 construct and the other uses the LDO\Landgraff option (except for the 1M gain pot). And finally, on the pure TS-808 build, I used box film caps and on the LDO version I used NOS Panasonic film caps. (And no, I could and can not hear a difference. Just thought I try it.) The TS-808 version is first in the chain.
In laying out the controls, I found six separate controls to be somewhat gangly and still get it placed neatly into a 125BB. In this case, I chose two non-standard approaches. The first was to use concentric pots & knobs, and the second was to use a Gorva S90 (125BB near equivalent) enclosure. The Gorva enclosures have nice lines and slight curves as you’ll see in the photos.
The clipping diode options employed are pretty straight-forward. Germanium, None and Silicon are the options. To prevent the standard difference in volume between germanium and silicon diodes I chose very specific silicon devices and doubled up (in series) the germanium diode selections. For silicon, I chose UV LEDs. They seem to have the lowest Fvd of all LEDs at around 0.78v. And the 1N34A germaniums used will render a total Fvd of about 0.72v as there are 2 in series for each point in an asymmetrical configuration. However, in the None (“X”) position, there is no clipping and therefore notably louder than the other 2 selections. Sort of like a “Bender” mode.
To coordinate the visual queuing for working the controls, you can see how one stompswitch is on blueish background and the other stompswitch on a greenish background – then note how the knobs are surrounded by different colored concentric circles. The outer blue knob circles represent the controls for the blue side (TS) stompswitch and the inner green knob circles represent the controls for the green side (LDO) stompswitch. Were I ever to do another one of these, I would have orients all 3 concentric pots in the same direction. As you see, the middle (‘Tone’) pots are upside down compared to others. Considering how the knobs are mounted to the shafts, the direction orientation is dictated by grooves in the pot-shafts. So I had to re-visit the graphics design to correct this over-looked discrepancy.
The finished Screaming Eagle:
Gutshot. I wanted top-mount jacks on this build and in that choice found there was not enough room to use Barry’s 3PDT Wiring PCBs (like I usually do) in here. (And yes, I straightened out the switch at final assembly time):
Before application of the enclosure graphics, it’s a good idea to dbl-check the stuffing procedure:
In doing most of my builds, I prefer to use components and plan things out in such a way as to allow the guts to be stuffed and un-stuffed without the need to solder anything. For me, this makes troubleshooting and enclosure graphics sizing\testing & finishing so much easier. (Once the trannies were inserted, I tac-soldered the lower leg of each to ensure they would not vibrate or jostle out of place.) Here are the guts – unstuffed:
Finding concentric B25K pots proved problematic when considering also finding matching knobs across the 3 separate pot values used in the “Tube Screaming Ultra” build – so I went with the B50K (linear taper) concentric pots and modded them with 50K resistors in parallel across lugs #1 & #3 to achieve an equivalent C25K (reverse log\audio taper) concentric pot. Considering it’s the “Tone” pot, I was not concerned about the change in taper. So here’s a close-up of the concentric pots and how I managed their respective mounting:
Anyway, thanks for looking and\or reading.January 24, 2020 at 1:25 pm #10056wilkie1Moderator
Beautiful build and a fantastic discussion! Many thanks!January 24, 2020 at 7:59 pm #10082BarryKeymaster
That is an excellent build and I appreciate the extra effort to describe what you did. I love the concentric pots so you are taking up a lot less room but can do most everything a KOT can do. Stunning visually.January 24, 2020 at 10:40 pm #10086
Thanks fellas! That means a lot coming you both.January 30, 2020 at 5:32 pm #10400ChuckParticipant
Um, based on your previous and following posts here I believe you need to adjust the pathetically short name of this magnificent build.
ChuckJanuary 30, 2020 at 9:18 pm #10401
Chuck – LOL! Thanks for the kind and humorous comment. You may be right. Four syllables is probably just too short. 🙂
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