@cybercow
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Instead of a “buffer” of any sort, I’ve found an excellent solution from AMZ – a “Guitar Pickup Simulator” . . . .
I’ve built them into my fuzzes . . . .
And built them as stand alone pedals . . . .
I’d start by socketing C1, C2 & C7 and increasing C1 to 100nF, C2 to 10nF and C7 to 100nF. (Mind you, it’s an educated guess. I don’t have or play a bass to test it.)
Mikromegas – it’s a bit difficult to follow the spaghetti wiring. Shorter wiring runs might prove helpful. A clearer shot of the component & solder-side of the PCB may prove helpful. Also, dbl-checking all the component values might reveal an incorrect value of a resistor or cap. (It happens.)
Originally, the first Sunn amplifier was created in the late 60s by a bass player who thought his amp was not powerful enough for large stages. The first model T was marketed as an amp that could suit both guitar and bass, a 150 Watt beast with four 6550 tubes, inspired by the Fender Bassman 5F6A amp. The GuitarPCB “Sunn-T” actually is “bass ready”.
C1 in the GuitarPCB’s “Sunn-T” is just high frequency rejection. C3 & C7 see to the bass-readiness. The only other places where a bass guitar might benefit are at C4 & C5 (both 22nF) and you could easily bump them up to 47nF or 68nF potentially better low frequency pass-thru. (IMO)
Coda-Effects has a good write up and analysis on the Sunn model T here: Sunn-T
I can barely make out that you’ve used 2N5457 JFETs. And while they are correctly oriented for this build, did you use 4 matched JFETs? That is crucial. Also, the trimmer is VERY sensitive and has only a very small arc of rotation that will get the effect working. That trimmer MUST be moved in extremely small increments during the setup when tweaking it.
When I built my first Muff’N, I also found Kit’s and the Coda-Effects sites for their schematic references on a BMP. The first thing I noticed was that the part IDs do NOT match. So I printed out several different schematic from Kit & Coda, then printed out a larger version of the Muff’N. Then I started mapping all the different part IDs onto the larger Muff’N schematic. With that freshly marked-up Muff’N schematic, I was then able to cross-match all the various parts and compare values in the Muff’N’s BOM options list. I found several components were very close in value while others varied wildly in their respective values. (That’s where the different BMP versions were given rise.)
R25 was added to the Muff’N to better cope with different gain values of the selected BJTs used in the project. Without R25, depending on which BJTs are used) the gain can be pretty hot and R25 is just there to tame the levels. Use sockets for R25 and test different values or even a jumper. It won’t hurt the circuit but can make it sound different. That final cap is important as it prevent DC from directly reaching the output.
Hope this helps.
Just an additional note on the trimmer – it is VERY sensitive and the “sweet spot” is a very narrow range of the trimmer’s sweep. Move it VERY slowly to see if it will dial in.
Still, I’d lift one leg of each of those two resistors and re-measure them – just to be sure. In the photos I see, the colors appear identical.
IMO, the Super Tone TwEQ will deliver the most flexibility and a good amount of level increase with the Bass, Mids and Treble pots turned up along with the volume. I like the added benefit of the Bass, Mids & Treble being “active” controls where above 12 o’clock they boost the level and below 12 o’clock they cut the levels for tone shaping while still being able to boost the level via the master volume control.
One important note to face about using multiple diodes in a clipping circuit . . . .
The fewer diodes/LEDs in series, the lower the volume will be. It’s the total Fvd of the combined in-series diodes/LEDs that affect the volume. The lower the total Fvd, the lower the volume. That how clipping elements work.
