Hello All, well it seams as if all the fun of Christmas and the new year has all been washed away on this another raining day :(
How ever I have been working hard recienty on some more projects, and the weekend I bread boarded a Jordan BossTone. I thought I’d share some of the things I’d found with every one here. First off the transistors, I spend a while going through and measuring the hfe of all the ones in my junk box. and I ended up with a 2N3904 for Q1 and a 2N3906 for Q2, the reasons why? Well remembering the rule of thumb for fuzz was transistors with a gain between 70 and 130, the 2N3904 had a gain of 72 and the 2N3906 had a gain of 112. I also tried out several combinations of higher gain transistors (BC548's, BC183L, and 2N2222). These higher gains ones did produce a marked difference in the sound made by the circuit. The lower gains produced a more broken up sound than a smooth stylings of high gain ones.
The voltages I measured for Q1 (ebc) = 0, 0.6, 5.63
and for Q2 (cbe) = 0, 5.68, 6.43
How does this compare to any one else's?
I'm pleased with it so far, I just wanted to know how these findings compared to everyone else's?
Peace.
The suggested "magic hfe" ratings/readings actually stem from the design of the Fuzz Face, where the clipping stems ONLY from the way the germanium transistors behave in that particular gain structure. Although the Bosstone also uses transistors, it also includes a pair of clipping diodes, and that is where the brunt of the distortion is created.
The hfe reading should not be interpreted as a preset gain, but more as a *potential* gain that can be created when other components are set appropriately. If the circuit design anticipates higher-gain devices then using them can make a difference. If the design anticipates what they used to call TUP/TUN in Elektor magazine ("transistor-universal-PNP, transistor-universal-NPN") then higher hfe devices, or finicky selection of hfe will likely provide little audible benefit.
In the case of the Bosstone, the sound you get is likely much more a product of the diodes used and the components connecting the transistors to V+, than the actual transistors. To be sure, you DID notice changes in the sound with different transistors, and that may be because the provides a certain amount of overall gain (contingent on both the V+ connections and trannies) that pushes a larger and smaller amplitude signal across the diodes.
With any sort of diodes-to-ground type fuzz as this, it is the proportion of time spent above clipping threshold that determines the tone. If the overall gain of the circuit is such that the signal quickly falls below the clipping threshold of the diodes as the note decays, the fuzz will appear to be intermittent and so less "smooth". With greater overall gain, the signal remains well above the clipping threshold of the diodes for an extended period of time, by which point the user may well have moved onto other notes. The effect will seem to "flicker" less under those circumstances.
cheers for that it makes a lot of sence. I'll continue experimenting and see what happens. and i'll post what i find, i had a suspision that the magic hfes were for fuzz face but i thought they might apply here, you dont know untill you try though. Thank you for that insight.