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Greetings all: About to start the Fuzzy Bee build. I notice that it calls for a matched Tone Bender set. I understand the principle in general: using a charge pump to bring an oppositely grounded circuit into the centre-negative world. But details as to how the TB set is matched (i.e. Hfe and leakage figures) would be greatly appreciated. I have a number of NOS Germaniums and an Atlas Peak to hand and would like to do the matching here if possible. Any help gratefully received and best to all, mybud
Matching TB (or most any other germanium-based multi-transistor fuzz\boost\distortion circuits) germanium transistors is a matter of obtaining proper Hfe (gain) ratios.
I did just find some notes on my Fuzzy Bee build: “I used a couple of AC125s for Q1 / Q2 that are low leakage and hFE is about 60 – 62 and for Q3 I used a CV7112 that is 220 hFE and leakage about 270.” (It appears that that Q3 calls for “some” leakage.) So those are the Hfe ratios that should work in a Fuzzy Bee. And from the build doc you can note that the Fuzzy Bee is based on the old “Burns Buzzaround Fuzz” – there are lots of Google references for that build to help you sort out the gain ratios is the ones supplied do not suffice.
For biasing, I would definitely socket the bias resistor points so you can “find” the correct bias for each tranny. I use a trimpot to dial it in, then locate a resistor or parallel pair to achieve that found bias resistance for each.
Good luck!
Thanks Cybercow. I’ve noted all your suggestions. Since I don’t have access to anything close to an Hfe of 220, I’m going to try a silicon PNP for Q3 as an experiment. I’m assuming by bias resistors you mean those connected to the base of Q1 and Q2, so R1 and R2 (voltage divider?) and R4? I’ll also check out the Buzzaround info on the web.
Thanks again and all best, mybud
I approached the biasing issue (which I’ve found quite problematic in previous builds) by breadboarding the circuit first and using trimmers for R3, R6 & R7 as per your suggestion. I did not start with the charge pump but reversed the battery connections on the breadboard to get the correct polarity.
The Hfe and leakage figures follow: Q1 = 64 and 0.1mA, Q2 = 79 and 0.2 mA, and Q3 = 123 and 0.8 mA. R3 measured at 9.98k (fairly close to 10k) but after measuring the others I adjusted R6 to 24k and R7 to 20k so as to obtain -4.5V between ground and the collector of Q1. Once this was obtained the others fell into place really easily and I committed to the PCB with charge pump as per the schematic.
The circuit functions according to plan, with sustain operating as it should from the build notes. I used two Russian Ge transistors for Q1 and Q2 (GT402Bs) and a NOS OC75 for Q3.
Thanks Cybercow, I really appreciate the advice.
BTW according to Internet folklore, I believe the original was a favourite of Robert Fripp, of ‘Court of the Crimson King’ era.
mybud – glad to help. My first shot at Barry’s “Fuzzy Bee” was a disaster until I learned that germaniums generally require manual biasing to find the right bias resistance values. Then I ripped out the trannies from the Fuzzy Bee PCB, applied sockets, and started auditing different PNP geranium transistors. I went thru several different variants till I found the right balance. It was a PITA, but a great learning process.
I’m now in the process of constructing a Burns Buzzaound Fuzz testbed board using trimmers instead of fixed bias resistors. I also have a screw-down turret-style (solder less connections) testbed board for trying even more variants of tranny combos. This one is a positive ground rendition. I am working on another that uses a chargepump to provide use with a standard DC power brick with a negative center (negative ground for the voltage supply – and I’m also swapping the polarity of the power supply, e-caps and the diode to see what kind of goodness I might get from NPN germaniums.
I imagine I will ultimately construct a testbed with trimmers instead of fixed value bias resistors to better understand the circuit.
And yes, Robert Fripp did use a Baldwin-Burns Buzzaround Fuzz, He was one of my guitar heroes growing up.
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