BE: Fuzz Buffer

Not that anyone is likely to, but please don't rush out to build this - it's a concept that should work, but I have not tested it yet.  Might need some fine-tuning.

It's a combination of the AMZ pickup simulator and a Pete Cornish buffer - so basically a fuzz buffer to drop in front of anything that does not like being behind other pedals.  Typically a fuzz face.

out from previous pedal  >  buffer  >  into a transformer (pickup coil)  >  regular guitar volume and tone control > into the fuzz pedal.  

I have a few transformer options to experiment with, so see how that works out.  Switching might be interesting, as I think a loop would be good here.  i.e.  switch the fuzz on/off via the buffer.

BE: Fuzz Face with external bias control

Just jotting down some notes, cause I doubt anyone else will be using this layout.  It's a little impractical in parts, but I just had some spare board this size, and a pair of transistors that I liked on the breadboard that needed a home.  It's a progression on this somewhat more practical layout.   

If you're wondering what the BE part is about...  

BE FUZZ FACE V3 - EXTERNAL BIAS

Notes:  all links under the board.  Maybe reduce the 10k bias pot a little with a parallel resistor.  Cleans up well, solid fuzz.  Breadboard values: 1k / 6k8, maybe 5k6 at around 30 degrees.  10uf bypass cap, battery 8.5v

BELL & HOWELL: Model 601 amplifier

Picked up another Bell & Howell Gaumont today, with the speaker cab - a Model 601 from 1950 (based on the capacitor dates).  Nice to see the original speaker still in the cab - I gave a quick test, sounds fine.  

The 601 is the same amp as the 621 (full details here).  The 601 and 621 amplifiers share the same part number (202000); I believe the model relates to the projector more so than the amp in some cases.

It came as the complete package with the projector and what appears to be a really exciting Australian training film about bandages from 1975.

Not sure where I will go with a conversion just yet.  I did quite like the last one that I did using an early Gibson circuit - so that's probably top of the list at the moment.  

BELL & HOWELL PROJECTOR AMPLIFIER - MODEL 601

A few minor differences with this one - transformer ends are painted, and there are a couple of large wirewound resistors that I've not seen in these before - quite good quality by the look of them.  

OUTPUT TRANSFORMER MEASUREMENTS

~8.4K with 16 and 8 ohm loads

Primary DCR 470 Ω 

10.35 VAC across the primary and measured two secondary taps:

• Tap A: 0.454 VAC

  • Turns ratio (Vp/Vs): 22.80:1

  • Impedance ratio (N²): 519.7

  • 0.454 V with 16Ω → 8.32 kΩ p-p

• Tap B: 0.319 VAC

  • Turns ratio (Vp/Vs): 32.45:1

  • Impedance ratio (N²): 1052.7

  • 0.319 V with 8Ω → 8.42 kΩ p-p

So far, on all of these that I've had, the plastic on the fuse holder breaks when I try to check the fuse.  Not great, as this leaves an uninsulated 110v conductor sticking out the back.  Bit of a death trap, but it will be replaced with a new one.  

The really large tin can capacitor was not great - it was heating up at relatively low voltage, and did not want to reform.   So time to go.  

I like that, back in the day, someone clearly thought about protecting the speaker, adding this tea-cosy-style cover.   These are normally branded as B.A.F Type 60 (British Acoustic Film) - which look just like a Goodmans Axiom from the same time period. 

The valves mostly tested OK - one of the 6V6 is a bit average, but not from the output pair, so that's good.  There is a mix of English Mullards, Australian Miniwatts.

Bell & Howell Part Number 202000

BE: Fuzz Face, SZ-3 (Sziklai pair)

Just one of my little side projects - it's a pretty hot day here, so not one for playing with germanium transistors in a big black box with a tin roof (also known as my garage / workshop).  The leakage goes nuts, and they sound like balls...  

While playing around with a bunch of old low-gain silicon transistors with moderate success, I remembered the Sziklai pair.   A minute later, and it was silicon fuzz heaven, so I had to come up with a layout to build one, hence the post.

BALMORAL ELECTRIC, SZ-3 FUZZ FACE

There are a few random values used that obviously aren't for everyone.  They just happen to be what's on my breadboard.   But hey, the post isn't for everyone; it's mainly for me to come back to later.

Transistor types are not listed, in part cause I can't recall what is on the breadboard.  They are all very low gain silicon transistors - I think about 50hfe or thereabouts.  I'll update the post with details later.

The Szik collector measured about 4.3v on a 9v supply.

SZIKLAI PAIR

What's a Sziklai pair?  It's a bit like a Darlington pair, but it uses an NPN and PNP transistor to create a single high-gain transistor out of the two low-gain devices.   They tend to act more like a single transistor than a Darlington does, which makes it handy for a fuzz face.

Before you get too excited, this works best with silicon; it's not a magic bullet for not so great germanium transistors, as leakage and noise are also multiplied.  

FURTHER READING

Small Bear has an article on Darlingtons and the Szik

D*A*M: Maggot Brain MB-71

Just a little fuzz face variant from D*AM - the Maggot Brain from 2019.  There are some more recent variations on this as well.   Could not see the cap and pot values, so just a partial trace.  Being a fuzz face, you kind of know what they might be.  I mostly breadboard before building a fuzz face cause they are so small, so I'm really just taking advantage of the form factor of the layouts at times.    

There's also a version using BC109 transistors, with a different bias set-up.  33k on Q1-C and 5k9 on Q2-C.  Some Maggot brains have a 15n output cap.  

D*A*M MAGGOT BRAIN - VERO LAYOUT

BIXONIC: Expandora

OK - so this is what happens when you agree to make a pedal, before knowing what someone might ask for.   I'm not sure that this is 100% my kind of thing, but here it is.

Yes it's a huge layout, but it is going in a 1590XX enclosure, so why not.  I started this layout using the Dirtbox Layouts Expandora vero layout (and basically made it wider), as the first version that I did had a few too many rows, for the space available in the enclosure - and I will probably only be making one of these.  So credit where credit is due...  

I may still add the guitar / bass switch - see how it sounds.  There is room on the board for it.  Not hard to work out if you want to add it.  

If you are unfamiliar with the signal flow on the Expandora - it's kind of a Rat with an extra gain stage up front, and an unusual compressor like gain control that's always on, which is combined with a couple of switches to help set the overall gain of that stage.

The fun doesn't start until "forbidden mode" is engaged - which opens the gain right up.  Talking big ugly square waves.  The Expandora moves from a fairly innocuous drive or mild distortion, to a full blown fuzz monster.     

BIXONIC EXPANDORA

This is it on the bench for some testing - just a bit of rough / temporary wiring to confirm all works as expected, before I wire it up properly.    I think the tin can LM308 opamps look cool, and they were all I had.

It's been a while since I worked on small vero, or should I say normal size.   It took some adjustment, and I did have a tiny little copper trace left on a cut that took a decent amount of time to track down.  It took a magnifying glass and a multimeter to track it down - the damn thing was about the size of a bee's dick (which is a unit of measurement in Australia).