D*A*M: Buzzotron, Tag Board Layout

The Buzzotron is almost identical to the original layout for the Buzzaround, which was also built on tag board. 

It sounds pretty good - a bit low on output on some settings, but otherwise a very nice sounding MKIII variant.  

The Buzzotron only has minor differences to the Buzzaround - bias resistors on the base of Q1 are different, and it also has a 220pf capacitor across the base and collector of Q1 like a normal MKIII - this is not present on Buzzarounds.

The tone control may have a different corner frequency on the treble side, but this is entirely dependent on what Buzzaround schematic you compare it against, as I've seen two different versions.   One of the only components that I can't see in photos of the Buzzotron is the small capacitor hiding behind or sometimes under the 220n capacitor. I have seen a 1n, on a Buzztronix ZZ.1, and this is the stock value of a Buzzaround, so I think it's a safe bet.

Buzzaround    15 kHz      10k resistor, 1n capacitor

Buzzaround     3.7 kHz    43k resistor, 1n capacitor

Buzzotron        15 kHz    10k resistor, 1n capacitor      (early version)

Buzzotron        4.8 kHz    33k resistor, 1n capacitor     (later version, this increases the level and gives a better sweep, but it does lose a bit of the original flavour)

I've seen Buzzotron vero layouts using a 33k resistor with a 4n7 capacitor - which equates to 1 kHz.   Not sure where they got these values from, but 1 kHz seems low compared to 15 or 4.8 kHz.  I haven't found a photographic reference, schematic or another source to confirm this (not to say that it doesn't exist, maybe I just haven't found it yet).

D*A*M BUZZOTRON - FIRST TAG BOARD LAYOUT

LATER BUZZOTRON TAG BOARD LAYOUT

Basically the same, but with some minor tweaks.  The later version has a 33k resistor paired with the 1n capacitor on the output (lowering the frequency of the highness filter), and the resistor to the Balance pot is 27k instead of 22k that's found on the earlier model.

Anyone that can read resistor values obviously doesn't need this and might wonder why I bothered - but I'm not yet one of those people, so I do need it.

SCHEMATICS

BUZZOTRON ON THE BENCH

Metal oxide resistors, tropical fish & styroflex caps, axial electrolytics, OA7 germanium diode, and OC45 transistors.  Technically an OC45 should not work very well in Q3 of a Tone Bender MKIII style circuit - not enough leakage and a relatively low hFE.  I think it sounds great here... I preferred it over everything except an OC44, but I only have two of those, so saving them for something else.     

I did swap the 10k on the treble side to a 33k, and I like it, but I think I might also try an internal trimmer to fine-tune the frequency.  The 33k is great in that it has more output, but it also lost something compared to the frequency content of the 10k.

FINAL

So I added a trimmer to tune the treble side, which is handy but hardly essential.  If you don't have a trimmer, I would recommend breadboarding this with a 10k, 22k, and 33k on the forming the high-pass filter on the treble side to fine-tune this to tase.

ON THE SCOPE / FFT

Signal:  440hz sine wave, approx 130mv

 

Bass

 

 

 

Treble  note:  2n2 capacitor used instead of 1n

 

 

 

50/50 mix Bass / Treble