Layout 1: Original PNP
Layout 2: NPN Version
Tuesday, 2 May 2017
Hornby Skewes Bass Boost
Another super rare Hornby Skewes pedal, so rare in fact I can't even find a video for it. Similar to the treble booster, but boosts the bass frequencies instead of the treble. I'm certain just like any other vintage Hornby Skewes pedal it's gonna sound great.
Layout 1: Original PNP
Layout 2: NPN Version
Layout 1: Original PNP
Layout 2: NPN Version
Hornby Skewes T.B. 2 Selectatone
Another classic. Not much info on this one either. It's super rare, just like 99% of the Hornby Skewes pedals. Essentially, it's a set booster that you can switch between either bass or treble boost. Rumor has it that it was used by Ritchie Blackmore during the 1960s up until 1974, as well as Jethro Tull on Aqua Lung. Schematic is over at FSB.
Layout 1: Original (PNP)
Layout 2: NPN
Layout 1: Original (PNP)
Monday, 1 May 2017
Hornby Skewes Zonk Machine II
Best info I could find on this creamy classic fuzz goodie.
The 1967 John Hornby Skewes Zonk Machine II is an extremely rare, and vintage pedal enthusiasts have long coveted both the original Zonk and its successor, the Zonk II. The Zonk II was the result of a re-engineered Zonk Machine I, which was based upon the Sola Sound MK I Tone Bender circuit. Featuring (2) PNP M2N 4403 Silicon transistors, instead of the earlier (3) Germanium transistor based Zonk Machine I, the Zonk Machine II is more stable, smoother, and less dark sounding. Effectively designed to be a complete and practical unit, the Zonk II’s predecessor was intended to be used in conjunction with the JHS Treble Booster unit (essentially like a Rangemaster) as to enhance the articulation and clarity of the otherwise muddy Zonk. Interestingly, John Hornby Skewes did offer both units within one box, and it was re-branded as the famous Shatterbox.
The rolled steel casing with a blue Hammerite finish is very reminiscent in design to the gold MK I Tone Bender: with two basic controls on top, and the input and output next to one another on the back, the straight-forward aesthetic is a reflection of the absolute perfect simplicity of the circuit within. It is loud, robust, full-range, and complementary with most any rig. It is sweet, subtle, and sings with sustain. Completely inspirational to play through, the Zonk II offers endless enjoyment, and tone otherwise unavailable via a reissue, clone, or kit.
Layout 1: Original PNP
Layout 2: Original NPN
The 1967 John Hornby Skewes Zonk Machine II is an extremely rare, and vintage pedal enthusiasts have long coveted both the original Zonk and its successor, the Zonk II. The Zonk II was the result of a re-engineered Zonk Machine I, which was based upon the Sola Sound MK I Tone Bender circuit. Featuring (2) PNP M2N 4403 Silicon transistors, instead of the earlier (3) Germanium transistor based Zonk Machine I, the Zonk Machine II is more stable, smoother, and less dark sounding. Effectively designed to be a complete and practical unit, the Zonk II’s predecessor was intended to be used in conjunction with the JHS Treble Booster unit (essentially like a Rangemaster) as to enhance the articulation and clarity of the otherwise muddy Zonk. Interestingly, John Hornby Skewes did offer both units within one box, and it was re-branded as the famous Shatterbox.
The rolled steel casing with a blue Hammerite finish is very reminiscent in design to the gold MK I Tone Bender: with two basic controls on top, and the input and output next to one another on the back, the straight-forward aesthetic is a reflection of the absolute perfect simplicity of the circuit within. It is loud, robust, full-range, and complementary with most any rig. It is sweet, subtle, and sings with sustain. Completely inspirational to play through, the Zonk II offers endless enjoyment, and tone otherwise unavailable via a reissue, clone, or kit.
Layout 1: Original PNP
Layout 2: Original NPN
Nocentelli MMR Fuzz
Description for this outide-the-box-thinking fuzz circuit is up at freestompboxes with the original schematic. Seems rather nice.
Hornby Skewes Zonk Machine I
Well got time for another study break, so it's that time for another layout. Just like the last layout I posted, here's another uber rare fuzz, a gift from the fuzz gods that no worshiper of fuzz should be without IMHO.
One of the more famous Tone Bender MKI influenced fuzz boxes and now almost as legendary as its golden cousin was the John Hornby Skewes Zonk Machine. A little more wacky in the graphics department, but not as heavy duty or robust as the MKI, the Zonk Machine was almost identical in its circuitry. Made between 1965 and 1966 in Leeds, England, the Zonk Machine like the MKI was only made in small numbers before the pedal was updated with a more modern and easier to produce unit.
Layout 1: Original PNP
Layout 2: Original NPN
Some suggested gains and tips I found over at DIYSB:
Q1=53hfe
Q2=126hfe
Q3=98hfe
Q1=70hfe,
Q2=116hfe
Q3=97hfe
One suggestion with the leakage:
Q1=180hfe/.142ma
Q2=176hfe/.177ma
Q3=195hfe/.124ma
Values taken from an Original Unit
Q1=TI AO2 650 Hfe= 180, leakage= 0.12mA.
Q2=Mullard OC75 Hfe= 78, leakage= 0.29mA
Q3=OC44 Hfe= 58, leakage= 0
Tips for other builders interested in the Zonk Machine:
1. Socket all transistors because you’re likely to go through a bunch of them before you find some that work well.
2. The Zonk is very bright. Play around with the input cap and try values between .001uF and .01uF. Maybe even set up a three way switch to toggle between different values.
3. Definitely use a log/audio taper “Fuzz” pot. I used linear at first but it greatly limits the useful range of the pot. The name “Fuzz” is a bit of a misnomer as it doesn’t really fulfill most people’s definition of a fuzz control. It essentially adjusts the bias of Q2. The Sola Sound Tonebender Mk1, which is a topographically identical circuit (sans the 33K resistor), called this pot “Attack” which is a bit more appropriate IMO.
4. Set up an SPST switch to bypass the 2.2M resistor for nasty, all-out craziness!
5. Some came with 25k Log Fuzz pot, and 220k resistor instead of 470k.
One of the more famous Tone Bender MKI influenced fuzz boxes and now almost as legendary as its golden cousin was the John Hornby Skewes Zonk Machine. A little more wacky in the graphics department, but not as heavy duty or robust as the MKI, the Zonk Machine was almost identical in its circuitry. Made between 1965 and 1966 in Leeds, England, the Zonk Machine like the MKI was only made in small numbers before the pedal was updated with a more modern and easier to produce unit.
Layout 1: Original PNP
Q1=53hfe
Q2=126hfe
Q3=98hfe
Q1=70hfe,
Q2=116hfe
Q3=97hfe
One suggestion with the leakage:
Q1=180hfe/.142ma
Q2=176hfe/.177ma
Q3=195hfe/.124ma
Values taken from an Original Unit
Q1=TI AO2 650 Hfe= 180, leakage= 0.12mA.
Q2=Mullard OC75 Hfe= 78, leakage= 0.29mA
Q3=OC44 Hfe= 58, leakage= 0
Tips for other builders interested in the Zonk Machine:
1. Socket all transistors because you’re likely to go through a bunch of them before you find some that work well.
2. The Zonk is very bright. Play around with the input cap and try values between .001uF and .01uF. Maybe even set up a three way switch to toggle between different values.
3. Definitely use a log/audio taper “Fuzz” pot. I used linear at first but it greatly limits the useful range of the pot. The name “Fuzz” is a bit of a misnomer as it doesn’t really fulfill most people’s definition of a fuzz control. It essentially adjusts the bias of Q2. The Sola Sound Tonebender Mk1, which is a topographically identical circuit (sans the 33K resistor), called this pot “Attack” which is a bit more appropriate IMO.
4. Set up an SPST switch to bypass the 2.2M resistor for nasty, all-out craziness!
5. Some came with 25k Log Fuzz pot, and 220k resistor instead of 470k.
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