# Hybrid Fuzz Driver



## Chuck D. Bones (Jul 6, 2020)

This completes my collection of the Skreddy Holy Trinity: Lunar Module (Aldrin), Screw Driver & Hybrid Fuzz Driver.  All very similar circuits; a booster driving a modified Fuzz Face with a variable bass cut in between.  There are just enough component value tweaks to make them all sound different.  As with the Screw Driver, I built this on the Aldrin board. The only place I deviated from the Skreddy design was the two silicon transistors.  I was out of BC109C's, so I used BC549C's for Q1 & Q2.  The specs are nearly identical.  Q3 is a germanium AC127, just like the real HFD.  The one I installed had a fairly high HFE, around 160.  I A/B'ed this one against a real HFD.  With all controls at noon, the real one was louder and had more low mids.  Turning up the Volume & Tightness a little on mine fixed that.  The difference could be component tolerances, variation in pot tapers, IDK.  I compared the bias points of the two units, they were pretty close.  The AC127 on mine is running about 25% higher collector current.  I moved the board, pots & stomp switch up a little closer to the jacks to make room for the (optional) battery.


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## K Pedals (Jul 6, 2020)

Chuck D. Bones said:


> This completes my collection of the Skreddy Holy Trinity: Lunar Module (Aldrin), Screw Driver & Hybrid Fuzz Driver.  All very similar circuits; a booster driving a modified Fuzz Face with a variable bass cut in between.  There are just enough component value tweaks to make them all sound different.  As with the Screw Driver, I built this on the Aldrin board. The only place I deviated from the Skreddy design was the two silicon transistors.  I was out of BC109C's, so I used BC549C's for Q1 & Q2.  The specs are nearly identical.  Q3 is a germanium AC127, just like the real HFD.  The one I installed had a fairly high HFE, around 160.  I A/B'ed this one against a real HFD.  With all controls at noon, the real one was louder and had more low mids.  Turning up the Volume & Tightness a little on mine fixed that.  The difference could be component tolerances, variation in pot tapers, IDK.  I compared the bias points of the two units, they were pretty close.  The AC127 on mine is running about 25% higher collector current.  I moved the board, pots & stomp switch up a little closer to the jacks to make room for the (optional) battery.
> 
> View attachment 5328
> 
> View attachment 5329


Nice!!!


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## Barry (Jul 6, 2020)

Very nice!


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## jubal81 (Jul 6, 2020)

Super build!
Mind giving a quick description on how the three compare? Got a favorite?


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## Nostradoomus (Jul 6, 2020)

Sick, is that one of Taydas hammerite boxes?


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## Chuck D. Bones (Jul 6, 2020)

Nostradoomus: yes, it is a Tayda Copper Hammer Tone box.  I was fortunate to get some before K Pedals bought them all .

Jubal81: Marc Ahlfs describes the differences in detail on the Skreddy website.  Here are my impressions...  
The Lunar Module (AKA Aldrin) is the hottest of the three and my least favorite.  Thru my rig, in a small room, the distortion is too harsh for my liking.  It was the first of the three that Mr. Ahlfs designed.  His intention was to recreate David Gilmour's guitar tones on DSOtM, hence the name "Lunar Module."  It's an all silicon design.  Plenty of gain & brightness.  Next came the Screw Driver.  It is much smoother and my personal favorite.  It's the first of the three that I built, which may well be a factor in why I like that one the best.  Marc retuned & renamed the BODY (SHARPNESS) & BRITE (BRIGHTNESS) controls, reduced the gain in the first stage replaced the 1st stage silicon BJT with a MOSFET and the last transistor in the chain was changed to germanium.  All of the controls are useful over their entire range.  With FUZZ and SHARPNESS set to zero and BRIGHTNESS dimed, it's a (mostly clean) Treble Boost.  Set everything to noon and you have a bluesy amp-like overdrive. Last out of the chute was the Hybrid Fuzz Driver.  It's kind of a mash-up of the LM and SD.  According to Mr. Ahlfs, the HFD is optimized for humbuckers.  The 1st stage went back to being a silicon BJT like the LM, but the Pre-gain is tuned to act like a Mid Boost instead of an everything boost like it is on the other two pedals.  Three of the low-pass filter caps were deleted in the interest of "clarity."  The bias was changed in the FF stages and the gain was reduced.  The HFD is probably the most amp-like of the three.  The distortion can be varied from almost clean to bluesy. No metal sounds in there.

I reacquainted myself with Bill's Law again last night.  I wasn't satisfied that my pedal sounded _close _to the Skreddy HFD, they should be nearly identical (within the limits of component tolerance and transistor variation).  I reviewed my parts list and board... Lo & Behold! I had installed the wrong value input resistor (R2).  I had put in the 56K that the Aldrin board calls out on the silk screen instead of the 10K resistor used in the HFD.  I switched that resistor out and Viola!  Now they sound the same.  Only difference is that the TIGHTNESS pot is wired backwards compared to the Skreddy HFD.  That's because on the LM, clockwise rotation increases bass, but on the HFD and SD, clockwise rotation reduces bass.  Easily fixed, but it's not that big of a deal.


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## cooder (Jul 7, 2020)

Chuck D. Bones said:


> Nostradoomus: yes, it is a Tayda Copper Hammer Tone box.  I was fortunate to get some before K Pedals bought them all .
> 
> Jubal81: Marc Ahlfs describes the differences in detail on the Skreddy website.  Here are my impressions...
> The Lunar Module (AKA Aldrin) is the hottest of the three and my least favorite.  Thru my rig, in a small room, the distortion is too harsh for my liking.  It was the first of the three that Mr. Ahlfs designed.  His intention was to recreate David Gilmour's guitar tones on DSOtM, hence the name "Lunar Module."  It's an all silicon design.  Plenty of gain & brightness.  Next came the Screw Driver.  It is much smoother and my personal favorite.  It's the first of the three that I built, which may well be a factor in why I like that one the best.  Marc retuned & renamed the BODY (SHARPNESS) & BRITE (BRIGHTNESS) controls, reduced the gain in the first stage replaced the 1st stage silicon BJT with a MOSFET and the last transistor in the chain was changed to germanium.  All of the controls are useful over their entire range.  With FUZZ and SHARPNESS set to zero and BRIGHTNESS dimed, it's a (mostly clean) Treble Boost.  Set everything to noon and you have a bluesy amp-like overdrive. Last out of the chute was the Hybrid Fuzz Driver.  It's kind of a mash-up of the LM and SD.  According to Mr. Ahlfs, the HFD is optimized for humbuckers.  The 1st stage went back to being a silicon BJT like the LM, but the Pre-gain is tuned to act like a Mid Boost instead of an everything boost like it is on the other two pedals.  Three of the low-pass filter caps were deleted in the interest of "clarity."  The bias was changed in the FF stages and the gain was reduced.  The HFD is probably the most amp-like of the three.  The distortion can be varied from almost clean to bluesy. No metal sounds in there.
> ...


Awesome, thanks for the dscription, I'm a big fan of the Lunar Module and the Screwdriver, I have not had a chance to build the Hybrid Fuzz Driver though. Interested in that, where would I find a schematic to see the differences? Cheers Chuck!


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## Chuck D. Bones (Jul 7, 2020)

Here's a schematic I traced from an HFD.  Ref designators are per the Skreddy board silkscreen. This unit was all thru-hole assembly.  They also make an SMD version.  Compare with the Aldrin.


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## cooder (Jul 8, 2020)

Chuck D. Bones said:


> Here's a schematic I traced from an HFD.  Ref designators are per the Skreddy board silkscreen. This unit was all thru-hole assembly.  They also make an SMD version.  Compare with the Aldrin.
> 
> View attachment 5378


Excellent, thanks you Sir!


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## HamishR (Jul 9, 2020)

Cool!  And a lesson in how to make your solder go further.  

I agree - the Screwdriver is my fave but I do like all three.


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## bschobs (Jul 9, 2020)

Nice!


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## Chuck D. Bones (Jul 9, 2020)

I hooked up this pedal combo and it sounds Sofa King goooooood.

Guitar -> Delegate -> HFD -> VFE Merman (Sea Monk) -> EM-600 (Behringer stereo delay) -> 2 amps

The HFD & Merman are each set for mostly clean with just a touch of distortion.  The Merman fattens up the HFD's tone.


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## HamishR (Jul 11, 2020)

Ok I'll build one.


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## Chuck D. Bones (Jul 11, 2020)

HamishR said:


> Ok I'll build one.


If that doesn't make your Sea Monk sound good then it's gotta be built wrong.


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## iamjackslackof (Dec 18, 2022)

Bit of a necro bump, but @Chuck D. Bones , can I take the schematic you posted here and compare part values to the Fuzz Aldrin and build the HFD? I see you left of a couple caps, etc, so I'm not sure. I might just make a PCB from the schematic you posted, but I'd love to take an existing Lunar Module board and build and HFD.

EDIT: I found the other thread on this, disregard.


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## Chuck D. Bones (Dec 18, 2022)

Yes.  The one above is built on an Aldrin board.  It's the quickest, easiest & cleanest way.  Use my board pic as a reference.  Print out the Aldrin build docs and mark them up with the mods.  When making mods, I recommend installing the modifications first.  It's easier to avoid mistakes if done in that order.  Double-check each mod part for value and placement before soldering, you'll be glad you did. 

Good luck!


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## iamjackslackof (Dec 18, 2022)

Chuck D. Bones said:


> Yes.  The one above is built on an Aldrin board.  It's the quickest, easiest & cleanest way.  Use my board pic as a reference.  Print out the Aldrin build docs and mark them up with the mods.  When making mods, I recommend installing the modifications first.  It's easier to avoid mistakes if done in that order.  Double-check each mod part for value and placement before soldering, you'll be glad you did.
> 
> Good luck!


Thanks Chuck! Good point on doing the mods first as well. Just added 2 more Fuzz Aldrins to my cart!


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## Chuck D. Bones (Dec 18, 2022)

There is a related pedal called the Animals Diamond Peak.  It's derived from the HFD.  HamishR & I discuss it here.


(No need to requote my post.)


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