# Aldrin (Lunar Module) to Hybrid Fuzz Driver transformation - BOM comparison updated



## Chuck D. Bones

EDIT - The BOM comparison PDF file contained an error: C11 is 22uF in the HFD.  It has been corrected.
This mod is even easier than the Screw Driver.  Attached is a BOM comparison between Aldrin (Lunar Module) Screw Driver and Hybrid Fuzz Driver.  Using that, you can build a Screw Driver or a Hybrid Fuzz Driver on an Aldrin board.  Also included are Marc Ahlf's description of what he changed from the Screw Driver and Aldrin to get to the HFD, and why.  Plus some gut shots and a schematic that I traced from the one I bought today.  Gotta say, the build quality is excellent, the case is solid and heavier than the ones we get.  Snug fit in a 1590B box.  Sounds similar to the Screw Driver, but different enough to keep.  Enjoy.


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## HamishR

Wow - thanks for this!


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## jubal81

Hybrid OD. ???T0-92, BC109C, AC127. Mostly SMD.


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## Chuck D. Bones

Can you read the numbers on the TO92?

How many knobs?  3 or 5?

Gotta be a relative of the Screw Driver.


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## jubal81

3 Knobs. Major is blotted out, so looks like same PCB as Major OD. 47n input cap. 
Q1 is 2N5210


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## Chuck D. Bones

Oh well, thanks for looking...


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## MattG

Quick question Chuck - on your schematic, you have C7 at 1nF.  This corresponds to C14 on the PedalPCB Aldrin board (2n2 value for stock build / Lunar Module).  In your Screw Driver post, you said:





> The Screw Driver has a 33K in parallel with C14 [on the PedalPCB board/your C7 here] that alters the Volume pot's taper slightly. C14 is 4.7nF in the Screw Driver, but with the 33K left out, I kept C14 at 2.2nF.


My question is, does the Hybrid Fuzz Driver have a single capacitor as drawn in your schematic (and how the PedalPCB board is built)?  Or does the actual Hybrid Fuzz Driver have a cap plus resistor (like the actual Screw Driver)?

Thanks!


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## Chuck D. Bones

The HFD I traced does not have a resistor in parallel with C14.  AFAIK, only the SD has a resistor in parallel with C14.


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## MattG

In terms of tweaking the HFD: if one wanted to add a bit more bass, and/or reduce the high-end a bit, what would be the best components to manipulate?


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## Chuck D. Bones

There are a few parts you can fiddle, depending on where in the signal path you want to shape the tone.  Have you built or breadboarded one?  I ask the question because the HFD contain a bass cut control (TIGHTNESS) and a treble cut control (PRESENCE).  Do they not do what you want?

These caps limit the bass and can be enlarged for more bass.  You don't need to increase all of them.
C1
C2 influences how muddy it gets when FUZZ is dimed
C3 influences how much the bass freqs are boosted when the MID BOOST is turned up

As far as reducing the top end...
C14 limits the high-freq content before the distortion stage
C5 limits the high-freq content in the distortion stage, but it has little effect when FUZZ is dimed
C7 & C11 cut the high-freq content after the distortion stage


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## MattG

Chuck D. Bones said:


> There are a few parts you can fiddle, depending on where in the signal path you want to shape the tone.  Have you built or breadboarded one?  I ask the question because the HFD contain a bass cut control (TIGHTNESS) and a treble cut control (PRESENCE).  Do they not do what you want?



Thanks for the tips, Chuck!  I indeed built all three Aldrin variants.  While I like them all, the HFD looks to be emerging as my favorite.

Where I'm coming from with the question: to my ears, it sounds like a fair amount of low-end/bass gets killed when I engage the HFD.  I don't hear a huge difference when adjusting the Tightness (Body) control.  But then again, maybe it would sound flubby/muddy at the higher gain settings if too much bass comes through?  Maybe the bass cut I think I'm hearing is what makes the remaining signal sound so good?



Chuck D. Bones said:


> Marc Ahlfs intended the HFD to be more humbucker-friendly by backing off on the gain and low freq response.



And similarly, he's mentioned multiple times that most (or all?) the SD design was done with single coils.

I should add that my question is based on using the HFD with single coils (G&L jumbo MFD).  It's been a while since I've used my humbucker-equipped guitar with the HFD, but I want to say the bass cut isn't as noticeable.  And maybe that's consistent with the design.

I kind of wish I hadn't read that the SD was designed for single coils, and HFD for humbuckers.  While those pairings do sound optimal to my ears, I can't tell if that's what I'm truly hearing or simply confirmation bias.  I regularly switch between my two guitars, and don't want to have guitar-specific pedals.

I am under the (quite possibly mistaken) impression that bass can be tricky in a dirt pedal.  If not done right, it can easily get muddy.  And even if the muddiness can be avoided, a guitar with too much bass might get lost in a band setting, making for a home-use-only pedal.  I haven't yet had a chance to try this pedal in a band context - I have high hopes (internet hearsay seems to suggest it should be a good in a live mix).  So I'm hesitant to go futzing with it until I've put it through all its paces.

I made good on the high frequencies sound by simply turning my amp's high EQ down a bit - still sounds good clean, and now the HFD highs are where I want them.  Simplicity FTW!

I think I need to just bite the bullet and spend some time learning to simulate pedal circuits.


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## Chuck D. Bones

One simple mod you can try with the HFD is to add a FAT switch that selects either 2.2uF (less bass) or 100uF (more bass) for C2.  This mod is only apparent when RANGE is turned up.

I am constantly confronted by confirmational bias because I'm always looking at schematics and running sims.  I can see what Mr. Ahlfs changed between the various versions of this circuit and i hear pretty much what I expect to hear.  Some of the differences I expect to hear are so subtle as to be non-existent to my ears.


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## MattG

FYI, I found this Facebook discussion where Marc Ahlfs describes a tweak he made to the Hybrid Fuzz Driver Presence control (aka "Brite" for LM, aka "Brightness" for SD):


> I took the opportunity to make an improvement to the Hybrid Fuzz Driver.. I've added an extra resistor in-line with the "Presence" control which adds to that control's ability to trim down the high end but without changing its frequency corner.  So now at minimum, this control will add a more intense amount of darkness to the signal.  (At max, it's a little less piercing, but I doubt many people use this control cranked anyway.)  This is for all you who have maybe tried the Hybrid Fuzz Driver and found it to be too bright with your guitar and\or amp.  Starting today, it can go darker than before.
> 
> The resistor being used for the Screw Driver and Lunar Module is small enough that it doesn't do much; only the Hybrid Fuzz Driver will have a noticeable change.
> 
> And, FYI, the Hybrid Overdrive has always had a more powerful Tone control than the Hybrid Fuzz Driver, so no change there.
> 
> See where the .22uf output capacitor feeds into the CW input lug of the Presence control?  You can either cut that trace on the PCB and splice in a 10k resistor or else de-solder the .22uf capacitor and then re-install it with the 10k resistor between the cap and the Presence control.  This is the mod.



If I am interpreting this correctly, he's talking about *C12* on the Fuzz Aldrin board.  C12 is 15n in the Lunar Module, but 220nF (i.e. 0.22uF) in the HFD build.


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## Chuck D. Bones

That is correct.  Adding 10K in series with a 100K pot will lower the brightness at the CW end and make the adjustment less touchy.  It will have very little effect at the CCW end of rotation.  You can also tweak C13 to adjust the range of the PRESENCE control.

I have a Hybrid Overdrive schematic that I traced from photos.  Unfortunately, most of the caps are unmarked SMDs, so I can only guess at their values based on the LM, SD and HFD schematics.  For sure there is a resistor in series with the TONE control, and another low-pass cap as well.  I have not tried breadboarding this one for the obvious reasons.


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## nickquack

Anyone know how to mod a HFD to a Major Overdrive? Marc has said before that there are only 3 resistor value differences between the pedals.


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## MattG

I revisited the Hybrid Fuzz Driver (built in the Fuzz Aldrin board, per Chuck's BOM) the other day. Forgot how much I like the sound of this pedal!

I had stopped using it after trying it once at band practice, and felt I was getting lost in the mix. Last night I tried again, still felt it's place in the band mix wasn't ideal. I messed with the controls a bit, but ultimately felt like I had to keep turning it up (which isn't the right solution, just turns into a loudness war that everyone loses). Turning up the presence knob also helped it cut... but in an ice-pick kind of way.

The previous time I tried this experiment, I had the Screwdriver on the board at the same time. I thought the Screwdriver cut through much better.

Last night, the other dirt pedal was the Cattle Driver (Buffalo td-x). I thought it cut a lot better than the HFD as well.

To my ears, both the Cattle Driver and the Screwdriver add some low mids ("punch"?), that, at least in my band, seems to implicitly be "my" spot. At least that's my hypothesis.

This is with single coils by the way (g&l jumbo mfd). I suspect I'd have more "girth" with humbuckers. I'm wondering if there's some way to add some "weight" to the fundamental HFD tone?

Any thoughts or ideas?


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## Chuck D. Bones

As I recall, Marc Ahlfs used a strat when designing and tuning the Lunar Module & Screw Driver.  He tuned the Hybrid Fuzz Driver specifically for humbucker pickups.  The thing he changed that most affected the HFD's bass response was he decreased C2 (Aldrin schematic) from 100uF to 2.2uF.  That's the first thing I'd change to fatten up the HFD's tone.  If that doesn't do it, try increasing C1 to 1uF.  If you want more midrange when the LM BODY control is above noon, then increase C6.  Note that the BODY control is wired "backwards" i.e. turning it down (CCW) _increases mids & _lows.


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