Crystal Drive

[Chuck D. Bones]

Submitted for your approval: The EQD Chrysalis, AKA Crystal Drive.

I made a few minor "improvements" it is The Way.





I scaled up the impedance of input circuit (VR1, C2 & R3) by 5x to reduce pickup loading. The Schottky diodes were replaced with Germanium. I bumped C5 up so that it actually does something. I rearranged the TONE control so that it does not change the volume when rotated. C6 was increased slightly and moved off of the board. Details are shown in the bottom pic. The one "glitch" to the way I implemented the TONE mod is the rotation of the TONE pot is now backward. I can live with that. I scaled up the impedance of Q2's bias network (R7 & R8) so it doesn't load the tone network as much. Sounds great. Low to medium gain, soft asymmetric clipping. The bass is a bit weak. Increasing C4 to 10uF would fix that, just not sure I want to do it since I have plenty of other dirt pedals with a strong bottom end.

 

[Chas Grant]

That's really sharp with the clear knobs and white LED! It has a real clean look to it.

 

[Chuck D. Bones]

Thanks! I Considered putting it in a clear box in keeping with the crystal motif.

 

[Chas Grant]

Thanks! I Considered putting it in a clear box in keeping with the crystal motif.

So how do you keep the noise down in a plastic box. The aluminum box acts as a Faraday cage somewhat But plastic won’t do crap to interference. Or is it not really that bad?

 

[Chuck D. Bones]

Take a look at what I did HERE. Shielding from a metal box is good, but not absolutely necessary. The ground planes on the board provide local shielding. Shielded wire took care of the rest. Grounding the pot bodies is a good idea, either thru direct contact with a metal chassis or by soldering ground wires to the pot bodies, as is done inside electric guitars. High-gain pedals, such as the SOFTii, depend on enclosure shielding much more than a low-gain like the Crystal Drive.

 

[cooder]

Excellent! Thanks for sharing, might give that a go as well with your mods!

 

[Chas Grant]

Take a look at what I did HERE. Shielding from a metal box is good, but not absolutely necessary. The ground planes on the board provide local shielding. Shielded wire took care of the rest. Grounding the pot bodies is a good idea, either thru direct contact with a metal chassis or by soldering ground wires to the pot bodies, as is done inside electric guitars. High-gain pedals, such as the SOFTii, depend on enclosure shielding much more than a low-gain like the Crystal Drive.

Gotcha, Thank You! I’m always battling noise. I live in an old house in an old neighborhood where the houses are close together. The incoming power is a mess and the amount of radio waves is nuts. While testing a circuit outside of a box I’ve picked up radio signals by changing the gain pot?? I’ll test some of these out to see if they help any.

 

[Chuck D. Bones]

Questions:
Do you have properly grounded outlets? It's a safety thing as much as it is a noise thing.
Is there a radio station nearby?

I used to work at a place that was a few miles from the KNX (1070KHz) radio transmitting tower and we used to have to install "KNX filters" in some of our more sensitive equipment to reduce the interference.

 

[Chas Grant]

Questions:
Do you have properly grounded outlets? It's a safety thing as much as it is a noise thing.
Is there a radio station nearby?

I used to work at a place that was a few miles from the KNX (1070KHz) radio transmitting tower and we used to have to install "KNX filters" in some of our more sensitive equipment to reduce the interference.

It's definitely plugged into a grounded outlet. There are a few radio antenna near me also, I'm sure that's where the signal was coming from. Once the circuit is boxed the radio signals are not as discernable but I still have a bit of noise. Ensuring proper grounding in the box and beefed up filtering caps does a lot for the noise. I've been complimented on how quiet the pedals are when I am somewhere with less background noise and cleaner power.

 

[HamishR]

I wonder how this would compare with, say, a Baby Blue Overdrive? I'm wondering if it's worth a build... If I did I would certainly use a 10µF at C4.

Oh, and clean build! One of your wires is a bit crooked but I'll overlook that.

 

[Chuck D. Bones]

Oh, and clean build! One of your wires is a bit crooked but I'll overlook that.

It's supposed to be that way... I tuned all of the wires by ear for best sound. ?

 

[HamishR]

Calcite, huh? I once went out into the desert in the middle of Western Australia with a geologist and we drove through an old creek bed. (We also drove through a flock of emus - that was crazy!) We stopped in the old dry creek bed to look for minerals and found a fair bit of calcite, which was to be expected given how calcite is formed. Calcite looks just like limestone except then I found some bright yellow calcite so showed it to the geo. He said that's what I was wondering if we might find - that's uranium. He explained to me how the calcite and uranium are soluble in water and are leached by rainwater from granite, etc etc... I never thought I would one day be thousands of kms from anywhere holding a piece of uranium in my hand.

Unusual name for a pedal. But calcite is fuzzy and rock so it makes sense I guess.

 

[Chuck D. Bones]

Calcite is a crystal, so there's that. Single calcite crystals are birefringent. When you look thru a clear one, you see double. Yeah, I know, there are other ways of seeing double. ?

As for finding radioactive shit, have you been to Maralinga?

 

[HamishR]

Maralinga is even further from anywhere! No I haven't been there - pretty sure a lot of it is fenced off, which understandably pisses of the locals for whom it has been home for many thousands of years.

I was just amazed to see uranium in the wild. It was not what I was expecting - I mean it is a really bright yellow. And kinda furry. You often find it with calcite because they are leached from the same granite rocks.

 

[Chas Grant]

It was U-238, with a half life of over 4billion years, Completely Harmless ???

 

[HamishR]

The geo I was with said that if I held that little lump in my hand all day I'd probably have my years worth of radiation exposure right there. So far my hand's been fine.

 

[SteveScott]

I built one of these in the original format, with a toggle to be able to use germanium diodes. It sounds OK, but the entire sweep of the tone pot does not produce a massive difference, I mean there is a difference from all the way down to all the way up, but it's not as drastic a difference as most of my pedals. Is that the way it is supposed to be?

 

[Chuck D. Bones]

Maybe try a larger value for C6. It's not a BMP tone control if that's what you were expecting.

 

[HamishR]

I'm going to build this on Vero tomorrow. Should I make R6 go to Tone 3 and Tone 1 go to C7 if I want the conventional rotation? And I might use BAT46s as I have no Ge diodes right now. Will it explode?

Wow. This is an old thread.

 

[Chuck D. Bones]

Should I make R6 go to Tone 3 and Tone 1 go to C7 if I want the conventional rotation?

Yes. TONE should be C-taper, although B-taper will be ok below 3:00.

And I might use BAT46s as I have no Ge diodes right now. Will it explode?

Schottky is perfectly acceptable. If you want to approximate the Ge tone, insert a 100Ω resistor between D2/D3 & GND.