# Clandestine Preamp



## caiofilipini (Sep 15, 2021)

I've been busy with a whole bunch of other stuff, so not building many pedals, but here's a super fun project: the Clandestine Preamp (Chase Tone Secret Preamp).
I was thinking about buying this one for a while, and I ended up getting one about a month or so ago. Opened it up, it looked pretty cool, with Orange Drop caps, carbon film resistors and whatnot. Very well built too.

I decided to try and trace it. I got 98% of it done, then I messaged @PedalPCB asking if he'd be interested. He helped me figure out a few details around the power supply section. After a little back and forth, he sent me the prototype boards and I just finished building it. Here it is:










I decided to go overboard and used CDE Orange Drop caps, KOA Speer carbon film resistors, Nichicon audio electrolytics and a Fairchild 2N5457. Sounds delicious! To top it all off, I put it in a Gørva C65 white enclosure and used a hip looking synth pointer knob from Smallbear. Super happy with the results!

Huge thanks to @PedalPCB for trusting me with this one and helping me figure out the power supply stuff.


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## caiofilipini (Sep 15, 2021)

@fig I guess now you understand what all those Orange Drop caps you saw on the picture of my breadboards were for!


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## fig (Sep 15, 2021)

That looks really nice, inside and out! Those caps set it off and provide all the the ooziness needed.


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## caiofilipini (Sep 15, 2021)

fig said:


> That looks really nice, inside and out! Those caps set it off and provide all the the ooziness needed.


Thank you!


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## jjjimi84 (Sep 16, 2021)

I am looking forward to this release! Looks great!


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## caiofilipini (Sep 16, 2021)

jjjimi84 said:


> I am looking forward to this release! Looks great!


Thanks, Dan!


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## JamieJ (Sep 16, 2021)

Secret verification of a secret preamp. Very nice as always @caiofilipini


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## caiofilipini (Sep 16, 2021)

JamieJ said:


> Secret verification of a secret preamp. Very nice as always @caiofilipini


Thank you, Jamie!


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## Boba7 (Sep 16, 2021)

Very nice!!
Any chance to see the schematics @caiofilipini ?


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## caiofilipini (Sep 16, 2021)

thewintersoldier said:


> what is the optimum voltage for the jfet?


My original measures 12.46V, with a Vref of around 22V.


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## Boba7 (Sep 16, 2021)

caiofilipini said:


> My original measures 12.46V, with a Vref of around 22V.



Usually I prefer to bias at 2/3, and I remember an Echoplex schematic that showed a bit more than 14v for the jfet.
But it shouldnt make any difference


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## Boba7 (Sep 16, 2021)

I wonder if he's using the 500k pot as a voltage divider (like a standard volume pot) or as a resistor to ground (like the echoplex does). 

Also with 1N5817 the charge pump should output around 26v I believe, not 22v. Curious to see the schematics


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## caiofilipini (Sep 16, 2021)

Boba7 said:


> Also with 1N5817 the charge pump should output around 26v I believe, not 22v. Curious to see the schematics


There's a 1N4748A Zener diode used to bring the 26V down to about 22V at the end of the power supply.


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## Boba7 (Sep 16, 2021)

caiofilipini said:


> There's a 1N4748A Zener diode used to bring the 26V down to about 22V at the end of the power supply.


Right, of course! Thanks


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## cooder (Sep 16, 2021)

Super sweet build! Good on ya guys for getting the schematic figured out, looks a treat and I bet it sounds too!


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## Preverb (Oct 14, 2021)

I ordered one of these PCBs.  I am wondering if the 3 hole predrilled 125b from Tayda would line up since there are no 2 hole versions?


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## caiofilipini (Oct 14, 2021)

Preverb said:


> I ordered one of these PCBs.  I am wondering if the 3 hole predrilled 125b from Tayda would line up since there are no 2 hole versions?



Not sure, maybe @PedalPCB could chime in.


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## Onkelmike (Oct 22, 2021)

Hey can anyone tell me where the R5 (240k) resistor is in circuit? Wondering how much difference a 221k would make there.


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## mdc (Oct 22, 2021)

I don't think the schematic for the secret preamp has been shared yet, but here's the echoplex it's based on.

The 220K resister "references the output to ground, and keeps the output from floating positive if left unconnected." I don't think the value is too critical there, but I could be entirely wrong. The Tillman preamp is similar and uses a 51K resistor in the same spot.


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## Onkelmike (Oct 23, 2021)

mdc said:


> I don't think the schematic for the secret preamp has been shared yet, but here's the echoplex it's based on.
> 
> The 220K resister "references the output to ground, and keeps the output from floating positive if left unconnected." I don't think the value is too critical there, but I could be entirely wrong. The Tillman preamp is similar and uses a 51K resistor in the same spot.


Thanks!


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## Robert (Oct 23, 2021)

Preverb said:


> I ordered one of these PCBs.  I am wondering if the 3 hole predrilled 125b from Tayda would line up since there are no 2 hole versions?



Tayda Pre-Drilled Enclosure (Clandestine Preamp)


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## Preverb (Oct 26, 2021)

Robert said:


> Tayda Pre-Drilled Enclosure (Clandestine Preamp)


Thanks!  I assume you select custom drill service and at the checkout, they will provide links to upload the drill coordinates?


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## Big Monk (Oct 26, 2021)

Preverb said:


> Thanks!  I assume you select custom drill service and at the checkout, they will provide links to upload the drill coordinates?



Use the link from @PedalPCB above and save it under your Tayda Drill dashboard. After you purchase the enclosure and custom drill service it takes about 10-15 minutes for the job to show up in your queue in Tayda Drill. When it does, you simply assign the Drill plan to that job and you are good to go.


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## Jiuk (Oct 29, 2021)

I made my Aion Ares pedal w/ MPF4393 and it really works. I like Catalinbread's version, so added Bias knob and pre buffer out switch. I hate Fat mode, too. 47uF is unusable value. So I will try 10nF again.

This is my modded Ares version's schematic.


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## Big Monk (Mar 22, 2022)

@caiofilipini 

If you get a chance sometime soon, can you measure the voltage going into the circuit after the diodes and charge pump? 

I’m going to measure my Aion Ares and see what I have to. I’m trying to get some ideas for a higher voltage feed into a UniVibe style pedal and trying to keep a 9 vDC input.


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## caiofilipini (Mar 22, 2022)

Big Monk said:


> If you get a chance sometime soon, can you measure the voltage going into the circuit after the diodes and charge pump?



22.46V with a 9.37V supply.


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## Big Monk (Mar 22, 2022)

caiofilipini said:


> 22.46V with a 9.37V supply.



Nice. I bet another round of diodes and caps would bump that up to around 25 vDC.

My Ares is right around 22 ish vDC as well.


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## caiofilipini (Mar 22, 2022)

Sorry, just to be clear, it does get bumped up to around 26V, it's the 22V Zener that brings it down to about 22V.


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## Big Monk (Mar 22, 2022)

caiofilipini said:


> Sorry, just to be clear, it does get bumped up to around 26V, it's the 22V Zener that brings it down to about 22V.



Even better. I didn’t have the schematic in from of me and forgot about the Zener.


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