JHS - AT (Andy Timmons) Signature Drive  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
User avatar
Ichabod_Crane
Resistor Ronker
Information
Posts: 354
Joined: 26 Apr 2016, 15:11
Has thanked: 83 times
Been thanked: 36 times

Post by Ichabod_Crane »

Thank you, I got what you mean. We can say there's no reason to add a second 100nF cap in the power section, considering I'm using a different layout.
Eexactly I will use a veroboard layout of the Crunch Box, where I'm going to add a 3-way switch for the three kind of clipping, silicon diodes, LEDs and nothing, to replace the trimmer for an external presence control and add at least one 100nF cap in the power section that, actually, Crunch Box doesn't have).
The two pedals are identical.

User avatar
Satch12879
Information
Posts: 17
Joined: 08 Jun 2010, 23:41
Has thanked: 3 times
Been thanked: 2 times

Post by Satch12879 »

It's filtering for the Opamp's positive and negative DC pins. Standard practice for uni-polar supplies is to use a small value and a large value capacitor each to clean up low frequency and high frequency variations in the DC supply. For bipolar supplies, this is typically done for both the positive and negative rails and as close to the opamp as practicable. Really, the small value is more critical and is described in almost every opamp datasheet. You can use a single small value between the positive and negative supplies.

See here for discussion on opamp power, section 3.2, here:

https://sound-au.com/dwopa.htm

User avatar
Ichabod_Crane
Resistor Ronker
Information
Posts: 354
Joined: 26 Apr 2016, 15:11
Has thanked: 83 times
Been thanked: 36 times

Post by Ichabod_Crane »

Hello.
I started from a Crunch Box veroboard layout to convert it in the JHS AT version.
Almost the same thing, I just used an external pot fot trimmer to have the Air pot and a 100nF in the power supply. ANd I added 1k resistor before the lug 1 of the Gain pot.
The EQ pot is a reverse log, following the layouts of the Crunch Box and the Angry Charlie (old tonestack versions, of course) and the PedalPCB schematic. But I tried a 10k linear pot, as we can see into the original JHS pedal. But with EQ and Air pot at half the sound is a bit muddy, and the EQ pot begin to bright up the sound about in the last quarter.
But I can't hear the JHS AT in the demos on youtube, sounds too much muddy with the controls at noon. Do you?

Post Reply