Here we have a rare bird from the early-mid 70s. A tweaked version of the the circuit found in Freedam Preamp amp found its way into some Big Muff enclosures. Original is very pricey and rare.
The original ran on two 9v batteries for bipolar power supply for the op amp section but I added a bipolar voltage converter so you can use with your normal power supply. A Master control is added at the end of the circuit so you can crank the volume control to achieve overdrive at reasonable levels. Also, the trimpots value remains unknown but I would shot for 10k...
The facory schematic is avaiable HERE.
shouldn't there be a link between pins 2-3 and 5-6 of the 4558?
ReplyDeleteand what's the deal with the 2.2m and 27k resistors? they're not in either schematic...
ReplyDeletealso is the capacitor between pins 2-4 on the 7660s incorrect on the schematic? 10u does seem the correct value to come of as per the Vero
ReplyDelete2,2m resistor is just a pulldown resistor to avoid switch pops. I always include it in my layouts, it won't affect the overall sound by any means.
DeleteThe 27 k resistor is in the factory schematic, I forgot to add it in my schematic, it is now updated.
Yes, 10uF is the most commonly used value for the charge pump, you can use values between 1uF up to 100uF. I've changed the value in my schematic to 10uF.
Pin 2-3 and pin 5-6 should not be connected. If you look at both schematics, the lines overlap each other.
Thanks for taking a look, is this a planned build?
It is. Just making an order for the parts I don't have 😊
Deleteoh heck yes - I was just about to request this! excellent!
ReplyDeleteAnnoyingly my suppliers out of 5087s, but I have some 2N3906s here, reckon they be ok?
ReplyDeleteyes, but if you curious enough, socket them
DeleteI've built it and works so you can tag it with one change (there's a mistake on the Vero)...
ReplyDelete-The 22n and 10k coming off tone 1 need to be swapped around (the 10K should be going to ground, not the capacitor otherwise the tone pot does nothing as I discovered).
Trimpot...mine seems to like about 450ohms before it squeals out, very sensitive.....no distortion seems to start happening until about the trimpot hits 1k-600ohms or so.
Bite squeals the 4558 out from about 3/4 turn, not figured out why though so could just be what it is.
The trimpots a give and take if you want overdrive the more I play...
ReplyDeleteLower trimpot value, more gain but tone and bite will squeal if turned up. I've baised mine by turning tone/bite down, volume full. Adjust trim until squealing starts.
If you want to use tone or bite you turn volume pot down accordingly to avoid squeal.
Oh used same parts as build including the 2n5087 (found one in the end)
ReplyDeleteThanks for verifying and for the info about the trimpot. The layout has been updated. So, there is not any demos for this, how does it sound, is it worth building?
DeleteI can whip something up, when I googled it I only find examples of the amp (which weren't great quality vids either). I lidded the pedal this morning and just gotta add knobs/labelling later.
DeleteI'm not sure how useable it us atm to be honest. At trim values past 1K it's essentially just a clean boost with tone, and the overdrive can only just so far unless you roll off the tone and bite.
https://youtu.be/BGj0T0AhmUM
ReplyDeleteHere you go, naff vid but the pedal