Hello,
I am building a 1981 inventions DRV (https://1981inventions.com/) clone on veroboard.
All is going well so far, but I just realized that I don't have any 22nF and 390pF capacitors left :(
I am considering using 33nF (instead of 22nF) and either 330pF or 470pF (instead of 390pF), but instead of swapping values blindly, I would like to know what do these capacitors do in the circuit, and what the value change would make? Would it make a big difference? Should I stick to the scehmatic value, or try a bigger or smaller value?
(https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-29ZXjSsS6n6zEdD4BmPrvUhK0NhB0yQOTCMVUYVdPyKGM9d6qA998Zxp-9HU6W0jog-96V0fM0B-wPTdFfJUdZ8w6j0CJ0fj9446eqWyhe2PDc9sRFWd_0aHjIUFnct04AlRcoh3tRKD/s1600/DRV+schem.png)
https://www.pedalpcb.com/product/pcb224/
https://effectslayouts.blogspot.com/2019/06/1981-inventions-drv.html
http://dirtboxlayouts.blogspot.com/2019/06/1981-inventions-drv.html
22nF (C5 & C10) and 2M2 (R9 & R14) form high pass filters of about 3.2Hz corner frequency..
By using 33nF instead you lower respective corner frequencies to 2.2Hz..
You may use them with respective resistors values retained or lower those resistors down to 1M5, in the cost of IC2_A & IC2_B input impedance..
(both are more than fine..) :icon_wink:
390pF (C3) and 10k (R5) form a low pass filter of about 40kHz cormner frequency..
You may use either 330pF (raising corner frequency) or 470pF (lowering corner frequency) (use f = 0.159 / C*R formula)..
You can, of course, tweak R5 value for retaining original corner, in the cost of IC_1B stage gain..
Thank you, Antonis,
That makes perfect sense and it's very clear.
From what I understand, it's in the signal path (by that, I mean : not in the side-chain part of the circuit), right? If so, I'll be glad to rise the lowpass filter a bit :)
I think I will stick to 2M2 resistors and use 10nF, in order to reach a broader bandwidth (7.2kHz if i'm not mistaken).
I will also try a 470pF.
Duh!
I have misread your post and swapped in my mind "highpass" with "hicut" and "lowpass" with "lowcut" :P
(So I thought the pedal was operating in the 40Hz-3.2kHz frequency range, but in fact it goes well beyond that : 3Hz to 40kHz !? :o Wow :icon_biggrin: )
Quote from: snk on May 06, 2024, 11:44:27 AM3Hz to 40kHz !? :o Wow :icon_biggrin: )
No. Those aren't the only filters, their corner frequencies were chosen as to not interfere with the ones that actually matter. There's also no "side-chain".
Quote from: snk on May 06, 2024, 11:38:34 AMI think I will stick to 2M2 resistors and use 10nF, in order to reach a broader bandwidth (7.2kHz if i'm not mistaken).
Smaller caps will decrease the bandwidth. 10n+2M2 => lower cut-off 7.2Hz (not kHz). The 10nF will work but I'd probably go with the 33n's, mainly because it's more like the 22n's but also because you can get minor noise increases with the smaller caps.
Changing the 390p to 470pF will be fine.