How can I improve this circuit?

[Albescu]

First post here!. So, I'm kind of new in the world of building pedals, but I'm studying an electronics degree and this is my final project. The idea is the basic circuit of the rat, with switchable EQ between a baxandall and the HM2 EQ section. It also has switchable diodes, switchable boost and you can completely remove the diodes from the circuit with a toggle, tho I'm thinking about changing that to a toggle that can select the position of the diodes between regular (hard clipping) and on the LM308n (soft clipping). Also I want to add an adjustable HPF on the OP AMP filtering so I can have a tighter sound on lower tunings.

I know it may be a bit too much for a first self-designed pedal. but I think I can manage to make it sound acceptable (I already like the sound, but when I add the eq stage it gets a little bit quirky).

One thing that happens is that when I switch between the baxandall and the HM2 eq, it takes some time for the HM2 to get to normal volume, I don´t know if it has something to do with capacitors.

So what I'm asking you is, given that concept and the scheme, how can I improve the design? either in terms of making a more stable circuit or improve what´s already in there. Also there may be some elements that I may completely delete from the design,since I just smashed a couple of circuits so there could be capacitors that don´t do anything, redundant components, nonsensical resistors or resistors that could be messing the impedance.

I have everything on 4 protoboards so It's getting out of hand but I think I can have something to be proud of.

*Note: I know I put the diodes in one of the rotary switch the wrong way, I have them right on the protoboard but I messed it up on the schematic. Thank you!

 

[Robert]

I could be missing something in the switching scheme, but it looks like your GNAW EQ has no bias voltage on IC3A (pin 3).

Shouldn't there be a VREF pull-up resistor here?

 

[Albescu]

I could be missing something in the switching scheme, but it looks like your GNAW EQ has no bias voltage on IC3A (pin 3).

Shouldn't there be a VREF pull-up resistor here?

You are absolutely right, I must have missed it while replicating the original circuit, I don´t know what value to use tho

 

[DailyDovetails]

I have been working on something somewhat similar to this as well. I would consider an 8 way rotary for the clipping and set it up with something like no clip, led-led,led-4148,led-bat41,4148-4148,4148-bat41,bat41-bat41, and maybe just lock out the last position with the washer. The build I am working has toggles but they have a lot of redundant positions and require a bit of knowledge of the circuit to figure out.

For the adjustable high pass filter you may consider switching in a cap into the negative feedback loop like on the fat rat.

This circuit https://docs.pedalpcb.com/project/PedalPCB-Stockade.pdf uses 8 way rotary switches for both clippings and caps on the OP amp.

I think the placement of your boost is smart. I am working on something like that myself. With the rat as the gain is lowered the mid hump moves from about 2.5k or so to 800hz or so. if you put a boost after it you can get some of the expected rat gain characteristics with the mid hump in different spots.

For circuit layout I don't see IC5b I'm guessing it's tied to grounds. IC2b also appears to be tied to ground I'm wondering if you could use IC2b in place of 5A or vice versa.

It's an interesting concept. What size enclosure are you thinking it would fit in? I would guess a 1590BB or maybe even an XX.

This is the project I am working on. https://forum.pedalpcb.com/threads/the-hella-rats-chronicles.24686/ The fat rat is shown on one of the schematics if you scroll down.

 

[Albescu]

I have been working on something somewhat similar to this as well. I would consider an 8 way rotary for the clipping and set it up with something like no clip, led-led,led-4148,led-bat41,4148-4148,4148-bat41,bat41-bat41, and maybe just lock out the last position with the washer. The build I am working has toggles but they have a lot of redundant positions and require a bit of knowledge of the circuit to figure out.

For the adjustable high pass filter you may consider switching in a cap into the negative feedback loop like on the fat rat.

This circuit https://docs.pedalpcb.com/project/PedalPCB-Stockade.pdf uses 8 way rotary switches for both clippings and caps on the OP amp.

I think the placement of your boost is smart. I am working on something like that myself. With the rat as the gain is lowered the mid hump moves from about 2.5k or so to 800hz or so. if you put a boost after it you can get some of the expected rat gain characteristics with the mid hump in different spots.

For circuit layout I don't see IC5b I'm guessing it's tied to grounds. IC2b also appears to be tied to ground I'm wondering if you could use IC2b in place of 5A or vice versa.

It's an interesting concept. What size enclosure are you thinking it would fit in? I would guess a 1590BB or maybe even an XX.

This is the project I am working on. https://forum.pedalpcb.com/threads/the-hella-rats-chronicles.24686/ The fat rat is shown on one of the schematics if you scroll down.

The concept is very similar! yeah I think I'm going to focus more on the clipping side of the circuit than on the EQ, the first schematic you show is very interesting and I want to do something similar but with an additional switch that chooses between placing the diodes on the opamp or tie them to ground so it hard clips, the enclosure I bough was a 1590DD, pretty big, mabye too big but I can keep It for a future bigger project.

Also yeah my placing of the HP is wrong and I should put it where you suggest .

 

[jesuscrisp]

I have so many questions and criticisms here... not to say it's a total mess but it is. Sorry.

Boost section:
Why 2x 1M in series for the pulldown resistor instead of just a 2M2?
If you want a buffered Vref, that's not how to do it.

Rat section:
Why the boost before the clipping diodes? Any amplification you get from the Rat gain stage will just smash the boost and the boost will then go to the diodes.
Why the low cut before the boost and diodes? You are losing a ton of signal with a passive low cut like that and you already are post gain just like the 2 EQ sections which can also cut bass post-gain. Superfluous. And if the resistance reaches 0 ohms, you ground the signal without a limiting resistor.
Why 2 rotaries (or is it 2 poles?) for clipping just to add a switch that bypasses it completely?

EQ stage:
unless you also want to cut with the EQ, which isn't useful, you don't need a dual gang control on the HM2 EQ. Just put A5K in the feedback loop and connect all gyrator inputs at the inverting input of the op amp.