Buddy's Breadboard and Circuit Design Notes

[BuddytheReow]

Will definitely read the bias pdf tonight when I have some time. Maybe my definition of "bias" is incorrect

You're right that the this sets the bias for the op amp so the virtual ground is 1/2(supply voltage) (i.e., Vref). The resistor provides a path from the buffered voltage divider reference to set the bias of the op amp. This is an AC-coupled circuit, so the bias has be be supplied. R3 is a load that provides a DC return path for Vref and sets the AC impedance.

Maybe my own definition of "bias" is incorrect. I will take a look at the link you sent tonight when I have some quiet time to "study". Virtual ground puzzles me too.

 

[BuddytheReow]

View attachment 14452

On my list to build/tinker!

 

[benny_profane]

Will definitely read the bias pdf tonight when I have some time. Maybe my definition of "bias" is incorrect

I don’t think so? You were just stuck on why that resistor was there. Think of DC bias as the starting point for the DC voltage swing. It’s called virtual ground because it becomes the steady reference for the signal to go above (positive) and below (negative).

With a +9V single supply circuit, there’s a 9V delta. In order to get the most usable headroom, the reference voltage is put at half that figure (4.5V). This is the ‘virtual ground’ that the signal uses as a ‘home base’ of sorts. If you add a voltage inverter, you can create a -9V rail. In this case, 0V is in the middle and you don’t need to provide a reference voltage via a resistor divider network, just filter the 0V from the supply to deal with ripple. Vref is 0V, the positive rail is +9V, and the negative rail is -9V (and is effectively used as the negative ground supply).

 

[BuddytheReow]

I don’t think so? You were just stuck on why that resistor was there. Think of DC bias as the starting point for the DC voltage swing. It’s called virtual ground because it becomes the steady reference for the signal to go above (positive) and below (negative).

With a +9V single supply circuit, there’s a 9V delta. In order to get the most usable headroom, the reference voltage is put at half that figure (4.5V). This is the ‘virtual ground’ that the signal uses as a ‘home base’ of sorts. If you add a voltage inverter, you can create a -9V rail. In this case, 0V is in the middle and you don’t need to provide a reference voltage via a resistor divider network, just filter the 0V from the supply to deal with ripple. Vref is 0V, the positive rail is +9V, and the negative rail is -9V (and is effectively used as the negative ground supply).

Appreciate the input, but still a little confused. I will circle back to this. In my head, biasing a circuit meant changing the 9v to another value using a voltage divider such as in an LPB1. But if I have 4.5v coming out of there and I throw a 1m resistor after that the voltage drops to nothing and THAT's what goes to the input pin in the IC? Again, I have to relearn some of the boring theory behind it all.

 

[BuddytheReow]

I took some time this afternoon to try out a tone stack (treble, mid, bass). Marshall Guv’nor seemed like any place to start. Here’s the schematic


It seems simple enough on paper, but it took quite a while to figure it out on a breadboard. Because this is a passive tone stack that throws certain frequencies to ground it needed a booster at the end. Going to try different tone stacks soon to see what I like. I’ll also try it with some op amps now that I kinda know how they work.

Without further ado, I present an Electra distortion with variable gain and diode selector (4148s or red/green led) into a Marshall guv’nor tone stack into an lpb1. You can kinda see the 3 sections on the breadboard how I laid it out.

I call it the “Crooked President”.

 

[benny_profane]

Check this site out if you haven't already:

TSC in the web

 

[benny_profane]

Appreciate the input, but still a little confused. I will circle back to this. In my head, biasing a circuit meant changing the 9v to another value using a voltage divider such as in an LPB1. But if I have 4.5v coming out of there and I throw a 1m resistor after that the voltage drops to nothing and THAT's what goes to the input pin in the IC? Again, I have to relearn some of the boring theory behind it all.

Biasing can involve that, but it doesn't mean that necessarily. All you're doing it establishing a known, stable operating point for an active part, circuit block, or whole circuit.

The voltage doesn't drop to nothing when it goes through the Rin resistor (1M in the case of the discussed circuit). Note that it's unusual to have those values in the voltage divider and the input resistor (that's discussed in the electrosmash article and the linked pdf). Essentially, that resistor has two purposes:

1) Provides a load that determines the input current to the op amp.
2) Sets the input impedance to the circuit.

Check out this resource (particularly Figure 4.3.2 and the inclusion of R5) for a more detailed breakdown with example circuits.

 

[BuddytheReow]

Biasing can involve that, but it doesn't mean that necessarily. All you're doing it establishing a known, stable operating point for an active part, circuit block, or whole circuit.

The voltage doesn't drop to nothing when it goes through the Rin resistor (1M in the case of the discussed circuit). Note that it's unusual to have those values in the voltage divider and the input resistor (that's discussed in the electrosmash article and the linked pdf). Essentially, that resistor has two purposes:

1) Provides a load that determines the input current to the op amp.
2) Sets the input impedance to the circuit.

Check out this resource (particularly Figure 4.3.2 and the inclusion of R5) for a more detailed breakdown with example circuits.

Thanks, Benny. I'll check these out with some light reading

 

[BuddytheReow]

My Tayda order came today!! I took some time to whip up a "protoboard" with my order and some items lying around the house. @fig had a great idea regarding potentiometers from a previous thread found here. Previously I used solid core wire soldered to the pot and found that it kinda worked. If I were to turn the knob the connection would go in and out. Thanks for the tip, fig! This daughterboard will definitely help. I've got extra room on it and thinking maybe a separate power section with a voltage divider? May be worth my time.

Also wondering how I can mount a few switches as well to make it more "permanent" on the daughterboard. If anyone can chime in here that would be great.

Mounted everything with some putty for now and so far it holds. I know this is kinda ratchet looking (a term my wife uses a lot) using cardboard and duct tape, but this is temporary until I make a trip up to Home Depot to get a piece of lumber and finish it. What size should I get? 8x12?

IMG_0699.HEIC

drive.google.com

IMG_0698.HEIC

drive.google.com

 

[BuddytheReow]

Not all breadboards are created equal!!!! You can see in the pics of my previous post that there are 2 different breadboards: my new one from Tayda and other one from "Elegoo". I'm assuming the later is a cheap, Chinese knockoff and it shows! It is the whiter one of the two. Many of the holes were tough to put jumper wires in and various component leads. Some of the pins came out of the jumper wires while removing them from the board and I was careful!!! This other one from Tayda is much nicer and all the leads/jumpers fit nice and snug, but not overtight.

Lesson learned...

 

[BuddytheReow]

Still fooling around with some tone stacks.

This is a Ross Distortion (very similar to MXR Dist +) with some mods. First, a negative feedback loop capacitor selector (between 47n and 22n and I like the 22n better). Then an asymmetrical, hard clipping diode selector (4148s and Red LEDs) into a Baxandall Tone stack. This tone stack was easier to figure out the layout than the guvnor one I did the other day. Prolly cuz there's only 2 pots instead of 3.

Does this make it more original rather than putting stock building blocks together? I'd like to think so, but I'm far off from a true original circuit. Would love some comments, but if not, that's fine. This thread is merely me writing down my thoughts, knowledge obtained on the internets, and tinkerings.

Here are some pics of the breadboard. I definitely gotta find a way to clean up all those jumper cables. Looks like a rat's nest. I guess part of the breadboard learning experience is changing the layout to reduce them. Or I find shorter cables.

 

[BuddytheReow]

Looked around PedalPCB site and decided to try out the Heavy Spider (Epider Sound Heavy Metal). Simple circuit and schematic below. Since I've been doing a lot of reading lately I have a basic understanding of how this circuit is put together and what part does what.


I put switches on both sets of diodes to hear the difference in clipping. Noticeable volume drop in the hard clipping section (D3 and D4). The soft clipping section (D1 and D2) was too subtle for my ears. Perhaps I didn't wire the switch correctly? Anyway, this has an interesting sound. There is a bit of gating, but not too much; just enough to give it some flavor. I found the sweet spot by rolling back the volume knob a bit and adjusting the "attack" knob a bit. In my opinion, this dooms...

 

[benny_profane]

The soft clipping section (D1 and D2) was too subtle for my ears.

Those aren't soft-clipping diodes. That's a crude noise gate / noise reducer that results in crossover distortion. The same scheme is used in the Boss HM-2.

 

[BuddytheReow]

Those aren't soft-clipping diodes. That's a crude noise gate / noise reducer that results in crossover distortion. The same scheme is used in the Boss HM-2.

Either way I couldn’t tell the difference with them. How do I know that’s a gate/noise reducer? Simply because there are 2 diodes going opposite ways? I guess I’ll have to do some reading about the hm2. Thanks for pointing that out to me!

 

[benny_profane]

Soft clipping diodes are in the feedback loop of an op amp gain stage. These are in series with the signal and set a baseline for the signal to pass. For example, if the Fv of the diodes is 600mV, only signals above that threshold will pass because they are arranged in anti-parallel. The issue with that arrangement is that it creates crossover distortion when the signal passes from positive to negative and vice versa. There's a lot of other distortion happening in the circuit, so that won't be the dominant sound, but it is there. The main purpose is to create a noise gate and reduce transients.

I think that the ATTACK knob reduces the parallel resistance and lets signal bypass the diodes as it's turned up. In that case, the gating effect would be lessened and the pick attack more apparent as it's turned.

 

[BuddytheReow]

Soft clipping diodes are in the feedback loop of an op amp gain stage. These are in series with the signal and set a baseline for the signal to pass. For example, if the Fv of the diodes is 600mV, only signals above that threshold will pass because they are arranged in anti-parallel. The issue with that arrangement is that it creates crossover distortion when the signal passes from positive to negative and vice versa. There's a lot of other distortion happening in the circuit, so that won't be the dominant sound, but it is there. The main purpose is to create a noise gate and reduce transients.

I think that the ATTACK knob reduces the parallel resistance and lets signal bypass the diodes as it's turned up. In that case, the gating effect would be lessened and the pick attack more apparent as it's turned.

Gotcha. Your explanation makes sense. I thought the attack knob was merely a tone filter. Still a little confused if cap/resistor are in series if it's a high or low pass. More reading for me I guess. Thanks, Benny

 

[BuddytheReow]

Going to be tweaking the Heavy spider shortly, but I wanted to share a “tool” that I built over the weekend. I shared previously a big muff tone stack which is a great multi purpose tone stack given the few number of parts it needs. The problem with that is it’s a passive filter and sucks out a lot of volume.

what’s the solution? Build a booster after it! This comes from tagboard and is a BMP tone stack with an LPB-1 booster. The trimmer is merely the output volume and obviously can be adjusted to taste. Although it is a stripboard layout I have slightly modified it by putting sockets where the power, ground, input, and output wires go. Jumper cables fit surprisingly well on them. To help me identify which socket is which I have labeled them. For the power socket I simply used a bit of my wife’s nail polish carefully on the sides and top.

definitely useful when breadboarding a circuit and realize the sound is not quite right…

 

[BuddytheReow]

Using my newly created toy, I tacked this on to the heavy spider still sitting in my breadboard. Added at the end of the circuit right before the volume pot. I also added 2 gain controls, one on each emitter going to ground. I also took out the diode switch near the “attack” pot since @benny_profane mentioned this is merely a noise filter. The hard clipping diode switch still remains.

after playing around with it I think I have dialed everything in to my taste and am happy with the sound. Gain 1 should remain as is in the circuit (emitter straight to ground) gain 2s sweet spot to me is around 560 ohms.

sorry about the crappy camera work. I only have my phone.

Edit: video link here. I only changed the diode clipping switch.

 

[fig]

How's that pot-board working? That's slick!
I think Chuck mentioned something about grounding the pot housing to reduce noise in sensitive circuits, but my bench, room, house, has so much noise it causes tinnitus anyway.....my plan is to line the walls, floor, and ceiling with copper and solder my pinkie toe to it.

I am ground! [using Groot's voice]

 

[BuddytheReow]

Pot boards working great. No issues so far. Definitely more room for switches, etc.
Edit: How would I go about grounding the pot board?