Buddy's Breadboard and Circuit Design Notes
- Thread starter BuddytheReow
- Start date
BuddytheReow
Breadboard Baker
Yea, I haven't looked into the chip itself and what's under the hood. I just know how to hook it up (kinda) and what it sounds like.
benny_profane
Well-known member
The datasheet has a lot of great information.
BuddytheReow
Breadboard Baker
Look what I built! This was my project over the weekend. I found some scrap wood in my attic and decided to make a board for my breadboard. I couldn't tell if it was pine or cedar (not super knowledgeable), but I knew it wasn't oak cuz it wasn't heavy. I used some cherry stain I had leftover from my guitar build and decided to put it to good use. Sanded it down as best I could with my orbital sander, 2 coats of cherry stain, and 3 coats of poly. Now I can "show off" some of my builds without it looking super ratchet, lol.
If anyone's curious, those are 2 overdrives sitting on the board: one is a tubescreamer I'm experimenting with.
I also had a few mod boards from GuitarPCB come in today so I will post again once I've got them ready to go. Thanks @thewintersoldier for this suggestion! They can be found here https://guitarpcb.com/product/dpdt-wiring-board/. I'm also trying to figure out the rotary board from there too since it seemed pretty cool. Will have to use my DMM to figure that out when I have time.
If anyone's curious, those are 2 overdrives sitting on the board: one is a tubescreamer I'm experimenting with.
I also had a few mod boards from GuitarPCB come in today so I will post again once I've got them ready to go. Thanks @thewintersoldier for this suggestion! They can be found here https://guitarpcb.com/product/dpdt-wiring-board/. I'm also trying to figure out the rotary board from there too since it seemed pretty cool. Will have to use my DMM to figure that out when I have time.
Attachments
Chuck D. Bones
Circuit Wizard
Here's the schematic for reference.
Most circuits using the LM386 ground the -INPUT. It could be left floating, but might pick up noise or RF interference. That leaves the emitter of Q2 biased at 2 Vbe above ground. Q5 and Q6 form a current mirror; they try to keep the collector currents of Q2 and Q3 equal. R2 biases Q4's base close to ground, so Q3's emitter is biased to about the same voltage as Q2's emitter. Because Q2-E and Q3-E are at nearly same voltage, very little DC current flows thru R5 & R6. All this leads to the fact that the DC current thru R3 & R4 is about the same as the DC current thru R7. Notice that R3 + R4 is twice the resistance as R7, so the voltage drop across R3 + R4 is twice the voltage drop across R7. The only way that can happen is if Vout is close to 1/2 Vcc. The negative feedback thru R7 ensures that Vout = 1/2 Vcc.
With pins 1 & 8 open, the AC and DC gain of the LM386 is 20x. Any small DC imbalances in the Q1-Q6 circuit is magnified by 20x and appears at the output. With pins 1 & 8 jumpered together, the AC and DC gain of the LM386 is 200x. Any small DC imbalances in the Q1-Q6 circuit is magnified by 200x and appears at the output. But... if we connect a capacitor between pins 1 & 8 instead of a jumper, then the AC gain is 200X but the DC gain stays at 20x. Less DC offset on the output.
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benny_profane
Well-known member
@Chuck D. Bones Thank you for the detailed explanation. I’m still a bit confused regarding the topology of the BD. In the BD, you have pin 1 grounded via a resistor and cap. How are the AC and DC gains affected with that arrangement? Does that increase the amplification by further increasing the DC offset?
BuddytheReow
Breadboard Baker
Really digging this 386 analysis! Great stuff
Chuck D. Bones
Circuit Wizard
What I did in the BD has a similar effect to bypassing R6. I didn't invent that method. It's convenient if you want a gain other than 200x. The cap is mandatory because pin 1 is not at DC ground.
It increases the AC gain without affecting the DC offset.
It increases the AC gain without affecting the DC offset.
benny_profane
Well-known member
Ah okay. It’s starting to make more sense now. Thanks again!
BuddytheReow
Breadboard Baker
Took some time last night to put together my 2 mod boards. One is a dpdt mod board, the other is a 2p4t rotary mod board. I've got 2 extra dpdt boards and maybe bring them out at a later time. I socketed everything and took a lot more time than I thought. Since the board itself had the wiring/pinout diagram on it and got covered up with all the sockets I decided to color coordinate everything with a bit of nail polish (thanks, Babe 
). I've been interested in mosfet clipping for a bit now so maybe I'll rebuild the Dist + with tons of clipping options to see what sounds good/bad.
). I've been interested in mosfet clipping for a bit now so maybe I'll rebuild the Dist + with tons of clipping options to see what sounds good/bad.Attachments
BuddytheReow
Breadboard Baker
Like a kid in a candy store with allowance money in his pocket, I was itching to use my new mod boards. What's one of the more simple dirt pedals to mod? The MXR Dist +, of course! Here is a simple schematic taken from Beavis Audio. The original opamp is a 741 (single opamp) and has a different pinout than the 4558 listed here, but we are only using one of the opamps and they behave similar.
To give the high level view of this circuit, it is a Dist + with switchable feedback capacitors, on/off soft clipping diodes, increased gain potential, switchable hard clipping diodes, and a BMP tone stack thrown on toward the end. I would consider this a modified, but more modifiable circuit.
Items in purple are what I swapped out or made switchable and will explain below. The red areas are where I added things.
For the reds, in the feedback loop I added asymmetrical clipping 1n4001 diodes and made it switchable on/off. Using these had a noticeable volume drop and was very subtle in tone, but that is the nature of soft clipping. Turn the gain back and you've got an overdrive! Cleans up nicely with the volume knob on my LP and Strat.
The other red item after the hard clipping diodes I added my BMP tone stack w/LPB1 booster that I shared in a previous post. The booster itself is only used to bring back the volume drop from the tone stack. Here is the schematic for the tone stack itself and is very simple, but effective.
Now the purples:
I swapped out the 1m resistor for a 1.8m for more gain
. Was happy with the sound so I left it there. Of course you can go higher if you want and see what happens...
For the 4.7n cap I decided to whip out my rotary mod board for this. The purpose of this capacitor is to decide which frequencies get passed through to the opamp and amplified. Since my board had 4 spots I chose the following values: 10n, 33n, 100n, and 330n. The larger the value, the more bass comes through. If you want to get more specific in choosing the specific frequency for the cutoff you will have to adjust the 4.7k resistor accordingly. It can be tacked on to the mod board too if anyone's interested on the outer sockets with additional jumpers.
The other area begging to be modified was the hard clipping diodes. I used my DPDT mod board and found 2 combinations of diodes I liked: one is a BAT41/1n4148 and the other a red LED/1n4148. LEDs give a volume boost for some reason and my curiosity wants me to dig around the interwebs to find out why.
I am very pleased with the tonal possibilities of this circuit and am debating whether to commit this to stripboard or to come back to it another day. Breadboarding is slowly becoming an addiction for me once I begin to understand how circuits work.
To give the high level view of this circuit, it is a Dist + with switchable feedback capacitors, on/off soft clipping diodes, increased gain potential, switchable hard clipping diodes, and a BMP tone stack thrown on toward the end. I would consider this a modified, but more modifiable circuit.
Items in purple are what I swapped out or made switchable and will explain below. The red areas are where I added things.
For the reds, in the feedback loop I added asymmetrical clipping 1n4001 diodes and made it switchable on/off. Using these had a noticeable volume drop and was very subtle in tone, but that is the nature of soft clipping. Turn the gain back and you've got an overdrive! Cleans up nicely with the volume knob on my LP and Strat.
The other red item after the hard clipping diodes I added my BMP tone stack w/LPB1 booster that I shared in a previous post. The booster itself is only used to bring back the volume drop from the tone stack. Here is the schematic for the tone stack itself and is very simple, but effective.
Now the purples:
I swapped out the 1m resistor for a 1.8m for more gain
. Was happy with the sound so I left it there. Of course you can go higher if you want and see what happens...For the 4.7n cap I decided to whip out my rotary mod board for this. The purpose of this capacitor is to decide which frequencies get passed through to the opamp and amplified. Since my board had 4 spots I chose the following values: 10n, 33n, 100n, and 330n. The larger the value, the more bass comes through. If you want to get more specific in choosing the specific frequency for the cutoff you will have to adjust the 4.7k resistor accordingly. It can be tacked on to the mod board too if anyone's interested on the outer sockets with additional jumpers.
The other area begging to be modified was the hard clipping diodes. I used my DPDT mod board and found 2 combinations of diodes I liked: one is a BAT41/1n4148 and the other a red LED/1n4148. LEDs give a volume boost for some reason and my curiosity wants me to dig around the interwebs to find out why.
I am very pleased with the tonal possibilities of this circuit and am debating whether to commit this to stripboard or to come back to it another day. Breadboarding is slowly becoming an addiction for me once I begin to understand how circuits work.
Attachments
benny_profane
Well-known member
Since the Vf of the LEDs is higher than that of the BAT41 and 1N4148, less of the signal is clipped and a higher amplitude signal is allowed to pass. You're experiencing that as more headroom before compression and a higher volume level.
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Feral Feline
Well-known member
Or to put it another way, the diodes are dumping signal to ground and the order of magnitude from most to least is:
Bat41
1N4148
Light Emitting Diode
Like a leaky garden hose, the less water that's leaked to ground the more pressure and volume of H2O gets to the sprinkler's output.
Bat41
1N4148
Light Emitting Diode
Like a leaky garden hose, the less water that's leaked to ground the more pressure and volume of H2O gets to the sprinkler's output.
BuddytheReow
Breadboard Baker
More tone stacks! This is a Marshall TMB tone stack with an LPB1 booster afterwards as a recovery. Found the stripboard layout on the interwebs. My new tool, er, toy. I mean tool, yea. Gotta keep it semi adult around here.
My project this evening. Feel free to copy. Works great!
My project this evening. Feel free to copy. Works great!
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BuddytheReow
Breadboard Baker
In an above post, I had a Dist + circuit with a capacitor selector. Sometimes I liked the "thin" sound with the smaller cap, but it was actually too thin. The opposite is true too: I had a larger cap that I like the deep bass coming through, but it was a bit too muddy.
What's the solution? Blend the two with a potentiometer! The little lightbulb went on for me when I was looking through various build docs and stumbled upon the Dingo Distortion circuit. This FAT pot allows you to blend the sound between the two filters produced with the 220n and 1u capacitor.
Depending on the circuit you may have to fool around with different tapers and values to find one you like best.
What's the solution? Blend the two with a potentiometer! The little lightbulb went on for me when I was looking through various build docs and stumbled upon the Dingo Distortion circuit. This FAT pot allows you to blend the sound between the two filters produced with the 220n and 1u capacitor.
Depending on the circuit you may have to fool around with different tapers and values to find one you like best.
BuddytheReow
Breadboard Baker
I've been taking some time to look at 8245039349002 schematics out there and I thought this one was interesting. This is a PCB from Rullywow called the SuperJudge. I whipped this up on a breadboard and it's a decent higher gain overdrive if anyone's interested in the sound.
I'm posting this here because when I was looking it over I noticed something interesting. This build requires a 1044 charge pump and for the life of me at first I couldn't understand why. Charge pumps are usually used to increase the voltage on many circuits that I have come across, but not always. This one utilized the -9v output so I thought "hey, why is this so special that it's using -9v?".
The answer became obvious after I breadboarded it and troubleshooted it (C3 was placed in the wrong hole on my board so user error).
Many times on opamp dirt circuits you will have a voltage divider in the power section (4.5v). THAT'S what goes to the other opamp input to bias the circuit, whether the positive or negative one (inverting or noninverting if you want to get technical). When I looked the circuit over again it dawned on me: the + input in both opamps goes to ground (0v) and that's EXACTLY midway between 9v and -9v that powers the circuit which acts as the bias!!
I thought this was interesting because it's another way to bias opamps rather than voltage divider resistors and should go in my "notes" thread. I don't have a breadboard pic unfortunately since I wanted to try another circuit over the weekend, but this is pretty simple to whip up if you've got some experience.
I'm posting this here because when I was looking it over I noticed something interesting. This build requires a 1044 charge pump and for the life of me at first I couldn't understand why. Charge pumps are usually used to increase the voltage on many circuits that I have come across, but not always. This one utilized the -9v output so I thought "hey, why is this so special that it's using -9v?".
The answer became obvious after I breadboarded it and troubleshooted it (C3 was placed in the wrong hole on my board so user error).
Many times on opamp dirt circuits you will have a voltage divider in the power section (4.5v). THAT'S what goes to the other opamp input to bias the circuit, whether the positive or negative one (inverting or noninverting if you want to get technical). When I looked the circuit over again it dawned on me: the + input in both opamps goes to ground (0v) and that's EXACTLY midway between 9v and -9v that powers the circuit which acts as the bias!!
I thought this was interesting because it's another way to bias opamps rather than voltage divider resistors and should go in my "notes" thread. I don't have a breadboard pic unfortunately since I wanted to try another circuit over the weekend, but this is pretty simple to whip up if you've got some experience.
Feral, I would use a large resistor to stop the hose leak from popping any further!!!
Feral Feline
Well-known member
Sorry, I'm not following this. Are you talking about switch-pop at the output? I was referring to hard-clipping to ground; you could add a resister in series with the LEDs to ... wait, is that a euphemism?
My mistake, I thought you had a leaky hose!!!
BuddytheReow
Breadboard Baker
Tayda order came today!!! An extra breadboard, some terminal block, PCB mount switches, and header pins. Was time to update my breadboard rig even more today.
Here's my rig as of right now. Look at what I made!!!!!!!!!
Test Box w/ built in audio probe. Found this on tagboardeffects
3 Breadboards
DPDT mod board from Guitar PCB - Very handy for diode selection or A-B'ing a cerain component
2P4T Rotary mod board from Guitar PCB
And my daughterboard consisting of:
-8 Terminal Blocks for PCB mount potentiometers with header pins for breadboard jumper mounting
-2 DPDT switches with header pins for breadboard jumper mounting
My daughterboard has been upgraded to a MOD-ERBOARD.
The circuit on there is from an earlier post I made today: PedalPCB's Acid Rain Fuzz. It's pretty good and worth your time breadboarding it, but it probably won't look as cool as mine does
Here's my rig as of right now. Look at what I made!!!!!!!!!
Test Box w/ built in audio probe. Found this on tagboardeffects
3 Breadboards
DPDT mod board from Guitar PCB - Very handy for diode selection or A-B'ing a cerain component
2P4T Rotary mod board from Guitar PCB
And my daughterboard consisting of:
-8 Terminal Blocks for PCB mount potentiometers with header pins for breadboard jumper mounting
-2 DPDT switches with header pins for breadboard jumper mounting
My daughterboard has been upgraded to a MOD-ERBOARD.
The circuit on there is from an earlier post I made today: PedalPCB's Acid Rain Fuzz. It's pretty good and worth your time breadboarding it, but it probably won't look as cool as mine does
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