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Boost Effect Breadboarding My Designs

Building a Simple Op Amp Booster – Breadboarding

After the introduction and analysis of two op-amp based guitar boosters, let’s see how they sound. I’ll breadboard them and try them out to make sure everything works as expected.

I’ll give some effect characteristics, do a breadboarding diagram, then do the actual breadboarding (with bill of material) and finally test both effects out.

Characterizing the Effects

I forgot to give some more details on parameters for the pedals. Normally I do it after the analysis, so here it is before I dive into breadboarding stuff:

ParameterMXR Micro AmpThunder
Input Impedance
(@1Khz)
7 Mohm900 Kohm
Output Impedance
(@1Khz)
500 ohm200 ohm
Gain0.5-26 dB0-24 dB
Current Draw
(without LED indicator)
4.5 mA4.5 mA
Operating characteristics

All values I got through simulation and all are approximate. Both pedals look really good in terms of general characteristics.

Breadboard Diagram

Here’s the schematic for Thunder once more:

Schematic of the Thunder booster effect
Thunder Schematic

I like to use DIY Layout Creator to prepare for breadboarding. This step is not strictly necessary, but I prefer to have it done this way. Makes my life easier when it comes to planning, and it looks way more professional for my posts.

I used pen and paper before discovering the tool, and that is such a tedious job. With the tool it is really easy to move things around to your liking.

For this, I just go straight from the schematic, I place the breadboard and the most important components first (in this case the op-amp chip). After that, I place all the other components next to the board.

For example, I place all 7 resistors next to the board first. I mark them all R1 to R7 exactly as on the schematic and give them correct values. I then take them one by one and place them on the board until I have placed all of them. In the end here’s the result:

Image showing plan for breadboarding thunder without a switch
Thunder on a breadboard

The way it is done above, the effect is always on. I have a DPDT switch on the board that I can use if I want to do a bypass. I need to only re-wire input and output jacks slightly and I can have a true bypass:

Image showing a plan for thunder on a breadboard with true bypass
Thunder on a breadboard with true bypass

The breadboard layouts look nearly identical. If you compare the schematic with the breadboard layout, component references are all the same, R1 on the breadboard corresponds to R1 on the schematic.

Here are the DIY files if you wish to play with them:

Following the Connections

Sometimes it is hard to follow connections between schematic and breadboard. Schematic is great because we deal with abstract symbols, but when it comes to breadboarding, we have physical components which impose their own limitations (e.g. size of each component is fixed).

Here are a couple of examples:

Side by side schematic and breadboard diagram showing two connection points highlighted
Example of two connection points

Highlighted in yellow are connections to the 2nd pin of the TL072 chip. On both, the schematic and the breadboard diagram, I can follow one lead of R4 connected to a lead of C5 to a blue wire going to pin 2 of the potentiometer to 2nd pin of the chip.

Highlighted in blue is Vref connection. It’s a bit harder to follow because in schematic, even though the blue parts are not connected, the connection is named Vref on both parts of the schematic. That means that they are connected in reality, naming them just simplifies the schematic so I don’t need to run connections all over the place.

Looking at the highlighted part on the breadboard (going from right to left) R9 is connected to R8, connected to positive lead of C6. Then, there’s a jumper wire going to R3. The connection goes underneath R2 and it’s not connected to it.

Hopefully the two examples above help with following how the components are connected and how to even do it from scratch.

Breadboarding

Once I have the layout worked out, breadboarding is really easy. I just literally follow the layout, I plug the components in and put in the jumper wires exactly as on the diagram (and I even try to match the colours).

Now, truth be told, I like to prepare everything in advance so it looks good on the videos and photos. I do clip the leads to a more appropriate size and I cut wires to size from a spool I have etc. But when it comes to rapid prototyping, I sometimes just go directly from the schematic and just plug in components and wires as I go along without much consideration for aesthetics.

Bill of Material

Let me get the list of components that I’ll be using here first:

Thunder

DesignatorsComponentNotes
BreadboardFull size breadboard
Battery and battery connectorI’ll be using battery for testing the effect
Jumpers and Jumper wire
INSwitchcraft 12In – stereo Jack (alternatively use mono jack since I don’t use ring connector)
OUTSwitchcraft 11Out mono Jack
VR110K Linear PotI used ALPHA RV16AF-41
DPDT SwitchAlps SPPH410100 latching switch
I use it to bypass the effect so I can compare dry sound from guitar and with the effect on
C1100pFCeramic cap (NP0/C0G)
C2100nFMetal film PET cap
C31uFElectrolytic cap 25V
C422uFElectrolytic cap 25V
C5150pFCeramic cap (NP0/C0G)
C647uFElectrolytic cap 25V
C7100nFCeramic cap (X7R)
R1, R6100 ohms1% 250mW metal film
R2, R32.2M
R4, R5680 ohms
R7, R8, R910K
U1TL072IPTL072 in 8 pin DIP package
List of components for Thunder

MXR Micro Amp

I don’t have breadboard diagram for this one, I’ll do it ad-hoc, but lots of it will be similar to what I have for Thunder.

DesignatorsComponentNotes
BreadboardFull size breadboard
Battery and battery connector
Jumpers and Jumper wireI’ll also use crocodile clips to connect pot without soldering it
INSwitchcraft 12
OUTSwitchcraft 11
VR1 (R5)500K Reverse Audio PotI used PDB181-GTR01-504C2 (Bourns guitar pot … because it looks beautiful)
C1100nFMetal film PET cap
C247pFCeramic cap (NP0/C0G)
C34.7uFElectrolytic cap 25V
C41uFElectrolytic cap 25V
C515uFElectrolytic cap 25V
R1, R210M1% 250mW metal film
R31K
R451K + 5.1KI’ll use 2 resistors here in series because I don’t have 56K handy
R62.7K
R7, R8100K
U1TL072IPTL072 in 8 pin DIP package
List of components for MXR Micro Amp

I didn’t have 22M resistor, so I used 10M for R1. This won’t make a difference in sound, it will lower the input impedance just a bit, but nothing significant.

Trying it out

Let me thus do both approaches in the video below. I’ll follow the diagram very closely for Thunder, but for MXR Micro Amp, I’ll just go straight from the schematic and do a very quick breadboarding attempt.

Note: sound is not great but it is still good enough to show that the effects work. Audio is from my phone that I used for recording.

Note 2: I fixed breadboard diagram in this post. I made a mistake when breadboarding Thunder, I misplaced R2. It didn’t break the effect but caused it to have less gain. I’ll re-record video at some stage, but even with the mistake, the effect will work.

Breadboarding and trying out two op-amp based boosters

Here are some photos of the finished result:

Photo of breadboarded Thunder effect
Breadboarded Thunder

As you can see from the photo, the breadboarded effect is nearly 1-to-1 like I planned it.

Photo of breadboarded MXR Micro Amp effect
Breadboarded MXR Micro Amp

I did ad-hoc plugging all the cables and components for MXR Micro Amp. It doesn’t look much, but it works, and it will work just fine if care is taken. Troubleshooting it is a different matter, long leads can touch causing issues, it is hard to trace wires, but it is OK for a quick job.

Some final thoughts

It does not matter much which approach you take – pre-plan and keep everything neat, or just do it ad-hoc and leave wires dangling everywhere. The idea here is to have the effects breadboarded to confirm they work. Then the follow up idea is to experiment to nail the components and desired sound exactly as desired.

The difference between two approaches is mostly esthetic, more cables and lengthier wires and components leads might pickup more noise, but only slightly more. With number of various devices and interferences in our environment it is pretty much random what you gonna get in terms of noise.

It is worth noting that the final pedal will be noticeably quieter than either of the breadboarded effects.

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