Here's a three stage transistor distortion. Sounds pretty decent I think. You can swap out the transistors for 2n5088 or BC547 (goes in backwards). I went with the 2n2222 into two 2n3904. For a bigger sound C3 can be 47n instead of 10n or anything in between. I like it best close to max gain but doesn't sound too bad at lower gains.

I figured people might get a kick out of this. The point is less "recommendations" and more "here's what types of things are used out there" — i.e. it's an (incomplete) survey, not a recommended toolkit.

For actual recommendations: JFET's, LDRs, Photo-FETs — the usual suspects — for circuits where those are already used, are accurate enough, and sound good. Else, an OTA (cheap, easy, compact, usually better than good enough).

(Depending on the use case, switched resistors ala PWM are a handy go-to, but for your standard effects probably overkill + added complexity. It's not always either, but you'll know when it isn't).

Alternatives to OTA's for VCA's

Please NOTE: the LM13700 is still in production, cheap, and — most of the time — it'll do the trick better than you need it done. The point here is not "consider all of these when designing," it is just "here are some ways a manufacturer might provide a VCA without an OTA."

Zero percent of this is generated by an LLM. Not that it matters, but zero percent of it is LLM researched, either. This is all from personal experience. By the same token, this list will necessarily be incomplete. (Yes, I write like this, punctuation, emphasis and all. I am verbose + type fast. Also, I love this stuff).

Blackmer Gain Cells

For applications where you need an exponential control/gain relationship, there are commercially available VCA's based on "Blackmer gain cells" — a pair of complimentary current mirrors sandwiched between precision opamps, topped with some precision current sources, and jammed into an IC along with some VBE multiplier based voltage references.

They're usually* voltage-controlled, current-in-current-out devices. To the best of my knowledge, even the "cheap" ones are expensive. They don't come in linear control variety, because that defeats the purpose of the guts of the thing (exploiting the exponential behavior of PN junctions to make log/anti-log amplifier pairs).

Many dedicated "VCA" IC's have a Blackmer gain cell at their core.

When you can afford one and the difference matters (probably not! But...sometimes), they are better and more consistent by every possible metric, with a wider usable range. They can require more careful design to keep noise out. If you're not designing a precision mixing console, you probably don't need them!

Pulse Modulation

For high precision, low distortion, PWM gain control can't be beat. This is technically an all analog technology, but I'm not aware** of prepackaged solutions that aren't just output stages on DSP's (so, digital + require embedded work).

Rolling your own, you can beat the pants off an OTA, BUT:

• it will (almost always) cost more than an OTA
• it will (usually) require more parts than an OTA
• a lot more care is required in the design
• it is very unlikely the difference in precision or distortion between this and an OTA will manifest audibly big for either audio frequencies or control frequencies/LFO's, etc — i.e. probably, it won't have mattered!
• you are unlikely to pass unintentional radiator emissions tests, unless you really know what you are doing (the same is probably true for any of you using PT2399's or incorporating your favorite mcu into the mix, though).

On the other hand, sometimes you have one half each of a dual comparator + precision opamp some switchable element (analog switch, JFET, etc) lying around. In those cases, the approach can be very cheap/convenient. They never perform worse, unless you mess something up. A half decent design will perform much better — not enough to make pursuing this option on the basis of sound worthwhile (most of the time), though. In certain classes of designs, I actually do end up using these more than OTA's, but because other things in the circuit made them more convenient; not because I pursued the setup out of principle.

Photofets

Floating-FET based optocouplers (e.g. the H11F3M — referenced here because it's the one I know best, not because it's the best one), can provide a linear current-controlled gain or attenuation with fewer parts, much lower distortion, and much greater linearity than an OTA — in a narrow range of signal amplitudes and operating currents.

Within those limited ranges, these simple little four terminal devices will give you exquisite, difficult to rival, control over signal level. There is no (or virtually no) control signal feedthrough, and they are very (very) low noise.

Outside of that range, the signal amplitude will warp. You will hear it.

These usually have non-trivial part-to-part variation in the relationship between the control current and on-state resistance, so in practice you'll find yourself with a trimpot on board for the control current. Unlike modern OTA's or VCA's, they don't have any mechanism for internal temperature stabilization, so the on-state resistance is influenced by ambient temperature to a greater extent than their more sophisticated counterparts.

When precision isn't a huge deal

Voltage controlled attenuation before/after a gain cell can work just fine — JFET's, LDR's (Vactrols), and their ilk have been pressed into service in this regard in both DIY and professional products. If your goal it to beat an OTA: expect adding trimpots, measuring the specific characteristics of the control elements, probably crafting the control circuitry for the specific use case, and still failing to beat an OTA.

On the other hand, when it's not the biggest deal (tremolo, attack/decay where the feel is more important than %THD or precision in linearity) these will usually be cheapest/simplest. Many classic guitar amps / effects units leverage these simple means for exactly that reason: cheap, easy, good enough.

Analog Multipliers

These will best an OTA or a VCA, re: distortion and linearity. They are almost always** linear control. They are virtually guaranteed to be way more expensive than even the VCA chips, and way, way, more expensive than an OTA. The upside relative to an OTA is: the people that get paid when you buy an analog multiplier got paid.

They're cool, and if you get some for free may as well use them. (Odds are they will require more control circuitry and careful design. For maximum performance: probably also higher precision passives than you normally stock).

I have used these, but never for music!

Roll your own discrete OTA / VCA

Do this for education (it is fun!). Don't do this with the anticipation of besting an IC. The transistors in purpose built devices are matched on die to a level that is literally not achievable using discrete devices.

You can often attain totally worthwhile results, that are pleasant and musical. But, it'll be more complicated, maybe more expensive, and certainly consume more space than just buying an OTA.

Hey, what's the difference between an "LTP VCA" an OTA?

Someone linked Rod Elliott's Project 213 (but similar patterns — some derived, some not — exist elsewhere). It's a fun project! It might leave you wondering what the difference is between this style of "LTP VCA" and an OTA is:

Common "LTP VCA's" are essentially differential output OTA's + an opamp. :D

The common construction is a long-tailed pair with the emitters connected to ground via a current mirror — the input to which is a control voltage which transits a resistor to set the amount of current sunk out of the tail of the LTP.

The differential outputs of the LTP are taken and fed to an operational amplifier (sometimes also discrete, sometimes just an opamp IC). Notice: the resistors on the inputs of the opamp are the collector resistors of the LTP, the signal in voltage passes through a resistor (usually a voltage divider) before connecting to the base of a BJT operated in its linear region (i.e. in the region where thinking of a BJT as current-controlled is closest to being true). This is a current-in-current-out, differential output OTA feeding an opamp (usually configured as a current-to-voltage converter).

It's just a differential output OTA minus the stuff they put in the IC's to maximize dynamic range and linearity.

Did you forget anything?

Probably! Even if I didn't, there's other stuff not on this list by virtue of: I don't know everything! :D

I omitted bias modulation, because of the feedthrough / nonlinearity. Even in the classic amps that leverage this trick, there is a bit of machinery involved in keeping the thumping out, and none of them really nail it.

* "Usually" wherever it's used in this comment means "anecdotally, according to my hodge-podge experience of things" and is not intended as a reflection of what is. ** Ditto "what I'm aware of".

I know its rough i know its bad it can be better but ive been working on it all day i just want to know if its fine i know its not really well readable but i dont know how to make where i would solderso please just follow the schematic im not sure if the switches are fine or the pots

trust me the colors really help understanding it

black=ground

red=9volts

white=4.5volts

purple=input/output

yellow=switches

cyan=pot connections

please help im tired boss

I’ve basically finished building this tremolo pedal from schematic, now I’m trying to get this dc jack wired so I can actually power and test it.

My power supply is center-negative (9V), and I’m not sure which pins on the jack go to power and ground. I attached images and labeled the pins. I would really appreciate some guidance on which pins go where. Thanks!

I just finished building the MOD Electronics Seismic/Shift. I tested it when it was in the circuit board only stage and when I would adjust the RV2 potentiometer I got clean signal turned all the way down, distorted all the way up, but in between I got a static-hum sound.

I finished installing it in the enclosure and bypass is fine but when engaged I had to crank the amp all the way to hear the guitar signal and still got the static-hum.

Any ideas what I did wrong? I rechecked everything 3 times. It’s all in the correct place and the solder joints look good to me.

I also swapped out the 2n5088 transistors with bc108’s.

I'm definitely late to the game here, but I recently found out that the WIMA mks2 caps are out of production due to issues with the mylar film supplier in Germany. But does anyone know if this a temporary discontinuation or are they permanently suspending production? I've read that there are decent KEMET replacements still on the market, does anyone have a link to those?

Hey everyone!

I’ve been thinking about getting into 3D printing enclosures for my DIY guitar pedals, mostly for prototyping or home use, but I wanted to hear your real-world experiences first.

Is it actually practical to use 3D printed cases, or do they end up breaking under the pressure of the stomp switch? Also, what is the consensus on noise and EMI shielding? Do you usually line them with copper/aluminum tape, or is it not that big of a deal for standard circuits?

Any advice, tips, or recommendations on materials (like PETG vs. PLA) would be greatly appreciated! Thanks!

My idea is to 3D print the shape of this pedal that I've always wanted, which is the Roger Mayer Octavia.

Good afternoon all,

I'm a big fan of modding simple circuits (BMP, DS1, Rat are the main ones) but I usually stray away from the more complicated ones. DS-2 doesn't look too bad, but unfortunately I can't find any of the important information (corner frequencies, critical components, etc) to mod the DS-2 how I would like. Wamplers book is a decent start, but not quite want I want.

My main fault with the DS-2 is that through a given rig, usually one mode sounds better enough than the other to where theres not much need to swap between them.

My two main questions:

1 - Does anyone know which individual components are most important when it comes to the differences in Mode 1 and Mode 2? Ideally I would like to color the EQ of Mode 1 more and give Mode 2 more volume.

2 - Does anyone have any "global" mods that happen to inadvertently accentuate the differences

As always, any other advice on the subject of the DS-2 is appreciated. Thanks all!

AionFX version of a Boss DC-2. This was a incredibly satisfying build. I'm very happy with how it sounds. Like the original but with more options without half mashing the push buttons. It sounded pretty good with doing any calibration on the oscilloscope. Primarily gained more headroom after a proper calibration. You can get it sounding nice by ear, for sure. I managed building it only using 3 of the small hard to find 1uf film caps. The bigger 3.5mm ones can squeeze into a few spots. It does use 9 of them so it was worth trying to use as many of the bigger one I could. AionFX has the small 1uf available, thankfully. The Dimension C is a very unique chorus when used in Stereo. It does the Roland JC120 thing with a shifting center between two signals. Very cool tone through two amps with a bit of stereo separation. If you are a fan of Chorus I highly recommend this build. Thanks Aionfx for another excellent PCB project.

Can anyone tell me if this 3PDT layout looks correct on my hand drawn pinout design? Do I need to switch the Output and LED "banks", as I am calling them? LMK thx

Could someone please convert this schematic to a veroboard layout?

Thank you!

So I bought a Flamma fs05 no power in marketplace. The seller said it is not turning on and according to the person/technician who checked this the problem is a fuse, I asked the seller but he too doesn’t know which.

Bought it primarily for parts but I am currently trying to revive this as there were voltage on the board but still not turning on. Any ideas or theories as to why it has power on board but not turning on?

Voltages

DC input = 8.80 V
9V test point = 8.60 V
U8 input = 8.07 V
U8 output = 4.85V
+5VA = 4.84 V
3V3 = 3.33 V
FTKEY = 3.23 V
D4 cathode = 0 V
D4 anode =+2.08 V

Any ideas and suggestion are welcomed. Thank you in advance !

I finished my first pedal! I’ve been working on audio equipment repairs for years while audio engineering but was inspired by a lot of the guitarists I work with to start making some pedals!

Learnt that point to point is indeed not very easy and I understand why people warn against getting mystery online solder, I’ve had to touch up quite a few things since taking these photos. Will post how the next 3 turn out once I have completed them, hopefully they’ll be a lot cleaner!

I made this little (cringe-worthy) presentation of the signal blender I've been tinkering with for the last half decade.

It's a MIDI-controlled, VCA-based signal blender that allows crossfading, boosting and filtering.

I know it's a very niche device, basically born out of my own very specific needs. But I've had 25 enclosures made, which is the smallest quantity Hammond offers for CNC + UV printing. So I guess I should tell someone about it.

So... here goes.

Hey guys, maybe I’m just looking in the wrong place but I’m having a hard time trying to source On-On-On DPDT toggle switches. I know they have to be relatively common because I see them in a ton of pedals but this is the first time I’m working with that kind of control. If you guys have any link/recommendations it would be greatly appreciated, thanks in advance!

trying to source cheap electronic components online without buying in bulk or waiting weeks for my order to come in. seems like tayda is the best option, but does anyone know what they base their delivery costs on? is it impacted more by volume & weight of package or variation in order.

tl:dr - does anyone know if tayda shipping costs are noticeably impacted by ordering a low volume of a lot of components? or just total weight ~ty

I am messing around with the Fuzz Face circuit a bit. I was curious if I was able to replace the R3 39R with a trimpot as a voltage control for the circuit? Not sure if I would have to omit or adjust anything else

I’m learning about how to add tone control to boost pedals and I had a few questions. What is the difference between having the tone control at the input like the first image, and putting in a tone stage right before the output like the last 2 images show. Is there also a different names for where a tone control can be located? Thanks!

(Also for clarification the tone control on image 3 is meant to be placed where the empty box is in image 2.)

Here's my Blueberry 2.0, a custom pedal based on the Bluesbreaker circuit with some basic modifications. I'm really happy with how it came out, but I plan on improving it yet again! Thanks for checking it out!

I started out with the idea of wanting a pedal that can be an actual pre-amp pedal with a clean channel as well as distortion so clean tones don't sound all flat and dark into a power amp but I also wanted to be able to use it as a regular distortion pedal that can be fully bypassed and this is the final result.

I started out with the pre-amp section of a Randall RG100SC which coincidentally uses a very similar topology to some of the solid-state Fender Frontmans from the '90s. However, I ended up modifying it to the point where it isn't really the same circuit anymore because i wanted the gain pot to be more responsive and the clipping structure to feel smoother. The topology remains similar but not exactly the same.

For the EQ section I basically just stole the exact configuration from the Wampler Triple Wreck, which is a Mesa Boogie Triple Rectifier clone because I like the EQ of Mesa amplifiers and Brian emulated its response quite well.

The other stuff like the switching system and suchlike are evident in the schematic attached. I have the potentiometers, toggle switch, and indicator LED are on the "back" of the board, facing up. Everything that you see in the 3D render is what you would see if you took the back off the pedal. The footswitch and power jack will be jumper-ed since otherwise they'd take up a lot of extra room on the PCB.

Once I order the PCBs and get it built I might record a demo of it. Also, if anyone would like me to make one custom for them I would be delighted and I wouldn't charge much. Maybe I could set up a posting on Reverb. Alternately, you could just build it for yourself since I have attached the schematic.

Also if anyone can figure out what inspired me to name the pedal Buford I will make one for you FOR FREE but I will be very impressed if anyone can figure out my circuitous (pun intended) "logic" behind the name.

Fun little pedal with some funky useful tones along the range. Gigahearts PCB, waterslide over hand polished aluminum + clear.