Choosing components?

dethronedemperor

New member
Hi all! So, I've built a few DIY effects pedals at this point prior to picking up a few PedalPCB boards to start some new projects and most of those previous kits were already put together as a bundle rather than having to choose my own components. So, looking at the build docs for the boards I grabbed there is a parts list but looking them up on Tayda there are obviously a lot of different choices sometimes per value.

So, yeah, extreme n00b question...

Any recommendations on a guide or where to go for gaining some basic knowledge of electronic components that will help me make educated choices on some of these parts? I know enough to make sure to chose the correct voltage so I don't blow up the circuit, but as an example on the Hyped Fuzz circuit it calls for 47n capacitors. Searching on Tayda there are quite a few options that come up.

Let the hazing begin, haha...
 

PedalPCB

Administrator
Staff member
Generally I use:
Ceramic disc capacitors for anything in the pF range
Box film caps for 1nF - 1uF non-polarized
Occasionally MLCC for 330nF - 1uF non-polarized (when physical space won't allow for a box film type)
Electrolytic for uF range

There are always exceptions. Some folks like to use MLCC for all pF capacitors. Some folks avoid MLCC altogether.

As for electrolytics, make sure the working voltage is suitable, but don't go too crazy or they won't fit the space on the board.
 

dethronedemperor

New member
Generally I use:
Ceramic disc capacitors for anything in the pF range
Box film caps for 1nF - 1uF non-polarized
Occasionally MLCC for 330nF - 1uF non-polarized (when physical space won't allow for a box film type)
Electrolytic for uF range

There are always exceptions. Some folks like to use MLCC for all pF capacitors. Some folks avoid MLCC altogether.

As for electrolytics, make sure the working voltage is suitable, but don't go too crazy or they won't fit the space on the board.
Awesome, greatly appreciate this! Thank you!
 

Paradox916

Well-known member
Generally I use:
Ceramic disc capacitors for anything in the pF range
Box film caps for 1nF - 1uF non-polarized
Occasionally MLCC for 330nF - 1uF non-polarized (when physical space won't allow for a box film type)
Electrolytic for uF range

There are always exceptions. Some folks like to use MLCC for all pF capacitors. Some folks avoid MLCC altogether.

As for electrolytics, make sure the working voltage is suitable, but don't go too crazy or they won't fit the space on the board.
So let me ask you this. I ran across a few articles saying ( at least to my limited understanding)using MLCCs are beneficial for reducing distortion. So reguarldles of a physical space issue, could using say a 1uf MLCC instead of a box film in say a circuit like a delay, reverb or gate result in a “cleaner” sounding signal? Or am I interpreting what I am reading completely wrong.
 

peccary

Well-known member
So let me ask you this. I ran across a few articles saying ( at least to my limited understanding)using MLCCs are beneficial for reducing distortion. So reguarldles of a physical space issue, could using say a 1uf MLCC instead of a box film in say a circuit like a delay, reverb or gate result in a “cleaner” sounding signal? Or am I interpreting what I am reading completely wrong.

I believe that ceramic/MLCC's actually create more distortion for the little I've read. I think that using them here and there in effects pedals isn't an issue, but it may cause issues for hi-fi, audiophile grade stereo equipment. You wouldn't want to use them as a replacement for your poly caps, though.

Here's a long, boring academic article I read a while back and that I think I've seen posted here a time or two. Keep in mind that in reality I have zero electronics experience other than my Google degree: https://www.ti.com/lit/an/slyt796/slyt796.pdf?ts=1615217126361
 

Chuck D. Bones

Well-known member
Any recommendations on a guide or where to go for gaining some basic knowledge of electronic components that will help me make educated choices on some of these parts? I know enough to make sure to chose the correct voltage so I don't blow up the circuit, but as an example on the Hyped Fuzz circuit it calls for 47n capacitors. Searching on Tayda there are quite a few options that come up.
Believe it or not, this question has been asked and answered more than once on these forums. To recap, my personal recommendations are:
Capacitors:
Silver Mica for 510pF and below. If you can't get/afford them, use Film or MLCC.
Film from 470pF to 1 or 2uF, as space allows.
Tantalum for 1uF to 33uF.
Aluminum above 33uF.
Not a hard and fast rule, but a good guideline. Measure the pin spacing and part footprint to make sure that what you're buying will actually fit on the board.
Tayda & Mouser are my preferred capacitor suppliers.

Resistors:
1/8W 1% metal film. You can get them for a penny apiece in quantity from Tayda or Mouser. Might as well buy a bunch, this pedal building thing is addictive.

Semiconductors:
Avoid eBay unless you know how to test them and like to gamble. Reliable suppliers are Mouser, DigiKey, Small Bear and sometimes Tayda. There are other suppliers, but I have not used them so cannot recommend them.

Pots:
Tayda & Small Bear.
 

giovanni

Well-known member
Here's a long, boring academic article I read a while back and that I think I've seen posted here a time or two. Keep in mind that in reality I have zero electronics experience other than my Google degree: https://www.ti.com/lit/an/slyt796/slyt796.pdf?ts=1615217126361
That’s a very interesting article! Thanks for sharing. A few takeaways, iirc:

(1) for coupling caps (which is the focus of the article) it’s very important what the input impedance of the following stage is. The article measures up to 20kohm, which is actually not the highest you can find. Many circuits have input impedance in the Megaohm range (I believe that’s true for most transistor stages and most op amps with negative feedback, but don’t take my word for it!), which would probably make the noise almost negligible.

(2) the noise is higher for higher input levels. From the chart, it looks like anything below 70mV has more or less the same amount of noise and it goes a bit up from there, but even at 200mV (really the highest input guitar signal I would expect) the noise is small. It’s a different story once you have preamplified the guitar and the voltages get higher, eg, hard clipping distortions typically go up to 700mV, where the noise is like 25dB higher (still pretty small in absolute numbers, but relatively higher), but at that point there is already so much distortion that the cap probably won’t make much of an audible difference.

(3) higher MLCC values give you lower distortion because of... physics. That’s good to know but given takeaways (1) and (2) I suspect you wouldn’t notice the difference anyway because of the nature of guitar signal chains.

(4) film, tantalum and electrolytic capacitors have a bit lower distortion than the corresponding MLCC, by about 20dB (although the article doesn’t actually directly compare them with a MLCC of the same exact value so I’m extrapolating here).

TLDR, I would say in high gain but very clean circuits (!) you should prefer film over MLCC? I think the article’s main focus is low distortion hifi preamps, so I would take it with a big pinch of salt for guitar applications.

I hope my interpretation is helpful (and correct!)!
 

fig

Well-known member
Chuck,

Any source you can share for silver mica with build-size lead spacing?
 

Chuck D. Bones

Well-known member
Good article, when taken in context. The context for this article is precision analog signal processing at audio frequencies and the use of very small, high-capacitance capacitors. Some of this is relevant to guitar pedals, most of it is not. If you're designing a smart phone or sound card, then this article is very relevant.

Here's what TI doesn't say:
1) High-permittivity dielectrics like X5R are best used in switching power supplies and as power supply bypass capacitors. They were never intended for precision signal processing.
2) There are many considerations when choosing a coupling capacitor. Voltage coefficient is only one of them.
3) The -103dB noise floor in the graphs corresponds to a 17-bit A/D converter. It's the noise floor of the TLV320ADC5140 evaluation module.

The graphs all plot THD (total harmonic distortion) + N (noise) vs. frequency. The noise part of the signal is around -103dB w.r.t. a 1Vrms signal. 1Vrms = 2.83Vp-p for a sinewave. Db is a logarithmic scale. For voltage or current, every 20dB corresponds to a 10X change in amplitude. -103dB w.r.t. 1Vrms is 7uVrms or 20uVp-p. Changing the signal level has no effect on the noise, it only affects the distortion. THD = -60dB is equivalent to 0.1% THD. This is lower than any guitar amp or speaker cabinet at gig volumes.

Peccary is on the right track, but let me clarify a few things.
1) Total series impedance matters, not just the input impedance of the next stage. Some of the time, but not always, the input impedance of the next stage is the dominant factor.

2) Noise does not change with signal level. Signal levels inside a pedal can run as high as the power supply rails. For example, the maximum signal that comes out of an MXR Distortion+ might be around 400mVp-p, but the opamp inside is saturating and the signal level there is over 7Vp-p.

3) The higher MLCC values can have lower distortion for the same dielectric material. Still does not make them a good choice. Good luck finding a 47uF thru-hole MLCC that will fit on a pedal circuit board.

4) Film and tantalum are better for audio signal processing based on all of the factors. For us, the primary factors are size, leakage, noise, reliability and microphonics.

Parting shots:
Worrying about <1% distortion in a coupling capacitor when you're building a guitar pedal makes no sense to me. We deliberately make distortion in a dirt pedal. The noise and distortion of a PT2399 is off the scale on these graphs. The 1uF MLCCs that I bought from DigiKey to use in my Arachnid are X7S dielectric. According AVX: "X7S dielectric chip usage covers the broad spectrum of industrial applications where known changes in capacitance due to applied voltages are acceptable." A pretty poor choice if you're looking to squeeze the last drop of clarity from a high-end audio amplifier, but they sound just fine in the Arachnid. I used them them because that's what fit.
 

Chuck D. Bones

Well-known member
Chuck,

Any source you can share for silver mica with build-size lead spacing?
They're not easy to find anymore. Try looking for parts dealers that cater to the Ham Radio crowd. Electronic Goldmine has some values for a good price. Get on their mailing list and wait for stuff to go on sale. An electronics store near my house has some, but their stock is rapidly depleting. Most of the boards of mine you see in the Build Reports or Chucks Boneyard will have one or two SM caps. Some are a bit chubby, but usually fit. Here's a Covert with four SM caps.

Catalinbread DLS Mk III [Covert Overdrive] innards 01a.jpg
 

peccary

Well-known member
Good article, when taken in context. The context for this article is precision analog signal processing at audio frequencies and the use of very small, high-capacitance capacitors. Some of this is relevant to guitar pedals, most of it is not. If you're designing a smart phone or sound card, then this article is very relevant.

Here's what TI doesn't say:
1) High-permittivity dielectrics like X5R are best used in switching power supplies and as power supply bypass capacitors. They were never intended for precision signal processing.
2) There are many considerations when choosing a coupling capacitor. Voltage coefficient is only one of them.
3) The -103dB noise floor in the graphs corresponds to a 17-bit A/D converter. It's the noise floor of the TLV320ADC5140 evaluation module.

The graphs all plot THD (total harmonic distortion) + N (noise) vs. frequency. The noise part of the signal is around -103dB w.r.t. a 1Vrms signal. 1Vrms = 2.83Vp-p for a sinewave. Db is a logarithmic scale. For voltage or current, every 20dB corresponds to a 10X change in amplitude. -103dB w.r.t. 1Vrms is 7uVrms or 20uVp-p. Changing the signal level has no effect on the noise, it only affects the distortion. THD = -60dB is equivalent to 0.1% THD. This is lower than any guitar amp or speaker cabinet at gig volumes.

Peccary is on the right track, but let me clarify a few things.
1) Total series impedance matters, not just the input impedance of the next stage. Some of the time, but not always, the input impedance of the next stage is the dominant factor.

2) Noise does not change with signal level. Signal levels inside a pedal can run as high as the power supply rails. For example, the maximum signal that comes out of an MXR Distortion+ might be around 400mVp-p, but the opamp inside is saturating and the signal level there is over 7Vp-p.

3) The higher MLCC values can have lower distortion for the same dielectric material. Still does not make them a good choice. Good luck finding a 47uF thru-hole MLCC that will fit on a pedal circuit board.

4) Film and tantalum are better for audio signal processing based on all of the factors. For us, the primary factors are size, leakage, noise, reliability and microphonics.

Parting shots:
Worrying about <1% distortion in a coupling capacitor when you're building a guitar pedal makes no sense to me. We deliberately make distortion in a dirt pedal. The noise and distortion of a PT2399 is off the scale on these graphs. The 1uF MLCCs that I bought from DigiKey to use in my Arachnid are X7S dielectric. According AVX: "X7S dielectric chip usage covers the broad spectrum of industrial applications where known changes in capacitance due to applied voltages are acceptable." A pretty poor choice if you're looking to squeeze the last drop of clarity from a high-end audio amplifier, but they sound just fine in the Arachnid. I used them them because that's what fit.
Thanks for the translation, Chuck. I appreciate the time you take to explain things like this. There is so much voodoo that goes in to describing what various components do or don't do that it's nice to have the voice of reason come in to help make sense of things.
 

fig

Well-known member
Yes sir. I am grateful for the exposure to such a vast and reliable source of knowledge. As rare as silver mica capacitors on the internet.
 

fig

Well-known member
resistor sample books seem to work well for piece-building. I spot check them but never found a gremlin though I did once own an AMC Gremlin...groovy ride
 
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