A few noobie questions about general stompbox building

[deadlyshart]

Hi guys, I had a few really basic questions I've run into during my last few projects, I was wondering if someone could help me out with--

1) Is there any real difference in sound quality between mylar and disc capacitors? I ask because in Craig Anderton's Electronic Projects for Musicians, this one parts list says "mylar preferred, disc acceptable."

2) They make this distinction between line level and low level... would line level basically be after it's already been amplified? So, if I just planned on doing guitar -> pedal -> amp, I would want a low level pedal?

3) It seems like the same 3 or 4 op amps are used in all these pedals I see: 4558, LM358, TL072, and maybe a couple more I'm forgetting about. How does someone choose these? What are the main differences? When can I safely replace one with the other?

edit, another:

4) So usually I'm using a metal chassis, which is ground. The input, output, and power jacks all have an outer part that connects to the chassis, so can I assume that they're all connected to ground, or should I also connect them to the ground of the breadboard? For example, could I connect the ground and V+ of my power jack to the board, but then only connect the signal pins (and not the ground pins) of the input and output jacks, because I can assume theirs grounds are connected to the circuit through the chassis?

Damn, I'm sure I had other questions... anyway, any help would be much appreciated. I'm trying to learn and understand this stuff. Thanks!

[PRR]

True disk caps may be going out of style. They used to be cheap, but cheaper caps have come onto the market. These are all "ceramic". Low-value (<1000pFd) ceramics use a glass-like dielectric which is essentially perfect. Higher values use a "salted ceramic" which varies a lot with voltage and temperature. You would "never" use a hi-value ceramic in a fine hi-fi amp, the distortion might be measurable. I'm not sure they are always "bad" for guitar effects.

Mylar is never wrong for audio.

Hi-fi (and some g-amp) geeks will argue about the virtues of the many Mylar-like plastic films. They may have a point, or they may be fooling themselves. IAC the objective differences are surely small.

Most op-amps are designed to replace other op-amps and will work 98% the same. The killer difference in some circuits is that some designs drive inputs or outputs all the way to the negative rail, and most chips won't come closer than a volt. This is rare in the audio path but trem LFO and other control paths may be critical. Another noteworthy part is LM308, which is exceptionally slow by opamp standards, thus favored for a certain distorter (but other amps can be filtered to throw less high-freq hash).

"Line Level" comes from another world. In telephones you have a weak microphone. This must be amplified to "telephone line level" so it won't be corrupted as much by external electric crap. Line level is also a good point to do volume and tone adjustments, or mixing. To get to a speaker you need a power amp which raises line level to speaker level. You generally do not want to manipulate speaker-level signals, you paid too much for those Watts.

Recording systems and studios use similar levels and terminology. (For some decades, most music crossed the USA on radio network rented telephone lines.)

Hi-Fi has a notion of "line level" with similar voltage and much less current, because "lines" are 3 to 10 feet not 5-50 Miles so easier to drive.

Guitar is its own world. Guitar can be as weak as a strong microphone, or as strong voltage (not current) as a low line level. I'd be wary of stuff described as "line level", it may be aimed at studio or hi-fi work and need adapting for guitar-cord work.

[GibsonGM]

4) good observations, man.  Your pots, jacks etc. are OFTEN connected to ground.....probably MOST often.  At times, only ONE of them is, to make a really nice 'star ground' point...this may make the circuit quieter in some instances, if done correctly.      For stomps, I connect BOTH jacks to ground.   If one jack comes loose and it is the only gnd point for the enclosure, you get BAD NOISE BRRRRRRRRR.     

In theory, if the ring is connected to gnd for any particular jack, yes you can only connect the tip (signal) wire.   You've been warned, tho 
You can always use your DMM (digital multi-meter) continuity test function to be SURE the item is grounded..that's what it's for.  Don't "assume"   

> the 'line level' or 'low level' stuff will come later.  Don't worry about it now.  Use common sense....you won't feed a 60V signal from a tube preamp right into your amp's input, LOL.   And if you try to plug headphones into your stomp box, 99.99% of the time you won't hear anything, and it won't hurt anything.  Identifying this stuff will come in time, and you'll evaluate things like that as a matter of course, automatically.

These things are made for guitar use, so we're pretty much ok, and it will typically tell you if there is some odd thing about a circuit you need to know...

[amptramp]

This page will give you an idea about high-value ceramic caps:

http://diyaudioprojects.com/mirror/members.aol.com/sbench102/caps.html

As you can see, the effect is worse at low voltages.  High-value ceramic caps tend to be piezoelectric so voltage fed in partly goes out and partly goes into bending the plate.  The output is more distorted with low voltages across the capacitor than large voltages where the plate is bent but there is very little variation with small voltage variations.  This shows up as distortion.

[LightSoundGeometry]

4) good observations, man.  Your pots, jacks etc. are OFTEN connected to ground.....probably MOST often.  At times, only ONE of them is, to make a really nice 'star ground' point...this may make the circuit quieter in some instances, if done correctly.      For stomps, I connect BOTH jacks to ground.   If one jack comes loose and it is the only gnd point for the enclosure, you get BAD NOISE BRRRRRRRRR.     

In theory, if the ring is connected to gnd for any particular jack, yes you can only connect the tip (signal) wire.   You've been warned, tho 
You can always use your DMM (digital multi-meter) continuity test function to be SURE the item is grounded..that's what it's for.  Don't "assume"   

> the 'line level' or 'low level' stuff will come later.  Don't worry about it now.  Use common sense....you won't feed a 60V signal from a tube preamp right into your amp's input, LOL.   And if you try to plug headphones into your stomp box, 99.99% of the time you won't hear anything, and it won't hurt anything.  Identifying this stuff will come in time, and you'll evaluate things like that as a matter of course, automatically.

These things are made for guitar use, so we're pretty much ok, and it will typically tell you if there is some odd thing about a circuit you need to know...

recently I have taken apart some well known, super expensive, "boutique" style pedals and noticed a lot of them do not have the output jack grounded for whatever reason. A lot of them filled with tayda parts lol.  I experimented and found no issues, so far lol. 

[deadlyshart]

4) good observations, man.  Your pots, jacks etc. are OFTEN connected to ground.....probably MOST often.  At times, only ONE of them is, to make a really nice 'star ground' point...this may make the circuit quieter in some instances, if done correctly.      For stomps, I connect BOTH jacks to ground.   If one jack comes loose and it is the only gnd point for the enclosure, you get BAD NOISE BRRRRRRRRR.     

In theory, if the ring is connected to gnd for any particular jack, yes you can only connect the tip (signal) wire.   You've been warned, tho 
You can always use your DMM (digital multi-meter) continuity test function to be SURE the item is grounded..that's what it's for.  Don't "assume"   

> the 'line level' or 'low level' stuff will come later.  Don't worry about it now.  Use common sense....you won't feed a 60V signal from a tube preamp right into your amp's input, LOL.   And if you try to plug headphones into your stomp box, 99.99% of the time you won't hear anything, and it won't hurt anything.  Identifying this stuff will come in time, and you'll evaluate things like that as a matter of course, automatically.

These things are made for guitar use, so we're pretty much ok, and it will typically tell you if there is some odd thing about a circuit you need to know...

recently I have taken apart some well known, super expensive, "boutique" style pedals and noticed a lot of them do not have the output jack grounded for whatever reason. A lot of them filled with tayda parts lol.  I experimented and found no issues, so far lol.

Hmm, so just to be clear, when you say "do not have the output jack grounded", do you just mean they're not "explicitly grounded" (i.e., it's still grounded through just being connected to the chassis through a metal-metal mechanical connection, but it's not connected "explicitly" with a wire), or the jacket is literally not grounded at all?

[vigilante397]

Hmm, so just to be clear, when you say "do not have the output jack grounded", do you just mean they're not "explicitly grounded" (i.e., it's still grounded through just being connected to the chassis through a metal-metal mechanical connection, but it's not connected "explicitly" with a wire), or the jacket is literally not grounded at all?

Exactly that, yes.

[deadlyshart]

True disk caps may be going out of style. They used to be cheap, but cheaper caps have come onto the market. These are all "ceramic". Low-value (<1000pFd) ceramics use a glass-like dielectric which is essentially perfect. Higher values use a "salted ceramic" which varies a lot with voltage and temperature. You would "never" use a hi-value ceramic in a fine hi-fi amp, the distortion might be measurable. I'm not sure they are always "bad" for guitar effects.

Mylar is never wrong for audio.

Hi-fi (and some g-amp) geeks will argue about the virtues of the many Mylar-like plastic films. They may have a point, or they may be fooling themselves. IAC the objective differences are surely small.

Most op-amps are designed to replace other op-amps and will work 98% the same. The killer difference in some circuits is that some designs drive inputs or outputs all the way to the negative rail, and most chips won't come closer than a volt. This is rare in the audio path but trem LFO and other control paths may be critical. Another noteworthy part is LM308, which is exceptionally slow by opamp standards, thus favored for a certain distorter (but other amps can be filtered to throw less high-freq hash).

"Line Level" comes from another world. In telephones you have a weak microphone. This must be amplified to "telephone line level" so it won't be corrupted as much by external electric crap. Line level is also a good point to do volume and tone adjustments, or mixing. To get to a speaker you need a power amp which raises line level to speaker level. You generally do not want to manipulate speaker-level signals, you paid too much for those Watts.

Recording systems and studios use similar levels and terminology. (For some decades, most music crossed the USA on radio network rented telephone lines.)

Hi-Fi has a notion of "line level" with similar voltage and much less current, because "lines" are 3 to 10 feet not 5-50 Miles so easier to drive.

Guitar is its own world. Guitar can be as weak as a strong microphone, or as strong voltage (not current) as a low line level. I'd be wary of stuff described as "line level", it may be aimed at studio or hi-fi work and need adapting for guitar-cord work.

Thanks for the advice. So just to be sure I get it, chances are I want to do the "low level" versions of the circuits? For example, in this recent schematic I was making:



if you notice, C1 and R8 have asterisks next to them, because he said that those values are for the "low level" version of the circuit, but if you want to make the "line level" version, replace them with 470pF and 100kOhm, respectively (I think), the idea being that you need less gain because it's already a large signal? I went with the low level version.

[nachus001]

The problem with ceramic capacitors is mostly the dielectric material. It's generally characterized by temperature stability, so you have to read manufacturer datasheet to know capacitance change curves, and by what parameters it varies
The common dietectric types, Y5V C0G X5R, X7R are specified for thermal stability. Y5V will be used for capacitances fron 10n on up to 300uF but with extremely low esr, but with a capacitance  variation v. bias voltage of up to an 80% over the specified cap voltage. C0G instead will withstand higher voltages, will have the best thermal stability, but will allow for capacitances from 1pf  to 4700pf or more, but with bigger packages.

X7R will yield high capacitance values, in order of 10's of uF and more, and will whitstand very high currents with very low esr, but will cost a lot more than Y5V at the same capacitance value

Microphonie is an issue with ceramic caps imho

With mylar and film caps in general this problem is avoided and if the preferred device for audio