Part Sub and Photocoupler Question

[hagcel]

Hi,

Can I sub a 3300pf 50v ceramic Cap in place of a 3n3 film cap for C3 or C9 in Collosallis? When I placed my order I only ordered 1 3n3 cap 

Related question: Why is a 3300pf Ceramic Cap smaller than say a 680 pf 50v Ceramic cap?

How do I install photocouplers? I have never used them before. This is for a nautilus build. I ordered from small bear. I assume the dot lead goes in the square hole?

Thanks!!

[jkokura]

1. 3300pF = 3n3. No sub, that's the proper value.
2. I don't know why the size difference. Often size is related to a combination of value and voltage rating. It's possible the 680pF is rated higher, but there are so many variances between maufacturers...
3. The Vactrol is essentially two parts - LED and LDR. The LED side is the dot side. The long leg needs to go into the + side of the LED part of the photocoupler. That's likely the Dot side and the square pad. The other side, the LDR, is non-specific, so you don't need to worry about that side at all. As long as the LED is oriented correctly, you're good to go.

Jacob

[hagcel]

Thanks,

Yeah I guess I just wasn't sure if ceramic can sub for film in all occasions. I take it that it can?

I guess I've never seen it written anywhere that this should be true but I think of pf as ceramic caps and nf as film caps

Thanks Jacob!

[RobA]

As far as working as a capacitor goes, then they are interchangeable. But, they do sound different from each other. In general, film caps have better audio characteristics than ceramic. But, this isn't always true and depends on the model of each cap. If you have good C0G ceramic caps, the results will be good. If they are cheap ceramic disk caps, you may not like what they do.

[hagcel]

Thanks. Excellent info! Yeah they are just cheap ceramic caps from mammoth. I'll just use it for now to check out the circuit and i'll replace it next time I order from small bear.

C9 is connected to ground from pin 5 of the JRC4558 so I'm guessing that wouldn't be in the audio path and I may be fine with a Ceramic.

As long as we are on the subject: what are the audio characteristics of a typically grey film box cap vs the brown poly film caps?

[jkokura]

Without knowing the specific caps you mean, there's no way to tell. That's like asking whether guitar A sounds different than B, we'd need to know what guitar A is and what guitar B is.

Generally, what Rob posted is correct. However, to be more specific, Ceramic caps are generally noisier, not better or worse sounding. They sound different, and some of their characteristics may have drawbacks when using them in guitar pedals.

Film caps, be they box or chicklet, whether they're mylar or some other sort of poly, are film caps. There are some that are noisier, and some that have better characteristics than others. I cannot scientifically guarantee this, but I would (figuratively) bet a house that %99 of the time the type of Film cap you use doesn't matter and you couldn't hear the difference if you tried.

Ceramic caps have been used in hundreds of thousands of amps and pedals, if not millions, for decades. They're featured on countless hit records, are used in countless touring rigs, and they're inside the devices we use to listen to the music produced using them. Not to mention the mics, the consoles, and all the other electronic devices used for producing music.

Film caps are used in all these devices too. Sometimes it's better to choose film instead of ceramic. But rarely does it negatively affect the quality of music made with the devices.

I'll go out on a limb here and state that the only reason we use Film caps in pedal building is a combination of marketing and form factor. I say form factor because I like using Film caps better than ceramic, especially with box caps because they tend to have uniform size and shape. Chicklets are fine this way too. I say marketing because we've been 'sold' to believe they're better in every way compared to Ceramic. While somewhat true, this isn't the whole truth. Film caps are more expensive, and in some cases they are much, much, much more expensive.

We have the 'luxury' of being able to use these devices because we can, but don't let anyone out there fool you into believing something is 'inherently and always better' just to sell you something more expensive.

/rant. Sorry this got away from me a bit. I'm not trying to tell you or Rob you're wrong, just share a little bit of what I've learned.

Jacob

[RobA]

Looking at the schematic, I'm not sure which is better. The problems with ceramic caps will still happen with paths to ground, especially when they are being used to set a filter frequency. One of the main issues with ceramic caps is that their capacitance actually changes with varying voltage (as is the case with an applied audio signal). So, this causes the filter cutoff frequency to wobble and that causes the circuit to be non-linear and introduces distortion. C9 is in the regen/feedback loop right? But, it may not bother you at all. My old classic MXR pedals are filled with really crappy ceramic caps.

It depends on the make/model of the film caps. I tend to use either Wima or the Epcos box caps. I do have some of the grey box caps from Smallbear and they seem fine too and the Panasonic brown dudes are also fine in my experience. If you want to get really picky for filtering caps, then the Wima FKP (Polypropylene) caps are actually better. Basically with film caps it's the material that makes the difference (from good to best): Metallized Polyester, Polypropylene, and Polystyrene. Although, I honestly can't hear any qualitative difference between polypropylene and polystyrene.

Pretty much, all the film caps are OK. The only weird thing I've ever seen with them is that in some blind listening tests I did, the famous Orange Drop film caps came out dead last.

[wgc]

Sorry wrong thread!

[jkokura]

Pretty much, all the film caps are OK. The only weird thing I've ever seen with them is that in some blind listening tests I did, the famous Orange Drop film caps came out dead last.

That's really cool to hear. I've never done true blind tests with caps, I've only heard/read results of them, and the results vary so much it's like trying to decide which is my favourite shampoo. The semi-blind tests I've done myself are generally unscientific, and generally inconclusive.

Jacob

[RobA]

I've got to note that these were blind tests, not double blind. I did two types of tests. In one, I'd play and change the caps and have others listen and judge. This has obvious limitations and bias. In others, I'd play and listen, but have someone else do the changing of the caps where I couldn't see. This is a bit better but still not rigorous. Someday, I need to get really organized and set up some true double blind tests. But, it's been 8 years or so since I did the other tests, so it's not likely to happen any time soon. Also, cheap film caps are, em cheap, so I'm pretty happy with them.

I've been able to do real double blind listening/playing tests with op-amps. The trouble there is that the results change with every circuit.  I'm sure that this might happen with double blind cap tests as well. If you could put in the effort to test a bunch of caps in a bunch of (musical) circuits, the results would likely be varied. The only thing I put any real consideration into is when there are demonstrable physical effects that can have negative impacts on the sound. I think the best place to get relatively unbiased info is the application notes and spec sheets from the manufacturers of the parts that you aren't trying to compare. For example, lots of app notes for op-amps and CODECs give decent advice about what types of caps to use in different circuits.

[hagcel]

Great posts guys. Thanks a lot!

Sounds to me like you could spend a small fortune on caps or a few dollars and the difference may be fairly subtle in studio and unnoticeable live. I'd guess OpAmps are most important for sound fidelity?

I've come to the understanding that the TL072 is far superior to the JRC4558 but I see the JRC4558 used in a lot of projects here. I'm guessing it's more complicated that just one chip is better than the other, how it's used, filtered. etc.

In my own experience I've found that replacing the JRC4558 with TL072 in vintage EH boxes can make a great improvement. I decided to try it after I saw that Analogman was surprised at how much of a difference they make.

BUT perhaps this is just because of the circuit and low input impedance present in vintage EH designs?

[jkokura]

An equally complicate subject, and I'm not the scientist to truly answer what's going on (Perhaps Rob, or Paul, or Scruff, or any number of guys here could answer better but...)

Yes. Sometimes a lower fidelity op-amp is better. The LM741 is still used in Dist+ or 250 builds, but it's a pretty crappy Op-Amp. As is the LM308 for rats really. But some of the charm is found in these poor quality devices. A TS9 or TS808 isn't quite the same without a 4558 in it.

Jacob

[RobA]

Yeah, it's is really more complicated than just the 4558 is crap and the TL072 is better. Really, they are both crap but do better jobs in different situations. The thing to remember about op-amps is that they are just a collection of transistors. The characteristics that influence which transistor you might choose in a given situation will also influence which op-amp you might select.

For example, I did a build of the Tremulus Lune last week and thought it would be a good idea to put an OPA2134 in as the audio op-amp. The noise was horrible -- click, pop, whack, whack. I put a JRC4558D in it and it sounded great. So, I went through various op-amps and discovered that every FET input op-amp had horrible noise and every BJT input op-amp worked. In the end, the LM833N sounded pretty good but the OPA2227 sounded great. The LM833N is pretty much junk and the OPA2227 is relatively expensive ($0.15 to $2.50 or so). The LM833N would actually be fine in the pedal. Some people would probably prefer the JRC4558D because it's a bit darker sounding and more mellow.

With op-amps my rule is socket it and change them around until I find what I like.