Are ceramic disc caps OK to use in this circuit?

[Philtre]

I'm building the Mad Professor Deep Blue Delay clone from this vero layout - http://tagboardeffects.blogspot.co.uk/2012/02/mad-professor-deep-blue-delay.html (the first vero layout there).

There are two 100nF capacitors at the bottom right of the larger IC, that look like they are ceramic types. Ideally I would like to use good quality polyester film capacitors, or NP0/C0G multilayer ceramics. But I can't find any small enough to fit in that tight space. I've been told that using plain ceramic caps is bad for audio.

So, what are my options?

[somnif]

First thing: Part placement on vero layouts will always be awkward/janky looking. You will occasionally just have to throw the parts at the board, button up the case, and pray no one ever looks at it.

Second, yeah ceramics will work fine. At the fidelity we work with, you are unlikely to notice any of the noise commonly associated with ceramics (with a few exceptions). The one thing I'd suggest taking care with is the tolerances on them can be MASSIVE, 20% is not uncommon. So I would strongly recommend testing them with your DMM to find those closest to the value you actually want.

Yeah their capacitance will fluctuate a bit with temperature and use, but again, we're not dealing with super high fidelity studio-board sound levels here. The PT2399 will muck up your tone far more than a X5R cap will. Unless your ears have been replaced with oscilloscopes, you won't be able to tell (again, with a few notable exceptions).

So, take your choice. Bend the leads of a couple film caps and crowbar them in, or use a couple wee tiny orange drip ceramics. The circuit will function the same. Tolerances will wobble a bit, but not really in any way a human ear will notice.

[bsoncini]

They might cause a little bit more noise.

But look in the schematic.  They might be for power supply filtering which they are perfectly fine for.

[Philtre]

Thanks for the info, guys. Much appreciated. 

The schematic is this one - http://the7line.clan.su/_pu/0/92883033.gif

The two 100nF caps are strapped across pins 9/10 (OP1-OUT and OP1-IN) and 11/12 (OP2-IN and OP2-OUT) of the PT2399. So I'm guessing they're quite important?

[somnif]

The two 100nF caps are strapped across pins 9/10 (OP1-OUT and OP1-IN) and 11/12 (OP2-IN and OP2-OUT) of the PT2399. So I'm guessing they're quite important?

Eh, they're nothing spectacularly important. They're coupling the output and input of two internal op-amps. Its just filtering. 100nf means it won't really cut any frequencies in the audio range we care about, that's about all the value really matters for. (For comparison the original Princeton datasheet specified 82nF for those caps, and some people noted a bit of treble loss. May be apocryphal, but there you go)

[m-Kresol]

if you're feeling posh and have money to give away, there are new film capacitors available from Rubycon. They are SMD, similar to polyester in electric characteristics, but very small sized in comparison due to a multilayer structure.

Since it is not a piezoceramic like most MLCC (X7R...), they don't have the buzz in the audible frequency range at high voltages. Nothing that usually concerns us, but Rubycon claims they are especially suited for audio applications:

https://www.digikey.com/product-detail/en/rubycon/50ST104MA13216/1189-1826-1-ND/3719964

[Philtre]

I guess my question, now, is, is it OK to use general purpose 100nF multilayer ceramic caps in those two positions?

Specifically, these - https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_75_70&products_id=219

[drog_trog]

i rarely use the old skool orange ceramics but when it comes to choosing caps i always go by this: in modulation effects multilayered ceramics are fine all round even up to 1uf. in overdrives and more so distortions I tend to use the MLCC upto about 820nf, the 1uf's then i like to use box film caps. Does all depend where in the circuit certain caps are and whay they're doing but as a general rule I go by what I said.

[somnif]

I guess my question, now, is, is it OK to use general purpose 100nF multilayer ceramic caps in those two positions?

Specifically, these - https://www.bitsbox.co.uk/index.php?main_page=product_info&cPath=65_75_70&products_id=219

Sure, they'll work just fine. Any 100nF cap would work.

Just be aware that you need to be careful bending the leads on multi-layer ceramic caps, as you can crack the ceramic if you put too much torque on the body itself. Use a pair of pliers to hold the lead and bend under them, or something similar, just to avoid the stress.

Or just be careful and bend them gently one at a time. Really its unlikely you'll hurt them.

(In reality this really is a slim risk at best, and in most cases not an issue at all, but I did it once in my early days and have been paranoid about it ever since)

[Philtre]

Thank-you all for the advice. :-)

As a relative newbie to pedal building, I'm trying to use components that won't degrade the audio signal or be microphonic. I've already de-soldered and removed some cheap ceramic discs and electrolytics that I got off eBay and replaced them with decent NP0/C0G multilayers and Panasonic electrolytics. It's been a challenge finding the right quality caps and small form factor!

[Willybomb]

I've become a massive fan of the blue monolithic capacitors. Small form factor, non polarised, and at higher values fit far better into cramped vero builds.

As a general rule, I use them for 100nf, and 1uf (simply because I picked up a 100 pack of each!), but the 1uf are a great size.

[Philtre]

I've become a massive fan of the blue monolithic capacitors. Small form factor, non polarised, and at higher values fit far better into cramped vero builds.

As a general rule, I use them for 100nf, and 1uf (simply because I picked up a 100 pack of each!), but the 1uf are a great size.

"blue monolithic capacitors" - Is that a brand type?

[somnif]

"blue monolithic capacitors" - Is that a brand type?

Nah there are a few brands that use a blue dip on them. Murata is pretty decent, TDK too. But don't go overboard and buy super high end components for a pt2399 delay. The chip itself is 90% of the tone in that circuit, and its a VERY basic design. Any cap will work in it. From little orange disks to high end C0G's, same difference.

Thats part of what is great about them. You get designs like the Rebote or Deep Blue, which are damn near the datasheet circuit diagram on a pcb, a handful of cheap components and instant echo-box. 9v in, repeats out. 

As a relative newbie to pedal building, I'm trying to use components that won't degrade the audio signal or be microphonic.

Very little risk of either of those in most cases. Only circuits that go microphonic regularly are super simple fuzz designs (fuzz face, tone bender, etc) that just love AM radio. In terms of audio degradation you have more to worry about from long cables than most components in the circuit itself. As long as you use the right voltage rating on the caps and are careful about polarity of things you will Always* be fine.

The one MAJOR exception to this rule: Don't buy ICs on ebay. You aren't saving money, you're usually buying crap. There are a few real humans on the site, and you might rarely get lucky with the chinese scrappers, but seriously, spend the extra couple bucks and get them from reputable suppliers.

Honestly, I have built plenty of circuits with 100% Tayda sourced parts and they're fine, sonically speaking. Pots might be a bit stiff and the plastic hardware a little flimsy, but the circuits themselves work as intended. I wouldn't sell them commercially, and their lifetime is probably a little shorter than one with "pro" parts, but for the way I use them, I don't care. Hell, if a cap dries out I'll just replace it