Capacitors ... resistors too I guess: How close is close enough?

[brucer]

Hi All.

A newbie question for you.  I'm starting to collect parts for an Aion Refractor (Klone) build.  The BOM calls for 27nF and 390 nF box capacitors.  These values aren't stocked at Small Bear.  Would 22nF and 330 nF be close enough to not change the character of the pedal or should I always match values?

Similarly, for resistors, is it close enough to choose resistor values within the +/-% tolerance range of the one called for in a BOM or should you always match to maintain the target tone?

I'd appreciate some of your wisdom on this.

Thanks!  Bruce.

[Stomptown]

Small Bear does have those values so I would just stick with the actual values rather than approximate them. Here are the links and remember that 27nF = .027mF and 39nf=.039mF

.027mF (27nF):

http://www.smallbearelec.com/servlet/Detail?no=162

.039mF (39nF):

http://www.smallbearelec.com/servlet/Detail?category=Capacitors+-+Low+Voltage+Film%3ATopmay%3ATMC05+Radial&no=890&param_referer=http%3A%2F%2Fwww.smallbearelec.com%2Fservlet%2FCategories%3Fcategory%3DCapacitors%2B-%2BLow%2BVoltage%2BFilm%253ATopmay%253ATMC05%2BRadial&searchpath=555679

[brucer]

Thanks Jon.  Good advice (and better searching).

[Stomptown]

Thanks Jon.  Good advice (and better searching).

No problem! And I personally wouldn't worry too much about measuring resistors.  I have measured resistors in the past when a circuit calls for an odd value that I don't have on hand (e.g. a circuit calls for a 392K and all I have on hand is a bunch of 390Ks), but I wouldn't stress too much about tolerance. I use 5% carbon and 1% metal films and believe that both are fine. Some people may notice a difference, but I don't...

[culturejam]

It depends on the role of the component in the circuit. But in most cases +/- 10% is well within the range that can be subbed without drastic changes to tone. There are a few cases in which part values need to be very close, but mostly this is not the case.

[midwayfair]

If we're talking about stuff in the audio path, you want an idea of what you're going to end up with. Capacitor-resistor networks form filters. You can plug in the values to a frequency calculator and get some numbers:
sim.okawa-denshi.jp/en/CRlowkeisan.htm

Numbers are just numbers, though, and don't really tell you a whole lot. If you really want to get deep into this, one neat way might be to use a digital audio work station and a graphic EQ plugin to play with the cutoff frequency of a representative recorded sample of guitar notes. Set a -3db cutoff point for the "correct" value from the schematic, and then for the value of the substitute you have available. Spoiler alert: Most of the time you probably won't hear a difference. The other way, of course, is to set it up on the breadboard, but obviously you would need both values to make it work, and you'd also have to breadboard the entire circuit. (I don't seriously consider a DAW a substitute for breadboard + real amp, though, when it comes to hands-on experience.)

Things do get a little dicier in the higher registers, where small component value differences can start jumping huge gaps. Also, sometimes frequency cutoffs can be an integral part of the sound, especially in certain modulation effects.

[Willybomb]

I was going to post something similar.  I got my BOMs for a Pork Barrel filled in at the local Jaycar, but they couldn't do the 8n2 caps, and replaced them with 10n. 

How's that going to work out (I doubt it'll do anything much at all)?  Are we looking at fire and brimstone coming down from the skies? Rivers and seas boiling? Forty years of darkness? Earthquakes, volcanoes..The dead rising from the grave? Human sacrifice, dogs and cats living together... mass hysteria!???

[RobA]

I was going to post something similar.  I got my BOMs for a Pork Barrel filled in at the local Jaycar, but they couldn't do the 8n2 caps, and replaced them with 10n. 

How's that going to work out (I doubt it'll do anything much at all)?  Are we looking at fire and brimstone coming down from the skies? Rivers and seas boiling? Forty years of darkness? Earthquakes, volcanoes..The dead rising from the grave? Human sacrifice, dogs and cats living together... mass hysteria!???

Those two caps are in the pre and post filtering networks for the BBD. The filters are low pass filters  set up to match the sample rate of the BBD (pretty much like you would need to do for an AD/DA converter). You got me interested in how the network works, so I put it in Spice and simulated it. The 8.2nF helps to set and sharpen the knee of the filter while maintaining a flat response in the passband of the filter. It's a pretty neat design really with using only a transistor to get it. Moving to a 10n will darken the sound a bit, but it also causes a slight hump in the passband near the cutoff of the filter (makes it into a very slight resonant LP filter.) The whole filter sits in around 5kHz. I would guess that you could hear the difference, especially since the two filters are essentially cascaded together. 

Personally, I'd stick with the 8.2nF in this case. You could always socket them and get the 8.2's at a later time and put them in to see if they make a difference to you.

[alanp]

A newbie question for you.  I'm starting to collect parts for an Aion Refractor (Klone) build.  The BOM calls for 27nF and 390 nF box capacitors.  These values aren't stocked at Small Bear.  Would 22nF and 330 nF be close enough to not change the character of the pedal or should I always match values?

Sorry for the dredge.

I'm building a Chimaira, which is pretty much the same thing, but from Rej

I can only source the 390nF (or 0.39uF) in greenie cap format, which I don't like. I used one on my Kingslayer (since I couldn't find a 390nF box cap back then either) and I don't like using a gargantuan cap that winds up sitting on top of everything else like a big blob of green playdough.

Anyone know where to get a 390nF box cap? Smallbear doesn't have 'em. Can I get away with a 330nF?

[GermanCdn]

Just got my last order in from Tayda - the new 390 nF are 5 mm lead spacing in the brown covers (similar to the Panasonics), so you don't have to have that big green wart sticking up anymore.  Glad I ordered eight!

Alternatively, take a 330nF box cap and piggy back a 68 nf onto it's legs.

[Morgan]

Anyone know where to get a 390nF box cap? Smallbear doesn't have 'em. Can I get away with a 330nF?

Got mine from mouser (it's a panasonic though): http://www.mouser.com/Search/ProductDetail.aspx?R=ECQ-V1H394JLvirtualkey66720000virtualkey667-ECQ-V1H394JL

Here's a box cap: http://www.mouser.com/ProductDetail/Kemet/MMK5394K63J02L165TA18/?qs=sGAEpiMZZMv1cc3ydrPrF17gIuUB4mH1V5y9k5depUM%3d

If the build were for me though, I would have no qualms at all with sticking a 330n in there. If it's for someone else asking "does this sound exactly like a Klon?", I'd go ahead and stick with the spec'd value.