Coupling capacitor question

[StevieLaser]

Hi folks,
I'm building a pedal which contains multiple gain stages separated by coupling capacitors.  The schematic calls for 1uF non-polarised capacitors for this application. Up until now my limited experience has stuck with ceramic caps for low capacitance and polarised electrolytic caps for the higher values, and it turns out that I only have 1uF in polarised electrolytic form.

So, I've looked at what is available from Maplin and RS components and I realise that I have no idea if any of these are suitable 

Metallised polyester 1uF: http://www.maplin.co.uk/metallised-polyester-pet-capacitors-98158
Ceramic multilayer 1uF http://uk.rs-online.com/web/p/products/538-1578P/

Could you comment on which of these would be best, or what I should use instead, and why!

Thanks,
Steve

[Main.Ace.FX]

I prefer the poly caps...but that might just be a preference issue on my part

[DavenPaget]

Hi folks,
I'm building a pedal which contains multiple gain stages separated by coupling capacitors.  The schematic calls for 1uF non-polarised capacitors for this application. Up until now my limited experience has stuck with ceramic caps for low capacitance and polarised electrolytic caps for the higher values, and it turns out that I only have 1uF in polarised electrolytic form.

So, I've looked at what is available from Maplin and RS components and I realise that I have no idea if any of these are suitable 

Metallised polyester 1uF: http://www.maplin.co.uk/metallised-polyester-pet-capacitors-98158
Ceramic multilayer 1uF http://uk.rs-online.com/web/p/products/538-1578P/

Could you comment on which of these would be best, or what I should use instead, and why!

Thanks,
Steve

the multilayer has a tolerance of 20% , if you don't like 20% ( which what all electrolytics are ) then the "metal flim" poly cap will do (usually 5% i guess) . Oh btw , if you do , you might as well order from tayda/farnell instead .
Maplin sucks .

[StevieLaser]

Thanks Main.Ace.FX. So, I can use the poly ones. cool.

And I had a listen to your pedals on your page. very nice sounds, and I like the look you;ve given them too.
Cheers
Steve

[StevieLaser]

Hi DavenPaget,
Thanks for the info, I hadn't looked at the tolerances  

Could you give me any pointers on how to work out if or how much a 0.8 to 1.2uF tolerance on a coupling cap is going to affect the operation of the pedal? It's creating a high-pass filter to stop the DC, but how do I figure out where the roll-off happens and how fast?
The circuit in question is the Wampler Triple-wreck, schematic below:
http://www.freestompboxes.org/download/file.php?id=12170
And the caps in question are C6, C9, C11, C13, C15 and C25 on this schematic.

On the suppliers, Maplin has the advantage of being just down the road. But I agree that that is probably the only pro in their favour! Farnell I am well aware of, but Tayda is a new one to me so thanks for pointing them out.
Cheers,
Steve

[StevieLaser]

Something funny happened with that URL. I'll try again.
http://www.freestompboxes.org/download/file.php?id=12170

[StevieLaser]

OK, I don't understand what is happening there. Here is the link as text.

http://www.freestompboxes.org/download/file.php?id=12170

[StevieLaser]

 

I can't figure this out. Anyway, it is the Wampler Tripler-wreck, as given on the 5th page of the topic on freestompboxes.org in the boutique pedals forum, posted by Eisy.

Here's the forum page, in the hope that it works.
http://www.freestompboxes.org/viewtopic.php?f=7&t=10737&start=60

[artifus]

http://www.muzique.com/schem/filter.htm

tolerance is how close to the stated value the component is likely to be.

http://www.bitsbox.co.uk/

http://www.doctortweek.co.uk

[StereoKills]

I can't figure this out. Anyway, it is the Wampler Tripler-wreck, as given on the 5th page of the topic on ....org in the boutique pedals forum, posted by Eisy.

Here's the forum page, in the hope that it works.
http://www.....org/viewtopic.php?f=7&t=10737&start=60

You're having problems because it's a link to the "other" forum. Links and all mention to that forum are disabled.

[StevieLaser]

I can't figure this out. Anyway, it is the Wampler Tripler-wreck, as given on the 5th page of the topic on ....org in the boutique pedals forum, posted by Eisy.

Here's the forum page, in the hope that it works.
http://www.....org/viewtopic.php?f=7&t=10737&start=60

You're having problems because it's a link to the "other" forum. Links and all mention to that forum are disabled.

Ooops. Sorry, I didn't realise that was disallowed. My apologies. Should I delete or edit my previous posts?

[CynicalMan]

It isn't against the rules to talk about the other forum, there are just some automatic word replacements. I usually use goo.gl to link to the other forum. For example, here's your Wampler Triple Wreck link: http://goo.gl/3fcFX

For the capacitors, there's no difference between ceramic and poly worth worrying about for stompboxes. Either will be fine.

You can also take two 2.2uF polarized electrolytics, tie their negative ends together, and connect the positive ends in the place of the 1uF capacitor. This in effect makes a 1.1uF bipolar capacitor.

[StevieLaser]

It isn't against the rules to talk about the other forum, there are just some automatic word replacements. I usually use goo.gl to link to the other forum. For example, here's your Wampler Triple Wreck link: http://goo.gl/3fcFX

For the capacitors, there's no difference between ceramic and poly worth worrying about for stompboxes. Either will be fine.

You can also take two 2.2uF polarized electrolytics, tie their negative ends together, and connect the positive ends in the place of the 1uF capacitor. This in effect makes a 1.1uF bipolar capacitor.

OK,glad I didn't break the rules.

Alright, ceramic and poly are fine. I'll go with cheapest or simplest to get hold of.

That's interesting. I should have enough bits to do that. It just highlights that I have no idea why polarisation is important to an electrolytic and why this solution is OK. So much to learn 

[StevieLaser]

http://www.muzique.com/schem/filter.htm

tolerance is how close to the stated value the component is likely to be.

http://www.bitsbox.co.uk/

http://www.doctortweek.co.uk

Hi Artifus, thanks for the info. I'm already a customer at Dr Tweek and I'll add bitsbox to my list of bookmarks for suppliers.

For the filter calculation I assume that I have to come up with the equivalent resistance between the output end of the cap and ground if there is no single resistor there?

Thanks again

[StevieLaser]

And it lives!  Sounds pretty good at first listen!

Used CynicalMan's suggestion of making my own bipolar cap from 2x 2.2uF electrolytics that I had. Looks a bit untidy but I'll replace with single caps when I get them.

Thanks everyone for all the info. As usual it has been both interesting and informative coming on here.

Cheers

Steve

[DavenPaget]

Hi DavenPaget,
Thanks for the info, I hadn't looked at the tolerances  

Could you give me any pointers on how to work out if or how much a 0.8 to 1.2uF tolerance on a coupling cap is going to affect the operation of the pedal? It's creating a high-pass filter to stop the DC, but how do I figure out where the roll-off happens and how fast?
The circuit in question is the Wampler Triple-wreck, schematic below:
http://www.....org/download/file.php?id=12170
And the caps in question are C6, C9, C11, C13, C15 and C25 on this schematic.

On the suppliers, Maplin has the advantage of being just down the road. But I agree that that is probably the only pro in their favour! Farnell I am well aware of, but Tayda is a new one to me so thanks for pointing them out.
Cheers,
Steve

Yeah i say maplin sucks because many people call them , craplin's . 
You could just use electrolytics , doesn't really matter , just wire them right .

[PRR]

Poly is fine for audio. (Cork-sniffers will argue the various types of poly, but we are simple guitarists.)

Ceramic is fine below 1,000pFd. Values above 0.01uFd are a different kind of "ceramic" and may distort audio. (This is not invariably "bad" if you don't expect "sonic transparency".)

"Multi-layer ceramic" is more likely to be SMD, without leads, which is still awkward in most DIY work.

Except very narrow filters, all audio caps may be +/-20%. In many cases we use a cap 1,000% bigger than absolutely necessary, so wild "errors" are meaningless. This is like building a porch. Calculation says a 2-inch joist will break, we over-over-specify a 6-inch joist, and we are not upset when the stuff in the store is 5.5 inch.

[alparent]

What about Mylar and Monolithic caps? OK for audio?

[amptramp]

Mylar is OK.  Monolithic is another name for ceramic and large-value ceramic capacitors will distort sound because they act as piezoelectric transducers as well as capacitors.  Instead of voltage in = voltage out for a coupling application, you may get voltage in = bending of ceramic + voltage out.  You may also get some susceptibility to external acoustic noise which may give you a rather strange feedback mechanism that varies with pedal position.  A guide to capacitor linearity is here:

http://greygum.net/sbench/sbench102/caps.html

and

http://greygum.net/sbench/sbench102/caps2.html

[DavenPaget]

What about Mylar and Monolithic caps? OK for audio?

Mylar ,  10% fine .
Monolithic , in my experience , umm , NO , never , don't attempt it .