C18Q1 Learn electronics and build a pedal

Danny1969

Ceramics have a very low ESR so are used for decoupling generally on the supply rails, or for controlling parasite oscillations in high gain high bandwidth opamps etc .... they have some strange properties if one end is dc biased, value goes all over the place and they can contribute noise. So not used in general for actual audio coupling
Generally for actual audio coupling your be using poly family, larger but bomb proof pretty much from a design consideration

Danny1969

We can split caps into 3 main types and uses  

The best cap is no cap .... the reason there's a lot of caps in pedal design is a lot of them are based around opamps which are designed to have a dual supply .... guitarist only has battery or 9V single supply to get round this we bias the opamp at half the supply to create sudo 0V  ... often called Vfef on schematics and then have to use caps everywhere to stop the bias voltage going into other stages. If you run an opamp from a dual supply then you don't need to do this 

ESR means equivalence series resistance .... a capacitor has an internal resistance ... as much as a few Ohms for a Electrolytic and around 0.010 for a ceramic. So when choosing a cap for a job we look at the value in uF needed, the ESR and the material and physical size 

Electrolytic : high value of Farad for size but needs to be DC biased, high ESR so slow in action ..... good for power supply reservoir .... supplying extra current when the power supply output dips like a water tank in the loft. 

Ceramic : small value of Farad but low ESR so very fast in action, for best decoupling put them as close to the supply rails on the chip as you can 

Poly \ carb \ ester \ film \ etc low value of Farad for size but well behaved in almost all areas for audio coupling 

Philtre

Thanks for that @Danny1969 ! :-)

Adam_MD

Philtre said:

Thanks, @Adam_MD and @Danny1969 - so for low value ceramic caps (22pf, 150pf, 470pf, etc) if I choose a brand that says "NP0" or "C0G" dielectric these should be OK for audio?

Danny has it bang on the only thing I’ll add is whenever I’ve used cheaper ceramics and then replaced them with a NP0 or C0G the pedal has been quieter and without question sounded better.  

When I started this hobby I bought a lot of cheaper parts from places like tayda, eBay etc and to be honest my early pedals sound a lot like joyos.  whereas when I started using higher quality tighter tolerance parts the sound difference between my early pedals and later ones is huge.

Adam_MD

Sorry for the large pics these are posted straight from my phone.  

The red pedal in the picture below is a sweet honey clone (my second pedal) made from a bitsbox kit which I was really happy with at the start.  Then I compared it to the blue movall pedal behind it (also a sweet honey clone) and the movall sounded a little better and was a little quieter.  I was pretty frustrated at this stage I think I paid £15 for the movall second hand.  



I cant seem to find a finished gut shot for the sweet honey this appears to be the only one I have.  The 3pdt in this pedal also developed problems within 6 months of building it.



After I had started using tighter tolerance parts and was generally more confident building pedals I had another go at the sweet honey and built this one.  The difference when comparing the above pedal to this is massive everyone who has tried these two pedals can easily tell them apart in a blind test.  



IMHO the biggest contributing factor to the difference in the sound and noise quality of these two pedals are the ceramic and mlcc caps in the red one.  With my early crappy wiring coming a close second.  

Philtre

Thanks guys. Greatly appreciate your help and mentoring. :-)

So far, I've used good caps for the nF ranges (yellow polybox, green mylar, red metallised polyester), and some NP0s from bitsbox for the low pF ceramics (100pF, 47pF, 22pF), but in some unfinished veros that I'm working on I used some cheap ceramic discs and eBay electrolytics.

In the Timmy clone I built I used two cheapo ebay 47uF electrolytics. These are just for power smoothing so I think I should be OK.

Right now, I'm putting together an order from CPC. I'm getting bulk supplies of Panasonic electrolytics (1uF, 10uF, 100uF, 22uF, 4.7uF and 47uF) and a variety of NP0 / C0G ceramic discs for the low pF values. Then I'm going to swap out the cheaper ones I've used in my ongoing projects.

Philtre

Hmmm..some of CPC's NP0 / C0G ceramics are made by "Multicomp". I Googled this and this brand doesn't get a good rep.

Philtre

Sorry to be a pain in the rear @Adam_MD but I found that CPC do C0G multilayer ceramics by Vishay like this one http://cpc.farnell.com/vishay/k221j15c0gf53l2/capacitor-220pf-50v/dp/CA06820 - is this type OK or does it have to be non-multilayer?

Adam_MD

Philtre said:

Sorry to be a pain in the rear @Adam_MD but I found that CPC do C0G multilayer ceramics by Vishay like this one http://cpc.farnell.com/vishay/k221j15c0gf53l2/capacitor-220pf-50v/dp/CA06820 - is this type OK or does it have to be non-multilayer?

No problem Phil for 220pf I order these ones from RS.

https://uk.rs-online.com/mobile/p/ceramic-multilayer-capacitors/6994973/

I tend to use RS first and then check cpc, farnel etc if RS don’t have what I want or are too expensive.

though to answer your question those Vishay caps are fine.

Philtre

Great! Thanks @Adam_MD - What do you think of the Murata brand? They seem to be cheaper for some values.

Adam_MD

Is that on cpc Phil?  I’ve not used that brand before but in all honesty if the specs are right they’ll probably be fine.  

Philtre

@Adam_MD ; That's on RS https://uk.rs-online.com/web/p/products/1335689/

Adam_MD

I’d buy those Phil they look fine.  

Philtre

Great, thanks. Sorry to be a pain. I'm putting an order together of these multilayer C0G caps and I just want to get it right. :-)

Adam_MD

No problem dude shoot me a pm with codes if you want me to have a look.  

Philtre

I built another pedal. :-)

This time it's the Lunar Module Deluxe from here - http://tagboardeffects.blogspot.co.uk/2012/02/great-modern-take-on-classic-fuzz.html





I'm pleased with the LED mounting. I didn't use a bezel, but soldered the LED to a small 5x5 piece of vero with a hole in it to mount the LED and glued that to the underside of the enclosure with a 3mm hole. The idea came from this post - http://www.diystompboxes.com/smfforum/index.php?topic=107252.msg973532#msg973532

This one caused me a few more problems. Apart from some dodgy solder joints I'd inadvertently bought pots with differing shaft lengths, 15mm and 17mm, and the knobs (Boss type) sat way too high on the shafts. So I had to cut off a couple of mm with a junior hacksaw. I must pay more attention when ordering pots to get the same shaft length!

@Adam_MD - Is there anywhere else to get pots from apart from Bitsbox and Tayda? I checked RS and CPC and they don't seem to have these type.

Adam_MD

Looking good Phil your posca pen work is a lot tidier than mine would be.

Bitsbox and Tayda are the only places I order pots from you can get them from Banzai or smallbear but the postage is a lot more expensive than Tayda especially smallbear the postage is a killer.

I always order the same type just in different values.  These are right angle pcb mount with a solid 6mm shafts I usually build on pcb but if I'm using vero I just snip leg off where it turns.

The main details are available for each pot giving you the dimensions for each part i.e. shaft length, diameter etc

https://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/logarithmic/100k-ohm-logarithmic-taper-potentiometer-round-shaft-pc-mount.html

I tend to use bitsbox in an emergency because they don't always come with the dust caps but the ones from tayda do.  These days I plan builds out in advance so order all the pots I need for a lot of projects in one go so usually have some I can pinch if I decide to build something on a whim.  Tayda are also considerably cheaper than anywhere else I've found to buy them usually half price compared to other sites which can be quite a bit of cash when you're ordering 50 of them.

Philtre

Thanks, @Adam_MD That's what I'll do. Strange that no-one else really sells these types in the UK.

BTW - how are you finding the quality of the Alpha 3PDT switches from eBay? I ordered a few of those. I'm hoping they're genuine and not knock-offs!

Adam_MD

Philtre said:

Thanks, @Adam_MD That's what I'll do. Strange that no-one else really sells these types in the UK.

BTW - how are you finding the quality of the Alpha 3PDT switches from eBay? I ordered a few of those. I'm hoping they're genuine and not knock-offs!

I tend to use optical switching with a dpdt so don’t use many 3pdts anymore but if you’re ordering from this guy all the ones I’ve had have been legit.  They seem to be hard to find from a UK supplier

https://m.ebay.co.uk/itm/Alpha-Taiwan-3PDT-Footswitch-with-Solder-Lugs/253111548438?epid=2198267762&hash=item3aee9fba16:g:LG0AAOSwkklZndUX

Philtre

@Adam_MD Yep, those are the ones. Are you getting your opticals from here? https://shop.pedalparts.co.uk/OptoPuss_Optical_True_Bypass/p847124_17567620.aspx