Supply problems

[digideus]

Hi all,

This is my first build.  I decided to go with the schamatic for a Crunch Box.

while trying to put together the parts for it however, I ve hit on a snag...

Being in the UK we have several major component suppliers in this country such as RS and Maplins and a handful of smaller ones, but I'm having a lot of trouble finding capacitors rated under 1uf from all of them.

The Crunch Box schematic im using is a plain board layout drawn by Mr.G and is labeled CRUNCHY (based on Madbeans PCB Layout with the tone control replaced with a BMP style TC) I dont have a link, but the parts are the same as other schematics for the crunch box.

On the parts list, the 12 caps are listed varying from .022uf to 100uf and a couple of 100pf's in there as well.

the first cap on the list is rated at .022uf which im having a lot of trouble locating.  Of the ones my local Maplins had, they were rated at 63 volts!  surely that's well outside the ones I need.

Any UK builders out there got some idea of places to get components?

[Govmnt_Lacky]

Of the ones my local Maplins had, they were rated at 63 volts!  surely that's well outside the ones I need.

Actually, you COULD use those. As long as the caps are rated for over say.... 16V, you should be good! 

[JKowalski]

Small value capacitors (under 1uF) are usually found in high voltage ratings because they can still be small due to the small capacitance, so why not make them more versatile by upping voltage ratings? For example, nearly all normal ceramic capacitors are around 50-60 volts, and they are miniscule. Using a cap above rating is fine as long as the dimensions are okay, and if you have room it's always recommended to overvalue caps within reasonable limits.

If you are still worried check dimensions, either from the site you are ordering from or the manufacturer's website.

[markeebee]

I'm always impressed with Bitsbox. Sensible range of parts, good pricing, quick delivery. I think a lot of the other UK guys here use them too.

[PRR]

> rated at 63 volts!  surely that's well outside the ones I need.

I have to hang a decoration weighing less than a pound. I find and study strength of nails and screws...... my cheapest nails are good for 20 pounds and my little screws can take 50 pounds.

Yes, pFd caps often are not offered less than 500V, 0.0?uFd caps often not stocked under 50V-100V except as extra-cost micro-nano-size. 

So you use the 20-pound-capacity nail because you just can't find a nail "just right" for a 1-pound load, nor anything cheaper.

[digideus]

OK, so I can use higher rated voltages, but Im still having trouble locating some capacitors and ive just been told by Bob at Bitsbox that the ones im looking for dont exist!

I think the schematic im following is incorrect.



maybe the problem here is that this layout isnt verified.  I checked it against another layout (crunch'd box layout) and the components and layout dont match up.

Can anyone point me to a verified layout?

[Govmnt_Lacky]

I guess the next logical question is..... What velues are you looking for?

I am pretty sure that Steve over at Small Bear will ship international.

[digideus]

specifically, its the .007uf Caps.  I managed to find everything else (and learned a LOT in the process!)

[suregork]

specifically, its the .007uf Caps.  I managed to find everything else (and learned a LOT in the process!)

You can probably find 6.8nF caps..

Edit: Musikding.de and Banzaimusic.com have a large selection of effect-oriented components and shipping inside EU is cheap.

[Electron Tornado]

> rated at 63 volts!  surely that's well outside the ones I need.

I have to hang a decoration weighing less than a pound. I find and study strength of nails and screws...... my cheapest nails are good for 20 pounds and my little screws can take 50 pounds.

Yes, pFd caps often are not offered less than 500V, 0.0?uFd caps often not stocked under 50V-100V except as extra-cost micro-nano-size. 

So you use the 20-pound-capacity nail because you just can't find a nail "just right" for a 1-pound load, nor anything cheaper.

And that, dear friends, is a fundamental lesson in engineering.   

Anyone new to this hobby should read PRR's post again and hopefully this -->  <-- will happen.       

[Govmnt_Lacky]

You can probably find 6.8nF caps..

+1. You can use .0068uF (6.8nF) caps without any change in performance. As long as you follow the +/-10% rule you should be fine.

[digideus]

Excellent - Thanks guys. 

At this stage, I now have everything sourced except the IC, which Maplins tell me they no longer carry as stock (either the EC833 or the TL072).  As soon as I find it, I will be building this and testing it.

[petemoore]

  TL072, Tl082, JRC or any 4558, many others...
  I would guess from states here that Maplins has a dual opamp, jfet input.
 Standard dual opamp. There are many numbers of chips that will work here:
 Dual opamp [gotta be a dual amplifer]
 Jfet input [high impedance..
 For this, if just the header description of data sheets matches the description of what you need [available on data sheet header statement] it'll work.
   

[digideus]

Thanks Pete.  Ive located someone local that supplies the TL072.

I'm not sure I understand the complexities of Op-amps, Jfet's the like.  Is there a reference anywhere that people can refer to about the differences between the different models of IC's can produce?

[petemoore]

  I read Jfets at GEO, data sheets etc., high impedance input that applies to Jfet imput opamps as well, except without the wierd' bias deal of Jfets @9v supply.

[PRR]

> 0.007uf Caps.

? ? ?

As Lacky says, 10% even 30% "off" is often no-difference in audio. In tone-controls, a key fine-tweek technique is to look at a 0.005u cap and try 0.002u and 0.010u to shift the action-point up and down the audio band.

*Maybe* someone got carried-away and liked 0.007u (0.005u+0.002u) best for HIS particular sound and music.

The other thought, since 0.007 is such an odd value and there is no note or provision for using two caps 0.005u+0.002u, is that it is a typo. 0.001u? Or a round-off. 0.0068u?

I don't know the whole plan, to guess what might really be intended. However there's a 22K nearby, and 0.007u against 22K is 1.1KHz, a nice midrange point. And 0.005u against 22K is 800Hz, also a nice midrange point.

I'd get a couple 0.005u (now sold as 4.7nFd just to confuse us). Try one, but leave space to tack the other across it.

> 63 volts!  surely that's well outside the ones I need.

Another angle: In that plan, R1 dissipates at most 0.000,000,1 Watts. But nobody stocks micro-Watt resistors; if they did, you couldn't see one. There are 1/16th Watt (0.06W) resistors, but 1/8W are cheaper, and 1/4W are usually the same price and comfortable size. Yes, you are "forced" to use a resistor 100,000-200,000 times bigger than needed, and that's OK.

Dang near "any" dual op-amp will work here. I'd favor the TL072/TL082 because it is cheap, known-good for gitar effects, and the R3 R8 values are typical TL072 size. But 558, 833, and many others will be fine. If you shop guitar-pedal vendors, their "most popular dual opamp" will be fine.

[digideus]

Thanks for the info PPR.

I have read about some 0.007uf caps being used as a tone cut cap in fender guitars on other forums, but its probably an obscure part from some far eastern supplier from back in the day.  I found a supplier of 0.63pf caps anyway, so I will exchange them in the build and see what happens!

I also got the TL072 IC sorted.  i doubt I will get anything before the latter part of next week because its a bank holiday weekend here in the UK and everything is closed until tuesday

[Gurner]

Top tip for the British**  on here - register an account with RS UK....& they'll deliver your order *free*  - next day service too  (no matter how small the order - sometimes I only need a couple of resistors, but out of 'virtual' e-embrassment I'll bump my order up a little).

Sure often they're a little more expensive than the likes of Rapid, Farnell....but you can't argue with free next day postage for parts totalling under a fiver!

I thought registering an account with them would be a bit of hassle ....but it was a piece of the proverbial. (there was no need to prove you're a business etc)

(**rule Brittania)

[Perrow]

OK, so I can use higher rated voltages, but Im still having trouble locating some capacitors and ive just been told by Bob at Bitsbox that the ones im looking for dont exist!

I think the schematic im following is incorrect.



maybe the problem here is that this layout isnt verified.  I checked it against another layout (crunch'd box layout) and the components and layout dont match up.

Can anyone point me to a verified layout?

I don't know about verified or not, but I do think that you should raise R1 to at least a "semi standing" position going from row 1 to row 3. That way your IN, Drive 1 and Drive 2 goes from zig zag to straight. But that's just how I'd do it.