5pf capacitors instead of 4.7pf

[rockaffe]

Hello everyone, I have a noob question about a Greg Fryer Treble Booster: the schematic call for a 4.7pf capacitors, but I only have a 5pf. Does it makes a big difference in the final results?
I'm asking because the pedal works but, on my AC30, if I raise the master volume, strange whistles and cracling noises starts to appear...

Thank you!

[deadastronaut]

theres not going to be a lot if anything in it when you consider 'tolerance'

a 4.7 is likely a 5 anyway....but then it might be a 4.1...

i'd just use it...

[Govmnt_Lacky]

Hello and Welcome to the Forum!!!

You should be OK with the 5pf cap. Typically, a 10% +/- tolerance is acceptable with capacitors (unless specified) so that is not a problem. Your "whistes and crackles" are more likely a problem with the build elsewhere. It could be caused by any number of different things.

I would suggest you follow the troubleshooting steps in the link below and re-post your findings in the "Building your own Stompbox" sub-forum

https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[rockaffe]

Thank you for your replies guys!

[wavley]

Yep, I sincerely doubt anybody can hear the difference between 4.7pF and 5pF.

Whistles sound like an oscillation to me, are you using a known layout?  Double check your wiring, move it around to see if it changes.

edit: just looked at a vero layout for it, that should be a 4.7nF not pF, the only pF caps are the two 10pF

edit 2:  looked at a schematic that had a 4.7pF, maybe you should link to the schematic/layout you're using

[rockaffe]

Thanks again, I think I've solved the noise and whistle issue just by taking the circuit away from the amp (I was triyng it keeping the circuit on top of the amp)
By the way this is the schematics I'm following:

https://paulinthelab.blogspot.com/2013/03/greg-fryer-brian-may-treble-booster.html

[Rob Strand]

Variations in the transistor's collector-base capacitance will be vastly larger than 0.3pF.
It can vary say 2pF to 6pF.  The gain of the transistor is about 100.
The input capacitance is then Cin = 100 * 2pF to 100*6pF = 200pF to 600pF.
The variation alone is near 1000 times larger than 0.3pF.

IMHO the 4.7pF will be ineffective for most RF.

[antonis]

How "fresh" is your 5pF cap..??

(never happend to find a 5pF cap in my over-30 years old drawer..)

[rockaffe]

How "fresh" is your 5pF cap..??

(never happend to find a 5pF cap in my over-30 years old drawer..)

Just bought it on Amazon last week

[Rob Strand]

never happend to find a 5pF cap in my over-30 years old drawer..

I don't think I've ever bought  5p 50p 500p etc.  here in au but I've definitely pulled a lot out of equipment from the 70's upto 1990.    A good deal of US electronics magazines (and effects pedals) from the 70's used 500p, 5n, 2n, 20n.