Author Topic: 5pf capacitors instead of 4.7pf  (Read 2887 times)

rockaffe

5pf capacitors instead of 4.7pf
« on: November 14, 2018, 08:11:10 AM »
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

Re: 5pf capacitors instead of 4.7pf
« Reply #1 on: November 14, 2018, 08:30:07 AM »
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...

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Govmnt_Lacky

Re: 5pf capacitors instead of 4.7pf
« Reply #2 on: November 14, 2018, 08:30:56 AM »
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
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rockaffe

Re: 5pf capacitors instead of 4.7pf
« Reply #3 on: November 14, 2018, 10:24:59 AM »
Thank you for your replies guys! :)

wavley

Re: 5pf capacitors instead of 4.7pf
« Reply #4 on: November 14, 2018, 11:13:56 AM »
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
« Last Edit: November 14, 2018, 11:20:51 AM by wavley »
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rockaffe

Re: 5pf capacitors instead of 4.7pf
« Reply #5 on: November 14, 2018, 02:30:22 PM »
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) :icon_mrgreen:
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

Re: 5pf capacitors instead of 4.7pf
« Reply #6 on: November 14, 2018, 04:59:09 PM »
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.
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antonis

Re: 5pf capacitors instead of 4.7pf
« Reply #7 on: November 15, 2018, 10:31:48 AM »
How "fresh" is your 5pF cap..??

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

Re: 5pf capacitors instead of 4.7pf
« Reply #8 on: November 15, 2018, 10:54:54 AM »
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

Re: 5pf capacitors instead of 4.7pf
« Reply #9 on: November 15, 2018, 10:59:50 PM »
Quote
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.


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