51pf capacitor is 50pf ????

[rogeryu_ph]

Say guys I do have 50pf marked on a ceramic cap and i'm looking for 51pf for tubescreamer is this already 51pf ? Why 100pf marked as 101 and 470pf marked as 471.... Which is which?

Roger

[raulgrell]

The markings on capactors are annoying.

The last digit is a multiplier. 47x = 47*10^a pf

[bancika]

Say guys I do have 50pf marked on a ceramic cap and i'm looking for 51pf for tubescreamer is this already 51pf ? Why 100pf marked as 101 and 470pf marked as 471.... Which is which?

Roger

Also, tolerance on caps is at least 5% so you can use 51,50 or even 47pF without a problem...

[Mark Hammer]

If you can hear the difference between a 50 and 51pf cap in a Tube Screamer, then I suggest you stop using it because your ears are so sensitive they need protection from loud sounds.

Seriously though, if you measured all the components you used, you would quickly realize that the values shown in a schematic are really an idealized hypothetical circuit.  Real circuits are always a little bit different from each other unless you take deliberate steps to measure everything and select components very carefully.

[rogeryu_ph]

Of course I can't hear the difference . But more of my question is capacitor coding which just get me recently confused co'z I'm breadboarding this TScreamer now. I already bulit one TS clone using 47pf before co'z that time I don't have 50pf. So the answer would be 51pf marked on ceramic cap is actually 50pf in value? Second question Mark, what is the magic of 51pf on TS while Boss SD1 almost the same in circuit has none? I already finished the TS breadboard and I did try to hear what sound if no 51pf on it but it's almost no difference. Again of course in electronic theory has the answer but I'm not much with the theory man.

Next i'll try the mosfet clipper and the AMZ tone control by JACK ORMAN.
Thanks,
Roger 

[ejbasses]

the small value cap across the feedback loop controls the noise way up high

[MikeH]

So the answer would be 51pf marked on ceramic cap is actually 50pf in value? Second question Mark, what is the magic of 51pf on TS while Boss SD1 almost the same in circuit has none? I already finished the TS breadboard and I did try to hear what sound if no 51pf on it but it's almost no difference. Again of course in electronic theory has the answer but I'm not much with the theory man.

Ceramic caps in the 1-99pf range are usually marked just marked with the value in pf, like "47", "51", or "7".  When you get over 100 they start using the multiplier like, 101 = 100pf, 471 = 470pf etc.  So to answer your first question; 51 = 51pf.  The answer to your second question, there's no magic in the 51pf.  You could use a fairly wide variety of values there with only subtle differences.  The reason it's 51pf is because that's what someone at Ibanez used 30 years ago (errr... 40 years?) because that's what they liked and it's been that way ever since.

[Mark Hammer]

When gain is controlled via the feedback resistance, increasing the gain by increasing that resistance results in a gradual lowering of the upper frequency rolloff point.  To some extent, what that does is produce more "growl" at higher gain without incurring more "snarl".  That is, while all harmonic content is increased by turning up the gain, the presence of the cap results in the rolloff being progressively lowered with more gain such that lower order harmonics are unscathed while upper-order harmonics are tamed.  That is one part of the "smoothness" formula.  The overarching goal is to add an approximately equal amount of low-order harmonics across the range of notes.  A secondary goal is to prevent unwanted high-frequency oscillation.

A value of 51pf provides a rolloff commencing at 1 / [2*pi*.551M*.000051uf] = 5.66khz at max gain.  At lower gains, the filtering effect disappears.  So, if the gain pot is set to 100k resistance, the rolloff now begins at 20.7khz.  Bear in mind there is a subsequent lowpass filter immediately after the gain stage which supplements that rolloff.  Any treble-trimming that takes place above, say, 15khz and maybe even 10khz is going to be inaudible because of that 1k/.22uf network, and because the speakers simply can't reproduce it.  There is a logical reason why you hear no difference with or without it when the gain is at less than max.

[johngreene]

When gain is controlled via the feedback resistance, increasing the gain by increasing that resistance results in a gradual lowering of the upper frequency rolloff point.  To some extent, what that does is produce more "growl" at higher gain without incurring more "snarl".  That is, while all harmonic content is increased by turning up the gain, the presence of the cap results in the rolloff being progressively lowered with more gain such that lower order harmonics are unscathed while upper-order harmonics are tamed.  That is one part of the "smoothness" formula.  The overarching goal is to add an approximately equal amount of low-order harmonics across the range of notes.  A secondary goal is to prevent unwanted high-frequency oscillation.

A value of 51pf provides a rolloff commencing at 1 / [2*pi*.551M*.000051uf] = 5.66khz at max gain.  At lower gains, the filtering effect disappears.  So, if the gain pot is set to 100k resistance, the rolloff now begins at 20.7khz.  Bear in mind there is a subsequent lowpass filter immediately after the gain stage which supplements that rolloff.  Any treble-trimming that takes place above, say, 15khz and maybe even 10khz is going to be inaudible because of that 1k/.22uf network, and because the speakers simply can't reproduce it.  There is a logical reason why you hear no difference with or without it when the gain is at less than max.

When there are diodes in the feedback loop, I consider it to be just a little more complex than this. Simply because the diodes are going to limit any signal above a certain level therefore leveling the gain over a much wider frequency range than what you just calculated. I say this in comparison to what the response would be if you operated the circuit at levels such that the diodes do not ever conduct. It is quite a different response. In my mind (which can be a rather unconventional place) I view the 50pF cap as more of a slew-rate or rise-time limiter, rather than a frequency roller-offer. If you put a filter with the exact same frequency roll-off -after- the opamp, it will affect the waveform much differently. It may be just semantics to most, but given my previous example, it fits better to me.

--john

[Mark Hammer]

I follow you.  Indeed, most lowpass filtering IS a sort of slewing process.  From the plug-in-and-rock person's perspective, this shows up as differences in spectral content.  One is the process; the other is the audible result.

No need to apologize for thinking analytically.

[johngreene]

I follow you.  Indeed, most lowpass filtering IS a sort of slewing process.  From the plug-in-and-rock person's perspective, this shows up as differences in spectral content.  One is the process; the other is the audible result.

No need to apologize for thinking analytically.

But when you have diodes in the circuit limiting the signal, the effect is different than just filtering. IMO. My point being if you have the same filter after the opamp that you have in the feedback loop, the frequency response will be quite different for this reason.

--john

[rogeryu_ph]

Thanks MikeH and to all of you guys,
Strange why Boss SD1 does not have 51pf on its feedback loop

Roger