Bass Attenuation Coupling cap voltage division

[Tonewood]

I don't understand DC voltage division on caps.



If the 0.047 is a 630 volt cap, will that block the DC so that the following caps be of lesser voltage rating?

Thanks.

[Mike Sulzer]

I don't understand DC voltage division on caps.

[ATTACH=CONFIG]38429[/ATTACH]

If the 0.047 is a 630 volt cap, will that block the DC so that the following caps be of lesser voltage rating?

Thanks.

Only if you provide a dc path to ground at the right side of the .047 capacitor. Its maximum value (safe for turn on or other transient condition) cannot be determined without knowing the load connected to Out.

[Enzo]

The point of voltage ratings is to protect the cap. If that first cap shorts, the full voltage is across the later ones.

[Tonewood]

Only if you provide a dc path to ground at the right side of the .047 capacitor. Its maximum value (safe for turn on or other transient condition) cannot be determined without knowing the load connected to Out.

Thanks for the info Enzo & Mike.

Mike, the path "in" is from an anode at about 150vdc and the "out" goes to the center of a 1M pot so it can be anywhere from 1M to zero ohms to ground. Thanks again.

[R.G.]

I think this is a step sideways. In the absence of the rest of the circuit so I could actually tell something about the circuit, I think that the 10M resistors are there to keep the DC voltage across each of the switched caps down to zero. This eliminates any popping, as would happen if the 10M's were actually a few giga-ohms ( that is, a couple of inches of air).

Switching caps for different responses is common in pedals, and a network like that would make sense there too.

[Steve A.]

I've seen arrangements like that (minus the switching and the resistors) in BF style tone stacks fed from the anode. My assumption was that the higher rated initial cap allowed for lower voltage ratings on the subsequent caps... or was I mistaken?

Steve Ahola

[J M Fahey]

Not knowing what the rest of the circuit is, this looks like a hybrid between Orange's FAC (Frequency Analyzer Control)

which is intended as a pre-distortion bass cut control (as in: rise volume as much as you wish, then stary cutting *just* enough bass so you cut mud/farting without sounding too thin) and an experimenter's mod to vary between a "fendery" coupling cap (~.022) and a "Marshally" one (~.0022), adding a "half way" value (.0047).

That said, the purpose is defeated because it feeds the wiper of a reverse wired 1M volume control so low cut frequency varies all the time, since it can be anything between 1M and 0.

The proper use, both in the Orange and the Fender/Marshall choices , is to feed a constant load , either a 470k/1M standard volume pot or a 1M grid resistor, so what you choose makes sense.

In old style electronics (introducing Op Amps changes the game rules) expected results are achieved the old style way, such as fixed gain blocks driving passive volume and tone controls, fixed attenuators and EQ nets, etc.

Active variable gain is more suitable to SS electronics.

Last week I saw at DIY Audio (where else?) a nonsense *Tube* graphic equalizer, with tube gyrators, tube "Op Amps" , a 13 tube mess , simply a standard plain vanilla graphic equalizer with voltages multiplied by 10 ... it even run on symmetrical supplies of +/-150V !!!!!!!!!!!!!!!!!!!!!!


Notice they mindlessly copied the original (proper) Op Amp circuit so much that they did not fit input and output coupling caps !!!!!!!!!!!!!!!!!
*Might* work at the input, but at the output, even if roughly "balanced" , I expect quite a few volts offset, easily up to + or - Volts.
Obviously the "designer" didn't even build it (at most it was simulated).

What did they expect to get?
Piss poor performance for sure.

Funny thing is that some pedal circuit sites (ROG among others) regularly "turn tube circuits into SS ones" , replacing tubes with fets (unmatched to boot) which need an individual trimpot to "bias" the resulting mess, but now the reverse is starting to happen.

Where was that circuit originally published? .... at "Glass Audio" of course .

[potatofarmer]

The earlier FAC that Matamp put into their amps (before they started making amps for Orange) actually includes another taper resistor between the volume pot's wiper and ground so the load is more variable, with more bass being cut as the volume is turned up. Plus it's in a way better spot in the preamp. And I prefer the corner frequencies in the Matamp, but that's just my opinion.

Not the most legible schematic, but...

[Mike Sulzer]

Thanks for the info Enzo & Mike.

Mike, the path "in" is from an anode at about 150vdc and the "out" goes to the center of a 1M pot so it can be anywhere from 1M to zero ohms to ground. Thanks again.

Then I think you better use high voltage capacitors for them all.

[R.G.]

The problem with series capacitors is that the voltage divides by their capacitive impedance for changing/AC situations, but divides by their ...leakage resistance... for DC condition. The DC leakage resistance is not really too related to the capacitor's value, especially across different technologies.

The 10M resistors might help keep most of the voltage across the incoming resistor. But I still suspect freedom from popping may be the target.