Voltage sag control question.

[Focalized]

So in a circuit with a protection diode like 2n5817 etc, would the sag control pot go before or after the diode or make no difference?

[antonis]

As far as they're in series (without any shunt branch) it should make no difference..

edit: Could you plz define your sag control configuration..??

[Focalized]

[Focalized]

Actually I feel stupid now thinking of the sag on my power supply. Which is obviously before.

How about the pot resistance? That one is 2k but I've seen 25k and 100k used.

[stonerbox]

1-10k will be well enough. Just don't hook it up like I did, for the first time over 10 years ago. 9v to pin one, voltage to circuit from pin two and... pin three to ground! Yeah, you figure out how that ended

Actually I feel stupid now thinking of the sag on my power supply. Which is obviously before.

How about the pot resistance? That one is 2k but I've seen 25k and 100k used.

[GibsonGM]

...you let out the magic smoke 

[antonis]

For a useful pot wiper travel, place a resistor in series with lug1 of value about 3 times that of the pot..
(e.g. 15k for a 5k pot..)

[Mark Hammer]

I apologize for being an old man shaking his fist at the sky, but what gets called "sag" generally isn't.  True sag is that phenomenon when a power source can momentarily provide more current, to support gain, but can't continue to and drops back to something less.  It is NOT a stable reduced voltage/current.  That's just less voltage or current.

True sag yields a kind of compression, as the battery or amplifier power supply recovers.  Gain is somewhat reduced as current supply surrenders a little and then recovers.  Reducing the voltage and/or current of a stable supply will give you the same tone and dynamics no matter how hard you strum, because it is stable and not buckling (sagging) under demand.

That does not make what people like to call "sag" musically irrelevant or even bad sounding.  It's just not the same thing.

[drdn0]

I apologize for being an old man shaking his fist at the sky, but what gets called "sag" generally isn't.  True sag is that phenomenon when a power source can momentarily provide more current, to support gain, but can't continue to and drops back to something less.  It is NOT a stable reduced voltage/current.  That's just less voltage or current.

True sag yields a kind of compression, as the battery or amplifier power supply recovers.  Gain is somewhat reduced as current supply surrenders a little and then recovers.  Reducing the voltage and/or current of a stable supply will give you the same tone and dynamics no matter how hard you strum, because it is stable and not buckling (sagging) under demand.

That does not make what people like to call "sag" musically irrelevant or even bad sounding.  It's just not the same thing.

So I'm guessing that could be achieved with some sort of envelope filter controlling input voltage/series resistance from the power supply without -too- much difficulty?

[mzy12]

So I'm guessing that could be achieved with some sort of envelope filter controlling input voltage/series resistance from the power supply without -too- much difficulty?

Your best bet would be having an RC combo that has a time constant long short enough to actually enter the range of audibility, hooked up to the output of, say, an LM317, which would allow you to simulate different battery voltages, plus some small resistors on the +V and GND rails that represents the internal resistance of a battery. I've been wanting to create a circuit like that for a while. I'll draw something on KiCad tomorrow.

EDIT: Meant to say short, not long for the RC time constant. You'd also need to be careful that you're filtering enough of the output of the voltage regulator that it doesn't introduce unwanted noise but not enough to eliminate the "sag" you want. The RC filter is complicated by the fact that you have one load for charging the capacitor, i.e, the resistor in series with the output of the vreg, and one exponentially more complex load for the discharge of the capacitor, i.e, the pedal circuit itself.

[Mark Hammer]

So I'm guessing that could be achieved with some sort of envelope filter controlling input voltage/series resistance from the power supply without -too- much difficulty?

I don't know if it would be "without too much difficulty", but you're thinking in the same direction as I am.  "Sag" is a dynamic thing, not a steady one.

And again, that does NOT mean steady limitations on voltage or current are incapable of producing great sounds, but "sag" is different.  At least, from my perspective.  I understand that others may hold a different view.

[mzy12]

I understand that others may hold a different view.

I agree completely with this. Sag is just a great marketing term that means nothing, usually. It's most accurate when applied to tube amps, but the understanding of what makes tube amps sag and what it means for sound is, generally, limited.

[teemuk]

I would just wire the envelope control to directly control clipping thresholds, that's what it most prominently does.

How this is mostly done in commercial apps is making up an envelope follower (of the signal) with some preferred filtering / RC constants. Detract it from preferable DC reference and there's your control signal. Now you can harness that to drive a voltage regulator or just use it as DC reference for clipping diode (invert it for the other polarity).

Personally I would skip the regulator (that alters headroom of gain stages, therefore effecting clipping thresholds) and just go directly to altering those clipping thresholds (of a diode clipper). 

[drdn0]

So I'm guessing that could be achieved with some sort of envelope filter controlling input voltage/series resistance from the power supply without -too- much difficulty?

I don't know if it would be "without too much difficulty", but you're thinking in the same direction as I am.  "Sag" is a dynamic thing, not a steady one.

And again, that does NOT mean steady limitations on voltage or current are incapable of producing great sounds, but "sag" is different.  At least, from my perspective.  I understand that others may hold a different view.

If you are using the output of the envelope to control series resistance/voltage (assuming with some sort of delay), is that not dynamic?

[aron]

If you want more "feel" could a compressor do this? Slight compression for me does it.

[Focalized]

So the layout above didn't work unless I used a 1M pot. Cut down to around 4v. But this way below worked as shown. Drops to 2v.

[Focalized]

Still trying this. The Voodoo Lab Superfuzz I'm trying this in craps out below 7v. With that layout on a breadboard I increased the 2.2k until it didn't drop below about 7v. But when wired in the fuzz the range goes back to 2.5v and 9v. I can't figure out what it's doing.

[artofharmony]

1-10k will be well enough. Just don't hook it up like I did, for the first time over 10 years ago. 9v to pin one, voltage to circuit from pin two and... pin three to ground! Yeah, you figure out how that ended

Okay I have to ask: what caused the smoke? I would have hooked it up the exact same way 

[antonis]

what caused the smoke?

Definitely, it's not my business but, smoke usually comes out of over-current item..

[ElectricDruid]

Okay I have to ask: what caused the smoke? I would have hooked it up the exact same way 

Carbon track pots can't handle much current, so if the circuit draws enough milliamps, you can easily burn holes in the pot track. 0.125W is fairly common as a maximum rating, and that's only 14mA at 9V.