Sag control on basic fuzz face

[Ginsly]

Is it hard on a pot to be inserted that close to the source voltage? I stumbled upon a thread the other day where people were lamenting all of the pots that would die an early death being used in this way! I've seen this solution over and over, so I can't imagine it would be that hard on pots. I'd love an informed perspective on this - although I agree with @Big Monk, it seems like 9 times out of 10 a transistor bias control would be a targeted way of achieving what most are looking for in a "power starve" control. Bosstones excluded.

 

[jwin615]

Sure, but a “sag” control doesn’t simulate a dying battery.

I think we had this discussion in the forums a couple years ago and a proper battery simulator circuot has more parts than the Fuzz Face does!

Yep. You need to current limit it as well... In short.
Ole Mr Ohm rears his ugly head again.

Exactly. It’s basically a a global bias control but I personally don’t want to play with the bias on Q1.

I see no benefit either. It's pretty much a clean amp/buffer anyway.
Since you're (generally) no where near saturation... Not much benefit

I have seen a little bit of sweet spot if you bias the second stage hot, then add a global starve. But it's tricky and dependent on each transistor...
Found it in production, or without breadboarding each circuit isn't viable. A PITA in other words.

 

[jwin615]

Is it hard on a pot to be inserted that close to the source voltage? I stumbled upon a thread the other day where people were lamenting all of the pots that would die an early death being used in this way! I've seen this solution over and over, so I can't imagine it would be that hard on pots. I'd love an informed perspective on this - although I agree with @Big Monk, it seems like 9 times out of 10 a transistor bias control would be a targeted way of achieving what most are looking for in a "power starve" control. Bosstones excluded.

Modern pots are rated for more than the current ta fuzz pedal will use.
They're not rated for watts + beer.
Audio + beer... Okay.
You do have to be careful in design as well to keep audio and DC off the same pot. You'll get a wonderful near speaker destroying scrape sound if not.

 

[Feral Feline]

The fuzz foundry already has a sag control, but it’s called stab (stability).

Yes, I mentioned that, noting that SAG is called STAB, in my post #13...
The OP was asking how to add SAG to a regular Fuzz Face — that's why I originally suggested in post #2 that the OP should take a look at the Fuzz Foundry.
Then I illustrated that fact in post #6, showing how to transfer the Fuzz Foundry's SAG (nee STAB) to the SiliSmile (standard Fuzz Face).

So...

 

[giovanni]

Yes, I mentioned that, noting that SAG is called STAB, in my post #13...
The OP was asking how to add SAG to a regular Fuzz Face — that's why I originally suggested in post #2 that the OP should take a look at the Fuzz Foundry.
Then I illustrated that fact in post #6, showing how to transfer the Fuzz Foundry's SAG (nee STAB) to the SiliSmile (standard Fuzz Face).

So...

Yeah sorry, I missed some bits and I saw the sag next to the stab control and was like, wait a minute…

 

[pricklyrobot]

I’ve got a Fuzz Factory clone I made many years ago (can’t even remember where the layout came from…)
I think the Stab/Sag control definitely produces some cool sounds, even if it’s not a “genuine dying battery simulator”.

General question, not specific to this circuit, if you want to use a pot as a variable resistor, what’s the advantage of jumpering the wiper to one side vs. only using 2 of the lugs?

 

[Big Monk]

I’ve got a Fuzz Factory clone I made many years ago (can’t even remember where the layout came from…)
I think the Stab/Sag control definitely produces some cool sounds, even if it’s not a “genuine dying battery simulator”.

General question, not specific to this circuit, if you want to use a pot as a variable resistor, what’s the advantage of jumpering the wiper to one side vs. only using 2 of the lugs?

It’s so that if the wiper fails, the pot defaults to its full resistance instead of going open.

 

[pricklyrobot]

It’s so that if the wiper fails, the pot defaults to its full resistance instead of going open.

So more one of those “best practices” things than “you need to do this to make it work”.
Makes sense. Thanks.

 

[jwin615]

So more one of those “best practices” things than “you need to do this to make it work”.
Makes sense. Thanks.

It's a lot easier to troubleshoot if a failure does occur.
This pot doesn't work vs this circuit doesn't work.
It is more important when dealing with high power stuff vs audio.

 

[Ginsly]

Modern pots are rated for more than the current ta fuzz pedal will use.

That's kinda what I figured, but I've seen many discussions where it's recommended to incorporate a resistor (I see 1k a lot) so that the pot doesn't "burn out". There are other reasons to add a resistor to a pot in different situations (so that Vol doesn't cut out completely, etc), but I've specifically seen it as a safety measure as well. I'm just not sure when it's necessary, but it certainly seems like this is one of those times.

So generally speaking, I shouldn't worry about installing this type of voltage starve off of the power supply?

 

[Ginsly]

Using the Fuzz Foundry as an example to building SAG into your SiliSmile:

- Lift one end of each D100 and C100, the ends that meet, ie don't solder those ends to the board, just the ends that go to power-input and ground respectively;
- solder the diode and caps loose ends with a wire together,
- other end of wire goes to your pot SAG's lug-1 & jumper lug-1 to lug-2.
- solder a wire from SAG lug-3 back to the remaining pad for D100 (or C100, whichever is more convenient).
- Fire up the board (you've already populated/soldered with all components jacks pots etc) and congratulate yourself on having added a SAG pot.

I'm looking at what I did to add a Starve to the Executive/Bosstone, but it was a much simpler process. Robert suggested:

"Omit R5 from the Executive Fuzz PCB.
Connect a wire from the top pad of R5 to lug 3 of your new Starve pot.
Connect a 10K resistor from lug 2 of the Starve pot to the lower pad of R5 on the PCB."

Is that just down to the two circuits being set up differently, making it slightly more complicated on the Fuzz Face?

@jwin615, starving the Exec is actually where I first became concerned about wrecking pots when used as Starve or Bias controls. Pedal Builder had said about the Exec Starve: "I like to use a 1k resistor and a B50k pot here. The 1k pot limits the current through the pot and prevents it from burning out"

It's not the end of the world to replace pots, but I'd really love some clarity on when it's crucial to add a resistor for protection, and what the minimum value would need to be. Sounds like the idea of a Starve pot's life being short is untrue...?

 

[pricklyrobot]

The datasheet I could find for Alpha 16mm pots says the Linear pots are rated for .125 Watts (non-Linear are .06W).
At 9V that gives you 13.88mA. I’m guessing a FuzzFace or similar pedal probably pulls quite a bit less than that.

 

[jwin615]

The madbean Woodshed(Arbiter Fuzz Face) build doc notes a current usage of ~2mA
Same for the bosstone/Fuzzly bear

 

[Ginsly]

The datasheet I could find for Alpha 16mm pots says the Linear pots are rated for .125 Watts (non-Linear are .06W).
At 9V that gives you 13.88mA.

That's great info, thanks!

The madbean Woodshed(Arbiter Fuzz Face) build doc notes a current usage of ~2mA
Same for the bosstone/Fuzzly bear

Absolutely, I tried using an mA meter on a Bosstone once and it didn't even register! Super low power consumption.

 

[Feral Feline]

I'm looking at what I did to add a Starve to the Executive/Bosstone, but it was a much simpler process. Robert suggested:
...

You'll see in that post that I eventually arrived at a very simple solution;
I reasoned it out and realised lifting this and that and the other thing were all completely unnecessary.
Everyone got to take a peek inside my puny grey-matter and see my thought processes...

Next time I'll edit my post to only include the final version. Better yet, I'll reason it out before posting, that way if I can't figure it out ...
Better to keep one's trap shut and have everyone think you're a fool than to open one's trap and remove all doubt!

 

[Ginsly]

You'll see in that post that I eventually arrived at a very simple solution;

Haha gotcha!

So why couldn’t one just leave everything as-is and simply insert the Starve pot between the DC jack and (+) on the board, leaving D100 in place?

 

[Feral Feline]

Haha gotcha!

So why couldn’t one just leave everything as-is and simply insert the Starve pot between the DC jack and (+) on the board, leaving D100 in place?

That wouldn't work, because ...D100 isn't able to protect the pot from...
That wouldn't work, because ...the flux capacitor could not regenerate the gigawatts in the compensator that...
*sigh*
That wouldn't work, because I didn't think to do it that way, so yeah, that wouldn't work for me.

Might work for you, though...






Geeze, there's always some smart-a** that has to one up me and come up with an even more streamlined method, the simplest solution possible.
I suppose that's better than a dumb-a** one-upping me...


I tip my hat to you, sir, I tip my hat.

Just make sure the CLR and LED are coming right off the DC-Jack and not the pot.

 

[Ginsly]

@Feral Feline hahaha… I was really, truly asking!

I’m also not sure why I couldn’t have done that with the Bosstone, where I lifted R5 and inserted the Starve there. I’m sure Robert suggested that for a reason, though! It seems like I could have just placed the pot between the DC jack and (+) power pad and adjusted R5 if necessary, but still solder it in as usual. My guess is that would present a problem, at least with the Bosstone circuit…

 

[pricklyrobot]

Or maybe you want your LED to dim along with your Starve level…

 

[Ginsly]

Or maybe you want your LED to dim along with your Starve level…

Ahhh ok, I didn't consider that! This is what can happen when using a starved power supply like the Danelectrode.