freestompboxes.org

R21 / R26 are 1K.. unfortunately no pic of the Sizzle pot value, but I'm fairly certain the schematic is correct for this revision.

I made a frequency response compare of the Sizzle filter with both potentiometer values (10 kOhms and 100 kOhm).
Thereby the value steps were 1 kOhm respectively 10 kOhms.
The 10 kOhms potentiometer gives more significant changes than the 100kOhms potentiometer does.

Manfred wrote:I made a frequency response compare of the Sizzle filter with both potentiometer values (10 kOhms and 100 kOhm).
Thereby the value steps were 1 kOhm respectively 10 kOhms.
The 10 kOhms potentiometer gives more significant changes than the 100kOhms potentiometer does.

Very cool, much appreciated!

10K was definitely used at some point so it'd certainly be worth trying it. I'm going to build a couple of these so I can A/B them and I'll make a note in the build docs about the alternate part values.

k. nice.

thanka guys! and thanka to the dude that did the video dissecting the unit. he got it from every single angle. there was 2 parts that were hard to find but they were all identifiable. the hardest was the 220R but it was caught also for a brief moment under a pot and you caught a glimpse between pot terminals!!! lol

id like to hear the A-B n look forward to the feedback Bugg. ill have to see if i have an extra 10k pot.

We are assuming no other changes like caps thou!

equinox wrote:We are assuming no other changes like caps thou!

Yep, of course. I'm just interested because of Manfreds simulations with the 10K pot in the existing circuit.

I have no doubt the traced values are correct for that revision of the circuit.

One question I have is - why the CA3240EZ op amp? and what else would do the exact same job without changing values on the circuit?

FeVeR2112 wrote:One question I have is - why the CA3240EZ op amp? and what else would do the exact same job without changing values on the circuit?

-Very High Input Impedance (ZIN) 1.5TerraOhms (Typ)
-Very Low Input Current (II) 10pA (Typ) at +/-15V
- Slew rate ~30Volts/Microsecond
All of these properties make the CA3240EZ very close to a so-called "ideal Op-amp",
that means the circuit is nearly independent of the OP-amp and is almost determined by the external circuity.

- wide Common-Mode Input Voltage Range (VICR):
Can be Swung 0.5V Below Negative Supply Voltage Rail
That avoid issues due to OP-amp blocking.

Manfred wrote: - Slew rate ~30Volts/Microsecond

Oh, too good to be true. It's slew rate is 3x times lower, around 10 V/uS.

plush wrote:

Manfred wrote: - Slew rate ~30Volts/Microsecond

Oh, too good to be true. It's slew rate is 3x times lower, around 10 V/uS.

Thanks for the hint, you are right.
I got that value from an OP-amp list, that is obvious wrong.
I had a look at different datasheets and find a slew rate between 7 to 9V/us.
This gives a maximum frequency of ~248 kHz repectively ~318 KHz at an operating voltage of 9 Volts,
up to this frequencies the sine swing remain undistorted.
I think that is good enough for audio.

While the op amp may be close to ideal, since we socket the IC, we can test out whether the Op Amp chosen here makes that difference in tone. From pin-out it is compatible with the usual OP Amp suspects like OPA2134, TL072, 4580....

I will breadboard it up and see what happens - maybe some feline fusion.

I builted it up with PCB from PedalPCB.com few months ago. Of course, Sizzle was A100k. My first feeling was something wrong. Cuz it's too much treble. I did not know why.. Should I change A100k to A10k for Sizzle to fix it?

mutante wrote:I builted it up with PCB from PedalPCB.com few months ago. Of course, Sizzle was A100k. My first feeling was something wrong. Cuz it's too much treble. I did not know why.. Should I change A100k to A10k for Sizzle to fix it?

Sure, you can try something with lower value, (50, 25 or 10k).

Also, if you are can't decide what to change, online circuit simulators with real time simulations (https://www.falstad.com/circuit/) can be very handy. You can simulate a part of a circuit to decide which part does the thing. I won't recommend them for simulating complicated circuits though.

Here the Bode-plots for further potentiometer values in steps of 10% for each.
The lower the potentiometer value and the larger is the change of the frequency depend on the potentiometer setting.

I liked the tone in the video that showed the 10k with the 1k resistors, soo I'll probably changing my components out to support this.

The fact is that the "Sizzle" control is a presence control, it is similar to the circuit on the Wampler Phanteon.

plush wrote:

mutante wrote:I builted it up with PCB from PedalPCB.com few months ago. Of course, Sizzle was A100k. My first feeling was something wrong. Cuz it's too much treble. I did not know why.. Should I change A100k to A10k for Sizzle to fix it?

Sure, you can try something with lower value, (50, 25 or 10k).

Also, if you are can't decide what to change, online circuit simulators with real time simulations (https://www.falstad.com/circuit/) can be very handy. You can simulate a part of a circuit to decide which part does the thing. I won't recommend them for simulating complicated circuits though.

Sizzle potentiometer was changed to A10K a few minutes before. Everything is perfect. A10K is correct value.

Looking forward to it. Going to use A10k Sizzle and I'll put 10k's on R21 and R26. Then put 1k's across they 10k's and see which I like better which should total 990 ohm or within 1%, so should be close.

WHAT is the result of increasing or decreasing these resistors?

I think I messed up the last board as could not get working and 1st one with Buggs layout and design and put the switch on the wrong side and soldering and desoldering. This one is virgin, so I'm expecting no issues. Board should be today so I'll populate and hook up tonight

equinox wrote:Looking forward to it. Going to use A10k Sizzle and I'll put 10k's on R21 and R26. Then put 1k's across they 10k's and see which I like better which should total 990 ohm or within 1%, so should be close.

WHAT is the result of increasing or decreasing these resistors?

I think I messed up the last board as could not get working and 1st one with Buggs layout and design and put the switch on the wrong side and soldering and desoldering. This one is virgin, so I'm expecting no issues. Board should be today so I'll populate and hook up tonight

The change of both values to 10k does not influence the frequency response noticeably.
The filter formed by C2,R21,R19,R22 has a flat frequency response within the audio frequency range, with R21 = 10k the high roll-off frequency changes to about 16 kHz.
The change in value of R26 to 10k changes nothing.

bugg wrote:R21 / R26 are 1K.. unfortunately no pic of the Sizzle pot value, but I'm fairly certain the schematic is correct for this revision.

[ Image ]

I saw the 3pdt or footswitch and asked myself "how can I get this?"