This Week on the Breadboard: The 'lectric Mama Flanger

OK, not completely fixed. There is still a slight tick in the LFO/Clock chip near one end of the sweep. It's an artifact of the chip code. I must reluctantly remove the 4KNOBFLANGE chip from the design because once you hear the tick, you can't un-hear it. Standby for further developments.

Regarding the external BLEND control, what exactly do you want it to do? Bear in mind The 50/50 mix provides the deepest flanger tone.
a) Sweep from 100% dry to 100% wet. The wet end would be pure vibrato with no characteristic flanger tone. We'd want a pot with a center detent so we can easily find the 50/50 mix.
b) Sweep from 100% dry to 50% wet.
c) Sweep from 50% wet to 100% wet.
 
I agree, it's disappointing.
You might want to breadboard the circuit and give it a listen. If you avoid the top-end of the sweep range, there's no tick. Unfortunately for me, that's the end of the range I prefer to use. Plan B is to try using the STOMPLFO chip and the original clock osc. The advantage of the STOMPLFO chip is we have access to 8 different LFO waveforms, so that could be fun. Plan C is to revert to the all-analog design.
 
At long last, I think I'm done massaging this beast. Presenting The 6-knob Flanger.

SPEED - DEPTH - MANUAL - COLOUR - BLEND - WAVEFORM

Per Big Monk's request, I installed a BLEND control and it comes in handy with some of the more "out there" settings.
The LFO is realized in the Electric Druid STOMPLFO chip. ED provide the HEX file for free to DIYers. I burned the code into a PIC 16F18313. That chip sells for a little over a buck. The schematic is on two sheets to make it more readable. The audio path is on sheet one. The power supply, LFO and clock gen are on sheet two. I annotated the voltages I measured on my breadboard. I designed it with all B100K pots. Most of the eight waveforms available from the STOMPLFO chip are useful. The sine and triangle produce the traditional flanger sweep. The two random waveforms are fun. There is a hyperbolic "sweep" waveform that is of no use with this clock VCO because the VCO has a hyperbolic response to control voltage. If you only wanted two or three waveforms, that could be achieved with a few resistors and a SPDT toggle switch in place of the WAVEFORM pot. The STOMPLFO chip also has a Tap Tempo input that I did not use. It basically overrides the SPEED control. Any of the four control pots on the STOMPLFO chip could be replaced with an expression pedal or an external 0 to 5V control voltage. The SPEED, DEPTH and MANUAL controls have a huge range. I typically set SPEED below noon and DEPTH below 10:00.

'lectric Mama v3.2 page 1.png

'lectric Mama v3.2 page 2.png
 
Last edited:
The proximity of the capacitors to the IC note...is that to reduce inductance between them? If no, perhaps a brief explanation please?
 
I increased C23 to 560pF which moves the clock VCO range lower and the Electric Mistress tones are definitely there! Set the WAVEFORM to Triangle, MANUAL to zero, BLEND to max and you're there. Put a fuzz in front of it for the full jet-engine effect. So far, I've tried a Servo FF and Chuck's FZ-1 and they both sound bitchen. With other control settings, we can get a nice chorus or some spaced-out atonal synth effects.

Controls L-R: WAVEFORM - SPEED - DEPTH - MANUAL - COLOUR - BLEND

Chips L-R (top row) STOMPLFO (U6), clock VCO (U5), clock driver (U4), BBD (U3), 5V reg (U7).
(bottom row) mixer and Vref buffer (U2), preamp and pre-emphasis (U1).

Colour & blend trimmers are huddled under the COLOUR control.

The top power bus is Vdd (+5V).
Blue row below that is digital ground.
The middle red/blue pairs are Vcc & analog ground (2 rows of each)
Bottom red row is Vref.
Bottom blue row not used.

The notes about cap placement are to keep the digital noise originating in U6 from getting into the analog circuitry and to keep U6's control inputs from being upset by any noise pickup.

'lectric Mama breadboard v3.2 02.jpg
 
I have a little more testing / tweaking to do. I put the Flanger after a pedal containing a charge pump and the charge pump's switching freq was beating with the BBD's sample rate and making it "squeal like a piggy."
 
  • Like
Reactions: fig
Investigation & Findings:
The pedal that contained the charge pump mentioned above was a modified Chela as described here and here. I tried another pedal with a charge pump in it, the Crunch Captain Deluxe and observed the same squeal. Next, I replaced the 'lectric Mama with a commercial Flanger, a Monoprice yellow Flanger which appears to be a relabeled Mooer E-Lady. It exhibited the same squeal behavior.

The cause of the squeal is some of the charge pump's 40KHz switching noise sneaks out of the pedal via the output jack. When that 40KHz noise gets into a sampled circuit, like a BBD delay, chorus or flanger, the 40KHz signal is aliased down into the audio range when the sample clock is within ~10KHz of the charge pump noise. When the flanger clock is swept toward the longer delay end on the range, that's exactly what happens. Noise problems like this can be attacked on two fronts: the transmitter and the receiver.

We can make the transmitter end less noisy by filtering the signal before it gets out of the box. The modded Chela, which Cooder aptly named "Rippa," has a PRESENCE switch at the end which varies the high freq cutoff. Either the up or down position of the PRESENCE switch provides enough high freq attenuation to kill the squeal. The Crunch Captain Deluxe has no output filter on-board, so I will have to kludge one in.

We can make the receiver less susceptible by filtering the signal coming in to remove as much of the 40KHz switching noise as possible. I improved the 'lectric Mama's filtering upstream of the BBD by increasing R2 and C4, and adding another filtering stage with R7 and C5. I had to retune the filtering on the output side of the BBD (C9, C10 & R12) to restore the overall freq response. While I was at it, I tweaked the Vref voltage (increased R19) to maximize the BBD's headroom. While all of this helped, it was not sufficient to kill the squeal. It is also necessary to make sure that any pedal containing a charge pump does not transmit excess switching noise.

'lectric Mama v3.3 page 1.png

'lectric Mama v3.3 page 2.png
 
Thanks, that answers a lot of questions (I think). If the charge pump is the source, wouldn't all circuits utilizing similar charge pumps, BBDs and clock chips exhibit similar results?
 
10 votes on the wish list guys. We can do better.
Remember, the voting is done on the top right area of the post, not the normal "LIKE" for a forum post.

wolf-of-wall-street-rookie-numbers.gif
 
Chuck D. Bones said:
Investigation & Findings:
The pedal that contained the charge pump mentioned above was a modified Chela as described here and here. I tried another pedal with a charge pump in it, the Crunch Captain Deluxe and observed the same squeal. Next, I replaced the 'lectric Mama with a commercial Flanger, a Monoprice yellow Flanger which appears to be a relabeled Mooer E-Lady. It exhibited the same squeal behavior.

The cause of the squeal is some of the charge pump's 40KHz switching noise sneaks out of the pedal via the output jack. When that 40KHz noise gets into a sampled circuit, like a BBD delay, chorus or flanger, the 40KHz signal is aliased down into the audio range when the sample clock is within ~10KHz of the charge pump noise. When the flanger clock is swept toward the longer delay end on the range, that's exactly what happens. Noise problems like this can be attacked on two fronts: the transmitter and the receiver.

We can make the transmitter end less noisy by filtering the signal before it gets out of the box. The modded Chela, which Cooder aptly named "Rippa," has a PRESENCE switch at the end which varies the high freq cutoff. Either the up or down position of the PRESENCE switch provides enough high freq attenuation to kill the squeal. The Crunch Captain Deluxe has no output filter on-board, so I will have to kludge one in.

We can make the receiver less susceptible by filtering the signal coming in to remove as much of the 40KHz switching noise as possible. I improved the 'lectric Mama's filtering upstream of the BBD by increasing R2 and C4, and adding another filtering stage with R7 and C5. I had to retune the filtering on the output side of the BBD (C9, C10 & R12) to restore the overall freq response. While I was at it, I tweaked the Vref voltage (increased R19) to maximize the BBD's headroom. While all of this helped, it was not sufficient to kill the squeal. It is also necessary to make sure that any pedal containing a charge pump does not transmit excess switching noise.

View attachment 19191

View attachment 19192
Click to expand...
Strymon might have to look at this!!!
 
You must log in or register to reply here.
Back
Top