Combined LFO/BBD Clock chip for Chorus/Flanger

[12Bass]

Cool project!  Definitely curious to try this out when I get a chance.

Second, what I witnessed was Mike Irwin's MN3007 adaptation of the A/DA flanger.  There was no discernible change in level as it swept to ever shorter delays.  Keep in mind that it is at the shortest delays that any flanger's worth is displayed.  If the BBD loses any substantial level at highest clock frequencies, then the intensity of the effect should suffer, as the dry/wet balance strays from a perfect 50/50 blend.  I didn't hear any of that.

Even a buffered SAD1024 loses about 1.5 dB as it sweeps up to the shortest delays.  My guess is that it is an unavoidable aspect of the technology (unless circuit gain is adjusted with clock frequency).  I've found that the ideal 50:50 ratio only exists for a moderate range of clock frequencies.  Go lower and gain increases slightly.  Go higher, and gain is reduced.  Another difference from the Panasonic BBDs is that the Reticon chip has considerably more extended high frequency response, which should help fidelity and make the cancellations more dramatic, as least if the filtering allows for it.

[Fender3D]

(unless circuit gain is adjusted with clock frequency

Yep,

Tom if you have an extra pin left, please provide a voltage proportional to clock, so we can drive an OTA or a photoresistor and compensate for gain reduction...

[ElectricDruid]

(unless circuit gain is adjusted with clock frequency

Tom if you have an extra pin left, please provide a voltage proportional to clock, so we can drive an OTA or a photoresistor and compensate for gain reduction...

It's an interesting idea, but this is a digital chip, so probably the best you'd get would be a PWM output that you could filter to get a voltage proportional to the clock. And then you'd still have pass that voltage through some components that compensate for the particular gain curve of the BBD you're using. It gets a bit complicated, all to avoid a drop of a handful of dB at the far extreme end.
I suppose I could do that gain curve with a lookup table, but that'd assume that all BBDs are the same, or reasonably similar.

I'll think about it.

[mth5044]

How's the project, Mr. Druid?

[ElectricDruid]

Well, it's timely that you ask, because after a break doing other stuff, it's actually back on my desk.

I want to sort out the feedback circuit, and add tap tempo to the software, and then I'll call it done. I haven't got enough pins to also include the up/down direction feature, so I either have to pick one and leave it, or I have to do more clever tricks to read two switches with one digital IO pin (not impossible - there are various techniques).

With the feedback, I wanted to have a centre-zero control with positive regen in one direction (CW I suppose) and negative regen in the other direction. That gives both options without needing a switch. The problem is that the maximum amount of signal before it runs away into oscillation isn't the same for positive as it it for negative, so it's hard to get the zero actually in the centre, at least without one of those special centre-tapped pots, but I'm staying away from rare parts like that.

So - that's the state of play.

Tom

[mth5044]

Thanks for the update! Really cool project!

[YouAre]

A bit off topic, but do you think it's possible to create a new design that expands on the static delay to provide tap tempo for 3208/3205 Delay designs?

[ElectricDruid]

 ZOMBIE THREAD ALERT: Please have favourite anti-zombie weapon handy


It's taken a while, but I have actually finished this off, or at least got it to a point that other people can do something with it. There's (finally) code and schematics up on my website. I might have programmed chips and PCBs available in the new year.

http://electricdruid.net/flangelicious-a-super-dooper-flanger/

The current code is a fairly experimental seven-waveforms-plus-manual-mode flanger. I might write a more conventional four-knob-flanger code and then do the programmed chips with that code, since I suspect that might be more popular than the current crazy soundscapes version. Opinions welcomed on this.

Thanks for reading!

Tom

[dbp512]

Welp, this affirms the fact that I need to get a programmer. Once I'm done with exams I can get started, at least reading up on things and learning the language. As it is I have a growing list of circuits waiting for their turn under my iron, but this really piqued my interest. 
 
Also, I wanted to build a dimension p, which is a dual chorus with pt2399's. I believe it accomplishes that by using a simple triangle wave and an inverting buffer for the second channel. It looks like with only minimal tweaking this chip could be used in that circuit as well.

[samhay]

Nice job Tom - well done on getting it finished(ish).

Is the 12F1501 brand new? It looks useful for this sort of thing.

[ElectricDruid]

Nice job Tom - well done on getting it finished(ish).

Hohoho! Thanks, I think. Getting the sweep as smooth as possible was the biggest difficulty. It might be digital, but I don't want to *hear* that it's digital.

Is the 12F1501 brand new? It looks useful for this sort of thing.

Yeah, the 12F1501 is one of the newer "Enhanced" chips. The new NCO and CWG peripherals are what you need. The NCO acts as your BBD clock, and the CWG module is able to generate the biphase signal, even including a small deadband betwen the phases. So yes, definitely "useful" for this kind of thing. Pretty much ideal, actually. There are other chips that have the same peripherals, and I think there are some other 8-pin ones too, so it's not the only option.

Tom

[armdnrdy]

Cool stuff Tom!

Not a programmer myself so...I hope you find the time to add programmed chips to your collection of goodies.

[alanp]

That is a seriously clean flanger PCB. That would be perfect for a "first" flanger project for people still getting their feet wet with complicated projects and debugging them.

I noticed on your website --

One problem is that the 8-pin chip only offers three analog-to-digital channels (CV inputs). This means that if you want to add a "Waveform" control, you have to drop the usual flanger "Manual" control.

Would it improve matters to use a PIC with more pins? I know nothing about PICs, other than they do all kinds of magic, and I have one or two FCUK Eurorack modules with your PIC magic.

[ElectricDruid]

Cool stuff Tom!

Not a programmer myself so...I hope you find the time to add programmed chips to your collection of goodies.

Thanks. The plan is definitely to do some programmed chips once I'm happy with the features.

That is a seriously clean flanger PCB. That would be perfect for a "first" flanger project for people still getting their feet wet with complicated projects and debugging them.

That's the general idea. Flangers are generally so complicated that the plan with this was to try and make a really simple one.

Would it improve matters to use a PIC with more pins?

Yes, it would. I was trying to keep it down to an 8-pin chip, but that was just me trying to replace the MN3102. I've got a future plan for a 14-pin BBD clock chip that includes *all* the options. A bigger chip with more CV inputs and more program memory would make all sorts of things possible.

I'm thinking of a couple of simple 8-pin chips specialised for chorus and flanger, and then a 14-pin one with all the options and then some.

[boogietone]

Cool project.

[boogietone]

Where are you getting your bbd chips from?

[greymedicine]

How is the PIC able to create adequate clock voltage for the BBD? Is it because you're only running the BBD at 5V?

[ElectricDruid]

How is the PIC able to create adequate clock voltage for the BBD? Is it because you're only running the BBD at 5V?

Exactly! You could do it the other way, and boost the PIC's output to 9V, and run the BBD at the higher level, but it'd use more parts and makes things more complicated.
The reduced headroom isn't such a massive issue since BBDs don't let you use the full 9V anyway. Companding would help with noise levels, but that's always the case for flangers. I'm going to put a compander in the next flanger I do, the all-the-bells-and-whistles one.

Tom