MXR Micro Flanger Schematic parts/circuit question

[bushidov]

I really like the sound of the old MXR Micro Flanger and looking at an old post from Mark Hammer in 2010, I think I can build one based off the schematic he posted and substitute parts to newer versions (transistors, and such). I think I can assume the chopped off part on the right is just a trace that connects the R26 line to the output jack's stomp switch.

The part I am not sure of is how to convert the SAD512D to something like an MN3207/3007. Also, if I were to do that, do I need to add a BBD clock (MN3102/3101) or is there already something I can use to do that on the current schematic?

Really curious, as I like the idea of the two-knob flanger as well. Simple, but effective.

[Mark Hammer]

Conversion from SAD512 to MN3207 will be a bit more complex than you imagine.  Those Reticon chips were designed to take in a single-phase clock pulse and divide it down internally to provide the required tick and tock.  The MN-series chips, whether P or N type, assume receipt of a dual-phase complementary pre-divided clock pulse.  So you'd need to redesign the clock generator.  Not impossible, but between that, and the change in BBD, I'm not entirely sure you have an MXR Micro-Flanger at the end of it.  That's not a bad thing in itself.  But if you're aiming for a particular tonal target, you may not hit the bullseye after all that work.

[ElectricDruid]

You should be able to take the SAD512 out and plonk a MN3207/MN3007 in fairly directly. There are a couple of things to watch for. The input of the MN chip needs biasing, so you'll need a voltage divider or preset to set the bias voltage and a cap to couple the signal into the input. The SAD512 in the schematic seems to just grab signal straight from the emitter of that transistor filter. The second thing is the output. They've just tied the BBD's two outputs together with a 47K resistor to ground. You see this sometimes on MN circuits where they're trying to save every part (I think Boss CE-2 is an example, IIRC). Otherwise you can add a preset in here to balance the two outputs, which sometimes helps with clock noise a little bit.

For the clock, you've got everything you need, but (like Mark said) you'll need to tweak. The SAD512 is only using a single phase clock, and the MN will need a biphase clock. The MN chip is going to have more clock input capacitance than the SAD, so a bit more drive would help. Luckily for us, there are 3 unused stages in that 4069. I'd parallel another one up alongside the pin 11/10 one (to give you two buffers driving the clock output), and then I'd use the other two in parallel driven from pin 8 to get the second out-of-phase clock output. That should cope with the extra capacitance, and you don't need any more parts. Finally, since the clock won't get divided by 2 by the BBD any longer, you would ordinarily double the 50pF cap to 100pF to keep the same clock range - but in this case, the delay length has doubled (512->10-24 stages) so having the clock running twice as fast actually keeps the delay time the same as it would have been...I think! .

[bushidov]

Nice responses. I figured it wasn't "straight forward", but I was still curious. Going on what Mark Hammer said, I also figured there would be some tonal differences, but also as Mark said, it may not be a bad thing. I want to try and tackle this one and hear for myself. I redrew the schematic from MXR to EAGLE. My only problem was that it wasn't clear on some of the values, so I wasn't sure what R7 (1.5K or 15K) or C18 (1.5uF or 15uF) were. I guessed there were decimals there, but then again, the schematic is blurry.



So, after reading ElectricDruid's (whom I guess is the guy behind the microcontroller PIC chips on SmallBear?) comment, I redrew using an MN3207. Did I get it correct, ElectricDruid? And, that being said, which of the 4046 leads goes to the CP1 and CP2? Also, where you were going on the output, should I have a second "R18" 47K resistor going to ground, one for OUT 2 and one for OUT 1? And if so, then how do I tie them together to R17? With just a trace? Sorry if I sound like a noob on this one.

[ElectricDruid]

I redrew the schematic from MXR to EAGLE.

Nice work.

My only problem was that it wasn't clear on some of the values, so I wasn't sure what R7 (1.5K or 15K) or C18 (1.5uF or 15uF) were. I guessed there were decimals there, but then again, the schematic is blurry.

R7 makes a HP roll-off with C4. That makes me think 15K is more likely than 1K5, because 1KHz seems more likely than 10KHz for the roll-off.
C18 seems to be the cap that sets the LFO rate, so that one is probably "adjust to taste" anyway. 1.5u sounds likely.

ElectricDruid's (whom I guess is the guy behind the microcontroller PIC chips on SmallBear?) comment

The same!

I redrew using an MN3207. Did I get it correct, ElectricDruid? And, that being said, which of the 4046 leads goes to the CP1 and CP2?

Yes, the buffers paralleled up like you have them was what I had in mind. And yes, they go to CP1 and CP2 (CP="clock phase", I think).

Also, where you were going on the output, should I have a second "R18" 47K resistor going to ground, one for OUT 2 and one for OUT 1? And if so, then how do I tie them together to R17?

If you have separate resistors on the outputs, you typically see 100K. Hence when they're combined into one, they become 47K (2x100K in parallel is close enough to 47K). Here's an example of the "separate resistors with trimmer" style of joining them (my own Flangelicious pedal):

https://electricdruid.net/wp-content/uploads/2015/06/Flangelicious-Pg2.jpg

Alternatively, you can go for the "minimum parts" style of just connecting them together. If it's good enough for Boss, it's good enough for us, right?

https://www.hobby-hour.com/electronics/s/boss-bf2-flanger.php

The only other thing to note is the BBD's input biasing. Going straight into the BBD from the collector of the pre-delay filter isn't quite enough. The Boss BF-2 adds a bias adjustment at that point (hard to see exactly). I used a fixed bias on my Flangelicious. Either way, it needs something, it won't work right how it is.

Good luck!

[bushidov]

Thanks for the info Electric Druid!

So, assuming I guessed which of the 4069's leads go to CP1 and CP2 (I might have gotten them backwards), I redrew the schematic again. I think for the moment, I'll keep a single 47K resistor on the output of the MN3207, but I will probably fiddle with a bit of off-boarding on that later to see what improvements it will create.


So, now I have two more sets of questions.
1. Does it matter which of the 4069's leads goes to CP1 and CP2 and if so, what would happen if they were backwards? Just a curiosity on that one.
2. As of the input biasing, I thought that was the purpose of R15 and R16? I am guessing now that I am incorrect. If I am, should I add a 100K pull-up/down resistor between R16 and pin 3 of the MN3207 and if so, bring that up to a voltage divider of two more resistors and a decoupler cap? Lastly, what kind of voltage should this hard-set bias be, ball-park figures? On your Flangelicious, it looks like you are trying for 2.727V or 11/20 of the 5V rail.

and, now that I see it, I may want to "PIC" your brain on your Flangelicious. Is that 8-pin driver a PIC12F? Is it simply just being an "MN3102"? Also, what IDE and programmer are you using for your PIC stuff? I was using CCS Compiler and an ICD-U64 for programming for a while at work, but it started to get expensive so I started converting things to ATMEL and Atmel Studio/AVR-GCC. Now that microchip bought Atmel, I was hoping to see the PIC stuff go to AVR-GCC or Atmel Studio, but alas, nothing.

[Scruffie]

Don't hold me to this but I think about 8 years ago I came to the same conclusion as ElectricDruid and tried building this with the 4069 producing both clock phases for an MN3207 and it wasn't clean enough to work properly so you might need to use a divider (3102 or 4013). I suspect you will.

As for bias, those 3 series diodes from U1A are dropping the voltage down suitably for the SAD512D and the BBD bias is tied to the V.Ref trimmer, you just need to remove them for the MN3207 as it doesn't need as low a input voltage as the 512D.

I wouldn't bother with BBD output mixing resistors or separate pull down resistors, yeah they're better practice but flanger clock frequencies aren't that low and this is quite heavily filtered so noise shouldn't be too much of a concern, plus you'll be running at twice the clock frequency which will improve the sampling anyway, I doubt you'll get even the slightest audible change.

[bushidov]

As for bias, those 3 series diodes from U1A are dropping the voltage down suitably for the SAD512D and the BBD bias is tied to the V.Ref trimmer, you just need to remove them for the MN3207 as it doesn't need as low a input voltage as the 512D.

So, I can remove D1, D2, and D3? And what do I remove from the MN3207 for the BBD bias?

Don't hold me to this but I think about 8 years ago I came to the same conclusion as ElectricDruid and tried building this with the 4069 producing both clock phases for an MN3207 and it wasn't clean enough to work properly so you might need to use a divider (3102 or 4013). I suspect you will.

I've seen John Hollis's Ultra Flanger, and it did something like that with a CD4046BE, I think. I did build the Ultra Flanger once, but it was rather difficult to get the Flange sound out of it. I mean, it eventually did, but it wasn't very flexible. Probably because I followed a bad schematic.

[Scruffie]

You just remove and short those diodes then the bias voltage comes through the op amp and Q1 and is set by the existing bias trimmer. Nothing removed from the MN3207.

A 4046 isn't a good choice as that's serving as the VCO and clock in the ultra flanger, you'd take the clock frequency from pin 10 of U2 and feed it in to a dividers (again, a MN3102 or 4013) input and take the clock pulses from that. You'll need to halve C15.
For the 4013 if you look at an electric mistress schematic, just treat pin 10 of U2 the same as the output of the LM311 and for the MN3102 the datasheet tells you which is the clock input.

Edit: Another consideration, I don't know what the original clock frequency of this is off the top of my head but a 4013 will only drive a 3207 to about 800kHz unaided (I suspect the 3102 wont be any better which rules it out) so if you're doubling the clock frequency it may go above this so you'll want to parallel both halves of the 4013 as I don't think the inverters of the 4069 will offer enough current drive to buffer it.

[Govmnt_Lacky]

You could always use an R5106 as the BBD. I believe some of the micro flangers incorporated these. I believe there are only minor changes involved.

[Mark Hammer]

I own two Micro-Flangers: one of the plastic-box units and one of the 1590B-enclosure units.  They're okay, but nothing particularly noteworthy; at least to my ears.  By the time one takes steps to adapt the circuit to use of another BBD, and makes whatever mods one might wish to make (e.g., sweep width), one will have essentially built a different flanger.

So maybe the thing to consider is to start out by building a different flanger with a known design (and maybe available tested layout)?  Just a thought.

[Fender3D]

Another consideration, I don't know what the original clock frequency of this is

I opened a thread on the other site with clock values for flangers and choruses:

MXR Micro flanger:
I powered it with a stabilized power supply @ 9.6V
max clock freq at SAD's pin 1 is 850KHz (@ min rate)
min clock freq at SAD's pin 1 is 133KHz (@ min rate)

[Scruffie]

Another consideration, I don't know what the original clock frequency of this is

I opened a thread on the other site with clock values for flangers and choruses:

MXR Micro flanger:
I powered it with a stabilized power supply @ 9.6V
max clock freq at SAD's pin 1 is 850KHz (@ min rate)
min clock freq at SAD's pin 1 is 133KHz (@ min rate)

Ah, thank you, I remembered the thread and tried to find it but the other sites search function isn't so great and the google site: method doesn't work all that well on it either for some reason.

I didn't realise it was so high, a 3207 seems like it's going to be a poor choice... also that sweep ratio is a lot worse than I expected of the design. Edit: Forgot that's divided internally so maybe not so bad, was thinking it would need to be 1.7MHz.

[Fender3D]

Edit: Forgot that's divided internally so maybe not so bad, was thinking it would need to be 1.7MHz.

lol those tiny SADs always confuse me too, when dealing with clock or delay estimating or comparing with other BBDs...

Then one could just drop in half 4013 after the stock clock, or use 4 NAND gates for VCO + divider....
But, as Mark said:

I'm not entirely sure you have an MXR Micro-Flanger at the end of it

and

So maybe the thing to consider is to start out by building a different flanger with a known design

[ElectricDruid]

By the time one takes steps to adapt the circuit to use of another BBD, and makes whatever mods one might wish to make (e.g., sweep width), one will have essentially built a different flanger.

Yeah! Exactly! Great, isn't it?!

That's probably how >90% of "new" pedal designs are derived, in fact...

[Mark Hammer]

True, innit?

I don't think that's a bad thing, and I hope it to didn't come off as critical.  Rather, if one has to make accommodations anyway, and someone else has already done that in a different design, and worked everything out, there's no point in being married to the thing you thought you wanted to build at the outset.