Flanger & Chrous

[Jyka]

Hi,

I want to build a Dod Flanger 575 A and a Dod chorus FX65.

Here are the schemtaics :

http://www.schematicsunlimited.com/d/dod/dod-575-flanger-fx-pedal-schematic

Thanks =)

[micromegas]

So... are you asking for advice?

[Scruffie]

Some advice to start is you can't build a DOD 575A, uses the SAD512D, finding a working one for sale will be next to impossible.

[lars]

You could mod the circuit to use an MN3204, which is still fairly easy to find. The MN32xx series of chips are about the easiest BBDs to retro-fit into any circuit that originally used SADxxxx Reticon chips. The biggest consideration is your power supply. The Reticon chips ran at higher voltages than the MN32xx's can handle, so you'll want to regulate the power between 5-8volts. I've also found that the clock circuit will have to be regulated at the same voltage as your BBD. You can't simply drop in an MN32xx series chip and leave the clock circuit at the original voltage, it either doesn't work at all, or has terrible clock noise. Properly modded, it will sound every bit as good as the original.

[Scruffie]

You could mod the circuit to use an MN3204, which is still fairly easy to find. The MN32xx series of chips are about the easiest BBDs to retro-fit into any circuit that originally used SADxxxx Reticon chips. The biggest consideration is your power supply. The Reticon chips ran at higher voltages than the MN32xx's can handle, so you'll want to regulate the power between 5-8volts. I've also found that the clock circuit will have to be regulated at the same voltage as your BBD. You can't simply drop in an MN32xx series chip and leave the clock circuit at the original voltage, it either doesn't work at all, or has terrible clock noise. Properly modded, it will sound every bit as good as the original.

You wouldn't just need to mod the circuit you'd have to completely redesign the clock circuit, the SAD512D takes a single pulse (doesn't have to be a clock signal) and does the rest internally, the MN3204 needs a proper 2 phase clock.

Regulating the voltage would be the easy bit and not entirely necessary, the 320X series are fine up to 10V so you could just use a 9V supply it's just that they don't hold bias well with changing voltage so it'd have to always use the same supply or be re-biased. A 78L05 lifted above ground to 7.4v with four diodes would suffice as the chips do have improved THD & S/N specs as voltage is increased.

Clock voltage does affect the BBD biasing point yes if you check the datasheet.

Also I wouldn't say the MN3204 is easy to find and also has a lot more capacitance on its clock pins so may need buffering unlike a SAD512D.

[lars]

Oops, I didn't realize the SAD512D only took a single pulse to operate. That being the case, wouldn't it be possible to simply run that single pulse into a CD4013 to get the two-phase output for a different BBD (similar to a DOD680 clock circuit)? A little more complicated of a retro-fit, yes, but it wouldn't be completely redesigning the clock circuit or changing the sound/behavior of the pedal.

[Scruffie]

If I remember, the DOD575 doesn't provide a proper square wave rather than just a pulse (the SAD512 isn't so fussy about a pure square clock like the Panasonic BBDs) so you can't just split it, might be mistaken though.

Don't forget though, despite the clock, the 512 is exactly that, a 512 stage device, the clock may not get it in to the original delay range without the help of buffering for a 1024 stage BBD like the 3007 & 3207 which are the only readily available BBDs with that fewer stages which would mean a CMOS clock buffer as well.

The MN3207 can be clocked to the ranges of the MN3004 a 512 stage BBD according to the datasheet, but all the MN series of BBD chips have quite a lot more capacitance on their clock pins than the SAD range so may still need the clock buffer to overcome this for proper operation, depending on the frequency range of the original clock.

I'm sure it can be done, but, quite the hassle, especially for someone that has said they'd like to build particular effects and not 'how can I' so i'm guessing this might go a bit further than they hoped for.

[lars]

Agreed on the complexity. It's very interesting to dive into the "ancient" technology of BBD devices. I've learned the hard way through trial and error what works and what doesn't, but still have tons to learn. I'm going to post my findings on a DOD680, since I recently got a broken one and brought it back to life by retro-fitting an MN3205. As far as I can tell, the original MN3xxx series of BBDs are of higher quality because I don't have any of the noise problems people have mentioned with original SAD4096s. The pedal is almost freakishly quiet for a vintage analog delay. I expected a lot of hiss at max.