Reticon SAD1024 Delay Chip

I don't entirely know what the effect pedal does, but if the requirement is to capture audio and delay it and perhaps re-feed the output to the input, then there's another (quite exotic) chip, which too is obsolete but is still available occasionally on ebay due to not being so popular in the audio sphere.

It is the FX802LS, by CML micro.

It's main advantage is that the codec is integrated, no need for separate codec+DSP/FPGA. However its main technical disadvantage (apart from the obsoleteness : ) is that it is intended for speech, so has a 3kHz bandwidth. I don't know how badly that would impact a guitar sound.

Anyway, it is quite an unusual chip because it allows simultaneous record/playback, which is what is needed to implement a delay, but could also do extra effects with little effort, because the instructions to tell it what to do can come over a reasonably slow serial bus, enabling even an Arduino to control it. The simultaneous thing was a specific use-case for this chip compared to other basic speech recorder chips of that era.

I have 2 of these chips, unused, plus equally vintage 1Mbit DRAM chips that should work with it. I do remember constructing up a speech recorder with this chip, it was feasible with point-to-point wiring on a perforated board, since the FX chip is quite large PLCC sized, and the DRAM chip is 486 PC era : ) I can't recall what microcontroller I used to control it, probably a 6805, nothing speedy.

It would be a fun project for someone familiar with Arduino perhaps, but as you say spending the £60 is easier and cheaper than the time to prototype this and write the code. Besides, it may sound totally different to the original pedal.

I think for the money, i'd be prepared to pay the £70 or so for an original chip..... To buy an original pedal is around £300 so it is cost effective even spending that money on a chip

I don't know much about musical stuff, but from that circuit I'd say that the flange effect comes from sweeping the clock up and down in frequency.

The 470p being charged by the transistor (set up as a current source) and then being reset by the comparators is evidently the actual clock. The period of that clock is determined by the slower triangle waveform generated by IC4a (the 22u integrates up and down depending on the state of the flip-flop IC3a, which flips backwards and forwards in the way that flip-flops like to do).

Unless you could simulate that I don't think you would have flanging, though you'd be able to do other interesting stuff with it.

Oh I see! Yeah I wasn't sure what specifically the flange sound was, and what it might translate to in requirements, even after scanning briefly through the video (although I am most definitely a fan of the Police!!).

The really hard part about exact replication is that the BBD (Bucket Brigade Delay) device varies its sampling rate as the clock changes and the clock in the flangers is swept. This means that data is sampled at one clock speed but then passes into the delay chain and may be sampled at the output at a different rate from that at which it was captured.

Typical ADC - DSP- DAC chains sample at  a constant rate and will have serious issues if swept sampling is attempted (and only ultra pricey parts can go fast enough). It is possible to achieve the entire effect with constant rate sampling but the DSP will be required to interpolate and resample at both input and output and I would guess that an audio sample rate of 192kHz will be needed to come close to the behavior of the SAD1024. This kind of DSP stuff is possible with DSP chips or FPGA (@ DAB - way out of PSOC league). The development effort in software is significant (if I were quoting a customer I would allow 8 weeks for the FPGA HDL work).

The other way to do it is to use a non-conventional chain with SAR ADC and ladder type DAC where the sampling is on demand with negligible latency. 16 bit 2MHz parts will be needed to match the SAD1024 dynamic range and speed. The FPGA needs to do very little other than buffer the data (needs 2k bytes of internal RAM so a Lattice ICE40 series part would do - and would keep the power low.

The problem is that the 16 bit 2MHz ADC and DAC are quite expensive.

MK

Oh I see.. I hadn't realized that is what a flanger did : (

I guess at some stage it just makes sense to do all this in software on a PC or DSP. I have a friend who works in the sound industry, he uses some fancy gear to generate virtually any sound programmatically, essentially a DSP connected to a PC, and he downloads either instructions or scripts to it. But, at the same time he also uses low-tech too, he will use a mic and record anything interesting and then play with it to make the effect he is seeking.

Motorola/Freescale had a nice dev-board (probably still available on ebay) which had a DSP (56k series, so quite old : (, enough RAM for echo-style effects, and codec, and I think a serial port for downloading the program to it. It could make a nice universal effects pedal!

just be aware that those reticon SAD chips are really prone to just dying on you, they are sensitive to static and even if you buy one now theres a real good chance it will on some random day just stop working. the MN300x series are generally used and recommend are modernish replacements for the old BBD chips of the past. be aware that these are reissue MN3007s on smaller and the like.

now if memory serves correct you can replace the SAD4096 with the MN3205 but rigging up an adaptor board (geofx or somewhere like that might have the exact details details). the MN3207 is used all over as replacements for old pedals so google some adaptor schematics ect and lets us all know how you go.

I had a surprise in the last few weeks. I received an email from a gentleman named Niels who said he had 2 SAD1024 chips at work that they didn't need. Without any further ado he mailed them to me free of charge!!!

I emailed him back and said i wanted to pay-pal him some money as a token gesture which I did to cover postage and give a small bit on top as a thank you. people I've met through this forum have been really helpful, and selfless and will always try to help where they can..... This has got to be one of the best support forums for electronics out there.

many thanks Niels, you have saved me a lot of heart ache, and expense.... i'll be sure to post the end result of the build on here once it's been completed.

HAVE A GREAT 2018 ALL, MAY THE COMING YEAR BE GOOD TO ALL

I have 5 original SAD-1024A Analog Delay IC's Line New still in the package w/the spec sheet (Sealed - Never opened)

Im an American ham radio operator W5TXR.

e-mail me at  w5txr B(at) w5txr   

(dot)ty West

Of course ignore the West

An(net)te

The address is intentionally messed up to fool bots.

interested I can send you some pics

Email will be sent

Andy