Fairfield Circuitry - Randy's Revenge

DWBH · Post by **DWBH** » 15 Jul 2009, 23:23

Just listened to this:
And OMG OMG OMG.
Wonder what's inside and if it's DIYable.
http://www.fairfieldcircuitry.com/RR.html

WhiteKeyHole · Post by **WhiteKeyHole** » 15 Jul 2009, 23:54

Yeah, been hoping for some guts for a while.

soulsonic · Post by **soulsonic** » 16 Jul 2009, 00:02

Wow, funny that this came up... I just got done visiting that page and listening to it myself!

Whatever is inside it, I can assure that it woudn't be difficult to build a DIY ring mod that can do similar things.
I recommend the checking out the Frequency Analyzer. It uses an AD633 analog multiplier chip for the ring mod effect... and it can get some very similar sounds to that!

DWBH · Post by **DWBH** » 16 Jul 2009, 12:42

The EHX one (at least from the demos I've heard) sounds more metallic and less musical. But of course, it all depends on what you're playing.

I've done some searching and the maker himself gave a little info about what's inside.
Quoted from harmony central forum:

Yes, I'm using the ICL7660 to get +-9V. I wasn't getting good results (if none at all) operating the modulation IC on a single supply.

Initially the plan was to use a split supply derived from a 15VAC adapter. I was a little skeptic about using a charge pump, what with the high frequency switching and all. Ends up it sounded just as good and much more convenient.

I experimented quite a bit with transformer-diode modulation. Some very nice sounds, but the frequency range and carrier suppression of the IC are what sold me.

I'm using the AD633, a little pricey but it does what it's supposed to do very well. I started with what was in the datasheets and worked from there. No real secret here. You should be able to get some good results, do you remember what the problems were?

I also tried the Gilbert Cell mixer. Worked but the transistor matching was too critical.

EDIT: Oh, and found this in experimentalistsanonymous' archive area

soggybag · Post by **soggybag** » 16 Jul 2009, 18:11

I suspect the key to getting a smooth ring mod sound is the sine wave carrier. A carrier that has a hard edge such as a square ans a triangle wave add extra harmonics to the mix.

From recent experiments with the Stompboxology Ring Modu matic, I noticed the low pass on the carrier frequency really smoothed out the ring mod sound. You could easily this to any ring mod to increase the range of sounds.

soulsonic · Post by **soulsonic** » 17 Jul 2009, 03:46

Ha! I knew I heard the signature tone of the 633!

I was playing with a Frequency Analyzer clone on breadboard, and I was able to get clear bell-like tones very easily. It sounded very much like the bell tone you hear at the beginning of the Randy's Revenge clip. The only thing the Frequency Analyzer doesn't do is the tremolo thing, but with a different oscillator, that wouldn't be hard to take care of. That function generator chip the Frequency Analyzer uses is too damn expensive anyway...

Whoismarykelly · Post by **Whoismarykelly** » 17 Jul 2009, 04:29

The FA uses a sine wave AFAIK but the LFO doesn't go below the audio range. Im sure if you tweaked the LFO caps and put them on a switch you could get it to do tremolo.

soulsonic · Post by **soulsonic** » 17 Jul 2009, 05:30

Frequency Analyzer doesn't use a standard LFO oscillator setup, it uses an ICL8038 function generator. Looking at the datasheet, yes, it can do very low frequencies, but for any DIY thing, I would recommend something else for the carrier signal oscillator because the 8038 is obsolete and expensive/hard-to-find.

The schematic from Experimentalists Anonymous is probably a great starting point, but that kind of oscillator doesn't do sine wave... though, I found that there isn't a dramatic difference in sound between sine and triangle; slightly more harmonics, but very subtle.

soulsonic · Post by **soulsonic** » 17 Jul 2009, 05:32

The sine wave oscillator from Moosapotamus' site would probably be something worth trying.

earthtonesaudio · Post by **earthtonesaudio** » 17 Jul 2009, 20:14

I want somebody to try this:
http://www.audioscientific.com/28_Simpl ... lters_.jpg

soggybag · Post by **soggybag** » 18 Jul 2009, 01:15

The AD633 needs +-15V to operate well. The Randy's Revenge description claims it runs on 9V. It could have a voltage doubler. Then again maybe it uses something different.

earthtonesaudio · Post by **earthtonesaudio** » 18 Jul 2009, 03:03

Hm... you could use one of the charge pump ICs, add another oscillator close to it in frequency, and make a wide-range beat frequency oscillator out of it. That would be fun!

Whoismarykelly · Post by **Whoismarykelly** » 18 Jul 2009, 08:27

The RR does have a charge pump. I believe it says so on the web site.

soggybag · Post by **soggybag** » 18 Jul 2009, 17:06

I think the Fairfield site says only that the Randy's Revenge is "Powered by +9V power supply".

Whoismarykelly · Post by **Whoismarykelly** » 18 Jul 2009, 21:01

soggybag wrote:I think the Fairfield site says only that the Randy's Revenge is "Powered by +9V power supply".

Youre right I must be thinking of a post from a forum somewhere. Either way its got headroom and thats not happening at 9v.

salocin · Post by **salocin** » 19 Jul 2009, 07:47

Found at HC- posted by the man himself:

I'm using the ICL7660 to get +-9V. I wasn't getting good results (if none at all) operating the modulation IC on a single supply.

Initially the plan was to use a split supply derived from a 15VAC adapter. I was a little skeptic about using a charge pump, what with the high frequency switching and all. Ends up it sounded just as good and much more convenient.

I experimented quite a bit with transformer-diode modulation. Some very nice sounds, but the frequency range and carrier suppression of the IC are what sold me.

I'm using the AD633, a little pricey but it does what it's supposed to do very well. I started with what was in the datasheets and worked from there. No real secret here. You should be able to get some good results, do you remember what the problems were?

I also tried the Gilbert Cell mixer. Worked but the transistor matching was too critical.

It runs off typical 9V adapters. No room for a battery in this one. Current draw is around 125mA

soggybag · Post by **soggybag** » 20 Jul 2009, 03:51

Very interesting. That's good info.

salocin · Post by **salocin** » 20 Jul 2009, 10:33

About to order some ICL7660. At a brief glance looks like a good substitute to MAX1044. Quite keen on a ring mod at the moment, but need +/- power supply for the AD633 (which I have a few of) and the ICL7660 now looks like a better (cheaper) option than the 1044.

soggybag · Post by **soggybag** » 21 Jul 2009, 03:17

From what I understand the 7660 is pin for pin replacement for the 1044, with lower quality specs. I think the 1044 clock at a higher frequency.

Barcode · Post by **Barcode** » 21 Jul 2009, 04:07

i believe the main difference is that the max1044 has a frequency doubler to raise any power supply "whine" up above hearing levels.