I have been itched to get hands on That 80 Rack Chorus. I'm currently working on learning the design behind it with a hope to recreate it or even design a better one. I need some help on figuring out the block diagram of the Fulltone TERC to start. Here are some pictures of TERC that I have pulled out. It sounds instant Landau/Huff/Lukather for sure. Also, it is based on TSC-618 or CS-5 Songbird Dytronics which is a legendary unit.
(https://i.ibb.co/zHMgZSy/374-AEDE1-F2-A1-41-F8-A25-A-0-C4954602-D28.jpg) (https://ibb.co/2Y9rdjD)
(https://i.ibb.co/0ZsqW5R/03-E5509-E-E7-D1-4366-9-F39-A9-C3-B2404-DD8.jpg) (https://ibb.co/jGJhxtP)
(https://i.ibb.co/5WxXc15/AE35-A410-DEFB-4-E79-9-A15-DB9812-F59-BCF.jpg) (https://ibb.co/1fJY209)
(https://i.ibb.co/VVPGwyr/6-B8-F77-B7-B09-D-4-C2-B-B805-5221-F638087-B.jpg) (https://ibb.co/jh1YJKB)
(https://i.ibb.co/mBp4C9T/E05532-BC-3202-4-B90-B091-A13356-CB9866.jpg) (https://ibb.co/PYkgZcj)
(https://i.ibb.co/YRGZNFz/1-C9-EB51-C-56-B5-4-C94-B71-B-4911-BF6-FC30-E.jpg) (https://ibb.co/QbGdJ32)
(https://i.ibb.co/M60mCCr/E4-DD9-D06-2887-40-A8-8057-6-B3-F4057108-A.jpg) (https://ibb.co/Vm4sqqR)
(https://i.ibb.co/c2FMvLD/9-A44-D26-B-6-C09-4-DD1-B4-E0-1-F062-DD2052-E.jpg) (https://ibb.co/WByq3tg)
It looks like there are some Op amps and BBD ICs. Three BBD for sure with share intensity/speed. The chorus part I think something can be tweaked with proper calibration like flanger. Also, there's VU meter to show the output levels L/R. The input can be instrument or line. It looks like if it's line instrument then it goes to buffer.
If anyone can chime in the idea of building great TSC then I would appreciate the help
There was one more Tri Stereo Chorus clone, The Wave, by an Italian company (Shiva/Red Seven.) They built 35 and then moved on to other things: https://www.redseven-amplification.com/the-wave-t-a-m-c/ . No schematics or internal pics, unfortunately. They say their Lil'Wave chorus pedal (still made) is a derivative and uses one of the three delay lines in a mono format. For a DSP version, Eventide's TriCeraChorus is supposed to be pretty good.
Would the Jurgen Haible Triple Chorus be a starting point? Pretty sure the schematics are still out there. Not sure of the Fulltone unit would share the same blocks but it's pretty well documented last time I was marveling at it.
Quote from: mauman on January 10, 2023, 04:32:51 PM
There was one more Tri Stereo Chorus clone, The Wave, by an Italian company (Shiva/Red Seven.) They built 35 and then moved on to other things: https://www.redseven-amplification.com/the-wave-t-a-m-c/ . No schematics or internal pics, unfortunately. They say their Lil'Wave chorus pedal (still made) is a derivative and uses one of the three delay lines in a mono format. For a DSP version, Eventide's TriCeraChorus is supposed to be pretty good.
Mike, I contacted Red Seven and they have no Shiva left. If they have, then I'd love to get that. I think that is also built based on Dytronics/Chuck Monte design. I talked with Chuck last year and he said that it's really hard to find one and he sold his last unit last year. He is retired and doesn't recall any info related the TSC. The best luck to recreate it or study the design will be through TERC or something similar. I have Eventide TCC which is great and that is currently used in my Dann Huff's rack. However, it is still big mystery to me to unveil TERC or TSC.
Quote from: zombie_rock123 on January 10, 2023, 04:57:49 PM
Would the Jurgen Haible Triple Chorus be a starting point? Pretty sure the schematics are still out there. Not sure of the Fulltone unit would share the same blocks but it's pretty well documented last time I was marveling at it.
This is good info though not really TSC. The concept theory is there. Here are some couple references that I got so far
https://gearspace.com/board/so-much-gear-so-little-time/980440-any-one-know-how-make-tri-stereo-chorus-effect.html
https://www.freestompboxes.org/viewtopic.php?t=30909
In 2012, LaceSensor also interested with the same topic. I'm not sure if he got it or he dropped the effort due to he found something else
https://www.madbeanpedals.com/forum/index.php?topic=4942.0
Any idea what the vacrols are for? That and the number of trim knobs are intriguing.
Quote from: Bio77 on January 10, 2023, 07:25:01 PM
Any idea what the vacrols are for? That and the number of trim knobs are intriguing.
The trimmers are intended for calibration. There are certain frequencies to get that schmo which it can definitely get calibrated by reading the voltages or look over the signals on the scope.
For the vactrols, that I have no idea. Again, still mystery to me.
Yeah, for the trims, looks like the six around the BBDs are clock freq and bias for each 3007, 3101 pair. The two at the front and the other one, I have no idea. The vacrols, seriously, no idea ;D Looking forward to seeing this develop.
There are a few short threads on the original TSC over at fsb.org, search there for "Tri Stereo Chorus." One has some interesting details cut & pasted from other threads on harmonycentral and Reddit.
Quote from: mauman on January 10, 2023, 08:11:26 PM
There are a few short threads on the original TSC over at fsb.org, search there for "Tri Stereo Chorus." One has some interesting details cut & pasted from other threads on harmonycentral and Reddit.
That would be this link https://www.freestompboxes.org/viewtopic.php?t=30909
There is another resource that explaining how chorus BBD works but I can't recall it. I'll keep research on that. The best way to trace is to use photoshop (I guess) and start to match the top and bottom layers. After that, then I can work on the schematic. Once the schematic is complete then I can study more the concept behind it. It'll take some time for sure.
Looks like the three chorus sections are identical so if you trace one you get them all. The vactrols are might be for the three intensity knobs if I'm guessing. Taking the output of the LFO to split it to the three clocks maybe?
Or do they use the vactrols for bypass similar to how Fender and Mesa used them for preamp switching?
Quote from: madbean on January 10, 2023, 09:40:14 PM
Looks like the three chorus sections are identical so if you trace one you get them all. The vactrols are might be for the three intensity knobs if I'm guessing. Taking the output of the LFO to split it to the three clocks maybe?
That is correct. The chorus section looks like are the same with different calibration
(https://i.ibb.co/P9Vyp24/CD00-E432-E853-4-E64-924-C-A118751-E5262.png) (https://ibb.co/4Y0LybM)
Just as a total aside, I put in quite a bit of work last year on a DC-2 implementation using the PT2399. I got it sounding pretty good but in the end decided it was probably too many parts to warrant it (over an FV-1). I wonder though if that idea could be expanded into the TriChorus type thing and then come up with a solution to offset the LFOs from each other.
I read some of the stuff on FSB and one thing I'm not clear on is the third chorus circuit. Is that output being fed to the Left and Right chorus inputs? Or, does it run in parallel with them?
Is that output being fed to the Left and Right chorus inputs? Or, does it run in parallel with them?
In general, I think it will run in parallel with Left and Right. There are two modes that you can stack them together as well. I'm still in the process tracing the board. Just had to do more photoshop and put them on transfer paper.
FYI there was an American company that made a Tri Stereo Chorus clone:
http://www.rtelectronix.com/pThreewaychorus.htm
I have one, but have never ABed it against the TERC, which I also have
Quote from: SugarKeys on January 29, 2023, 11:34:04 PM
FYI there was an American company that made a Tri Stereo Chorus clone:
http://www.rtelectronix.com/pThreewaychorus.htm
I have one, but have never ABed it against the TERC, which I also have
I heard about these guys. It's gotta be rack unit though to get that schmo lol
Quote from: fair.child on January 10, 2023, 10:55:55 PM
Quote from: madbean on January 10, 2023, 09:40:14 PM
Looks like the three chorus sections are identical so if you trace one you get them all. The vactrols are might be for the three intensity knobs if I'm guessing. Taking the output of the LFO to split it to the three clocks maybe?
That is correct. The chorus section looks like are the same with different calibration
(https://i.ibb.co/P9Vyp24/CD00-E432-E853-4-E64-924-C-A118751-E5262.png) (https://ibb.co/4Y0LybM)
those trimmers adjust the DC offset going into the BBDs and adjust the center frequency of the VCOs for the clock oscillators. Same as the TSC.
The optos are for the manual LFO for adjusting the frequency and to make it a sine wave oscillator. Also same as the TSC.
I'm just curious to know if any progress has been made on this?
I have a TERC and recently lost the left output. I've been doing my best to chase the signal through each of the three "bucket paths" and all looks good, but one of the 4558's (U7) near the output has 7.5V on the B output (pin 7). My gut tells me that one of the 5457's failed, but a schematic, or even that section of a schematic would be helpful before I feel compelled to pull up the board.
Fulltone hasn't bothered to respond, despite that this unit should still be under warranty.
EDIT: Found the issue...U7 was bad. Replaced it and it's all good now. Still wouldn't mind a schematic if there's one out there though. Thanks!
I'm glad yours is working now. I got busy with other stuff these days. After NAMM this year, things are going busier. I do have half-baked schematics but they aren't complete. Mike Fullerton was there at the NAMM show and he said he won't making TERC in the future.
Thanks, I'm glad to having it working again too but disappointed that Fulltone never responded. I guess that the new manufacturing agreement with them probably also means that any warranty work is also out of the question. I wonder what's going to happen to all those MN3007's he has?
Prior to fixing my TERC, I fixed my TC1210 which turned out to have a faulty BC547 AND a faulty 4013 on one of the Delay Cards. The experience inspired me to attempt to reverse engineer the calibration process and redesign the card to work with a couple of mn3007 chips rather than the impossible to find mn3010's. It's a work in progress, but could ultimately lead to recreating the 1210.