TC Electronics - Stereo Chorus Flanger [pcb+layout]  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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Fender3D
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Post by Fender3D »

Apply signal at effect input, you won't get signal @ C5 since it's op-amp's inverting input, hence a virtual ground.

Remember what I said before, you have to hard trigger the gain cell to get THD, then you must feed enough signal, but of course, you wouldn't exceed too much the overload level indicated by L2...

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Post by arjepsen »

Ok, back again.
After frying a couple of ne570's ( :applause: :slap: ) I've finally got my hands on a few more to fiddle with.

I found a tone burst program - and are using my sound card to send the signal to the breadboard.
If I understood correctly, I should make adjustments to VR4 untill the dc voltage between the tone bursts are as straight a line as possible.
It makes sense, since I can adjust the "slope" of the dc voltage with VR4.

However, I'm wondering what amplitude I should aim for on the input signal bursts??
I understand that the amplitude of the input signal should be big enough to "hard trigger" the gain cell, but the slope of the dc voltage changes when I change the amplitude even a little bit, so what should the aim be here?

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Post by Fender3D »

According to datasheet, the op-amp in NE57x's variable gain cell provides a drive signal which will be linear for small signals, but very non linear for large signals.
(We're talking about 0dBm input signal here)

I usually set my signal generator @ 100~125mV RMS when toying with pedals, here you have a gain control...
I'd suggest you apply ~100mV RMS @ pedal input, then raise the gain control until LED starts blinking, decrease gain slightly from there and set the trimmer as suggested before.

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Post by the_philth »

Not intending to bring up an old topic, but I searched the web for info on the SCF, and it brought me here, and I noticed my SCF is a tad different from most of the images posted within this absolutely fascinating thread.

I just wanted to add a couple of images for posterity -- so if some guy who wants to research his old 1979 SCF, he'll probably notice similarities in the images I'm posting.
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TCCF4L Card
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Post by DimebuGG »

Finally, I was able to finish redrawing almost everything in the layout based off of bajaman's Sprint trace. Ommitted the transformer though and replaced a dc jack instead. I've reviewed the layout several times as per schematic and baja's trace and it's good to go. Guess I already have a spare time to waste building this. :lol: Let's see. I've ordered boards already.
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Post by DimebuGG »

Boards arrived and populated the board, tested, tweaked the pots, trimmers and switch, and there is a light chorusing/flanging present somehow. However, status LED is not blinking. I thought I had a bad LM339. I replaced with a new one, still the LED won't blink, means the LFO didn't work. Swapped the transistors from BC547/BC557 to 2N5088/2N5087(I suspect them earlier thinking it might be fakes, whatever). Still no blinking . After an hour of debugging, I finally found out the problem. Now this is weird because when I accidentally put the multimeter's probe on either legs of D104(in between the toggle switch & Width control), there you go!!! the LED blinks now as I turn the Speed knob up and down. Again, I thought it might be a bad one, I replaced it but still the same - it won't blink unless if there is some kind of "antenna" attached to it or myself touching it using a conducting pin(ie from a resistor leg). Any idea what's going on?

Now, since the amount of chorusing is not really that strong. Initially I used these values; R8=39K, R11=47K, R18=9k1, and R20=33K. So I looked at the_philth's photo, (since calibration procedure is not really known), I used the same values in his photo for the ff: R8=36K, R11=51K, R18=13K, and R20=39K. And there you go, I set all the trimmers at 12o'clock BTW this time, I tested and IT WORKED!!!!! The chorus sound is very evident almost like, of course, an SCF :lol: (then tweaked the trimmers which I think works for me) BUT like I said above, some sort of antenna is attached to D104 to make the LFO work. Suggestions to fix this one?.
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IMG_20190321_222522.jpg
IMG_20190321_223215.jpg
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Post by DimebuGG »

Just an update. I replaced the status LED from blue to red and now the LFO is working as it should without the "antenna" thing. :applause:
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Post by DimebuGG »

Here's the box unlabeled
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Post by arivabox »

DimebuGG wrote:Here's the box unlabeled

Great and great work, congratulations on the new pedal!

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Post by bossman »

DimebuGG
Please where did you buyed these PCB's ???

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Post by DimebuGG »

bossman wrote: DimebuGG
Please where did you buyed these PCB's ???
These are from JLCPCB. I'll attached the gerber files later when I'll reach home.
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Post by pervyinthepark »

Gerbers PLS? xD

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Post by rafikian »

Yes DimuGG, hope you didn't lost your way home :cry:

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Post by iznogoud »

Wow, DimbuGG!!!! :applause: :applause: :applause: :applause: :applause:
Actually, I wasn't sure anybody would succeed at building one considering how tricky it is.
It'll have took 36 years before someone managed to build a copy.
Congratulations

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Post by FeVeR2112 »

DimebuGG wrote:
bossman wrote: DimebuGG
Please where did you buyed these PCB's ???
These are from JLCPCB. I'll attached the gerber files later when I'll reach home.

DimebuGG: Did you make it home yet? :D

Could you be so kind to post your gerbers (and/or sprint files)?

Much Appreciated!

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Post by jdub »

Hi all...so, for the past several months I've been hacking away at this thing using the images that Bajaman posted (many hours of photo editing to convert them to usable PCB images!) I've made boards and populated them, and now comes the troubleshooting. Once I get this thing working (getting only buzz so far), I'll be glad to post the materials I have- provided that Bajaman is OK with it- but I gotta get it functioning first. In order to do that, I need the IC voltages-all of them- from a working unit. Anybody able to provide these for me?

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Post by jdub »

Belay that request- after tracking down a ground issue, the bugger works! Still need to calibrate & tweak etc., but will post info once done and I have time. :thumbsup

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Post by iznogoud »

It's obvious that a full tutorial about calibrating it would be necessary : it's probably the worst thing to achieve with such a circuit.
Actually, the best thing would be a method to calibrate without serious equipment (oscilloscope, etc) as most of DIYers don't have more than a multimeter... Although IDK if it'd be feasible...

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Post by Lani »

Just thought I would add this to the thread. Trying to read that schematic was making my head hurt. Plus there are alot of values that are not on the original schematic. Its a hard circuit to draw out with all the different IC's. I'm in the process of making a SMD PCB to see if i can can fit it in a 125B with only one board... but I might be dreaming. If you guys see any glaring errors let me know and I will update schematic.
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Schematic_TCF - TC ELECTRONIC - TCF.pdf
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Post by jdub »

Hello everyone, sorry it took me so long to post this info- the pandemic has shifted priorities for me as I’m sure it has for you. Hope everyone is doing OK.

First, a couple of notes and part specs:
• First, the layout is derived from Bajaman’s pics earlier in the thread (thank you, sir!). I modified and made a couple corrections to the layout (notably L2 and C26, which were both backward), removing the transformer and relocating some parts on the top board. This was done because it’s impossible to find a round SPST switch like that in the original, so I altered this area on the top board so the alternate switch wouldn’t be pushed too far over to the side. I am including parts layouts for the modified boards. This layout can be run on an 18v DC or higher standard adapter (center negative).
• I used a 125-BB enclosure- a 1590B was too shallow.
• Standard long-pin PCB mount pots need their legs modified (narrowed vertically) to sit properly (with backs of pots on board). Alternatively, you could solder extensions to solder-lug or short-pin PCB mount puts.
• Corners of input and output jacks need modified or won’t fit into 125-BB because the corner supports of the enclosure are in the way (this was done on originals, too). Do not remove sleeve contact of output jack- slide out of housing and switch it to other side. If not there to make contact with jack sleeve, you will get noise.
• Circuit is grounded by sleeve lug of ext. bypass jack; be sure jack is solidly connected to chassis. Alternate grounding directly to chassis may be preferable.
• I put a 100k between tip and sleeve of output jack to eliminate floating ground.
• I mounted trimpots to underside of bottom board to allow access while operable. Obviously, this means they operate backwards.

Special parts:
For the board interconnects I used Molex 6p bottom-entry PCB receptacles for the top board (Mouser part # 538-22-14-2064 ), and Sparkfun long breakaway header pins for the bottom board, as these were the longest I could find (Mouser part # 474-PRT-10158 ). The boards are connected via holes drilled in the top board underneath the bottom-entry receptacles (see notes on parts layout). These parts ended up working great, but it is tricky getting them to line up when housing the completed boards, so care is needed. The Zener diode is a BZX79C4V3, also available from Mouser.

I’ve included a sized .pdf to print, as well as the PCB image files. Also attached is a modified panel image (again, thanks Bajaman!). I’ve also linked to photos of the boards, some with notes. I’ll try to get up some sound clips if I get time.

Not gonna lie, this is definitely not an easy build, and I undertook it simply for the challenge- if you want to do it for the effect itself, you might be better off buying one. Honestly, I have no calibration gear such as an O-scope, and simply tuned by ear and multimeter, which is not the proper way to do it. I think I got lucky, because it sounds rather good- however, the trimpots give very little audible effect, so if I ever get access to proper gear, I will try calibrating the right way.

I think that covers it, but let me know if you have questions. Special thanks to all who have posted in this thread, and of course to Iznogoud for beginning it in the first place. Your generosity, observations and hard work made it possible for a hack like myself to complete this truly challenging build. I hope that the materials here help anyone who cares to give it a try!


Build photos:










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top board layout.png
TC SCF top board.png
TC SCF bottom board.png
TC  front panel.jpg
bottom board layout.png
TC boards print.pdf
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