Erica Synths DIY BBD Delay/Flanger

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Girts23
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Erica Synths DIY BBD Delay/Flanger

Post by Girts23 » Sun Oct 28, 2018 5:47 am

Dear colleagues, we realized, there are very, very few BBD (bucket brigade delay) chips based DIY modules available, so we decided to fill the gap. Here's Erica Synths BBD Delay /FLANGER! The module is designed to provide variety of effects from flanger to delays with adjustable flavors and plenty of modulation possibilities. It utilizes 4092 stage BBD, has built in LFO with selectable shape and dedicated LFO output, delay time CV input with an attenuator, selectable feedback overdrive (you have lots of customization available here) and feedback Send-Return connectors, so you can apply external effects on feedback signal. Maximum feedback settings put the module in self oscillation, so it can be used as an experimental sound source, as well.

Image

And here's a demo by Synth DIY Guy:

[video][/video]

Even the basic kit comes with BBD chips included. Check it out:
Erica Synths DIY BBD

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ronski
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Post by ronski » Sun Oct 28, 2018 7:24 pm

Cool, I'd love to build it and give it a go :)

{EDIT}

When will this be available at thonk?

Would be great if the LFO would have a CV input, I assume this was tricky?

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Monobass
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Post by Monobass » Fri Dec 21, 2018 8:01 am

Thonk - CLICK HERE - Modular Synth DIY + Eurorack Accessories Store

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Post by ehafh » Fri Dec 21, 2018 10:56 am

Will this be available at Synthcube or Modular Addict in the states?

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Post by talfred » Tue Dec 17, 2019 6:38 am

Hello,

I need a little help with this module. Bought the full kit from thonk this summer and finally got round to build it now, but I can't get sound output. I'm thinking the problem might have something to do with the feedback overdrive circuit. I'm not so experienced so I can experiment with different ways to do it, and the manual was a litte bit shady regarding this part. And there are minor differences between different revisisons of the boards enough to confuse me. I don't have an oscilloscope, but I have multimeter.

I got signal coming from the LFO output, so it's not totally dead.

Here are some closeups:

Image

Image

Image


In the manual, I think it says that the resisitor for drive gain is optional, so I haven't put anything in there. Is that the problem? And what do I put in there if so?

There are a few pieces left after building: one 10k resistor, one 104 capacitor and two diodes


Thanks everybody!

Tommy

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Re: Erica Synths DIY BBD Delay/Flanger

Post by talfred » Wed Jan 15, 2020 4:32 pm

Anybody?

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synthetek
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Re: Erica Synths DIY BBD Delay/Flanger

Post by synthetek » Wed Jan 15, 2020 5:46 pm

I think you need to populate R71 Drive Gain, Its saying the value you use depends on what diodes or LEDS you use,

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Re: Erica Synths DIY BBD Delay/Flanger

Post by kamielsd » Fri Jan 17, 2020 4:23 am

I recently got this working, after installing a 33k resistor at the drive gain location, my first trial session resulted in seeing the lfo led go on and off, being able to adjust Its frequency, and, as a grande finale, just at the moment I pulled out A cable going into the mixer in order to connect that to the output of the delay, A very loud “peng”-ish sound - apparantly I reversed polarity of 1 of the 47 uf caps on the powerlines. :sb:

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Re: Erica Synths DIY BBD Delay/Flanger

Post by ixtern » Fri Jan 17, 2020 5:57 am

1. In the assembly document there is stated that recommended values are 33k for R71 and 100k for R72 (but I think this is a mistake as on schematic R72 has value 10k).
2. Assembling such complicated module without a scope is like playing a russian roulette.
3. Please notice that Controls pcb is not very well designed - metal back legs of many pots are placed directly on different tracks, not only on the ground plane. Tracks are protected by tiny soldermask but it may not be enough and in some cases there may make shorts. I always cut back legs in such cases (partially or whole), as in attached photo.
4. As I am still assembling my BBD Delay/Flanger module, I can't say much more at the moment.
IMG_20200117_114202.jpg
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Re: Erica Synths DIY BBD Delay/Flanger

Post by quollism » Tue Mar 10, 2020 11:01 am

I got stuck with a non-working module for about a month and a half. (I built the 106 Chorus eurorack as well and that waited over a year for a replacement BBD before I heard it make any sound. I have crappy luck with BBD-based modules!) I even ended up buying a oscilloscope specifically to troubleshoot this build and get it working, even... so hopefully these fix notes help!

Like you I also thought the feedback overdrive circuit was broken but once I got it fixed, I found out the feedback overdrive only comes into play when the BBD is clocking, even when using the Insert Return. Once I got the scope I found that there was no action on the BBD's clock at all. The schematics show the clocking signal for the BBD clock originate from of pin 11 of the NAND logic IC on the back (IC code is CD4-i-am-too-lazy-to-look-it-up).

One of the transistors just above that IC had a shorted collector and base - the big clue was the voltage difference between the near and far side of the 56K resistor which feeds into the transistor bases. (Schematics are awesome.) The voltage that's meant to pass through that resistor is meant to hit the base of the transistors and causes that part of the circuit to output a clock signal. Instead, the transistor with the short across its base and collector was STEALING all that lovely voltage and sending it to ground through another resistor. Very naughty. The lack of voltage going through the whole circuit stopped it from oscillating.

Once I replaced that 2N3904.. it was all good. Hah. Like hell it was...

I had to replace yet another transistor on the control board, the one right next to the LFO. Again, the dead transistor was holding one side of the LFO at a high voltage compared to ground as well - current wasn't flowing, so the LED wasn't lighting up. So I replaced that 2N3904 as well.. but once I had those sorted and wiggled the long boy BBD around a bit in its IC socket.. sprayed some isopropyl on the pin headers.. THEN it came good. Now I'm afraid to move it in case it starts oozing purple ctoplasm or something.

The schematics and scope really helped to troubleshoot and complete the build. A sawtooth seventh chord out of Chord Organ sent through this module with some spring reverb on the insert and delay for colour is like having my old Solina chorus back :)

Troubleshooting tips follow.

With power off

* Test continuity across the LED lights in the diode circuit with your multimeter, reverse polarity across one LED should make the other one light up - not that useful for troubleshooting but fun to see :)
* Check for shorts between the base and collector/emitter of the transistors

With power on

* Look up the pin-outs for the ICs and test all the ground and supply voltage pins - make sure op amps are getting their +/- 12V rails on the appropriate pins, make sure ground is reading as ground, etc
* Look up the pin-out of the NAND logic IC and probe the in and out pins to make sure it's behaving logically
* Plug an audio signal into IN and make sure that centre dry/wet pot works
* Plug an audio signal into the INS RET, turn the dry/wet knob all the way WET and make sure the Colour switch at the top right of the panel changes the timbre of the signal
* Check voltage between pins 3 (ground) and 8 (Vgg) of the BBD clock - it should be about 5.6V
* Make sure Clock 1 and Clock 2 of the BBD clock IC (pins 2 and 4) are the "opposite" from one another - if Clock 1 is high, Clock 2 should be low
* Make sure Clock 1 and Clock 2 are getting to the BBD IC

The BBD IC (that weird long IC with only eight pins) and BBD clock IC (normal sensible eight pin IC) are respectively a BIG chain of sample and hold circuits joined together and a clock signal generator which makes the chain pass its charge along. If the BBD IC doesn't get a clock signal, it holds whatever voltage it last sampled on its output pins. So probe the BBD IC's two output pins and make sure they're outputting a steady voltage.

I found out that If you short pins 6 and 7 of the BBD clock (ALTHOUGH YOU DO SO AT YOUR OWN RISK) it makes the BBD clock oscillate at 6MHz and with an active input signal that might change the voltage of the BBD IC output pins and possibly the respective high/low phases of the BBD clock IC clock outputs too. (AGAIN, YOU DO THIS AT YOUR OWN RISK. It is just a weird thing I noticed.)

Good luck and I hope you get yours working!

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Re: Erica Synths DIY BBD Delay/Flanger

Post by JakoGreyshire » Fri Jul 24, 2020 1:53 pm

The BOM doesn't state if the caps are film or ceramic. I've seen different pictures of builds where there are film caps in various locations. Can I get an explanation on this? Does it matter if I use only ceramic caps?

It would also be cool if we could get some feedback on different diodes people have tried.. I'm going to put some UV LEDs in the diode LED pairs to see what that will do... I guess at that point I'll be too lazy to remove them and try out different LEDs..

Maybe i'll solder in some sockets so I can switch them out easily.....
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Re: Erica Synths DIY BBD Delay/Flanger

Post by ixtern » Sat Jul 25, 2020 8:45 am

JakoGreyshire wrote:
Fri Jul 24, 2020 1:53 pm
The BOM doesn't state if the caps are film or ceramic. I've seen different pictures of builds where there are film caps in various locations. Can I get an explanation on this? Does it matter if I use only ceramic caps?

It would also be cool if we could get some feedback on different diodes people have tried.. I'm going to put some UV LEDs in the diode LED pairs to see what that will do... I guess at that point I'll be too lazy to remove them and try out different LEDs..

Maybe i'll solder in some sockets so I can switch them out easily.....
In audio signal path there should be film capacitors (C22, C26) and/or NP0(C0G) ceramic (C27, C28). C19,C20 and C34 also (film or C0G/NP0). Others may be ceramic X7R.
As for LEDs.. this part of effect is useless for me so I didn't tried too much. Maybe for guitar is cool but not for synthesizer.

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Re: Erica Synths DIY BBD Delay/Flanger

Post by JakoGreyshire » Sun Jul 26, 2020 3:36 am

cool! Thanks ixtern...
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Re: Erica Synths DIY BBD Delay/Flanger

Post by JakoGreyshire » Mon Jul 27, 2020 11:12 pm

From the assembly manual and other people's pictures.... Are C36 and C37 also NP0 (C0G)?

Also... side note.... are the LEDs in the feedback circuit backwards in Talfred's post above? (circa Dec. 2019) That could be why it wasn't working. On top of the Drive resistor missing...
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Re: Erica Synths DIY BBD Delay/Flanger

Post by JakoGreyshire » Mon Jul 27, 2020 11:15 pm

I'm probably just going to make all the ones ixtern listed Film caps...
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