Blueshift - DC-2 dimension chorus : No bypass signal

[eh la bas ma]

Hello,

I have exactly the same issue as newjackruby in this post :

https://www.diystompboxes.com/smfforum/index.php?topic=124902.msg1186818#msg1186818

Unfortunatly, the conversation stopped before the solution could appear.

On my build there is a beautiful chorus when the circuit is engaged. In bypass there is almost no sound, like -20 db : the signal is just a faint shadow. Same with both mono and stereo outputs.

About component  orientation, I assumed the dot on the opto H11F1 was pin 1...

Both trimmers don't seem to have any obvious effect : Test points 1 and 2 show a steady 3.6 V and when i turn the trimmers the value move slightly to 3.5 V and get back to 3.6 V. And yet, the chorus sounds fine.

https://aionfx.com/app/files/docs/blueshift_documentation.pdf

Here are some pics, in case someone can spot something I missed :














Any help would be welcome.

[idy]

This has special bypass arrangement, or choice of arrangements, what Aion calls "stock" and "minimalist" options. Which did you use? Double checked the jumpers for that option?

[eh la bas ma]

I used the stock bypass. Jumpers are in place, you can see them at the bottom of the last picture.

I've been doing some testing and I think the trimmers might be ok : there is some distorsion appearing in the audio signal when i tweak them. I do have several chorus settings, everything sounds fine on the modulation side.

There is only this silence in bypass...

I tripple checked the wiring, the jumpers, the soldering, components orientations... I had a feeling about the outputs grounding but i can't find anything.

[Mark Hammer]

My standard advice: get an old toothbrush and something that dissolves flux (I use methyl hydrate) and clean the damn board.  Flux residue is not the "cause" of anything untoward, but has a way of hiding solder bridges and lousy solder joints.  Remove it and you may have an easier time tracing down whatever is impeding proper functioning of the circuit.

[eh la bas ma]

There is a signal when i touch  the pcb on the opto pads. I think my jumpers on the opto are wrong.

I put them on the component side, and it's not following the layout on the soldering side. I will try the other way.

[eh la bas ma]

https://aionfx.com/app/files/docs/blueshift_documentation.pdf
There is a diagram to set the jumpers on the opto coupler, p.15. I assumed it is shown from the component side point of view.

But there is a layout on the soldering side :



Which one do you think is  the real stock bypass layout?

[EBK]

I believe your jumpers are/were correct for stock bypass (i.e., the diagram shows component side).

That's how I built mine.


My guess as to your problem is a missing/broken ground connection.  Don't ask me where though. 

[eh la bas ma]

Solved !! I followed the silkscreen back of the pcb, as instructed :

"The silkscreen on the PCB shows the jumpers in "Stock" mode" , p.15

thank you very much for your help !

What a great chorus...

[eh la bas ma]

I am using TL072 for IC1 and IC12.

Do you think using two OPA2134 will make a noticeable improvement there ?

What do these chips do in the circuit ?

[Mark Hammer]

I doubt use of a "better" op-amp will contribute anything.  Why do I say this?

1) The delay path will aim for a very modest bandwidth, as most delay paths do, and won't include much gain, if any.
2) Most noise in the circuit will come from the BBD clocking, which the op-amp won't affect.
3) Most noise-control in the circuit will come from the compander chips included.

The 2134 is a good op-amp.  Save it for where its performance will "count".

[matopotato]

Any thoughts on choice of Stock or Minimalist bypass? Which one is "better"?
I understand that there is probably an element of taste, personal preferences etc, but ever so often there are two options where one is the actual preferred one and the other for a few builders who like something else for some reason...

[iainpunk]

Any thoughts on choice of Stock or Minimalist bypass? Which one is "better"?
I understand that there is probably an element of taste, personal preferences etc, but ever so often there are two options where one is the actual preferred one and the other for a few builders who like something else for some reason...

its an element of taste, yes.

i think that when people don't buy a kit, but build a perf or vero board, 99% would go for 'minimalist' true bypass, but if there is provisions on the PCB, stock or buffered bypass is better as long as you're not putting the pedal in front of a vintage style fuzz.

i personally would choose the stock/buffered bypass

[matopotato]

Thanks a lot @iainpunk, appreciate it!

[sharp01]

Stock or minimalist bypass - both are buffered in this case, so no true bypass here.

And by the way - test points on pcb are for use with oscilloscope. Measuring voltage is useless on them. Trim pots adjust voltage on the inputs of 3207 (leg 3) so you can measure voltage directly there. Test points are located after transistor buffers, which are isolated from bbd by capacitors, so their DC levels are not affected by biasing

[matopotato]

Thanks @sharp01