Aion Blueshift Troubleshooting: Dry signal when engaged - Bad BBD's?

[DangYankee]

Hello Guys,

I'm super excited to find this website, I just finished this marathon of a build to find my pedal has the exact same issue as Philthy's build in this thread https://www.guitargear.net.au/discussion/index.php?topic=52185.msg593916#msg593916. I also posted this there, but the auto-mod message recommended creating a new post due to inactivity, so here we are...

Symptoms:
1. Bypass signal  - fine.
2. Engaged signal  - no chorus effect. Sounds just like the bypassed signal with maybe a tad fewer highs (or more lows).

I have traced the circuit with an audio probe and have found that my signal "dies" at both of the BBD chips. I have signal from my guitar going into pin 3 of both BBD's, but nothing on pins 7 or 8 of either chip which I believe to be the output pins.

I am using a pair of MN3102 + MN3207 chips that I purchased on Ebay from vendor named diy-electronic. They had fairly good reviews, so I wasn't too concerned about the quality of the parts until now. Is it possible that I received a faulty pair of BBD chips? I ended up purchasing a new set of cool audio clone chips from Smallbear and will try those when they ship, but I will be waiting a week and my mind will continue to dwell on this project haha... I'm just wondering if there might be another issue I am overlooking.

My voltages are as follows: All measurements were taken with all switches in the down position. (Exclamation marks denote where my voltages differ, * shows fluctuation.)

IC1 (OPA2134)   IC2 (NE570)   IC3 (MN3207)     IC4 (MN3102)   IC5 (TL072)    IC6 (TL072)   IC7 (TL022)
4.6                    1.0                0                        6.6                   4.0-5.0*        2.8-4.0*        0.6-6.0*! (This fluctuates fairly quickly, almost like a switch, its either 0.6 or 6.0 in 1.5 sec intervals)
4.6                    1.8                3.16                   3.1                   1.1-1.5*        3.3                3.0
2.3!!(why half?) 1.8                3.38                   0                      1.3-1.9*        3.3                2.2-4.2*
0.0                    0                   6.14                   3.2                    0                   0                   0
4.6                    1.8                6.58                   4.8-5.8*            3.3                1.2-1.9*        3.3
4.6                    1.8                3.15                   0.8-1.8*            3.3                1.1-1.5*        3.3
4.6                    3.2                4.0                     4.0-5.0*            3.0-4.0*        4.2-5.0*        2.6-4.1*
9.3                    1.8                4.0                     6.1                    6.3                6.3               6.66
                         1.8
                         1.8
                         1.8
                         1.8
                         9.3
                         1.8
                         1.8
                         0.12
                         

IC12 (OPA2134) IC11 (NE570)   IC9 (MN3207)     IC8 (MN3102)  OPTO (H11F1)
4.6                    0.95                0                        6.5                 1.3
4.6                    1.8                  3.1                     3.0-3.1*          0
4.6                    1.8                  3.4                     0                     0!!!
0                       0                     6.1                     3.1-3.2*!         4.25
4.6                    1.8                  6.56                   4.6-5.4*          3.8
4.6                    3.0                  3.1                     .8-1.8*            4.25
4.6                    3.0                  4.6!!!                  4.3-4.9*
9.3                    1.8                  4.6!!!                  6.1
                        1.8
                        3.0
                        3.0
                        1.8
                        9.4
                        1.8
                        1.8
                        1.0









Any help would be appreciated!

-DangYank

[Cybercow]

Coupe of points . . . .

1) eBay specialized IC purchases, (especially from China), are a crap-shoot at best. They could very well be fakes or bad pulls and cleaned up. China sellers have been known to sand off the markings and re-ink them for whatever they want.

2) But let's assume they are good and\or genuine MN3102 + MN3207 chips . . . . if they are the real deal and in working order, those trims pots for setting the bias each have a very narrow sweet-spot. And according to the Aion BlueShift builddocs, an o-scope is needed to get those trimmers dialed in correct. Kevin also states that it can be done (near-passably) by ear, recommends an o-scope. I didn't see in your post that you had tried setting them in any fashion, so I have to ask: Did you try adjusting the trimmers to acquire a proper bias for each chorus section? He has a full description of biasing with your ear and o-scope on page #7 of the build docs.

Short of a biasing issue, when the new chips arrive, they will need to be re-biased when you swap them. If the new one(s) work, at least you can request a refund on the ones you got from China.

Good luck!

[DangYankee]

Thanks for the help!

1: I have been having pretty good luck from the-bay lately so I decided to roll the dice on those chips. I have since ordered genuine Cool Audio chips from Smallbear and am awaiting their arrival. Hopefully, they plug and it plays!

2: I should have clarified this in my original post... I have biased the BBD chips to his suggested baseline setting, which supplies 3.4v to pin 3 of each BBD. This setpoint has been documented to achieve an acceptable chorus effect in several other builds with most people just leaving it there without additional precision. Further biasing with an o-scope or by ear is necessary to remove potential distortion from the effect, not to create the chorus effect. I have access to a programable o-scope at the electronics lab at work and do plan to properly bias it once I can verify proper functionality at rough settings.

Again, Thanks for the help! I will update this post once the new chips arrive... Any ideas on why the voltage is so low on pin 3 of IC 1? Reports from other builds show that it should be closer to 4v, but mine is 2.3v. I have measured the voltage on either side of R5 (1M) and am getting weird numbers after the voltage divider.

[Scruffie]

It's your meter, it has an internal resistance of 1M, hence the exactly halve voltage.

Your voltages look reasonable but getting reputable supplier chips is the only way to be certain.

Just because some people had luck with a specific bias voltage, doesn't mean that will always work out to be the case, why not try audio probing the BBD output pins and adjusting it?

[DangYankee]

I didn't think about biasing with a probe! That's a good idea. Thanks again!

[DangYankee]

Update: the new chips arrived.

I pulled the old ones out, popped the genuine ones in, and it fired right up! I've only roughly biased it using the voltmeter and it sounds fantastic! I plan on biasing it with a scope this week and can't wait to hear it after a proper setup... Thanks again guys, that's what I get for trying to be cheap haha.

[DangYankee]

Oh... and here is the obligatory completed photo.

[danfrank]

Nice! I really like the color of the box.

[Philthy]

nice colour - hope the LED is purple too

[gordo]

Very nice build, top notch graphics.  It's maddening when you get tangled up troubleshooting chips. It's nice to have the luxury of having known goods ones and THEN go bargain hunting.  Glad it all came together.