Choral Reef Oscillation

[bsoncini]

I just finished the choral reef and it is oscillating like a synth.  All the controls work.  speed, depth mix, etc all change the sound.  The switch completely changes the sound in all 3 positions.  If I set the speed slower it sounds kinda like a police siren.  My guitar signal is there also but the sound of the oscillation is much louder so I only really hear the guitar if I turn the mix pot all the way down.  I seems as I play with knobs and the switches that the signal is chorusing and flanging.

I have a mn3008 that I bought off here, but it is badged as a mn3005.  I have tried repacing all the ic's except the 3008.  I built another choral reef recently and a friend begged me to sell it to him.  So I could always ask to borrow that one to try another 3008 if need be.  But it seems to me that the 3008 is working.  If I play with the bias trimmer it seems to have some chorusing.  I have a signal on pin 10 that oscillates between 150khz-200khz

with an audio probe I never hear the guitar get to the 3008

Here are the voltages.  build doc on the left.  Mine on the right

8.7volts at the dc jack

TL2074
1  4.88      4.58
2  4.88      4.58
3  4.86      4.53
4   8.9         8.36
5  4.88       4.58
6  4.88       4.58
7  4.88       4.58
8  6.1         5.0
9  6.1         5.0
10 6.06       5.0
11  0            0
12  3.86       3.6
13  4.88       4.58
14   4.88       4.58

4047

1 8.11    7.3
2 0.115   0.04
3  7.06   6.4
4  8.26  7.35
5  8.26  7.35
6  8.26  7.35
7  0       0
8  0       0
9  0       0
10  4.16    3.7
11  4.16     3.7
12  0          0
13 8.14     7.3
14  8.25     7.4

mn3008
1 8.25   7.35
2  4.16  3.66
6  6.09  5.00
7  3.09  5.00
8  0       0
9 4.16    3.56
13  5.99  4.7
14  0       0

358
1 varies    varies
2 4.02      3.8
3 4.00      3.7
4 0           0
5 varies    varies
6 2.18      2.0
7 varies    varies
8 8.9        8.36

5087
c 0   0
b 4.88  3.5
e5.49   4.1

5088
c 8.9   8.35
b 8.86  8.32
e 8.25  7.74 





Any help is greatly appreciated and thanks in advance.

[Aentons]

It looks like your 47uf cap is in the wrong spot on the right side of your switch board.

[bsoncini]

It looks like your 47uf cap is in the wrong spot on the right side of your switch board.

If you look at the old vs new switching board connections the two 47ufs are flip flopped

[Aentons]

Ok, sorry... I haven't built one of the new boards yet. I built my Choral reef last night as well and it too is all jacked up. I just get crakles and pops when turn knobs

[bsoncini]

Ok, sorry... I haven't built one of the new boards yet. I built my Choral reef last night as well and it too is all jacked up. I just get crakles and pops when turn knobs

No problem.  It was a good idea.  It took me a minute to figure out where to put the capacitor.

[bsoncini]

I've been poking around a bit.  If I jumper from r21, the side that touches the c12 to r14 the side that touches the diode.  I get a chorus effect.  So seems like the mn3008 is good.  Maybe I'll have to just replace all the parts in between those two, one by one to see where I messed up unfortunately.  Not very easy to do rework on these boards.  Unless anyone else has an idea

[Aentons]

I took mine apart and found the issue was just that one of the footswitch connectors was touching the middle lug of the output jack... It's alive now. Whew

[bsoncini]

I took mine apart and found the issue was just that one of the footswitch connectors was touching the middle lug of the output jack... It's alive now. Whew

Glad to hear.  It really is a cool pedal

As for me, If I jumper r21 it works but justs distorts a bit.  I've tried to drop the the r21 3k3 to as little as 100 ohms and it still oscillates until I jumper it.  I'm gonna call it a day and see if anyone a bit smarter than me has any ideas and pick up again tomorrow

[blearyeyes]

I took mine apart and found the issue was just that one of the footswitch connectors was touching the middle lug of the output jack... It's alive now. Whew

Glad to hear.  It really is a cool pedal

As for me, If I jumper r21 it works but justs distorts a bit.  I've tried to drop the the r21 3k3 to as little as 100 ohms and it still oscillates until I jumper it.  I'm gonna call it a day and see if anyone a bit smarter than me has any ideas and pick up again tomorrow

I Will try this one later. Well I'll try the three I have been looking at for awhile. Sheesh.



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[bsoncini]

Glad to say that I got it working. I accidentally put a 3.3 ohm resistor for r27 instead of a 3.3k

One thing I don't get that I noticed from debugging this.  In the switching doc it says v- is just another bias voltage for the choral reef and that it should output 7.35v.  But unless I'm missing something it looks like a simple voltage divider of 8k2 and 10k which by my calculation should give around 4.95v for a 9v supply

[madbean]

You are absolutely right. That is an error on the switching doc...it should be about 5v. I will correct it now. Thanks for the catch.

[blearyeyes]

WOW! That saved me some heartache! Thank you for figuring that out! 
I guess it's time to start building It.