ECHO Base build issues. Could use some help!

[strungout]

Heyp!

So, I have an Echo Base on my breadboard. After a whole day on it, what I have is dry signal (good sound and clean),  I got the LFO working, a flashing LED and the mod speed pot works. Looking through the forum I probed pin 14 of the pt2399 and I get echo/repeats but it immediately turns into intense feedback, it's low and very distorted.


Here's some info:

I used this schematic from musicpcb: https://static1.squarespace.com/static/54696a3ee4b05a85cbfe56e5/t/5469759be4b05145d3fd695e/1416197531945/Echo-Base-build-PDF-updated-051810.pdf

I subbed the 2n5089 for a 2n5088. I didn't make any other changes or mods.

Voltages:

Vcc: 9.32
Vref: 4.99
GND: 0

7805
1: 9.30
2: 0.09
3: 5.05

2n5087
E: 0.01
B: 0.06
C: 0.59

2n5088
E: 0
B: 0
C: 8.92

IC1 - TL072 - LFO
1: 4.60 - 5.40     
2: 5.04
3: 5.04
4: 0
5: 4.60 - 5.60
6: 5.04
7: 3.80 - 6.50
8: 8.50 - 8.60

IC2 - PT2399
1: 5.03
2: 2.51
3: 0
4: 0.01
5: 4.09
6: 2.51
7: 2.29 - 2.35
8: 2.30 - 2.38
9: 2.50
10: 2.50
11: 2.50
12: 2.50
13: 2.50
14: 2.52
15: 2.50
16: 2.50

IC3 - TL072 - Buffers
1: 5.05
2: 5.05
3: 5.05
4: 0.01
5: 4.56
6: 5.05
7: 5.05
8: 9.32

IC4 - MC14066
1: 4.63
2: 4.63
3: 0
4: 0
5: 0
6: 4.42
7: 0
8: 1.78
9: 1.74
10: 4.63
11: 4.63
12: 8.93
13: 9.11
14: 9.32

I'm getting some mV on the ground. Not supposed to, it should be a flat 0V?

Here's hoping someone can trigger something to help me debug my build!

Thanks!

[strungout]

A little update.

After finding 2 dodgy connection, I now get echo and modulation, though I'll need to tinker with it some more.

I get a loud hum at the output, though... unless I use my probe, connected at the output jack lugs... Anyone have any idea why that might be? I used an n-p 1uF for the probe lead, is that what's taking the hum away?

[patrick398]

Sounds like your output jack isn't grounded properly. If it hums, but the audio probe doesn't, that's the first place i'd look. Jumper the output sleeve to a GND point on the pcb for a quick test, see if the hum goes away.

Patrick

[strungout]

Hey patrick,

I jumpered the output ground to my breadboard ground, no difference. Then I thought: maybe the first jack is broken or I mixed up the signal and ground lugs... Haha... Guess which... I tried another jack to confirm. The hum was significantly lower, but still present. Since that's the switch I'll use in my build I rewired the first switch and put it back in. No. Hum. At. All. Great! Now I can start messing around with the circuit and see what I can get out of it.

Thanks, man! Often for me, it takes an outside mind to trigger some thought that eventually leads to discovering the problem and it's solution. I get 'too close to see', I guess. 

[strungout]

Sigh.

The modulation effet comes and goes. After fiddling with the knobs and switches, it will appear, then fiddle some more to get echo and it disappears.

I've seen in this schematic: https://www.aronnelson.com/DIYFiles/up/Echo_Base_-_Stereo_Dual_Echo_-_complete_schematic.pdf where the 1uF cap is switched on and off (as mod on/off), contrary to the other schematic  https://static1.squarespace.com/static/54696a3ee4b05a85cbfe56e5/t/5469759be4b05145d3fd695e/1416197531945/Echo-Base-build-PDF-updated-051810.pdf where the 1uF is always connected in the feedback loop and the switching connects pins 1 and 2 of the LFO through a wire connection. That's not the same thing electrically, is it?

[patrick398]

The modulation effet comes and goes. After fiddling with the knobs and switches, it will appear, then fiddle some more to get echo and it disappears.

It's worth establishing whether this is a problem with the LFO section itself of the LFO's interaction with the rest of the circuit. Do you have a rate indicator LED hooked up?
If not, disconnect the LFO from the transistor into the PT2399 and stick an LED and current limiting resistor off pin 1 of U1 so you can visually see what the LFO is doing. Adjust the depth, speed, etc and verify it's working as it should.
If the LFO is working correctly but it's still intermittent when connected to the pt2399 i'd be looking at the transistor. Sounds like it could also be an intermittent connection on the breadboard itself.

[strungout]

The LFO was working. The LED was flashing and going faster along with the speed pot rotation. The control voltage didn't reach the pt2399.

But I figured out what the problem was: a bad pot! The Depth pot was almost dead (it's dead now) so moving the pot was like flipping a coin. Sometimes it lands on working, sometimes not When I replaced it, the delay came to life! And it's a very cool pedal, my thanks to Ian M.! Now I'm building other stuff while I'm waiting for the pcb from musicpcb. And I need to test all my pots just to make sure... yeah.

I appreciate you coming to help me out! Thanks!

[patrick398]

Glad you got it working!
More often than not i'm in your position, asking for help here, so happy to assist where i can