Echobase problem

[EOdy]

Hi guys. Would anybody be able to take a look at my Echobase readings and suggest what might be wrong?

There is a lot of noise. There's a general hum plus a 'helicopter' kind of noise that seems to be coming from the LFO as it gets louder if I touch the LFO speed pot terminals. Some delay is coming through, the level knob seems to work. Feedback all the way up makes makes it self oscillate but it distorts far more than you'd expect. The rate knob appears to work. The LED flashes with the rate of the LFO but the LFO makes no sound.

Source of the circuit (URL of schematic or project) = http://static1.squarespace.com/static/54696a3ee4b05a85cbfe56e5/t/5469759be4b05145d3fd695e/1416197531945/Echo-Base-build-PDF-updated-051810.pdf

Any modifications to the circuit? N

Any parts substitutions? BC549 instead of 2N5089 (I originally put a BC550 in the wrong way round. Bypass wasn't working and I traced it to this and swapped the parts. Now the bypass section seems to work)

Positive ground to negative ground conversion? N... I don't think so

What is the out of circuit battery voltage? = 8.6V (The circuit seems to eat batteries so this keeps getting lower as I'm testing. This is the level after testing the IC pins)

I'm suspicious of one the ceramic capacitor value, which appears to say 561 on it. It should be 470pf value. It's very hard to read and I don't have anything to measure it with.

I have the circuit wired up on a breadboard to test (I've checked and double checked the layout and connections, don't think the problem is there). The circuit is on MusicPCB printed circuit board. http://www.musicpcb.com/pcbs/echo-base-delay

IC PT23899
P1- 4.97
P2-2.48
P3-0
P4-0
P5-3.01
P6-2.49
P7-0.17-0.27
P8-fluctuating around 0.9- 1.1
p9-2.48
p10-2.48
P11-2.48
P12-2.48
P13-2.48
P14-2.49
P15-2.48
P16-2.48

IC4066
P1-2.83
P2-2.83
P3-0
P4-0
P5-0
P6-0.74 LED goes out when I probe here
P7-0
P8-2.5
P9-2.5
P10-2.84
P11-2.84
P12-7.3
P12-8.9
P13-8.57

TL072 (Left of board)
P1-4.97
P2-4.97
P3-2.48
P4-0
P5-4.95
P6-4.97
P7-4.98
P8-8.56

TL072 (Right of board)
P1-Fluctuates between about 4 and 6
P2-3.44
P3-4.97
P4-0.77
P5-3.75
P6-4.97
P7-Jumps all over the place between about 2 and 7. The range of this jump seems to be affected by the LFO rate knob.
P8-7.7

Are there any other points in the circuit where I should check the voltage? Thank you in advance!

[slacker]

Your voltages look Ok. Sounds like the LFO is working because the LED is flashing, so the problem is probably either with the wiring to the modulation depth pot or around the BC560 or whatever PNP transistor you've used. Make sure all three lugs of the depth pot are connected and that the PNP transistor is the right way round. To check if the helicopter noise is caused by the LFO, assuming you've used sockets remove the right hand opamp and see if the noise goes away. With this removed and the mod depth pot turned down all the other functions of the delay should work fine.

Welcome aboard

[EOdy]

Hi, thanks for the reply! I've removed the opamp and it didn't fix the problem. The helicopter noises seem to appear when the time knob is set to a longer delay time and this introduces some distortion to the sound as well.

The transistor is in the right way to match up with how it is on the PCB and it is a BC560.

How can I check the connections on the depth pot? There's continuity between the solder join on the underside of the board and the pot's pins.

I've also just noticed I've used a 50k pot for Time instead of 47k as on the schematic.

[duck_arse]

50k, 47k, makes no difference in our circuits.

[slacker]

It definitely sounds like a problem round the BC560, if you turn the mod depth pot all way down and set time to the shortest delay what sort of delay time do you get, it should be chorus like. If it's still a noticeable delay then there's a problem somewhere between the LFO and the PNP transistor. Double check all the components and connections between pin1 of UA1 (the opamp top right on the pcb) and pins 4 and 6 of the PT2399.

[EOdy]

You legend. It works. I reflowed the components you suggested and it sorted it out. Thanks very much for the help!

[slacker]

Cool, glad you got it working.