Building the Echo Base PCB

[Sanguinicus]

Well I attempted to box up the circuit board and hit a problem. The Mod speed knob doesn't work now and the LED no longer flashes. After digging around here I've replaced the TL027 and still have the same problem, reflowed basically every joint on the board (again!) and checked component values paying particular attention to the parts around the LFO opamp and the BC560 on the way to the LFO. I'm pretty bummed about this now. Any suggestions?

I also found removing the opamp doesn't do anything, it just turns the LED off. Input voltage is a good 9V.

Voltages for the opamp:
Pin 1: 5V
2: 5V
3: 5V
4: 0.7V
5: 3.9V
6: 5V
7: 2V
8: 7.3V

[slacker]

Your pin 8 voltage is too low, it should be at least 8 volts, the LFO stops working if the voltage drops that low. If you're using a battery replace it with a fresh one. If not check the connections to pin 8.

[thanal9999]

Hello... I just finished building the echo base and I have an issue... It is self oscillating constantly by itself... Is there an obvious solution...? I will start debugging but since this is my first delay project I am just asking if there is something obvious that I might have done wrong... Thank you in advance for all the help...

[jez79]

Hello... I just finished building the echo base and I have an issue... It is self oscillating constantly by itself... Is there an obvious solution...? I will start debugging but since this is my first delay project I am just asking if there is something obvious that I might have done wrong... Thank you in advance for all the help...

Maybe you're testing it with the feedback/repeats set very high?
Maybe check connections and components around the feedback pot

[Sanguinicus]

Your pin 8 voltage is too low, it should be at least 8 volts, the LFO stops working if the voltage drops that low. If you're using a battery replace it with a fresh one. If not check the connections to pin 8.

Tested everything, took out the resistor to be sure it was 220R and it is. 8.9V input and still got nothing. The 220R is dropping 1.8V across it. Obviously too high.

[thanal9999]

Hello... I just finished building the echo base and I have an issue... It is self oscillating constantly by itself... Is there an obvious solution...? I will start debugging but since this is my first delay project I am just asking if there is something obvious that I might have done wrong... Thank you in advance for all the help...

I noticed that I have misoriented the pots... Is this posible to cause the problem...? It doesnt oscillate only when the feedback and pot is all the way up (or down since I have put it the wrong way) but when it starts I cant stop it... 

[Taylor]

Hello... I just finished building the echo base and I have an issue... It is self oscillating constantly by itself... Is there an obvious solution...? I will start debugging but since this is my first delay project I am just asking if there is something obvious that I might have done wrong... Thank you in advance for all the help...

I noticed that I have misoriented the pots... Is this posible to cause the problem...? It doesnt oscillate only when the feedback and pot is all the way up (or down since I have put it the wrong way) but when it starts I cant stop it... 

So, if the Feedback pot is all the way down (or up) it doesn't self-oscillate, but if you begin turning the Feedback pot up from there slowly, does it instantly begin oscillating or does it start when Feedback is, say, somewhere around halfway? If it works that way, it sounds normal but you could lower the overall feedback amount by increasing the value of the 20k resistor right below the feedback pot.

[thanal9999]

Hello... I just finished building the echo base and I have an issue... It is self oscillating constantly by itself... Is there an obvious solution...? I will start debugging but since this is my first delay project I am just asking if there is something obvious that I might have done wrong... Thank you in advance for all the help...

I noticed that I have misoriented the pots... Is this posible to cause the problem...? It doesnt oscillate only when the feedback and pot is all the way up (or down since I have put it the wrong way) but when it starts I cant stop it... 

So, if the Feedback pot is all the way down (or up) it doesn't self-oscillate, but if you begin turning the Feedback pot up from there slowly, does it instantly begin oscillating or does it start when Feedback is, say, somewhere around halfway? If it works that way, it sounds normal but you could lower the overall feedback amount by increasing the value of the 20k resistor right below the feedback pot.

It starts oscillating The moment I start turning it... not even halfway... I resoldered everything... even changed all the ICs and some components but the problen remains... I sould check the voltages  but I havent done it yet...

[Sanguinicus]

Your pin 8 voltage is too low, it should be at least 8 volts, the LFO stops working if the voltage drops that low. If you're using a battery replace it with a fresh one. If not check the connections to pin 8.

Tested everything, took out the resistor to be sure it was 220R and it is. 8.9V input and still got nothing. The 220R is dropping 1.8V across it. Obviously too high.

Replaced the resistor with 120R, no change. So I shorted the connection and it works now. So strange. Any ill effects from shorting the connection? Do I need a tiny load there?

[Taylor]

Your pin 8 voltage is too low, it should be at least 8 volts, the LFO stops working if the voltage drops that low. If you're using a battery replace it with a fresh one. If not check the connections to pin 8.

Tested everything, took out the resistor to be sure it was 220R and it is. 8.9V input and still got nothing. The 220R is dropping 1.8V across it. Obviously too high.

Replaced the resistor with 120R, no change. So I shorted the connection and it works now. So strange. Any ill effects from shorting the connection? Do I need a tiny load there?

I believe that and the other 220R are there to isolate the dual opamp that creates the LFO from the rest of the circuit's power supply, to make it less likely that the LFO pulling current would cause ticking to get into the audio path. Shorting it removes this isolation so you're powering that dual opamp directly from the same supply as the rest of the circuit, so you might get some ticking, or not.

[slacker]

Replaced the resistor with 120R, no change. So I shorted the connection and it works now.

The fact it didn't work with 220R means there's something wrong with that part of the circuit causing it to draw too much current but I guess if it works fine with the resistor shorted then there's no harm doing it.

[Sanguinicus]

Interesting. Well I haven't done any extensive testing yet but it seems to be working pretty well. I'll post a photo of the finished box and the svg of the graphics shortly.

How does a resistor isolate the supply?

[Sanguinicus]

Some pictures and svg of the finished project

Inkscape SVG file: https://www.dropbox.com/s/8yn7df64h483i5f/ebd_new.svg?dl=0

Print the drill template to obviously drill the holes, print everything except the drill template and controls footprint layers to print the finished graphic.

The knobs are to suit the 1/4" knurled shaft 16mm pots. Got them off eBay out of China for pretty cheap. The toggles are sub miniature size. The LED bezel was bought of eBay also. Obviously change the graphics to suit your own controls. Don't mess with the pots too much as they're placed as close to the top as possible.

The toggles could probably stand to go down a few millimetres as they're almost touching the lugs on the pots.

[slacker]

Looks great, I like the layout of the controls.

[bluebunny]

Hey!  Similar theme:

   

[Sanguinicus]

That looks awesome!

[mwynwood]

Hi everyone - just a couple of quick questions about the MusicPCB board...

The LFO Switch
If the DEPTH and SPEED knobs are all the way down, is the LFO switch necessary?
Is that equivalent to having the LFO switched OFF, or is it more effective to use the switch?
I'm just trying to save some space...

Extra Holes
There are lots of extra little holes in the board... are these for modding or testing or something else?

[bluebunny]

Mine ^^ has no LFO switch.  As you say, if the depth is zero, then there's no need.  I can't see your picture (curse my employers!), but I guess you're referring to vias, which connect the top and bottom layers of the board.

[duck_arse]

I can see the board - yes, they are vias. complex tracks wander along the pcb top, then via a via, a plated-thru hole, continue wandering along the bottom of pcb (and sometimes, vise-versi). they are not for us to use.

[mwynwood]

Ah! That explains it!
Thanks guys, you learn something new every day