Building the Echo Base PCB

[mwynwood]

I've just finished my build, and I have a couple more questions....

It went into self-oscillation waaay too early in the pot range, so I swapped the 20k resistor for a 100k, and it seems better.
As described here: http://www.diystompboxes.com/smfforum/index.php?topic=98093.0

But my big issue is that I don't think my modulation is working!
My "LFO DEPTH" seems to just fine tune the delay time, and the "LFO SPEED" does nothing at all.
I have installed the LFO SHAPE mod, so I might try taking that off in the morning, to see if that helps.

I'd be encouraged to know if this is a problem other people have seen before, and it's a simple error on my part which is easily fixed!
Thanks again

[Taylor]

So, the LFO is made up by the TL072 on the right side of the board, and surrounding parts. First check the voltages on that IC, and post them here. Check over the soldering in that area for a short or iffy solder joint. Potential reasons it might not oscillate could be that there's a short across the 1uf film cap, the LFO SW pads are bridged, too low of a voltage at pin 8 of the '72, or a cold joint on one of the resistors in the feedback path around that IC.

[mwynwood]

 

Alright... well... it's working perfectly now.

I started getting voltage readings, and noticed that my battery was reading around 7-8 volts.
So, I changed over to a solid 9v wall wart, and now everything is getting enough power and it's all working as expected!

I have the "Kill Dry" mod, the "Dub Madness" mod, the "LFO Shape" mod, the "Modulation Switch", and the "Tails Switch" all doing their thing.

Thanks heaps for the help guys - now it's time to box it up!

[slacker]

Yeah that's a flaw or feature of the LFO, it stops working with a low battery.

[1878]

Is there a way of making the repeats distort ??

Thanks.

[Taylor]

There are diode clippers in the feedback path, but I can't think of a simple way to get increasing distortion with successive repeats. You could insert some simple distortion circuit between the feedback pot's wiper and the pad it's supposed to go to. Or maybe try changing the input buffer to be more than unity gain, which would distort everything more.

The PT2399 is pretty grimy already, so perhaps you could get where you want by just removing some of the filtering on the delay signal and hearing how distorted it actually already is?

[slacker]

You could do the opposite of the "humbucker mod" make one or both of those resistors bigger, that should make the PT2399 distort.

[1878]

Ooh ok. I've been using a distortion circuit after the EB with very good results, but my original signal was (obviously) effected also. I'm after that background wash thing that all the booteek pedals seem to charge an arm & a leg for at the moment. Funnily, they are the same sounds I couldn't help but achieve when I first started playing !?!?

I'm an avid single coil user so I'm not too sure the 47k mod would work for me. I will try it though cos it seems the easiest.

[Seven64]

busted mine back out, and now the stomp switch makes a loud pop that echo's through all the repeats.  could this be a grounding issue, as i just painted the inside of the box?

[trjones1]

Just finished my modded to the gills Echo Base after years of wanting to build one.  Huge thanks to Slacker, The Tone God and Aron for making this project possible.



However, does anyone else notice tone suck on the clean signal, both bypassed and with the effect engaged?  I used a TL072 splitter to send the input signal to the circuit board and the dry output, and it's really obvious the clean signal through the Echo Base loses some sparkle when compared with the dry signal.

[slacker]

That looks great, I like the dip switches very neat.
I've never noticed any tonesuck, but if you're getting some here's a couple of things you could try. The second opamp stage cuts high frequencies above about 15Khz, which you might be able to hear. I would start there, just remove the 1n cap between pins 1 and 2 of U3A and see if you get any high end back, if you do then replace the cap with 100pF to 470pF, what ever you've got the value doesn't matter that will raise the cut off to above audio frequencies.
The input impedance is 500k set by the two 1M resistors before pin 5 of U3B you could change those to 2M2 resistors, that would raise the input impedance to about 1M.
The only other thing I can think of is how have you done the FX loop? there could be some way that has done something to the frequency response.

[trjones1]

That looks great, I like the dip switches very neat.
I've never noticed any tonesuck, but if you're getting some here's a couple of things you could try. The second opamp stage cuts high frequencies above about 15Khz, which you might be able to hear. I would start there, just remove the 1n cap between pins 1 and 2 of U3A and see if you get any high end back, if you do then replace the cap with 100pF to 470pF, what ever you've got the value doesn't matter that will raise the cut off to above audio frequencies.
The input impedance is 500k set by the two 1M resistors before pin 5 of U3B you could change those to 2M2 resistors, that would raise the input impedance to about 1M.
The only other thing I can think of is how have you done the FX loop? there could be some way that has done something to the frequency response.

Thanks for the suggestions, I'll look the cap at U3A.  I took the signal for the effects loop after the 10k resistor from pin 14 of the 2399, into an IC buffer, to the send jack, from the return jack, into another IC buffer and back to the three caps that 10k had been connected to.

Regardless of that little quibble, I love this pedal.  I'm usually not a fan of modulation on delays, but the Echo Base's sounds great.

[pgorey]

Would it work to use a tantalum or non-polarized electrolytic for the 1mF cap?  Small Bear is out of the 1mF and i have the tantalum and electrolytic on hand.  Also, when I see people that have the speed of the modulation reflected by the LED dimming at matching speeds, is that a mod or part of the circuit?

[Taylor]

The non-polar electrolytic would be fine. The flashing LED is part of the circuit, so you don't need to do anything special for that.

[pgorey]

Could I also do the tantalum 1mF as well?  Just curious what the difference is.

[Taylor]

I haven't ever used tantalum caps. Early on I read that they can fail explosively, at voltages just barely over the rated value. Then there are the ethical issues surrounding the mining of tantalum. I steered clear and don't have any experience with them.

So, I actually don't know. That cap is just in the feedback path of the opamp, not connected to the power rails. Hopefully somebody with proper EE knowledge will stroll through and let us know if it would be safe.

I found this - top answer is very informative:

http://electronics.stackexchange.com/questions/99320/are-tantalum-capacitors-safe-for-use-in-new-designs

[pgorey]

Yikes regarding the Tantalum mining.  No more of those! 

Last question...for now

Can I use a linear pot for the mod / LFO speed?  I only have a linear 1M but could find some other parts to order from small bear if I had to so I could get the log 1M

[Taylor]

The schematic calls for a linear pot there, so you're all set.  The only difference would be that with an audio taper pot, most of the knob travel would be slower speeds, and then the speed would ramp up a lot at the clockwise end of the knob.

[pgorey]

Am I reading the board layout and parts list wrong or am I confused on what is log or linear?  it says B1M.  Is that not log?

[pgorey]

it's linear and i was confused.  bummer.  have to wait for thus ONE PART!