Author Topic: Echo Base LFO sort of working - help needed!  (Read 327 times)

djg413

Echo Base LFO sort of working - help needed!
« on: December 30, 2017, 01:07:44 PM »
Hey guys.

I just built the Echo Base on vero board (second one, first done with Taylor's PCB). I used Harald Sabro's layout. http://www.sabrotone.com/?s=echo+base No substitutions on parts anywhere. I didn't add the humbucker switch, or the feedback switch, and instead jumpered from the humbucker switch 1 to the feedback 2 rail. Everything is working just fine, except for the LFO. It functions as it should from between 3-4 o'clock, up to being dimed. However, when I turn counterclockwise, it goes from a fairly fast rate at the 3-4 o'clock range, to no oscillation at all. I'm familiar with the range of speeds, having built this before, so I know it's not an issue of the taper of the pot (I tried log, linear, and reverse log just to be sure I'm not just a moron before posting.) I've double checked all components multiple times to be sure they're correct, and properly oriented. I'm also completely confident that there are no bridges/cold joints anywhere. I'm lost. Might be worth mentioning that I ended up going back to a B1M pot, and all of my findings are with that installed.
Here are the voltages for the TL072 that the LFO uses:
pin 1: 5.09v (with LFO switch OFF) / 3.89v to 6.31v (with LFO switch ON)
pin 2: 5.09v
pin 3: 5.08v
pin 4: ground
pin 5: 5.60v (with LFO switch OFF) / 4.66v to 5.93v (with LFO switch ON)
pin 6: 5.08v
pin 7: 7.56v (with LFO switch OFF) / 2.15v to 7.66v (with LFO switch ON)
pin 8: 8.21v (with LFO switch OFF) / 8.19v to 8.30v (with LFO switch ON)

I've built a number of pedals in the past, but this is the first that I have built from scratch (no factory made PCB) that has an LFO. I've made mods to pedals with them, and in all of my experience, the LFO was either fully functional, or didn't function at all. I'm really confused as to what the issue may be. Thanks in advance for any and all help!
-Dave

EDIT: It may, or may not, be worth noting that I've tried swapping out the transistors, and also tried a number of TL072's as well as a variety of other dual op-amps, but the results were the same.
« Last Edit: December 30, 2017, 01:16:50 PM by djg413 »

garcho

Re: Echo Base LFO sort of working - help needed!
« Reply #1 on: December 30, 2017, 01:54:52 PM »
most likely something wrong with the fact that pin 7 isn't the same as 5 and 6 with the LFO off, upon cursory inspection.
"...and weird on top!"

djg413

Re: Echo Base LFO sort of working - help needed!
« Reply #2 on: December 30, 2017, 05:37:34 PM »
most likely something wrong with the fact that pin 7 isn't the same as 5 and 6 with the LFO off, upon cursory inspection.

Thanks, that was a much quicker response than anticipated! Do you have any of why it's so far off, or a suggestion on how to get pin 7 down to 5v?

garcho

Re: Echo Base LFO sort of working - help needed!
« Reply #3 on: December 30, 2017, 07:11:13 PM »
Honestly, though I know this is probably aggravating to hear, I would just double, triple, quadruple check your vero board and the soldering. There is no more accident prone way to wire up a circuit than vero.
"...and weird on top!"

djg413

Re: Echo Base LFO sort of working - help needed!
« Reply #4 on: December 31, 2017, 07:39:12 PM »
Honestly, though I know this is probably aggravating to hear, I would just double, triple, quadruple check your vero board and the soldering. There is no more accident prone way to wire up a circuit than vero.

Well, I'd much rather hear something like "oh, it's a leaky cap" or something along those lines, but I wouldn't say any suggestion is aggravating. The situation aggravates me, but suggestions never do! I've been over it checking that all components are the proper values, and in the proper places countless times now. I check all my resistors with my DMM one by one as I populate the board too, but unfortunately, I have no tools on hand to check caps. I also scored between all of the traces with one of my needle files and checked all of the cut points with a magnifying glass to eliminate the possibility of microscopic bridges. I'm just kinda crossing my fingers that Ian will happen along, come across this, and know what the deal is. Oh well, I still have my literally mint vintage polychorus, a Small Clone that I modified to do tremolo, vibrato, flanging, AND some pseudo-ring mod stuff by changing the LFO cap and speeding it up ridiculously fast, and a BYOC ping pong delay (first pedal I ever built!) to cover my delay and chorus needs! This has actually just been a time killer project because I had surgery on the 15th, and won't be returning to work for a couple more days. It's still a great pedal that I'd love to have back in my collection, fully functioning again, so I'm going to keep at it. Thanks for the suggestions so far though, much appreciated!

Kipper4

Re: Echo Base LFO sort of working - help needed!
« Reply #5 on: December 31, 2017, 09:29:52 PM »
The voltages look ok to me.

Although I don't see a use for switching off the lfo in any delay?

I found a schematic. In future it would be helpful to include a link to one so we don't have to go looking.

Double check the 27k min resistance between integrator and Schmitt.
If this value where too low the lfo would go too slow.

That vero link says it's verified. Is it?
 Post up some pics of your build.
Voltages

Help us to help you.

Edit. I think the voltages are ok based on the triangle output has less swing than the square.

« Last Edit: December 31, 2017, 09:37:53 PM by Kipper4 »
Jellybean dodging since 2012.
Smoke me a Kipper. I'll be back for breakfast.