Echo Bender

[jghfslk]

Hey everyone

I've been attempting to build pedals (mostly from layouts at tagboardeffects)  and after too many failed projects I'd like to get a better understanding of why my builds aren't working.  I'm currently troubleshooting an echo bender and am hoping someone can help me out.  I have been messing around with my audio probe and I lose signal after the 510K resistor on the second row (the row also has a link to the third row, a 5pF cap, and pin 2 of the TL072).  I get signal back at the top row with the dry 3 lug.  I can also get signal at the output and it seems as though the dry and wet pots are working.  When the power isn't plugged in I still have signal at the second row.  Is this normal to lose signal at the second row when the power is plugged in but still have signal without power connected?

Another question: When following the schematic, I see that after the 510k resistor the signal goes to pin 6 of the TL072.  On the layout, the resistor is on the same row as pin 2.  Does this not matter since eventually the signal gets to pin 6 after going through other components?

Unfortunately I don't currently have a camera to take pictures but I'll try to get one soon..

Here are my voltages (all pots turned all the way up):
TL072
1.  4.68        5.  4.68
2.  4.68        6.  4.68
3.  4.52        7.  4.68
4.  0.00        8.  9.38

PT2399
1.  4.97        9.  2.48
2.  2.47       10.  2.48
3.  0.00       11.  4.05
4.  0.00       12.  0.18
5.  3.05       13.  2.08
6.  2.47       14.  4.92
7.  4.40       15.  2.48
8.  0.74       16.  2.48

7805
I.   9.36
G.  0.00
O.  4.97

I also tried a 78L05 and replaced the TL072 but didn't have any luck with either.

Here is the layout:  http://tagboardeffects.blogspot.com/2013/03/casper-electronics-echobender.html

Here is the schematic:  http://casperelectronics.com/images/finishedpieces/echo/V2/Echobender_v_02.jpg

Any help is greatly appreciated!

[Silver Blues]

As far as the resistor goes, it actually doesn't matter because the TL072 IC is actually two equivalent TL072 op-amps on one chip. What matters is the relationship between the pins; for example, The set of pins 1,2 and 3 are one op-amp and 5,6 and 7 are another. The schematic is labelled a certain way because that's how it was configured on the original, however either op-amp on the chip can be used in either position. It was likely just more convenient for the layout to use one over the other (because the pins for each amp are opposite each other physically). To put it in simpler terms, IC2a and IC2b on the schematic can be interchanged with no change in functionality, and this is what's happened on the layout here.

[Beaker]

Well it works ok as I have built one.

As always check EVERYTHING methodically on both component side and solder side, and don't rush your checks. Take your time.

If you are having consistent failures, build smaller simpler circuits before going for tricky builds like this one.

Mobile phone photos are usually good enough, so post up what you can, as soon as possible.

[ξεναγος νεκροπολης]

hi there!
your pt2399 voltages are not good.
the whole right side should be around 2,5V
check your cuts (under the ic) again.
also pin7 should be way lower.

i've also build that board and it's 100% ok

[jghfslk]

Am I correct in understanding that pin 1 serves the same purpose as pin 7, 2 for 6, and 3 for 5?  Is it normal to lose signal when there is power but have it when there is no power?

[jghfslk]

I checked and recut some cuts around the PT2399 but nothing seemed to change..  I noticed that if I hold the probe so that it touches pins 11 and 12 at the same time I get a reading of around 2.5 volts. I was checking some values of capacitors and resistors (already soldered to the board) and got readings that were different than the capacitors value.  I'm guessing that this isn't an accurate way to test components since there are other things going on.  Should the value change when there is power and when there isn't?  I was checking the 82nf capacitor between pins 11 and 12 and when I had power to the board I think I got a reading of 0, but with no power got a reading of around 40nf (I'm not able to have the board right in front of me so I'm trying to remember what was going on)

Thanks for the replies!

[jghfslk]

I think I have it working!

[DatsunMan]

Hi! I know this is an old thread but I'd love to know how you fixed it, if you can remember. I've built mine twice, on two different Vero boards, and the result is the same. I've checked the breaks, links, and component orientation and it's all good. I had to replace some capacitors with alternate values but they're close. So stumped...