Echo Base Debugging

[slacker]

Always happy to except a beer, virtual or otherwise 

Just been looking back through the thread and noticed this "Q3 USED 2N5088" that's an NPN transistor, Q3 should be PNP, you need to change that before the modulation will work properly. Still need to fix IC1 first though, the voltage on pin 4 is way too high, it should be less than a volt. Are you sure R8 is 220 Ohms, it's hard to tell in the photos but it looks the same same as R10, which is 220K Ohms. If it's 220 Ohms and is definitely connected to pin 4 of IC1 at one end and ground at the other, then I would try replacing IC1.

[maurice]

Thanks, you're right I used a 220k instead of 220r.  My bafoonery astounds me!

Will also replace IC1 and Q3.  Any recomended substitutions for Q3?  Don't have a 2N5087.  If not I'll re-order the part and let you know how it goes.

[PRR]

Without a schematic I'm shooting blind.

But it does not make sense for IC1 pin 4 to be anything except dab-smack ZERO.

Yet the layout shows no clear path to zero voltage (ground).

Has this layout worked for anybody else?

[slacker]

Here's the schematic http://www.aronnelson.com/gallery/main.php/v/slackers-stuff/album170/echobaserev2.png.html IC1 on the layout is the LFO. Note, the layout uses different sections of the CD4066 to the schematic.

For the PNP BC560 or 2N3906 both work fine.

[PRR]

> it does not make sense for IC1 pin 4 to be anything except dab-smack ZERO.

As someone up-thread said, pin 4 has to be "less than 1V".

I still say the 220 resistor from pin 4 to Ground does not make sense, but it is there, and should work, IF the 220r goes to ground. 

[slacker]

Yes, you're right Paul, it probably doesn't make sense. I designed this 6 years ago when I knew a lot less about this stuff than I do now. It was an attempt to isolate the LFO from the supply to stop ticking, it seemed to work, so I went with it.
This version of the pedal also includes a number of mods and fixes to problems that people found once it was released into the wild. There's a number of things I'd do differently if I was starting from scratch today.

[maurice]

OK, so my parts JUST arrived from China... I've since replaced IC1 with a different chip and now used a 2N3906 for Q3.

It all seems to be working apart from the mod pots have no effect on the sound whatsoever.  The LED only comes on if I link Bypass SW1 to GND but it does pulse based on the position of the mod speed pot.

Almost there... any suggestions?

[slacker]

The LED is supposed to come on when the bypass is grounded, that is effect on, ungrounded is effect off. I noticed from your photos you didn't seem to have the tails switch fitted, you need that fitted before the bypass switch will actually turn the delay on and off, without it the bypass will just turn the LED on and off.
If the LED is flashing that means you have solved your IC1 problem, if the mod depth pot does nothing check all the connections between pin 1 of IC1 and the base of the 2N3906.

[maurice]

Right, I've just had time to return to this project but I'm still having trouble.  Now I've fitted a tails switch and connected bypass to gnd but while the LED flashes in response to both Mod pot positions it does not effect the sound.

I've checked connections from pin1 of IC1 and the base of the 2N3906 but cant see any obvious issues.  Any suggestions or advice?

P.S, just wanted to double check I wired tails switch correctly... Tails2 in the middle of switch with 1&3 at either end?

[maurice]

any suggestions?

[slacker]

Yes the tails switch wiring sounds correct, does it work?

On the modulation problem, if you turn the delay time down all the way do you get a very short delay like a chorus sound or do you still get quite a long delay?

[maurice]

ues tails switch is working but still no mod effects.

When delay is turned down I get a very short delay.  Any ideas how i could get mod speed & depth working on the audio?

[maurice]

Hi folks, does anybody have any suggestions as to why the mod effects are still not working as per previous post?

[maurice]

Any new thoughts on this one?  I'm struggling to beat the final hurdle

[slacker]

I think you said before that the LED flashed and the speed of the flashing could be controlled by the mod speed pot, so we know the LFO is working. Something must be wrong some where between the LFO and the PNP transistor. See if you can trace the modulation signal from pin 1 of IC1, through R6 and C24 to lug 3 of the mod depth pot. You should be able to measure about 1.5 to 2 Volts on lug 3, modulating in time with the LED. If you get signal there see if it appears on the wiper of the mod depth pot, turned all the way down you should measure 0 Volts and all the way up the same as lug 3. Then follow it through, R11 to the base of the PNP transistor. Also check R16 is the correct value, check the time pot is connected correctly and check for any missing trace cuts or jumpers around the PNP.

Hopefully one of those things should find the problem.

[maurice]

I'm sure I've had the LED pulsating a few months back (perhaps before replacing components or re-soldering connections) but now it just stays on when bypass is connected to GND.

Before I follow the steps from previos post (following from pin 1 of IC1), what could I do to resolve the LED problem of not showing the modulation?

[maurice]

ok, so I'm a bit embarressed that a fresh 9v battery solved the LED not flashing problem (more power was required for the LFO).

Measurements taken from IC1 through to wiper of Mod speed are fine and fluctuate in time with the LED.

Mod Depth is fluctuating between 4.9-6v but does not read zero when tuned down, so I guess there's a problem here...  What can I check for that?

[slacker]

I see you've found the low battery notification   this is a flaw in the design where the LFO stops working with a weak battery.

Sounds like you don't have the anti clockwise lug (lug 1) of the mod depth connected to ground.

[maurice]

Ground seems to be connected to lug 1 of mod depth and I've tested continuity.  ANything else I could try?

[slacker]

Turn the mod depth pot all the way down and check for continuity between lug 2 and ground, if you don't get continuity then you have either a bad connection from lug 1 to ground or a bad pot.