Echo base build, need a bit of help

svstee · May 21, 2009, 04:30:07 PM

Built the echo base http://www.diystompboxes.com/smfforum/index.php?topic=60662.0 using this layout http://www.aronnelson.com/gallery/main.php/v/slackers-stuff/echobasefinal.jpg.html?g2_imageViewsIndex=1

I'm having a few issues with it. First, is a TL082 a direct drop in replacement for a TL072? If not, I think I found my problem, I only had one 072 and replaced the 2nd with the 082.

slacker · May 21, 2009, 04:42:09 PM

A TL082 should work fine in place of either of the TL072s. Pretty much any dual opamps will work, you might get more ticking with certain ones in the LFO position but the pedal should work.

There's a whole load of debugging info in the main Echo Base thread if you need it.

svstee · May 22, 2009, 01:27:54 AM

I'm going through the thread again, thanks. You seemed to have given a lot of people a lot of help in that thread!
Anyways, I got it (mostly) working. I flipped my in/out wires. Delay, level and feedback work great, but I don't have any modulation. Is this an easy fix or should I take voltages?

svstee · May 22, 2009, 03:49:18 PM

Well, I checked voltages and I am finding some things that confuse me.

PT2399
All normal, except:
7 and 8 are 3.3v instead of 0.5

4066
1 and 2 are 2.8 should be 4.6
3 and 4 are 0.0 should be 0.4
5 is 0.0, normal
6 is really weird. It should be 0.45 on 4.5 on, but I get .08 off, and when it is on and I touch it with the meter lead, the effect turns off.
7 is 0.0, normal
8 is 2.26 should be 9.0
9 is 1.92 on and 0.0 off should be 3.0 on and 0.32 off
10 and 11 are 2.89 should be 4.6
12 is 8.5 on, normal
13 is 7.5 should be 8.5
14 is 9.0, normal

TL082, top left of vero, U3
all normal except:
6 is 3.37, should be 5.0

TL072, bottom left of vero, U1
all normal except:
2 is 3.62 should be 5.0
5 stays at 4.12, should change.

Voltage regulator and all transistors work the way they should.

svstee · May 23, 2009, 11:45:34 AM

bump

slacker · May 23, 2009, 12:31:53 PM

I would double check all the connections round pin 6 of the 4066, there's definitely something wrong there.
Do the bypass and tails switching actually work or not?

It looks like the LFO isn't working properly. Does the voltage on pin 1 go up and down? If not then you need to check everything around the LFO opamp to make sure all the connections and trace cuts are correct. Once you've got it working trace the signal, through the mod depth pot to the base of the PNP transistor to make sure it's going where it should.

svstee · May 23, 2009, 12:38:51 PM

The bypass and boss/tails work perfectly.

The base of the PNP transistor is going up and down, does that mean the LFO is working?

slacker · May 23, 2009, 01:01:41 PM

Does the speed the voltage changes alter if you adjust the mod speed pot and does turning the mod depth pot affect it. If it does it looks like the LFO is working.
If the voltage is getting to the base but there's still no modulation it means you've either got a bad transistor or there's a short round there somewhere that is stopping the transistor working properly. Double check everything round the PNP transistor.

Sounds like you've almost debugged it

svstee · May 23, 2009, 07:04:33 PM

Just double checked the whole back of the board with a 7x loupe. No solder bridges, incomplete trace cuts or anything.

Speed and modulation knobs are effecting voltage change on the PNP's base.
I replaced the transistor, no luck. Then, just for giggles, I turned it around in case my transistor had a weird pinout. It worked exactly as before.

What is going on?

svstee · May 25, 2009, 12:19:23 PM

anyone?

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Echo base build, need a bit of help