Building the Echo Base PCB

[garcho]

How do you think, is there a way to add LFO in to the circuit?

There is a LFO already; it's used to modulate the pitch of the repeats. Did you want to add something else?

[slacker]

If you want to feed in an external LFO then disconnect the clockwise lug of the mod depth pot and connect your external LFO there, depending on what voltage your LFO puts out you may need a resistor in series with the pot, same as the 240k in the schematic.

[telebiker]

garcho, I'm talking about external LFO to manipulate the effect

slacker, thank you!

[tombaker]

Check to make sure the three 10k resistors connected to pin 2 of the top left opamp are really 10k. If one of those was the wrong value that could cause a volume boost. Check the soldering on those as well, a bad connection could also cause it.

Thanks slacker. I used carbon film resistors for all 10k
and 20k slots just to change it up but their tolerance wasn't as great. I might replace those three.
Thanks

[tombaker]

tried replacing the three 10k's off the TL072 to no avail.
The signal just overdrives if I play hard. This is without anything before the echo base. I played a gig the other night and ran a cs-3 into it at a lower gain and it was fine but it's just too hot. I don't know enough about the circuit to know where to "lower the gain". Would that mean increasing the resistance?
Maybe before the first opamp?

Any tips would be appreciated.
Thanks

[slacker]

Strange one, the bypass signal shouldn't have any gain the output should be the same level as the input. The first opamp stage is just a buffer, no gain, the second stage with equal value resistors, the 10ks also has no gain.
The only way it can have any gain is if the resistor in the feedback loop of the second opamp is bigger than the resistor from the first stage, if you've checked these are definitely 10k then I'm not sure what's going on.

I would maybe try audio probing the circuit and see where the volume increase happens.

[tombaker]

Cool, I'll try that. Probably should've tried that first, but anyhow.

When I first assembled the pedal I had the diode lift mod included and I removed it while trouble shooting some initial problems, would a dead diode effect the sound/be causing the distortion?

[slacker]

A problem with the clipping diodes would only affect the delayed signal.
If you want to make sure the problem isn't being caused by anything on the delayed signal path pull the CD4066 and the PT2399, this leaves just the dry signal path.
Voltages on all the opamp pins might help, the one top left on the board.

[azrael]

Has anyone figured out how to add an effects loop to the echo base?  that would be ultimate!

There' s various way's to do it, depending on what you want, here's a schematic with 3 different places to try http://www.eskimo.plus.com/fxstuff/echobasenotes.png

A. The first repeat and all subsequent ones are affected, but each repeat only goes thorough the pedal in the loop once so subsequent repeats don't get more and more affected.
B. The first repeat is clean but every subsequent repeat goes through the pedal in the loop, so the repeats get more and more affected.
C. The first repeat is affected by the pedal in the loop and every subsequent repeat goes through the pedal in the loop, so the repeats get more and more affected. To add the loop here you would need to add buffers before and the FX loop and maybe move the 20k resistor and 4n7 capacitor to after the Loop.

I was also curious about adding diodes to the repeats knob to prevent self oscillation from getting super loud-

Already has this.

Does anyone still have this? Or slacker, do you have it still? Link is down.

EDIT: LOL found it in my hard drive, after a bit of searching. here it is for anyone else who wants it.

[tombaker]

A problem with the clipping diodes would only affect the delayed signal.
If you want to make sure the problem isn't being caused by anything on the delayed signal path pull the CD4066 and the PT2399, this leaves just the dry signal path.
Voltages on all the opamp pins might help, the one top left on the board.

Will get around to this asap. i was just inside the echo base before I got on here and I'd removed the clipping diodes which has cleaned up the signal somewhat, but I'll pull the two chips tomorrow and see what the go is.

On the build pdf it recommends swapping two 47k resistors to 22k for humbuckers which I did. But how does less resistance create a cleaner signal for a hotter signal? Or does the resistance create distortion somehow?

[tombaker]

A problem with the clipping diodes would only affect the delayed signal.
If you want to make sure the problem isn't being caused by anything on the delayed signal path pull the CD4066 and the PT2399, this leaves just the dry signal path.
Voltages on all the opamp pins might help, the one top left on the board.

I took out the chips as you suggested and the pedal still retains a fuzz when I play harder.
I tested voltages on the pins by placing the grounding lead of my DDM to ground on the circuit and the red lead to the pin

The TL072 on the left of the board
1 - 5.02
2 - 5.02
3 - 2.5
4 - 0
5 - 5
6 - 4.98
7 - 5.02
8 - 9.2

The one on the right reads
1 - 5.02
2 - 5.02
3 - 5.01
4 - 0.8
5 - 2.81
6 - 5.01
7 - 2.23
8 - 8.35

I hope this can shed some light on my problem.

[slacker]

On the build pdf it recommends swapping two 47k resistors to 22k for humbuckers which I did. But how does less resistance create a cleaner signal for a hotter signal?

The gain of the PT2399 stages is roughly set by the ratio of the 47k resistors and the input resistors for that stage, if you look at the schematic azrael posted above for the first PT2399 stage (pins 16 and 15) the input resistor is the 20k to the right of "C" this give a gain of about 2 47/20.
For the other stage (pins 13 and 14) the input resistor is the 10k off pin 12 giving a gain of about 5 47/10. This give a total gain of about 10 which will cause hot signals to distort the PT2399. Changing the 47ks to 22ks reduces the gain to about 1 for the first stage and about 2 for the second stage, giving a total gain of about 2, so you can feed it hotter signals before it distorts.

I can't see any obvious problem from your voltages, for the first opamp all the pins should be about 5 volts, the low value on pin 3 is probably just your meter reading low because of the high resistor value connected to that pin, it's a common thing, the fact that pins 2 and 3 are correct probably means it's Ok. Have you tried changing the opamp?

When you say the pedal has a fuzz do you still mean the output is louder than the input, or is it just distorted but about the same level?

[tombaker]

I can't see any obvious problem from your voltages, for the first opamp all the pins should be about 5 volts, the low value on pin 3 is probably just your meter reading low because of the high resistor value connected to that pin, it's a common thing, the fact that pins 2 and 3 are correct probably means it's Ok. Have you tried changing the opamp?

When you say the pedal has a fuzz do you still mean the output is louder than the input, or is it just distorted but about the same level?

First of all thanks for explaining the resistance/gain thing, that makes perfect sense.
I'll try swapping out the opamp, I haven't had a chance to audio probe the circuit yet due to work commitments.

When I say fuzz, I mean that the pedal still jumps in level but instead of jumping cleanly, it gets fuzzier when I play/strum at a hard level. If I play gently the signal comes through clean albeit, louder, but when I hit harder a fuzz is introduced. This occurred with the chips taken out as well as with them in.

I'll try swapping out the opamp and get back to you.
Thanks for all your help. I learn a great deal from my mistakes and have been learning a lot lately.

[tombaker]

I swapped out the opamp and even though the Voltage readings are the same the "fuzz" is gone!

Another amateur builder helped!
Thanks slacker, your name does not do you justice.

If you're ever in australia and need a designated driver, let me know, it's the least I can do.

[slacker]

Excellent glad you got it working, if I'm ever in Oz I'll give you a shout.

[4floorsofwhores]

Hi folks. built this and everything appears to be in the right place. my feedback pot does nothing and i'm only getting one delay. I've tried resoldering the pot and changing the pot,and changed all the ics. Any thoughts about where i should be looking? thanks in advance. i've built pretty much all taylor's boards without any problem but this one has me beat

[Taylor]

Did you do any mods? Have you tried audio probing through the feedback section?

[tombaker]

Hi folks. built this and everything appears to be in the right place. my feedback pot does nothing and i'm only getting one delay. I've tried resoldering the pot and changing the pot,and changed all the ics. Any thoughts about where i should be looking? thanks in advance. i've built pretty much all taylor's boards without any problem but this one has me beat

Hiya,
The same thing happened to me, but I had the feedback mod attached to the feedback pot. Have you done this?
If so check the wiring of the switch, make sure you're centre lug is the common and the outer lugs are to different options. This fixed the single delay problem for me.

[4floorsofwhores]

Hi folks. built this and everything appears to be in the right place. my feedback pot does nothing and i'm only getting one delay. I've tried resoldering the pot and changing the pot,and changed all the ics. Any thoughts about where i should be looking? thanks in advance. i've built pretty much all taylor's boards without any problem but this one has me beat

Hiya,
The same thing happened to me, but I had the feedback mod attached to the feedback pot. Have you done this?
If so check the wiring of the switch, make sure you're centre lug is the common and the outer lugs are to different options. This fixed the single delay problem for me.

Thankyou. I'll give that a go this evening. I tried the feedback mod then removed it-no change. Maybe i killed a pot

Oh and Tom. Do you know Matt Rhodes? Long shot but i have only heard of a few Tom Bakers 

[tombaker]

Thankyou. I'll give that a go this evening. I tried the feedback mod then removed it-no change. Maybe i killed a pot

Oh and Tom. Do you know Matt Rhodes? Long shot but i have only heard of a few Tom Bakers 

I do not believe I do know Matt, but then again I'm terrible with names. I'm in Australia if that narrows it down.

Maybe the pot or perhaps the resistor that is connected to the mod. But I think if you're only getting a single repeat then the signal isn't making it through that pot. Try the audio probe or just some alligator clip leads to bypass the pot before you wire in another. If it's the pot you should get a plethora of repeats by bypassing the pot.