Echo Base - a new PT2399 delay

[Taylor]

I just made a second Echo Base. For this one, I decided to use a 1Meg linear pot for the delay time.

Haven't timed it yet, but at maximum I'd say this gives you around 10 second long delays. Of course, there is a fair amount of noise and distortion/bit crushing going on at this setting, but for my purposes it's quite fun. I stuck a lowpass filter after it. It's a bit more lo-fi than the Lo-Fi Loop Junky, and not as much time, but it has one excellent feature that no other lofi looper has - overdubs.

It sounds the same as my other one at short delay settings.

Unsurprisingly, high notes are useless here because you have to filter them out to filter out the noise, but for you guitar guys, the low end of the neck is reproduced reasonably well. The lowest octave of my bass doesn't come through so well at these long times; I think the low notes are creating too much distortion to be heard clearly.

So, overall, a very fun mod. If you're into weird stuff, give it a shot. It kind of makes the Echo Base into a whole new pedal - it was already an analog-ish digital delay, chorus, and vibrato, but now it's a lofi looper.

And now a question: I find the Mod depth and speed knobs to be hard to pin down. It seems that there's only a narrow area where the knobs do anything, which shifts around depending on other settings, and once you hit that area, you're immediately in Skronkville. Does anybody else find this to be the case? Any thoughts on how to make the Mod section a little more predictable?

Also, since people are using it to do chorus and vibrato, it might be nice to turn the delay volume control into a mix control, so you can have just the vibrato without the clean if you want. I don't have time right now to draw this up, but I think it would be more useful than the way it's currently set up.

EDIT: Don't try this yet! May be bad. See below.

[Taylor]

So, after typing the above, I decided to go play with it some more, and find out the actual maximum time.

Now I have no delaying going on. Could I have killed my PT2399 by asking it to delay this long? I have more of them, but if the chip can't handle this, I don't want to keep frying them.

Is there any reason that underclocking the 2399 would kill it?

Edit: Well, it's not dead, because I turned it back on and it worked for a bit, then stopped again. Hmm, what's going on here?

[jimosity]

The previous post made me wonder, would there be a way to add another footswitch and bypass the delay signal only and use the unit as a chorus pedal or vibrato only pedal?

[Taylor]

You mean bypass the clean signal only?

If so, check out the 10k resistor that's attached to pin 1 of the upper right TL072 (assuming you're using the perf/PCB layout). I'm pretty sure you could use an SPST stomp to connect/disconnect that junction between the R and pin 1. This would still let the input go to the delay, and the delay to the output, but kill the dry signal.

[jimosity]

No, I mean bypass the actual repeats and have only the mods.

[Taylor]

Ah, well, that's not possible, because the modulation is the delay. You see, the vibrato is not just vibrato tacked onto delay. The vibrato is created by changing the delay time. By playing back the delay slower than you recorded it, the pitch goes down, and by playing it back faster than you recorded it, the pitch goes up. So there is no vibrato without delay.

You should be able to turn the delay time and repeats down all the way, and turn the mod depth low, and it should sound only like vibrato, without a noticeable delay between playing and hearing.

[svstee]

The only way I can think of off the top of my head to accomplish that would be to switch between sets of pots, either mechanically (4pdt?)  or with some kind of relay setup. You would need to switch between delay time and modulation depth at minimum. I've thought about it, but it means too many pots for me.

[slacker]

And now a question: I find the Mod depth and speed knobs to be hard to pin down. It seems that there's only a narrow area where the knobs do anything, which shifts around depending on other settings, and once you hit that area, you're immediately in Skronkville.

The speed pot shouldn't be affected by other settings, the mod depth will be affected by the delay time, there's nothing you can do about that though.
It might just be that the controls have too much range for you, when I built it I deliberately made it so the pots could produce stupidly extreme sounds as well as useful ones, I figured this was better than limiting the pedal to more subtle modulations, when some people might like the madness.
If you want to tame the modulation depth then make the 240k resistor before the mod depth pot bigger. You'll have to experiment with values but hopefully that will give the pot more of a useful range. For the mod speed if you want the fastest speeds to be a bit slower then make the 27k resistor after the speed pot bigger, and if you want the less of a range overall make the speed pot smaller.

Also, since people are using it to do chorus and vibrato, it might be nice to turn the delay volume control into a mix control, so you can have just the vibrato without the clean if you want. I don't have time right now to draw this up, but I think it would be more useful than the way it's currently set up.

Someone has done this, there's a schematic somewhere in this thread. You have to go true bypass and  lose the delay tails though. If you want to keep those you'd have to redesign the electronic switching.

Cool mod by the way. I don't think you can damage the PT2399 by underclocking it I seem to remember mine locking up sometimes when I tried it and it wouldn't work again until you pulled the power.

The previous post made me wonder, would there be a way to add another footswitch and bypass the delay signal only and use the unit as a chorus pedal or vibrato only pedal?

Simple way is have a switch that shorts out the delay time pot. That will set the pedal to the shortest delay time which will give the chorus/vibrato effect. This might not work too well in practice though, because the settings of the rest of the pots that sounds good for chorus might not work too well for delay.
Like Taylor said the modulation isn't a separate effect it's just sweeping the delay time, just like grabbing the delay time pot and turning it back and forth.

[slacker]

hi !

my echobase doesn't work!!!
i've got dry sound when the pedal is in and out, the led works
i change all the IC's, i check everythings but...

so there is some pictures, if you see something wrong!

Welcome to the forum

I can't see anything wrong looking at the pictures. If you are getting no delay at all then it probably means the sound isn't getting from the PT2399 to the output. I would check the wiring of all the pots especially the level pot.
If that doesn't solve the problem then make an audio probe, have a look here for instructions http://www.diystompboxes.com/wiki/index.php?title=Debugging. Then use this to check for signal around the PT2399, that will hopefully show where the problem is.

[Slade]

Could be a way for this pedal to add a "Repeats Decay Pot", to control how the repeats decay?... If I wanted only 3 repeats, or 2 repeats at the same output level (or very closer)...
I think this would be a great mod, but I can't figure out how..

[exterm]

Welcome to the forum

I can't see anything wrong looking at the pictures. If you are getting no delay at all then it probably means the sound isn't getting from the PT2399 to the output. I would check the wiring of all the pots especially the level pot.
If that doesn't solve the problem then make an audio probe, have a look here for instructions http://www.diystompboxes.com/wiki/index.php?title=Debugging. Then use this to check for signal around the PT2399, that will hopefully show where the problem is.

thanks! sorry for my poor english, so...



i check the trannies they 're ok, they "flip" with the switch.
i've got delay on the PT2399 (pin 13 if i remember!)

i've got time this afternoon, i will spend some time on it...

wait and see

[cpm]

Could be a way for this pedal to add a "Repeats Decay Pot", to control how the repeats decay?... If I wanted only 3 repeats, or 2 repeats at the same output level (or very closer)...
I think this would be a great mod, but I can't figure out how..

i dont think thats possible with a single delay chip, when you get sound at the delay output you cant know how many times it has been "feedbacked"

you can have 2 (3,4...) single repeats using 2 (3,4,...) chips with no feedback, taping each ones output

[slacker]

thanks! sorry for my poor english, so...

Your English is fine

i've got delay on the PT2399 (pin 13 if i remember!)

That's good that means the signal is reaching the PT2399. See if you have delay on pin 14, if you have check pin 10 of the CD4066 then pin 11 and on all the pins of the level pot. If the signal stops at any of these the problem is somewhere in that area.

[exterm]

thanks slacker, i will check this soon! in july...!

i want this working

[mth5044]

So, probably about a year later, I finished my echo base    I've made a pact to start finishing things instead of ordering all the parts, soldering 4 resistors then starting something new 

Besides the 5 volt reg and 4001 not fitting in my sockets (then a huge PITA to get the solder out), it went pretty swell. The sound is there, but I'm still getting around the modulation part (never had a modulated delay). Anybody know any good settings off hand?

The only actual problem I'm having is the LED doesn't work (of all things). I'm thinking I need to change the LED resistor, as the LEDs I have are beyond superbright.. you have to squint to look at my pedalboard 

Anyway, cheers slacker, this is fantastic. I'm a bit bummed the PTAP couldn't get sorted out for this project. I don't think the delays are really long enough now that I've played around with it.

Oh well.


Fantastic Slacker. You win in my book 

[decc]

... I'm a bit bummed the PTAP couldn't get sorted out for this project....

I've been getting quite a few emails about this recently so I finally sat down and built the LFO section and patched it in to my delay using a 50k analog pot. After playing around for a while (it does sound great, wish I had done this earlier ) I took some measurements.

1. I should have noticed this earlier from looking at the schematic and earlier posts in the thread, but the LFO is DC coupled into the delay control line. This means that the "Depth" pot & PNP transistor not only mix in modulation, they mix in what is effectively a DC offset as well which will in turn increase the base delay time. This is trouble since the higher the depth setting the further off the tap-tempo will be.

2. The PNP transistor / 39k resistor combo doesn't behave like an ideal resistor. With the depth control at minimum, which is the worst case current draw and the best chance the PTAP has for being able to calculate the delay time, there will be about 0.6V at the collector. If my arithmetic is correct then across the full sweep of the 50k delay pot the "effective resistance" due to the 0.6V can be anywhere from ~16k down to less than a hundred ohms. However the collector voltage itself varies with the delay pot setting in a non-linear fashion since it is dependent on the current flowing through it, not to mention the particular transistor being used.

So it looks like all the theory points to the Echo Base and the PTAP not being a good match. (Note that these problems are not present in an AC-coupled LFO scheme such as with the Magnus Modulus.)

However I still wanted to know what it would actually be like to play with the LFO & PTAP together. I put a 1k resistor in series with the digital pot and gave it a shot.

First I tried using no modulation and manual control of the delay. So far so good. I then dialed in a really nice chorus with the delay pot at min (plus the 1k). So we can get a chorus sound without breaking the digital pot at least. Finally I tried tap-tempo with the modulation off. As expected the timing was off due to the varying effective resistance of the transistor. I re-programmed it to try and take this in to account and it was much better, however there was still enough variation that I wouldn't call it a success.

In the end I think there are too many compromises to a stock Echo Base + PTAP. I did end up converting the LFO to be AC-coupled by mimicking the Magnus Modulus and everything worked that way just fine. So if you're thinking of adding a PTAP to and Echo Base I would first make this modification and make sure you're still happy with the sound and the effect of the controls as it is slightly different. Another possibility, if you don't mind having another control, would be to have a "modulation on/off" switch that swapped the PNP/39k with a 1k.

[Paul Fehr]

Hello,
I believe this echo base will be the first pedal I will build.  I have made a parts list for myself, and decided to share it with everyone else so that its a bit easier for newcomers like me.
I believe I am not missing anything.  All of these parts can be had from smallbear electric, although I'm buying a few parts from pedalpartsplus to save money .



echo base parts list:
 (quantity and part name)
IC's:
2 tl072   
1 pt2399 
1 cd4066

diodes:
1 1N4001
2 1N4148

resistors:
3       2.2M
10     10K
5       1.5M
3       220K
1       10M
1       20K   (or 2 20k resistors for people who don't want to change how fast it oscillates)
2        47K
1        39K
3        220
1        240K
1        27K
1        680K
1        100K
1        100K  (this is for switching one of the 20k resistors to 100k, so that you get more usable feedback control)

NPN/general purpose amplifier?:
1 2N5089
1 BC560  <-- replace with a 2N5087 because I couldn't find it at pedalpartsplus or smallbearelec (this chip has to go in reverse)


capacitors:
12      100nF
2        47nF
2        1nF
2         220nF
1         4.7nF
2         15nF
1         470pF
1         1uF
3         47uF
1         100uF

Potentiometers
3 100k Log
1  1M Lin
1   47K Lin
1   25K Lin (if you want to do the wave shape mod)

OTHER
1   DPDT Foot Switch
1   BB case (or similar)
2 Mono 1/4"  Jacks
1 DC Power jack
1 9V Battery clip
1 LED
and the necessary wire.




That should be everything, i used http://chawk.files.wordpress.com/2008/02/echo_base_pcb.pdf to make this parts list.
If I'm missing anything, let me know. 

And if you guys have any tips for first time pedal builders, let me know

[Taylor]

What kind of board are you building on? An Echo Base on perf or vero is a pretty ambitious first project. I would use a PCB if you can.

[Paul Fehr]

What kind of board are you building on? An Echo Base on perf or vero is a pretty ambitious first project. I would use a PCB if you can.

Definitely on the PCB.  I'm pretty sure I'll be able to pull this off.  I'll be building it with a friend (making two), and I plan on ordering the parts pretty soon.  I live in Mexico, so it might take awhile before I go to the USA to pick up the parts though.  Hopefully won't be too long.

[mth5044]

... I'm a bit bummed the PTAP couldn't get sorted out for this project....

I've been getting quite a few emails about this recently so I finally sat down and built the LFO section and patched it in to my delay using a 50k analog pot. After playing around for a while (it does sound great, wish I had done this earlier ) I took some measurements.

Well I'm glad I could be one of those emails  That's fantastic that you went through all the trouble to see if it would work (and I didn't have to  lol jk(ish)), but it's too bad it didn't work. I've got mine closed to all boxed up, so I'm not really up to doing the mods to get it close to working, but I do have a question for you, if slacker doesn't mind a slighty OT post. I've been thinking about making a digital binson echorec 'clone' by using 4 pt2399 chips in series to simulate 4 different tape heads. Could the PTAP be used to and significant use in this project? 4 tap tempos for 4 chips would be a little out of control, but could there be a way to get it to control all 4? Thanks