Echo Base - a new PT2399 delay

[FunkyGibbon]

Hi,

Thanks, Slacker, for this great project.

I've been working on a dual Echo Base design, a little different to CPM's ping-pong.

What I want is two more-or-less separate delays (the delay lines are parallel, not in series like in the ping-pong), that I could use to generate rhythms. I have most of the routing sorted (i.e. buffers, clean path, two delay paths, switching for mono or stereo output, tails or true bypass, grounded delay input when bypassed, etc), but the time functions have me a little stuck.

My first idea was to have a dual gang pot, so that both delays could be adjusted to the same delay time, and then a "fine" pot would change delay 2 by a bit.

Of course, I realised that this is not what I need.

I need a delay time for delay 1 (resistance "R" at the VCO lug (6) of the PT2399), and then the same resistance value is then divided for the delay time of delay 2 (i.e. R/2, R/3, R/4, R/6).

I'm assuming that smaller values for R give shorter delays.

I've hit a brick wall w.r.t. my knowledge and experience. Does anyone have any suggestions?

(I'll post a diagram of where I'm up to once I have my horrible scribblings converted to a nice circuit diagram).

Thanks in advance,

Christopher

[rogerinIowa]

I guess it could work, but don't really know about the range of values of the "bright cap", maybe slacker could give us a guide about it.
I was thinking about it many times before and I think it's a really good idea to have this "options" for the repeated signal

Greetings!

I dont really know about the ranges either, I guess I would need to breadboard them them to see starting with the stock 15n(?) and moving up and down from there...with that switch I mentioned I figure I may as well try to utilize all 6 throws, not too sure if all settings would be usable.. let alone musical. I plan to just run jumpers from the 15n cap spot on the PCB to a small breadboard and audition some differing values of caps. Who knows what might come of it!

just thinking

R

[Slade]

I guess it could work, but don't really know about the range of values of the "bright cap", maybe slacker could give us a guide about it.
I was thinking about it many times before and I think it's a really good idea to have this "options" for the repeated signal

Greetings!

I dont really know about the ranges either, I guess I would need to breadboard them them to see starting with the stock 15n(?) and moving up and down from there...with that switch I mentioned I figure I may as well try to utilize all 6 throws, not too sure if all settings would be usable.. let alone musical. I plan to just run jumpers from the 15n cap spot on the PCB to a small breadboard and audition some differing values of caps. Who knows what might come of it!

just thinking

R

I think that cap is acting just a high pass filter to the delayed signals, so it would be easy to find several usable values for this.

[Radamus]

How much current does this unit draw? I'm going to be building this and a power supply, and I want to make sure I order the right transformer. Thanks.

[FunkyGibbon]

Hi,

Thanks, Slacker, for this great project.

I've been working on a dual Echo Base design, a little different to CPM's ping-pong.

What I want is two more-or-less separate delays (the delay lines are parallel, not in series like in the ping-pong), that I could use to generate rhythms. I have most of the routing sorted (i.e. buffers, clean path, two delay paths, switching for mono or stereo output, tails or true bypass, grounded delay input when bypassed, etc), but the time functions have me a little stuck.

My first idea was to have a dual gang pot, so that both delays could be adjusted to the same delay time, and then a "fine" pot would change delay 2 by a bit.

Of course, I realised that this is not what I need.

I need a delay time for delay 1 (resistance "R" at the VCO lug (6) of the PT2399), and then the same resistance value is then divided for the delay time of delay 2 (i.e. R/2, R/3, R/4, R/6).

I'm assuming that smaller values for R give shorter delays.

I've hit a brick wall w.r.t. my knowledge and experience. Does anyone have any suggestions?

(I'll post a diagram of where I'm up to once I have my horrible scribblings converted to a nice circuit diagram).

Thanks in advance,

Christopher

Perhaps one way to tackle this might be to slave the second delay chip from the first one's clock out, and use some kind of frequency multiplier before it goes to the second delay. I'm trying to read about this now, but does anyone already know how this is done?

Thanks,

Christopher

[slacker]

I guess it could work, but don't really know about the range of values of the "bright cap", maybe slacker could give us a guide about it.

If you just want to brighten it a bit I'd try 10n, the problem is if you go too small it starts getting noisy on longer repeats. One thing I tried was to replace the 15n with a 100n in series with a 47k pot. This gave a reasonable tone control that goes from a bit brighter to much more filtered.

How much current does this unit draw?

Mine draws about 25ma.

[Slade]

I guess it could work, but don't really know about the range of values of the "bright cap", maybe slacker could give us a guide about it.

If you just want to brighten it a bit I'd try 10n, the problem is if you go too small it starts getting noisy on longer repeats. One thing I tried was to replace the 15n with a 100n in series with a 47k pot. This gave a reasonable tone control that goes from a bit brighter to much more filtered.

Thanks, slacker, I like that, I'll give it a try.

[ringworm]

Does anybody know the metric dimensions for the second, smaller layout pcb by anonymousfacelesscoward?
Much appreciated.

[Dimitree]

Hey Slacker, I added a passive send/return loop just before the filter on pin 16/15, so before the join of 10k and 47k..
Results: every repeat gets effected always more (this is what I want), but soon it get to feedback and oscillation (and the volume level is high).. I putted on the loop a whammy, then another delay..but it always oscillate.. Now I should try to put the loop after the 10k on pin 14, so before the splitting to out and to feedback.. You said that in this place the level is very high, so I'm not sure that there it would work well.. I want to send to the effect loop a "guitar" signal, if you know what I mean (sorry for my bad english)..

or maybe the problem is that this loop is passive?

[andrew_k]

Dimetree: I had the same problem, and I was using a JFET buffer on the send and another on the return. I ended up putting the loop after pin 14 and it worked well. I never check the level without the buffer, but if it is high the buffer is taking care of it without adding any clipping.

[Dimitree]

wow thanks for the info!
so you mean right after the pin 14, or after the 10k resistor?

I think that would be the perfect place, because the output signal is taken there, so why not take a part of this signal, put an effect on it and then bring  it back to delay 

[andrew_k]

Inserted at the junction of the 10k and the three caps, as slacker described in an earlier post.
With phaser, chorus or envelope filter is sounds great but with distortion effects it still howls a bit.

When I get home from work I'll write up the details of the EQ mod I did. I messed around with various tone and gain recovery circuits but the end result is quite useful without much loss in repeats or additional noise.

repeat clipping - my echo base tends to clip with a humbucker guitar, even though the pickups are only ~8k. Can anyone suggest mods to raise the headroom? If it's likely to fix it, I'm willing to add a 9V regulator and run the opamps off a higher voltage. Any suggestions are very welcome

[fhsueh]

So I successfully eliminated the ticking by placing a 4.7 uF cap from Pin 7 of the LFO op amp to ground. (That was the only cap I had). Thanks for that tip, Ian.

repeat clipping - my echo base tends to clip with a humbucker guitar, even though the pickups are only ~8k. Can anyone suggest mods to raise the headroom? If it's likely to fix it, I'm willing to add a 9V regulator and run the opamps off a higher voltage. Any suggestions are very welcome

andrew_k: I was going to post the exact same problem.  I just noticed that there is clipping/distortion on the very first repeat when playing through my Ibanez PF200 (Super 70's humbuckers pickups).  The only way I could minimize/eliminate the clipping is by turning down the guitar volume quite low.  It's not a problem playing through the single-coils on my Strat. I too hope there is a mod that can address this. 

[slacker]

repeat clipping - my echo base tends to clip with a humbucker guitar, even though the pickups are only ~8k. Can anyone suggest mods to raise the headroom?

I take it the dry sound is fine, which means the problem isn't with the opamp input and output buffers.
A couple of people have mentioned problems with humbuckers, unfortunately none of my guitars had hot pickups when I built it so it wasn't ever a problem for me.

I can think of a couple of things that could be causing it.
1. If your signal is hot enough it could be causing the diodes in the feedback loop to clip, especially at higher feedback levels. Try removing the diodes connected to the feedback pot and see if that solves it. If it does then either leave them out completely, or try replacing them with 2 diodes in series each way, or even LEDs. The only downside to doing this is that the self oscillation will be louder, which may or may not be a problem 

2. The opamp stages in the PT2399 might have too much gain. You can reduce this by reducing the size of the 47k resistors attached to pins 14 and 15. Try temporarily putting another 47k in parallel with one or both of them and see if that solves the problem. If it does then replace them with 20k - 30k resistors, you might find the tone of the delay changes a bit doing this, but if it solve the clipping problem, I'll figure out how to change the caps in those stages to get the tone the same.
It might also reduce the volume too much for you, but you can probably get that back by decreasing the size of the 10k that follows the level pot.

[andrew_k]

Thanks Ian 
The clipping diodes idea came to me last night  but I didn't have a chance to test it. When I first built the E.B. I tried some Ge diodes and of course the result was heavy clipping... all the time! Of course if I switch to LEDs I'm going to have to mount on so it's visible from the  top of the pedal 
I'll try your suggestions tonight and report back.

I also have delayed signal bleeding through when bypassed. Quite a bit actually, enough to make it unusable at gigging volumes. BUt one thing at a time, I'll focus on the clipping first.

Thanks again.

[bayonetblue]

What type of stomp switch is used in this circuit?

I have one built up...just need to go pick up the switch.

Thanks

[Radamus]

How much current does this unit draw?

Mine draws about 25ma.

Thanks.

Hey Slacker, I added a passive send/return loop just before the filter on pin 16/15, so before the join of 10k and 47k..
Results: every repeat gets effected always more (this is what I want), but soon it get to feedback and oscillation (and the volume level is high).. I putted on the loop a whammy, then another delay..but it always oscillate.. Now I should try to put the loop after the 10k on pin 14, so before the splitting to out and to feedback.. You said that in this place the level is very high, so I'm not sure that there it would work well.. I want to send to the effect loop a "guitar" signal, if you know what I mean (sorry for my bad english)..

or maybe the problem is that this loop is passive?

When you get that figured out, I would really like to see a schem for the mod. I think having that option would be really cool, like running it through an envelope filter, so every delay becomes more focused at the low end, etc. It's like one of those DJ effects.

[fhsueh]

What type of stomp switch is used in this circuit?

I have one built up...just need to go pick up the switch.

Thanks

I used a DPDT stomp switch (just one side of it).

[andrew_k]

REPEAT CLIPPING If your echo base build has distorted repeats (but clean bypassed signal) remove the clipping diodes next to the feedback pot.

I love it when the simplest solution is the one that works! 

[fhsueh]

REPEAT CLIPPING If your echo base build has distorted repeats (but clean bypassed signal) remove the clipping diodes next to the feedback pot.

I love it when the simplest solution is the one that works! 

Great. Will try this tonight. By the way, do we need to remove both diodes? What happens if you remove just one?

And don't the diodes prevent the feedback from getting too loud (when knob is turned CW all the way)?