Tap tempo modded Echo Base PCBs in the works - vote on features

[Taylor]

I'm working on a nice pro double-sided PCB for the Echo Base, with the usual amenities of silk screen and soldermask. It's designed to fit in a BB enclosure, and so far it offers the following mods:

tap tempo for the delay using the PTAP
double time mod using a second PT2399
effects loop
modulation kill switch
feedback filter, to get filtered analogish repeats
oscillate momentary stomp switch
board mounted pots
mix pot

All of these are optional. You will be able to build a totally stock Echo Base with this board. Because of the physical limitations of a BB box, it won't be possible to fit all of these mods in a single build unless you were to step up to a larger box. For example, you just can't fit 3 stomp switches in a BB and have them really be usable, so you can't do both the tap tempo mod and the oscillation stomp switch in a BB (unless you made the byass a toggle switch). The tap tempo at this point only controls the delay time, which I know a couple of people will be bummed about. I just don't see tap tempo control over modulation to be universally wanted enough to warrant the extra size of the board.

As with the Gristleizer board, it has board mounted pots. This is to make what was before a massive amount of offboard wiring go a lot quicker, so this build will be much more leisurely and less prone to noise. But if you're into the wiring, or prefer a different pot layout than the board has, you can of course do offboard pots.

I'm running short on room, but are there any other features or mods you'd like to see incorporated?

[jkokura]

Just a question about the effects loop - will that be for effecting the 'delayed' signal only? Could that loop be switchable - pre delay signal, delays only, post delay signal? I have no idea of if an on/on/on dpdt switch would handle this.

I would probably put this pedal in an 1790ns personally. A DD would handle the three switches better, but it's a little too big for just one delay pedal. the 1790 might be a little small for three stomp switches, but would easily house all the knobs and switches for this project.

Is there a way to have it either be a mix pot or a level pot? Like depending on the builders desire? Or is that a part of the PCB that's either one or the other.

I want this board when you're done Taylor. Also, I'd love to know if you're going to do that tap tempo trem board too.

Jacob

[Taylor]

Yes, the mix pot is just an option, you can do the regular level pot if you'd rather.

It's possible to do the loop in a couple of different ways, but the main one is where each repeat gets more effected by whatever's in the loop (the fx loop is in the feedback loop). I can't think offhand of what would be gained by putting an effects loop before the repeats, but if you want to effect the repeats only once - putting reverb on them for example - that should be doable. The trick here is making it easy to build for people who don't want every option - the more stuff you add the more jumpers and confusion come into play when just building it stock. I'll try to find the right balance.

I do plan to do the tap trem, but haven't begun on it yet. There seems to be a flurry of new work done on that tap chip, so I'm kind of waiting for that to get stable.

[slacker]

Cool, that will be an impressive board.

If you're going to add a mod kill switch you might be interested in this.



That's how I've implemented it in mine. This makes the LED flash when the modulation is on and just light up when it's off as well as acting as the effect on/off indicator, that way you don't need a separate modulation LED. It's best to use a super bright or ultra bright style LED that way you can use a big current limiting resistor like 50k or so, that way you don't run the risk of it ticking.

[Taylor]

Ooh, that's very clever Slacker. I was planning to just short that 1uf cap, but that's a cool trick, I'll have to add it.

And I'll just take this chance to give props for my favorite of all the projects DIYSB'ers have come up with - the Echo Base is such a fun, great-sounding circuit, and a slick design to boot. And I find something strangely pleasing, aesthetically, about the schematic... 

[slacker]

And I find something strangely pleasing, aesthetically, about the schematic... 

Cheers, took me almost as long to draw the schematic as it did to design the thing.

[Morocotopo]

You might want to check my version of the thing:

http://www.diystompboxes.com/smfforum/index.php?topic=78403.0

[Taylor]

You might want to check my version of the thing:

http://www.diystompboxes.com/smfforum/index.php?topic=78403.0

Will do.

After digging, I realized that the Echo Base's LFO won't work right with the PTAP, so I may have to do a different LFO...

Also, I think I'll have to do the dual PTAP, so you can either do a single PT2399, or 2, but if you want tap tempo, you'll have to have 2 PT2399's. Can't think of a clean way to allow using either the single or dual PTAP.

[mth5044]

tap tempo for the delay using the PTAP

I thought the PTAP wouldn't work (accurately) with the echo base without disconnecting the modulation?

[Taylor]

Yep, see reply #7... someone said the Magnus Modulus (which is just the Tremulus Lune LFO) works with the PTAP, so I may go that direction.

[slacker]

It's not the LFO that PTAP doesn't work properly with, it's the fact that it uses a transistor to do the actual modulating. You can keep the LFO, but do the actual modulation using the method from the Magnus Modulus, which uses a resistor with a cap to add the modulation signal if I remember correctly.

[jkokura]

the Ping Pong delay (I think from BYOC ) is a dual PT2399 that offers a longer delay amount. I would like to see this unit contain w Pt2399's. The Echo Base, Rebote and PT-80 all use one PT2399. I'm going to be building the latter two both with the ptap function, so one with more delay would be fun to have, and I would of course be adding the tap tempo function. That's just what I think though.

Jacob

[slacker]

You might want to have a look at this thread as well http://www.diystompboxes.com/smfforum/index.php?topic=78047.msg642998#msg642998 it's got an improved version of the buffers that make the pedal a lot quieter.
Add those plus the other mods I posted and that's what mine's like at the minute, it's got a slightly reworked LFO as well but that's not really worth bothering with.

[Taylor]

the Ping Pong delay (I think from BYOC ) is a dual PT2399 that offers a longer delay amount. I would like to see this unit contain w Pt2399's. The Echo Base, Rebote and PT-80 all use one PT2399. I'm going to be building the latter two both with the ptap function, so one with more delay would be fun to have, and I would of course be adding the tap tempo function. That's just what I think though.

Jacob

Jacob, as mentioned in the first post this will have a second PT2399 for double time.

[mth5044]

Wait... the PTAP works with the EchoBase now?










ARRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRUUUUUUUUUUUUUUGGGGGGGGGGGGGGGGGGGGHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH



Did anyone ever try adding a compander to the echobase?

[jkokura]

Jacob, as mentioned in the first post this will have a second PT2399 for double time.

Sorry, I thought that this was an idea, not a confirmed plan.

Jacob

[Taylor]

Sorry, I thought that this was an idea, not a confirmed plan.

Jacob

Yep, everything in that list should end up in the PCB, unless for some reason it just can't be done. I've budgeted space for all that stuff, and the PCB is mostly filled. Just working out the finer details of the PTAP. Besides integrating the LFO and the PTAP, we actually need a customized PTAP for this, since having 2 PT2399s means each one needs to be programmed for half the tapped time. I'm trying to verify with the maker of the PTAP that we can get this to happen.

[Taylor]

It's not the LFO that PTAP doesn't work properly with, it's the fact that it uses a transistor to do the actual modulating. You can keep the LFO, but do the actual modulation using the method from the Magnus Modulus, which uses a resistor with a cap to add the modulation signal if I remember correctly.

So is it as simple as this?



If that's all that's necessary, and I hope this doesn't come across the wrong way, but why did you decide to do the modulation with the transistor?

[SPAZ]

  Very nice features, looks great to me! what about calculating dotted 8Th's' etc ?

[slacker]

So is it as simple as this?

Yeah, that should do it. You'll probably need to tweak the value of the 240K resistor between the LFO and the depth pot, or remove it all together, because that's dropping the voltage down to what the transistor wants. I haven't actually tried this method so I don't know how the performance compares with my method, but the clips of the Magnus Modulus sound good.

If that's all that's necessary, and I hope this doesn't come across the wrong way, but why did you decide to do the modulation with the transistor?

Perfectly reasonable question the short answer is I didn't know you could do it like that. I've no idea how ForcedFIre came up with that idea, but it's a very neat solution.

The long and boring answer is that no one really knows how the delay is set in the PT2399, except that changing the resistance between pin 6 and ground controls the time, that's all the data sheet tells you. There's plenty of speculation about how it works, but as far as I know no one's ever figured it out.
So everyone who's ever attempted to voltage control the chip, except Mr ForcedFire, has used some sort of voltage controlled resistance to do it. A couple of people here added LFOs to Rebotes using vactrols to control the delay time, that's what started me off on the Echo Base. I decided not to use vactrols because depending on where you come from they can be difficult to get hold of and can be expensive, and if you roll your own the results would be too variable and you'd need to add trimmers or do a lot of tweaking to get consistent performance.
I researched it a bit and found a couple of synth DIY guy's had done VC PT2399 designs, one used a JFET, but I decided against FETs mostly because I didn't have any and partly for the same reasons as for vactrols. The other design used a more complicated method using a transistor so I went down that route but using something simpler.