PTAP: PT2399 tap tempo control

[Auke Haarsma]

Thanks for the EchoBase explanation Ian. I'll be looking forward to your review of the taptempo+echobase

[decc]

On the Echo Base when the modulation level is set to minimum the PNP transistor + 39k combo looks like a very small fixed resistor, I don't know the value but its probably less than 100 Ohms. Providing the PTAP doesn't need the 1k series resistor for timing accuracy or current limiting purposes it will work fine like this. If it needs the 1k for any reason you would need to add this, this would then raise the minimum delay time so the chorus type sounds with the delay time pot on or very near minimum will probably be affected. 
Even if you don't need the 1k resistor, according to the datasheet for the MCP41050 (page 14) the minimum resistance when used as a variable resistor is around 125 Ohms, so the chorus type sounds might be affected anyway.

The 1k resistor is taken in to account with the lookup tables for timing and current limiting. I think the delay may not be able to get low enough for chorus. (2.5V / 1mA = 2.5k min total R for a min delay time of about 56ms. Good enough for 16th notes at 250bpm though!)

Does it sound smooth though, because on some digital delays you can hear that the delay time is changing in distinct steps. What I'm talking about here is grabbing the pot and sweeping it back and forth as an effect not just setting the delay time with it, I should have made that clearer when I first asked the question.

Looking at the datasheet and the traces of changing from setting 0x7F to 0x80 I'd say it looks like they didn't bother using a grey-code in there. The resistance bounces around for a couple hundred nano-seconds before settling down. So in theory, no. However trying this out I'd say at human scales it seems to work. It's not really intended for that though.

Just thinking aloud here, I wonder if you could replace the voltage divider feeding the MCU with a CV in and modulate the delay time using the digital pot. That would be fantastic 

Good idea, not sure it would work though. The code is averaging out the input specifically to avoid the situation where the ADC varies around a bit transition leading to unintended modulation. Then there's the problem of the digital pot transitions as well. So at this point I would say that it is not well suited to modulation circuits. However I also was trying to make the modifications of the host delay circuit to use this controller minimal. Maybe some good old analog cleverness thrown in can help out and make the PTAP "Echo-Base Compatible".

A couple questions then for you: What is the min/max voltage swing and frequency of the modulation, and min/max delay times?

[roseblood11]

Hi,

did anyone try to put the MV-52 into a pt-80, rebote or echobase? Looks really interesting:

http://www.smallbearelec.com/Detail.bok?no=795

http://www.moltenvoltage.com/mvcart/index.php?main_page=product_info&cPath=66&products_id=215&zenid=f4ad791fc6889fb91e077b6075735c0a

[slacker]

The MV-52 can't be used as a tap tempo to control the delay time, well it probably could with a lot of extra circuitry, but the PTAP is a much better solution for that. Have a look at this thread http://www.diystompboxes.com/smfforum/index.php?topic=75600.0 for more info.

You could use the MV-52 to make a tap tempo LFO for the modulation in the Echo Base, and use the PTAP to do the delay, that would be pretty cool.

[mth5044]

Anybody get anywhere with this yet?

On the echo base in particular 

[decc]

No one that has one has given me any feedback yet, unfortunately. (I hope this just means everything's working great, right? )

And even though I posted this in the Echo Base thread I guess here would be the more appropriate place for the layout:





There's the PTAP2 for dual PT2399 delays now too, BTW.

[RonaldB]

Just orderd a PTAP from your site 
I'm looking forward to this.

[decc]

People have been asking about PCBs as well so I had a few made up for both versions (PTAP, PTAP2).

Again thanks for all the help from everybody!

[Auke Haarsma]

looks sweet!

[mjcyates]

I purchased this kit and am a little confused as to how to hook it up. I have built several pedals but my knowledge of this stuff is limited.  Can someone post a picture or simple diagram of this kit hooked up to a PT2399 delay (mine is rebote 2.5). My end game is to have two rebotes in one box, one always on for ambience, the second hooked up to the ptap for rhythmic stuff. Any help would be greatly appreciated. 

[decc]

Pardon me for asking, but have your read the manual? There is also a schematic for the PCB that goes with the PTAP.

Basically the delay pot is disconnected from the rebote and is re-connected to R1, and the 3-points labelled J1 go to the rebote board where the delay pot was before. S1 is where the momentary tap switch is connected. And of course don't forget +9V/GND.

Here's a rebote before modification. As you can see all that was done was disconnect the delay pot on the left:


Next is with the PTAP board installed. The delay pot is connected to the points labelled R1 at the top, and the points labelled J1 go back to the rebote board.



Hope that helps

[mjcyates]

Well yes I did read the manual and yes I saw the schematic. As I said my knowledge is limited. I can follow cook book recipes and wiring diagrams (aka general guitar gadgets project files, etc.) and such. The pictures should help. Thanks.

[edd29]

Pardon me for asking, but have your read the manual? There is also a schematic for the PCB that goes with the PTAP.

Basically the delay pot is disconnected from the rebote and is re-connected to R1, and the 3-points labelled J1 go to the rebote board where the delay pot was before. S1 is where the momentary tap switch is connected. And of course don't forget +9V/GND.

Here's a rebote before modification. As you can see all that was done was disconnect the delay pot on the left:


Next is with the PTAP board installed. The delay pot is connected to the points labelled R1 at the top, and the points labelled J1 go back to the rebote board.



Hope that helps

can you post the  video in youtube . thanks

[kristoffereide]

I'm sorry, but what IC's do I use? I'm at my work computer and can't enlarge any photos. Will it work woth ANY 2399-builds??? This is genius!!!

[ppatchmods]

hey just bought the ptap and pcb for my rebote. is there a way to have a rate led atached to the board? thanks

[kristoffereide]

mini-bump: What IC do I use? I can't enlarge the schem...

[mth5044]

Not sure what IC you mean... the IC's for the PTAP are in the instructions, and it's for PT2399 builds.

It won't work quite right with any PT2399 that don't have the 1k resistor coming out from pin 6, like the echo base.

[Taylor]

mini-bump: What IC do I use? I can't enlarge the schem...

If I understand your question, you are looking to build this with off-the-shelf ICs? Like, stuff you can get at Mouser? You can't, because you need the preprogrammed MCU from user "decc".

[kristoffereide]

Oh, thanks! That was the answer I was looking for... Well it's not expensive, so I'll guess I'll just have to try it out

[ppatchmods]

What's the best option:  the rate led attached to the delay circuit or the ptap? Anyone done this?