King Dubby PT2399 x 2 delay

[nocentelli]

Here's a variation on the deep blue delay; two PT2399 chips and a current mirror delay pot give around 2200ms delay, although beyond 700ms gets pretty lo-fi. There are two points where a momentary SPST can be used to briefly connect the input to the delay input on select phrases (dub mode), or to bypass the repeats feedback resistor for self-oscillation on demand. I use a DPDT toggle switch to choose dub or oscillation mode using a single momentary footswitch.

I recorded a video whilst trying the switching out on the breadboard:

https://m.youtube.com/watch?v=ioN-4r8J9MA

[rocket88]

Man this looks and sounds awesome. No joke you had me at king tubby. Instantly on my build list, now I just got to get some momentary stop switches. Fantastic job man, fantastic job.

[Travis]

I agree this sounds awesome. Must build! My friend has been bitching at me to build him a delay and this is the excuse I needed

Thanks for sharing nocentelli. Sounds really cool, I love the clip!

[Synsound]

Just as my to do list was clearing up. I agree about the awesomeness of that sound. I will have to do this one. Thanks

[Synsound]

What is the reason for the "+9v and ground" notation between the top two ic's?
I see that the ground rail continues to yhAt point but the 9v has a low value resistor in line. Are you indicating another connection here?

[nocentelli]

I just stuck those texts there as place markers when I was starting on the vero layout, to remind myself where to connect the IC and regulator, it doesn't indicate another connection is needed. The red wire is where the 9+ supplied by the battery (unwise) or more likely adaptor should be connected: the point marked "+9v" will not actually measure 9v, more like 8v since the 33r will drop a bit of voltage, alongside the filtering effect it has with capacitor.

[Synsound]

Great. Thanks for the clarification.

[tabbycat]

thanks nocentelli, this sounds shit hot. am looking forward to the vero.

re the functionality. the momentary dub switch the blue button box you keep pressing, that seems obvious (delay circuit engaged/disengaged). but i wasn't entirely sure where the momentary oscillation switch came in during the clip (8m22s sounds like what i would imagine it to sound like, but that looked to result from cranking a pot rather than hitting a switch?).
looking at the schematic it appears to make a feedback loop between pin 14 of ic2 and pin 16 of ic1 via the repeat and feedback pots, so it will be positive feedback with each repeat increasing in volume?

apologies for the maybe obvious questions but am getting increasingly curious about the tweaking potential of the pt2399 and you seem to know it pretty well.

as an aside i thought i would throw this into the mix in case anyone hadn't heard of king tubby.



i remember john peel playing this in the late 1980s (i used to record all his shows and listen back to them on the train to college) and it became the bridging track that led me from 60s stuff like prince buster and blue beat to the more 70s dubby side of things like augustus pablo, scratch perry, etc. still classy.

[nocentelli]

Yeah, it's not brilliantly demonstrated...

In oscillation mode, the momentary switch bypasses the series 5k resistor in the feedback path so boosting the level of the feedback: The effect this has on the sound depends on the repeats pot setting (as well as delay time and guitar input level) so with just a handful of repeats, the switch makes them more prominent; with medium repeats, the fade out is extended; if you increase the repeats pot to the point self oscillation, then back off a little, the momentary switch will boost the feedback so it builds to oscillation.

If you watch carefully at 3m07, i flick the toggle switch on the left to switch to oscillation mode: There are then a few examples of how this works - the repeats are present all the time but pressing the momentary button raises the level of feedback and triggers the fading repeats to veer into oscillation which drops off when the button is released. I've looped that section here -

http://loopthetube.com#ioN-4r8J9MA&start=185.565&end=230.934

(The pots are - left to right: MIX, REPEATS, TIME)

All PT delays have feedback from the delay output to input (pin 14-16) or they would only do a single repeat. They usually have an RC network which dampens the level and treble content of this feedback to dampen runaway oscillation, reduce hiss and help mitigate low sample rate graunchiness at longer delay times. There is usually a pot to control the exact level: More level means repeats are recirculated for longer before they are bled to ground and fade out (in the dbd, the RC network is a bandpass filter, with the 22n restricting bass, and the 2k and 47n progressively trimming treble, so repeats become more middle-ly as they fade or built to oscillation, though it's possible to change this to any tonestack you like, e.g resonant LPF). I also added a pair or diodes to the repeats pot wiper, because i found that when it went into self-oscillation, there was a prominent transition from clean-ish repeats to (PT2399) opamp clipping. The echobase has these diodes, and it just means there is a more graceful slide into the whistling of the oscillation, much like the way diodes are used to smooth the clipping in an opamp dirt pedal. The repeats are clean if they fade, but if they get louder and start building due to self-oscillation, the diodes limit the level by clipping the peaks to ground before the PT starts to clip itself.      

I built a vero yesterday, and i'm going to box it today so i'll hopefully be able to post a verified vero asap (and maybe a video that better illustrates the oscillation mode).

King Tubby - Dub fi Gwan!

[rocket88]

I'm so glad others here know about king tubby. The first two dub albums I bought were the upsetters "blackboard jungle," and harry muddie meets king tubby in dub conference volume 1. Still two of my favorite albums ever.

[tabbycat]

nocentelli wrote

Yeah, it's not brilliantly demonstrated...

well it convinced me i wanted it, which is most of the battle. i must have missed the switch flick as i was mesmerised by all the other things going on. you should do that thing with three cards in covent garden. £10 a game, you'd clean up.

big thanks for the explanation of how the thing hangs together as a circuit. definitely useful to get the pt2399 working detail. the diode addition was something i was curious about. so they are working in a slightly gatey way, rather than the downright distorted-dirty way they do as clippers in a fuzz.

am dreading (see what i did there) the size of this vero layout, but i think this is too good to do without. bring on the pain.

rocket88 wrote

I'm so glad others here know about king tubby. The first two dub albums I bought were the upsetters "blackboard jungle," and harry muddie meets king tubby in dub conference volume 1. Still two of my favorite albums ever.

if you are into effects you can't ignore tubby or dub. he's definitely up-there in the ranks of need-to-know-about. though my tubby pablo etc thing was more a phase i went though (a module i opted for at the uni of john peel) than a lasting thing it seems. also sharing a house with a dub head who listened to scientist etc 247 overexposed me. ended up swapping my double tubby lp with him for the blast first 'nothing short of total war' double lp (rare sonic youth, big black, etc cuts). which i then played back at him 247. a most appropriate album title.

but i still hear tubby in the bands i listen to and love now. see that girl move...

[Beaker]

I'm a massive Dub fan too, so I have to build this I have a super rare Teac Echo 8, the only onfo that I can find on it, is that King Tubby had one in his studio. Good enough for me. It's being repaired at the moment though.

Talking of hearing King Tubby's influence today, have you heard "From Kinshasa" the debut album by Mbongwana Star?

Check this out - but PLAY IT LOUD!!!



Then be blown away by this!

[rocket88]

oh man beaker, i actually have. soooooooooooooooooooooo good.

you know tabby? i really got tired of the yea yea yea's after there hit maps. it literally drive me insane, and i thought they were just another talentless scene kids. but you know what? i really dig it. might have to give them another chance now that they seem to have grown up. lol

[Beaker]

Oh Zach, I knew I could rely on you!  

It's the best thing I've heard in years, a glorious mash up of Congolese Rhumha, post-punk Dub basslines, German Techno synths, and distorted guitars from outer space.

[tabbycat]

re the yyys, first album was a 9/10 for me, a mighty debut. the second a 7/10. and the rest has been hit-and-miss since then. they seem to have been stuck in a permanent awkward 'white album-y' phase of experimentation and groping around for a post-garage idiom that fits since the second album. sometimes striking gold, sometimes the other stuff, but the class is there is spades when it all does come together.

karen o is always magnificent, and nick and brian can compete with any four-piece band for balls and thunder. i have faith in the fundamentals so the rest is holding on for the sweets and forgiving the dead ends.

[Synsound]

Am I the only one that can no longer see the veto layout? Was it pulled?

[tabbycat]

Synsound wrote

Am I the only one that can no longer see the veto layout? Was it pulled?

according to nocentelli's post above the vero is still being verified.

nocentelli wrote

I built a vero yesterday, and i'm going to box it today so i'll hopefully be able to post a verified vero asap (and maybe a video that better illustrates the oscillation mode).

[Synsound]

Oops,
Sorry I must have skipped right over that.
Thanks

[tabbycat]

hey nocentelli, is the other ic an OP275/AD712 as per deep blue? am going to do a bits order before the weekend and wanted to make sure i have it ready. thanks for the confirmation.

[nocentelli]

Sorry for the (ahem) delay in responding, I've been away: Tabby - I would think any dual opamp will do, I've got a TL072 going in mine. Synsound - My vero is yet to be verified: I built it a while back but the bastard thing didn't work, then I went away for a week. I'm convinced the schematic is correct, and pretty certain the vero matches the scheme, so it's likely to be an error in my build. I'll have a poke around at it and post the vero when I get it working.