King Dubby PT2399 x 2 delay, momntary dub/oscillation switch

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Nocentelli
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Post by 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: Either 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.
The attachment king dubby_schem_nocentelli.jpg is no longer available
I've also done a vero, but won't have a chance to build it for a week so it's not verified yet:
king dubby_schem_nocentelli.jpg
I recorded a basic video while I was testing the switching arrangement on a breadboard:

vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

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Post by storyboardist »

Working on a PCB layout of this and one question: are the emitters of the PNPs connected just to each other or do they go to 9v or 4.5v?

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Nocentelli
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Post by Nocentelli »

They're just grounded, there's no significance to to different symbol.
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

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Post by Dirk_Hendrik »

I may be mistaken but fail to see how those PNP's conduct in this arrangement :scratch: The sudden use of a different ground symbol is confusing indeed.
Sorry. Plain out of planes.

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Post by Nocentelli »

Dirk_Hendrik wrote:I may be mistaken but fail to see how those PNP's conduct in this arrangement :scratch: The sudden use of a different ground symbol is confusing indeed.
It's lifted straight from the rebote 3 with no changes. The rebote 3 schematic shows the emitters connected to pin 4 (i.e. digital ground) but I always link pin 3 and 4: The different symbol IS confusing, I apologise again, but I copd thedelay section from the rebote schematic where a different symbol is used for digital ground.
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

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Post by Dirk_Hendrik »

I see what you mean. I'd say the Tonepad orientation of the transistors is wrong (someone reversed a top view and bottom vieuw) and the schematic was drawn from the layout.
Sorry. Plain out of planes.

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Post by storyboardist »

Here's my go at a layout for this thing.

Image

Dimensionally it could fit in a 125B, but if it were me...

Image

:mrgreen:

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Post by rock soderstrom »

Hi Nocentelli, I really like your King Dubby Delay with the momentary footswitch and I ask myself if I can do the same with the Multiplex Echo Machine? What do you think, is there any problem if I do the the same around IC2? :scratch: cheers
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Post by Nocentelli »

Because the multiplex has that 3P3T switch that gives either one PT, two PTs in parallel, or two PTs in series, i think you'd need to put the momentary switch for dub/punch-in between the output of the first opamp and SW1A.
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

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Post by rock soderstrom »

Nocentelli wrote:Because the multiplex has that 3P3T switch that gives either one PT, two PTs in parallel, or two PTs in series, i think you'd need to put the momentary switch for dub/punch-in between the output of the first opamp and SW1A.
Thanks, I will test it tomorrow. :thumbsup

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Post by Sirppi »

What transistors did you use? I built this using the first pair of pnp's i encountered in my transistor bin, and the time pot doesn't act very linear.

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Post by Nocentelli »

No, it's not very linear. I started off using a dual gang pot for time, but switched to the current mirror because I reasoned many diy-ers won't necessarily have duals kicking about in their parts stash. I can live with the 'reverse log' action of the pot, as it spreads the shorter (more useable?) times 80-500ms over the first half of the rotation where you might want more precision to match time to tempo, and the longer 500-2000ms, sample rate reduced graunchy repeats are restricted to the latter half of the rotation (I have three tap tempo digital delays to choose from if I want a much longer beat matched delay). If you reference the top of the time pot to 5v instead of 9v, you get a shorter maximum time, but it *seems* to respond slightly more smoothly.

I used BC559s for the pnps, I don't know if a different part would respond differently, may be worth trying.
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

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Post by Nocentelli »

Sadly on hold. I built a vero and it didn't work but I had no time and little appetite for debugging. It's currently sitting on my kitchen sideboard giving me occasional venomous glances. I'm not keen on posting a vero that is not verified by me (although I am fairly sure it's sound and I just screwed up the build and can't see it), but i'll post it in projects in progress so maybe some kind soul would lend another pair of eyes to check it over.
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

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Post by aishabag23 »

FWIW... I know this is an old thread, but I have built Storyboardist's PCB layout and it works beautifully.
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Post by Pedal Jerk »

Hi there. If I wanted to whip up one of these, but I wanted to use a dual-gang pot for the Delay Time rather than the current mirror configuration, what value/taper would you recommend for the pot? And do I just wire up each gang as a variable resistor from pin 6 to ground on each chip? I want to have a really smooth time control, and preferably limit the delay time range from 40ms to a little over 700ms on this unit. I have no need for super long, degraded delays. Thanks for any replies!

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Post by bsoncini »

Just built one of these from the tagboard site layout. Worked first try. Thanks for the circuit.

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Post by dgarlans »

Ancient thread, but I just build one of these (using the tagboardeffects layout) and while everything "works", the pedal is basically unusable and sounds horrible.

The reason is, according to my scope, the 5v supply for the pt2399 chips gets pulled down 5-10% when you strum the guitar, which slows the delay down and basically makes the delay sound like it's being dragged down, so you end up with the first repeats being slightly out of tune. the louder you play, the worse the sag is. It makes it sound like someone's trying to harmonize with you, but their guitar is significantly flat.

Any idea what could be causing the problem? I saw some youtube videos of a guy who built the pedal and had the exact same problem, his delays were getting modulated unpleasantly as he played.

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Post by computerchemist »

Funny thing is, I'm just doing some research before building the same thing and I did recall (can't remember where now) that when you're running two PTs from the same regulator then Bad Things Happen, including motorboating, interference and all kinds of nasty shit. The general consensus was to make two regulated feeds, with two 78L05s, one for each chip. There can't be that may dual PT projects so it should be easy to find on one of the forums.

I'm wondering how much current the 2 PTs draw and if it's the L05 going into protection mode that is causing the problem, AFAIK they can't do more than 100mA without going frumpy. Could you check current draw of the whole thing you've built in quiescent and in playing something loudly modes? It would clinch it if that's the case. Or just throw a 1A TO220 7805 in there instead and see if everything suddenly works.

One last thought, if (like me) you bought a shedload of PTs from china, it might be worth going through all of them as some clone chips work better than others. (May draw more current that others?)

Do report back please if you get any results! I'm thinking now to breadboard it until I get it working might be a better option than going straight in for the kill :(

dgarlans wrote:Ancient thread, but I just build one of these (using the tagboardeffects layout) and while everything "works", the pedal is basically unusable and sounds horrible.

The reason is, according to my scope, the 5v supply for the pt2399 chips gets pulled down 5-10% when you strum the guitar, which slows the delay down and basically makes the delay sound like it's being dragged down, so you end up with the first repeats being slightly out of tune. the louder you play, the worse the sag is. It makes it sound like someone's trying to harmonize with you, but their guitar is significantly flat.

Any idea what could be causing the problem? I saw some youtube videos of a guy who built the pedal and had the exact same problem, his delays were getting modulated unpleasantly as he played.

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Post by Nocentelli »

computerchemist wrote: One last thought, if (like me) you bought a shedload of PTs from china, it might be worth going through all of them as some clone chips work better than others. (May draw more current that others?)
I have not experienced this problem with >1 PT2399 sharing a 5v regulator, and I know there are a few DIY designs using this arrangement including The Abductor delay designed by deadastronaut (who posts at DIYSB), which uses 3xPT2399. However, as you point out, the quality of PT2399 varies depending on the supplier (e.g. some pt2399 seem much more susceptible to lock-up on powering up with a low resistance to ground from the delay time pin).
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

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Post by dgarlans »

I just ordered some real 7805's rather than the little 78l05 or so when those come in I'll swap it out and see if it is able to maintain regulation. I bought my pt2399's from a decent source but I'll try swapping them around too, I have two or three spares.

computerchemist wrote:Funny thing is, I'm just doing some research before building the same thing and I did recall (can't remember where now) that when you're running two PTs from the same regulator then Bad Things Happen, including motorboating, interference and all kinds of nasty shit. The general consensus was to make two regulated feeds, with two 78L05s, one for each chip. There can't be that may dual PT projects so it should be easy to find on one of the forums.

I'm wondering how much current the 2 PTs draw and if it's the L05 going into protection mode that is causing the problem, AFAIK they can't do more than 100mA without going frumpy. Could you check current draw of the whole thing you've built in quiescent and in playing something loudly modes? It would clinch it if that's the case. Or just throw a 1A TO220 7805 in there instead and see if everything suddenly works.

One last thought, if (like me) you bought a shedload of PTs from china, it might be worth going through all of them as some clone chips work better than others. (May draw more current that others?)

Do report back please if you get any results! I'm thinking now to breadboard it until I get it working might be a better option than going straight in for the kill :(

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