Wednesday, 18 April 2012

Merlin Blencowe's One Chip Chorus

Another one of these nice little PT2399 projects to try out.  This was a from a schematic posted by Merlin Blencowe and it seems to give a nice range of vibrato and chorus sounds for such a simple design, using just the PT2399 IC and nothing else driving it. 

Clip made by Merlin (he posted that any noise was due to his recording setup and not the effect).

Yes the chips can be temperamental, but the results can be great for some of these effects.  Just don't forget to buy 10 x PT2399's and keep trying them until you find one that works :o)


36 comments:

  1. Battled this for a while yesterday, and can't seem to get it right. I get the signal through, but it's just kind of an strange overdrive. Tried on all my PT2399s, but that's not the problem. Transistor can be unplugged, and that changes nothing. Should the led be illuminated? Mine isn't.

    I'll continue debugging procedures on this once i have the time...
    +m

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    1. Just been over the layout mate, and I've got the 100n from IC pin 8 going to the wrong row. It should go to pin 3 not pin 4. Layout updated.

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    2. Nah. Didn't change a thing. Forgot the say earlier that the rate pot also does nothing.

      There might be something else wrong with m,y build too, since i don't think that the voltages on the right hand side are healthy:
      Pins 1-8: 4,99|2,48|2,16|4,97|2,49|0,09|4,60
      Pins 9-14: 2,48 (yes, all of them)
      Pins 15 & 16: 4,49

      We got guests, so i have to stop for this evening.. :(
      +m

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    3. Grounding problem mate. Pin 3 should definitely be 0 volts, it's linked directly to the ground rail, and so if it isn't then either the soldering of the link is dodgy, or the ground rail isn't grounded. Did you put the double link under pin 3?

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    4. Yes double link is ok.. I just notices that the piece of paper i wrote the voltages do read:
      Pins 1-8: 4,99|2,48|0|2,16|4,97|2,49|0,09|4,60 - so i just forgot to write 0... There's only 7 voltages on that earlier comment.
      +m

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    5. Post a front and back pic mate. I've been over the layout a few times and it certainly looks right to me

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    6. I think there is something else badly wrong where. I have broken boards before by letting them have too much voltages in the wrong places. I'll rebuild it...
      +m

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    7. I've just been reading the "One Chip Chorus" thread on DIYStompBoxes and there is a post on there by Brymus which sounded very similar to what you describe. And a couple of pages later someone else posted that they had the same problem but swapping the PT2399s cured it.

      I'm confident the layout matches the schematic now, but I haven't read any other positive outcomes from Merlin's schematic other than from Merlin himself so I don't know if the schematic is 100% correct. He did make some corrections in the thread but the image didn't seem to change so I'm not sure what happened there.

      Maybe this is one to put on the backburner for a while until I can confirm a few things with Merlin.

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    8. Silly me. I could have read that thread too.. :)

      It's not that importantat circuit to me right now. I have built perfectly working Little Angel v4, which is more than enough. This just seemed like fun little board to try out. I thought about naming it "[sic]" as in "single ic chorus" :)

      If he confirms, let us know!
      +m

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  2. Any news on this? I really want to make it :)

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  3. i built a few different versions of this, but none of them seem to work. it's VERY temperamental as to 2399's...the last incarnation i built was working, so i boxed it up.

    sucker never worked again. i DID get it to be a one slap echo messing with it some, but so far i've found 2399's to be really problematic in general...no consistency to their quality control.

    i've bought from tayda, smallbear, ebay...all of 'em seem to have issues, and they all seem to randomly lock up.

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  4. Hmm. If you're using the schematic from merlinblencowe's photobucket, it seems to have 10µ from IC pin2 to ground and not 47µ. Pin2 is labeled REF, so that could be it. I might rebuild this to try it out.
    +m

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    1. Copy and paste syndrome! :o) I suspect it won't make any difference though. It's an internal vref and so it's just like the difference in using 47u or 100u for filtering in various other layouts. Both will work and higher values will have more of an affect.

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    2. I just built it per schematic, using 47µ for filter and 10µ for vref.. It's pretty ugly pitch bending phase/chorus :) Tried on all my PT2399s and at least it is consistent, as all of them work exactly the same :)

      I'll go through any mistakes i may have there tonight.. Right now i need to do something else :)
      +m

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    3. Oh. I had only one deviation from the schem/layout. The 91K resistor that sets the range of range pot - i used 100K, but that shouldn't contribute to pitch bending...
      +m

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    4. Someone on DIYSB mentioned it was more extreme than the other one chip chorus, so your description probably makes sense. So was the 47u to 10u the only change and can this be tagged?

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    5. Another thing to try by the way mate which is something that caused problems in the Deep Blue Delay until I made the change, is to ground pin 4. That's supposed to be a digital ground derived internally, but until that was attached to the board ground the IC kept locking up. Certainly worth soldering in a temporary link to see if it makes any difference anyway.

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    6. Ok. So, "extreme" means just bad sounding modulation... And i just now compared my circuit with the demo above - and it is just like that. Probably should have listened to that link earlier on... (Personally wouldn't exactly call that a chorus, but a "bad space junker")

      So 10µ was the only change and yes. It can be tagged. LED might want a + sign on top lead...

      I also grounded the pin 4. That didn't change anything.

      Are we likely to see that other, James Howard's "One Chip Chorus" from DIYSB? Demo of that sounds like it could be better...
      +m

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    7. Cool I'll tag it and I'll check out the other chorus. Cheers matey

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    8. Ooh. I just checked my wiring, and the depth is in reverse. I noticed that yesterday, but there was other hazzle going on.. So i forgot to say it...
      +m

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  5. problem solved? did not work here ..... what could it be?

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  6. my changes: 91k - 100k
    820k - 840k (620k+220)
    not work ... anyone succeeded?

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  7. Hello, I wanted to build this circuit and also the little angel chorus, to use with bass guitar. Is this reasonable or should they be modified in some way, like input caps etc? thanks

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    1. miguel, double the values of the coupling caps in the audio path and you should be good bro.

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    2. Thanks. Which would those be? I can imagine that the input 100n and the output 10n but I don't know if there are more in between.

      best

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  8. guys, i got this in an email the other day from one of the gents at bob keeley's site.. i hven't tried it, but just passing it on!

    Subject: Re:_Jimi_Pocius_Dot_Com

    Hey Pinkster,

    We were doing some searching for the PT2399 latch-up issues and found your problems on the tagboardeffects website and we had the same problem as you with the latching up everytime we powered it on and only after unplugging and waiting to plug it back in did it start working again…. We may have found a fix which is a 0.01uF capacitor across pins 2 and 3 of the PT2399. Worked for us anyways.

    Let me know if this fixes your problem!!

    Craighton Hale

    Keeley Electronics, Inc.
    www.robertkeeley.com
    1733 S. Fretz Ave. Suite C
    Edmond, Oklahoma 73013
    405-341-2025

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    1. Sorry Jimi, I'm going through some threads because I keep coming across posts that I missed last year when I was away at various times, and this is one of them. Did you try the cap and did it solve your issue?

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    2. nope, it just killed the only working build i had of this kinda thing (little angel).
      it's the fucking chips. they just plain suck!!

      Delete
  9. Breadboarded to save vero & solder... No overwhelming ticking and doesn't break up with humbuckers. I like it- it's like a lofi memory man set to slap back.

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  10. Hello, this one built, no ticking problems, but I have a volume loss with the circuit engaged. Is this normal?

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  11. Depends on the depth pot a bit- deeper setting can sound a bit lower in vol. I've tried SHO & Tillman preamp circuit after for vol recovery, preferring the Tillman.

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  12. I should also note I am using a 500kc pot for speed (slower) & I raised the input resistor to 1M to increase headroom (does cut vol a little).

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  13. anyone use a tranny diff than BC337?

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  14. Just thought I'd pop in and saw that a 10ohm or 20ohm resistor from pin 4 to ground should stop almost all lockups...

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  15. This is verified layout ??? Somebody explain please...

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