How to "Sshhhut" up a PT2399 once and for all!

Earthscum · July 02, 2011, 11:59:47 PM

So, I was running through ideas on the Little Angel thread HERE and going through the new data from Merlin and it dawned on me...

On the Datasheets, there are only 2 ends terminating to digital grounds. Merlin made note that the Pin 4 "Digital Ground" can be left unconnected, because it is already connected to analog ground through a 10 ohm resistor.

So, I have tried this on a Little Angel, and my noise pig Sewer Pipes Ringverb. I could not get the SP to shut up, no way, no how.

All we gotta start doing is connecting the delay resistor between Pins 6 and 4. That's it. No more "SSHhhhh" until the signal dies out. Awesome stuff!!!

Anyone else want to confirm this for me? I have quiet PT effects, finally! It's too sweet.

frequencycentral · July 03, 2011, 05:04:12 AM

$h!t yeah!

Looking at the PT2399 datasheet, the delay resistor is actually connected to digital ground, not analogue ground. How have we all missed this crucial peice of information for so many years?

Genius David!

If this is as good as it sounds I'm amazed, excited and in awe!

WhenBoredomPeaks · July 03, 2011, 07:05:38 AM

I am thinking about how to realise this on my Tonepad Rebote 2.5 pcb without too much destruction.

edit: it looks like that i should cut the connection right between the legs 3-4 and probably should ground that 47uf cap from leg 2 to an analog ground.

Earthscum · July 03, 2011, 11:22:24 AM

yep, apparently the delay resistor just gets connected straight to pin 4 from 6. I'm still using LA Ver1 with 10n integrating caps and 1n filter caps, and it's still a bit hissy, but it's the regular hiss (may be getting most from the 5532, got an hour or 2 before I have to load stuff up for a show, so I'm gonna check it out now). I did no other mods to the circuits, and was about to start digging for tants, rewiring grounds, etc, bigger caps, and thought about this. So, I do believe this may be the final cure-all for the noise issue. I'm stoked to really start putting some pain to sound with these now... and I can realize my new project (noise was going to be the biggest issue, running harmonics only through delay).

I bet James' (anchovie)Noise Ensemble would even sound "GREAT" with this fix!

ETA: Yep... 100p across the 470k feedback took off the top hiss in the LA... now I think the last bit of digi noise I have is from the Vref. It's just slight clock noise I can hear now that the hiss is gone.

Derringer · July 03, 2011, 12:28:39 PM

Hi guys, I haven't built a delay yet but have just recently ordered some pt2399 chips to finally give it a go

I'm looking at the Echobase schematic here: http://www.eskimo.plus.com/fxstuff/echobase.png
from Slacker's thread : http://www.diystompboxes.com/smfforum/index.php?topic=60662.0

Are you saying Earthscum, that i would simply eliminate the jumper between pins 3 and 4 on that schematic?

slacker · July 03, 2011, 01:58:51 PM

Yeah, just remove the connection between pins 3 and 4.
I'm going to try this on my Echo Base and see if it makes a noticeable difference, should be easy enough on the vero layout it just means cutting a jumper and moving one resistor.

Quote from: frequencycentral on July 03, 2011, 05:04:12 AM
How have we all missed this crucial peice of information for so many years?[/b]

I don't think it's that people missed it, on most schematics when you have separate digital and analogue grounds you connect them together at a single point, this is what everyone has done. There's nothing in the data sheet to indicate that there is an internal connection between pins 3 and 4, so it's natural to assume that they both have to be connected to ground.
It's only Merlin's experimentation that has brought this to light, although I seem to remember a couple of years ago someone saying they had accidentally missed the connection between pins 3 and 4 and their pedal worked, I don't think anyone ever followed that up though.

skiraly017 · July 03, 2011, 02:52:37 PM

I'm very excited but a little confused.

Earthscum says, "All we gotta start doing is connecting the delay resistor between Pins 6 and 4."

And then Slacker says, "Yeah, just remove the connection between pins 3 and 4."

I understand Slacker's instructions but not Earthscum's. There's the delay resistor that comes off pin 6 in series with the delay pot that sets the minimum delay time but I don't see a resistor between pins 4 and 6 on the Rebote schematics. Earthscum, are you referring only to the Echo Base? For the Rebote, are we just clipping the trace between pins 3 and 4? Thanks!

Earthscum · July 03, 2011, 04:11:48 PM

Basically, on the datasheet schematics, there are 2 grounds that terminate to digital grounding. We all assumed that the grounding was all universal, however I believe that we've been looking at it wrong, and that the delay resistor should be connected to pin 4 instead of ground, and the bridge between pin 3 and 4 cut so that the delay resistance shunts noise back into the "digital ground". I think it's more of a digital ground IN, rather than a normal ground.

Got a show to play... we have about $2500 in big fireworks, should be fun! I'll get back on this tomorrow afternoon, probably.

skiraly017 · July 03, 2011, 04:45:54 PM

Quote from: Earthscum on July 03, 2011, 04:11:48 PM
Basically, on the datasheet schematics, there are 2 grounds that terminate to digital grounding. We all assumed that the grounding was all universal, however I believe that we've been looking at it wrong, and that the delay resistor should be connected to pin 4 instead of ground, and the bridge between pin 3 and 4 cut so that the delay resistance shunts noise back into the "digital ground". I think it's more of a digital ground IN, rather than a normal ground.

Got a show to play... we have about $2500 in big fireworks, should be fun! I'll get back on this tomorrow afternoon, probably.

So we're looking at something like this?

Govmnt_Lacky · July 03, 2011, 04:53:29 PM

Quote from: skiraly017 on July 03, 2011, 04:45:54 PM
So we're looking at something like this?

Can anyone say.... Rebote 3.0??

iq01221 · July 03, 2011, 05:11:16 PM

Is that verified?

slacker · July 03, 2011, 05:12:25 PM

Yeah exactly like that.
I've just done the mod to my Echo Base, I haven't had chance to do any tests to see if it's any quieter but it works fine. I'll do some tests tomorrow.

rockhorst · July 03, 2011, 05:45:15 PM

The other day I did all the resistors on the Rebote PCB...I'm gonna wait a little longer to finish it until someone verifies this stuff

iccaros · July 03, 2011, 06:42:01 PM

could be not just pull pin 4 out of the socket on already created PCB's to get the same benefit, as 4 can say unconnected, and not go to ground.

Govmnt_Lacky · July 03, 2011, 06:55:15 PM

Quote from: iccaros on July 03, 2011, 06:42:01 PM
could be not just pull pin 4 out of the socket on already created PCB's to get the same benefit, as 4 can say unconnected, and not go to ground.

I think the reasoning is that the resistance set on Pin 6 needs to be grounded to the "digital ground" on Pin 4. So the process has 2 phases:

1) Seperate the digital ground on Pin 4 from the rest of the "analog" grounds.
2) Remove the "analog" ground side of the delay resistance coming off of Pin 6 of the PT2399 and re-ground it to the digital ground on Pin 4.

Of course... I may be waaaaayyyyyy off base

iccaros · July 03, 2011, 07:16:28 PM

Got ya.. So on the Rebot 2.5 we cut the trace between Pin 3 and 4 lift the ground side of the 47uf from pin 2 and send that to system ground

Govmnt_Lacky · July 03, 2011, 07:22:13 PM

Quote from: iccaros on July 03, 2011, 07:16:28 PM
Got ya.. So on the Rebot 2.5 we cut the trace between Pin 3 and 4 lift the ground side of the 47uf from pin 2 and send that to system ground

I reckon that is correct

For ease of trouble... you could connect the negative side of that 47uF directly to Pin 3 of the PT chip.

THIS IS ALL SPECULATIVE AT THIS POINT! I am merely commenting on what has been explained above. I do not guarantee that this is in any way a VERIFIED fix!

iccaros · July 03, 2011, 08:26:21 PM

Quote from: Govmnt_Lacky on July 03, 2011, 07:22:13 PM
Quote from: iccaros on July 03, 2011, 07:16:28 PM
Got ya.. So on the Rebot 2.5 we cut the trace between Pin 3 and 4 lift the ground side of the 47uf from pin 2 and send that to system ground

I reckon that is correct

For ease of trouble... you could connect the negative side of that 47uF directly to Pin 3 of the PT chip.

THIS IS ALL SPECULATIVE AT THIS POINT! I am merely commenting on what has been explained above. I do not guarantee that this is in any way a VERIFIED fix!

Yes, non of these results are meant as a cure for any disease and have not been evaluated by the FDA

Govmnt_Lacky · July 03, 2011, 08:31:23 PM

Quote from: iccaros on July 03, 2011, 08:26:21 PM
Yes, non of these results are meant as a cure for any disease and have not been evaluated by the FDA

An FDA evaluation would be a walk in the park compared to evaluation by some people here!!

Mugshot · July 05, 2011, 05:09:47 AM

definitely deserves a helpful bump! :-)

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How to "Sshhhut" up a PT2399 once and for all!