pt2399 noise. solution?!

[gtangas]

Hi friends

I was surfing the web looking for some reports of jumper pin 3 and 4 of the PT2399 (my sea urchin sometimes stop the delay... and yes in my case it solved the issue..so far) and found a post on dsb that reports a supposed solution for the usual noise of the 2399

I would like to ask to you guys read it and make your comments..

"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:
$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:
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:
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"

here is the link for that post
http://www.diystompboxes.com/smfforum/index.php?topic=92515.0;wap2

[otsismi]

Hi friends

I was surfing the web looking for some reports of jumper pin 3 and 4 of the PT2399 (my sea urchin sometimes stop the delay... and yes in my case it solved the issue..so far) and found a post on dsb that reports a supposed solution for the usual noise of the 2399

I would like to ask to you guys read it and make your comments..

"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:
$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:
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:
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"

here is the link for that post
http://www.diystompboxes.com/smfforum/index.php?topic=92515.0;wap2

Can this mod be used on the cave dweller?

[RobA]

It's hard to tell what's supposed to be done with the PT2399 because the spec sheet sucks. But, I think this is where the info being discussed is coming from http://www.valvewizard.co.uk/smalltime.html and specifically http://www.valvewizard.co.uk/PT2399_Data_Notes.pdf.

And, it is definitely true that if you measure the resistance betweens pins 3 and 4 you get a very low resistance. On the one I just tried, it was about 30Ω.

In general, when there is a digital and an analog ground the point isn't that they are two different grounds and need to be run separately or anything like that. It's because to reduce noise, the two grounds need to come together at a point of a large conductive mass. This isn't possible to do in the chip, so they are brought out individually and connected on the PCB. I have no idea if that's the intention on the PT2399 though, because the spec sheet sucks (I'll probably say that again soon too).

It's interesting that the timing resistor is shown going to the digital ground. If the intention of the Agnd and Dgnd is what you normally see, that wouldn't matter much. on the other hand, it does seem weird that there is an internal connection between Agnd and Dgnd to begin with and maybe their intentions are completely different. But, we'd never know because the spec sheet sucks.

[gordo]

So what you're saying is the spec sheet sucks?

[RobA]

So what you're saying is the spec sheet sucks?

I wasn't sure I'd made that point strongly enough.

I'm still trying to figure out how connecting the delay resistor to ground via pin four through the 10Ω and thus through pin three is supposed to reduce noise compared to just hooking it to ground. (Assuming, that the diagram from Valve Wizard is the whole story.)

[jkokura]

So...

Basically, we're saying 'we've been doing it all wrong' with the PT2399?

I dunno. I'm gonna have to breadboard this I think. I won't believe it till I can compare the 'normal' vs the 'updated'.

Jacob

[otsismi]

My cave dweller will not make it to an enclosure if the digital artifacts/noise on repeated delays is not eliminated. I was going to post a sound clip but haven't had time.

How does the sea urchin/ deep blue prevent this kind of noise? We sell the mad professor pedal at work an I've never heard that kind of noise come through.

[gtangas]

Jkokura.. Any news on that breadboarding?

Enviado de meu AT10-A usando Tapatalk 4

[culturejam]

I've not be able to hear a difference in noise by connecting or disconnecting pin 3/4 or connecting the resistance off pin 6 to pin 4.

I think what it boils down to is that some chips are just really noisy, and most are somewhat noisy, and a very rare few are actually quiet.

My advice? Filter heavily, filter often. 

[gtr2]

I've tried many things to limit noise in those chips.

C.J. has it right above, filter...filter....filter... or live with some noise

Josh

[otsismi]

How does the deep blue / sea urchin filter it out?

[jkokura]

I haven't breadboarded it, but I still have heavy doubts. Seriously. We've all be playing with these chips for a long while now. But all of the sudden, someone comes up with some sort of solution that we haven't seen before?

Jacob

[otsismi]

How can you filter out the noise but maintain fidelity?

[culturejam]

How does the deep blue / sea urchin filter it out?

Aggressive passive low-pass filtering on the delay line.

How can you filter out the noise but maintain fidelity?

I don't think it's possible. Maybe with a compandor and a light amount of low-pass filtering, but it's a pain in the ass.

[kothoma]

How does the deep blue / sea urchin filter it out?

Aggressive passive low-pass filtering on the delay line.

Active lowpass filters at the input and output of the PT2399 and additional passive lowpass at the output, like most designs based on the Rebote 2.5.
The Cave Dweller is different, the two opamps of the PT2399 are not used as filters, only passive filtering is applied.

How can you filter out the noise but maintain fidelity?

I don't think it's possible. Maybe with a compandor and a light amount of low-pass filtering, but it's a pain in the ass.

Right.