So, I was running through ideas on the Little Angel thread HERE (http://www.diystompboxes.com/smfforum/index.php?topic=86297.660) 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.
$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!
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.
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 (http://www.diystompboxes.com/smfforum/index.php?topic=87493.0) 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.
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 (http://www.eskimo.plus.com/fxstuff/echobase.png)
from Slacker's thread : http://www.diystompboxes.com/smfforum/index.php?topic=60662.0 (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?
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.
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!
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.
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?
(http://i6.photobucket.com/albums/y208/skiraly017/ReboteModified.jpg)
Quote from: skiraly017 on July 03, 2011, 04:45:54 PM
So we're looking at something like this?
(http://i6.photobucket.com/albums/y208/skiraly017/ReboteModified.jpg)
Can anyone say.... Rebote 3.0?? ;)
:icon_surprised: Is that verified?
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.
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 :icon_mrgreen:
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.
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 :icon_rolleyes:
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
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 ;D
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!
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 ;D
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
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!! :icon_eek:
definitely deserves a helpful bump! :-)
Just now, on the bench, I have been unable to measure any change in noise performance with the delay resistor connected to digital ground rather than analog ground. I am wondering if something more subtle is going on in Earthscum's examples?
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 have made this horrible cut between those traces, my knife is balls deep in the pcb but they (pin 3 and 4) are still connected according to my dmm.
(http://img37.imageshack.us/img37/1751/agfhdfj.jpg)
Should i go deeper? (inception)
Well, first you should see if there's 10R between them or 0. Both will cause a "beep" on a continuity test.
Quote from: WhenBoredomPeaks on July 05, 2011, 05:59:20 AM
I have made this horrible cut between those traces, my knife is balls deep in the pcb but they (pin 3 and 4) are still connected according to my dmm.
Even if you cut all the way through your pcb you will still have continuity. It looks like pins 3 and 4 are internally connected. I tested a pt2399 out of a circuit and I read 9 ohm between pins 3 and 4.
If you read 0 ohm it looks like you haven't cut deep enough on the trace, but if you read a very small resistance it's normal.
Unless you've soldered the PT2399 in, pull it and then measure between the traces.
You guys were right, when i pulled out the chip, there were no connection between the legs, when i measured it in the socket, there were about 15 ohms resistance between those legs.
Now i lift that 47 uf cap and connect it to analog ground and will update the thread with the results.
Just to make sure, this should "eliminate" the noise from the repeats?
Quote from: WhenBoredomPeaks on July 05, 2011, 10:05:19 AM
Just to make sure, this should "eliminate" the noise from the repeats?
It
SHOULD, and has so far for me. What I have been able to eliminate with it is the digital hiss that gates in while you play, and suddenly disappears when you mute your strings. That hiss has been plaguing me with these things for awhile now, and thus far has only been able to be hushed with extensive filtering on the output amp and integrators.
Playing with the LA, I am still running 10nF in the integrators, but bumped up from 1nF to 10nF in the amp stages. I still get a bit of bleedthrough at longer delays... to be expected, bandwidth considerations and all. I also did the bias upgrade, and added a 150pF cap across the 470k in the buffer amp. Now it's REALLY quiet... even with the smallish integrator caps. Only issue I had was that I stupidly put in one of the newer chips, so I had a bit of a fuss firing it up (since I used a pot to adjust delay, I just cranked that up before I plugged in).
As for the Sewer Pipes, that thing was inspired (and originally started on the board) as anchovie's Noise Ensemble. That one was most noticable. I still get all the nice reverber-ish sounds, but no more digital hiss gated in during the playing. I'm gonna try his NE out again when I get home tonight and see if it works with that noise monster. Should make that circuit alot more fun to play with.
This fix hasn't gotten rid of any of the normal hiss, just cuts out a major portion of the digital hissing that comes through during playing. I don't think this will affect the op amps' noise figures, just isolation of the digi from the analog so the chip can compensate for clock noise internally.
Nice developments, lads! :)
I'm in the middle of doing a layout for a tube amp with a Belton brick. The Belton (which is said to contain multiple PT2399) also has two grounds, signal ground and power ground. I was just looking at the GGG D-Verb schematic, it has the 7805 common hooked up to power ground, with no connection to signal ground apart from however it's connected within the Belton. May be something, may be nothing, but I'm wondering if we do the same with PT2399 - connect the common of the 7805 to digital ground - we might well shed some more unwanted audio artefacts?
http://www.generalguitargadgets.com/pdf/ggg_verb_sc.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a
Quote from: frequencycentral on July 05, 2011, 06:53:34 PM
----
but I'm wondering if we do the same with PT2399 - connect the common of the 7805 to digital ground - we might well shed some more unwanted audio artefacts?
Hmmm... That would put the reg ground ~10 ohms above analog ground. Would that 10R make a difference in the performance of the 7805, or just limit current (which the chip does anyways, right?). 5V/10=500mA, or am I thinking from the wrong end of the voltage? lol. Good eye. I'm gonna try and motivate on a SP that is complete tonight (gotta buffer some things, and some diode limiting), so I'll probably give it a shot as well.
If we can get a good method of stability down, I can forsee a whole new slew of PT2399 abuse and torture in the near future. Especially if it leads to wider useable bandwidths at longer delays.
Breadboarded a Rebote 2.5 and tried both, delay pot to analog ground AND digital ground
there's no change in the digital hissing
btw, i assume, you're talking about the digital hiss on the repetitions? that distinction hasn't been made clear yet
cause there's three hiss sources on Rebote Delay:
power source hiss (easily solved by big caps to ground)
opamp hiss (102-103 caps in the feedback loop)
repeats hiss (unable yet to find a cure)<---is this the one? ???
....Tried it. No noticeable change. Your experience with this 'mod' might be different, though.
Fp
Quote from: Earthscum on July 05, 2011, 11:20:15 AM
It SHOULD, and has so far for me. What I have been able to eliminate with it is the digital hiss that gates in while you play, and suddenly disappears when you mute your strings.
I had the same problem once, which turned out to be a bad connection. I discovered that if I hit slapped the strings in 'just the right way' the PT would shut up, but I could make it hiss again by stroking the strings in 'just the right way'. Reflowing the joints fixed the problem.
I don't think you will ever get good bandwidth with long delay times because it is fundamentally limited by quantization noise. The slower the clock, the worse the digitisation gets, and no amount of effort can change the inside of the chip! More's the pity...
I just had a look at the datasheet for the HT8972, which is Holtek's pin-for-pin replacement. Their application circuit has the caps from pins 7 & 8 going to digital ground, as well as the delay time pot.
Ok i did the mod on Francisco's board. I tried to find out what happened through monitoring it with earphones through an interface.
The repeats are dirty (that is the chip's fault) and my guitar's noise levels are bigger than the other parts of the circuit but i think it sounded the same the last time i heard it.
Quote from: merlinb on July 06, 2011, 03:51:12 AM
I don't think you will ever get good bandwidth with long delay times because it is fundamentally limited by quantization noise. The slower the clock, the worse the digitisation gets, and no amount of effort can change the inside of the chip! More's the pity...
Well, the solution is 2x PT2399. Or more... :icon_lol:
Quote from: merlinb on July 06, 2011, 03:51:12 AM
Quote from: Earthscum on July 05, 2011, 11:20:15 AM
It SHOULD, and has so far for me. What I have been able to eliminate with it is the digital hiss that gates in while you play, and suddenly disappears when you mute your strings.
I had the same problem once, which turned out to be a bad connection. I discovered that if I hit slapped the strings in 'just the right way' the PT would shut up, but I could make it hiss again by stroking the strings in 'just the right way'. Reflowing the joints fixed the problem.
I don't think you will ever get good bandwidth with long delay times because it is fundamentally limited by quantization noise. The slower the clock, the worse the digitisation gets, and no amount of effort can change the inside of the chip! More's the pity...
I'm having the exact same hiss problem Earthscum describes. But instead of a bad joint it appears it can be traced to the stompswitch. Sometimes after engaging the pedal the hiss it there, sometimes it is not. I figured it might have to do with some static discharge going into the circuit too as it is very heavy on the feedback. ( listen here: http://www.youtube.com/watch?v=8KauS8rvR3o ) (that is without the hiss, straight from the breadboard)
I'll try the digital ground sugggestions here and see if it makes a diffference in my circuit. The pin 7,8 caps to digital ground do seem to make sense too. Seperating the 78L05 GND to digital ground is interesting too.
Quote from: merlinb on July 05, 2011, 05:47:53 AM
Just now, on the bench, I have been unable to measure any change in noise performance with the delay resistor connected to digital ground rather than analog ground.
I couldn't hear any difference either. I can't tell any difference just by disconnecting pin 4 from analogue ground either. In my pedal there's already quite a lot of filtering of the audio so maybe that's masking any improvement gained doing this. Perhaps designs with less filtering will benefit from this.
The only change I noticed was with pin 4 disconnected, the pedal latched up and gave no delay with the delay resistance at minimum at power up, this is less than the now recommended 1k, I don't recall it ever doing this before. This might just have been a one off thing though, I haven't tried to repeat it.
I've been tinkering with the PT2399 yesterday and found that reducing the pin 7 and 8 capacitors made a big difference in my circuit.
I'm running it with a 560 ohms resistor to digital ground and caps for pin 7, 8 to digital ground too. With this short delay set up I was experiencing noise but only when sound was running through. When the input signal is gone there is no noise. It's not a constant hiss, but more of a crackling sound. This was with the pin 7, 8 caps at .1u at default value. It seems that the crackling noise can be shifted up in ffrequency by lowering the cap values there. I found 15nF to be optimal.
Also I tried swithing Dgnd to Agnd and noticed quite a difference. With Agdn connected to Dgnd I had more volume and a more bassy/hi-fi sound. With it disconnected, a little less volume and some bass loss. It preferred the separated Agnd, Dgnd sound. Also it seemed that the delay time was a little less stable with Agnd and Dgnd disconnected. It seemed to move around a (tiny little) bit, which added character.
So all in all, I did experience a difference, but not in noise. It took other tinkering to get the noise down.
I think we're not finished exploring this IC.
why dont we just email the manufacturer and ask info about the pins and ground (A/D) connections? i mean, we cannot rely on their datasheet alone, but working blindly on this chip could take so much time.
R.G tried that I believe
Quote from: ~arph on August 02, 2011, 02:46:20 AM
R.G tried that I believe
did he get a response? im curious as well. once the manufacturer sheds light on some of the mysteries of this IC, im imagining a slew of other projects from the creative guys of DIYSB ;)
Come to think of it, I believe I read that he called princeton to see if a version with a longer delay time would be availble. Don't think it was about the pt2399 specs.
so how does this look for altering Tonepad's Rebote 2.5 pcb?
pin 4 would still be connected to the delay pot lug-1
(http://i215.photobucket.com/albums/cc241/guyatron/rebote25compare.jpg)
and I do see that some folks feel that the pin3/pin4 connection/disconnection doesn't seem to make much of a difference
but I just had an urge to play with the pcb layout anyway ... if only to get the decoupling between pins 1 and 3 closer
as per Merlin's write-up of the PT2399
thanks!
I'm not sure if this is anywhere near correct... but are these the changes required on the Vero from Sabrotone.
Original Vero:
(http://www.sabrotone.com/wp-content/uploads/2011/10/Rebote-Delay-2.5.gif)
My dodgy attempt at making the changes:
(http://i49.tinypic.com/1zmzez5.gif)
I think I could be *way* out, but I'm new at this :icon_redface:
Thanks guys!
Quote from: Derringer on May 13, 2012, 02:20:48 PM
so how does this look for altering Tonepad's Rebote 2.5 pcb?
pin 4 would still be connected to the delay pot lug-1
(http://i215.photobucket.com/albums/cc241/guyatron/rebote25compare.jpg)
and I do see that some folks feel that the pin3/pin4 connection/disconnection doesn't seem to make much of a difference
but I just had an urge to play with the pcb layout anyway ... if only to get the decoupling between pins 1 and 3 closer
as per Merlin's write-up of the PT2399
thanks!
just to follow up, I could not get the Rebote 2.5 to work in the manner I indicated above
it would only work in the stock configuration .. and it isn't noisy enough stock to bother me anyway
I tried it on the breadboard first (thankfully) and found that if I powered the circuit up in the stock configuration AND THEN disconnected pulled pin-4 from GND, it would work.
But if I powered the circuit up without pin-4 connected to GND, it would not give me delay.
Quote from: Derringer on June 19, 2012, 12:01:18 PM
Quote from: Derringer on May 13, 2012, 02:20:48 PM
so how does this look for altering Tonepad's Rebote 2.5 pcb?
pin 4 would still be connected to the delay pot lug-1
(http://i215.photobucket.com/albums/cc241/guyatron/rebote25compare.jpg)
and I do see that some folks feel that the pin3/pin4 connection/disconnection doesn't seem to make much of a difference
but I just had an urge to play with the pcb layout anyway ... if only to get the decoupling between pins 1 and 3 closer
as per Merlin's write-up of the PT2399
thanks!
just to follow up, I could not get the Rebote 2.5 to work in the manner I indicated above
it would only work in the stock configuration .. and it isn't noisy enough stock to bother me anyway
I tried it on the breadboard first (thankfully) and found that if I powered the circuit up in the stock configuration AND THEN disconnected pulled pin-4 from GND, it would work.
But if I powered the circuit up without pin-4 connected to GND, it would not give me delay.
i had this very problem, has been found what causes it? are there some versions of the pt2399 that respond well to this trick and some that dont? .....ive found it to work once in like 30 attempts... when it doesnt, theres no delay, and the 7805 heatens like crazy... when it works, it indeed cuts all digital crackling from repeats, and that motorboating sound in long repeats that i hate
i couldnt get the PT2399 to give me delay with the digital ground lifted. dont know why, but the chip got really hot and the output i wasnt getting any delay. buffered output was working though of course.
It's seems strange that it wouldn't work considering that the Deep Blue Delay is wired just that way.
When looking at the (old) PT-80 schematic and layout, it seems that the "Sshhhut mod" would be:
1. Remove the jumper from pin 4 to ground
2. Move the 47uF cap between pin 2 and 3 to pin 2 and ground
Is that correct?
Edit: Pin 3 = GND, so the cap is already between pin 2 and GND ;) That only leaves the removal of the jumper?
Schematic: http://www.generalguitargadgets.com/diagrams/pt80schem.pdf
(http://img.sait.nl/pt80lo_cropped.png)
Tried it, but it didn't work. The only way to get the delay chip started was to jumper in 4. After the delays were working, I could remove the jumper, but that didn't fix anything.