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PT2399 noise problem improved by simple mod in delay circuit

Started by rring, September 02, 2012, 02:31:00 PM

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I am posting a schematic of my approach to using the PT2399 for a delay. I can get long .7sec repeats with little noise and I don't need a compander! I did some different things than the standard circuits out there. The trick in my design is using a much larger cap (.47 uF instead of .1 uF) between pins 9 and 10. This gives an increase in signal output but the noise stays the same. Then I reduce the output at the wet dry mixer and the noise goes way down. Also the wet/dry mixer is the op amp between pins 13 and 14.  Instead of using this Opamp as a filter, I used a switch cap filter IC, but all kinds of other low pass filters could be used. I must say that it really does the job and only uses 1 cap to set the cutoff freq from 1Hz up to 5KHz. Check out the audio sample.

J M Fahey


I added a coupling cap and replaced the schematic with the error.


Very cool, excellent sound quality...I may have to build one of these.
Life is what you make it.
Still rockin' the Dean Markley K-20X


I have posted on www.circuitsalad.com, an alternate filter design, if the thought of spending $7.00 of the MAX7401 makes you ill  ;) To me the simplicity and adjustability of the filter makes it well worth it.


Looks nice.....

I want to add a reverb to my amp, but.....  >:( can´t find PT2399 or reverb tank here in Argentine Patagonian  :grr

J M Fahey

No reverb tanks commercially available in Argentina. Period.
Amp makers import or build their own.
But you can order some from the USA, using your International Credit Card .... if Kristina lets you  ;)
Last time I asked her, she answered:


Why the hell his Maximo dont like to play guitar???!!!!!

These days coming new baby for my wife and my, so no many time for hobby, but anyway, that will make my next challenge.....

Some kid of here want my Coihue 50, so i thinking sell it to my cost of a new Coihue 100W 2x12 "reverb and footswitch" EDITION.

Taking your old suggestion of take note for every interesting idea, plannig split SansAmps GT2 in two channels, "fenderish" for clean, "MARSHAMESA" for crunch, footswitch selectable, and so clean,hot, hi gain selection. 3-band baxandall tonestack for each channel.

Amp stage, 2 x 7294 or 3886, each one driving one Fahey 12A80.

Sound nice?

PS: jammed Coihue 50 several times, around 2 hours each, with no problem. Perhaps a few °C on heatsink (huge one)


New guy here. Attracted by the PT2399 noise problem improvement I saw. I have a noise problem with my pt2399 circuits (doesn't everybody?) and I learned to live with it, until I saw this posting (a little late I have to admit). I absolutely loved what I heard but puzzled by what I saw. I would really, really love to play with this circuit but the schematic is unintelligible... What are the following:

it is always good to explain what you mean when you introduce abbreviations...

Where is the opamp (LP2, shouldn't it be U*??) between pins 13 and 14?

Is BAS16LT3G really necessary or a 1N4148 would do in its place? When you introduce specific components it is good to explain why you need the extra 200mV forward voltage and low leakage current of the specific device over the "generic" type. Same goes for the MCP1804T, why this device to regulate 9V to 5V when a generic 7805 would do the same... If there is a reason for the substitution it must be documented...

Great work but if you had my Electronics professors in college, they would fail you without a second thought...

I am not trying to be judgmental or anything, just trying to say that a schematic that is clear as day to you might be clear as mud to others. When you take the big decision to publish it even on a forum you must make sure it is clear and helpful to everybody. This is why there are rules out there on how to design a schematic. This is why we all use the same symbols for resistors ,capacitors, transistors, etc.

If you clear this schematic up, I would be the first to jump in, play with it and give some feedback on it. This is the main reason, we all share the same notation: collaboration!!!


Hey There

I think you could be a little more diplomatic with your post

You could just say your having some trouble reading my schematic and ask me to clarify. I am smart enough to refine my formatting and style- when someone gives defacto feedback by asking questions.  Lots of people have emailed or posted with questions and I have happily answered them. It difficult to tell where to draw the line with detail so I figure anyone who actually wants to try to build or experiment with the circuit - will put forth the effort to reach out. All of the symbols are referenced to the various jacks and switches at the pedal level. You can just mark them out - if they confuse you?

A number of people have built this "unintelligble" circuit with no problem and have conveyed to me excellent performance - so I am sure you and your professors can figure it out too ;)

seriously though if you have questions I will answer them and lets leave it at that.
A number of parts are arbitrary choices based on what I had floating around others matter. The regulator for example draws less  standby current, allows for a smaller drop for regulation and I beleive has a better transient response than a 7805. Sure the diode could be anything.


Sorry for not being more "diplomatic" as you said. You are right... I wasn't. Actually I was totally out of line...
Once more, I have to apologize for my complete lack of diplomacy but I got excited when I saw the posting and immediately crashed when I saw a schematic I could not "read" immediately and figure out what is happening... It was frustrating as you can imagine  :grr 
I had to learn electronics from some very "bitchy" teachers and apparently they gave me their attitude (it's true what I said about failing you without a second thought...).
I see that you are trying to help. it is obvious when you put up all this effort to put together the circuit, troubleshoot it, optimize it, and finally publish the schematic and and a result (sound file) from it!!!
But why do all this in a way that makes people asking you questions just to figure it out? My teachers used to say that a schematic, a few pages of documentation  and in some cases a mechanical drawing and a layout (for RF, etc) should be all that you need to build an analog circuit... If your documentation and/or schematic does not allow this, there is something wrong (and you fail the class  :'( )
Thank you for providing your help and answering some of my questions but I could use some more help as I don't I have a clue to all the abbreviations on the schematic and what they mean. I see some of them are probably there instead of "wires" connecting different parts of the circuit since they have the same name (despite the fact that they are not on a bus or something) but others are simply there not pointing to anything... Any help on this will be deeply appreciated!
PS: What happened to that Opamp???


Yes all those symbols are for me - I probably should have posted a more generic schematic. All those references are for the 2.1mm jack sw to disconnect the battery when an adaptor is used, the other jack switch is from a streo input jack, where one connection isused to only connect the ground circuit when pluged in, ect - this is all the making it a "standard pedal" connections and I was trying to keep them straight when I built the damn thing! So point taken. All my wires go to the board - (from the pots, switches, etc) so you are seeing all of my inter-switch and jack to jack wiring take place on the board. I have reflected this on my schematic. So every symbol is a wire connection on my board. You can ignore everything but the input, out put B+ to the regulator and the switch for the tails fet switch, etc. Not sure what you mean about the op amp? Yes there is an op amp in the chip, but functionally you only need to connect to the pins as shown. I imagine you want see what the topology the op amp circuit in isolation and not just connections to pins for informational purposes?

here is a simplified schematic  - maybe this will help - you don't need the PMOS - just use a diode if even that. This further reduction may clarify some of your questions



Thank you very much for this schematic!!! Now everything is clear as day. I had a suspicion that the symbols/flags were there to help you organize your PCB better or to "remind" you of any off-board connections but I still couldn't figure them out. I guess the fact that my background ranges from radars and other electronic warfare equipment to biomedical instrumentation and not stompboxes didn't help either... Armed with this schematic and a stompbox, last night I realized what you were depicting there and now it all makes sense (even the old schematic).
As far as the opamp goes, well, if you mention an integrated peripheral or device in documentation and the schematic it is good to include a detailed "break down" of your IC, for "informational purposes" as you very well put it. Anyway it's not a very important omission since a good look at the PT2399 datasheet can clear the landscape there too (not the best datasheet I've seen but good enough for this kind of IC)!
Good job and thank you very much!!!


yes over all its a pretty simple circuit and you can breadboard in a couple of hours. I think you will be very pleased with the performance. I found having the regulator output pin as close as you possibly can to to VCC pin of the chip helps tame it. This probably will alos be the case with a 7805.


I'll sure try it out! I guess in the weekend if I manage to find the time (if time is money, I'm a very poor man...).
I guess the closer you put a regulator to an IC input the better. I see you also put a hefty capacitor on the output too, always a good idea! An 100nF ceramic right on the input pin would be nice too since these LDO regulators require very low impedance sources to regulate properly. Despite its horrendous power efficiency, a simple linear like the 78XX is more immune to this and only require a good amount of capacitance if they are very far from the targets.