Introducing the "One Chip Chorus"!

[pinkjimiphoton]

you'll need some sort of booster circuit, unless you maybe raise the gain of one of the opamp stages...may be tricky, as it could distort.
try smaller input cap, to make it brighter..

[anchovie]

Yeah, lowering the value of the input cap might help if you want to shave the low end off both the wet and dry sounds. I wouldn't bother making a booster - there isn't a great deal of headroom in a PT2399 so you'd be better off replacing R3 with a 1M trimpot and setting that to the best level.

Whilst lowering the input cap will reduce the bass, the heavy filtering that most PT2399s use could still reduce brightness. Try lower values for C12 and find the treble/hiss balance on the wet signal that works best for you.

I had trouble with the LFO locking up when the variable resistance was too low. You could try adding a few more Kohms in series with R8.

[Ark Angel HFB]

what about this...

Dropping R11&12(The resistors that determine mix) down to 1k. Dropping C13 down to 1uf or even 1.1uf. Then and raising R13 up a good bit...

wouldn't the over all effect be...

R13 Increased = More resistance to ground so increased volume.

R11&12 lowered the same amount = Same balance but less resistance so increased volume. (Now we have a hotter than unity signal that is bass heavy)

C13 Lowered = Bass is cut away leaving a brighter over all sound with the same 50:50 blend of dry and wet signal.

If this all works outs... then simple messing with the value of R13 and R11&12 till you get the volume back to close to unity but with less bass...

OR... add a (R14 between signal and the out and a just values till it is right.)
 

[anchovie]

Give it a try! This is one of the circuits that revealed that not all 2399s are created equal, so by that fact it's a tinkerer's playground!

[jogina111]

is the 47pf cap a critical part of this circuit? What other values can I subtitute for that?

[Ark Angel HFB]

is the 47pf cap a critical part of this circuit? What other values can I subtitute for that?

http://www.taydaelectronics.com/

Just order some buddy... shipping is cheap. ^_^

[Ark Angel HFB]

On a side note... could we possibly take the lock up fix from the "Little Angel" chorus and apply it to this?

[Vikt0r]

Hi, everyone!
I am new to this forum, but I must admit I enjoy it a lot, though reading through 46 pages of "Little Angel" could be somewhat braindamaging 
The reason I am posting here is something I've already mentioned in Merlin Blencowe's thread about pt2399-based reverb, but as for me, the issue is
serious enough to be repeated here, and anywhere the PT2399 is ever mentioned, as to become a part of PT2399 FAQ.
There are literally hundreds of posts complaining about non-working PT2399, strange problems, lockups etc. Especially interesting are the posts
mentioning some PT's pulled out from working delay circuits are simply not working in some others...why? Gonna tell you!
When I first realized the problem it hit me so much by it's obviousness, that I simply DO NOT UNDERSTAND, how can such a basic issue pass in front
of so many eyes without being spotted? Also, how could such genius designers simply ignore A BASIC RULE OF MIXED-MODE CIRCUIT design while designing
their PT-based circuits???
The PT2399 IS a mixed-mode circuit, meaning it has an analog, as well as a digital part inside. Either part has to get POWER. And while the power rails
of these parts are tied together within the chip, their GROUNDS are split apart and represented by pins 3 and 4 respectively. Now here comes the
part of wonder - WHY DO YOU GUYS IGNORE THIS??? Pin 4, which clearly seems to be unconnected in EVERY PROBLEMATIC CIRCUIT - represents the
digital ground of the IC. The PT2399 datasheet clearly states this pin MUST be also connected to the ground (in real mixed-mode circuits I used to design
this is done via a ferrite-bead inductor or a small resistance). Guess what happens, if you leave it unconnected? Bingo! All the strange problems you guys get with those "wrong
batches of IC's" etc.etc. It's because you leave the digital part of the circuit WITHOUT POWER (or getting some power through parasitic ways causing strange behavior)
I just can't emphasize enough - PIN 4 MUST BE ALWAYS CONNECTED TO THE GROUND - and voila: any PT2399 starts working!!
Try checking those delay circuits you pull your working (but otherwise misbehaving) PT's out, and you'll find the reason I'm talking about - those circuits surely
have pin 4 grounded! Everybody - please read and memorize this forever!
Now, coming back to the mysteries of PT2399. It is proven now (I have on my bench some IC's of either kind), that older batches of PT's had their grounds connected WITHIN
the IC's with a smaller resistance (about 15 ohms), so those older circuits DO WORK without grounding the DGND (pin 4), while some newer ones DO NOT HAVE this done internally. Either kind IS okay since the datasheet REQUIREMENTS are fulfilled. Circuits that work with pin 4 unconnected are an exception rather than a rule, and this exception
shouldn't be ever exploited, being done the correct way.
I sincerely hope that this post will help to bring clarity into the hassle around PT2399 misbehavior and will also serve well for all future PT2399 experimenters.
Please, all those ever had problems with their PT2399's or particular circuits - try applying this simple fix - I think the majority of problems are going to get resolved.
Wishing everyone all the best and many-many successes in our beloved hobby!
Long live DIY! 

[Mick Bailey]

Many problems with PT2399 circuits do stem from bad ICs. I've experimented for hours with grounding schemes and many batches of ICs before concluding that there are numerous substandard ICs out there that won't work properly, no matter what circuit they're in and no matter how pins 3 & 4 are configured.

My Repote2 delays work perfectly and pin 4 is grounded. Some ICs instantly lock up and get hot. Not just odd ones, but every one from a given batch. Others are noisy beyond use. The ones that work fine are a mixture of old and new production. Other builders have found the same. So what are we all missing here in circuits with pin 4 grounded and PTs where some work, some dont?

[Vikt0r]

Well, perhaps some IC's out are bad indeed, coming from defective batches - I can't state surely. I had about 3 dozens of these IC's going through my hands, bought at different time from different suppliers (chinese e-bay sellers, usually the cheapest ones) - and never met one really defective, apart from the only difference mentioned above. This difference can be easily spotted by measuring resistance between pins 3 and 4: if there's no 10-15 ohm resistance between them, the IC will definitely not work with pin 4 left unconnected, and very likely to work fine with both pins (3&4) grounded.
Now, what we are definitely missing _here_ is pin 4 grounded - that will 100% cause problems with some of the IC's. Of course, thet's not a universal cure if the particular IC is faulty (which case personally I never met).

[Vikt0r]

Also probably worth adding here, that for those PT2399's having no internal connection between grounds, might be a good idea to connect pins 3 and 4 through a small 10-15 ohm resistance or(/and) a smaller inductor for a couple of microhenries. This is a standard practice in mixed-mode circuit designs and significantly reduces the noise injected by the digital circuitry into the analog power rail.
I am going also to try powering the chips from a PS built using negative-rail regulators (7905) with the positive rail serving as their common virtual ground and feed the DGND and AGND separately.

[Mick Bailey]

The 15 ohm resistor reminds me of the same value component used to seperate the signal ground from chassis ground in some Fender products (notably the reissue standalone reverb). It effectively elevates the signal ground by the voltage drop across the resistor, eliminating grounding noise.

If you short this resistor out these reverbs make a lot more noise.

In seperating the digital and analogue grounds in the PT2399, would it be a better situation to ground the digital side (pin 4) and leave the analogue ground (pin 3) elevated on its 15 ohm resistor?

[Vikt0r]

I've just measured the built-in resistor - actually it's exactly 10 ohm, not 15, but that doesn't matter too much.

M.B. >> If you short this resistor out these reverbs make a lot more noise.

Indeed, I have tried this on a breadboard - adding this 10 ohm externally between pins 3&4 seem to affect the noise floor somewhat.

I think that the initial release of the chip included this resistor, but in the latter revision the designers simply decided to give
some more flexibility to the consumer by being able to choose way they want to connect grounds - that's why these IC's don't have their grounds
connected internally anymore.

M.B. >> In seperating the digital and analogue grounds in the PT2399, would it be a better situation to ground the digital side (pin 4) and leave the analogue ground (pin 3) elevated on its 15 ohm resistor?

I don't think so - because it's exactly the analogue circuitry being affected by the noise, therefore it's recommended to keep it's ground potential as close to zero, as possible. In the Fender amps you've mentioned, the chassis ground (the chassis itself works as an antenna) represents the same kind of noise source, as the digital circuitry in our case.
Thus, by adding the 15 ohm resistance, I would it's say the chassis potential being elevated above the signal ground - but considering there's no current flow, we don't have potential elevation, but do have interference attenuation. By elevating the analogue ground above the signal ground we would artificially achieve the effect of the ground
loop - something that designers try to avoid all the time.
But, further developing your idea I came to another one: even better noise attenuation could be achieved by separately bypassing the digital and analogue ground pins to the positive rail, prior to connecting them together with a 10 ohm resistance.

[Vikt0r]

This is how I mean

[Vikt0r]

Along the day I was playing around with these circuits.
Built the one by merlinb, but didn't like the effect - it sounds more like a phaser. Threw into disassembly queue.
Went back to anchovie's original design but with the ground fix (from previous message) and dry/wet mix pot implemented,
and Wow! All the noises gone! Sounds fantastic, doesn't have too much versatility, but also doesn't seem to require that.
Really, really grateful to anchovie!
Spent about 2 hours to design, etch, drill and populate a PCB. If anyone is interested in the layout - just give me a shout...

[Mick Bailey]

Think we'd all be interested - go a head and posti it!

[Vikt0r]

Okay then Here it is. Simple as sh!t
The board size is 41x33mm. The layout presented from see-through top view, so it doesn't need to be mirrored
for printing. It also has one wire bridge beneath the chip (didn't want to mess with too thin traces to keep the
layout DIY-friendly) - make sure you install this before the IC socket.


Parts placement. The 10 ohm resistor is necessary only if your particular PT2399 doesn't have it built in - a good
idea would be to check it between pins 3 and 4 before installing the chip. But in either case it wouldn't harm



Layout for printing, 300 DPI resolution. Make sure you don't mirror it.
Oh, yes, and it IS verified (i've got mine working).

[Vikt0r]

Just for curiosity - built also the Little Angel, and I must state, that despite higher complexity it sounds worse
(okay, perhaps worse is a too strong word - but different, and definitely less chorus-y),
even with all mods applied and increased depth control.
So, just like always - the simpler is the better Thumbs up anchovie! 
I just  love performing Metallica's "Sanitarium", or Dream Theater's "Pull me under" intro through this little gem!!!

[Ark Angel HFB]

I going to give this another shot tomorrow... will see how it turns out.

[Ark Angel HFB]

Thought I'd drop an update.

I built this again today with some tweaks.

I removed R11 and R12, in order to do the mix pot option. I used a 10K lin pot, which brought the volume up a good bit above unity... Will try bringing the volume to perfect unity by ether lowering R13, or adding an R14 of about 2.2k to the output of the mix pot.

Next I lowered C13 from 10uF to 1uF. The sound had been a tad on the low side for me and the reduction of some of the bass, coupled with an overall volume increase really helped the pedal sparkle nicely.

Lastly I added 10 ohm resistor from ground to pin 4, as talked about above on this page. I tested a pt2399 that had been locking up previously and guess what... no lock up. Played for a solid hour and greatly enjoyed the sound and options the circuit was giving. I even left it on and alone for another 30 minutes just to check and see if it might lock up... never did.

Over all I'm really very happy. I'm going to try and take some time in the next day or so to make a graphic for it and try my hand at some water slide decal'ing... Will post pics... thanks for this great circuit.