"Little Angel" - Super Simple PT2399 Mini Chorus

[culturejam]

Testing is underway...

So far, 5K is definitely a good option for the Delay Time control. Too much more than that gives very noisy repeats. Unusably noisy.

One issue I'm having, however, is that on this build, if I hit notes pretty hard, I get some clipping/farty sounds. I've tried LF353 and 4558 for the op amp, and I've tried two different 2399 chips. Same result.

I've noticed, however, that the different op amps had different min/max LFO speeds. Interesting. The 4558 goes faster (with every other value in the LFO being the same). I'm out of NE5532.

I'm using a pair of 182K resistors in place of the pair of 220K in the LFO. That's the closest value I have.

[Earthscum]

Here's the mods I used last night. TI TL072BCP, Mylar Films on the .1uF's in audio path, ceramic for the others. Poly caps for the .01 & .001's. I may have used a ceramic across the inverting feedback on the LFO... it was acting strange. I'm gonna use a poly for that and see if it acts more normally next time I crack it open.



1 - I changed the 470k pot to 100K. It gave me more useable range on the pot. This is probably due, as noted by culturejam, to the difference in OP Amps on the LFO... just a guess.

2 - The variable delay helped thicken up the low end with the extra shift in time... also adds a bit to the tricks you can get it to do!

3 - The "Wet Out" pot helps keep this out of flanging territory. I was getting too much wet signal and loosing the effect when the delay increased. This lets you drop the delayed signal a bit more into the background so you can still keep the nice chorusing effect. Also, within the usable (to you) range, you'll find a whole set of different tones available.

4 - The 10K on the output is just for trimming back the volume if you find, like with my setup, that the overtones really drive hard and throws your sound too far above everyone else when the pedal is engaged.

These pot mods use the existing (if you etch a PCB) resistor pads. You just solder the resistor between the center and outer lugs right on the pot. The output mod (referring to the layout http://i210.photobucket.com/albums/bb292/frequencycentral/LittleAngelPCB.gif ) you just cut the trace between the R14 pad and the C12/C15/OUT trace. If you drill a hole right next to the pad (to the right, under the right pads of C12 and C13), you can run a wire through from the top, fold it over and solder right to the R14 pad. Wire the other end to the output pad, run the output from your center lug and you're set!

[my7of9]

.....and the PCB apparently will fit in a 1590A! This might well be my excuse to try my hand at a 1590A build. solderman? danielzink? valoosj?

I don't wish top be a party pooper but...
I have to report that I do not believe this will fit into a 1590A.
The board is exactly as wide as the outer dimensions of the enclosure. While you could perhaps lean the board I do not believe you would have room for the footswitch and especially jacks with a leaning board.

I will say it will fit a 1290 very nicely however.

If someone can prove me wrong...(Daniel Z. ?) .. I will certainly tip my hat to you!  

[culturejam]

It took all damn day, but I figured out what was wrong with my second build. I had the wrong value caps connected to pins 9/10 and 11/12. I had 100pf when it should be 10nf. Whoops!

With 100pf there, hitting the strings hard caused a crackly-static sound. With 10nf, it's gone.

What exactly do those caps do? The pins on the data sheet are marked OP1 in and out (pins 9 and 10) and OP2 in and out (pins 11 and 12).

[Earthscum]

That's one of the things I was asking about in this thread:  http://www.diystompboxes.com/smfforum/index.php?topic=86258.0

I think maybe it filters out the digital signal? I'm thinking about dropping some .015u's in place and see if it takes that bite off my sound on bass. ir maybe .022's. I definitely gotta swap some values in the input filter... again, I'm playing bass. I DEFINITELY don't have bass loss! At least not in the way that any signal is getting a noticeable bass cut. I actually have all the punch with the effect in, unlike other chorus' that seem to have some low end loss in the circuits. Simple IS good for Bass.

[culturejam]

I think maybe it filters out the digital signal? I'm thinking about dropping some .015u's in place and see if it takes that bite off my sound on bass. ir maybe .022's.

The Princeton "data sheet" has one example circuit with 0.1uf in those spots. Hmmm.

[culturejam]

With a 10K pot as the Delay Time control, only the last bit of the sweep introduces nasty noise in the wet signal. Bigger values (longer delay times) bring in a lot more noise.

So yeah, with a chorus-like modulation effect, the 5K DT pot works great. But I'm wondering now, as us DIY folks often do, if I up the value of the OPF1/2 caps from 10n to 47n or 100n...will that allow for cleaner longer delay times. Or maybe the HPF pin caps. I'm assuming that means "high-pass filter".

It really pisses me off that Princeton is so stingy with their info. 

[culturejam]

Okay, here's the good data sheet:
http://www.princeton.com.tw/downloadprocess/downloadfile.asp?mydownload=PT2399_1.pdf

So apparently, the OP1/OP2 are internal op amps. And here's what the sheet says:

"OP amplifier 1 input/output. This pin can be used as modulated/Demodulated integrator by connecting capacitor
OP Amplifier 2 input/output. This pin can be used as Modulated/Demodulated Integrator by connecting Capacitor"

It would help if I understood what a "modulated/demodulated integrator" did. 

I'll probably just dick around with cap values and see what happens. 

[Slade]

Hey, I've retraced the PCB to tonepad's layout style and made a PDF with 6 ready to print boards.

Click on the image to download:



Regards,
Fernando.-

[joethugs]

Thanks for this nice layout!

[culturejam]

Hey, I've retraced the PCB to tonepad's layout style

What software do you use for that style layout?

Thanks.

[joethugs]

was also thinking about that?.. It's not DIY layout Creator? Right?

[Slade]

It's made line by line and hole by hole with the only design program I use... Adobe Illustrator.

I shared this proyect in a chilean forum, and as it's a "beginner's" proyect I just made an easier-to-etch-PCB and an easy to build layout with the component values on the layout. Enjoy!

[joethugs]

no wonder your etching technique is superb because you design them in illustrator which is vector based as opposed to photoshop pixel based..

[Lurco]

Okay, here's the good data sheet:
http://www.princeton.com.tw/downloadprocess/downloadfile.asp?mydownload=PT2399_1.pdf

So apparently, the OP1/OP2 are internal op amps. And here's what the sheet says:

"OP amplifier 1 input/output. This pin can be used as modulated/Demodulated integrator by connecting capacitor
OP Amplifier 2 input/output. This pin can be used as Modulated/Demodulated Integrator by connecting Capacitor"

It would help if I understood what a "modulated/demodulated integrator" did. 

I'll probably just dick around with cap values and see what happens. 

It`s all about Delta Modulation http://en.wikipedia.org/wiki/Delta_modulation

[earthtonesaudio]

Okay, here's the good data sheet:
http://www.princeton.com.tw/downloadprocess/downloadfile.asp?mydownload=PT2399_1.pdf

So apparently, the OP1/OP2 are internal op amps. And here's what the sheet says:

"OP amplifier 1 input/output. This pin can be used as modulated/Demodulated integrator by connecting capacitor
OP Amplifier 2 input/output. This pin can be used as Modulated/Demodulated Integrator by connecting Capacitor"

It would help if I understood what a "modulated/demodulated integrator" did. 

I'll probably just dick around with cap values and see what happens. 

It`s all about Delta Modulation http://en.wikipedia.org/wiki/Delta_modulation

I would say it's mostly about delta modulation, but there's some other fun stuff going on too.


The input signal goes through LPF1 and into the inverting comparator input and is converted to a 1-bit data stream.  This data then goes into OP1 through the box labeled "MOD" in the datasheet.  With the external capacitor, OP1 inverts and integrates this data and is fed back into the non-inverting input of the comparator, closing the loop of the delta modulator.  With too small of a cap, the differential signal at the comparator is very small, so it has a hard time saying whether the input signal is higher or lower than the reference, and the result is drastically reduced gain, except at very high slew rates, where the too-small cap is just barely sufficient to let some signal through.

Because this integrator is part of an overall negative feedback loop, making its capacitor larger reduces the integrator's gain (starting at high frequencies) but increases the gain of the A-D stage as a whole.


Finally, another area of interest is the "MOD" section, which I believe to be a SPDT switch.  The pole connects to pin 8 and so the circuit becomes a switched-capacitor resistor of approximate value R=1/(fC), where f is the clock frequency and C is the capacitor from pin 8 to ground.  So when the clock frequency decreases, the resistor going into the integrator increases, and the integrator's cutoff frequency decreases.  Again, because this occurs in a negative feedback loop, the overall effect is the opposite, such that a decreased clock frequency results in pre-emphasis of treble at the A-D stage.  Meanwhile, the output after the delay goes into OP2, which is similarly modulated by the clock, but here the decrease in clock frequency causes a treble cut, which helps you get away with lower fidelity at longer delay times.

[culturejam]

Because this integrator is part of an overall negative feedback loop, making its capacitor larger reduces the integrator's gain (starting at high frequencies) but increases the gain of the A-D stage as a whole.

Right. So I'll start dicking around with cap values here and see what happens. 

Finally, another area of interest is the "MOD" section, which I believe to be a SPDT switch.  The pole connects to pin 8 and so the circuit becomes a switched-capacitor resistor of approximate value R=1/(fC), where f is the clock frequency and C is the capacitor from pin 8 to ground.  So when the clock frequency decreases, the resistor going into the integrator increases, and the integrator's cutoff frequency decreases.  Again, because this occurs in a negative feedback loop, the overall effect is the opposite, such that a decreased clock frequency results in pre-emphasis of treble at the A-D stage.  Meanwhile, the output after the delay goes into OP2, which is similarly modulated by the clock, but here the decrease in clock frequency causes a treble cut, which helps you get away with lower fidelity at longer delay times.

I'll pop the hood on my Echobox, as I recall Brian from Subdecay mentioned something about how it was filtered. It gets about 1 second of relatively clean delay, which is insane considering the THD on this chip at that delay time.

I assume the DEM section is "demodulator". The data sheet calls pin 7 (DEM) and pin 8 (MOD) "Current Control" 1 and 0, respectively. And both application circuits have a 100n cap to ground from these pins. Again, I'll have to just goof off with changing cap values and see if I can hear anything.

[jimmybjj]

no wonder your etching technique is superb because you design them in illustrator which is vector based as opposed to photoshop pixel based..

sorry for the OT but does this make a difference?

[slacker]

It`s all about Delta Modulation http://en.wikipedia.org/wiki/Delta_modulation

Thanks for the link, the datasheet block diagram finally makes sense to me

[Perrow]

I just love watching a new pedal be born