"Little Angel" - Super Simple PT2399 Mini Chorus

[Grendahl]

PT2399 DataSheet for those that need it.
http://www.datasheetcatalog.org/datasheet/PrincetonTechnologyCorporation/mXyzsyzt.pdf

[p_wats]

Funny...I was just searching around for a simple chorus to try out. I think I'll have to build this and see how it goes!

Thanks for the excellent design (and for the expert tweaks here and there).

[Renegadrian]

Also a PT2399 is cheaper than say a MN3007. And the BOM is smaller than a Zombie.
Having some PTs handy, I think I am gonna get into it. (already working on a vero layout, FIY)

[frequencycentral]

I think it would really benefit any potential builders to wait a while until this design 'stabilises'. I'm hoping to breadboard Tomas's mods later this week - that will be the version to build. BTW, I was 3/4 of the way through a perf/PCB layout when Tomas posted his mods.

I was driving around doing chores earlier, just idly wondering if it would be worthwhile replacing the 2n3904 with an extra opamp stage, then running the two LFO opamps from the 5v supply rail to easily get the LFO wobble bang in the middle of 5v and ground. Then, if we're adding an extra opamp for the LFO, why not add a second dual (or a single quad) and use the spare as an output buffer? This moves away a little from the (desirable) simplicity of the original concept.........Tomas?

[Brymus]

I was just looking over the data sheet,
Nothing new to you guys ,I was just noticing that the lower the delay time the lower the THD,which is good IMO especially in this instance.
What would changing out the 100R at pin 6 for a 1-5K pot do to the effect sound ?
It would increase the delay(a little) but is would it sound bad ?
Might it add more(usable?) sounds to the palatte ?
I will try to breadboard this, this week,ahead of other stuff since its so simple.
Maybe I can accidently find something useful to contribute, or at least verify it works for me.

[culturejam]

Then, if we're adding an extra opamp for the LFO, why not add a second dual (or a single quad) and use the spare as an output buffer? This moves away a little from the (desirable) simplicity of the original concept.

Just make two layouts:

* Little Angel
* Medium Angel




I really dig the simplicity of the first posted schematic. It sounds great. Of course, improvements are always welcome, but I sure do love a small, tidy layout.

[JKowalski]

And I thought the Vref on the chip was buffered...? Even if it isn't, I have no idea how you are getting adjustment in delay times by modulating Vref.

[frequencycentral]

What would changing out the 100R at pin 6 for a 1-5K pot do to the effect sound ?
It would increase the delay(a little) but is would it sound bad ?

Look at the data sheet:

1.08k = 40.6ms
4.9k = 86.3ms

..too long for chorus. But.....

0.5k = 31.3ms

0.1k = ?

0.0k = ??

....so for chorus it is desirable to get the delay time as low as you can go.

And I thought the Vref on the chip was buffered...? Even if it isn't, I have no idea how you are getting adjustment in delay times by modulating Vref.

Yeah, the block diagram on the data sheet shows the vref only connected to the opamps. But it works........

[Brymus]

So maybe a 1k pot might be useful then,?
I will try myself and report back.
FWIW I havent done anything with LFO's or modulation of any kind yet so this is new to me.
And really thanks for posting another useful circuit Rick,and for everyone helping (Tomeque,ect)

[DougH]

Cool project!

Okay, now this is funny:

http://www.taydaelectronics.com/servlet/the-63/PT2399-2399-Echo-Audio/Detail

Okay.. Seems about right.


http://compare.ebay.com/like/260453494074?ltyp=AllFixedPriceItemTypes&rvr_id=122814086475&crlp=1_263602_263632&UA=WXF%3F&GUID=cb6d3f2a10c0a041b291fd31fff7dccf&itemid=260453494074&ff4=263602_263632

Not bad. About what you would expect...


http://compare.ebay.com/like/270597040866?ltyp=AllFixedPriceItemTypes&rvr_id=122835671300&crlp=1_263602_263632&UA=WXF%3F&GUID=cb6d3f2a10c0a041b291fd31fff7dccf&itemid=270597040866&ff4=263602_263632

WTF?!? 

[frequencycentral]

I buy mine fom Tayda, so cheap you can buy a half dozen without breaking a sweat....

....which affords one the luxury of doing unlikely things to the wrong pins (without worrying about toasting it) in the hope of discovering something new!

[armstrom]

Not bad. About what you would expect...
http://compare.ebay.com/like/270597040866?ltyp=AllFixedPriceItemTypes&rvr_id=122835671300&crlp=1_263602_263632&UA=WXF%3F&GUID=cb6d3f2a10c0a041b291fd31fff7dccf&itemid=270597040866&ff4=263602_263632

WTF?!? 

that's for 460 pcs

[slacker]

Just breadboarded the first version and it sounds pretty good, the chorus is quite subtle on the slower setting but it's a nice sound definitely worth exploring. Thanks for sharing it Rick.
I wouldn't say the delay time is significantly shorter than you can get by modulating the resistance on pin 6, but it does the job a lot simpler.

I was driving around doing chores earlier, just idly wondering if it would be worthwhile replacing the 2n3904 with an extra opamp stage, then running the two LFO opamps from the 5v supply rail to easily get the LFO wobble bang in the middle of 5v and ground. Then, if we're adding an extra opamp for the LFO, why not add a second dual (or a single quad) and use the spare as an output buffer? This moves away a little from the (desirable) simplicity of the original concept.........Tomas?

That should work fine, you'll need to use something like an LM358 for the LFO though, a TL072 style opamp won't run off 5 volts. If you're doing that I would change the LFO for a standard 2 opamp type, like in the Echo Base, that will give a "better" triangle output and uses the same number of parts as buffering the LFO you have already.

[clamup1]

i cant wait to give this one a try, its #3 on the list

[anchovie]

0.5k = 31.3ms

That's actually 0.5R, so I think that's their way of saying it's as low as you can go!

[frequencycentral]

0.5k = 31.3ms

That's actually 0.5R, so I think that's their way of saying it's as low as you can go!

Damn, you're right! I completely mis-read that! Thank you!

[Renegadrian]

Not bad. About what you would expect...
http://compare.ebay.com/like/270597040866?ltyp=AllFixedPriceItemTypes&rvr_id=122835671300&crlp=1_263602_263632&UA=WXF%3F&GUID=cb6d3f2a10c0a041b291fd31fff7dccf&itemid=270597040866&ff4=263602_263632

WTF?!? 

that's for 460 pcs

Collective buy?!

[frequencycentral]

So, assuming the PT is running close to the fastest it can. At 5 volts. The datasheet says it can handle 6.5 volts absolute maximum. The question is, if we give it 20% more volts (ie 6 volts) are we also then going to over-clock it into 20% faster delay time? Theoretically we could shave off 6.4ms........?

[Mugshot]

hey rick, what about setting the resistance to ground of pin 6 variable instead of being shunted to ground? would it get it closer to a modulated delay something?

[frequencycentral]

hey rick, what about setting the resistance to ground of pin 6 variable instead of being shunted to ground? would it get it closer to a modulated delay something?

Yes, but slacker's Echo Base does modulated delay better, and with multiple repeats and a host of other useful functions. But with Little Angel I think having any more than the absolute minimum resistance between pin 6 and ground is missing the point. Little Angel is a chorus, so it's desirable to keep the delay time as short as possible.