Introducing the Cherub pseudo chorus and vibe (for the last few soles who haven't built a Little Angel, or who never managed to get one to work).
Not long ago, I started playing with the Little Angel chorus on the breadboard (http://www.diystompboxes.com/smfforum/index.php?topic=106680.0).
With a little prodding from Rob, it mutated from a LA-derived circuit, to something a bit further from the tree. This is where I ended up - sorry for the thread proliferation, but I figured a clean slate might be helpful.
The input stage is non-inverting for lower noise and higher input impedance. As the circuit is fairly minimalistic, the op-amp is biased from the 5V regulator, like the 1590A layout of Rick's for the LA. This doesn't seem to cause any problems, and might save a couple of parts.
There is minimal filtering around the PT2399, which allows the use of the PT2399's output op-amp (pins 13,14) as a mixing/output buffer. The mix pot lets you pan between fully dry and fully wet signal, so you can have a vibe effect at one extreme and can use it as a pseudo depth control at the other.
The LFO is essentially lifted from the LA, but has been biased a little hotter and can go a little slower. We get modulation by playing with the resistance from pin 6 of the PT2399 - we've all seen this trick before, but I found it worked better at slower LFO speeds than modulating Vref (pin 2).
Q1 is our variable resistor. The choice of transistor is not too crucial here, but you may have to play with the value of R13 to get a reasonable amount of modulation. If R13 is too big, the delay time can get long enough to be a problem. Further, there is some regeneration via R2, which will give multiple 'repeats' and gives the effect a bit more depth at slower LFO speeds. The trade off is that the regeneration makes the delay more obvious if you play staccato as you can hear the multiple slap back. The value of R2 can be lowered for more regeneration, but it will begin to oscillate below ~18k.
A quick and dirty clip recorded direct.
https://dl.dropboxusercontent.com/u/11996927/Cherub.mp3
The schematic:
(https://dl.dropboxusercontent.com/u/11996927/Cherub_PT2399_Chorus_schematic.jpg)
I built this on perf using the below layout. It worked ok, and it should translate to a PCB fairly well.
(https://dl.dropboxusercontent.com/u/11996927/Cherub_PT2399_Chorus_perf_layout.jpg)
(https://dl.dropboxusercontent.com/u/11996927/cherub_guts.JPG)
Here is an untested PCB layout based on the perf layout above...
https://dl.dropboxusercontent.com/u/11996927/Cherub_PT2399_Chorus_PCB_transfer.pdf
Nice one, Sam. Yet another one for "the list". ;)
Thanks Marc.
One thing I should note. As it seems that PT2399s are a little variable, it might be good to try this on the breadboard first.
Looks cool Sam. Quick question what does D4 do?
I was wondering when somebody would ask about D4.
It is mostly just a relic from when I was trying to modulate the depth in a slightly more aggressive way - the idea was to offer some protection to the PT2399.
I left it, because it didn't hurt and I would otherwise have needed a jumper in the layout I used. It can be left out, or could be replaced with a small resistor or a 1-10k pot to give variable delay.
I tried to use an LED here instead, so that it could double as a LFO rate monitor. It almost worked, but didn't dim enough to quite cut it. The delay still modulated fairly nicely.
Quote from: slacker on April 09, 2014, 06:55:28 AM
Looks cool Sam. Quick question what does D4 do?
just to be updated on this project....
looks like D4 is a LFO monitor. :)
Ciao
It would have been cool if D4 was the LFO monitor. As it is, that job falls to D3 (which is optional of course).
great, you finished it...sounds much better/more full than the original, nice work man... 8)
I thought it was finished...
I quite like the vibe effect (fully wet), and am starting to wonder if a depth control might be a good idea, as it gets a bit sea-sickening at faster speeds.
Quote from: samhay on April 09, 2014, 11:28:48 AM
. . . it gets a bit sea-sickening at faster speeds.
Just avoid using after a kebab... ;)
Thanks Rob.
Marc - where would be the fun in that?
^ True! :D
Another case of mission creep:
I added a depth control last night. It is more useful than I thought it would be, and is a recommended addition. The 3 controls - rate depth and mix make for a rather versatile little circuit and the vibe effect (fully wet) is now quite useful right across the range of LFO speeds. I guess I better make a proper demo...
The schematic has been updated and the layout will need tweaking at some stage.
Cool, yeah depth is always a good option...look forward to hearing the update, 8)
Only just had a listen to the clip, sounds really good. Some of the more extreme sounds were particularly interesting.
Thanks Ian.
I added the depth control so that when wet it didn't always sound quite so 'interesting'. You can always increase the value of the depth pot for more extreme settings - an A1M pot could work ok.
The way Q1 is biased is a bit of a low-parts-count bodge that works much better than I thought it would. Less base resistance (R13 + depth pot) = lower base voltage = shorter delay time, but less wiggle. If you make the depth pot too big then the delay starts to get quite noticable / 'interesting'.
we all love 'interesting' ;D
8)
Rob - I bet it would sound awesome on the breadboard next to your X Fuzz...
i haven't got a spare breadboard :(, xfuzz/synthbox/spitty/ and some weird 4017 led thingy are occupying them at the mo... :)
(note to self, get another board) ;D
Fair enough.
Why am I not surprised you have at least LED 'thingy' on the breadboard?
i'm like a magpie...anything shiney i'm on it.. ;D
talking of which, my solar lights have a new life....sun!!!!!! Ahhhhhhhhhhhhh....at last... 8) 8) 8)
grab a solar bug or 2 or 3 from the 99p shops...they're brilliant.. 8) 8) 8) 8) 8)
Quote from: samhay on April 12, 2014, 05:39:22 AM
Another case of mission creep:
I added a depth control last night. It is more useful than I thought it would be, and is a recommended addition. The 3 controls - rate depth and mix make for a rather versatile little circuit and the vibe effect (fully wet) is now quite useful right across the range of LFO speeds. I guess I better make a proper demo...
The schematic has been updated and the layout will need tweaking at some stage.
Please man make an update with that; I stay tuned!! it sounds great man!!
any lockup issues with this circuit?
i don't wanna deal with the same probs as the LA seems to have. thanks!
killer sounding pedal... just don't trust 2399s too much these days...
^Please man make an update with that; I stay tuned!! it sounds great man!!
I will update the layout to show how I modified it. it's not pretty, but works. If anyone wants the diylc file to do a better job, then let me know.
As far as latch-up goes. I haven't had a problem, but it could potentially be a problem if it is powered up at minimum depth - this is part oft the reason I initially went for a max depth effect.
If people have a problem with the chip latching, an anti latch up circuit can be easily added.
Quote from: samhay on April 21, 2014, 04:10:04 AM
^Please man make an update with that; I stay tuned!! it sounds great man!!
I will update the layout to show how I modified it. it's not pretty, but works. If anyone wants the diylc file to do a better job, then let me know.
As far as latch-up goes. I haven't had a problem, but it could potentially be a problem if it is powered up at minimum depth - this is part oft the reason I initially went for a max depth effect.
If people have a problem with the chip latching, an anti latch up circuit can be easily added.
OK I wana´!!!!!!!!!!! please post!
^OK I wana´!!!!!!!!!!! please post!
I've updated the layout to show how I added the depth pot.
Two points:
1. I would strongly suggest you breadboard this first. PT2399s seem to be rather variable beasts, so you may have to tweak a few component values to get it to work as well as it should.
2. I am working on a new layout, which should be a bit less of a kludge. See below.
Here is another layout. It is a tad smaller, and the mix pot is now not routed half way round the board.
However, It is not verified, and may well contain some errors around the top side of the PT2399. When I get some more time, I will go over it again, but in the mean time...
(https://dl.dropboxusercontent.com/u/11996927/Cherub_PT2399_Chorus_perf_layout_V2o1.jpg)
I've had another look over the Ver 2.1 layout above, and there are no obvious errors.
I'm not likely to build another one for a while, so if anyone tries it, please let me know.
Quote from: samhay on May 03, 2014, 04:25:01 PM
I've had another look over the Ver 2.1 layout above, and there are no obvious errors.
I'm not likely to build another one for a while, so if anyone tries it, please let me know.
I stay TUNED please let know how it be; thanks!!!
Sounds better than my Behringer UC-200, i think :icon_eek:
^Sounds better than my Behringer UC-200, i think
I'm not sure that that is necessarily much of a compliment, but thanks. Have you built it?
That sounds great , I just got some PT2399's to play with so will have to give this a go on the breadboard. :icon_biggrin:
That reminds me - I really must do a proper demo.
The clip on the first page was recorded before I added the depth pot, which effectively was on max.
This was recorded (again, sorry for the cheap-and-cheerful quality) for the Dino's no-LFO chorus thread recently. In this case the depth was at min for most of it, but you get a little sense of what it can do towards the end.
https://dl.dropboxusercontent.com/u/11996927/cherub_v2_min_depth.mp3
Quote from: Ice-9 on May 06, 2014, 05:53:59 AM
That sounds great , I just got some PT2399's to play with so will have to give this a go on the breadboard. :icon_biggrin:
Glad you like it.
Quote from: samhay on May 06, 2014, 04:19:20 AM
^Sounds better than my Behringer UC-200, i think
I'm not sure that that is necessarily much of a compliment, but thanks. Have you built it?
Yep, in a breadboard... sounds great and is it absolutely noiseless.
^Yep, in a breadboard... sounds great and is it absolutely noiseless.
Excellent.
Quote from: samhay on May 06, 2014, 12:27:18 PM
^Yep, in a breadboard... sounds great and is it absolutely noiseless.
Excellent.
What lay is the verified??; you have photos?
The perf layout in the first post is verified.
The ver 2.1 layout (http://www.diystompboxes.com/smfforum/index.php?topic=106854.msg970043#msg970043) isn't verified (that I know of), but looks like it should work.
If anybody would like to do a better job, then I am quite happy or them to do so.
Nice job Samhay!! I was just in the process of deciding what chorus to make. I had my orderlist for Tonepads Corrall chorus ready, but i think i'll change it to yours. Sounds great and looks less complex.
Question: has the pcb-layout in your first post been updated too?
I have no experience in making layouts but i'm working on that
The PCB layout doesn't need to be updated, as the only changes were a flying resistor and pot.
However, the ver 2.1 perf layout should work ok as a PCB transfer too. I can post a scaled version of the trace if you like.
With all things, I would suggest you give this a try on the breadboard first. I would imagine it is quite a different beast to the Tonepad chorus.
Quote from: GodSaveMetal on May 06, 2014, 01:04:27 PM
Quote from: samhay on May 06, 2014, 12:27:18 PM
^Yep, in a breadboard... sounds great and is it absolutely noiseless.
Excellent.
What lay is the verified??; you have photos?
Disculpa, hermano, but I have no photos. This is the second version, i checked the schema with the new layout and so I made sure that were correct.
QuoteI can post a scaled version of the trace if you like.
I'lld like that very much Samhay. And i'll take your advice and breadboard it first as soon as i've got my PT2339.
Thanks!!
Here's the version 2.1 PCB layout - not verified!
https://dl.dropboxusercontent.com/u/11996927/Cherub_PT2399_Chorus_V2o1_PCB.pdf
It seems that if the circuit is powered up when the depth is set to minimum, the PT2399 can latch up. If the circuit is powered up with the depth set to max, it doesn't latch up, so this may be sufficent anti-latch up protection for some. However, I have added optional anti-latch up protection to the schematic in the first post and a perf layout incorporating this is below.
This is NOT verified, and the anti-latch circuit will effect the depth control to some extent, so the value of the 100k resistor (R13) that sets the minimum depth may have to be reduced. When I have some time, I will add the anti-latch circuit as a daughter board and see how it goes.
(https://dl.dropboxusercontent.com/u/11996927/Cherub_PT2399_Chorus_perf_layout_V2o2.jpg)
Added the anti-latch up protection shown in the schematic as a small daughter board. Works fine, and no need to change the depth control.
Note to self - modifying perf circuits is a PITA.
Some housekeeping:
Freppo has put together a vero layout for the Cherub, which I believe is verified:
http://parasitstudio.weebly.com/uploads/2/4/4/9/2449159/cherub_chorus.png / http://parasitstudio.weebly.com/guitar-fx.html.
I also made a quick direct recording yesterday to show how quiet the circuit is.
Recorded with tele single coils -> compressor -> Cherub -> audio interface:
https://dl.dropboxusercontent.com/u/11996927/Cherub2.mp3
sounds great sam...nicely done. 8)
Seems to me a good alternative to the Little Angel Chorus.
Thank you!
You're welcome, and thanks Rob.
Have been thinking about revisiting this for a while in the context of a 'Fat Cherub' with variable delay and maybe envelope control. As soon as I get the DiSCO built, I will have another play.
Hey everybody, this is my first time posting in the forum, any forum for that matter. I etched the 2.1 version and got everything working but the lfo seems to be a full wave rectified sine wave instead of a sine wave. I'm not sure if it's the transistor that's biased wrong or what. I'm using a 2n3904 instead of a 2n5088 if that makes much of a difference. The effect sounds ok the way it is but it bouncing up and down instead of normal wavy. Sam, thanks a lot for designing and posting this btw.
Does the wavy-ness of the modulation improve/get worse as you adjust the depth pot?
It seems like the effect is most symmetrical at the highest depth setting and at the lowest setting it sounds like how this looks.(https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcS-M0QrEhBeVuOTz3_3wPRufXE0CV4rwQbamZK3e291qEdDXQDjTA) I'm guessing that the transistor isn't "on" for the full cycle at this low setting... but i'm still new at transistors.
There is a 100k resisor in series with the depth pot to set the minimum depth. If you find there is a usable minium depth at some point mid-way through the depth control, then increase this resistor to set a new minimum depth.
It was a few years ago I last played with this on the breadboard, and I can't remember if I auditioned different transistors or not. However, I don't think I would have spec'ed at 2N5088 if a lower gain transitor worked as well. So... Alternatively, try a higher gain transistor.
awesome, I'll try the resistor first and I've got some 5088's on order. Thanks a lot for the help!