"Little Angel" - Super Simple PT2399 Mini Chorus

[culturejam]

I noticed, though, that my 500k pot only had about 1/8 turn as usable range... after I dropped the 33k. With the 33k in place, I was getting no wobbling. I triple checked everything, so not sure why it does this. Also, my 100k has only about 1/4 usable area. I'm done with it for the night, but if anyone has any suggestions, I'll try them out tomorrow.

On my build, I'm noticing that in order to hear how the lower range of either pot sweep is effecting things, the other control has to be set closer to maximum. For example, the change in Speed seems very subtle for the first half turn with Depth low, but when Depth is cranked, the Speed changes are far more noticeable.

[slacker]

I might have figured out how changing the bias voltage effects the delay time.
If you look at the block digram in the datasheet you'll see the output of the OP1 opamp (pin 9) is connected internally to the positive input of the COMP, presumably this is a comparator of some sort. The + input of the OP1 opamp is connected to the bias voltage, so changing that will change the output of the opamp and as the output is connected to the COMP it will have an effect on the signal coming out of COMP.
If COMP is like a comparator then changing the bias voltage would change the pulse width of the output which could then have some effect further down the line in the digital part of the chip.
Or maybe not who knows

[earthtonesaudio]

I don't think so.  Changing Vref causes no differential voltage change at the inputs of the comparator, because both its inputs are driven by opamps biased at Vref, both of which have a DC gain of +1.  This does not apply at high frequencies, but at LFO rates I think it does.

I think it's more likely that pin 2 is somehow tied to the internal VCO's circuitry.

[slacker]

Good point I missed that, yeah the most likely thing is that the VCO has a connection to the bias voltage.

[Earthscum]

On my build, I'm noticing that in order to hear how the lower range of either pot sweep is effecting things, the other control has to be set closer to maximum. For example, the change in Speed seems very subtle for the first half turn with Depth low, but when Depth is cranked, the Speed changes are far more noticeable.

Yep, I'm getting the exact same thing. I have to have them both within a certain range for them to be usable. If either one is out of the range, there's no audible modulation. This is actually the LFO itselfm it seems... I've tried different chips and get the same result. Tried different pots as well.


I just noticed... I'm an idiot. My 500k is audio tapered. I flipped it around the right way and now have more useable range from it.

[Earthscum]

Ok, so I figured out if you replace the 10k between pin 14 and the .01 with a 50k-100k pot, you can adjust the mix. I ended with a great mix at around 27k, This actually cured most of my problem.  As well, I dropped my 33k to ground down to 27k to get that top lope at full pot rotation. I may pop in a TL074 and make an LFO buffer and output buffer/mixer. It feels like that would cure a bunch of the LFO interaction issues that I'm experiencing.

The delay output pot is actually nice... I can sweep from a perfect chorus mix to flanging sounds to a dry and subtle sound.

The LA works pretty good for bass, except like I noted before, you lose effect on the lower notes. I tried a bazz fuss before it and it really gets snazz and pizazz! This actually is a nice thing for some songs where you want the low end to sit back a bit, but your hig strings just have too much bite. This makes the high end shimmer and actually settles it into the mix a bit better. I just gotta redo the input stage to get my punch back.

Again, big thumbs up on this one! This is a kewl little project!

[culturejam]

Ok, so I figured out if you replace the 10k between pin 14 and the .01 with a 50k-100k pot, you can adjust the mix. I ended with a great mix at around 27k, This actually cured most of my problem. 

I'm building another one soon for mods/tweaks testing, so I'll give this a try.

As well, I dropped my 33k to ground down to 27k to get that top lope at full pot rotation.

Funny, I just mentioned to Rick that maybe 27K would work as well, since he said 22K was a bit too low. 

[Earthscum]

Aye, I think it's probably too low for a complete build. I think the 33k is just about right... actually, I kept tuning, pulling and measuring and ending up around 29.5k for my personal lowest sweet spot. 27k seemed to begin introducing a small bit of audible lfo clicking, and lower by about about 5 k was just a bit too much for me to just slam the pot all the way.

I noticed an interaction while playing through my TKO, though. I put a 50k to ground from pin 6 (will probably go with a 10K), and when I used my mixer pot (which, BTW, should have a min setting resistor... it lets alot of hiss through at close to full wet) I could get a nice clear wet sound.

When I play my bass, the lower notes aren't coming through as well as the higher notes due to the time. For bass, this isn't necessarily bad. Basically at fastest delay, the lowest notes are mixing more readily at the output. When I set the mixer just right, I could get even mix, and tossed on a low pass before the junction from the output of PT. Now I have delayed highs, with my normal lowend punch! That's awesome for bass! The delay is a little over the top, but every part of this is a little bit of something kewl. Faux Delay, faux semi-flanger, faux Sonic Maximizer, and a space noise signal destroyer in one box. Seriously, my GF is into EBM and plays a bit of bass, and nearly started drooling as I swept through some settings.

Hit the input with a bazz fuss or other decent sounding dist, and this thing kills! Plain BF sounds gigantic. The filtering shaves off all the highs. Perfect circuit, IMHO, if ya want to add a small switchable dist. inside a box. Really, it sounded like I've never heard it before 

[frequencycentral]

As the PT can handle up to 6.5v, I'm still wondering if delivering more voltage than the accepted 5v would result in an over-clocked VCO and even shorter delay times.

actually, I can answer that. I tried that a couple years ago and according to my notes

with pin 6 grounded,
5V supply = 24ms
6V            = 18ms
6.5V         = 16.5ms
7V            = 15ms
7.5V         = 14ms
8.5V         = dead chip

also current draw nearly doubles from 28mA @ 5V to 58mA @ 6.5V

hope that helps

So who's going to replace the 7805/78L05 with a 7806/78L06? 

[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........?

 

[frequencycentral]

.....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?

[culturejam]

.....and the PCB apparently will fit in a 1590A!

I would've never guessed that. 

Actually, I was thinking it would be cool to have a layout that takes advantage of 1/8-watt resistors and multi-layer ceramic caps.

[culturejam]

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........?

 

Did it work? 

[danielzink]

.....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'm following the thread...yes yes.......I'm waiting for all "the dust to settle" and all the mods be sorted etc.




DZ

[Earthscum]

So... am I the first? I used this thing live, and it's so sweet!

I left to buy parts at 11:15 yesterday morning. Luckily I had an old MXR Auto-Q case that was drilled already. I actually finished, plugged it in to test, congratulated myself and my guitarist walks in. 5:00, bar opens at 6... I can't believe I actually made it, and it worked! lol.

BTW, I ended up using this thing on about half my songs last night. We had a buddy sitting in, so I had to  pit the Little Angel up against a G-K Roto Sphere. Rick, this is awesome... it actually held it's own! I was able to tweak the LFO and fill the space between the dry guitar, and Brooks' RS, without making even myself cringe. I was hoping we'd have some video or at least sound samples for ya, but someone in our band forgot to charge their vid camera...   

[culturejam]

I'm following the thread...yes yes.......I'm waiting for all "the dust to settle" and all the mods be sorted etc.

I'll be testing some mods over the next few days (just etched another PCB), so we should have at least a couple of verified, working mods pretty soon.

My first test will be to add a variable delay time control, a switch to go from 50/50 to "wetter" mix, and a feedback adjust switch. I doubt all that will fit in a 1590a, but you guys who work with those often surprise me.

More details to follow shortly. 

[Earthscum]

... I doubt all that will fit in a 1590a, but you guys who work with those often surprise me.
...

No doubt!!! I wanna give it a shot with the 2 pot mods I'm using. I just added a 100k pot into the wet return to cut the signal out, which intensifies the effect. Actually, more of "Effect Intensity", then. The only other thing I did was took the 100R and tied it between the wiper and lug to ground of a 10k pot, and tied the other lug of the pot to pin 6. At max delay, the 10K is still a bit too much, but it helps increase the intensity of the effect for bass by delaying the lower frequencies enough to cause an audible shift. I'd suggest a 5k. At one side, you have straight 10k resistance, which you could just tailor with a resistor strapped across wiper to lug, and on the other end of rotation, you have the 10k with the 100R across it, so effectively just a little under. I did this on purpose so WHEN I build my GF's, I can just order one of the PCB's and use the mod instead of a resistor. Don't have to drill extra holes, which is kinda what I think modding a circuit like this is about... using what 'you got' (or the designer's layout) and doing what you can with it 

[culturejam]

I'm populating the second board now. But I'm out of 220K resistors, so I'm going to try some different values and see what happens.

[Renegadrian]

...someone in our band forgot to charge their vid camera...   

And that was the best performance ever...Classic...

[Earthscum]

I got showed up by our 'walk-in', Brooks, lol.

Actually, I forgot my fuzz and the extension cord... our guitarist, Fred, forgot to charge his camera, and our drummer AND Fred forgot the signal cables for the monitor amp up in Cheyenne. We pulled it off. It was a good show, blisters and all.