"Little Angel" - Super Simple PT2399 Mini Chorus

[sundgist]

After you power it on with the depth maxed then it works normally?

Yes! But when I dial in my own favorite setting, and power it off and back on again, it latches! So each time I power up the Angel I have to max out the depth knob, and than bring the power on to get it working properly! After I've done this I can dial in my own settings and use it.

I read through this entire thread last night as I've just received parts to start building this.
There is a fix posted here http://www.diystompboxes.com/smfforum/index.php?topic=86297.msg774512#msg774512
There's a fair bit of info about the latching issue earlier in the thread.

[edit]
Just re-read the last few posts. Curious about this.

Also, when a PT goes into latch up once it will usually do it again even when the pin 6 resistor is more than 1k (something inside seems to burn out and it can't drive as much current at start up any more). You usually have to make it several k after that to avoid further latch ups, which explains why increasing R21 helped.

If the fix is in the build from the start, would there be any reason for it to ever latch up? Assuming (for simplicitys sake) that the cap in the fix is fully discharged between any switching off/on (accidental or otherwise) while depth is below 1k.

[Pigyboy]

All the chips seem to react different even with the fixes. Seems I read back somewhere that they work every time with a battery. Lots of the older ones seem to be fine but lately lots have been reporting iffy ones. I think Tim's discovery is on the right path....Rick!?

[merlinb]

If the fix is in the build from the start, would there be any reason for it to ever latch up? Assuming (for simplicitys sake) that the cap in the fix is fully discharged between any switching off/on (accidental or otherwise) while depth is below 1k.

Things are complicated by the modulation of Vref, because that also affects the internal pin 6 circuitry, so it depends on how the LFO starts up. Best bet would be to improve the latch up fix by putting the 47R resistor in series with the emitter instead of collector, and increasing the charge time (increase the 68k to 220k say). Alternatively, put a couple of diodes or an LED in series with the emitter and eliminate the 47R resistor completely; this will increase the time before the transistor starts conducting.

[Pigyboy]

Thanks Merlin,
I'll try to build a little pin 6 fix board with your suggestions. It may take me a day or two so feel free anyone else...

[sundgist]

Things are complicated by the modulation of Vref, because that also affects the internal pin 6 circuitry, so it depends on how the LFO starts up. Best bet would be to improve the latch up fix by putting the 47R resistor in series with the emitter instead of collector, and increasing the charge time (increase the 68k to 220k say). Alternatively, put a couple of diodes or an LED in series with the emitter and eliminate the 47R resistor completely; this will increase the time before the transistor starts conducting.

As far as I recall reading the latching only occurs at power up. Has anyone experienced it during use?

Supposing pin 2 was held at 2.5v until the cap at pin 6 had charged fully before letting the lfo do it's thing. Would this make things more foolproof?

My thinking is that this would allow the chip to start in ideal conditions.

[merlinb]

Supposing pin 2 was held at 2.5v until the cap at pin 6 had charged fully before letting the lfo do it's thing. Would this make things more foolproof?

That would probably work, but seems overcomplicated to add start-up circuits to both pins. The whole thing can be made fool proof if the pin-6 latch up fix is improved. As it is, it's a bit borderline. The transistor+LED version I'm using works every time even with PTs I have thoroughly burnt out in the past.

[rhcp_schipper]

Hello you guys,

Again I had a bit of a struggle with getting my angel to chorus! Even with the little fix of setting the depth to max and then power it on wouldn't help.

Now I discovered that when I put both the speed and the depth to max it will chorus like it has to do.

Thought I share with you all.

[Gary]

Rick (F.C.),

I built one of these (b-day edition) for our bass player, including a few mods here and there to get the sound he was looking for.

In the process, I think I've found an error in your b-day edition PnP file.  The problem appears to be R21/R22.  On the PnP, they form a divider at the collector of Q2.  According to the schematic, it should be R21 to ground off pin 6, then R22 in series to the collector of Q2.

I can verify your layout works with this corrected and adding in a couple of Merlin's tips.  (I added his suggestions of an LED on Q2 emitter and changing the 68k at Q2 base to 100k.  So far, so good.)

[frequencycentral]

Damn, yeah you're right. Thanks for your sharp eyes and heads up. I'll correct it ASAP.

[frequencycentral]

Corrected: http://www.diystompboxes.com/smfforum/index.php?topic=86297.msg790099#msg790099

Refresh your cookies, pour yourself another glass of milk. If the PnP says 'RH + KH 4EVA' in the top left you're seeing the corrected layout.  

[Gary]

Nicely done!  Thank you, Rick.  I really like your layouts.

I'd be interested to hear if this fixes the latch up issue without needing the LED on Q2's emitter.

[bhill]

Just wanted to say thanks, Rick, for a nice piece of work. I was sitting around yesterday playing through mine, switching guitars every so often and wondering what a lfo with several waveforms to select from would sound like in this circuit. Not that it sounds bad now, I like it as well as most other choruses I have played. Just one of those occupational hazards we all go through, wondering what mods can be done and will it add that something extra to the sound we look for. Then just for the heck of it I plugged in the P-bass. Took it into the shop today and had a couple other bass players I know try it out. All our responses were the same, somewhat along the line of OMFG!! Now I gotta build a couple more.

Thanks Rick
Bob

[markeebee]

If the PnP says 'RH + KH 4EVA' in the top left.....

You plum.  Congratulations.

[frequencycentral]

If the PnP says 'RH + KH 4EVA' in the top left.....

You plum.  Congratulations.

Plum? Peach! Thanks, it's tomorrow. 

[stash]

Hey!

Can anyone help me?? I made little angel using following layout:

http://www.diystompboxes.com/smfforum/index.php?topic=86297.msg726268#msg726268

but all I can get out of it is clean signal with about 0,5 s delay and some noise. Any idea what's the problem.

[frequencycentral]

If it's passing audio, and with delay too, the issue must be the LFO not working. Poke about around pins 1 to 3 of IC2, and the components in that area, as well as your wiring for the two pots, orientation of C9 and C10.....

[stash]

Actually there was nothing wrong except me being unable to recognize alphabet. So there was 100K instead of 100R. But thanks anyway. You made me re-read the schematic. Chorus is working well.

[Frances Rhodes]

did someone try to replace the LFO section by a different function generator, something in the idea of the EHX pulsar, square wave, sawtooth, and asymmetrical setting?
i'd be curious to know how this would sound like

[tasos]

Hey everybody!
Did anyone tried a substitute for the pot values?

[robmdall]

Pin 6 fix - Is this what Merlin was describing?