Author Topic: Questions about arph's Sentinel Droneverb circuit  (Read 409 times)

moid

Questions about arph's Sentinel Droneverb circuit
« on: August 30, 2021, 06:10:06 PM »
Hello everyone

I'm working on making a Sentinel Droneverb at the moment. I haven't got it to the stage of testing it (it's still being built) but I have a couple of questions about the circuit and hope that someone who may have built it/ understands it might be able to give me some tips please. I'm using the following layout:



The only schematic I can find of the circuit is this one, and I don't think this is the schematic that the vero board was based on... if anyone does have the right schematic please post it here!



On the vero layout it specifies a 3mm green LED to be used (connecting to pin 7 of the PT2399). Is the 3mm part vital? I don't have any and was planning on using a 5mm green LED instead - is that a bad idea? I'm not sure what the LED does (I know you can use them as clipping diodes, but I don't know if that is what this one is for). I do have a 3mm red LED if that would be better than a 5mm Green LED. Do the sizes actually affect the sound in any way? Should this LED also be visible through the enclosure to show that the circuit is on, or would I be better off using a separate LED and CLR attached to the 3PDT for that? I've put a socket in for this green LED so I can swap it out easily if required.

On the right side of the board there are connections to a bi colour LED for the rate. I've discovered that the bi-colour LEDs I bought have a common anode, not a common cathode as requested here. Can I put in two different colour normal LEDs here instead, with both their short legs connected together to the cathode point on the board? Or should I just use one of them and ignore one of the Rate LED+ connections?

I'm adding a mix pot so I can blend between the circuit output and the dry input (probably using a 100K Lin for that). I've also made the 25K trimmer (for fine control of the circuit) as a normal pot on the outside of the enclosure so I can adjust it as required.

Thanks for your advice and thoughts :)

« Last Edit: August 30, 2021, 06:13:36 PM by moid »

SmileyNK

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #1 on: August 30, 2021, 08:49:10 PM »
I love this one! The LED trick is one I've used on multiple delays since building this. The size of the LED shouldn't matter since the forward voltage is the same. Different colors will have slightly different effects. This LED just kinda regulates the runaway feedback that continuously sustains.

One or two LEDs for the rate should also work just fine.

Are you using a split n blend or similar to mix this or just a pot?

r080

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #2 on: August 30, 2021, 09:13:47 PM »
As far as I can tell, the green LED trick was originally worked out in this thread:

https://www.diystompboxes.com/smfforum/index.php?topic=101149.0

moid

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #3 on: August 31, 2021, 06:17:06 PM »
I love this one! The LED trick is one I've used on multiple delays since building this. The size of the LED shouldn't matter since the forward voltage is the same. Different colors will have slightly different effects. This LED just kinda regulates the runaway feedback that continuously sustains.

One or two LEDs for the rate should also work just fine.

Are you using a split n blend or similar to mix this or just a pot?

Thanks! I couldn't work out why size would matter (at least not in this case of course!) so I'll stick with a green 5mm LED then. I'll try two LEDs for the rate effect; I'm hoping that one will flash on while the other is off and vice versa. I was going to just use a pot for the mixing (100K Lin is my usual starting point for this sort of thing) and have the circuit output go into lug 3 and then have a cable from the footswitch input to lug 1 and send lug 2 to the footswitch output... is this likely to cause an issue? I assume a more correct thing to do would be to put a buffer with two outputs before the circuit, so one output goes to the circuit and one goes to the mix pot to remove any volume loss... is that what you were hinting at? I might try the cheap way first to see if there is any huge volume loss... and then curse and make a buffer / splitter circuit of some kind afterwards? If I happen to need to do that, is there a particular circuit you would recommend for this?

As far as I can tell, the green LED trick was originally worked out in this thread:

https://www.diystompboxes.com/smfforum/index.php?topic=101149.0

Wow that was fascinating, a bit of history I didn't know... that's something that needs to be played with the next time I try to build a PT2399 circuit - a switch to take out the usual capacitor that goes to pin 7 and replace with an LED might give an interesting alternate sound to the feedbacking delays. Thanks.

moid

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #4 on: September 02, 2021, 07:39:57 PM »
Well in the grand tradition of I made something and it didn't work... le sigh time chaps. Well this circuit partially works; it makes a not unpleasant crumbly distorted lo fi sound but the audio output is extremely low and many of the controls don't seem to do anything half the time... and I'm sure there is a ground issue somewhere, because if I touch the shaft of the Speed knob the blue LED lights up (I didn't have a bi-colour LED, so I'm using a blue and yellow one tied together on the short legs - the yellow is always on it seems, but the blue is more variable). I can light up the blue LED by touching other parts of the circuit with an audio probe, and also my fingers sometimes. I've knifed all the dodgy looking traces as far as I can see.

I've plugged the circuit into a 9V power supply (from a wallsocket) and have nothing in either audio socket, and I measured the ICs and got the following readings:

LM358
1.  4.422V
2.  4.376V
3.  4.427V
4.  0.005mV
5.  4.244V
6.  4.415V
7.  4.425V
8.  8.84V

PT2399
1.   5V
2.   2.499V
3.   0.006mV
4.   0.005mV
5.   3.2V
6.   2.431V
7.   567mV
8.   592mV
9.   2.507V
10.  2.507V
11.  2.505V
12.  2.505V
13.  2.506V
14.  2.506V
15.  2.505V
16.  2.506V

If anyone has any bright ideas I'm happy to hear them - to me the right side of the PT2399 seems a bit odd... no idea about the rest.

Will get some photos tomorrow in daylight, it's way past midnight here and the light isn't great for circuits.

Thanks for reading and thinking about this one!


bluebunny

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #5 on: September 03, 2021, 04:25:36 AM »
to me the right side of the PT2399 seems a bit odd...

The right side of the PT2399 looks just about as perfect as you can get!  The other pins look OK too.
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ElectricDruid

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #6 on: September 03, 2021, 09:53:49 AM »
+1 agree. The voltages look fine, so I don't think that's the problem.

moid

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #7 on: September 03, 2021, 07:07:56 PM »
Thanks chaps, at least that means I set that part of the circuit up correctly - one less part to check I guess! I'm off to the opticians tomorrow to get new glasses, so hopefully with those on I might see something that is wrong! I will run my audio probe around the circuit after the audio leaves the PT2399 and see if there is an obvious point that it loses volume at... although I think the issue may be something to do with ground, especially with the weird reaction the LEDs I added have. I don't yet have an LED attached to the footswitch, but I doubt that would be an issue. I do have a mix pot, but I'm pretty sure the audio volume is low before it gets to the pot... and the Speed pot being odd also needs looking at again... I'll be back soon once I have some more findings.

anotherjim

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #8 on: September 04, 2021, 05:12:18 AM »
There is no dry sound on that thing so the PT2399 has to be running to hear anything at all.
The PT voltages are perfect, except pin5. In a perfect world, it reads 2.5v. 3.2v is either how your chip shows up on a DC measurement (it should be a fast square wave thrashing away at near 20Mhz) or a sign that the delay clock isn't running at all.
You need audio input to show up clean on pin15. Then it goes thru the delay and out on pin12 then finally out on pin14.
Leave the Mod out for now -  disconnect the depth pot wiper.
Make sure the Width pot is at maximum resistance before you switch it on!
Croeso i Diystompboxes.

If they didn't hear you then you didn't say it.

moid

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #9 on: September 05, 2021, 06:37:24 PM »
Thanks anotherjim. I set my DMM to Hertz, Put the black lead on ground and connected the red lead to pin 5 and it says 15.48Mhz... which sounds too low from what you said? I don't have an oscilloscope to see if that value is a square wave or not though. Oddly enough my blue LED lights up when I probe pin 5 (that's the only pin that does that). Does this mean that the chip is locking up perhaps? I have tried swapping out the PT2399 for another chip but it behaves the same.

Audio input is clean on pin 15 and the same volume as it is on the input audio jack. Pin 14 is much quieter and very lo fi - more of a distorted broken fuzz sound with very little bass (I have to say it's quite good in it's own way if it is mixed with the clean input on pin 15! but no reverb / delay sounds in it alas). Pin 12 is slightly louder but is extremely fizzy and more lo fi than pin 14 (it doesn't sound good at all). I will try the disconnecting and Width pot in a few days - I had to spend  today trying to squirrel proof our loft because we have furry visitors that are freaking my wife out, and I am exhausted... the hottest day for months of course, and tomorrow I'm back at work and have two really crazy days to get through. I'll be back!

moid

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #10 on: Yesterday at 07:36:31 PM »

Leave the Mod out for now -  disconnect the depth pot wiper.
Make sure the Width pot is at maximum resistance before you switch it on!


Sadly tried this, and nothing changed :( So I soldered it back in, reflowed all the vero strips, knifed the hell out of the strips but no joy.... this might be headed towards my ever growing collection of shameful soldering mistakes to be cannibalised later...

anotherjim

Re: Questions about arph's Sentinel Droneverb circuit
« Reply #11 on: Today at 05:19:03 AM »
Audio probe. If sound on pin15 there should be delayed sound on pin12. No sound on pin12 then PT2399 is locked up.
Could be due to static. Power off and short all the chips pins together with aluminium foil for 10 seconds. Keep the width pot in the middle of turn when you switch back on and recheck with the audio probe.
Croeso i Diystompboxes.

If they didn't hear you then you didn't say it.