Small Time: PT2399 Delay with tails

[merlinb]

Just did a vero layout for this project:

[Colonel Angus]

Nice work!! That is Back to the Future BTW... 

[azrael]

Any demos of this design?

I thought it was pretty cool, so I designed a PCB for it, should be here soon.
Maybe I'll make a video once I learn how to play guitar haha

[John Lyons]

Any demos of this design?
First page, first link. 

[azrael]

Yes, I've seen that one. I wanted to see some videos with some people twiddling knobs as the demo goes, John. 

[John Lyons]

Ah, ok, gotcha. 
I built one and it's quite nice.
Very tame with no self oscillation as stock
but the sound was nice. No clips though. 

[bluebunny]

Built this today (see Pictures thread for evidence) and I really like it - thanks Merlin!   

A small "however"... 

I noticed that if I hit a loud note when it's bypassed, signal still gets through to the delay, but very distorted (and pretty quiet).  Sounds like the FET is never fully off.  Anyone else come across this?  Double-checked the circuit vs. layout and everything's fine and dandy.  The FET is definitely a J112 (according to the markings on it - and it came from a reputable source) and is otherwise doing its switching duty.

[Slade]

Hey, Merlin, thanks for sharing the design.
Is it possible to add just the tails circuit to other PT based delays?

[merlinb]

Is it possible to add just the tails circuit to other PT based delays?

Yes, it's just a generic FET analog switching circuit, so it could be applied to other circuits fairly easily.

[azrael]

Just built one, couldn't get it to delay until I grounded pin 4. Thoughts on connecting dGND to ground?

[bluebunny]

Interesting.  Pin 4 is connected to ground (at pin 3), albeit through a small (~10 ohm) resistor.  This according to some handy PT2399 notes prepared by Merlin.

[azrael]

Yeap, I'm aware of that, that's why I was a bit confused.

[merlinb]

Yeap, I'm aware of that, that's why I was a bit confused.

Maybe the internal resistor burnt out? Lots of people report weird issues with the PT2399, often attributed to fake parts. I've not yet experienced it myself. Anyway, you can ground both Agnd and Dgnd pins, it doesn't really make any big difference to performance.

[phizone]

I finished breadboarding this last night and although I haven't had a chance to try it at volume it sounds great so far. However, I used the BOM from the vero layout to pull parts and I noticed some oddities between the BOM and the schematic. These aren't showstoppers, but I wanted to note them here for future builders just in case they are ordering parts based on the vero BOM. Only the 3rd item would actually be an issue...

• C9 is listed in the BOM twice.
• C19 is listed as 47uF in the BOM, but as 100uF in the schematic.
• D2 is listed as an LED in the BOM, but as a 1N4001 in the schematic. The graphic for D2 in the vero is correctly shown as a normal diode rather than LED. It also seems to be oriented from +9v to ground rather than inline like it is in the schematic.

[deadastronaut]

hi merlin...

with reference to adding a tails to a TB reverb question..

http://www.diystompboxes.com/smfforum/index.php?topic=95632.msg829073#msg829073

as a dumbass who can't visualize it in the real world...

how would i wire the dpdt?

[maselectguitar]

Hey all,

I built this using the toner transfer from merlin's  PDF file last night but I still can't get it to work, it only works as bypass as if no signal goes through the PT chip.
Then did a search on google and came across this thread:

http://www.madbeanpedals.com/forum/index.php?topic=5904.0

which probably am facing the lock up as they stated there. I have so far tested with all the 5 PT2399 ICs that I have with me, but all with the same result.

I used J201 instead of J112 since that was only available in my local elect shop.

Now, since all you are super techies here, I thought I'd post here with the hope of having a solution to perhaps fix this on the same
build with minor tweaks/jumper and copper cuts.

Any thoughts?

much appreciated in advance.

maselectguitar

[merlinb]

which probably am facing the lock up as they stated there.

Try shorting pins 3+4 together on the PT2399. See bottom of page: http://valvewizard.co.uk/smalltime.html

[maselectguitar]

Hi Merlin,

Thanks for replying. 

As you recommended, I did solder the pin3 to ping4 but still same result, bypassed signal. I even changed both TL072 and PT to a newer set since I have them socketed.

If this helps, I did the voltage readings for both chip's pins as following, noting that I powered it with a 9v battery.

PT chip:

p1, 5.02v
p2, 2.50v
p3, 0v Grounded
p4, 0v Soldered to pin3
p5, 2.90v   ------- > Strangely receiving voltage even it is not connected to anything, probably internally?
p6, 2.50v
p7, 4.61v
p8, 4.61v
p9, 0v Grounded
p10, 0.01v ------- > Is this right?
p11, 0.35v ------- > Is this right?
p12, 4.69v
p13, 2.50v
p14, 0.28v  ------- > Is this right?
p15, 2.50v
p16, 2.50v

And the TL072 chip readings:

pin1, 3.56v
pin2, 3.57v
pin3, 3.24v
pin4, 0v
pin5, 3.54v
pin6, 3.54v
pin7, 3.54v
pin8, 7.06

And the voltage regulator am using is L78050v with readings on pin1 = 7.2v, pin2 = 0 Ground, pin3 = 5.02v

Also if this is of any use or a clue that even with the power switch in off position, all pins still show the same readings mentioned above !! 

Appreciate your follow up in advance.

Cheers!

[merlinb]

p5, 2.90v   ------- > Strangely receiving voltage even it is not connected to anything, probably internally? <<Yes, that's the clock output pin.
p9, 0v Grounded  << What do you mean grounded? It shouldn't be connected to ground...
p10, 0.01v ------- > Is this right? << Could be.
p11, 0.35v ------- > Is this right? << Could be.
p12, 4.69v  << Should be 2.5V, which is why pin 14 is slammed down to the rail.
p14, 0.28v  ------- > Is this right?  <<No, it should be 2.5V; see above.

And the TL072 chip readings:
pin8, 7.06  << Looks like your 9V battery is dead... or somethings sucking a helluva lot of current...

Solder bridge? Incorrect component?

[maselectguitar]

Hi Merlin,

Thanks again for replying. Much appreciated.

Solder bridge?

Yabsolutely! Got one on pin9! Even though I checked like a million time for SBs!! this was right on the pin 9 ground bridge as you pointed out that it should not! 

Still checking further possibilities of SBs, but haven't noticed any so far.

So, now that pin9 SB got sorted, pins 9 to 16 all read as 2.50v!? this should be correct as you mentioned? right?

And now reading for pin7 and pin8 are 0.60v? Is this corrected now? What should the reading be usually? These were 4.61v earlier.

Incorrect component?

Not sure! Probably not, cause I always get the components sorted with extra care to get them absolute right from beginning to avoid the later hassle, but double checking one more time to be sure.

pin8, 7.06  << Looks like your 9V battery is dead... or somethings sucking a helluva lot of current...

Got a new battery and reading is good on pin8 of opamp at almost 9v. 

My apologies for this, could you please help me figure out the POTs pins numbers to the PT and opamp pin number connections? I probably am being terribly wrong with the POTs! They do nothing at all either fully CCW or CW! 

Much appreciated.
Cheers!