Help - Rebote Delay 2.5 REPEATS problem

[slacker]

Sorry for any confusion about the pots I thought it used log ones but checking the schematic they should be linear so ignore what I said earlier. It probably time to read this http://www.diystompboxes.com/smfforum/index.php?topic=29816.0 and post your voltages, that might show something obviously wrong.

[Jaan127]

B25k is not logarytmic, it is linear. Doubble check the pot, measure it's resistance. In my opinion maybe You use even rev-log instead of Linear pot?

Then what does the B stands for?
it's in the back of the POT (Schematic)

I'll specifcaly get a log one then.

Sorry, You must get me wrong. I thought that You think that B on your pot stands for logarythmic. Don't change anything, stick to what You have on the schematic.
B- stands for linear A-for logarythmic - C - for reverse logarythmic

http://obrazki.diyaudio.pl/15781/434thi8kfalszknxz4pq_1396113618.gif

Ok but now we know I'm using linear and even thought the schematic tells me to use it, someone said that, that might be causing the problem. And you say I shouldn't change it.

The POT's resistance is right and that leaves without knowing what to try next.

[Jaan127]

Sorry for any confusion about the pots I thought it used log ones but checking the schematic they should be linear so ignore what I said earlier. It probably time to read this http://www.diystompboxes.com/smfforum/index.php?topic=29816.0 and post your voltages, that might show something obviously wrong.

Ok, sorry to you and Lothric. I didn't read this before my last reply.
I already saw other rebote delay 2.5 posts and checked my voltages to what some people said should be correct.
Anyway I'll give it a read and try to post that info.

[Beo]

Can't help you with your problem, but my trick for Pots, is that the A stands for AnaLOG. So B must be LIN.

[Jaan127]

In order to make everyone understand better the REPEATS noise I'm talking about I made an audio clip.
There I increased the repeats until getting the noise and also moved the Delay POT to show you how the noise matches the delay time.
~ BE CAREFUL WITH THE VOLUME. THE AUDIO MAY BE LOUD ~
https://www.dropbox.com/s/twr67fmc1syxutx/Grabaci%C3%B3n.m4a?dl=0

And also the voltage measures I made.

Q1 - T8L05 (Voltage regulator)
Input=9.05
Ground=0
Output=4.9

IC1 - PT2399

Datasheet: http://valvewizard.co.uk/PT2399_Data_Notes.pdf

P1=4.88
P2=2.43
P3=0
P4=0
P5=3.67
P6=2.44
P7=0.74
P8=0.80

P9 to P16 = 2.43


IC2 - TL072

Datasheet:http://www.circuitdiagramworld.com/uploads/allimg/201411/TL072-Op-amp-400x207.gif

P1=5.50
P2=4.50
P3=4.48
P4=0

P5=3.64
P6=4.52
P7=4.52
P8=9.03


Any ideas?

[ElectricDruid]

To be honest, that sounds pretty normal to me. Ok, the sound quality is crunchy, but this is a PT2399 at its longest settings.

The repeats go up to oscillation, which you say they shouldn't. For that to happen there has to be a little more than unity gain around the feedback loop. That takes us back to those filters, and errors there *might* explain the dismal sound quality, since the signal would be insufficiently filtered.

Tom

[Lothric]

did You substitute any of the parts in Your build?  What value is resistor on PIN 6 (PT2399), can You post traces of Your PCB?

[Jaan127]

did You substitute any of the parts in Your build?  What value is resistor on PIN 6 (PT2399), can You post traces of Your PCB?

Capacitor between pins 6 and 7 of the IC2b(TL072) is 10pf instead of 5pf
There are three 0.082uF caps: Input, pins 9-10 and 11-12 (PT2399), mine are 0.1uF
And that's all, no other values for resistors or anything.

-PIN 6 (PT2399) - That resistor is 1k, I checked.
-I didn't make a PCB, everything it's on breadboard.

[Lothric]

hmmmm, put  6.8k in series with a 5k trimpot (instead of 15k feedback resistor), and find the best "sweet spot" so the thing does not oscilate too much... on my one I have to use 12k resistor

[Lothric]

I have listened to the sound samples You provided, also I keep in mind that You still have everything on the breadboard. I found very helpfull information in the PT2399 PDF file You provided, check the statements about Vcc.

[Jaan127]

I have listened to the sound samples You provided, also I keep in mind that You still have everything on the breadboard. I found very helpfull information in the PT2399 PDF file You provided, check the statements about Vcc.

I don't really understand what they mean with "decoupling" Vcc. I am not familiar with that concept at all.
Could you explain that please?

The circuit does use the 7805 regulator and althought I have everything on breadboard I'm planning to make a PCB so making the zener follower circuit to replace the 7805 doesn't seem like a promising option right now
I'm surprised that whoever designed this didn't seem to be aware of these things and still, it seems to work for everyone else.

[Lothric]

The problem might be the lenght of your power rail to pt2399,thats what I ment to say, there is no problem at all if you use original tonepad layout. The vcc to pt2399 must be well stabilized in order to work ok. Check your power rail to IC

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[Jaan127]

The problem might be the lenght of your power rail to pt2399,thats what I ment to say, there is no problem at all if you use original tonepad layout. The vcc to pt2399 must be well stabilized in order to work ok. Check your power rail to IC

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That power rail was actually long, like 8 cm or so. I will change it then, to be directly from the 7805 regulator to pin1 of the PT2399.
what about the decoupling??

[Lothric]

decoupling capacitor subject:

https://en.wikipedia.org/wiki/Decoupling_capacitor

read one more time PDF which You provided for PT2399, keep Vcc rail as short as possible, keep that cap as close to IC as possible, change cap for tantalum one or use combination of caps (electrolytic+ceramic) I think thats it. Give us a shout how it goes when You make that Vcc rail shorter, good luck.

Pay attencion how close that 47uF capacitor is to pin3 (analog gnd)& pin4(digital gnd)in the original project:

http://www.tonepad.com/getFile.asp?id=98

The same story is with another 47uF caps, as close to vcc (pin1)and vref(pin2) and close to 7805, that might be the reason why it oscilated so much.

[Jaan127]

decoupling capacitor subject:

https://en.wikipedia.org/wiki/Decoupling_capacitor

read one more time PDF which You provided for PT2399, keep Vcc rail as short as possible, keep that cap as close to IC as possible, change cap for tantalum one or use combination of caps (electrolytic+ceramic) I think thats it. Give us a shout how it goes when You make that Vcc rail shorter, good luck.

Pay attencion how close that 47uF capacitor is to pin3 (analog gnd)& pin4(digital gnd)in the original project:

http://www.tonepad.com/getFile.asp?id=98

The same story is with another 47uF caps, as close to vcc (pin1)and vref(pin2) and close to 7805, that might be the reason why it oscilated so much.

So the decoupling capacitors were always there lol
Ok I made sure to connect the 7805 and all caps directly to Vcc and Vref instead of using rails
And... it IMPROVED a lot!!My rails were actually making noise
Now I had the same problem, just much closer to the repeats POT's maximum(like 80%).

(I don't have much knowledge so sorry if I say some nonsense)
And what I did was measuring repeats POT's max resistance between pin1(left pin in front view) and pin3. It was 20.1k, which is quite far from 25k.

That shouldn't be a problem with the repeats as I'm not even having that 25k max, BUT Repeats POT and Level POT are connected through their pin3. I guessed the Level POT wasn't seeing that 25k resistance but 20.1k and thus somehow that induced some noise.
So I added a 5.1k resistance in series with pin3 of the Repeats and the noise is almost gone. It only appears at maxed repeats pot and lasts like two seconds.

The repeats quality is quite poor so I still feel like the problems isn't solved and don't know if my conclusions are correct. 

[Lothric]

You have reached the limits of pt2399 chip, do not expect good sound quality at max delay. Read original PT datasheet for information why...
I would say Your build is absolutely ok now, can You post sound samples one more time?

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