PT2399

[michael_krell]

I am building a simple delay circuit and I built the circuit using the PT2399 that is displayed in the datasheet as (surround sound delay circuit). I am getting no output when i drive an input. what can i do to test this thing

[michael_krell]

Maybe i need some kind of buffer before the input of the delay circuit? my scope is set to 0dB


the output impedance of my scope is 600 ohms

[michael_krell]

kinda funny how the only person replying to this is me but i have more info. I am still not getting out of the output, and the output clock is putting out a wierd wave form. It looks like a retarded sine wave. also what is the difference between analog and digital ground. do i leave them seperate? im not sure about this. for those of you that dont know what circuit im using i have it posted here:

[puretube]

AGND and DGND must be connected: at 1 point - at the big PS cap- ...

[Rob Strand]

You could check your DC bias points: Pins 2 and pins 12 through 16 should be at 2.5V.  If these look bad check the cap on pin 2 is correctly orientated  - check it anyway.

Check for shorts or bad connections.

PS: your clock might be getting corrupted if you are using a x1 CRO probe- try a x10 probe if you have the option.  The CRO probe/lead capacitance can load down the pins.

[michael_krell]

it looks like the DC bias is correct on all the pins that you said. What i still dont understand though is the analog and digital ground. I connect them together? and what is the PS cap? even if i connect teh analog and digital ground I dont get any change

[puretube]

PS is power supply, and the big cap is 100µF from +5V to AGND in the upper left corner of the schem;

the grounds are seperated except at that one point, to avoid clock signals "leaking" into the audio-path;

BTW: what are you putting in?

[michael_krell]

Also. should i be using a lower level signal?? to accomidate for the head room of the digital IC?

[michael_krell]

Im putting in a sine wave at about 1kHZ at 0dB. I dont understand how the location of the ground effects anything. if they are connected then thats it right? The analog ground at the PS cap is the same as the analog ground everywhere. Either way, im not getting any output at all.

[Rob Strand]

if they are connected then thats it right?

As far as working at all, yes (there are rare and extreme circumstances where this might not be the case).   Proper arangement of ground and bypass caps can prevent artefacts getting into the audio, it can also prevent oscillations.

If you have connected all the grounds I doubt your problem is grounding.

I guess the first step is to check there is clean audio on pin 15.  Basically up to that point the input audio is just filtered by the low pass filter.  If there is no audio check that part of the ckt around pins 15 and 16.  While you are there check there is something resembling the audio signal on pin 9 - check at 100Hz, 300, 1k, 3k.  

The next step would be to disconnect the 15k resistor to pin 12 and inject an audio signal into the (now) free end of that resistor *via a 1uF or so cap*.  That cracks off the low pass filter at the output, the added cap prevent the DC bias getting stuffed up.  You should see signal at the output terminal.  The signal should be a low pass filtered vertsion of the input.  Again if this stage isn't working check the parts around pins 13, 14 and the output.

In the normal configuration, maybe check what's on pin 12 - I suspect nothing.

The above checks really just give you some confidence that key parts of the circuit are working.   You could also rig-up external connections to the opamps on pins 9 through 12.   The the parts of the signal chain are working then that leave only the digital block.  Given you DC values are OK I have a bad feeling this is the case.

If the clock isn't working  the delayed digital signal won't get through at all and hence you will see no output on pins 12 and 14.   Other than the clock out pins there's not much you can check, and there's very little you can do other than to replace the chip.

[michael_krell]

IT WORKS!!!!! woohooo. you are the man Rob Strand thanks alot. this is so wicked. Im sure ill have more questions so ill keep you posted

[michael_krell]

I was wondering, is there any way to get a better frequency reponse out of this echo circuit? i know its good for guitar but i need to use it for a full range application. Is there any way to change some caps and gett a better frequency response.

if i dont get a response ill repost this.

[Rob Strand]

If you change the unreadable 5.6k at the output, on pin 14, to 3.3k it should be an improvement.    IMHO, the original filter would lack "sheen" on the highs and the mod should put things right for a wide-band response.

Now whether that's enough improvement is another matter but it should be noticeable.  To get more highs again replace the 5 filter caps with the next smaller value (or two values smaller if you want to push it).  Try the mod first.

[Rob Strand]

change the unreadable 5.6k at the output, on pin 14,

I actually suspect the intended value may have been 2.7k - that would give a reasonable filter.  The 3k3 value gives a sightly "better" filter.  The 2k7 will give a fraction more highs but it also puts peaks in the response, which is undesirable.  My recommendation would be to use 3k3 and if that doesn't work start reducing the caps.

[michael_krell]

i swapped that 2.7k with 3.7k and i think it sounds good, the problem is my +-15V supply is taken apart right now so when i get my opamp circuit up I will let you know howoume it sounds at a higher volume.

[Rob Strand]

i swapped that 2.7k with 3.7k and i think it sounds good .

I'm a little confused now.

What did you have in there before 2.7k or 5.6k?

If it was 5.6k I can understand you will hear and improvent in the highs.  But going from 2.7k to 3.7k will cut more highs - and that doesn't make sense to me.

[michael_krell]

as i said before, i need to resurrect my amplifier circuit so i can actually hear whats going on. Then i can make a better decision.

[john3696]

Hey...I am trying to build a similar...if not the same circuit from this page.....

http://www.geofex.com/PCB_layouts/Layouts/pt2399.pdf

I get a loud constand ticking when I turn up the repeats pot..(no guitar)..
I don't totally understand the entire circuit (new to the game) but
I checked the volts after my 78LO5 and I am at 7.5 volts getting to the
PT2399.  would that overload the chip and ruin it?  or should I be checking somthing else on the chip??

any info would be great...thanks
graham

[Dirk_Hendrik]

From the 7805 you should get 5 volts. 7.5 is 33% higher which can be too high. Better check why there is no 5 volts without the PT chip mounted.

[michael_krell]

i am actually having a similar problem with my voltage regulator. I am getting the same input voltage at the output voltage.  I have another post discussing that.