Schematic for Digitech PDS-8000 wanted...Maneco maybe?

[Gripp]

Hi all!
Just bought a Digitech PDS-8000 and although it sounds fantastic I would  like to try to increase the feedback of the delay. Internet rumour has it that one of the trimmers fine tunes feedback. Problem is that there are lots of trimmers in there and one is said to adjust the clock frequency and I really don't want to touch that one! It is perfectly set so that the pitch/delay shift is 2 octaves on the main knob.
It would also be interesting trying to learn something about the inner workings of a digital delay. ..Maybe one day mod it for even more warp options :twisted:
Cheers!
/Pelle G

[ExpAnonColin]

Just  be fearless and mark them first, if it doesnt do what you want it to, say forget it and put it back to the original position.

-Colin

[ian87]

+1 to what colin said. modding those things for absurdly long delay times is super, super easy. just mark & tweak!

[Kilby]

Try this 20 seconds googling brought this to light and it looks like fun


http://www.loopers-delight.com/LDarchive/200105/msg00274.html

[Gripp]

Yeah, you're right guys, I should probably do this the no fear way. But they are single turn trimmers and even with markings it could be hard to get back to the exact same setting. I tweaked the bias setting of my Ibanez Phaser PT-909 this way (with markings) and it just doesn't sound exactly the same when trying to restore the original setting. Or maybe that's only in my mind...

Yes, I have seen that lopper's delight post (I visit there now and then) and that's where the inspiration came from.
It would still be nice to see the schematics to get a better understanding of how this beautiful thing works! ....and to know for sure what trimpot does what or to know the calibration procedure, I have axcess to a scope.
Best!
/Pelle G

[ExpAnonColin]

Use a fat sharpie and line it up on either side, instead of trying to do it with a skinny one.

-Colin

[Pedal love]

Trimmers are variable resistors. If you have a DMM, measure the resistance on each side of trimmer. You can be more exact, that way.

[bwanasonic]

I have opened the hood on mine a few times ( Try replacing the two TL062s with Bur-Brown OPA2604 chips ) , but since I use mine almost exclusively as a looper, I've had no real desire to muck with the trimpots. Mainly because I share your trepidation about being able to restore it's original state. Maybe if I had a scope (and knew how to use it) I would be more confident in calibrating it. I know the user manual is around in electronic form, but I don't remember it being too useful or detailed.

Kerry M

[Gripp]

Thanks for all the tips!
The opamp change is definetively something to look into. I'll mainly use mine as a looper also but more of a warper/textural looper, and I thought some self oscillation could fit in there :wink:
I even got the original papers from the guy I bought it from and the manual isn't giving any such details (also availible at
http://www.loopers-delight.com/tools/digitechPDS/digi_pds.html).
But I still would like to see what's going on in there and try to understand how it works.
Best!
/Pelle G

[NaBo]

Trimmers are variable resistors. If you have a DMM, measure the resistance on each side of trimmer. You can be more exact, that way.

err, not always... just most of the time in our uses, cuz they let us get the precise set-and-forget resistance needed in effects like choruses, flangers, phasers etc... trimmers are small just small big-pots, hence the 3 lugs.  in other words, variable resistors OR voltage dividers :wink:

[bwanasonic]

and I thought some self oscillation could fit in there

One thing to keep in mind is the regen knob also controls the overdub function. I'm not sure if you can set it up to both self-oscilate AND overdub. I use an analog delay with my PDS 8000. I set my analog delay to self-oscillate and then loop that with the 8000. I'm thinking of getting another looper, so I can loop my loops!  

Kerry M

[Gripp]

I'm thinking of getting another looper, so I can loop my loops!  

Me too! I've got a laptop runnning with the Gibson/Oberheim echoplex style program Moebius (freeware vst/standalone plug at http://www.zonemobius.com/) and a firewire soundcard for more rytmical looping. So far this setup is not stable enough for stage use so I might have to get a real Gibson digital echoplex too...
The only thing I'm really missing from the PDS8000 is a reverse function. It is a pedal with personality, loops leaking through when in bypass, the memory management when changing modes is really wierd but definitively a feature!
Cheers!
/Pelle G

[ESPguitar]

Another supercomputer? :lol:

[bwanasonic]

It is a pedal with personality, loops leaking through when in bypass

I just checked mine for this, and couldn't detect any leak-thru even with my amp cranked. I use the 8000 in the loop of my amp, and seem to get the best s/n with the output knob at between 10-11 o'clock.

Kerry M

[Basstyra]

Bump...

Yeah, I know, this thread is old. But my question is taht simple, I need this schematic... 

The fact is, my PDS8000 isn't working exactly well. All seems ok, except that the sound is kinda crappy. Lots of distortion, increasing with the repeats, and this goes with some annoying noises.

I tried to figure out what the trimpots do.One is related to feedback pot, one seems to control a bias, one seems to be related to the Time pot. The last one, I don't know.

I can't really figure out where I have to look with my scope to see if the signal is ok. There are lots of NAND gates and things like that. Nothing as clear as a BBD device. So if anyone has the schematic, it really would help...

[Gripp]

I actually got a schem but the resolution is really crappy. My PDS isn't totally happy either.
Maybe time for a recap job or something. The voltages or the trimmers themselves seem to drift... 
Sometimes they drift into the exact same sound you're describing.

You're right about the trimmers function though. I think there are two trimmers adjusting the clock, one more of a range trim and the other more of a base freq trim.

I emailed digitech once, asking for a calibrating procedure but got no reply. Maybe it's time to email them again, perhaps it helps if we both do. I got a scope too so that's no problem.

I'll mail you the schem if I get an address.
Best!
Pelle G

[Basstyra]

Thanks Gripp, your schematic, though crappy indeed, is really helpful.

So, one trim is the classical feedback trim. 2 trims are in the circuit of the LFO, with the Speed pot (this makes not less than 3 pots in this circuit). The last is a bias, around the NE570 compander.

The schematic is amazing. I didn't catch yet how exactly it works, but as far as I understood the thing, it used the same "clock controlled" trick than the BBD devices : the clock of the sequential logic devices is controlled by the Speed pot, slow clock allowing more delay time.

It's a great schematic to work on... 

[Gripp]

Good that you found it useful!

I didn't catch yet how exactly it works, but as far as I understood the thing, it used the same "clock controlled" trick than the BBD devices : the clock of the sequential logic devices is controlled by the Speed pot, slow clock allowing more delay time.

It's a great schematic to work on... 

Yes exactly! Primitive with a really cool sound (when it works ok...). I only wish I understood how the trigger mode is done.
I have in some setting been able to have it delay in time with trigger pulses and at the same time had the speed of the delay dictated by the clock. This in normal delay mode so new loops could be done easily. It's just that I can't repeat it.
It involved flipping the switches, inserting jack in some special order or something but it's not supposed to be able to do that. It was really great since you could have a rhythm made up by the sync and vary pitch by delay time. It's big brother Time Machine 7.6 does that and I think this feature might be lurking somewhere in here too. I just don't understand logic to this degree to make sense of it.

I find the bias trim and feedback trimmers touchy too. Easy to get to few repeats and easy to get into the really noisy distorted area.
Same with my drift problem or whatever it is. I really like to know where double delay time is for accurate octave up/down pitching of loops. Now I have to tune it right before every gig.

Hope we find a calibration procedure so we could know what the specs for a fresh PDS are.

[Basstyra]

I spend some times on the schematic. It's... old...    (notice how "old" is just one letter away from "odd"...)

First, the sound is converted on 8 bits... that's pretty lo-fi.

The conversion is done "in the feedback loop of a LM311"... That's a strange fact. I assume it's a question of stability or something.

The signal comes to the + input of the LM311, the output is converted (throught MC14559), then the 8 // bits are converted back (throught LA10-502) and connected to - input of the LM311... The effective digital signal comes out in serial communication, and goes into a "41 1024" chip, which logically should be the memory chip. It then goes out, is converted back (throught LA10-502), and so on, classical delay architecture.

The whole logical architecture, with flp-flops, and, nand, nor.. gates, and more, are a huge control of the 41 1024. There are 10 control inputs, 2^10 = 1024, hence the name of the chip.

I assume my problem is a NE570-or-around problem. It seems my delayed sound is over-compressed : the attack is way too violent. I'll try to bypass it.

I made a more practical schematic, with names rewritten, and some enhancement like this. If someone is interested, I can post it.

[Maneco]

I have a working pds8000,i found my way on its calibration,but the schematics i have are horrible...could not find time to re-draw it...maybe yours is better...basically you have to inject a sine wave and trace it with a scope at the output of the compander,ne570...if that's faulty,you can subs it with the sa571,no problem...smallbear has those...the hardest part to find is the 4559...bgmicro.com used to have some NOS at $1 ...everything else is easy,the ram used to be available from jameco...
Ask and i will try to help

I must go...PRISON BREAK is about to begin in FOX