can you piggyback pt2399 chips for longer delay?

[Quackzed]

i was curious about getting a longer delay time out of my pt2399 delay (modded fab echo)...
i used a 100k linear pot for a delay time controll... but anything past half and the signal gets noise added in and the repeats get kinda grainy...
or maybee theres another chip i could sub?

[Mark Hammer]

My guess is there is a) filtering on board for short delays but not suitable for longer delays, and b) no companding for noise reduction.  As such, cascading two of them is not likely to yield an improvement in noise, merely more of the same.

[Processaurus]

I tried that with a FAB echo, the 100K pot too .  50K was much better, to my ear.  I did try 1 Meg, but it started making funny LOUD squeals.  Anyway, the distortion/noise you hear when the PT2399 is trying to make a longer delay time than what its designed for is slew rate distortion, notice you hear it first on loud high notes.  Its different than noise you get from underclocked analog delays or digital echos that use the conventional digital method (I forget what its called).  If your interested, look up the chip # here along with "sigma delta" and you'll find some discussion on how it works, and why the high frequency stuff shows its weakness, and also why its a nice sounding chip for delay. 

If you want more delay time, I think it would work out fine to cascade two of the PT chips.  I'd leave the FAB echo alone, though, the tiny board, funky pots, and unaccomodating enclosure would make extensive modification a thankless task.  The simplest way for the DIY guy to experiment with cascading the PT chips would be to start over and make a Rebote Delay from tonepad (which the Danelectro is very similar to) and to some trace cutting and re-routing to stick another PT chip right in series with the first one, and use a dual gang 50K pot to control the delay time on each of them.  It would still get gross at the extreme end of the pots travel, but you'd have twice as long of a delay. 

For an easy, fully put together, debugged project you could just make, look at the Hazelwanter/Schwartz  SHecho, with 880ms of delay
http://generalguitargadgets.com/index.php?option=content&task=view&id=219&Itemid=244
It uses a Holtek HT8955A chip for delay, and the compansion and filtering like old analog delays used.

I'm keeping my FAB echo board to stick inside another future pedal, when it would be nice to add a delay section to another effect, without using a huge box, or having to assemble anything.  Should be easy because the board with the effect (the big board with the jacks just does the switching and power filtering) is so small...  I'm thinking about keeping the box and the switching board to use to quickly house a different simple DIY effect, maybe.  I did figure out the new delay pot (if its a 16mm alpha type) can probably go in the top of the fab echo, under the "B" in FAB, because the PCB is clear of components in that area.  Kind of a ridiculous project when you can get a (PT2399 based) PB&J delay for like $5 more, with a real delay time control...

[Quackzed]

True It is a bit like polishing a turd... i put my little pot in the middle slot(unused) inbetween the mix and repeat pots..had to move 2 caps to the other side of the board and drill etc... great cheap little delay now tho... just figured i'd see if there was a quick and dirty way of eeking out a little more delay without the noise / signal degredation... 50k linear would probably be right on for longest delay without issues... and for 12$ and 30 minuites of CAREFULL soldering / trace cutting etc... a super little pedal
thanks for the input and info guys!  always glad to be saved from a dead end idea. i'd probably have killed the little surface mount board if i just went ahead and tried messing with it too much...
besides, i realized i never really use that much long delay anyhow, i mean - it aint a sampler right?
Thanks again... back to where the streets have no name and cathedral...