What's the longest analog delay that anyone has a schematic for?

[ZiggyZipgun]

Yes, I have used the search function on here, and it did turn up a lot of good info on cascading BBDs, filtering, etc, but I just figured I'd ask. 

I'd like to build one, but most of the delays I use really are between 333ms - 667ms, and the occasional 1000ms, but I'm aiming to eventually replace my PODxt Live with hand-built units of the few models on it that I use.

[earthtonesaudio]

You might want to look into PT2395-based delays.  It's digital, but probably will fill your requirements with less hassle than any analog delay I can think of.

[ZiggyZipgun]

I currently have a 2 second digital delay.  With what I'm going for, I expect plenty of hassle.  A friend of mine is very clever with digital controls, so we'd like to try a few different things, like several effects in one unit with a global tempo control, with a note-value switch for each effect.  It'll take some time, but that's okay.  I'm just looking for an analog delay with fairly low noise and some headroom (probably 18V, maybe more, batteries will not be included).

[Nitefly182]

Sounds like analog for the sake of analog. Once you get above 600ms or so analog delays are so degraded that they aren't even a reasonable resemblance of the original signal. The volume also drops considerably and the repeats are so dark that theyre almost not there when you're playing. If you want a good delay build something digital with great filtering. Building an analog delay with over 1 second of delay time isn't a worthwhile pursuit IMO.

[earthtonesaudio]

If you don't mind the hassle, by all means go for it.  You might be able to get the delay times you want at reasonable fidelity and noise levels if you're clever about a lot of things... layout, filtering of clock frequencies, cascading chips only on longer repeats, etc.

That global tap-tempo idea would be amazingly cool.

[Mark Hammer]

Well, you CAN get analog delays longer than 600msec.  The question is, once you factor in the production costs, footprint, trouble-shooting and setting up, etc., it ceases to be really worth the time and effort.  For the pricepoint you'd have to sell it at, digital can do a more than acceptable job.  Perhaps equally, if not more, important, once you get delays out past 600-800msec, the functions one uses a delay for change/expand, and the kinds of control features one needs to attempt those functions simply aren't available in the analog domain.

So, lots of reasons to want to whip up an analog delay that does a respectable 500-600ms, but not nearly as many to want to go beyond that.  You know, at a certain point, there IS no point in souping up your car to do things that a truck woud do just as well or better for less money.

[R.G.]

Some thoughts on the topic.

- The reason analog delays are sought after, I believe, is that the first digital delays were so very bad. Today we think of 16 bit 44kHz sampkling (i.e. CD specs) as a starting point for fidelity. The early digital delays, especially in pedals, were as low as 12 bit samples, as low as 20kHz. Each bit of digital sampling depth theoretically improves the signal-to-quantizing noise by 6db, so a 12 bit sampler is going to be at least 24db (that's over 20 times) worse in quantizing noise than a 16 bit sampler. And that's just theoretical. Reality would be even worse. At the time, analog bucket brigade chips looked in spite of their flaws because they at least had no bit-number quantization noise. They did have other problems though. But we're left with a legacy of people thinking digital delay = bad.

- as far as 18V headroom, no analog (or digital!) delay circuits I know of can delay an 18V pk-pk signal. Maybe the opamps around the delay chips can, but in general the audio will be divided down to match the dynamic range of the delay circuits. If necessary, it would then be amplified back up.

- in general, digital delays today can do better than 16 bit/44kHz. Don't know if these are in any effects though. If not, they soon will be. Your Pod XT is for example, 24 bit sampling. 

- by the way, 16bit/44khz was chosen because it lies just outside the nominal limits of human hearing to distinguish from perfect. Yes, there may be people who can hear better than that. But it's not common.

- global tempo control is an idea I first read about from Craig Anderton as "synchro-sonics"

[ZiggyZipgun]

Wow, I posted that before I left for work, and by my lunch break, all the top minds have presented their case (where's Aron's contribution?).  Nice work!

I never was an "analog for the sake of analog" kind of guy, which is why I've stuck withe POD for the past few years, but I like to kick out an idea like that and look stupid if I have to.  This is how I learn.  Moog's got a 1000ms delay out, and I've seen a few units out with 600ms, but I don't know how they sound, or what or how many BBDs they're using.  Just been curious is all.  How long is the delay in the older Memory Man units? (Memory Men?)

By the way, the global tap tempo thing is how my POD is setup, and I have each effect set at a certain note value and everything always blends together nicely.  We also want to try bus switching and routing, with insertable effects loops, rotary encoders, a few presets, etc, a monster basically.  It's been done I'm sure, but that stuff is all on my friend's end, not mine.  I just like effects.