An analog echo and no reverb tank?

[Jmariner]

I have not come across a fully analog echo scheme in my searches, but about 14 years ago, I did manage to get an echo only using an op-amp and a phase shift ladder in the feedback path. I was still fairly ignorant in electronics at the time, so it wasn't something I kept notes on let alone produced a schematic.
It was just a single echo that would repeat once for a full 1 second after each time I played. Doesn't seem like much but it was pretty shocking. The same day with that same experiment, I also attained a full octave pitch shift using jumper wires, a diode, resistors and capacitors.

[ElectricDruid]

If half of that is true, you should get yourself down to a patent lawyer immediately because it's pretty much the holy grail. Analog echo of 1 second without any expensive and noise-prone BBD? Gold. Analog *pitch-shifting* of an octave? Aside from flip-flops (hardly *analog*!) that doesn't happen. Also pure gold. Far from "doesn't seem like much", those are both absolutely massive claims.

Unfortunately I'm going to file this in the "schematics or it didn't happen" bucket. Sorry, but big claims need big proof!

[Rob Strand]

I agree with ElectricDruid, no way 1 sec with an analog circuit at audio frequencies.  I've done DSP experiments with all-pass filters and even small delays would be equivalent to an impractically high order analog all-pass filter.

[PRR]

I had some acid like that once. I was also playing with a tape delay. For an hour. On a 45 minute reel. The tape ran out, echo kept echoooooing. Then everything went down three semitones. Then my friends took me out for orange juice. Quite a trip.

[amptramp]

You could make an analog echo with a speaker driver like an LM386, a small speaker and a microphone if you have a 50 foot length of garden hose.  Feed the signal into one end, have the microphone on the other end and you have the equivalent of a bucket brigade available from any hardware store.  But a repeat of once every second?  That would take 1100 feet of hose.

[Jmariner]

It's definitely not hot air bologna, but I have no certain idea on how I did it due to lacking significant education at the time. I jumper wired in caps, resistors and diodes, however, I know the shottky was wired in series with the output of the op amp with caps and resistors to ground into the 2nd stage of the op amp. When I added another jumbo carbon, low value resistor to ground, I got an insane pitch shift. I knew enough to identify a phase shift oscillator that I thought were just low and/or high pass filters. I was plugged straight into a now "vintage" Crate GX1200H head and no other devices.

The gain was through the roof, I was filtering out the insane amount of noise, and my presumption then and now is the shottky in series clipped off enough of the signal after enough phase shit, low pass and gain so I had what was definitely a full octave shift through isolating the lower frequency content that is normally inaudible.

You guys said my exact thought when it happened and that in regards to both, I had an ultra basic circuit doing something exceptional with very few parts.
The Schottkys I had then are the same I have now and are:
BAT49, 1N5711 and 1N6263; the blue glass case STM

I tried to replicate it the next day, but failed and it was before the cell cam days or I would definitely have pictures. The echo, in my mind at the time, seemed useless due to a lack of understanding but I thought might still be useful. Today, I know both results with such a general and basic topology would be award winning in the world of DIY opinion.
This is the entire reason I posted the thread!
I thought someone or someone-s would have an existing circuit relative to what I did 

My apologies, but I still have that dual gain stage that was a fairly standard soft clipper I still use to this day. I know quite a bit now, and will get back to experimenting with a phase shift oscillator and series schottkys in the signal path.

[Jmariner]

Well, here's irony. I know I am wordy due to being a literary person, but I found this literally a minute after my post.
Shocktave

Relative to what I said I was doing. Clipping in series with some high shunting, low pass filters, I believe some phase shifting, and plenty of gain. As I've mentioned, post these experiments and general ignorance, I went to college for electronics/electrical engineering. Just a 2 year degree and after 15 months, I had a 3.95 GPA, but left with an incomplete for my final term doing 6 month terms through a tech college. This reference made because dammit, I will figure the pitch shift out if nothing else! 

What I do still definitively have and will share is a very crude synth that was developed the same way. Heaps of gain, lots of shottkys in series, and various filters. The result is a trumpet emulation, some bagpipe sounds, and even some violin sounds. This thing is 14-15 years old lol.

I need to create a schematic, redesign it a bit so it's not passive, and will post it in it's own thread within the next couple of weeks. I had to really max out gain coupled with 2 op-amp stages, so there was an LM386 in there, but this is due to it being in a passive architecture. I will produce something a bit better and less clumsy that won't likely have an LM386. I like that chip for mic preamps and other audio purposes, but now avoid using it for guitar entirely. I went to college with the intention of starting my own general audio company focusing on musician's gear and Hi-Fi home and car audio, but a series of tragedies derailed this goal until most recently. I have heaps of manufacturing equipment from a CNC router to a laser cutter/engraver to a 3-D printer and well beyond.

Today, I realize sharing some designs and inventions will have no significant impact with how that goes. Since school, I have invented a new type of ultra efficient motor and a mess of other wild machines. I'm still far more determined to prevail by starting in audio first, and some mechanical machines irrelevant to this site's purpose.

[Mark Hammer]

You could make an analog echo with a speaker driver like an LM386, a small speaker and a microphone if you have a 50 foot length of garden hose.  Feed the signal into one end, have the microphone on the other end and you have the equivalent of a bucket brigade available from any hardware store.  But a repeat of once every second?  That would take 1100 feet of hose.

As the Festrunk Brothers would say: "Hosed? Count me in!" (4:25)

[merlinb]

I have a girlfriend but she goes to another school, and I can't show you my sick karate moves because it's too dangerous

[Jmariner]

lol
It's just a notch filter and the switches reverse it so it guts the signal at around 1Khz, or passes 1khz with a tone control to smooth it out. The Schottkies are in series in the signal path so it clips it into a square, or a sawtooth with enough of them switched into the signal path by running it through massive amounts of gain before and after. I knew very little then, but will design it properly and post the schematic soon. I have no problems sharing this stuff, but certainly not my gfs in Canada! 
This is also where I achieved the full octave pitch shift probing pieces around in the active portion. I literally clicked the Analog Alchemy after that previous post, and there was Shocktave. Dare I say it, but the result I had was better, but we'll have to wait and see what I come up with this time.

Today, I am building a huge rolling garage for my Raptor 4-wheeler and have to sidetrack this stuff before the snow hits. 

[printer2]

How many phase reversals would be needed to create a 1 second delay?

[Mark Hammer]

Why does that somehow sound like a how-many-X-does-it-take-to-screw-in-a-lightbulb joke?

[Rob Strand]

How many phase reversals would be needed to create a 1 second delay?

Rough ball park,  5 pairs of stages = 3.5ms, so 700us per pair of stage, so 350us per stage.  1 second = 2900 stages.
https://www.diystompboxes.com/smfforum/index.php?topic=24061.msg1254222#msg1254222

Reducing the bandwidth of the delay you can use less stages for the same delay time.

[printer2]

How many phase reversals would be needed to create a 1 second delay?

Rough ball park,  5 pairs of stages = 3.5ms, so 700us per pair of stage, so 350us per stage.  1 second = 2900 stages.
https://www.diystompboxes.com/smfforum/index.php?topic=24061.msg1254222#msg1254222

Reducing the bandwidth of the delay you can use less stages for the same delay time.

So not really all that practical? Might be hard to fit in a pedal box?

[Matthew Sanford]

How many phase reversals would be needed to create a 1 second delay?

Reducing the bandwidth of the delay you can use less stages for the same delay time.

Rob, just to confirm my thoughts, this is because each stage is an LPF so trying with just 1 would only pass DC at best?

[Rob Strand]

Rob, just to confirm my thoughts, this is because each stage is an LPF so trying with just 1 would only pass DC at best?

There's quite a bit more too it.

The plots in my link to the the old thread are for all pass filters which have a flat frequency response.   What varies with frequency is the group delay - think of that as the analog filter equivalent of delay.   The plots show for low frequencies the analog circuits (the all-pass filters) act like a delay - the flat part of the curve.    The upper frequency in those examples is in the order of 400Hz to 800Hz.  Above that frequency the effective delay decreases significantly.

If we use the same number of filters but lower the upper frequency, by using larger caps in the filters, then amount of delay will increase, ie. the intercept on the delay axis will move upwards. 

For example if we lowered the upper frequency by a factor of 10 to 40Hz we would get 10 times the delay but only upto 40Hz.   If we want to get 10 times delay without losing the delay at high frequencies (400Hz) we would need 10 times the number of stages.

A real BBD also has an upper limit frequency limit which is set by the clock frequency.   If we drop the clock frequency we can get a longer delay but the bandwidth of the BBD is reduced, due to the lower aliasing frequency.  So the BBD case suffers the same delay vs bandwidth trade-off as the analog circuit.  (Also, for wide bandwidth and more delay we need more stages.)

[Matthew Sanford]

Ok, I think I understand better after reading more on group and phase delay, the wave envelope, and many other factors that come in to play. Very interesting was negative delay, making me wonder if it's envelope could be used to preemptively modulate filters?

[Jmariner]

How many phase reversals would be needed to create a 1 second delay?

Rough ball park,  5 pairs of stages = 3.5ms, so 700us per pair of stage, so 350us per stage.  1 second = 2900 stages.
https://www.diystompboxes.com/smfforum/index.php?topic=24061.msg1254222#msg1254222

Reducing the bandwidth of the delay you can use less stages for the same delay time.

lol! Holy cow.
I was just taking a guess based on the result I got without doing any research after the loose theory I tossed out there. This was 13 or 14 years ago before I went to college, but I was definitely getting a full second, maybe even a bit more, using nothing but a dual op amp with heaps of gain, some notch filters and then probing around with resistors, diodes and capacitors. That experiment also achieved a full octave shift at one point.

I'm still confident I can replicate the octave shift I achieved, but just in general, have a lot of work to put into circuit analysis in electronics as a whole.
This also definitely answers my question on delay, and tells me I need to build my first delay circuit.

[Rob Strand]

lol! Holy cow.

In fairness, in the context of a reverb where feedback is present you could use less stages to get something that "hangs on" for a long period without *that* many stages.  If you take a flanger with a fairly short delay and carefully adjust the regen/feedback level you will get a tail which is somewhat longer than the delay time itself.   There's a point where you have to adjust the feedback level so finely it becomes impractical and it will oscillate instead of decaying.

[R.G.]

I wonder if there was some sympathetic oscillation going on.