Swell machine

[Kipper4]

Ok so after a miserable failure with a recent try at a swell type circuit.
I got to thinking could I do better and maybe devise one myself.
Maybe a compressor/limiter type front end with a Very quick recovery time that would cut off the initial strum and allow the note/chord to swell and come through.
That's about as far as I've got with ideas at this stage as I'm away from the breadboard for a week or two on vacation.
I think maybe I'd have trouble with the first compression stage letting the initial attack through and then even more trouble getting a fast enough recovery to allow the sustain and decay to swell as I would like it to.
Even more so making the recovery variable for differant swell length and timing.
Has anyone tried anything like this.
I would rather the build be as compact as is practical. Using common diy pedal parts that one would normally carry in stock.
Comments, ideas and all critiques are welcome.
Rich

[Mark Hammer]

The PAiA Gator is actually pretty decent, with the primary downside being that it uses a CA3080.  If someone was so kind as to redraw with a 13600/700 that would make many happy (not including myself - I already have one and it works fine).

https://www.paia.com/talk/viewtopic.php?f=6&t=204

[PRR]

> PAiA Gator ... uses a CA3080. If someone was so kind as to redraw with a 13600/700

Doesn't look like a tricky hack. The control scheme is un-common but does not rely on the 0.6V/1.2V drop at the Iabc pin.

So for LM13?00 parts: Pick one OTA side and use it with appropriate pin-numbers. The other OTA, short Iabc to V- (shuts-off unused OTA). Short pins 10 and 7 to V- (shuts-off buffers).

[Kipper4]

Brilliant I'll give it a blast as soon as I'm back thanks guys.

[Kipper4]

I'm thinking of using an lm324 for the quad op amp because it's rail to rail. However the TL074 has better bandwidth and just might be ok.
Which did you use please Mark? Or if anyone else cares to chime in feel free.
Thanks
Rich

[Mark Hammer]

You won't need the bandwidth.  Remember that all the treble is at the start of the note anyway, and a swell circuit suppresses the initial attack, only letting the signal become audible after 90% of any treble has dwindled away.

So feel free to use whatever op-amp makes the circuit function, with minimal regard for bandwidth.

Incidentally, one of the characteristics that distinguishes "reverse-tape/delay" from typical swell circuits is that, if you take a sound sample and perfectly reverse it, the treble content increases as you move from the fade-out, backwards towards the pick attack.

Waaaayyyyyy back in the 70's, I used to mimic reverse tape by setting my Univox compressor for modest compression, feeding it to my MXR Envelope Filter set for slowest possible Attack time, and feeding that to my MXR 6-band EQ with the lower 3 bands set to min and the upper 3 bands set to max.  The compressor would make the Filter sweep even more languidly, and not far enough to produce a clear "wah".  Since the sweep starts out low and goes high, AND since the EQ was set to downplay the bass and crank the mids and highs, the first part of the sweep was largely inaudible, and proceeded to a point where the combination of the EQ boost (and the MXR unit could be used an an overdrive, producing distortion at the highest boost settings), and sweep towards that end of the spectrum, made the portion of the note well after the pick attack much louder and brighter.

I'm sure that if I were to listen to that now, it would pale in comparison to the reverse delay on my Echo Park delay, but in 1977 or so, our reaction was most definitely "Holy crap!  Does that ever sound like running tape backwards!"    Perhaps swell pedals ought to include some sort of clipping circuit that increases harmonic content in a systematic way as the signal level increases.

[Kipper4]

Nice one Mark.
I'll audition some quads on the breadboard when I get back meantime I have a 4.5hr flight home tomorrow so I should have plenty of time to redraw the schematic with an lm13700. Now I have downloaded the pinout of all the possible op amps and OTA I will need.
Maybe I can work on the distortin mod when I have the initial circuit working and figure out a way maybe a candidate for an ldr/led combo.
Cheers

[Kipper4]

Post deleted

[Kipper4]

If anyone would be so kind as to give my schematic and layout the once over please I'd appreciate a second pair of eyes.
Rich




https://imageshack.com/i/f0DnSQKHj

[Kipper4]

Thanks

[lars-musik]

Thank YOU! I would very much like to try another gator.

I build the Boss Slow Gear and had several attemps on the EHX Attack-Decay. I got both working in the end and both got a big disadvantage. The SG-1 is not swelly enough (attack to short) and the EHX is VERY picky about the incoming signal.

My Paia Gator attempts (2) were both not sensitive enough for my guitar pickups. All the threshold-related modfications for the Gator (being originally deigned for a synth) summarised here: http://www.diystompboxes.com/smfforum/index.php?topic=80080.msg661923#msg661923 didn't work for me.

So I am very eager to hear if yours will work with a guitar.

[duck_arse]

I'd appreciate a second pair of eyes, too, these ones I gots are crap.

you have a short under C9, across C8//R17. probably those 2 10M resistors could be much lower value, and a more available op-amp could replace the lm308 and it's 10M's. I think R6 should be to Vb? the trigger jack should be switched mono, instead of stereo, as you have no connection to the rectifier stage unless a plug is in and shorting.

probably the experts could suggest uses for those extra bits of 13700, hate to see them go to waste. can an ota and buffer do Vb?

[Kipper4]

Thanks DA well spotted.on the short. I will breadboard it in the next few days and audition some more oppys for the input buffer and try some 10Ks to bias it. And try R6 to Vb too.
I'm not sure either if it's possible to use the other OTA to create a Vb. Time to google it me thinks.
Thanks for the link Lars. Intresting stuff. I'll get back to you later with a progress report.
I hope it works. It will be intresting to see how it works as a gate too.

[Mark Hammer]

Thank YOU! I would very much like to try another gator.

I build the Boss Slow Gear and had several attemps on the EHX Attack-Decay. I got both working in the end and both got a big disadvantage. The SG-1 is not swelly enough (attack to short) and the EHX is VERY picky about the incoming signal.

My Paia Gator attempts (2) were both not sensitive enough for my guitar pickups. All the threshold-related modfications for the Gator (being originally deigned for a synth) summarised here: http://www.diystompboxes.com/smfforum/index.php?topic=80080.msg661923#msg661923 didn't work for me.

So I am very eager to hear if yours will work with a guitar.

Mine works just fine, without modification, with medium output single-coils.

[Kipper4]

Great to hear Mark.
I doubt the OTA would make a good platform for creating Vb because of the way it designed to control currant on the output rather than voltage.

[Kipper4]

Feeling the need to vent.
Aghhhhhhhhhh
Either i have a bad connection on the breadboard or I have drawn it all wrong.
I'll leave it until morning now. Still having my doubts about that OTA ground to the op amp output.

[anotherjim]

That could be it. The OTA is a current output and 10k of the next op-amp is probably loading it too much.
Configure the OTA for non-inverting and the output op-amp as a unity voltage follower and you should be good. Alternative is to use your unused OTA darlington pair as an emitter follower as per usual schemes with that chip.

[Kipper4]

Thanks Jim I'll give it a shot

[Kipper4]

I tried a couple more things on the breadboard last night but still nothing. I even tried with lm308 ca3080 and two tl072 still nothing must be me or the breadboard. I'll keep trying. Geez.

[samhay]

I'm confused - the schematics I am looking at (see link) have the envelope modulating the OTA's negative supply, which is biased at half supply. How is that supposed to change the gain of the OTA, or work without horrible clipping?

http://gaussmarkov.net/layouts/gator/gator-schem.png