VIntage-style delay

[Mick Bailey]

I usually find a little project for Christmas to keep me occupied and this year I put together a vintage-style delay unit. My wife spotted the enclosure in a box of junk and encouraged me to buy it for the look so I gave £2 for what turned out to be a three channel passive mixer that was very crudely made. I thought it may make an amp-top delay unit to sit with my Reverberocket. The control positions were determined by what was already there and I put together a basic foot switch cut from the side of a PC enclosure. The aim was to build it entirely from parts and materials I already had lying around.

The internal circuit is a PT2399 described here, but with an opamp filter and some changes to the mixer stage as well as an LED limiter

https://circuitsalad.com/2012/09/04/...delay-circuit/

It works superbly. Does tails, very little noise on the repeats and will do infinite repeats without going out of control (but will do this as well if needed).

[Enzo]

Wow, that has the look of stuff I built in the 1960s. Cool.

[Leo_Gnardo]

Sounds like a winner, and like Enzo I'm diggin' the retro-primitive look. Even the dirt on the knobs - yusss! Way kool!

[Enzo]

Oh, the Dymo Labels really sell it for me. I remember when that stuff came out when I was a kid. You couldn't keep the Dymo Labels off of stuff.

https://en.wikipedia.org/wiki/Embossing_tape

[Justin Thomas]

I remember getting the"gun" type. I'd run around the house playing "phaser" with it, spitting out random labels & also "THIS IS MINE" on all our food. Good times. At least I thought so. Mom hated it.

The real kicker is seeing them on amps that now command $30k...

Justin

[Mick Bailey]

My Dymo labeller is a Dymo-Mite original and I also have one of the gun types. I'm looking for another Dymo-Mite with a metal wheel (or just the wheel) as mine is plastic and won't embosss metal tapes. I don't think there are many of these in the UK but they crop up regularly on USA Ebay. I have a lot of late 70s/early 80s tape that is still good.

I also like to pair up Dymo with some 70s self-adhesive heavy duty wood-grain vinyl for a retro look.

[Steve Blackdog]

I had a dymo. God only knows what happened to it! Love the retro vibe of the delay!

What is the longest delay on that one?

I had been thinking of buying an old reel to reel and making a tape echo, but it will be one of those “never got round to it” jobs.

[pdf64]

Nice job, very cool; but with a post pandemic mindset, I'd have given everything a good clean, vintage gunk patina not withstanding
It's a bit confusing how the link refers to the schematic as an analog delay.
I needed to see the chip info to get my head around the on-chip opamps http://www.princeton.com.tw/Portals/...t/PT2399_1.pdf

[Mick Bailey]

It's a pity the PT2399 never got improved or developed (as far as I'm aware) because it's a neat little IC and low-cost. The real issue is noise at longer delay times, which worsens with the number of repeats. Some noise adds tape-like quality and I have another design that modulates the delay time very slightly for tape warble. I wrote a piece on fake chips a while back and these were giving the genuine items a bad name with even more noise even with no signal being passed. I've also been supplied with fakes by reputable suppliers. The chip really needs it's own sharp cutoff onboard filter and more memory but it now seems to have been abandoned.

i take your point about the grime - my wife thinks the same way that it should be cleaned up. I guess I'm outnumbered.....

[Mark Hammer]

One of the things I like to do with both analog delays and PT2399-based delays is add just a little bit of lowpass filtering to the repeats/feedback loop. And when I say "a little bit", I mean one pole of LPF. Typically, there will be a mixing resistor that combines the feedback with the incoming audio at a mixing stage, before the delay. I will split that resistance into two common values. So if it's a 22k resistor, I'll split it into 12k and 10k, in series. I then do some quick math and run a cap from the junction of the two series resistors to ground. The cap value is calculated to yield a rolloff starting somewhere in the 800-1000hz zone.

The use of one pole is crucial. It means that there will still be upper mids and highs remaining to trim off on the next repeats. The delay sound gets progressively duller with each successive repeat.

This has 4 advantages:
1) Whether a BBD or PT2399, sound quality does get worse with each additional repeat, and the progressive filtering removes a lot of the accumulating audio grime.
2) In the real world, later reflections lose much of their high-frequency energy due to imperfectly reflective surfaces, so this progressive treble-trimming actually makes the delays sound a little more realistic.
3) When the repeats and mix level are turned up, the sound can get really cluttered really quickly, especially at medium-to-long delays. Trimming back the treble on subsequent repeats moves the delay to the background perceptually.. It's a bit like the way when Nintendo 64 implemented differential focus on foreground vs background information, that made it easier to concentrate on your character and ignore the irrelevant stuff.
4) You can crank the repeats up ALL the way without getting runaway feedback.

All of this can be easily defeated by using a SPST toggle to lift/connect the added cap to ground.