Reverb - look What’s in this mini pedal...

[soggybag]

I got on this kick to make a mini pedal board. On of the pedals is a Mosky "spring" reverb. Of course I have to open it up and see what's on the inside. I wasn't sure what to expect or if I'm surprised.








Looks three PT2399! Not quite a Belton Brick but that wouldn't fit in here.

[vigilante397]

I mean three PT2399 is basically a Belton brick Nice tidy layout there too, very aesthetically pleasing

[Rob Strand]

I wonder how they did the feedback.   Individual loops around each section or multiple feedback loops.   There were some carefully tweaked DSP reverbs with simple structures that sounded pretty good.

[merlinb]

blimey I wasn't expecting a pedal like that to be analog!

(Before anyone complains, PT2399 is just as analog as a BBD, just  using different architectures)

[11-90-an]

We need a *finally* accurate trace! 

Please... 

[anotherjim]

I can't make them out in the pic -  can anyone read the values on those pin6 timing resistors?
Are there any other chips in there?
The Belton has an LFO for shimmer to one of the delays. Anything like that in there?

[niektb]

I 'think' (but might be wrong) that they have the following markings:
R1 = 284
R3 = 503

I can't figure out R2

[11-90-an]

Hmm.. @niektb my eyes saw differnebtly...
I think niektb has more reliably values than what i see...

The resistor for pin 6 of the pt2399 in the top of the picture says "508"
The resistor for pin 6 of the IC in the bottom of the picture more or less is "_82" (can't read the first number...

@soggybag, if you still have some pics...

[anotherjim]

Bear in mind that the datasheet usable range for the p6 resistor is up to 27k (273), and at 27k, it's getting on for 350ms - far too long for reverb. I was seeing those big values too, which is why I don't believe my eyes!
502 I can believe but not 503.

[Rob Strand]

https://www.deeptronic.com/electronic-circuit-design/diy-reverb-pedal-circuit-from-spring-to-room-like-reverb-using-multiple-pt2399-ic-chips/

[Mark Hammer]

Bear in mind that the datasheet usable range for the p6 resistor is up to 27k (273), and at 27k, it's getting on for 350ms - far too long for reverb. I was seeing those big values too, which is why I don't believe my eyes!
502 I can believe but not 503.

I may be blowing smoke out of my hindquarters, but the attempt to go beyond 350ms is largely constrained by what sort of bandwidth one is aiming for.  Where obliging an analog sample to linger too long in those puny storage caps in a bucket-brigade device is simple asking for the signal to simply bleed away, once you move into the digital domain and the signal is encoded, you're not fighting against the signal bleeding away; you're grappling solely with how a much slower movement of the signal from memory location to memory location would result in aliasing/stair-stepping and potentially audible clock noise.  If one was aiming to be able to hear something that sounded "just like" the input signal, and could be made just as loud, that would clearly spell trouble.  But in this application, as an approach to replicating the seriously muffled and bandwidth-limited timbre of much later reflections (and heard at a much lower amplitude), the sort of lowpass filtering one could apply to that latter chip is not any sort of constraint on the usability of it.

At least from my vantage point.  Stand in the middle of any parking garage, yell, and listen to what you hear a few moments later, and what you hear will seem quite replicable via a seriously underclocked PT2399 with the right sort of filtering.

[knutolai]

Looks like a copy of the Malekko mini reverb pedal. I actually think they have two PT2399 based reverbs. The pink mini and the spring chicken. 

[soggybag]

I wouldn't be surprised Mosky also offers a mini OCD, Klon, and Deep Blue delay. Quick check of their web site, and they say:

"The Spring Reverb is budget guitar effects pedal manufacturer Mosky Audio's affordable version of the Malekko Omicron Spring Reverb, the first spring reverb mini pedal to hit the market. You get low-noise spring reverb with a near-bottomless depth thanks to a unique dwell circuit. You can control the reverb rate via the Dwell knob and the dry/wet signal balance via the Mix knob. Perhaps best of all, the Spring Reverb is less than a quarter of the price of a Malekko."

Ouch, I feel guilty for buying this. Its one thing to sell a clone, I feel the step of also advertising it as a clone and saying your' re selling it at less than a quarter the price and naming the company is a little too far.

[PRR]

> PT2399 is just as analog as a BBD

Disagree.

[vigilante397]

> PT2399 is just as analog as a BBD

Disagree.

Sorry Merlin, I'm with Paul on this one. If it has an ADC, RAM, and a DAC I have trouble calling it analog.

[jonny.reckless]

> PT2399 is just as analog as a BBD
Disagree.

Sorry Merlin, I'm with Paul on this one. If it has an ADC, RAM, and a DAC I have trouble calling it analog.

Both are discrete time, only one is discrete signal level.

[Rob Strand]

The ADC is a delta modulator, stores one bit at a time,
https://en.wikipedia.org/wiki/Delta_modulation

The integrator keeps track of the average level and you pump the integrator up/down to track the signal.

[ElectricDruid]

> PT2399 is just as analog as a BBD

Disagree.

Sorry Merlin, I'm with Paul on this one. If it has an ADC, RAM, and a DAC I have trouble calling it analog.

Another disagree from me, I'm afraid. A BBD is not terribly analog, and a PT2399 is even less so. To describe the pedal as "analog" is just too much of a stretch.

Are 3 x PT2399 cheaper than 1 x FV-1? It seems like an odd design choice.

[PRR]

> A BBD is not terribly analog

For amplitude, BBD is analog as hell. Hiss, warp, clip.

In time it is discrete but well below Nyquist that's no big deal.

[Rob Strand]

The PT2399 does have some characteristics similar to analog that straight digital systems don't have:
- the sampling frequency changes according to the modulation clock
- the effective delay when a sample exits corresponds to the average of the clock over the whole delay
- since the sample frequency is changing the sinc function hf roll-off is modulating with the clock

The characteristics follow from variable clock frequency.   For a fixed delay like a reverb the only thing you will notice is the sinc function hf roll-off.

Digital systems have a fixed sample clocks, although there's a number of schemes on how to do the sub-sample delay times for modulated delays like chorus and flangers.