Boss DD schematic questions

kozielek97 · October 17, 2023, 12:00:30 PM

Hi,

Could someone please explain me how Boss Digital Delays work. I'd really like to understand it. I mean I'm rather analog guy so reading digital schematics is not my thing. Could someone for example drew me a block diagram or write what are functions of every ICs on the board.

I'm looking for a way to add modulation to Boss DD6. More info linked here:
https://www.diystompboxes.com/smfforum/index.php?action=profile;area=showposts;u=66100

And schematics for Boss DDs here:
https://www.synthxl.com/service-manual/boss/

Thanks

Digital Larry · October 19, 2023, 09:10:23 AM

IC2 - input buffering/anti-aliasing filter
IC3 - further signal processing/clipping prior to A/D stage (not 100% about the details)
IC6 - A/D convertor
IC7 - D/A convertor
IC10 - uC to process the pot voltages
IC8 - main uC
IC9 - static RAM
IC5/IC7 - voltage regulators
IC1 - output buffer

There are three pots just doing a voltage division from VR4 for the front panel settings. I am guessing that you could AC couple an LFO onto the delay time wiper to get some modulation without having to worry about DC levels. Notice use of the word "guess". Other than the op amps which are fairly straightforward I just looked up the part numbers.

Regarding "how does this work" - since it's all run by microcontrollers, it's a program. Does it do intersample interpolation when you change the delay time? Who knows. It might not if it was not designed for modulation. If not you might notice a graininess to modulated delays. You might be able to tell by moving the knob as well.

DL

kozielek97 · October 20, 2023, 05:22:25 PM

Thanks, so there's nothing left but risk it all and try LFO in my own DD6

One more question. Could you tell me if DD3 Gate arrey (MN51010RBA BOS-008) has the same function as DSP (TC25SC080AU-104) / CPU (Mask) (M37470M2-333SP) in DD5?
What is a difference beside technological development over the years.

Digital Larry · October 21, 2023, 02:14:13 PM

Quote from: kozielek97 on October 20, 2023, 05:22:25 PMThanks, so there's nothing left but risk it all and try LFO in my own DD6

One more question. Could you tell me if DD3 Gate arrey (MN51010RBA BOS-008) has the same function as DSP (TC25SC080AU-104) / CPU (Mask) (M37470M2-333SP) in DD5?
What is a difference beside technological development over the years.

a) I don't know - but probably
b) I don't know - but probably

A gate array is "programmable logic". Within its limitations of cell and i/o count you can get it to do almost anything. The programming can look like a logic schematic or software code or a combination of both.

A CPU on the other hand is a computer with standardized I/O and resources for which you write a program.

Within the context of the delay pedal they are certainly running the show.

The use of a specific chip is probably dictated by materials planning. Someone is always trying to cost reduce these things and/or deal with obsolescence.

Glad I could help!

r080 · October 25, 2023, 01:15:45 PM

I had been looking for a way to add modulation to my DD5, and will try to make some time to experiment with that think you linked on the DD3. As Larry mentioned, it is possible the sampling of the control voltage won't be fine enough to sound right, but certainly worth a try.

Compared to the DD3, it looks like the DD5 and beyond uses the same base voltage to create the control voltages from the feedback, time and mode pots. Injecting a voltage right on the wiper without separating the time pot out with its own base voltage might also affect those other control voltages. It would not be noticeable on feedback, but would be really annoying if it changed the mode control voltage enough. The DD3 mode control is handled a different way.

ElectricDruid · October 25, 2023, 03:14:03 PM

On both the DD5 and DD7 schematics, it's pretty clear that the pots are just feeding a voltage between 0V and V_something to the processor's ADC inputs. After that, it decides what to do with the value it's given.

You can test what the specific V_something is by checking the voltage across the pots. That's important.

After that, you could theoretically substitute *anything* that provides a voltage between 0V and the V_something voltage you just identified (looks like 3.3V at a guess?). You can add op-amp mixer stages to mix external control voltages appropriately scaled down and extra op-amp inverter stages to correct for the inversion caused by the mixer stage. If you use proper op-amp mixer stages, you won't get crosstalk into the other voltages, so you don't need to worry about it affecting the Mode CV. The only thing you *really* need to make sure about is that the processor pins (the wiper pin of your current pots) don't *ever* see more than the voltage at the top of the pots.

Within those limits you won't damage anything. You might not get the response you want, depending on how fast Boss are sampling those pot inputs, and how much smoothing they've applied in the digital domain. You can't control that, and you just have to live with it. You might well be able to add significant new possibilities, but you'll have to be careful.

r080 · October 25, 2023, 07:11:20 PM

I tried this out on my DD5. I injected the LFO from a tremolo pedal right onto the delay time wiper. It was just as glitchy as moving the knob back and forth, so definitely not viable on the DD5. I have not tried a DD6 enough to know whether that is likely to have the same problem.

potul · October 27, 2023, 02:01:13 AM

Quote from: r080 on October 25, 2023, 07:11:20 PMI tried this out on my DD5. I injected the LFO from a tremolo pedal right onto the delay time wiper. It was just as glitchy as moving the knob back and forth, so definitely not viable on the DD5. I have not tried a DD6 enough to know whether that is likely to have the same problem.

Well, that's basically what you are doing.... exactly the same effect as moving the pot up and down.

ElectricDruid · October 27, 2023, 05:13:17 AM

Quote from: r080 on October 25, 2023, 07:11:20 PMI tried this out on my DD5. I injected the LFO from a tremolo pedal right onto the delay time wiper. It was just as glitchy as moving the knob back and forth, so definitely not viable on the DD5. I have not tried a DD6 enough to know whether that is likely to have the same problem.

That's a pity, but not a huge surprise. Getting the glitches out of a digital delay when modulated is a bit of work, so it's no wonder Boss didn't bother for a delay that doesn't include modulation.

r080 · October 31, 2023, 04:31:02 PM

Quote from: potul on October 27, 2023, 02:01:13 AMWell, that's basically what you are doing.... exactly the same effect as moving the pot up and down.

I was still worth a shot. Mostly I was just curious if any make/break noise while turning the pot or inherent difference between using the pot vs controlling the voltage externally could mean it would be smoother with the LFO.

kozielek97 · November 05, 2023, 01:01:17 PM

I checked it and DD6 Delay pot opperates between 0-3v3 so connecting LFO from link wouldn't be the smartest idea. I'll try run it somehow on 3v3 or worn 9V battery but I'm wondering if TL072CP will run on such small voltage.

ElectricDruid · November 05, 2023, 02:17:42 PM

Quote from: kozielek97 on November 05, 2023, 01:01:17 PMI checked it and DD6 Delay pot opperates between 0-3v3 so connecting LFO from link wouldn't be the smartest idea. I'll try run it somehow on 3v3 or worn 9V battery but I'm wondering if TL072CP will run on such small voltage.

A better plan would be to run the LFO and TL072 on the full 9V, and then scale it down to 3.3V afterwards, before you feed ít to the DD6. It's roughly a third of the level, so it's not hard to work out. I agree that trying to run a typical op-amp LFO at 3.3V will be tricky. There are op-amps that would do it, but it's not the easiest way.

News:

Boss DD schematic questions