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De-smarting the Marshall Uxbridge

292 points by fanf2 1 week ago | 93 comments

mysteria 1 week ago

If you're going through all the effort to design a PCB have you thought about driving the I2S input digitally? I skimmed through the AD85050 datasheet and it has internal DSP functionality which would have been already tuned for the drivers and box by Marshall. The reason powered boxes sound decent despite their relatively cheap hardware is because of the extensive processing they have in the background to compensate for any hardware defiencies.

As the AD85050 has a stereo I2S input there's a possibility for the actual crossover to be either done on the amp chip itself (with the same signal driving both channels) or done on the Amlogic SOC. The latter would be ugly as you would need another DSP chip on your board to do the crossover functionality, or perhaps you could program the AD85050 via I2C to add the appropiate low and high pass filters.

A two channel A/D converter would work on the front end, as you could drive both channels with a single analog input to get a stereo I2S out with duplicate channels to drive the amp. A USB input would be much messier if you want true stereo using two speakers unless you plan on doing routing on the software side. With SPDIF you probably could get away with splitting the signal and using a SPDIF to I2S converter chip in each speaker, but you would still need some way to separate out the left and right channels. The AD85050 has mixing functionality via I2C which may help with that.

And of course, all this might be more work than desigining an amp in the first place, and it really depends if you want to explore the analog or digital side of things.

f1shy 1 week ago

> The reason powered boxes sound decent despite their relatively cheap hardware is because of the extensive processing they have in the background to compensate for any hardware defiencies.

I will not argue that that could be one ingredient, but a couple of months ago I did a toy for my kids, I bought decent speakers, placed them in a cheap plastic box, and was absolutely amazed bybthe sound quality. The amplifier is a sub 1 dollar class D bought in a Raspberry Pi shop. No processing at all. If the box is sturdy and sealed, and the speaker is good, is incredible what you can do.

mysteria 1 week ago

Most cheap amp ICs perform well when they're outputting less than a watt, with distortion barely audible. Try connecting the same amp board to your main HiFi system if you have one and do some listening tests against the original HiFi amp. Then turn it up and it's a completely different story.

As always the speakers are the crucial part and having decent speakers will make a big difference. What a DSP can do is correct bad speakers to some degree. A typical cheap computer speaker has a muddy midrange, can't reproduce past 13 kHz or so, and has little bass due to the small driver. With DSP the manufacturer would typically low pass the amp input, smooth out the nonlinear frequency response, lift the bass a bit, and apply compression and limiting to increase perceived volume and protect the system. The results are still constrained by physics but the manufacturer is in this case able to save money on the drivers and box while getting similar sound quality.

f1shy 1 week ago

Yes, of course is not hifi. Not in any dreams, but for the price, being 2 orders of magnitude less money, impressive. Also in comparison with old little radios, much much much better.

acchow 1 week ago

I'm interested in which speaker and amp those were. Also, the plastic box :)

bayindirh 1 week ago

Not the OP, but if you have a little budget, HifiBerry's AMP2 [0] sounds great. After my dad gave his Hi-Fi stack to me (due to having no space at home), I built a small system with this and connected to a set of passive 2.1 Kenwood Hi-Fi speakers for him. They sound amazing, plus HiFiBerry OS is superb for connectivity.

I just want to note that software is built with collaboration of Bang & Olufsen. Both hardware and software oozes quality.

[0]: https://www.hifiberry.com/shop/boards/dealing-with-blocked-p...

Ringz 1 week ago

The hifiberry documentation is a mess. Let’s say you want to get rid of your Sonos system and start at zero with a Pi (it’s not my first one)… which features could be replaced by hb? What hardware should I buy? Which licenses?

bayindirh 1 week ago

I don't have a Sonos system, but I'll try my best to run it down for you.

Platform has two starting points: Raspberry Pi + AMPs (or DACs) or Beocrate [0]

If you go with the former, you need a Raspberry Pi 4 or 5 (even 2GB models are OK), HiFiberry board of your choice, a case (available from HifBerry), and a PSU in 19-24V range.

My setup is as follows:

    - Kenwood 2.1 passive Hi-Fi speakers.
    - HifBerry AMP2
    - Raspberry Pi 4 / 2GB
    - Steel case for Raspberry Pi + Board
    - 20V Meanwell power supply with a barrel jack.
If you prefer to use your own amp or powered speakers, there are DACs which you can directly connect to line level inputs. They support the same OS, and some are even support XLR outputs or multichannel I/O for production/studio needs.

If you want go all in, you can add a DSP into the mix which allows parametric eqaualization, and room compensation with optional USB Mic (similar to how B&O speakers measure room to self-optimize). Also you can design your own DSP chains and upload to the DSP.

Regardless of the OS you run (HifBerry OS or HifiBerry OS64 (which is beta)), you get the following services out of the box:

    - Roon
    - AirPlay
    - Spotify Deamon
    - Spotify Connect
    - RadioBrowser & TuneIn support
    - Squeezelite for Logitech/Squeezebox
    - Music (for local files)
    - Bluetooth
Spotify daemons require a premium (Spotify) subscription and Roon needs a license/subscription.

There are also extensions, but I don't use any of them and don't know what's available.

I use the system mostly with MPD to play music from my and dad's personal collections. MPD can also connect to a Samba server.

If you have any other questions, I will try my best to answer. Hope this helps.

[0]: https://www.hifiberry.com/beocreate/

Ringz 6 days ago

This helps a lot! Thank you very much!

Blackthorn 1 week ago

It's been shown that, at least for guitar speakers, the box they're in doesn't matter at all. The entirety of the sound quality or lack thereof is in speaker itself. Of course that is only one speaker , no crossover to worry about.

mrob 1 week ago

Jim Lill has a video on Youtube testing exactly that. It demonstrates conclusively that cabinet design for guitar speakers makes a difference:

https://www.youtube.com/watch?v=-eeC1XyZxYs

This is hardly surprising; cabinet design matters for every kind of loudspeaker. Note also that electric guitars can produce a wide range of frequencies, especially once you add distortion. Distortion generates additional tones both higher and lower in frequency than those already present.

Blackthorn 1 week ago

Oh man, I've got some egg on my face for this one. I actually have a guitar cabinet that has a special geometry that disperses the sound in an area instead of directionally like guitar speakers normally do, which I bought explicitly for that purpose! Despite this, I still said what I had said, a couple posts up. How embarrassing.

jdietrich 1 week ago

That's entirely untrue, particularly at lower frequencies. This isn't audiophile cork-sniffing - the behaviour of a loudspeaker can be radically altered by the design of the enclosure. Entire textbooks have been written on the topic.

https://www.amazon.com/Introduction-Loudspeaker-Design-John-...

Blackthorn 1 week ago

Guitar speakers, famously known for their low range.

TylerE 1 week ago

Open low E is 82hz. That’s pretty low.

bayindirh 1 week ago

Marshall speakers, from my experience, has a brand sound signature, and that tuning is not very optimal for every genre of music.

Replacing the DSP with a simpler amplifier may allow to get more detailed sound from the drivers and the box themselves and may create a more pleasant listening experience.

From what I have seen, the drivers seem pretty full-size for that box, and any disturbing sound characteristic can be tuned with a simple equalizer. A more dynamic approach might create audibly weird sound profile if done wrong.

Modern DSPs are magic, but I still prefer an audio pipeline where things show their deficiencies and not hide things real-time.

zxcvgm 1 week ago

I have the same thoughts about the approach, and I'm actually working (on the back burner) a similar thing. It's a harman kardon "smart" speaker with a similar design where the brains are on a separate daughterboard and that's now fried.

I've already figured out the control signals and have designed a new daugterboard with an ESP32 to drive the I2S output. I just need to figure out how to downmix the audio to mono and to DSP the L/R channels into tweeter/bass outputs, or to find some code already out there that does this. Any help/pointers here would be appreciated!

flyinghamster 1 week ago

One thing you might find helpful is to prototype things with GNU Radio and a GRC flowgraph. I'm not sure that would be useful for running on the ESP32, but you could at least tinker around with signal processing tactics that you could implement on it.

AstroNoise58 1 week ago

I assume you mean AD85050 (rather than AD8255). And yes, the last paragraph before "Going all-in" is about the idea of driving the I2S. But the I2C config sent to the ESMT chip would have had to be reverse-engineered as well...

mysteria 1 week ago

Fixed, thanks. Somehow the title of the datasheet pdf is AD8255 despite the chip being an AD85050.

gavinuhran 1 week ago

I have this speaker and cannot believe how annoying the smart features are. I'll be talking on the phone in my apartment and the speaker will think I'm trying to prompt it.

"SORRY. YOUR DEVICE IS NOT CONNECTED TO THE INTERNET. PLEASE CHECK YOUR BLUETOOTH SETTINGS AND TRY AGAIN." (at max volume!)

It's unbelievable. I'm not an EE, but would love to know how I can disable these incredible unsmart features.

seba_dos1 1 week ago

There's an article that tells you that. I believe it's linked somewhere above this comment.

bonzini 1 week ago

The article removes all the smart features (not just the annoying ones) and requires pretty serious knowledge of analog electronics. Probably it doesn't fit the bill for the parent comment.

seba_dos1 1 week ago

> and requires pretty serious knowledge of analog electronics

If you want to understand the whole thing in depth, then yes, I guess so. However, at the end it just links to the already made project published at MIT license that you can simply replicate with barely any knowledge. It's an equivalent of self-compiling a software project after checking out its repo, which sure, may seem overwhelming if you never did that before, but ultimately it boils down to some reading comprehension and step following exercise.

sbierwagen 1 week ago

>It's an equivalent of self-compiling a software project after checking out its repo

I would not assign this to someone as their first electronics project. They would have to order all the components and get the PCB etched themselves. There's a fair bit of soldering, and a usable soldering iron is not cheap. And there's no undo button in hardware: if you solder something in backwards and pop it, you get pay for a new component and wait for it to ship to you.

seba_dos1 1 week ago

Why would you bother with etching such PCB yourself if you can order 10 of them for $4, and that's including shipping? Get two sets of components in case you screw up and then just solder all this exclusively through-hole and one-sided stuff with cheapest iron around.

The hardest part will be ordering the components, or more specifically verifying that you got them right, as the KiCad project does not include a BOM. Other than that, it's as easy as it gets. Entry-level workshop stuff, about as complex as ArduTouch. People who never held a soldering iron in their life successfully learn on this kind of boards.

(and if you're willing to spare a few more bucks you could even get it assembled by a PCB fab and just receive ready-made boards in your mailbox - the prices aren't prohibitive there either)

dheera 1 week ago

I mean, it's a speaker in a box, so you could also just snip the speaker wires, ditch the circuit board, solder some extension wires, and plug it into an external audio amplifier box of your choice.

If you go that route you don't really need much EE knowledge.

(This is also only if you already have this box and want to reuse it. Otherwise I would just go to your next neighborhood garage sale and pick up some good speakers for $10)

bhaney 1 week ago

> I'm not an EE, but would love to know how I can disable these incredible unsmart features

I am an EE, so let me tell you.

Use a hammer.

adriand 1 week ago

The author of the article starts out asking, "why would someone throw them out like that?"

Now we have the answer.

Blackthorn 1 week ago

Jim Marshall is rolling over in his grave at what happened to this company.

tlhunter 1 week ago

Lately I've been wondering if there's a way to do this to Smart TVs. Personally, I like the name "stupify" better ;)

rotifer 1 week ago

A year or so ago I bought a Hisense 65U88KM, which comes with Google TV. During the setup procedure it asked me if I wanted to enable the "smart" features, such as Google TV, the camera and microphone, or connect it to a network. I said no to all of them, and that was that.

Now it just acts as a dumb screen for my Apple TV box.

Astronaut3315 1 week ago

I did the same with a Sony A80L, which also runs Google TV. I even uninstalled the bundled streaming apps for good measure, although I never see the home screen.

It behaves like a monitor. I never see the TV UI unless I ask for it.

RajT88 1 week ago

My LG could be configured to behave like this (and believe me, I am thinking about going that way).

I have a cheap FireTV which cannot be made to behave this way. If you disconnect it from the internet, it will still require you to interact with the (slow-ass clunky) OS in order to select a different input.

Your best case scenario with some of these smart TV's is the ones which run Android to replace the launcher. Possibly, this gets reset periodically, meaning you have to keep doing it.

Apparently there's a few Fire devices which can be flashed with LineageOS - I might try researching that and see if it is doable. A FireTV stick with LineageOS would be the best case scenario.

dexterdog 1 week ago

I find that most of those reset to some nonsense occasionally or whenever the power goes out. I make sure they have no internet connectuon, but I usually have to dig up the remote to get back to hdmi1 so my device interface will come back up. I accept the annoyance because I accepted the discount that they give to have all of the spyware crap on there that I am blocking. I wish they could sell something cheaper that is just a display, buy product managers will be product managers.

CharlesW 1 week ago

> I wish they could sell something cheaper that is just a display…

The "smart" part is what makes TVs cheaper, since that's what opens the door to a higher CLV. People willing to put their money where their mouth is can still buy dumb displays: https://www.bhphotovideo.com/c/browse/Multimedia-Displays-Di...

dexterdog 6 days ago

Which is why I buy them and then cripple all of that stuff by not giving it a network connection.

echoangle 1 week ago

What exactly would that do? Just select any video input, attach your preferred input device and never touch the TV remote again.

userbinator 1 week ago

Look up "universal scaler" boards.

05 1 week ago

There’s a project to load OpenWRT onto LinkPlay A31 [0], might be easier than basically replacing the insides..

[0] https://github.com/hn/linkplay-a31