I don't normally "blow my own trumpet"..... But this is the most incredible, loudest, and just everything under the sun awesome thing every I have heard.
I have been in the SRE listening room at B&W when they were based at Steyning, listening to some of the most incredible speakers on the planet, in the room they were designed and tuned in. And I have every respect under the sun for the incredible sounding products they produced.
However, me, a single person (not quite so amazing in lockdown), spent many years building some modified ZDT 3.5 speakers (or that should be "ZDT 3.5" speakers). They are close but the cabinets are different.
I have built both the original passive crossovers (tuned by my own tone deaf ears), and also my custom designed and built 192Khz/24bit digital crossovers. These speakers are awesome with the passive crossovers.
But I DARE anyone to try connecting them, through custom crossover hardware, through 8 channels of decent amplifiers you can find (original or fully refurbished commercial amps like my ones), and then compare to the 2 channel passive setup.
I am no true audiophile. I could not care less if you use the cheapest aluminum electrolytic capacitors everywhere, or use polyester capacitors instead. I will not hear the difference (and if you can, "hear a difference", maybe you should just go outside for a while and get some fresh air...).
But the difference between a passive 2 channel active setup, and switching to fully active 8 channel amplification, there is no contest.
8 channels of amplification, dedicated to the required frequency range of each driver, you will NOT match this with a passive setup.
I have a pair of Bowers & Wilkins CM10s here, in fact, whilst they have the "wrong" bass drivers (the spiders on the bass drivers are tighter than the actual commercial versions), they are an amazing pair of speakers, But the fact I can put a pair of homebuilt 3.5 way speakers. with 8 channels of commercial amplification, and they sound as good, or better in many cases, just shows what you can do for the the same price if you put a little effort in yourself.
So the noise is the attenuator box I built. I mean it is sat right next to the TV.
Well that was a simple fix! (Removing it that is).
Well this thing does sound damned good, but I hadn't done my "can I hear it" test...
How close can you get to the speaker before you hear anything. Well on the mid-range there is a bit of noise up close (1/2 meter or closer). Only when my plasma TV is on though. Interestingly it's exactly the same noise my you can hear the TV making anyway.
The output buffer board is the one I designed for the ADAU1966. The AK4468 recommends different filters, and much faster op-amps. The ADAU1966 app note has 10MHz parts, I am using 8MHz. The AK4468 recommends 80MHz parts from Texas Instruments!
So I may just design a new buffer board. I should have done it anyway.
There are no words or pictures to describe this.
So the PCM4202 and AK4468 are running at 192kHz/24bits.
This gives me goosebumps.
I am happy.
So I pulled out my crossover box.
I also built up an AK4458 DAC board with an AK4468 fitted to add some VELVET SOUND (they are pin compatible). This is now fitted, but not quite working yet! Need to get all the clock rates right, but it should run at 96kHz and possibly 192kHz all in hardware (pin control) mode. Unlike the ADAU1966 which was stuck at 44.1/48kHz in hardware control.
I have tuned up the termination resistors a little. Output pins from the ADAU1452 look fine at 75Ohms over the ribbon cables. The NB3L553 clock fan out seem better with 47Ohms. However the signal at the output end is not perfect as you can see some reflections interacting with the signal. That seems to be feeding visible jitter onto the clocks.
At the receiver end, where the signal "slopes off" a little at the top as in the picture above, you can see the signal moving around on the oscilloscope. It's different for each board so the PCM4202 looks different compared with the AK4468. So it's all down to compromise (unless you want to tune everything perfectly, which I might do sometime...)
It's giving me some more ideas for other designs. Would be interested to play with some designs with U.FL connectors/cables instead of ribbon cables. Try and reduce any interaction between signals. Plus U.FL has a small footprint so might work quite well.
Also look at adding some better driver ICs in (or better clock fan outs). I did have some nice ones I had found that are designed to reduce jitter. Have used them before and they are very very good. Although it will all add complexity and cost, and I really doubt I would hear a difference, and they are a PITA strange PCB footprint...
An electronics engineer and a long term electronics hobbyist. I like tinkering with stuff and making things.