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• more about WHUZY ZK-1002 | ZIZHI ZZ-1002 amplifier boards

  Davide Ercolano • 11/12/2022 at 15:39 • 5 comments

  Hello to everyone!
  On my research journey, I already talked about the WHUZY Audio ZK-1002 amplifier board but it is worth it to dive more deeply into that board and I bought it again lately.
  

  
  

  1. THE NEW NAME
  The new news is that probably you can't buy the "WHUZY" anymore: searching and buying "ZK-1002" I received the ZZ-1002 by ZIZHI Audio instead. Well, it's really the same board tho.

  
  

  2. NEW NAME, OLD PROBLEM

  Let me remind you about the problem with the AUX input stage of those boards: there is an RC filter with the wrong "C" value (10nF instead of 1nF) so the low-pass filter starts at 3.5kHz instead of 35kHz. I'm talking about C41 and C42, with R2 and R4 (4.65kOhm). To get back your hi frequency you must swap in the correct 1nF capacitors or you can remove them also; the remaining resistors will lower a small bit the volume (negligible), you could remove R2 and R4 too, and then bridge the pads.
  There is also a cut-out with a curve starting from 150hz down to 20hz due to the low value of the decoupling capacitors C37 and C39 (100nF): to fix this you must replace them with a 1uF instead (value from 0.47uF are good).
  

  Another problem is that the Bluetooth chip is always on (and the TPA3116 are on standby), but this turns out only annoying and not acoustically problematic.
  

  
  

  3. THE HIDDEN PROBLEM (yes, another one!)
  

  You have this board and when you rotate the volume POT you hear a scratching noise, but you are like "ah ok this POT is a cheap one but it's ok". Right?? you are WRONG, it's not "ok" and the scratching noise doesn't come from a cheap POT... the truth is much more insidious!
  The second stage before the POT is the Bluetooth one, with the IC by JieLi. This IC elevates the input audio signal (from AUX) and the output signal to the amplifier with 1.8v of DC current. Yes, DC current into the POT, that's the scratching sound you're hearing! Also, the fact you're hearing that, means that a DC current is going into your speakers! (tested it with a voltmeter and oscilloscope)
  Basically, the circuit design is wrong.

  4. HACK A FIX
  Well, electronically speaking it's just a matter of adding 2 more decoupling capacitors on the output of the Bluetooth chip, but to do so you have to cut 2 PCB traces. Here is my fix:
  

  
  As you can see I worked on the bottom of the PCB: is the only place before the POT with enough space.
  You must cut the traces, remove a bit of protective paint, and then solder on an SMD capacitor, I did it but I won't lie to you: it's a very hardcore fix, not for newbies.
  Did it work? Oh yes, it works now, smooth and silent! But unfortunately is not for everyone.

  5. FINAL THOUGHTS
  And here we are again, I paid 14.70€ shipped for this board, but at the end of the day I can suggest to ANYONE to buy it, and it's really a shame; I'm so frustrated by this that I'm thinking to design one by myself... Should I? ;)
  
  Thanks for reading me and stay safe.
  Davide, baugrafik
  

• And LittleJet! Desktop Version (finally)

  Davide Ercolano • 01/02/2022 at 11:35 • 0 comments

  Hello! Sorry for this long delay, but hey, better "later" than "ever".
  I finally shared the LittleJet! "desktop version", and you can download it from here: https://www.prusaprinters.org/prints/110700-littlejet-desktop-speakers
  
  The BOM is:
  

  • x2 - Peerless by Tymphany TC6FD00-04 2" Full Range Woofer
  • x2 - RCA panel jack
  • x2 - Inductance 1.05mH or close value
  • x2 - Resistor 3.7Ohm or 4Ohm (from 3W are good enough)
  • DC panel plug
  • This amplifier module here (non-affiliated link)
  • 19v - 4A Power supply
  • Stuffing material (polyester material)
  • 3D print all the files once

  
  HOW TO BUILD VIDEO:

• Finally - Closed Project!

  Davide Ercolano • 05/01/2020 at 10:39 • 0 comments

  Hello!
  After a lot of work, learned a ton, designing and tinkering, I'm finally happy to present the LittleJet speakers!

  (Italian language, but you can skip to 5:39)
  

  
  

  (how everything fit inside)

  (the final back design)

  *** Sine sweep full spectrum, recorded with Spectroid APP on a Honor8 smartphone and built in microphone at 50cm far  (see the red line; not smoothed) ***
  

• Final design is final!

  Davide Ercolano • 04/07/2020 at 15:08 • 0 comments

  Hello to everyone!
  Since my long waiting time for the needed electronics, I definitely closed the acoustic and aesthetics design! Yay! New frequency resonance for the TL (118hz instead of 165hz) and then a different TL shape, plus a front baffle added to improve the diffraction.

  BUT
  Meanwile the electronics did arrive and I was able to listen thoroughly to the amplifiers... And then I finally chose and this changed a bit the final "final" design :D (spoiler: no more light hole and the jack hole in front baffle).
  Anyway everything is really going to be concluded, see you really soon!
  

• The amplifier

  Davide Ercolano • 02/04/2020 at 16:58 • 11 comments

  Hello!
  Since this speakers are meant to be "stand-alone", I'm searching for a little amplifier with wireless connection and this features:

  • 15W rms power with lowest THD% with 12v
  • low heat working with 12v
  • bluetooth 5.0 (more on later)
  • volume POT
  • On/Off button
  • low budget

  I used to follow some YouTubers working in this field then I knew which IC amplifier to search, two of them actually: the Texas Instrument TPA3116D2 and the Yamaha YDA138-E.
  For the "budget" point, I'm searching on Aliexpress (a good platform indeed).
  Anyway, almost 2 months are elapsed now and I have some informations to share with you.
  
  

  FIRST BOARD: WUZHI AUDIO ZK-1002 - $13.09 shipped to Italy
  

  Really good PCB layout, pretty decent capacitors and inductances on the RLC filter and power line, volume POT with ON/OFF, two TPA3116D2 in single-channel mode... "Perfect!" do you would say... NO.
  The Bluetooth IC is a wild one, named AS19AP22702-25A4 from a company with a "greek Pi" as a logo (edit: is "JL" logo, by JieLi company); the input audio is managed by this chip, also the input from the AUX jack goes inside to this IC, then, is that bad?! Quite YES

  
  Using the AUX input  the amplifier is NOT linear and the signal get smaller from around 2.7kHz becoming really silly at 22kHz.
  Usually this behavior is caused by an incorrect RLC filter, but is this the case?

  Connected on Bluetooth you get a linear output till 19kHz... What happen later?...
  

  This! What is this? I really don't know, a noise I would say, but anyway it is crazy output therefrom 19kHz to 22kHz and up.

  So the Bluetooth IC it's not reliable and the AUX input is junk.

  Anyway, the TPA3116D2 in this single-channel configuration (two, one per channel) it's really good and actually listen to it by Bluetooth is nice, with hi-power and no distortion.

  SECOND BOARD: HAZY AUDIO XH-A354 - $14.86 shipped to Italy

  When I have chosen this board I was attracted by the YDA138 single-channel configuration, so to have more power on a 4ohm driver, like the one into LittleJet.
  

  The first impression on this board when it's arrived was so terrible: the codes on the Bluetooth IC have been erased, also on the controller for the SD and two more wild IC that I think are some OP-AMP (do someone of you know??). Also the volume POT doesn't have the on/off switch and the worst part: the inductances are ridiculously small. Finally the AUX input goes inside the Bluetooth chip, like the Wuzhi, then... Let's see...

  
  0.5 per division, almost 2v p/p and it is already REALLY distorted (1khz).
  And by bluetooth is the same...
  At full power the inductances get really hot and also the linearity (from 4kHz to 22) is a shame
  

  Measuring along the source path I found that the signal is good later on the decoupling filter (RC) and also later on the volume POT, then till the BL input, but it was absolutely distorted on the output of the Bluetooth IC.
  Listen to this amplifier is a pain, this board is simply garbage. DON'T BUY IT.
  
  Anyway I want to listen to a good YDA138 board, so I'm waiting for a new one (without Bluetooth connection).

  BLUETOOTH 5 CONSIDERATION
  

  The actual integration of the standard by these boards (everyone you can find now) is wild and not reliable then I will adopt a different approach: amplifier board (TPA3116) + Qualcomm CSR8675 module. The budget will grow up a little but we will have more audio quality and reliability.
  Anyway now everything is going very slow in China because of Corona Virus, so I don't know when I will have this configuration. Meanwhile I will design the integration for the Wuzhi ZK-1002.
  See you soon!
  

  
  

• First step: share it

  Davide Ercolano • 12/13/2019 at 18:34 • 0 comments

  Hello there, this is my first project here and I'm kinda excited for.
  I'm working on this by some months now and finally I have something to share. It is not a completed project yet anyway and I have some plans for it, infact my next step will be to implement (I already found it) an amplifier and a bluetooth connection and finally make the LitteJet a standalone speaker.
  I also want to verify my design for validation of the design process testing the speaker into an anecoic chamber.
  See you soon then!

  Davide Ercolano - Baugrafik.it
  

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