Bypass switch saga continued – and finally solved...
Previously I reported a problem I had with the bypass switch only outputting one channel (rh channel) with bypass switched off. I thought this had corrected itself, but yesterday I had to move the preamp about a bit while I played with various connections as I tried to resolve a second problem I had with my ZD3 DAC - and the bypass switch fault came back (I’ll touch on the ZD3 problem at the end).
So I decided to open up the ZP3 and have a look at the switch. I found a pretty good guide with videos showing how to strip the ZP3 down here:
https://drive.google.com/drive/folders/1V0L88g6Ip7iJedNP-ir9TOWCdg_SwIHd
First I had to remove the plastic side cover adjacent to the bypass switch to gain access to the 4 crosshead screws holding the metal side plate on - see 4th video in the link above. The video kind of skims over the plastic panel removal, in truth there is so much glue on it that it is not easy. I carefully used a sharp craft knife to slide between the plastic panel and the metal plate but it is virtually impossible to get it off without scraping some of the black paint on the underside of the plastic panel, as can be seen in the pictures below. With this removed simply remove the 4 screws holding the metal plate on which can then fall out with a bit of encouragement.
The switch assembly which holds both the bypass and HPF switches has one electrical connector which needs to be pulled off. Then remove the 4 tiny Torx head screws (Torx size 5 or 6) on the underside of the amp and the switch assembly can be removed.
On inspection the soldered pins of the bypass switch looked pretty bad, possible dry joints and a bit of a mess. As I only want to use the bypass switch in the off position (so I have use of the HPF) I put a big blob of solder between the 2 pins that should be shorted to one another when bypass is switched off – basically the blob of solder is doing the job that the switch itself isn’t – see pictures below.
Of course, now I have to make sure that I never inadvertently switch bypass to on, otherwise all 3 pins will connected at the same time and I have no idea what damage that might do to the amp, so after reassembly I put some electrical tape over the bypass switch to stop me knocking it by mistake.
Problem is now fixed, both left and right channels working with bypass switch (now permanently) in the off position.
Thoughts:
I have no idea why one channel still worked when the switch was in the bypass off position, I would have expected neither channel to work if the contacts weren't making.
Although the ZP3 can be stripped down for e.g. replacing op-amps, it certainly isn’t user friendly with the way the plastic side panels are stuck on. As can be seen from the videos I linked the rest of the strip down isn’t exactly a simple task either.
I might get in touch with Fosi to see if they will send me a replacement switch assembly and plastic side panel as it is certainly easier all-round than if I had sent the amp back under warranty. I haven’t reattached the plastic side panel yet just in case I need to open it up again (or Fosi send me a new one).
ZD3 problem – I mentioned this at the start though it has nothing to with the ZP3. I mostly only play CDs as my source and had an issue where with almost every CD I played I would get a short ‘wavetooth’ sound/interruption of about 0.5 seconds (think hammer drill sound). It only happens once per CD but with almost every CD I played. My connection from the CD driver to the DAC was with coax. I also have a DVD player connected via optical and have the same problem there but rarely use the DVD player.
So I changed the coax connection between the CD drive and the ZD3 to a USB connection (which is why I was moving my various Fosi separates around and managed to re-introduce the bypass switch fault). It’s early days yet but that problem seems to have gone away too. No idea why I get the annoying burst of ‘hammer drill’ sound with both coax and optical connections but not with USB, though I did read somewhere that with coax and optical connections the source controls the data flow, whereas with a USB connection the receiving DAC only accepts the data when it is ready for it. So some kind of timing issue?
