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|14th November 2005, 02:51 PM||#1|
Join Date: Aug 2005
Interference in off-board CD clock PSU
This is a cross-post (also in top > sources > digital), I'm sorry if that's against the rules (new here), but I'm not sure where best to post this.
Let me explain a little of the problem:
I've reclocked my Marantz CD6000 with a Tent XO module. To increase performance, I am trying to use an off-board PSU. See here for pictures and a discussion of its construction.
The 12v output of the psu is fed via twisted-pair cabling (CAT5) into the CD player. The 12v powers one of Andy's (ALW) Jung super regulators which outputs 5v into the XO.
The problem is that when switching the kitchen/dining room lights off; the surge/spike/whatever causes the CD player to **** out and display 'Error'. This is how the CD6000 reports a clock error, as I found out when I tried to switch on the player without the clock psu powered on!
Basically, switching lights on/off causes some kind of abberation in the clock PSU which is passed through to the clock which causes (I guess) some kind of sync error and the player stops working until it's switched off and on again.
I'd really like some suggestions on how to fix this problem which never manifested when the old clock was sharing the player's internal toroidal power supply.
One idea of mine is to take a small wall-wart supply (240V AC -> 12V DC) apart and house it inside the cd player. I'd feed its 12v into the super reg and power the clock from there, but I'm concerned about noise from the wall wart in terms of both EMI and **** getting through the super reg into the clock.
|18th November 2005, 10:25 PM||#2|
Join Date: Jun 2005
Location: Kent, UK
First thoughts are that your 3 terminal regulators are verging on being unstable and are being provoked into oscillation by mains spikes. There's a thread at here
that touches on instability and the importance of decoupling caps. Personally, I use a few microfarads on the input rather than the 100nF most people use, but the main thing is to keep leads short and use lots of caps! I've worked on lots of equipment that have peculiar instabilty faults that turn out to be 3 pin regulators with caps missing, and I've never seen any oscillation on a 100MHz scope so perhaps we're talking hundreds of MHz.
|20th November 2005, 12:57 AM||#3|
Join Date: Aug 2005
About a week has gone by now and I'm pleased to say that it's all sorted out and sounding better than ever I've even screwed the case back together in the false hope that I'm not going to do any further mods to it.
So, what have I done? Well, the EMC problem is now totally gone - I'm using an on-board PSU for the Tent clock and it's eliminated all the popping/stopping/error problems. I'll run through all the changes that have now been made to the player:
- Added Tent Labs XO module clock
- Added dedicated clock PSU (9-0-9 centre-tapped trafo, 4700u smoothing, ALWSR 5v)
- Replaced silicon rectifier diodes (1n4003) with schottkys (11dq10)
- Removed HDAM (2 op amps built from discrete components) daughter board
- Added AD8620 op amps in place of HDAM
- Replaced L7812CV / L78912CV monolithic regs with ALWSR +12v / -12v
- Removed muting transistors (they were blown anyway )
- Removed output capacitors
- Disconnected signal ground from the chassis (it's like that when produced)
- Added vibration-deading bitumen to just about every internal surface
- Disconnected headphone circuitry
- Added thick, shielded mains cable
- Replaced crappy mains cable clamp with nice tension-relieving jobby
- Removed crappy mains cable connector and soldered it direct to PCB
It took a while, but the sound is now Here's a few pics:
The AD8620s on the DIL adaptors:
Crazy wiring for the analog stage +12v / -12v and clock +5v:
The soldered mains cable, clock PSU and cable clamp:
A nice view of the sturdy tension bar (filled with bitumen underneath):
Gratuitous *** shot (showing the soldered-in MK plug and clip-on ferrite):
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