Hi all,
Yesterday I acquired a free Yamaha CDX-450 CDP by saving it from being thrown out. It is, for the benefit of everyone who hasn't spent the last couple of hours reading about it, a 1991 mid-range CDP utilising a Burr-Brown PCM67P. It's not great, but since it was free, it seems worth having a play with, since I've got nothing to lose. Having listened a bit, and opened it up to poke around a little, my thoughts are:
a) It sounds pretty good, actually. The only thing that worries me is the onboard digital volume control.
b) The opamps (IV stage) are rubbish, and replacement will most likely yield a worthwhile improvement (I'll probably take a crack at that tomorrow). The ones in there are duals, although I can't work out why, so I guess I'll swap them for some of my stock of OPA2132, and perhaps build an output linestage for it with OPA2107.
c) It skips really easily...the chassis integrates the front panel and front feet, so any taps or thumps on the front panel seem to couple straight through to the transport mounting. A little experimentation has shown that while the laser mechanism is shock mounted, any vibration which causes the spring-suspended mechanism to move more than about 2mm will cause it to skip. Perhaps the springs are too weak? I suspect chassis improvements can probably help here, but it may of course be symptomatic of issues with the aging transport.
Getting more involved in it, and I might as well:
I can't seem to figure out where the voltage regulators are, which makes experimentation with that a little difficult....some quick probing shows that most, if not all, of this player runs on either +5V or -5V. Does anyone have a schematic/service manual for this or a similar model? I'd like to try separating power supplies, perhaps with a couple of teddyregs.
Obviously there has to be some sort of digital signal running the PCM67P. What format would it be in? Is it possible to tap a SPDIF signal off the input pins to drive a separate DAC?
If anyone has can answer any of my questions, or contribute any worthwhile advice, that'd be great!
Yesterday I acquired a free Yamaha CDX-450 CDP by saving it from being thrown out. It is, for the benefit of everyone who hasn't spent the last couple of hours reading about it, a 1991 mid-range CDP utilising a Burr-Brown PCM67P. It's not great, but since it was free, it seems worth having a play with, since I've got nothing to lose. Having listened a bit, and opened it up to poke around a little, my thoughts are:
a) It sounds pretty good, actually. The only thing that worries me is the onboard digital volume control.
b) The opamps (IV stage) are rubbish, and replacement will most likely yield a worthwhile improvement (I'll probably take a crack at that tomorrow). The ones in there are duals, although I can't work out why, so I guess I'll swap them for some of my stock of OPA2132, and perhaps build an output linestage for it with OPA2107.
c) It skips really easily...the chassis integrates the front panel and front feet, so any taps or thumps on the front panel seem to couple straight through to the transport mounting. A little experimentation has shown that while the laser mechanism is shock mounted, any vibration which causes the spring-suspended mechanism to move more than about 2mm will cause it to skip. Perhaps the springs are too weak? I suspect chassis improvements can probably help here, but it may of course be symptomatic of issues with the aging transport.
Getting more involved in it, and I might as well:
I can't seem to figure out where the voltage regulators are, which makes experimentation with that a little difficult....some quick probing shows that most, if not all, of this player runs on either +5V or -5V. Does anyone have a schematic/service manual for this or a similar model? I'd like to try separating power supplies, perhaps with a couple of teddyregs.
Obviously there has to be some sort of digital signal running the PCM67P. What format would it be in? Is it possible to tap a SPDIF signal off the input pins to drive a separate DAC?
If anyone has can answer any of my questions, or contribute any worthwhile advice, that'd be great!
Well, I swapped out the C4570C's in the IV stage for OPA2132P's, and (taking into account I-did-it-myself syndrome and the placebo effect) it does seem to have made a difference - the noise floor is appreciably lower, and resolution appears to have been improved.
I'll post some pics later in the hope that somebody might help me work out the power supply.
I'll post some pics later in the hope that somebody might help me work out the power supply.
I think those OPA2132's are worth more than the whole player.;-)
The PCM67(&69) was an attempt to hybrid a bitstream dac(for low level linearity) and a multi-bit dac(for high level dynamics). Unfortunately, it did not work very well, in my opinion. I've had a chance to take one of these dac's(Theta Cobalt dac unit) as far as it could possibly go(power supply, output stage & clock-wise), and the result was utterly mediocre. A stock AA dac-in-the-box could still eat it for breakfast. In a Yamaha cd player application, there is no way I would personally consider it worth any effort.
The PCM67(&69) was an attempt to hybrid a bitstream dac(for low level linearity) and a multi-bit dac(for high level dynamics). Unfortunately, it did not work very well, in my opinion. I've had a chance to take one of these dac's(Theta Cobalt dac unit) as far as it could possibly go(power supply, output stage & clock-wise), and the result was utterly mediocre. A stock AA dac-in-the-box could still eat it for breakfast. In a Yamaha cd player application, there is no way I would personally consider it worth any effort.
Oh, I agree entirely - since I had the OPA's sitting around, it was worth a shot, though.
Is it possible to tab off some sort of usable signal to create a digital output? I realise there's very little to be gained by mucking around further with this DAC - I wouldn't have bothered at all, except that I picked it up for free.
Is it possible to tab off some sort of usable signal to create a digital output? I realise there's very little to be gained by mucking around further with this DAC - I wouldn't have bothered at all, except that I picked it up for free.
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