Philips CD650 mods

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#501
Yes, always!

He also provided a cosmetically mint 70's Pioneer SX-434 receiver, spotted on the way to school. A simple resolder of the output transistors sorted it, and it's now in my bedroom!

Today my two kids also came home with a DVD/Video combo deck, and a VCR as they know I salvage the transformers etc. as well...

As I say, well trained. So I don't look like a scab... :angel:

Sorry Simon.

Stuey
 
#505
Hi Stuey,

You've got him well trained 🙂
To be honest, I haven't done much with the 624. I deliberately got it for experimenting as it was cheap on ebay. I sniffed off the I2S from the decoder so I could build my first TDA1541 DAC. It was easy to do (these are quite rugged machines). Its a CDM4 and I was quite impressed that it would read any disc - the best player I've head for that actually.
Yes, its bitstream, which sounded respectable enough, but I think I've superceded it with my DAC. I think you could build a small NOS DAC and mount it internally and it would be a pretty good little player.
I'm not sure I'd mod the bitstream DAC, but that's probably because I'm more of a fan of multi bit DACs. It might sound very reasonable with modification.
Hope that helps.
Cheers,
Phil.
 
#509
Hi All,

I visited Martin last night, and we compared my PMD100, dual TDA1541A to his very nicely modded Naim CD player.
I was more pleased with myself than last time. I think they are closer in quality (I am not embarassed this time), but they are hugely, hugely different. It was really surprising.
I think its because of the differences between them. That's why they're different 😉

The Naim, and I hate saying this, had more of a Naim sound than mine. In fact sounded like a very nice Naim. A lot of presence and dynamics, sounded louder and brighter than mine at the same level on the pre amp. It is a superb player, and much better than mine was when it sported the 7220.
I also think mine was doing well. Perhaps mine was more laid back, but still able to recover subtle detail and present them sensibly in a nice soundstage.
We think the main differences are, obviously the digital filter is affecting the sound, perhaps Martin's S1 is recovering more detail, but my analogue stage is simply a single opamp and passive filter, whereas Martin has a specially modded opamp IV, active filtering, and biasing such that there is zero DC offset, and thus no output capacitor. Inherently, he has an output buffer that I lack. The preamp had a 10k input, so possibly my box was struggling to drive it properly.

Having said that, I'm really pleased with how well mine fared, but feel inspired to improve it more. I have always wanted to do something more sensible to the output stage. And have been taking an interest in better regulation (especially for my clock) in the last week or so. I also need to improve its robustness, so it can withstand Martin kicking it 😉.
 
#510
Thanks for that Phil, very interesting to hear that comparison. It sounds like you both have a little more work to do, or at least one of you may do... or else they'd sound about the same, by my logic, and I'm not sure about my logic 😉

Sadly I'm restricted to mini systems where I am now, but it's offset with plentiful sunshine, and where I'm staying is right on the sea-front 😀

Simon /in Gran Canaria
 
#511
Phil - good to see you again and nice write-up, thanks.

My take - Phil's PMD100/2xTDA1541, for what is esentially a proof-of-concept, has seriously good refinement and resolution already, and I'm sure has a lot more to offer. Comparing it with my player is probably misgiven in the sense that apart from the dac type...everything is different, as Phil hints above. There's no compelling reason the two should sound the same at all... similar, yes, they are similar: both do that clean musical enjoyment thing that the 1541 seems to deliver in spades.

Beyond that, from where I was sitting the obvious difference was in dynamics - we had to re-check but found we actually have identical gain throughout the I/V conversion to output, because mine sounded (to me!) very much more dynamic/weighty in comparison. And it would be unfair to 'call it' on this, for example, because so far Phil's dac has one poor dual opamp doing I/V and driving the output...

Not that it matters of course - we were having too much fun nattering and drinking beer to really care 🙂
 
#512
Yes, the 'beer mod' was working well 🙂
I agree, the dynamics of Martin's Naim really was nice. The output will probably be the next thing to do.
It was interesting to hear the probable difference that a beefier output can make. It'll be good to add a buffer on mine, and see what happens.
I'd like to tidy it up a bit, but I think it can wait 🙂
 
#513
(Disclaimer: Ray's design is perfectly fine for use with CD63. I had one built already so lazily just took it and used it when I first used the 7220 - thought I should have some form of filtering. Its seemed to work, but is perhaps not ideal for my setup).

Yeah, been looking at Ray's passive filter that I've been using.
At DC its essentially a potential divider that halves the signal (ish) and has an impedance of about 4k. That might explain a) why it seemed a lot quieter, and b) why the opamp was having trouble driving.
I'm going to redesign all this for my needs.:smash:
 
#515
Good points.
I believe the PMD100 wasn't doing the -6db thing (IOW it has a line for signalling +6db gain to the analogue gain stage for HDCD instead of compensating digitally - not that I use it, I just have to listen to less Beck. I'll fix that soon), and yes the current should be doubled into the IV stage, but I think its been given a tough job 😀.

We've definitely identified a bottleneck LOL!
 
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