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Old 8th February 2008, 11:45 PM   #1
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Default CD 7550 differences from a CD 104

Hi,
do you know how all the Grundig 7550 differs from a CD 104 ?
I read form other thread:

" generally cd104 is similar to cd7550 but cd7550 has extra special ground for kill HF intermodulation "
Where are them?

Some people think that these are small steps to improve the sound of cd7550.

Maurizio
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Old 20th July 2011, 09:17 AM   #2
IAN01 is offline IAN01  United Kingdom
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I originally posted a series of posts on the 'Philips CD104 tweaks' forum regarding a fault on my Grundig CD7550 which triggered some interest in the differences between this player and the CD304 MK1. The general consensus seemed to be that apart from some minor earthing differences and an AC filter comprising two shunt caps and ferrite choke the two models are identical with the exception of the casing and there was no firm evidence of anything that would account for the reported noticeable differences in sound quality between this and other early Philips based players.

Interestingly I have recently had to repair my 7550 as a result of losing all audio output suddenly. It proved to be a power supply fault which took the 7924 regulator out and hence the -18V line too but led onto me discovering something else. Out of respect to the 'Philips CD104 tweaks' forum I have chosen to continue this discussion here.

I had previously had an intermittent fault where the player would fail to read the TOC and just continuously spin. Undoubtedly down to the griplet issues with these boards I had resoldered the entire servo board at the time in an effort to solve it but once reassembled although working initially the player continued to display the same issue intermittently. Before I could look at it again it started working reliably again so I simply left it. However, when dismantling the player again to repair the power supply fault the old TOC fault reappeared again much to my frustration. So seeing how I had already reworked the servo board I decided to swap out the decoder board for the one in my spare CD104. This instantly fixed the issue and swapping them round again caused the fault to reappear. So I left the CD104 board in and put it all back together again.

However, when I plugged the player back into my system and started to play CDs much to my surprise I found the sound quality had completely changed and was quite recognizably the sound of my CD104s, gone was the lovely transparency and effortless sound quality that I'd loved from my 7550!

The original decoder board, which incidentally looks identical in all respects to the cd104 board apart from the use of the Philips blue electrolytics and even has the same factory mods, is now back in and delivering that wonderful sound quality, so be it I now have to wait a couple of hours for it to read discs (will sort the griplets out on this board at the earliest opportunity).

This has come as a total surprise and says to me that the sound differences I love have little to do with anything else in the grundig player and more to do with the decoder board ... but how would this seemingly identical component board make such a difference to the sound! If I get the time (which is in short supply at the moment) I'd love to take some readings and scope measurements to ascertain if there are setup/alignment differences between these two cards. I'm at a loss to explain such a difference.

Last edited by IAN01; 20th July 2011 at 09:24 AM.
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Old 20th July 2011, 01:40 PM   #3
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That is an interesting finding concerning the differences between the Philips CD104/304 and the Grundig CD7550.

Is it possible for you to post some pictures of the decoder boards of both your CD104 and your CD7550? From the ones I already have, I can not see any differences at all – and I have worked on over a dozen CD104/204/304.

As with all of these old Philips based machines, I would imagine that differences in the sound signature between one sample and the other (if no modifications or restorations have otherwise been done) are mainly down to the state of wear. That is what I have experienced, anyway.

By the way, the AC filter is present in some early CD104/204/304 as well, mainly the ones with build in RCA cord.

Cheers,

StefanAC
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Old 20th July 2011, 02:54 PM   #4
IAN01 is offline IAN01  United Kingdom
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Hi Stefan, sure ... when I pull it out again to do the griplet repairs I'll take some pics.

Like you, I don't believe there are any real differences between the boards. Peoples perception and preferences on sound quality are so subjective (including my own) and stated preferences for players etc are often simply down to the sound suiting their personal taste.

Without doubt though there are differences between every CD player I have ever listened too including all the TDA1540 based players I have. It's always fascinated and puzzled me that there should be such differences but as you say wear sets in over the 25 years or so most of these plays have existed for.

My Grundig player has a much more relaxed feel to the sound and seems like the music has a freedom and transparency and breathes more easily (see ... subjective descriptions again) when compared to my CD104 machines. Very easy to listen to for extended periods of time. It also has stunning mid range clarity and balance. But it lacks overall detail compared to the two 104s. The 104 decoder board I tried had a much tighter sound with a tighter extended bass range too but the overall musical impression sounded constrained compared to the original decoder board. Maybe it is just tolerance changes in components over time that bring about these changes. I have a 303 machine which has the best detail of any of my TDA1540 players but again it sounds very flat and one dimensional.

To be honest I'm just glad I have a player that suits my ears and never gets tiresome to listen to regardless of the reasons or technical explanations. It took me many years of looking to find a player I was happy with and suited my system.

Thanks for the update on the ac filtering to, I didn't know that.

Last edited by IAN01; 20th July 2011 at 02:59 PM.
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Old 21st July 2011, 11:02 AM   #5
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Hi Ian,

You are definitely right when it comes to peoples’ preferences for certain sound signatures – it is the same with me as well. But an equally important part is system matching. The CD player should suit the amp, the loudspeakers and the room.

After much try and error I have my choice of CDPs down to three that I use at home in different systems – a Philips CD304, a Philips CD304 MII and a Wadia WT3200/Marantz CD94 MKII hybrid. And these players definitely don’t sound alike.

The CD304 is extremely musical, with an awesome midrange and bass. But its top end could be a bit more extended and it’s not the last word in resolution compared to my other CDPs (but still miles ahead of more common CDPs). The CD304 MKII on the other hand does the top end absolutely right and has all the resolution issues covert, but it is a tiny bit less involving or musical in its presentation. Whereas the Wadia/Marantz hybrid does everything the other two do – and than some. But I have to admit that all three CDPs are completely restored and highly modified with different op-amps, high end foil output caps, additional voltage regulators for the DACs and op-amps, no oversampling and much more.

While these three CDPs all differ in choice of DACs, powersupply or circuit boards and therefore a different sound is to be expected, I also realized that there is a sound difference between the servo and decoder boards that are used in the CD204 and the CD304. I preferred the CD204 version with its through hole components and that’s why that combination works now in my CD304. Which brings me to your CD303 – that Philips uses different DAC versions and other ICs compared to your CD104/CD7550 which should result in a different sound signature.

Best regards,

StefanAC
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Old 21st July 2011, 08:20 PM   #6
IAN01 is offline IAN01  United Kingdom
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Please find the pictures of the decoder boards as requested as attachments at the bottom of this post. I subsequently discovered that the servo board makes a difference to the overall sound too having tried swapping those. Are these setup specifically to match the units cd mechanism’s output and the decoder board and as such if exchanged are no longer matched?

Whilst I accept that different DACs presumably must have some effect on the sound signature I am always a little puzzled by the differences in sound between the players based on the same DACs so be it there may be subtle differences in versions. If the DACs are set up correctly I wouldn't have thought the sound would have varied that much given that the audio stages hardly changed between the CD100 and the CD304.

My belief (which may be somewhat naïve) is that prior to the DACs output stage, the audio signal is effectively digitally encoded and given the design parameters it should be fairly tolerant of corruption assuming that the disc is being read correctly and not too many errors are creeping in there.

Surely the differences between any two DACs of the same type should not produce noticeably different sound signatures or one could argue they are not fit for purpose.

The audio stage is very simplistic and has barely changed from one model to the next so I wouldn't expect that to introduce much variance in the audio signal.

Summing that up, whilst in the digital domain there should be no discernable change in the encoded audio content by the transmission and manipulation of the bits on their carriers (square waves). If components are working within their design tolerances then this should and must be the case surely.

Are the differences we hear today simply the result of the component values straying out of their design tolerances due to age? Although I bought a Philips CD100 within 3 months of them being released, I never got to compare players at the time due to not many people having them and the expense of buying more than one. Would I have found little difference, if any, between players coming off the production line at the time?

Sorry to raise so many questions but I am very interested in understanding (or trying to) what is going on here and what the key factors are effecting the sound. I love the musical nature of the TDA1540 based machines and would love to improve the ones I have if possible. From your experience Stefan and your description of your modified players you seem a lot more knowledgeable than me. Any insight would be appreciated.

Out of interest aswell, what are the main mods you would recommend?
Attached Images
File Type: jpg CD7550 decoder board_1.JPG (209.1 KB, 190 views)
File Type: jpg CD104 Decoder Board_1.JPG (208.3 KB, 180 views)
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Old 24th July 2011, 04:20 PM   #7
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Hi Ian,

Thank you for the pictures. It was exactly like I expected – no visual difference at all between both circuit boards and most of the components.

Concerning the servo boards, there is no special matching between them and the drives. Sound differences are down to different state of wear, too. Most people think that taking care of the griplets is enough but they are completely mistaken. For having optimum sound, you need to replace the caps as well as resolder the complete board. Sometimes, it is even advisable to replace some transistors as well. Even the type and manufacturer of the caps make a difference, as well as the capacity and voltage rating. In some places, it is advisable to increase the capacity by a factor of 10, while sometimes, the capacity MUST NOT be altered.

Your view that the only difference in sound comes from the analog output stage is unfortunately completely wrong. The implementation of the DAC is of high importance as well as the other components like (oversampling-) filter, clock etc. Even the layout of the circuit boards and their material make a huge difference, as well as the choice of caps, resistors and other components.

Here a very few examples from my experience:

• I had a easy to follow change of sound (to the better) by changing the I/U resistor to a Vishay-Dale CMF55 non magnetic type
• Changing the caps around the ICs to Sanyo Os-con had high benefits
• Having film type decoupling caps of the RIGHT value and SAME type around the TDAs improved the sound very much
• Supplying the TDAs with clean power of the right voltage with the right grounding schema is very important – the TDA1541 needs +5V, -5V and -15V while several Marantz CD94 and Philips CD960 that I measured produced something like +6V, -6,5V and -13,5V

Depending on the engineer who did the design of the CDP you a get vastly different sound quality despite the use of the same ICs – both the NAIM CDI and the Philips CD460 use the same SAA7210, SAA7220 and TDA1541 components but are worlds apart sound wise.

Best regards,

StefanAC
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Old 24th July 2011, 08:13 PM   #8
IAN01 is offline IAN01  United Kingdom
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Hi again Stefan.

I agree, no design differences at all between the two boards. Nor is there between the servo boards either which are also interchangeable apart from having to swap the display controller chip as the displays are obviously different between the 304 and 104 units.

I agree with your comments on the griplets and resoldering, certainly when I did the servo board I re-soldered every joint ... with the boards being as old as they are it made sense to do that.

Thanks also for your recommendations regarding modding and component changes, I shall try and implement those in the near future.

With regard to your comments on the Digital side I still am slightly at a loss to understand the seeming lack of an 'exact science' bit on this. As I previously indicated, up until the DAC the music is still in the digital domain and it should not be rocket science to ensure that the ones and noughts remain uncorrupted in these stages. Take a computer for example, how would we cope if the programs we run were subjected to random or any other corruption of their program instructions or data. The fact is, operating within their design criteria the hardware does faithfully transport and manipulate the digital data without error time and time again. Why should this be any different for the audio encoded stream in a CD player, the hardware is still just dealing with ones and noughts and knows not whether its audio encoded data or any thing else. I accept that if this system starts to operate outside of its design tolerances then you could expect corruption of the data and subsequent audio distortion but otherwise surely the input to every DAC in any CD104, 204 or 304 based machine should be identical in theory. At this stage I could expect component and design issues to come into play as the stream has now been decoded into an analogue signal by the DAC and all the usual issues that we see with analogue electronics come into play (so things like layout issues, problems with ripple/digital clock frequencies on power supplies, poor choice of audio components etc to name just a few).

So in your example of the NIAM and the Philips use of the same chipsets, unless there are design inadequacies in the digital side there should be no discernable difference in the audio sound from the players unless that can be directly attributed to either:
  • An inability to read the disc data correctly or
  • The analogue stage design and or the quality of the components determining the DACs ability to do the D/A conversion
as the digital input should be identical in both cases!

I do appreciate though that when dealing with players of this age the component deterioration could easily (especially in the case of electrolytic capacitors) result in values falling outside of the design tolerances causing all sorts of problems. Bad enough in the analogue stage but would be very nasty in the digital stages. I suspect apart from a through replacement policy of suspect components then any further realignment/setup of the digital stages is beyond most of us who neither have the information or the equipment to carry this procedure out. The analogue stage is easier to deal with and tends to be what most modders seem to concentrate on from what I have observed but the old expression from the computing fraternity holds equally true here with regard to the digital side ... garbage in = garbage out

One other issue I've not touched on is the odd one of the NOS mod. It seems totally counter to the design philosophy to carry this mod out without altering the analogue filtering to remove the unwelcome signal components now sitting at the top of the audio band, and yet time and time again I see people doing this and saying it brings about an improvement in sound. I guess I will just try this and let my ears be the judge as it's easily implemented!

Many thanks for your help and comments and putting up with my lengthy thoughts on things It's appreciated.
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Old 25th July 2011, 11:41 AM   #9
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Hi Ian,

I think I need to get one thing straight – sound differences between a CD104, CD304 and a CD7550 are after almost 30 years mainly down to wear. The CD204 uses different boards, in that case it is wear and the different components (resistors, caps, transistors etc.).

But a CDP or a stand alone DAC are NOT computers. It is not just 1s and 0s you have got to deal with – that view is only taken by people who have absolutely no idea of how digital does work.

Just one difference of the many there are – while a computer can read a CD as often as it needs to get a bit perfect readout, a CDP has only got one go. And that one go is NOT perfect. Everything that is not read as it should need to be corrected by the CDPs error correction circuit (which does NOT work once in a while but is constantly busy). Herein lies part of the difference between different drives – the better the readout the less the error correction has to work. That part is covered by improvement to the CDPs servo board, casing, damping feet, better power regulation etc.

Speaking of power regulation, this is an extremely important part of any audio device. Every IC in a CDP has an influence on the quality of the power rails. In low class equipment, you have only the minimum number of power regulators (if any) that is necessary for functioning. In a high class component, you can have separate transformers, rectifiers, caps and voltage regulators for every major part of the CDP to minimise a cross influence. That is the difference between a Naim CDI and a Philips CD460 for instance.

Another main influence in the digital part of a CDP is jitter. I am not going to elaborate much about that as there is so much written about it elsewhere. But to minimise jitter, the quality of the clock, the layout of the circuit boards and many other aspects are important – therefore all the things that YOU think to be of no importance as you are still dealing with 1s and 0s (which, to be precise, you do not).

I would advise you to have a look at some other interesting threads at diyAudio before doing mods on your CDPs so that you have an understanding of what you are doing.

Best regards,

StefanAC
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Old 25th July 2011, 05:40 PM   #10
IAN01 is offline IAN01  United Kingdom
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Hi Stefan,
I decided to answer your last post in the form of included quotes and responses.

Quote:
I think I need to get one thing straight – sound differences between a CD104, CD304 and a CD7550 are after almost 30 years mainly down to wear. The CD204 uses different boards, in that case it is wear and the different components (resistors, caps, transistors etc.).
Yes, I'm pretty much coming to that conclusion now. Btw, I hadn't realised the 204 used different boards so that was news to me!

Quote:
But a CDP or a stand alone DAC are NOT computers. It is not just 1s and 0s you have got to deal with – that view is only taken by people who have absolutely no idea of how digital does work.
Well for anyone thinking there is no analogue sections to a CD player I can understand your remark. But between the initial A/D converter and the DAC it certainly is all ones and noughts and exactly like a computer and I challenge anyone to suggest otherwise. It's all digital switching circuitry which was the point I was trying to get across and was careful to state this was before the DAC. I have little belief that major issues associated with the sound are to be found here unless components have strayed outside of their design tolerances. I have a good understanding of this technology having worked on telephone digital transmission systems in the late 70s / early 80s with GEC Telecoms where we used time division multiplexing to transmit multi subscriber channels down optic fibre conduits.

Quote:
Just one difference of the many there are – while a computer can read a CD as often as it needs to get a bit perfect readout, a CDP has only got one go. And that one go is NOT perfect. Everything that is not read as it should need to be corrected by the CDPs error correction circuit (which does NOT work once in a while but is constantly busy). Herein lies part of the difference between different drives – the better the readout the less the error correction has to work. That part is covered by improvement to the CDPs servo board, casing, damping feet, better power regulation etc.
Here I believe we are getting to the crux of the problem. I have no past experience in this area and certainly believed the extraction of the data from the CD itself was a lot better than you are indicating. However I had already hinted at this being a possible cause of sound deterioration by my reference:

Quote:
An inability to read the disc data correctly
So it would seem as you suggest that there are sizable issues right at the data acquisition stage rather than the data processing stage. This may well be one of the prime contributors to the differences I have experienced in otherwise similar systems and answers a lot of the questions I had.

Quote:
Speaking of power regulation, this is an extremely important part of any audio device. Every IC in a CDP has an influence on the quality of the power rails. In low class equipment, you have only the minimum number of power regulators (if any) that is necessary for functioning. In a high class component, you can have separate transformers, rectifiers, caps and voltage regulators for every major part of the CDP to minimise a cross influence. That is the difference between a Naim CDI and a Philips CD460 for instance.

Another main influence in the digital part of a CDP is jitter. I am not going to elaborate much about that as there is so much written about it elsewhere. But to minimise jitter, the quality of the clock, the layout of the circuit boards and many other aspects are important – therefore all the things that YOU think to be of no importance as you are still dealing with 1s and 0s (which, to be precise, you do not).
I would whole heartedly agree with you on the section regarding power regulation. However, on the jitter issue, yes this will obviously affect the end quality of the sound but theory seems to dictate that it only matters around the DAC as the data is quantitised on arrival and then converted and the accuracy of the clock at this stage is of primary importance. Jitter anywhere else is neither here nor there unless the jitter is so bad the system stands no chance of working anyway. Hence my statement:

Quote:
The analogue stage design and or the quality of the components determining the DACs ability to do the D/A conversion
In essence I think we are in agreement on most points!

Quote:
I would advise you to have a look at some other interesting threads at diyAudio before doing mods on your CDPs so that you have an understanding of what you are doing.
That’s good advice and I will follow that.

Many thanks again for your input I have found it helpful.

Best Regards,

Ian
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