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Upgrading Arcam Alpha CD5+ Analogue Board
Upgrading Arcam Alpha CD5+ Analogue Board
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Old 4th April 2005, 03:35 PM   #11
filholder is offline filholder  United Kingdom
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I have heard that the best way to make this board sound better in to to a do a zero oversampling mod. which can apparently can be done by rewiring rather than needing anything extra.

Has anybody done this mod and could they describe how it is done.
I have found some very basic descriptions on tweakers asylum but it was way to general for me to fully understand
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Old 5th April 2005, 06:47 AM   #12
tubenut is online now tubenut  South Africa
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Easy peasy....

Isolate pins 1, 2 and 3 of the DAC chip TDA1541A from the pcb by either breaking tracks (yuk) or some other means...The DAC pins 1,2 and 3 must not be connected to anything... On my Mission CDP I have removed the IC, fitted a socket from which I removed pins 1,2 and 3 so the IC pins float above the pcb. Now solder wires linking the IC pins 1,2 and 3 of the TDA1541 to pins 1, 2 and 3 of the SAA7220 filter chip. Non os mod done.....
There is only one problem with this.. You have now defeated the muting function of the SAA7220 as you have bi passed it. To restore mute, a link needs to be made between the SAA7220 and the decoder chip. On the Alpha 5 I doubt this is a SAA7210 but something else and I do not know what pins to link to restore mute.
It will work without but you will hear sections of disk being played while starting play and skipping as well as pausing the player. It is just odd sounding but I believe harmless.

Others may well know the decoder chip type and the required pin links to restore muting after non o/s.
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Old 5th April 2005, 06:53 AM   #13
tubenut is online now tubenut  South Africa
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Forgot to say, if you fit a socket in place of the DAC chip but do not remove pins and into that socket you plug another socket but this one with the pins 1,2 and 3 removed you will be able to reverse the change without much soldering by removing the doctored socket and plugging the DAC back in. this may allow for faster AB comparisons 2. Once you know what you like minimise the use of sockets though!!!
On my mission I use a different arrangement, harder to explain but I effectively have made it so that I have a 3 wire fly lead that plugs the DAC pins to their original connections or to the SAA7220 pins 1,2 and 3 allowing very quick AB of non O/S vs 4 x os....
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Old 5th April 2005, 12:09 PM   #14
filholder is offline filholder  United Kingdom
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Cheers tubenut,

The chips on the analogue board are saa7220p/b obviously the tda1541a and then there are two small chips called 74hcu04n and 74hc175n. Apart from that just the opamps.

If anyone else know what pins it would be really helpful.

Thanks

Phil
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Old 5th April 2005, 01:23 PM   #15
juancho is offline juancho  United Kingdom
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Hiya,
I use the following method with the Arcam Alpha5+ and it sounds great! There are no glitches with muting etc done this way.


If you have the 1541 A then in the mode it is used pin 4 is not required - connect it to the adjacent ground pad ground (i think it's pin 5 from memory)


Non over sampling:
lift or cut pins 1,2,3,15,16,18 of SAA7220 from the board .Join the
vacated holes with wire thus: 1 to 18 2 to 16 3 to 15.

Hope that helps
David
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Old 5th April 2005, 10:55 PM   #16
tubenut is online now tubenut  South Africa
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Quote:
If you have the 1541 A then in the mode it is used pin 4 is not required - connect it to the adjacent ground pad ground (i think it's pin 5 from memory)
What is the role of pin 4? Does it have anything to do with muting? If not I can only assume the muting is done on the decoder chip, not the filter as standard.

Juancho's non o/s method seem elegant and can also be done with a stack of two or even 3 IC sockets for quick AB. Remove the pins that need "lifting" and plug the chip into this socket (1). use another socket (2) and bridge the pins on this socket with wire links at the bottom of the socket. Fit a socket (3) to the PCB. using all 3 sockets is non o/s and if you remove 1 &2 and plug chip into socket 3 for std 4 x o/s....
Again, once you know what you like use as few sockets as possible.
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Old 5th April 2005, 11:57 PM   #17
filholder is offline filholder  United Kingdom
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Thanks for the help guys. So all work is done on the SAA7220 apart from one line on the tda1541.

Just so we are all clear one what to cut can you possibly look at these pdfs of the parts to double check which lines to dissconnect.

http://www.alldatasheet.com/datashee...S/SAA7220.html

http://www.alldatasheet.com/datashee.../TDA1541A.html

I really dont what to trash the player for no good reason!!

Well i guess the search for higher fidelity is a good reason but you know what I mean

Fil

Cheers for all the help guys
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Old 7th April 2005, 09:01 AM   #18
juancho is offline juancho  United Kingdom
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Hiya,
If you can hang on a little bit I will take the board out of my Arcam and double-check for you.

One thing which probably won't bother you as you want to use the built in DAC is that you lose the digital out when converting to NOS.

I'm afraid I could never get the datasheets for the saa7220 or TDA 1541 so did this mod 'blind' but the person who told me it is very knowledgeable /reliable.
Cheers
David
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Old 7th April 2005, 09:23 AM   #19
tubenut is online now tubenut  South Africa
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Default I must check SPDIF

I think it is still active when using the isolate pins 1 23 of DAC and linking 123 of filter to it.......

Juancho method may be different. Perhaps it illiminated the SAA7220 completely, which is where the SPDIF out comes from...
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Old 7th April 2005, 04:00 PM   #20
juancho is offline juancho  United Kingdom
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Hi Guys,
I confirm the changes I suggested previously. There is one additional better clock mod that I use. That is to cut the track between Pins 2 and 4 of the TDA1541a chip.

Pin 4 as you'll recall from my previous e mail is now earthed /connected to Pin 5.

Cheers
David
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