Hello Everybody
Building a completely standard TDA1541A kit, very boring. However I've seemingly stumbled across an anomaly. Really hope this isn't discussed to death anywhere else, but I can't see it.
So, the TDA1541A has Cosc between pins 16 and 17 Datasheet clearly indicated that a 470pF cap should be placed between them.
So why do Philips and Marantz use a 680pF in what seems to be everything? (Polyester I think)
Is this a case of doesn't matter? I'd have thought that the oscillator might be important? seems it was important enough to warrant the A suffix
Any pointers would be appreciated.
Andy
Building a completely standard TDA1541A kit, very boring. However I've seemingly stumbled across an anomaly. Really hope this isn't discussed to death anywhere else, but I can't see it.
So, the TDA1541A has Cosc between pins 16 and 17 Datasheet clearly indicated that a 470pF cap should be placed between them.
So why do Philips and Marantz use a 680pF in what seems to be everything? (Polyester I think)
Is this a case of doesn't matter? I'd have thought that the oscillator might be important? seems it was important enough to warrant the A suffix
Any pointers would be appreciated.
Andy
and for the TDA1540 as well !
Notice the 14 dem caps are often not the same values (look at TDA1540 spec datasheet pdf) in their designs.
470 pF works fine with all 100 nF 14 DEM caps (Pedja Rogic at Audial) enough for 96 k Hz reccordings (192 upsampling ?)
100 pF works fine with all 330 nF 14 DEM caps (John from ECdesigns)
Both pins 16/17 work finer with a 6k8 resitor shunted to pin 15 (ECdesigns tip)
Look at all the inputs in the long thread from John about the TDA1541 and the explanation of clock lock and the DEM cap in relation to the Fhz and the values of the 14 DEM caps around !
Notice the 14 dem caps are often not the same values (look at TDA1540 spec datasheet pdf) in their designs.
470 pF works fine with all 100 nF 14 DEM caps (Pedja Rogic at Audial) enough for 96 k Hz reccordings (192 upsampling ?)
100 pF works fine with all 330 nF 14 DEM caps (John from ECdesigns)
Both pins 16/17 work finer with a 6k8 resitor shunted to pin 15 (ECdesigns tip)
Look at all the inputs in the long thread from John about the TDA1541 and the explanation of clock lock and the DEM cap in relation to the Fhz and the values of the 14 DEM caps around !
Thanks Eldam
I know there is a wealth of info on this site on the TDA1541, is it too cheeky to ask for a pointer to the thread? I *know* I have seen something about it in the past.
Just confusing to see two c values (when all dem caps all at 100pf) datasheet says one thing - Philips practice another. I'm leaning towards 'practice' rather than data but will keep reading.
Thanks again - Appreciate it
Andy
I know there is a wealth of info on this site on the TDA1541, is it too cheeky to ask for a pointer to the thread? I *know* I have seen something about it in the past.
Just confusing to see two c values (when all dem caps all at 100pf) datasheet says one thing - Philips practice another. I'm leaning towards 'practice' rather than data but will keep reading.
Thanks again - Appreciate it
Andy
Here is the huge thread ! http://www.diyaudio.com/forums/digi...e-nos-dac-using-tda1541a-520.html#post4045242
You can certainly beginn at the half of the thread.
You can look for also inputs by Thorsten Loesch and Pedja Rogic here and on the web.
There are also a lot of diyers who tried a lot of shematics by some brands around famous cd players with tda 1541-A.
You talk about the TDA1541, this one have the DEM timing cap embeded and "sounds" different. This is the latest TDA1541-A which needs a timing cap. In the huge thread there are some datas about the clocking frequencys and values about this cap to lock the signal. Even some tried external timing technic : P Rogic (Audial), John from ECdesigns (the given link gives you all the explanation about your question, but sorry no direct links to the posts, I used the search function).
regards
You can certainly beginn at the half of the thread.
You can look for also inputs by Thorsten Loesch and Pedja Rogic here and on the web.
There are also a lot of diyers who tried a lot of shematics by some brands around famous cd players with tda 1541-A.
You talk about the TDA1541, this one have the DEM timing cap embeded and "sounds" different. This is the latest TDA1541-A which needs a timing cap. In the huge thread there are some datas about the clocking frequencys and values about this cap to lock the signal. Even some tried external timing technic : P Rogic (Audial), John from ECdesigns (the given link gives you all the explanation about your question, but sorry no direct links to the posts, I used the search function).
regards
Hi Andy,
The exact value of the DEM cap isn't too critical and most players use a value somewhere in the range of 470pF to 680pF. In my own modded CD player I settled on 560pF.
Some builders advocate using a lower value in the range of 120pF. I tried this and found the treble was perhaps slightly cleaner but that the quality of the low frequencies suffered and this is supported by the datasheet.
For the bit decoupling caps 100nF is the datasheet value but many people find a higher value sounds better, especially on the MSB pins. I use 1uF MKS on the MSB's followed by 220nF on the others. The quality of the caps used is very important here and another excellent option is surface mount PPS film.
The exact value of the DEM cap isn't too critical and most players use a value somewhere in the range of 470pF to 680pF. In my own modded CD player I settled on 560pF.
Some builders advocate using a lower value in the range of 120pF. I tried this and found the treble was perhaps slightly cleaner but that the quality of the low frequencies suffered and this is supported by the datasheet.
For the bit decoupling caps 100nF is the datasheet value but many people find a higher value sounds better, especially on the MSB pins. I use 1uF MKS on the MSB's followed by 220nF on the others. The quality of the caps used is very important here and another excellent option is surface mount PPS film.
You can take PPS film caps as well for the 14 DEM caps, but as some noticed already : values are not always precise enough and it can drop after soldering (very fragile) !
You can buy more than 14 and sort them out with capacimeter or put the weakest values at the end of the DEM caps . According to me the 2.5 mm pitch Wimas are a good choice to avoid that.
An ultimate choice could be smt silver mica, but I believe it doesn't exist with such high value 0.1 uf is ! or in classic body cap with high space leads (so not so good inductance).
You may avoid ceramic for DEM caps, experienced diyers noticed bad results at ears. Here BG HQ will be a better choice, but not sure it is better than PPS or MKS Wima 2.5 mm pitch (at the price of the BG HQ I never tried myself , but science confirms what Mike P is writting!)
You can buy more than 14 and sort them out with capacimeter or put the weakest values at the end of the DEM caps . According to me the 2.5 mm pitch Wimas are a good choice to avoid that.
An ultimate choice could be smt silver mica, but I believe it doesn't exist with such high value 0.1 uf is ! or in classic body cap with high space leads (so not so good inductance).
You may avoid ceramic for DEM caps, experienced diyers noticed bad results at ears. Here BG HQ will be a better choice, but not sure it is better than PPS or MKS Wima 2.5 mm pitch (at the price of the BG HQ I never tried myself , but science confirms what Mike P is writting!)
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I found that the DEM frequency starts slow and then gets faster as the chip warms up. It takes a good 3 minutes to stabilise but not as long as 20 minutes.
The TDA1541 datasheet shows that distortion increases quite dramatically when the DEM frequency goes above about 250kHz so it's strange that some people like to use a very low value for the DEM cap like 180pF. My preference is to use a DEM cap value in the 470 - 680pF range.
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