Why not just use an external DAC?
I just completed a AK4396 DAC kit from eBay. I added a decent PSU, better voltage regulators, uprated op amps & capacitors, and got outstanding results. You can tweak things without being restricted by the build of your CD player and take advantage of any other digital sources you might have.
I just completed a AK4396 DAC kit from eBay. I added a decent PSU, better voltage regulators, uprated op amps & capacitors, and got outstanding results. You can tweak things without being restricted by the build of your CD player and take advantage of any other digital sources you might have.
What you would need to do is to either physically, or operationally bypass the oversampling digital filter unit. The old (out-of-production) fully-multibit DAC chips typically had the digital filter located on a seperate dedicated filter chip (such as, the DF1704) which then made it possible to contemplate a physical bypass of the filter unit. However, for a long time now, DAC chips usually have had the digital filter unit integrated with the D/A unit on a single monolithic IC. This most often meant that the filter unit could only be bypassed via software control, making DIY bypass likely impractical. A few chips do feature hardware pin-programmable control, which makes DIY bypass perhaps more practical, but maybe not by much. Either approach assumes, of course, that bypassing of the internal filter is a mode supported by the DAC chip, which it may not be, depending on the chip.
There are other potential show stopping obstacles as well. For example, the in-production PCM1794A chip permits hardware pin-programmable bypassing of it's internal filter. However, two PCM1794A chips are then required as this also forces the chip in to mono mode requiring independent left and right channel data stream signals, and so will not directly accept an multiplexed left/right I2S data signal. In short, this endeavor is likely to require much more planning and incur much more patience/frustration than you presently suspect.
P.S. - Most of the older DAC chips not featuring an integrated filter unit still required the multiplexed I2S data stream to be de-multiplxed in to seperate left and right streams by the filter chip prior to input. So, where a physical bypass of an dedicated filter chip might otherwise be practical the filter chip is likely still required for data stream de-mux'ing and correct clock signal frequency division. The only exception of which I'm aware is among the old Philips TDA family DACs that while not featuring in internal filter will accept a multiplexed I2S input signal.
There are other potential show stopping obstacles as well. For example, the in-production PCM1794A chip permits hardware pin-programmable bypassing of it's internal filter. However, two PCM1794A chips are then required as this also forces the chip in to mono mode requiring independent left and right channel data stream signals, and so will not directly accept an multiplexed left/right I2S data signal. In short, this endeavor is likely to require much more planning and incur much more patience/frustration than you presently suspect.
P.S. - Most of the older DAC chips not featuring an integrated filter unit still required the multiplexed I2S data stream to be de-multiplxed in to seperate left and right streams by the filter chip prior to input. So, where a physical bypass of an dedicated filter chip might otherwise be practical the filter chip is likely still required for data stream de-mux'ing and correct clock signal frequency division. The only exception of which I'm aware is among the old Philips TDA family DACs that while not featuring in internal filter will accept a multiplexed I2S input signal.
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thanks for that Ken, but its abit over my head, ie. all the intricasies of a DAC. Im in the novice stage now and becoming more befuddled by the day. Learning.
Take fair warning, learning how to design your own DAC, or to modify an existing DAC will not be a trivial undertaking. As an alternative, DAC kits, or an pre-engineered DIY design offer an alternative very likely to produce a more successful result for a novice. Also, some chip vendors offer what are nearly all-in-one IC devices which can be utilized without a great deal of design expertise.
If you're determined to design something for yourself, you'll first need to learn about electronics, from basic to advanced including analog and digital circuits. That alone could consume one to two years of focused study. Then, you'll need to study the specific application domain of digital-to-analog conversion. This domain not only involves digital circuits, but also Digital Signal Processing, high-speed analog cicuits, low-noise and low distortion analog circuits, analog filter circuits, low phase-noise oscillator circuits, impedance matched high speed line interfaces and more. All of those disciplines of study are why many of us find designing DAC design to be a particularly intriguing and satisfying DIY endevor.
No the AK4396 is 128 time oversampling
I put a lot of time and effort into building up a Kit, with various mods but it sounds far better than my Arcam CD72 player, which I had also spent a lot of time modifying.
I spent many weeks of spare time in the 'Room of Doom' building the DAC, but the family are now really enjoying the music!
The easiest is to defeat the oversampling in an old Philips/Marantz CD-player that has SAA7220B/P and TDA1541A inside. It is basically cutting some traces and wire jumping indeed. But then you might want to remove the oversampling chip altogether and install a better quality master clock. Then a better power supply, then a better analog section, then... then...
I am not a EE just an ET, 30 yrs with Hewlett Packard Co. Freq./Time div, USN Electronics school, local com. college ET course, 2 yrs at Fairchild semi.
Just never was into audio dacs till now.
There are some non oversampling dac kits on eBay that you might want to check out provided you are still tuned in.
Search for TDA1541 and TDA1543 NOS DACs. There are also others based around some of the older Analog Devices AD186x series devices that might be of interest.
We don't close threads unless they are rules breaking.
Search for TDA1541 and TDA1543 NOS DACs. There are also others based around some of the older Analog Devices AD186x series devices that might be of interest.
We don't close threads unless they are rules breaking.
That's to bad, oversampling is interesting stuff.
Oversampling in DA converters is used so part of the reconstruction filter (an essential part of a DA converter, if you want your output to be the same as your input) can be made digitally, highly reducing the complexity and cost of the analogue part of the reconstruction filter.
most replays were negative.
interesting yes but implementation not so much.
no body says cut this trace make this jumper use this part.
just get this DAC on ebay.
Or a long tutorial on dacs and oversampling. good info all and reason I have dropped the subject. way too complicated to start cutting traces.
I appreciate all replies. I got the answers I needed. also from another forum.
Yes, if the external DAC does not do oversampling. Some do, some don't.oldhifiguy said:
Three reasons for this:
1. in most cases doing this by modding the CD player is non-trivial and different for each chip set, and not possible for many chip sets
2. non-oversampling guarantees that you don't recover the original signal which entered the ADC in the studio
3. you can simply achieve non-oversampling by using an external NOS DAC
That is because it is usually not that simple. When people started explaining it to you we could see your eyes glaze over.
apologies for sending the wrong mgs.
Not critisizing anyone. A very technical subject for sure.
I understand the non-simplicity of the task .
Understand that it can be done but..... definatly not simple.
Ext. dac can show effect.
AM going to do that.
thanks again for all your help and info.
PS: I think I was looking for a cookbook approach .
Not critisizing anyone. A very technical subject for sure.
I understand the non-simplicity of the task .
Understand that it can be done but..... definatly not simple.
Ext. dac can show effect.
AM going to do that.
thanks again for all your help and info.
PS: I think I was looking for a cookbook approach .
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There are no cookbooks in mixed-signal circuits, no matter how much some people believe in them.
You will find that there are three levels of understanding:
1. people who know enough to make the mod correctly and maintain audio performance
2. people who know they don't know enough to do it correctly, so don't do it
3. people who don't know enough to do it correctly, but do it anyway and don't notice the degradation in audio performance
I am a level 2 person. There are some level 1 people on here, and lots of level 3 people who think they are level 1.
You will find that there are three levels of understanding:
1. people who know enough to make the mod correctly and maintain audio performance
2. people who know they don't know enough to do it correctly, so don't do it
3. people who don't know enough to do it correctly, but do it anyway and don't notice the degradation in audio performance
I am a level 2 person. There are some level 1 people on here, and lots of level 3 people who think they are level 1.
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