Hi,
TDA1545A is in my Philips cd723.
Any recommendations for the vref cap size or make?
Also the vref calc as attached picture:-
10000/(10000+15000) * 5V = 2V vref
I want to try the capacitor route before trying JohnW's external vref generator(adjusted) here :- http://www.diyaudio.com/forums/showthread.php?postid=300396#post300396
Regards,
Ashley.
TDA1545A is in my Philips cd723.
Any recommendations for the vref cap size or make?
Also the vref calc as attached picture:-
10000/(10000+15000) * 5V = 2V vref
I want to try the capacitor route before trying JohnW's external vref generator(adjusted) here :- http://www.diyaudio.com/forums/showthread.php?postid=300396#post300396
Regards,
Ashley.
Attachments
Konnichiwa,
The Vref input fundamentally drives both full scale current and offset current in the TDA1545, when using the original circuit it also becomes an input signal for the output stage, where it is at least passed through at unity gain.
You have de-factor around 7.5KOhm Resistance in the circuit to form a lowpass for supply noise.
You need a capacitor with VERY LOW ESR (as ESR limits the maximum attenuation) and good high frequency behaviour, which because of the crappy supply in this player also needs to be VERY LARGE in value to make sure you knock out at least 60db @ 100Hz, in other words the RC filter needs a turnover of 0.1Hz.
From that we get 220uF as minimum, I would say make it a Sanyo Os-Con, 6.3V while you are at it. When using traditional electrolytic capacitors something closer to 2,200uF/6.3V will likely be needed.
Finally, if you really want to get decent sound quality from the CD-723 consider re-building the entire powersupply as follows:
1) New well build regulated supply for analogue stage (+/-12...15V if using Op-Amp's).
2) Completely galvanically seperate supply for the DAC, given that the DAC has crappy PSRR on both Vref and Vdd pin you cannot do "too much" here.
3) Completely galvanically seperate supply for the Clock, the CD-723 definitly needs a seperate clock, Guido Tent's is afforable and works fine.
4) Leave the originally supply for the drive section in place, but beef it up.
5) Clean up the digital supply section (+5V) and use it to drive the transport logic only.
I found that LM6182 Op-Amp's make a superlative output stage, but whatch the peculiarities of that Op-Amp and give it well decoupled (RF!!!) supply and remove the reactive components from the feedback loop, 100 Ohm build out resistor in the output and a suitable filter capacitor to replace the filtering in the NFB loop complete this.
Sayonara
ash_dac said:
The Vref input fundamentally drives both full scale current and offset current in the TDA1545, when using the original circuit it also becomes an input signal for the output stage, where it is at least passed through at unity gain.
You have de-factor around 7.5KOhm Resistance in the circuit to form a lowpass for supply noise.
You need a capacitor with VERY LOW ESR (as ESR limits the maximum attenuation) and good high frequency behaviour, which because of the crappy supply in this player also needs to be VERY LARGE in value to make sure you knock out at least 60db @ 100Hz, in other words the RC filter needs a turnover of 0.1Hz.
From that we get 220uF as minimum, I would say make it a Sanyo Os-Con, 6.3V while you are at it. When using traditional electrolytic capacitors something closer to 2,200uF/6.3V will likely be needed.
Finally, if you really want to get decent sound quality from the CD-723 consider re-building the entire powersupply as follows:
1) New well build regulated supply for analogue stage (+/-12...15V if using Op-Amp's).
2) Completely galvanically seperate supply for the DAC, given that the DAC has crappy PSRR on both Vref and Vdd pin you cannot do "too much" here.
3) Completely galvanically seperate supply for the Clock, the CD-723 definitly needs a seperate clock, Guido Tent's is afforable and works fine.
4) Leave the originally supply for the drive section in place, but beef it up.
5) Clean up the digital supply section (+5V) and use it to drive the transport logic only.
I found that LM6182 Op-Amp's make a superlative output stage, but whatch the peculiarities of that Op-Amp and give it well decoupled (RF!!!) supply and remove the reactive components from the feedback loop, 100 Ohm build out resistor in the output and a suitable filter capacitor to replace the filtering in the NFB loop complete this.
Sayonara
Konnichiwa,
Well, the full scale current of the TDA1545 AND the bias (offset) current are both directly proportinal to Vref, with around 10db gain IIRC, so in effect -10db PSRR on Vref.
The PSRR on the supply line of the TDA1545 is listed as 30db.
In other words, unless both Vref and Vdd are squeaky clean, Vref to 18Bit levels and Vdd to 12bit levels the TDA1545, referenced to the output the chips performance will degrade, potentially very seriously.
Sayonara
eVITAERC said:Very informative post Kuei!
I have no idea that the PSRR of TDA1545 is THAT crappy
Well, the full scale current of the TDA1545 AND the bias (offset) current are both directly proportinal to Vref, with around 10db gain IIRC, so in effect -10db PSRR on Vref.
The PSRR on the supply line of the TDA1545 is listed as 30db.
In other words, unless both Vref and Vdd are squeaky clean, Vref to 18Bit levels and Vdd to 12bit levels the TDA1545, referenced to the output the chips performance will degrade, potentially very seriously.
Sayonara
Konnichiwa,
Well, the only DAC's that APPEAR to have have really good PSRR are differential, you can work out how good they REALLY are, as of course the noise only becomes common mode and is not actually removed untill you mix the two polarities together!
Generally "fancy" capacitors (assuming that fancy means low ESR, low ESL and low Distortion) and carefully designed supplies around DAC's do give material improvements, no matter what they are.
Sayonara
eVITAERC said:
Well, the only DAC's that APPEAR to have have really good PSRR are differential, you can work out how good they REALLY are, as of course the noise only becomes common mode and is not actually removed untill you mix the two polarities together!
Generally "fancy" capacitors (assuming that fancy means low ESR, low ESL and low Distortion) and carefully designed supplies around DAC's do give material improvements, no matter what they are.
Sayonara
Konnichiwa,
Fine, then get a service manual for mthe players schematics and build the supplies as instructed, plus upgrade the analog stage and clock.
No, in order to hear what the player is capable of you must sort out the powersupplies TOGETHER WITH OTHER ITEMS, that way it makes sense.
If you have to ask, please apply yourself first some basic works on electronics, at the core powersupplies are rather simple (really good ones are a bit more involved).
Sayonara
jzono1 said:
Fine, then get a service manual for mthe players schematics and build the supplies as instructed, plus upgrade the analog stage and clock.
jzono1 said:
No, in order to hear what the player is capable of you must sort out the powersupplies TOGETHER WITH OTHER ITEMS, that way it makes sense.
jzono1 said:
If you have to ask, please apply yourself first some basic works on electronics, at the core powersupplies are rather simple (really good ones are a bit more involved).
Sayonara
I have a basic understanding of electronics. I'm able to read fancy schematics and see how they are done when completed. But, the way you put it up there was too abstract for me to understand. I read on some other page what that involves, and now I understand more. There I also saw other improvements, ofcoarse I'm not so dumb that i upgrade just the powersupply. I'm considering that tube output stage I saw somewhere. The powersupply is the part I'm most uncertain about. Same thing with the amp I'm going to build, I was uncertain regarding the power supply there too.
Sorry if I was a bit dumb when posting the previous posts. I don't think clearly so late at nigth, but I just had to post, when I discovered that my new cd player is suited for modification. I'll order a service manual, and make sure I know enough before actually doing something. This will be a long term project, I recon.
Most stuff works out with enough time and research.
Sorry if I was a bit dumb when posting the previous posts. I don't think clearly so late at nigth, but I just had to post, when I discovered that my new cd player is suited for modification. I'll order a service manual, and make sure I know enough before actually doing something. This will be a long term project, I recon.
Most stuff works out with enough time and research.
Moin,
try this:
http://robinetron.free.fr/cd723/cd723.html
and read a little bit here:
http://perso.wanadoo.fr/pol.bct/exemples/721-723.htm
http://ndaviden.club.fr/723/723.html
Carsten
try this:
http://robinetron.free.fr/cd723/cd723.html
and read a little bit here:
http://perso.wanadoo.fr/pol.bct/exemples/721-723.htm
http://ndaviden.club.fr/723/723.html
Carsten
Hi,
For the vref capacitor I have some rubycon mbz low esr 1000uf caps lying around so I modelled the circuit in SwitcherCad, and it "modelled" ok so may try this cap out today or tomorrow.
Thanks for the pointers towards upgrading the power supply. I thought I misread the diagrams at first (+10/-10V supply for opamps was unregulated) but nope it's all there!
Oh dear
Kind regards,
Ashley.
For the vref capacitor I have some rubycon mbz low esr 1000uf caps lying around so I modelled the circuit in SwitcherCad, and it "modelled" ok so may try this cap out today or tomorrow.
Thanks for the pointers towards upgrading the power supply. I thought I misread the diagrams at first (+10/-10V supply for opamps was unregulated) but nope it's all there!
Oh dear
Kind regards,
Ashley.
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