carlosfm said:
At least on my system I don't think a second buffer is needed besides I preffer the simplest circuit possible. Do have BUF634 at hand but I don't think I'll use them for this application.
15mA for a CDP output dose'nt seem to low. I think the DIP package will have the same specs.
DIP version is out of stock at Digi Key. I also heard comments that adding BUF634 degrades sound somewhat.
As to the clock, I would try Elso's clock first, as it comes cheap if you build it yourself. I stil didn't try it though.
As to the clock, I would try Elso's clock first, as it comes cheap if you build it yourself. I stil didn't try it though.
Peter Daniel said:
Was thinking on the same lines, I have requested Elso allready for his latest implementation schematics but haven't received them yet. And yes I love to DIY since I get the most fun plus I always learn something on the process. (hopfully!)
Rudolf,rbroer said:Pedja,
AD844 won't do as common base I/V since the bias currents for the AD844 input stage are way below the fullscale current of your dac.
This rather applies to AD846 which saturates at 2mA. AD844 is claimed to work with 5mA continuous (10mA transient) inverting input current (MicroCap shows clipping at 7.3mA).
Pedja
Koinichiwa,
I really like that one. I have allowed myself to make this Black/Grey on White, I hope you don't mind....
Now some might say I only like this circuit because I suggested it, but no, It has a certain zen simplicity to it, despite the aparent complexity.
Methinks I'll have to build one of these using a TDA1545 in SMD as DAC and using a 12V Battery to drive the whole shooting match> I guess I need to get back to that friend of mine who said "SMD prototype board, no worries at all". I'll make him regret his rash words yet. going SMD on all but the big Os-Cons (at least that's what I'd use) should make a surpremely small DAC Board, even including a CS8412/14 and TL431 Shunts for all Supply Voltages....
Anyway, great stuff, love it.
Sayonara
apassgear said:
I really like that one. I have allowed myself to make this Black/Grey on White, I hope you don't mind....
Now some might say I only like this circuit because I suggested it, but no, It has a certain zen simplicity to it, despite the aparent complexity.
Methinks I'll have to build one of these using a TDA1545 in SMD as DAC and using a 12V Battery to drive the whole shooting match> I guess I need to get back to that friend of mine who said "SMD prototype board, no worries at all". I'll make him regret his rash words yet. going SMD on all but the big Os-Cons (at least that's what I'd use) should make a surpremely small DAC Board, even including a CS8412/14 and TL431 Shunts for all Supply Voltages....
Anyway, great stuff, love it.
Sayonara
Attachments
AD844...old news.....
LC Audio used this circuit back in the 90´s.
Both in the upgraded version of their first preamp(with built-in DAC) called AIR and later in their first DAC called ZAPDAC ( from what I remember they used the AD844 as I-V stage & BUF634 as output buffer).
Nicke
Pedja said:
LC Audio used this circuit back in the 90´s.
Both in the upgraded version of their first preamp(with built-in DAC) called AIR and later in their first DAC called ZAPDAC ( from what I remember they used the AD844 as I-V stage & BUF634 as output buffer).
Nicke
Kuei Yang Wang said:
You ought to, be prepared for some surprises. I would love to hear your coments on this one.
Time providing, next week I'll prepare a new schematic, one that can be read and printed and post it at the thread.
I'm delighted with my new CDP, so much that I think updating the clock and adding a better supply to the DAC will not bring much improvement.
Thanks for sharing and for your help.
OPA660 Circuit
Kuei,
In a previous post where you first described your circuit, which is now shown in its complete schematic form, you made the following recommendations for inclusion of a low-pass filter to eliminate the higher frequency duplicate images.
Excerpt quote:
****************************************************
This has no lowpass, I would recommend a 62nF capacitor to ground on the output, this forms with the 51 ohm build out resistor a 50KHz 1st order lowpass, sufficient if the DAC is operated with 4 Times oversampling or more. You could make the Filter 2nd Order by paralleling the I/V resistor with a suitable value capacitor.
For a 50KHz 2nd Order lowpass we use a 33nF capacitor on the output and a 1nF capacitor in parallel to our 1k5 I/V conversion resistor.
****************************************************
In the schematic, I do not see a capacitor to ground with the 47 Ohm build out resistor to form the other filter pole. Was this omitted by accident or found to be not required? I was preparing to build the circuit based on your original verbal design recommendations until I saw this recent schematic.
Could you please advise?
Schnitzer
Kuei,
In a previous post where you first described your circuit, which is now shown in its complete schematic form, you made the following recommendations for inclusion of a low-pass filter to eliminate the higher frequency duplicate images.
Excerpt quote:
****************************************************
This has no lowpass, I would recommend a 62nF capacitor to ground on the output, this forms with the 51 ohm build out resistor a 50KHz 1st order lowpass, sufficient if the DAC is operated with 4 Times oversampling or more. You could make the Filter 2nd Order by paralleling the I/V resistor with a suitable value capacitor.
For a 50KHz 2nd Order lowpass we use a 33nF capacitor on the output and a 1nF capacitor in parallel to our 1k5 I/V conversion resistor.
****************************************************
In the schematic, I do not see a capacitor to ground with the 47 Ohm build out resistor to form the other filter pole. Was this omitted by accident or found to be not required? I was preparing to build the circuit based on your original verbal design recommendations until I saw this recent schematic.
Could you please advise?
Schnitzer
That the -4mA going out from TDA1541 should be accepted by AD844 without a problems.apassgear said:
One notice: regarding the correction of the DAC’s output current, AD844 would seemingly work better with real (+2m) current source, than that I drawn (5V voltage source and 2.5k resistor).
Pedja
Re: OPA660 Circuit
Koinichiwa,
Well. First, the circuit, while inspired by my lunatic ravings is still fully designed and implementd by apassgear and I'm terribly chuffed that he gave me credit.
I am not certain if apassgears CDP retains oversampling or not. THe key I think is that adding lowpass filters and such is amtter of choice. If I where to make a commercial product I'd probably make both the suggested output cap and the cap in aparallel with the I/V Resistor switchable, simply because some systems will sound best with no filtering at all, while others will need loads...
What I did was to suggest several possible approaches that I have myslef employed in similar situations. I do belive in "pick and choose". Use of my ideas, writing philosophy and the like what suits you. I won't hold it against you if you like something I don't or dislike something I do....
Sayonara
Koinichiwa,
schnitzer said:
Well. First, the circuit, while inspired by my lunatic ravings is still fully designed and implementd by apassgear and I'm terribly chuffed that he gave me credit.
I am not certain if apassgears CDP retains oversampling or not. THe key I think is that adding lowpass filters and such is amtter of choice. If I where to make a commercial product I'd probably make both the suggested output cap and the cap in aparallel with the I/V Resistor switchable, simply because some systems will sound best with no filtering at all, while others will need loads...
What I did was to suggest several possible approaches that I have myslef employed in similar situations. I do belive in "pick and choose". Use of my ideas, writing philosophy and the like what suits you. I won't hold it against you if you like something I don't or dislike something I do....
Sayonara
Re: Re: OPA660 Circuit
Schnitzer
As you can see from my first post on this thread I'm still using a digital filter which I guess is a 4X oversampling. Though I might test a nonoversampling connection in the near future.
I have a gut feeling that this DF is better than a low pass filter at the analog stage, though I can't confirm.
As far as I know, correct me if I'm wrong, this is the first implementation of an I/V analog stage done with OPA660 so some precautions were taken to ensure that this implementation worked from the beggining and so it did.
For this reason I added a small cap, 1n, in // to the I/V resistor just to get rid of higher reflections, for what it might be worth. Since I would prefer the simplest circuit possible I may also get rid of this cap. But this has to be done with some foot on the ground to start tweaking.
Hope your implementation works as fine as mine, good luck!!!
Kuei Yang Wang said:
Schnitzer
As you can see from my first post on this thread I'm still using a digital filter which I guess is a 4X oversampling. Though I might test a nonoversampling connection in the near future.
I have a gut feeling that this DF is better than a low pass filter at the analog stage, though I can't confirm.
As far as I know, correct me if I'm wrong, this is the first implementation of an I/V analog stage done with OPA660 so some precautions were taken to ensure that this implementation worked from the beggining and so it did.
For this reason I added a small cap, 1n, in // to the I/V resistor just to get rid of higher reflections, for what it might be worth. Since I would prefer the simplest circuit possible I may also get rid of this cap. But this has to be done with some foot on the ground to start tweaking.
Hope your implementation works as fine as mine, good luck!!!
Kuei,
One question, a little off topic but reffering to this CDP.
I saw on the schematic of the Adagio posted on your web site that you use a reverse polarity for the additional cap on the MSB, a 15u Os-Con.
About a month ago I added a lytic on this position (3.3u, 50V Panasonic HFS) small enough to fit the tight space. Since I dont have access to the bottom of the main PCB when electricaly connected I could not check the polarity, even more, I'm not sure if this can be verified on a direct measurment.
For this reason I installed the cap with normal polarity and have not experianced problems so far.
I would like to have your confirmation that the reverse polarity is the correct way of installing these caps when using lytics.
One question, a little off topic but reffering to this CDP.
I saw on the schematic of the Adagio posted on your web site that you use a reverse polarity for the additional cap on the MSB, a 15u Os-Con.
About a month ago I added a lytic on this position (3.3u, 50V Panasonic HFS) small enough to fit the tight space. Since I dont have access to the bottom of the main PCB when electricaly connected I could not check the polarity, even more, I'm not sure if this can be verified on a direct measurment.
For this reason I installed the cap with normal polarity and have not experianced problems so far.
I would like to have your confirmation that the reverse polarity is the correct way of installing these caps when using lytics.
Peter Daniel said:
Peter,
As usual I think you are right. I'll wait and see what's involved on implementing this clock. I have yet to receive the schematic.
🙂 🙂 🙂
Koinichiwa,
Well, the schematic was drawn by a friend and contains some errors. However, the Tilter pin's of the TDA1541 are all negative in Voltage (I measured), so the Cap needs to go positive to ground. I used 3u3 BTW.
Sayonara
apassgear said:
Well, the schematic was drawn by a friend and contains some errors. However, the Tilter pin's of the TDA1541 are all negative in Voltage (I measured), so the Cap needs to go positive to ground. I used 3u3 BTW.
Sayonara
apassgear said:
Hi Tony,
Maybe you mean:
" I'm delighted with my new CDP, so much that I do not need the improvement brought by updating the clock and adding a better supply to the DAC "
best regards
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