Thanks.
I'm wondering if it's possible to run it into an LDR preamp, that I'm still finalising/ evaluating (thanks George and Rudi!!) I'm not sure it will drive that without a buffer. If George has a chance to try it that would be great feedback.
In my DAC (battery powered Audio Synthesis DSM using the PCM63k) I have changed the buffer to a OPA627 already and was considering the triple stacked ad844 as the I/V stage.
In my Sony DVP-Ns9100es (reclocked recapped etc (still trying to figure out what the "energy robbing devices" in the power supply are though??!!) I was/ am considering the Zapfilter, hence the question about other DACs
I'm wondering if it's possible to run it into an LDR preamp, that I'm still finalising/ evaluating (thanks George and Rudi!!) I'm not sure it will drive that without a buffer. If George has a chance to try it that would be great feedback.
In my DAC (battery powered Audio Synthesis DSM using the PCM63k) I have changed the buffer to a OPA627 already and was considering the triple stacked ad844 as the I/V stage.
In my Sony DVP-Ns9100es (reclocked recapped etc (still trying to figure out what the "energy robbing devices" in the power supply are though??!!) I was/ am considering the Zapfilter, hence the question about other DACs
Coupling cap
Well yes. I am doing that for a couple of reasons. I have my doubts that most 10 uF capacitors are of high enough quality. There is also a cost factor. A 0.1 uF film and foil is much lower in cost and physically smaller then a 10 uF. I used a Mundorf Supreme capacitor at one point and they are huge. As you pointed out there would be a low frequency roll off due to the 10 uF cap into most preamps. It seemed to me that the best solution was to do what some are doing with the AD844. A high input impedance buffer or opamp. The benefit there is a light load for the I/V. For buffers I like the BUF03 although it is quite obsolete. George has used the OPA627 with the PCM1704 so we know that works well.
TZ node resistor (I/V)
Hi canvas, The I/V resistor for standard CD output level with a TDA1541 (A) is 1.5K Ohms. I have used 2K and 2.2K Ohm there as well. You can parallel a number of AD844's. In doing this you average the currents in the current mirror portion of the chips. The AD844 is running fairly marginal current. The Voltage stays the same however across the I/V resistor. Think of it like putting a larger size battery across a resistor. The Voltage drop stays the same even though more current is available. This assumes the batteries are the same voltage. Might be a poor example however the best I can think of at the moment. Don't change the I/V resistor value with the triple stack. Hope that helps.
Depends on what the output impedance on Pedja's circuit is. This depends on it's own "TZ" resistor and in the circuit diagram it's 1.5kohm. http://www.diyaudio.com/forums/atta...using-ad844-i-v-pedja-rogic-ddnf-iv-stage.pdf
The Lightspeed is around 10kohm input impedance so if it's anything under say 1kohm output impedance (1:10 ratio all is fine).
But remember the input impedance of the poweramp has to be calculated into that as well. If it is also 10kohm then the buffer sees 5kohm total load, then it would be better if it's output impedance is then <500ohms to get a 1:10 ratio or better.
Cheers George
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Hi! Torchwood421,
Thanks. This is the answer I need to know. My DAC is a stacked AD1860 or PCM61PK (I had both) with same output current as TDA1541 (4ma). So, 1.5K it is. BTW, I think the current capability of TZ pin is the main reason Pedja turned to OPA861 or DDNF.
I just modified my DAC and put 4 stacked AD844s on each channel. The IV resistor remains the same (2.2K) without filter capacitor. I don't know what was the cause, but the sound is lack of detail and way too much bass. The LPF is ADA4627 followed by LME49990 buffer. Maybe I should use a breadboard and build the whole thing. The original LPF and buffer just don't work out for me.
Despite the excellent datashetn LM49900 is not liked as a buffer by many ! Maybe the PS and Layout around ?! But why not to use the excellent JG Buffer ? SHematic is free of right for personal use...
Some have also tried the DDNF of Pedja Rogic without JFet (only the BCs)... may work with the PCM1704 ?
What value of IV resistor do you use please with a DDNF stage for the PCM 1704 ?
regards
Some have also tried the DDNF of Pedja Rogic without JFet (only the BCs)... may work with the PCM1704 ?
What value of IV resistor do you use please with a DDNF stage for the PCM 1704 ?
regards
How do you solve the I/V if made on a different board than the dac chip's ?
DO we need a 1:10 impedance adaptation factor in current because the small amount of current ? How is it solved ? if the dac chip board has 50 ohms impedance, do we need the I/V next board to show a 500 ohms at his input ?
Torchwood, if not too expensive, get me in please for a board to match your 10 needed ! But I believe it could be more easy with a all in one board with uf-l input near the PCM1704 then the DDNF stage on the same PCB : 4 layers with the DGNG / AGND meeting point carrefully choosed ? But sorry totally off topic maybe !
DO we need a 1:10 impedance adaptation factor in current because the small amount of current ? How is it solved ? if the dac chip board has 50 ohms impedance, do we need the I/V next board to show a 500 ohms at his input ?
Torchwood, if not too expensive, get me in please for a board to match your 10 needed ! But I believe it could be more easy with a all in one board with uf-l input near the PCM1704 then the DDNF stage on the same PCB : 4 layers with the DGNG / AGND meeting point carrefully choosed ? But sorry totally off topic maybe !
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Hi Eldam,
I don't really have much time doing DIY work right now, so I chose the easy way. By replacing AD811 with stacked AD844s, only few more steps will make it work. I removed the feedback resistor and its capacitor. Solder the IV resistor on TZ pin to ground, then pass the output to the next stage.
Speaking of buffer, I've tried various OP amps including expensive 627BM, 2111BM and many kinds of audio grade OP. It turns out those ultra low noise types are better for my taste. I ended up with LT1028 and LME49990, but I found the latter has more bass, so it became my buffer. Thanks for the info on JG Buffer. I will look into it.
im trying to get ad844 to work with tda1387 dac.
i connect vref pin from the 1387 to 844's pin3. 1387's voltage remain around 0.9v from both l/r outputs and the vref pin.
the sound is fine but at the lowest level there is static, and when i play sine wave signal through the dac, (youtube clips) the higher freq signals have lower freq noise mixed in.
also, when the sound is played directly from pin 5, everything is fine! no static, no sine wave error, but when a buffer is added to the pin- various opamps in unity gain, jlh buffer, that's when the trouble starts. the dc offset from the pin5 is 2v, btw.
how can i get 1387 to work properly with the chip? abraxalito suggested current source but i'm wondering if there's a trick with the vref of 1387... or should i look into 1543? similar deal, i'm guessing.
thanks for your input in advance.
i connect vref pin from the 1387 to 844's pin3. 1387's voltage remain around 0.9v from both l/r outputs and the vref pin.
the sound is fine but at the lowest level there is static, and when i play sine wave signal through the dac, (youtube clips) the higher freq signals have lower freq noise mixed in.
also, when the sound is played directly from pin 5, everything is fine! no static, no sine wave error, but when a buffer is added to the pin- various opamps in unity gain, jlh buffer, that's when the trouble starts. the dc offset from the pin5 is 2v, btw.
how can i get 1387 to work properly with the chip? abraxalito suggested current source but i'm wondering if there's a trick with the vref of 1387... or should i look into 1543? similar deal, i'm guessing.
thanks for your input in advance.
I/V resistor
My plan is to use a 2.5K Ohm resistor with the DDNF as I did with a triple stack AD844 on my PCM1704 based DAC. George used 2.7K Ohm as I remember. The 1704 is well behaved as far as offset goes and should not be used with the 2 mA current source. The thing holding up my PCM1704 build with DDNF is the question of matching transistors. The ideal situation would be to direct couple the output of the DDNF. Maybe easier said then done!
Thanks for the input. All that reminds me a project by Painkiller fellow : http://www.diyaudio.com/forums/digital-source/254063-ad1862-pcb-layout-4.html#post3891624
AD1862 is outputting only 1 mA.
AD1862 is outputting only 1 mA.
Out board I/V
Hi Eldam, Not sure about your question. I take the small current off board on all of my builds. It is important to have a good ground return. The DDNF board is a common base, current mirror circuit. Pedja describes it better than I can. It's basic purpose is to increase the DAC's output current. In this situation it is all current up to the I/V resistor where it becomes a voltage. Pedja's circuit uses no feedback. Something I find important for natural sound. Nature doesn't use feedback! I have found it important to use a good buffer. This prevents loading down the I/V stage. It also solves loss of bass due to impedance considerations. My preamp's input is 50K Ohm. Not really high enough to directly drive with a DDNF board without a pronounced roll off in the bass. Redesign... At the moment I don't have those skills. Something that could be remedied in the future. I'd have to learn the circuit board software packages.
Yep, the same for me, a little bit lazy but I definitly have to learn a soft to design boards !
Well, question was just about outputing the weak current of the dac chip pcb towards the DDNF I/V pcb (in the case you design this last only) ! I asked myself if the break of ground is needing to make a 1:10 adapataion impedance to transport the weak curent with the less current loss as posible between the two pcbs ! Even with pcbs side to side... Well you answered : you put a bigger Gnd wire than the signal wire in your case.
I asked that because it's not RF where we use matched 50 ohms wires for the input I2S signal BETWEEN 2 PCBS for instance§ But as here it's current output... so I asked if this 2 mA could suffer of a breaked ground before the I/V conversion ? It was my simple thought as I have no technical background !
Well, question was just about outputing the weak current of the dac chip pcb towards the DDNF I/V pcb (in the case you design this last only) ! I asked myself if the break of ground is needing to make a 1:10 adapataion impedance to transport the weak curent with the less current loss as posible between the two pcbs ! Even with pcbs side to side... Well you answered : you put a bigger Gnd wire than the signal wire in your case.
I asked that because it's not RF where we use matched 50 ohms wires for the input I2S signal BETWEEN 2 PCBS for instance§ But as here it's current output... so I asked if this 2 mA could suffer of a breaked ground before the I/V conversion ? It was my simple thought as I have no technical background !
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Painkiller
Very interesting.... I was unaware of this thread. The PCM1704 is about 1 mA as well. Thanks for the link.
Transformer step up
I am aware that some have used transformers with high turns ratios to step up the output current on a TDA1541A DAC. Most used a tube stage following that. One advantage of a current out situation is that the impedance is quite low. Usually seeking to be grounded. I am thinking that a low impedance is less of a problem than a high impedance. So in this case you want an unbroken ground return. The DAC wants to source or sink it's output current at or near zero ohms. However in practice we need some output level so the I/V resistor is chosen with care to limit distortion.
TDA1357
I have no experience with that DAC. In general terms any output offset will need to be dealt with. Are you using a small cap across the TZ resistor? It could be that your hearing DAC noises that are apart of it's operation. PCM1704 for example is very good noise wise. TDA1541A less so. abraxalito knows his stuff so if he is suggesting a current source I'd consider that.