ISL28110 has a bit higher voltage noise, but the current noise (9 fA/sqrt Hz) is very low which is ideal for me (10k source resistance). The ADA4267 seems better in spec (speed, BW, current noise), but strangely it doesn't sound as good as ISL28110 on my circuit.
Hi Eldam -
I posted up an I/V for Felipe's PCM63 over here : http://www.diyaudio.com/forums/digi...-pcm63-dac-only-cd-transport.html#post4988419
Probably will work fine for TDA1541. I'd not recommend opamp I/V, classA sounds so much cleaner.
I posted up an I/V for Felipe's PCM63 over here : http://www.diyaudio.com/forums/digi...-pcm63-dac-only-cd-transport.html#post4988419
Probably will work fine for TDA1541. I'd not recommend opamp I/V, classA sounds so much cleaner.
Thank you for that,
I use this today : https://www.audialonline.com/static-files/pdf/OPA861_out.pdf (courtesey of AUdial https://www.audialonline.com/topics/opa861-zero-feedback-output-stage-of-aya-ii/ , free for non commercial use, a.k.a. diyers !)
with Rohpoint wirewound resistor for the I/V as well... (athough Auial uses an other resistor type...)
What fo you think about the discrete diamond stage with BC560/550 ?
I use this today : https://www.audialonline.com/static-files/pdf/OPA861_out.pdf (courtesey of AUdial https://www.audialonline.com/topics/opa861-zero-feedback-output-stage-of-aya-ii/ , free for non commercial use, a.k.a. diyers !)
with Rohpoint wirewound resistor for the I/V as well... (athough Auial uses an other resistor type...)
What fo you think about the discrete diamond stage with BC560/550 ?
Isn't the loading impedance for the output TD1541 pin 2 of the OPA861.
( what I/V resistor??)
Cheers George
The i/v is R415 : 1k5 ! I use 1K only without problem (it's give me iirc Something near 1.5V outputt which is enough for my 47 k Ohms pre, even when I disconect the buffer I hear no difference, the better buffer is no buffer most of the time)
Ah for the resistor type, you may ask Pedja if he want to talk about it, I'm not sure he want his BOM to be seen by all the factories of the planet ! He has a blog on his site to discuss about his products. Here the link I gave (though some valors of passive parts changed a little) is public though.
look for on DIYA : Painkiller ad1862 DAC to have a discrete diamond stage I/V shematic...
Ah for the resistor type, you may ask Pedja if he want to talk about it, I'm not sure he want his BOM to be seen by all the factories of the planet ! He has a blog on his site to discuss about his products. Here the link I gave (though some valors of passive parts changed a little) is public though.
look for on DIYA : Painkiller ad1862 DAC to have a discrete diamond stage I/V shematic...
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Sorry I thought you meant you were using a passive I/V resistor?? So pin two of the 861 is your 13ohm loading resistance for the TDA1541.
R415 is like the TZ resistor in the 844 I/V. with c407 as it's lp filtering.
If you reduced R415 to 1kohm did you increase C407 to 1500pf (1.5n) to maintain the same lp filtering?
Cheers George
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Do you mean there is 100% passive I/V conversion ? (with no tubes or transistors ?)
No I didn't change c407 ! I can't hear it ! Passive parts typology, and PS supply (and main cap values and type) has more effect on the result by far ! There are also caps I removed here, but you can do it only with vet quiet PS and quiet digital input stage : buffer, fifo, good clock).
No I didn't change c407 ! I can't hear it ! Passive parts typology, and PS supply (and main cap values and type) has more effect on the result by far ! There are also caps I removed here, but you can do it only with vet quiet PS and quiet digital input stage : buffer, fifo, good clock).
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Yes passive resistor is directlty on the tda's output, with a gainstage after it.
Yours is the 13ohm internal input resistance of pin 2 of the 861.
And yes to matain the same lp fiter as Pedja has with 1.5kohm and 1000pf, you've changed to 1Kohm so you need to make the cap 1500pf.
To maintain the -3db point at 106khz that Pedja uses for lp filtering.
Cheers George
Thanks for the tip. I asked him when I changed the value, he didn't find usefull to change 1500 pF cap value when I reduced the value from 1k5 to 1K (because I just dind I K with the 516 G Rohpoint wirewound I wanted to try). But sure I will try one day your value !
But I found the type of the I/V resistor (so the non so passive one but still passive part : 1k5) typology and also the serie one after the buffer changed more the sound as the way you feed this circuit . And the difference are not subtle, I tried many, many things from Black Gate N, NX, norma, polymer, old Panasonic, new Panasonic, Nichicon, hundred of caps... For me it's change more the result than the buffer stage IC !
But I found the type of the I/V resistor (so the non so passive one but still passive part : 1k5) typology and also the serie one after the buffer changed more the sound as the way you feed this circuit . And the difference are not subtle, I tried many, many things from Black Gate N, NX, norma, polymer, old Panasonic, new Panasonic, Nichicon, hundred of caps... For me it's change more the result than the buffer stage IC !
It will just let through more HF s**t from the 1541, instead of being-3db at 106kHz it will be -3db at 160khz, therefore letting through more dac noise, which the 1541 has got from what I've experienced, more than a 1704's got.
Cheers George
ok, i would proceed when have more time for DIY to an A/B test with the value you advise to check if I can hear a difference ! Btw I even find a tda 1541A s1 vs a TDA 1541A from 98 and Taiwan and genuine sound totally different ! More different than a tda1545 vs a TDA1543 which are totally different but less than two sort of tda 1541A!
So now i'm looking all this with a grain of salt... For HF things at the outputt of the tda1541, if the digital inputt stage is ok before, I find the HF things less important ! I'm more focused on the dynamic and tonal balance in relation to my whole hifi system + room !
Have to admit, I tweak in relation to the whole chain (amp + speaker + input stage and supplies) by ears only ! But actually it beats all what I've heard before : Soekris non tweaked, Subbu DAC stock & tweaked, etc...
I found you got a very good idea to input your lighted attenuator as an I/V : did you had time for that ?
So now i'm looking all this with a grain of salt... For HF things at the outputt of the tda1541, if the digital inputt stage is ok before, I find the HF things less important ! I'm more focused on the dynamic and tonal balance in relation to my whole hifi system + room !
Have to admit, I tweak in relation to the whole chain (amp + speaker + input stage and supplies) by ears only ! But actually it beats all what I've heard before : Soekris non tweaked, Subbu DAC stock & tweaked, etc...
I found you got a very good idea to input your lighted attenuator as an I/V : did you had time for that ?
No, I always wanted to somehow put the Lightspeed in place of the TZ resistor which should then give good variable gain, and to then drive the poweramp directly from the buffer stage output of the dac, but to be successful the TZ cap would also have to change it's value at the same time, for the lp filter to remain constant.
Cheers George
Are you sure than want you hear the most is the Low pass bandwidth and not the typology of the circuit, type of the cap: dilectric, ESl/ESR, layout and ground and PS... mostly ? I mean if a choice has to be made because you have not the possibility to print all the board one could want...
Not sure I can hear a difference with a lwo pass between 106 K Hz and 160 K Hz... but I can certainly more hear the layout of how it is populated (shematic, passive parts...) in the band far below !
Not sure I can hear a difference with a lwo pass between 106 K Hz and 160 K Hz... but I can certainly more hear the layout of how it is populated (shematic, passive parts...) in the band far below !
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It's not what you can hear at >100khz which one one can't, it's how much noise is let through at 20khz that matters.
And the -106db is better dac noise filtering at 20khz than the -160db, you will see it on a good scope.
Cheers George
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Diamond stage is push-pull, I prefer SE, which is why I designed my I/V stage as SE. Push-pull is needed when we have significant (or unknown) currents to drive, such as with headphones. In a line stage we can specify a minimum load impedance and hence no requirement for push-pull circuits with their corruption of the supply lines.
I prefer single ended to diamond differential outputs too. I dont know why. I thought maybe it was the HD profile with differential seeming to wipe out second harmonics and creating an odd harmonic dominated spectrum. But then the distortion levels are so low Im not sure they can even be heard.
Ive no idea what the "push-pull circuits with their corruption of the supply lines" is. Could that be an audible issue I think Im hearing?
The issue with classAB (push-pull) output stages is that they're drawing highly non-linear currents from the supplies. Each half of the push-pull supplies a half sinewave contribution to the output, those currents into the load are particularly rich in high order harmonics due to the effective 'slicing' of the waveform in two, to be handled by the two halves. Its not just the high order harmonics on the supply rails that are doing the damage subjectively its that those harmonics are strongly correlated with the signal so our brain interprets them as part of the music. The correlation means we can't separate them out and hear them as noise.
So in answer to your question - yeah I reckon that is what we hear with opamps and push-pull stages with light bias. We're hearing the noise from the supply fed through less than perfect PSRR in our amp circuits.
This is also the reason I reckon feedback gets a bad rap in audiophile circles - because when you wrap feedback around a push-pull stage the ultrasonic harmonics are fed back into the loop rather than just being harmlessly fed to the transducer. I note in Pedja's writing he thinks the OPA861 stops being an opamp when no feedback is used, that's kinda cute. The SQ problem isn't the feedback (as my SE stage which uses feedback sounds great) its the feedback combined with the lightly biassed push-pull stage.
So in answer to your question - yeah I reckon that is what we hear with opamps and push-pull stages with light bias. We're hearing the noise from the supply fed through less than perfect PSRR in our amp circuits.
This is also the reason I reckon feedback gets a bad rap in audiophile circles - because when you wrap feedback around a push-pull stage the ultrasonic harmonics are fed back into the loop rather than just being harmlessly fed to the transducer. I note in Pedja's writing he thinks the OPA861 stops being an opamp when no feedback is used, that's kinda cute. The SQ problem isn't the feedback (as my SE stage which uses feedback sounds great) its the feedback combined with the lightly biassed push-pull stage.