What's wrong with passive I/V
This is a balanced PCM1704K with a resistor between the inverted and non inverted dac.
The 150Hz spike is there independant of input and the 2 kHz -88dB is identical to what I get from my DENON 2900 line out (PCM 1792 with opamp I/V and supposed to measure -101dB THD @ 1kHz) which makes it likely that the soundcard creates the -88dB 2kHz harmonic.
The visible difference compared to the denon was less harmonics above 2kHz with my Balanced PCM1704 passive I/V dac.
If I had a better soundcard I would not (now) be surpriced if the passive I/V actually measured very close to or on spec with the PCM 1704K.
This is a balanced PCM1704K with a resistor between the inverted and non inverted dac.
The 150Hz spike is there independant of input and the 2 kHz -88dB is identical to what I get from my DENON 2900 line out (PCM 1792 with opamp I/V and supposed to measure -101dB THD @ 1kHz) which makes it likely that the soundcard creates the -88dB 2kHz harmonic.
The visible difference compared to the denon was less harmonics above 2kHz with my Balanced PCM1704 passive I/V dac.
If I had a better soundcard I would not (now) be surpriced if the passive I/V actually measured very close to or on spec with the PCM 1704K.
Attachments
Re: Resistor at Vref
http://www.diyaudio.com/forums/showthread.php?postid=366897#post366897
Yes:Bricolo said:
Thanks
Is there a reason for this specific value?
http://www.diyaudio.com/forums/showthread.php?postid=366897#post366897
Re: RE: Best opamp for I/V conversion? (DAC)
Which opamp is suitable as IV-converter after a DAC is described in the AD8627 datasheet page 15. Unfortunately this is not for Audio but industrial DACs. In the very interesting 1992 Amplifier Applications Guide from AD the AD 745 is recommended as IV for the AD1862. And in the AD797 datasheet that AD797 is recommended for the AD1862. BTW the 2nF cap at the current out of the DAC did not help at all to reduce HF noise. In the datasheet of the AD1862 the NE5534 or AD846 are recommended. Confusing.....?
In the old days Walt Jung was raving about the AD811 current feedback opamp as IV for the TDA1541. (Pooge Chronicles page 53 and further). The Pooge Chronicles are some articles taken form the Audio Amateur magazine. I can understand that, as the AD811 is the opposite of the TDA1541 lame sound.
I have tried the AD811 and the OPA603 and also a LT1026 for IV when I was still using a digital filter with the AD1864. I liked the AD811 the best in that configuration. Later I went NON-OS and tried all kinds of opamps, including my own discrete one, ending at the OPA604. If you read current datasheets for audio DACs you will see that AD recommends the OP275 and TI the OPA604 or OPA627. Well that's not too difficult to see through. See also:
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=50161&highlight=elso+ad811&r=&session=
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=51107&highlight=elso+current+feedback&r=&session=
http://db.audioasylum.com/cgi/m.mpl?forum=digital&n=33574&highlight=cfb-opamp+elso&r=&session=
But I keep searching!
Hi Gordon,Gordon McGregor said:
Which opamp is suitable as IV-converter after a DAC is described in the AD8627 datasheet page 15. Unfortunately this is not for Audio but industrial DACs. In the very interesting 1992 Amplifier Applications Guide from AD the AD 745 is recommended as IV for the AD1862. And in the AD797 datasheet that AD797 is recommended for the AD1862. BTW the 2nF cap at the current out of the DAC did not help at all to reduce HF noise. In the datasheet of the AD1862 the NE5534 or AD846 are recommended. Confusing.....?
In the old days Walt Jung was raving about the AD811 current feedback opamp as IV for the TDA1541. (Pooge Chronicles page 53 and further). The Pooge Chronicles are some articles taken form the Audio Amateur magazine. I can understand that, as the AD811 is the opposite of the TDA1541 lame sound.
I have tried the AD811 and the OPA603 and also a LT1026 for IV when I was still using a digital filter with the AD1864. I liked the AD811 the best in that configuration. Later I went NON-OS and tried all kinds of opamps, including my own discrete one, ending at the OPA604. If you read current datasheets for audio DACs you will see that AD recommends the OP275 and TI the OPA604 or OPA627. Well that's not too difficult to see through. See also:
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=50161&highlight=elso+ad811&r=&session=
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=51107&highlight=elso+current+feedback&r=&session=
http://db.audioasylum.com/cgi/m.mpl?forum=digital&n=33574&highlight=cfb-opamp+elso&r=&session=
But I keep searching!
Re: Re: RE: Best opamp for I/V conversion? (DAC)
Hi Elso,
I replaced JRC5534 with OPA627 and know the result ... I also tried AD843K instead and know the result as well.
http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm
http://web.telecom.cz/macura/opamp_mer_en.html
http://headwize2.powerpill.org/projects/showproj.php?file=opamp_prj.htm
http://tangentsoft.net/audio/opamps.html
http://members.cox.net/alexhardware/opa.htm
Though I am in doubts - is it worth to try AD8099 and OPA1632 as well or not, they both are not pin-to pin compatible ... but looks very nice. This is the reason of my question.
Elso Kwak said:
Hi Elso,
I replaced JRC5534 with OPA627 and know the result ... I also tried AD843K instead and know the result as well.
I did the same for PCM1704, and ended at OPA627 ... but in a few days I am going to try OPA655 and some other op amps (including AD811, AD8620, AD8066,OP275, etc).
Thank you for the information, I can add some more sources:If you read current datasheets for audio DACs you will see that AD recommends the OP275 and TI the OPA604 or OPA627. Well that's not too difficult to see through. See also:
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=50161&highlight=elso+ad811&r=&session=
http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=51107&highlight=elso+current+feedback&r=&session=
http://db.audioasylum.com/cgi/m.mpl?forum=digital&n=33574&highlight=cfb-opamp+elso&r=&session=
But I keep searching!
http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm
http://web.telecom.cz/macura/opamp_mer_en.html
http://headwize2.powerpill.org/projects/showproj.php?file=opamp_prj.htm
http://tangentsoft.net/audio/opamps.html
http://members.cox.net/alexhardware/opa.htm
Though I am in doubts - is it worth to try AD8099 and OPA1632 as well or not, they both are not pin-to pin compatible ... but looks very nice. This is the reason of my question.
Re: Re: Re: Re: Jocko's Circuit
Charles Hansen said:
It sounds to me like that ---
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Charles
Sorry for using this post. But I am trying to get quickly a copy of your paper on the HP339A mods. Can you email this to me please?
Fred
Good I/V opamp
Hi yall!
Any thoughts about the AD847/827?
I performed some listening tests while upgrading my cd-player and they outperformed OP275, OPA604 and OPA627 with ease.
That is, sonically. I dont' have plots or graphs to support this...
And of course it is very $$$$$$$$$$$$$$$$$$$$$$, but I think it's worth it when it concerns me enjoying the music!
Greetings,
Ray.
Hi yall!
Any thoughts about the AD847/827?
I performed some listening tests while upgrading my cd-player and they outperformed OP275, OPA604 and OPA627 with ease.
That is, sonically. I dont' have plots or graphs to support this...
And of course it is very $$$$$$$$$$$$$$$$$$$$$$, but I think it's worth it when it concerns me enjoying the music!
Greetings,
Ray.
Re: Good I/V opamp
I have some thoughts. It looks like AD847 produces high level of "pleasurable" even harmonics at the level of -90dB in the audio signal range, it means if you like "warm" sounding of tube amps, AD847/827 may be preferable for you. But they are not good for high-res sources like DVD-A Advanced resolution or SACD multi-channel, because the small reflected signals like shown here, for example, http://www.angelfire.com/clone/gordon0/DSP_Precision.jpg will be masked by distortions in AD847 and AD827 (fig.16 of the datasheet). Those distortions can mask non-perfection of CD mastering or quantization errors in your DACs as well, this is probably the reason why you liked them mostly, IMO.6h5c said:
This is what I am talking about, OPA627 and OP275 produce very low level of distortions ... any imperfection of CD signal will be revealed. This is why OP275 are used in the professional sound card Lynx Two B or L22 ... the profesiional audio engineers don't need to "mask" imperfections in sounding, they need to reveal them.
Re: Re: Good I/V opamp
Hi Gordon,
Indeed, the distortion + noise of the OPA627 is much lower. So it could be this opamp is sounding sweeter to your ears. But other things I noticed are the stereo-image and soundstage that sounded much "smaller" with OP275 for instance. With AD847 the whole image seemed to "open up". Could this be the lower settling time that is responsible for that?
Anyway, my experience uptill now is that most of the times you have to compromise if you look at the spec's of an opamp...
Greetings,
Ray.
Gordon McGregor said:
Hi Gordon,
Indeed, the distortion + noise of the OPA627 is much lower. So it could be this opamp is sounding sweeter to your ears. But other things I noticed are the stereo-image and soundstage that sounded much "smaller" with OP275 for instance. With AD847 the whole image seemed to "open up". Could this be the lower settling time that is responsible for that?
Anyway, my experience uptill now is that most of the times you have to compromise if you look at the spec's of an opamp...
Greetings,
Ray.
Re: Re: Re: Good I/V opamp
Indeed, the distortion + noise of the OPA627 is much lower. So it could be this opamp is sounding sweeter to your ears. But other things I noticed are the stereo-image and soundstage that sounded much "smaller" with OP275 for instance. With AD847 the whole image seemed to "open up". Could this be the lower settling time that is responsible for that?
Anyway, my experience uptill now is that most of the times you have to compromise if you look at the spec's of an opamp...
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I peronally don't like the upfront sonics of the 627, which co-incidentally doesn't dribve capacitance too well.
The 275 sounds a little anaemic to me and seems to need extensive warning up.
The 825 and 6172 sound best to me.
Indeed, the distortion + noise of the OPA627 is much lower. So it could be this opamp is sounding sweeter to your ears. But other things I noticed are the stereo-image and soundstage that sounded much "smaller" with OP275 for instance. With AD847 the whole image seemed to "open up". Could this be the lower settling time that is responsible for that?
Anyway, my experience uptill now is that most of the times you have to compromise if you look at the spec's of an opamp...
-----------------------------------------------------------------------------------
I peronally don't like the upfront sonics of the 627, which co-incidentally doesn't dribve capacitance too well.
The 275 sounds a little anaemic to me and seems to need extensive warning up.
The 825 and 6172 sound best to me.
One of the nice things about the AD847 is the relatively high open loop cross-over frequency of 10kHz+. The open loop (and THD curve) are almost flat across the audio band. Many other opamps start already to roll off at a few 100 Hz. To compensate for the early roll-off they start at a much higher open loop gain, in order to have some loop gain left at higher frequencies for the feedback to work with. The '847 has lower loop gain, but constant across the audio band. Output impedance is also quite flat out to 20kHz. And, not to forget, it seems to have the right ratio of 2nd to 3rd harmonic components. Because of the low open loop gain, the feedback factor is also lower, which is a Good Thing because it means much less intermodulation distortion resulting from high error levels returned to the input.
THD curves don't say a lot about audio performance under real music exitation, we all know that. But a lower, but constant open loop gain predicts a more benign behaviour, and this could be the cause for its friendly behaviour in audio applications. I would expect this opamp to sound sweet and warm, not shrill and hard.
A negative point is its relatively high input noise of 15nV/RtHz, but for anything but very low level apps (RIAA etc) this would not be too big a problem.
In short, I was not aware of the 847, but I will surely try it out in the future. Looks like a winner, at least on paper.
Jan Didden
THD curves don't say a lot about audio performance under real music exitation, we all know that. But a lower, but constant open loop gain predicts a more benign behaviour, and this could be the cause for its friendly behaviour in audio applications. I would expect this opamp to sound sweet and warm, not shrill and hard.
A negative point is its relatively high input noise of 15nV/RtHz, but for anything but very low level apps (RIAA etc) this would not be too big a problem.
In short, I was not aware of the 847, but I will surely try it out in the future. Looks like a winner, at least on paper.
Jan Didden
Sweet opamp.
My experience exactly. The AD847/827 sounds "friendly" and very musical to the ear, but it also gives a nice wide soundstage and lots of detail, something I did not expect because of it's friendly sound that may be a sign that it is in fact masking details.
I was pleasantly surprised when I compared it with OPA2604/2134. OP275 and LM6172. The AD847/827 is not one of the "fastest" sounding opamps, with lots of analytical detail, but it puts out a very natural stereo image with lots of air. It's worth to give it a try.
O.k., back to earth. Of course I also look at the spec's.
Sometimes. But then again, sometimes I just plug it into the socket and listen.
Greetings,
Ray.
My experience exactly. The AD847/827 sounds "friendly" and very musical to the ear, but it also gives a nice wide soundstage and lots of detail, something I did not expect because of it's friendly sound that may be a sign that it is in fact masking details.
I was pleasantly surprised when I compared it with OPA2604/2134. OP275 and LM6172. The AD847/827 is not one of the "fastest" sounding opamps, with lots of analytical detail, but it puts out a very natural stereo image with lots of air. It's worth to give it a try.
O.k., back to earth. Of course I also look at the spec's.
Sometimes. But then again, sometimes I just plug it into the socket and listen.
Greetings,
Ray.