AD1865 DAC singing

I failed to find a clear schematic of your DAC on your website. From the text description in your attachment, you apparently are using the internal op amps in the way that many of us recommend an external op amp be used for I/V conversion. Which is, to perform I/V conversion via a low value passive resistor, bandlimit the signal, then amplify the post I/V signal voltage. I've before designed and built ad1865 based DACs, one in transimpedance feedback mode using the internal op amp, and one using a passive resistor I/V. However, I hadn't thought to implement the passive I/V and signal voltage gain utilizing the internal op amp.

I believe that most of the criticism of the AD1865's internal op amp is when it's used in transimpedance feedback mode.
 
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Eldam

Banned
2012-09-13 12:25 am
France
Your shematics are too hard to read with no values no description parts. I see you work hard too on a Mercedes !
What are the black box near the Dac and the liitle white box between the two black box and near the Dac and Output?

The two DAC Chip seems to be fake maybe, or re-marked K grade but be low grade...
which caps do you use in shunt and near the chips ?

cheers
 

Eldam

Banned
2012-09-13 12:25 am
France
Hi,

I know about 2 serious vendor : Little diode ; Rochester Electronics. This last sell K grade at 52 dollars, but 5 pieces minimum order ! I need just one

If you talk about the Raindrophui 1865 Dac, I assume you have the 2 chips version without output stage. I have the one chip version with discrete stage (passive i/v).

Near the Dac chip, i leave the 3 tantal caps to solder them beneath the ad hoc FM caps. I leave the 3 green Vishay MKT. For the 2 analogs caps I put 22 uF KS Muse (no little decoupling). For the digital cap I test : 1 uF paper X2 mkt or 1 uF MKP, or 47 uF Oscon, or 22 uF nichicon HD, or 3,3 uF Wima MKS-4 (mkt). No ceramic, no silmicII, no tantal (but the 11 uF tantal moved under the FM cap near its reg).
I had acceptable success with that, but I follow too the advices found on DIYA about this chinese DAC: bypass the spidf transformers (Lampizator mod) and serie caps for the input on the CS chip, follow the constructor value with resistor and cap (670 nF & ...rtfm). I try 250R for passiv i/v and i plan to try it now with wirewound Rohpoint or Mills.... I remove too the 2 DC bloking caps and maybe will buy a true K grade, which imho is the last to do. I follow the advise of Abraxalito to play first with the layout... I assume a discret shunt like you do could be a great improvment...

cheers
 
Hi,

I know about 2 serious vendor : Little diode ; Rochester Electronics. This last sell K grade at 52 dollars, but 5 pieces minimum order ! I need just one

This seems to be a common problem with all R-2R class DAC chips that are specified for low distortion audio applications. Most such chips, such as the TDA1541, PCM63, and AD1862 (and AD1865) have long been out of production. The remaining few others, such as the PCM56 and PCM1704 are, I believe, somewhere close to end-of-life status. This means that the price for all of the better R-2R chips is high, assuming you can even locate them. PCM1704s are around 75 U.S. dollars each!

The only ready alternatiev seems to be those DAC chips targeted at digital waveform synthesis (which, to my mind, digital audio is a subset) and instrumentation. The problem with such chips is that they often don't feature particularly good harmonic distortion performance unless qunatizer linearity is calibrated via individual testing of each chip, and then stored locally in software via a look up table. Some of us have been looking forward to the releaser of the Arda DAC (Arda Technologies - AT1401 Flagship Audio D/A Converter), but it continues to be vaporware, as far as I can determine.
 
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Eldam

Banned
2012-09-13 12:25 am
France
Sure we are all waiting for the arda DAC. If our whish will be realised, writes will be beginning to challenge the 30 years of litterature about the TDA1541. I don't know about pcm1704, I've heard it is too much clinical ! But if it is in Dr House way, may be it is funy...Layout ?
The sourcing problem here for non vendor tweaker like me concerns : ad1865, ad1862... maybe pcm63. It's for me a psychological problem : what ! 70 euros for a chip. But in fact our hobby is far more expensive in parts and i don't speak about the speakers, the shoes for Madame to deal with waf... (the shoes is the lower ESR for the money)

But here it's easy to find a second hand player with two pcm56 (so: genuine) for 20 dollars.

I think that the real problem for non tech like me but with a long two cents experience is the good optimisation. For example i heard about true false ad1865, true tda1541, tda 1540, pcm56 & 63 : they are all good enough for my systems (Boston Lynfield 400L & Chord SMPB 1200 B ; Kef104/2, Proac D15).
The best result I had were with the PCM56 and i plan to build the ecdesigns conf.

That's why here i wrote that with playing with the layout of this chineese DAC I obtained very good result (IMHO & in my system) by experiment many conf with caps : solid tantal 11 uF near the LT1084 regs) & KS Muse near the analog power of the DAC, etc, etc . Old DC decoupling caps fur the output is already better than no caps. But It is just in this case and if I write too much this... people think that I can be a fool. I hope Vandernberg try it for curiosity with its old chineese IC... sometimes without shunt just with bad regs like 78005 well cooked, it can be good enough and if the big company vendors would work harder on that... Verdi could sleep better !

So in almost two words, the DAC chip in this chineese DAC is not all (like Abrax said in his manner) and IMO it's a AD1865 N or J Chanelised with white lips-stick in K grade. I'm more worried about the hardness for finding the good I/V for a tda 1541 or a PCM56... i have to experiment after the ecdesign with the Bernhard way (passive filter).
 
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it's not the chip that is the problem !!!

It is not the AD1865 version that is most important for good sound !
The other parts of the "speelgoed"DAK do a lot more.
of course a would like to hear the DAK with a real AD1865 K.
With 2 times AD1865 JK the DAK is really singing, come and listen to it.

Anybody who knows more about where these JK versions do come from or, are they fake please tell us.

greet marius
 

Eldam

Banned
2012-09-13 12:25 am
France
Yes, assuming we are talking here about ad1865 that's what I try to said : the last problem on the long list of things to do here. The grade of this chip is the kirsh on the pudding (la cerise sur le gateau like we say in France).

Maybe if you have time to try what I said with the chineese IC, tou will tell me if I'm right and if it's very far from a shunt reg. As I'm a non tech, I use the shem i find here or elsewhere. For me the simplier the better cause i have no tools to check the noise but my ears. Most of time, a simple reg is enough for my taste if the parts around are well choose, but when i use shunt reg, I use a old one popular in my country because very simple : tl431 + TIP142 or 147 for negative. I'm very surprise to see that most of the shunt i see here pump there current from the same caps used for filtering the current. I always use Pi just after diodes and not after shunt chip, even with a resistor if i have no inductance...

But I'm non tech, i have a look with your shunt shem and your 6np16 buffer (worse that the internal op of the AD1865 in yours experiment)...

Can you tell which exact decoupling value and technology caps are used near the dac chip... The grey are Arcotronics MKT ?
The DC converters are used as filter too ?

Thank you for your listening invitation:), I'm sure it's good because you try a lot of things, but too far for me before ours old industries make cars with full cells and CE goes with 250 kmh on fastroad:cool:.
 
It is not the AD1865 version that is most important for good sound !
The other parts of the "speelgoed"DAK do a lot more.
of course a would like to hear the DAK with a real AD1865 K.
With 2 times AD1865 JK the DAK is really singing, come and listen to it.

Anybody who knows more about where these JK versions do come from or, are they fake please tell us.

greet marius

Have you tried trimming the MSB adjustment feature provided for on the AD1865? I believe that hand adjusting the lowest grade devices via this feature can realize better THD performance than by using the most premium graded devices without adjustment. The procedure is covered in the datasheet.
 
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See page 6, figure 7, of the AD1865 datasheet. The main issue is having a tool to measure THD, such as via a quality PC sound-card. The PCB mounted parts required are minimal, two resistors and one multi-turn potentiometer, per channel.

http://www.analog.com/static/imported-files/data_sheets/AD1865.pdf


Also, see page 6 of the PCM56 DAC datasheet. It features an equivalent MSB trim feature, and it's datasheet provides a bit more information on the feature than does the AD1865's.

http://www.ti.com/lit/ds/symlink/pcm56.pdf
 
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