New AD1955 DA Build

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carlmart

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Joined 2001
preciseaudio.com
KlipschKid said:
If you look at the output impedance plots on one of the links I posted, you'll see the cap on the adjust pin increases the output impedance at low to mid frequencies, which supports Eric's (and mine) observations that the dynamics improve substantially. The cap on the output lowers the impedance at mid and higher frequencies. So balancing them to work together and avoiding low esr caps on the output are the way to go...

In a perfect world, I want a flat output impedance across the audio band for a balanced sound, and as low as possible for maximum dynamics.

I don't particularly like LM317 because it is hard to achieve a flat output impedance and it is never that low. This is why shunt regs and very good series regs like AMB's are better. I even prefer the sound of the humble 7805 which is mostly flat until the higher treble range. Some people have said LT1084 sound better than LM317 but I've yet to try.
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I'm basing my comments on impedance based on measurements made in TNT audio, where they changed the adj cap until it got to its lower point; on Walt Jung's measurements on his super-regulator article on The Audio Amateur; and on a topic on this forum, where a transistor was used on the adj leg and a cap + resistor series was used on output.

Now I'm working on a topic I will open on DIYForum on Sulzer and Jung supplies, which AFAIK are the lowest impedance supplies I know of, on how to DIY them in single-sided pcbs and avoid as much compromises as possible.

Of course I will be trying these supplies on the AD1955 DAC and on the AK4396 DAC.

Also AFAIK I have never seen shunt supplies measurements that were lower in impedance that Sulzer or Jung supplies. Would love to.
 
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carlmart

Member
Joined 2001
preciseaudio.com
KlipschKid said:
A low jitter xo will make a very noticeable difference. The best is the Crystek CCHD-957. It's not expensive and will make noticeable improvements in definition, space, decay, distortion, etc. How much difference depends on how good or otherwise the existing clock is.
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Nice suggestion about the crystal. This might be nice time for me to try that.

AD827 is really for video and is quite noisy. Compare that to AD8599 which is designed for audio pre-amps.

The ad1955 really wants an op amp that is fet or j-fet input, not bjt, in the I/V pair because it won't strain the ad1955 output, hence AD8620 or OPA2134 as possible substitutes. But try and see how it sounds eh ? If it blends with your system well, then job done. I'll be interested to hear your comments.
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Noise is not a demand for this stage, as the output is higher than 1v. The AD8599 is a low noise type, but it's also a medium speed type. The noise of the AD827 is 15 nV/√Hz, which should put it in the same lot with many other considered good sounding types. Like the old but faithful AD712, or the FET input AD744, used by Jung on his DAC mod for Philips CD960.

Noise on the AD827 might be due to poor bypassing.

You're right that FET input types may be better for this application, but it's the moment to try them all. A champion will probably be named.

I'm limiting my choices to DIP8 types, as I stated before, and try to avoid SMDs if possible.
 
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redjr

Member
Joined 2011
I finally got my LM4562 op amps (can casing) soldered onto the DIP8 Browndog adapters. I've included a few pictures below. I first trimmed the leads to just the right length, then positioned the 'can' with the correct orientation in the DIP8 adapter. Flipped it over, soldered and voila! It's easy enough to do as long as you have a steady hand. :D Haven't tried them in the DAC yet. Still burning in the AD827.
 

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R

redjr

Member
Joined 2011
KlipschKid said:
Yes, quite easy to do eh ? I didn't know they did LM4562 in cans. I have LME49710HA - the HA are cans and sound better than the MA which are so8, so I wonder if the canned LM4562 will also be better than the dip8 ones I have....
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One recommendation from someone in the thread was specifically for the LM4562 in cans (US made to be specific). I couldn't verify the country of manufacture but decided to go with them anyway. Now my collections of op amps is growing! :D
 
R

redjr

Member
Joined 2011
carlmart said:
You don't really need to solder a can type IC to an adapter to use it.

AFAIK (though I never tried it yet) you can simply line up the legs and insert them on the socket. At least that saves one contact in the path.

Of course, a DIP8 header or adapter is more practical to plug-unplug.
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Yeah, I just decided to put them on the little adapters for easy plug-in and removal. I needed some practice at micro-soldering :D, so decided to give it a go. It wasn't that bad. Now the SOIC8 may be another story altogether if I get some op amps in that packaging. I think the OPA827 are in that style, plus I would need to solder 2 on! :eek:
 
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