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Old 9th January 2013, 12:48 AM   #31
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Hey glt,

I was wondering the same thing - what about you ?

To get her running asap, I'll use a TL1963a 3.3V reg for the analog, and then when she's running and burned in, I'll try an AMB Sigma 11 with three IR leds as the Vref. They have a forward voltage of 1.14V each, so 3 will be 3.42V, to which I can add some gain to try higher voltages, or swap the leds for two red for 3.6V.... anyway, Sigma 11 is low impedance, low noise, high ripple rejection. A really good series reg imo.

The σ11 Regulated Power Supply

The TL1963a is a very nice sounding 3 pin reg - good punch and seems to have linear output impedance. Noise is not so good at 38uV. The DCY package fits on the board quite easily.

Linear Regulator (LDO) - Single Channel LDO - TL1963A - TI.com

So far I fitted both an adp151 3.3V for the digital and the TL1963a. Still waiting for parts. But so far :

Click the image to open in full size.

Last edited by KlipschKid; 9th January 2013 at 01:13 AM.
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Old 9th January 2013, 01:05 AM   #32
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Quote:
Originally Posted by enjoybiking View Post
On another thread I wondered aloud about SSM2141

http://www.analog.com/static/importe...ts/SSM2141.pdf

is that device even worth any chatter? What with all the high-spec op amps being considered? {I'm not likely to use any op amps after the I->V anyway}.
I see it deployed on boards on eBay:

WZ 21B SSM2141 Balanced Unbalanced Board Balance Input Output Unbalance | eBay

and for various reasons I have some interest.
[modding Behringer DCX2496 which has AKM AK4393 differential out DACs]. SSM2141 reminds me of the Broskie cathode follower:

http://tubecad.com/Product_PDFs/BCF%209-Pin.pdf

though I have no idea what SSM2141 or the tube circuit would spec out at vs ESS reference design [or the better stuff being discussed HERE]. Anyone seen it used anywhere in real life?
Are you going to use a balanced output ? What are you planning to use as the filter ?

I am still using single ended so I'm going to use something like LME49990 in the output buffer/filter,.....

.... but I was wondering, since we know the current and voltage output of the DAC, could we do something "nos" with the I/V like a simple shunt resistor ?

Another option would be to use the LME49713 and change some of the resistor values to suit it ?

http://www.ti.com/product/lme49713

Last edited by KlipschKid; 9th January 2013 at 01:09 AM.
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Old 9th January 2013, 01:22 AM   #33
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Quote:
Originally Posted by enjoybiking View Post
On another thread I wondered aloud about SSM2141

http://www.analog.com/static/importe...ts/SSM2141.pdf

is that device even worth any chatter?
From a quick glance at the data, no - its a slow (10V/uS, 3MHz) opamp and some closely matched resistors. Will contribute a lot of IMD in this application.

The part I was referring to earlier with the extra-linear input stage was this one: http://www.analog.com/static/importe...ets/AD8099.pdf

Its SOP8 (no DIL) and 12V max operation. But the noise spec will suit those looking to get close to the max possible from the DAC chip.
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Old 9th January 2013, 02:08 AM   #34
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Quote:
Originally Posted by abraxalito View Post
From a quick glance at the data, no - its a slow (10V/uS, 3MHz) opamp and some closely matched resistors. Will contribute a lot of IMD in this application.

The part I was referring to earlier with the extra-linear input stage was this one: http://www.analog.com/static/importe...ets/AD8099.pdf

Its SOP8 (no DIL) and 12V max operation. But the noise spec will suit those looking to get close to the max possible from the DAC chip.
Hi

I can't get AD8099 soic samples to try so I'll give that one a miss.

For the LME49713, it seems easy enough - remove the 100pF cap (C1 in the datasheet circuit) and change the 680R (R1) to 1.2KR.
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Old 9th January 2013, 02:14 AM   #35
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For pure CFB amps like LME49713 there are other tricks you can play which are outlined in this appnote from TI : http://www.ti.com/lit/an/slyt099/slyt099.pdf

Using the ferrite bead in series with the -ve input isn't something I've tried myself, but I sure plan to
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Old 9th January 2013, 02:49 AM   #36
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That's a very interesting read. It seems I could keep the 680R for better noise and use a ferrite, AG or HG grade with low Q ( BLM18AG601SN1 ) to connect pin2 of the op amp. It might even be possible to simply short C1, which would create a feedback of pure resistance around 87R and add the ferrite with an impedance around 600R @100Mhz ?

And cheap too :

http://hk.element14.com/jsp/search/b...questid=105100

Last edited by KlipschKid; 9th January 2013 at 02:52 AM.
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Old 9th January 2013, 02:59 AM   #37
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Those prices look rather expensive to me - I'm used to paying a maximum of 0.1rmb for a bead, but then I do usually buy a whole reel of them at one time as I seem to use them by the bucketful

These are my current flavour of 'cooking' bead, chosen for having highest inductance at lower freqs - I use MPZ2012S102 : http://www.tdk.co.jp/tefe02/e9413_mpz.pdf

I do put a resistor to shunt them though, depending on application as it looks from comparing the impedance graph with my measurements that the inductance is somewhat non-linear at lower freqs. I've used them to decouple capacitive loads and got instability which was fixed by adding the shunt resistor.
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Old 9th January 2013, 04:35 AM   #38
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Quote:
Originally Posted by KlipschKid View Post
Hey glt,

I was wondering the same thing - what about you ?

...
Want to try the Salas 1.1 for analog and the TPS7A47 eval board for the digital. But got to order the 1.2 V regulator first...
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Old 10th January 2013, 01:47 AM   #39
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Just a quick update on those ferrites - found the Murata AG grade in 0805 size and 600R here, US$2 for 25 :

https://hongkong01.rs-online.com/web...beads/7241494/
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Old 11th January 2013, 06:49 AM   #40
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Still waiting for parts, so in the meantime I fitted a socket for the oscillator. Positioning is tricky but it's doable. I made it low-profile by cutting off the legs, soldering bridges, and filing down so it sat flat on the board. Put solder on one pad and positioned the socket.

The angle of this photo is not so good - looks like C1 connects to the socket with solder but that's just the angle.

Click the image to open in full size.

The other angle :

Click the image to open in full size.

Before filing down, with a Crystek that's grown legs :

Click the image to open in full size.

For the xo decoupling cap C1, I soldered on a 0603 15pF to the board's pads and then a 1uF on top of it.

There's quite a lot of low esr ceramic caps on the outputs of the adp's. The datasheet says match the input and output caps, which I will do, but my experience with LM317s oscillating still makes me a little uncomfortable about this. What do you guys think ?

Last edited by KlipschKid; 11th January 2013 at 06:59 AM.
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