Using the AD844 as an I/V - Page 87 - diyAudio
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Old 20th June 2014, 06:09 AM   #861
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Thanks George - it may get a little messy on the PCB. Is it possible to 'steal' the I signal (pin 14) from the PCM1704 and run it to a separate board I make for the AD844? Or will it load the dac chip too much (if I leave the OPA627 unchanged)?
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Old 20th June 2014, 09:25 AM   #862
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Yes you can do that, but you'll have to cut the track that goes from pin 14 of the PCM1704 to the OPA627.

Cheers George
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Old 25th June 2014, 10:31 AM   #863
supra is offline supra  Australia
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I just built a 9018 dac with all of Ian's FIFO, isolater, clock etc and although it was very good, after a few days found it just too much like a Sabre dac, very accurate, highly technical but a bit soulless . Tried a nomber of I/V but eventually put an OPA861 on output.
Fixed it, enjoyable to listen to now, very close to my 1541 with stacked 844 in terms of musicality .
These trans conductance devices are something else, Pedja was on the money when he starting using them.
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Old 26th June 2014, 07:17 AM   #864
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Quote:
Originally Posted by supra View Post
I just built a 9018 dac with all of Ian's FIFO, isolater, clock etc and although it was very good, after a few days found it just too much like a Sabre dac, very accurate, highly technical but a bit soulless . Tried a nomber of I/V but eventually put an OPA861 on output.
Fixed it, enjoyable to listen to now, very close to my 1541 with stacked 844 in terms of musicality .
These trans conductance devices are something else, Pedja was on the money when he starting using them.
Ditto,
And if you do Abraxalito's bipolar 10uf 50v smd cap mod from + to - rail on the AD844 and on whatever buffer your using, you'll pick up a little more.
Using the AD844 as an I/V

Cheers George
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Old 2nd July 2014, 11:00 PM   #865
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After listening now for a while to Abraxalito's mod above, I can say it's very good in a subtle way. There is now a cleaner sense to the music, and the mirco detail is the most improved area.
Abraxalito can you give some techincal explanation on what happens, when your mod is in place, as I've look at it on the bench tests and there is nothing I can pick up on???


Cheers George
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Old 2nd July 2014, 11:23 PM   #866
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I haven't any technical measurements to back it up but it seems that its reducing the noise generated by the AD844 itself on its power rails. The self-generated noise is an issue for all circuits not running in pure classA in that there's a current taken which varies with the signal. The output stage is the biggest generaor of noise and this noise will depend on the load - the current drawn by the IC under load looks like a half-wave rectified version of the signal. So its frequency content is higher than the original signal, hence the need for higher frequency decoupling, beyond the audio band.
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Old 5th July 2014, 01:53 PM   #867
StevieK is offline StevieK  Germany
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Default Voltage- Input instead of CCs in Orginal circuit

Hello,
I got an Idea on the orgin circuit, so there is put CCS in the AD844, is it posible to
put voltage on the voltage Input and leave out the CCS to get zero Voltage at the
Output?
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Old 30th July 2014, 10:27 AM   #868
Bidule is offline Bidule  France
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Default Newbie Questions

Hello world

I've read a good part of this threat, but not every post yet....
So maybe i'll post some already answered candid questions, sorry about that.

1/ Did you compare stacked AD844 over OPA860 with and without internal buffers ?
Which one sounded best ? As I see that Pedja moved from AD844 to OTA.

2/ What should be done to use AD844 with AD1955 differential current sink ?
Would it be a good combo ?

3/ What do you think about using AD825 as "buffer with gain" out of AD844 TZ pin ?

Thank you for your answers.
Jean
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Old 30th July 2014, 10:45 AM   #869
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Don't know about one or two.
But if I had to use a buffer beside the BUF03 and it had to be an opamp with feedback then the AD825 is a good one. It's dynamic but not as effortless and big sounding as the BUF03.

Cheers George
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Old 31st July 2014, 02:02 AM   #870
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Quote:
Originally Posted by PreSapian View Post
and i just tried earlier today snubber (+bypass) for 1387 as per abraxalito's suggestion and also got a good improvement. hail, abraxalito.
Hi,

I'm also planning a tda1387 dac with ad844 active I/V. Can you share your implementation details please? Did you make any adjustment according to 1387's specs? One ad844 per Iout is going to be viable I think.

I somehow lost in thread and couldn't find the actual schematic with external buffer (BUF03) implemented.

Keantoken's buffer seems very good candidate for buffer.

Last edited by terranigma; 31st July 2014 at 02:08 AM.
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