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Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

8 x AK4490 with current output
8 x AK4490 with current output
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Old 18th January 2018, 03:06 PM   #11
UnixMan is offline UnixMan  Italy
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Quote:
Originally Posted by nemantree View Post
I'm about to try OPA1688.
tried that (on a DIYINHK AK4490 DAC board). Not bad, but later I have replaced it with ADA4627 (two of them, on an adapter board), which sounds even better.
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Old 13th February 2018, 12:47 AM   #12
nemantree is offline nemantree
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I've tried dual opamps OPA1688, OPA1612, OPA1642 and Sparkos discrete SS3601.
Hard to notice the difference between 1688, 1612 both are neutral. 1642 adds some pleasant color. SS3601 is absolute winner: musical with strong bass.
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Old 13th February 2018, 12:55 AM   #13
nemantree is offline nemantree
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With SS3601s I have not added bandwith limiting capacitors. Is it essential (for the already compensated amp)? If so, can it be ~1000pF (for ~400KHz)? Or more/less?
Thanks!
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Old 20th February 2018, 05:04 PM   #14
nemantree is offline nemantree
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I have chinese AK4137 based digital receiver board. It has 4 digital filters enabled. The same filters are always enabled in AK4490. Is this OK to run them two times?


Dimdim,
I'm trying to write my own arduino software for this DAC. I've analyzed your "Arduino controlled Dual Mono" code and studied the datasheet. I think I've programmed the initialization sequence like you did. But, for whatever reason the DAC is not initialized properly, does not work. Could you, please, describe just in few words what should be proper Power On + initialization sequence.
This DAC is 3-wire serial controlled. Left right channels have dedicated CSN wire. I have captured clock, data signals and they look fine - according to the datasheet. I have a feeling something is wrong with just initialization sequence or commination speed (it is about 80kHz). Also, I'm not sure how to do Synchronize Function which can be essential with multiple chips design.
Thanks a lot!
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Old 20th February 2018, 05:23 PM   #15
DPH is offline DPH  United States
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Originally Posted by nemantree View Post
I'm about to try OPA1688. According to modeling results it looks OK.
Well the whole idea behind having an 8x AK4490 through hefty current sharing resistors is to push noise down, right? I'd honestly be looking to push those resistors down in size (100 or so?) and use a high-falutin opamp on the back of this as a buffer/gain if you need more than 2 Vrms output. An OPA1688 is grossly underperforming what you have and wasting about 7 of the 8 4490's.
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Old 20th February 2018, 05:27 PM   #16
nemantree is offline nemantree
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I'm using Sparkos discrete opamps (4) in the inverter.
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Old 20th February 2018, 05:29 PM   #17
nemantree is offline nemantree
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What high-falutin opamp you would recommend?
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Old 20th February 2018, 05:37 PM   #18
DPH is offline DPH  United States
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For things like this I'd be looking at some sort of composite with a ADA4898/AD797/OPA1611 and a buffer (or TPA6120) inside the loop. And a stupid low feedback impedance. With 8x 680 ohm resistors in parallel, you shan't need much extra Rg to get something like a 200 ohm Rf for an inverted opamp structure.

But I'm biased away from the discrete opamp types, and really think we're running off very different philosophies.
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Old 20th February 2018, 05:42 PM   #19
Dimdim is offline Dimdim  Greece
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8 x AK4490 with current output
Quote:
Originally Posted by nemantree View Post
I have chinese AK4137 based digital receiver board. It has 4 digital filters enabled. The same filters are always enabled in AK4490. Is this OK to run them two times?


Dimdim,
I'm trying to write my own arduino software for this DAC. I've analyzed your "Arduino controlled Dual Mono" code and studied the datasheet. I think I've programmed the initialization sequence like you did. But, for whatever reason the DAC is not initialized properly, does not work. Could you, please, describe just in few words what should be proper Power On + initialization sequence.
This DAC is 3-wire serial controlled. Left right channels have dedicated CSN wire. I have captured clock, data signals and they look fine - according to the datasheet. I have a feeling something is wrong with just initialization sequence or commination speed (it is about 80kHz). Also, I'm not sure how to do Synchronize Function which can be essential with multiple chips design.
Thanks a lot!
If I were you I'd start by seeing if I can indeed communicate with the dac chip.

In my case (using I2C, not 3-wire mode) I would run an I2C scanner to see if it will detect the chip. Afterwards, I'd do a test read of a couple of registers to see if their values are the predicted ones.
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Old 20th February 2018, 06:00 PM   #20
nemantree is offline nemantree
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That is the pain: * The AK4490 does not support read commands in 3-wire serial control mode.

this is my init part (some of the version):
void setup() {
pinMode(PDN, OUTPUT);
digitalWrite(PDN, LOW);
pinMode(CSN1, OUTPUT);
pinMode(CSN2, OUTPUT);
pinMode(CLK, OUTPUT);
pinMode(DTI, OUTPUT);
digitalWrite(CSN1, HIGH);
digitalWrite(CSN2, HIGH);
digitalWrite(CLK, HIGH);
digitalWrite(DTI, LOW);

delayMicroseconds(pulse);
masterInit();
}

void masterInit()

{

digitalWrite(PDN, HIGH);
int autoData = C1_ACKS + C1_DIF24MSB;

writeChips(C1addr, C1_RESET);

writeChips(C1addr, autoData);
writeChips(C2addr, C2_ShortDFlt + C2_DeEmphasisOFF);
writeChip(0, C3addr, C3_PCM + C3_MONO_LEFT);
writeChip(1, C3addr, C3_PCM + C3_MONO_RIGHT);
writeChips(C7addr, C7_SoundCtrl1);


writeChips(C1addr, autoData + C1_RSTN_Normal);
}
// where
#define C1_RESET B00000000
#define C1_RSTN_Normal B00000001
















Last edited by nemantree; 20th February 2018 at 06:02 PM. Reason: bad format
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