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Building the ultimate NOS DAC using TDA1541A
Building the ultimate NOS DAC using TDA1541A
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Old 13th July 2018, 10:00 AM   #6301
john jones is offline john jones  United Kingdom
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Default best I2s and Dem mod

This is probably a bit out of place but I have read all 630 posts in this thread and am overwhelmed by the development over many years of the TDA 1541A.

I am a keen DIYer but by no means an expert. My own TDA1541A DAC is inside a Marants CD 63 player and I take the I2S directly from the SAA7345 and feed the TDA1541A in NOS mode. My I/V is via OPA 660 (the well known T.Loesch circuit) and I'm very hasppy with the sound. However, In this thread I read the benefits if I2S attenuation and improving DEM oscillator over the Data Sheet 470pf capacitor on pins 16 and 17 (which I have at the moment). I do not want to go down the road of reducing the DEM oscialltor to 50Hz as per recent posts....though I might expriment as I have several TDA 1541A chips.

My question is simply what is the best easy to implement I2S attenuator circuit, and best DEM oscillatror mod, bearing in mind I have I2S supply from SAA7345 and 16.9344Mhz clock (upgaded). I will make a new PCB so I can implement any circuit, I just wanted to know from people way cleverer than me, what circuits are recommended as I see many itterations in this thread over the years. I am a firm believer of simplicity over complex, so look for the best simple solutions.
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Old Yesterday, 03:35 AM   #6302
Hanze Khronye is offline Hanze Khronye  Australia
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Quote:
Originally Posted by john jones View Post
...best DEM oscillatror mod, bearing in mind I have I2S supply from SAA7345 and 16.9344Mhz clock (upgaded). I will make a new PCB so I can implement any circuit, I just wanted to know from people way cleverer than me, what circuits are recommended as I see many itterations in this thread over the years. I am a firm believer of simplicity over complex, so look for the best simple solutions.

Best time proven and simplest mod for DEM would be two 6k8 resistors, one each from pin 16 and 17 to -15V for DEM and keep the 470pF cap.

With 3.3V logic already (and not 5V) that is probably enough.

RE: attenuation, one current manufacturer (PR) of well regarded 1541A DACs suggests that I2S attenuation is a step backward from 3.3V.

RE: Johns low fDEM, one current manufacturer who is equally well regarded, and in addition has had unanimous commercial success with 1541A (TL), says its simply the wrong approach. DIYHiFi.org • View topic - TDA1541: simult mode; D9001: 24b Left Just, 96KHz; t matters

Like all, read between the lines and you will find your own way.

Last edited by Hanze Khronye; Yesterday at 03:43 AM.
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Old Yesterday, 02:10 PM   #6303
maxlorenz is offline maxlorenz  Chile
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I2S attenuation makes significant effect on TDA1543.
I cannot comment about the effect on its big brother...

Quote:
I am a firm believer of simplicity over complex, so look for the best simple solutions.
That OPA666 looks complicated enough by itself...there could be better, discrete solution...

Good luck.
M.
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Old Yesterday, 06:03 PM   #6304
john jones is offline john jones  United Kingdom
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Yes, I see your point, but if you take OPA 660 as a diamond transistor and buffer it is quite simple to implement and in terms of parts count just requires a handful of components. It is also highly regarded sound-wise. But I may try one of the later BF862 ECDesigns suggestions just for comparison
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Old Today, 11:53 AM   #6305
ryanj is offline ryanj  Australia
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Building the ultimate NOS DAC using TDA1541A
Default Attenuators, and 50Hz DEM

Hi john jones,
Quote:
Originally Posted by john jones View Post

My question is simply what is the best easy to implement I2S attenuator circuit, and best DEM oscillatror mod, bearing in mind I have I2S supply from SAA7345 and 16.9344Mhz clock (upgaded). I will make a new PCB so I can implement any circuit, I just wanted to know from people way cleverer than me, what circuits are recommended as I see many itterations in this thread over the years. I am a firm believer of simplicity over complex, so look for the best simple solutions.
I've attached an image with the attenuators im using with the corresponding waveforms below them.

Since your running in I2S mode - try using the diode based atten for BCK and the resistive based atten for DATA and WS.

If running in simultaneous mode (which you should because its much better) - Use Diode atten for LE and the resistive atten for DATA L, DATA R, and BCK.

Quote:
I do not want to go down the road of reducing the DEM oscialltor to 50Hz as per recent posts....though I might expriment as I have several TDA 1541A chips.
I've been running my DEM at 50Hz for the past month or so and am very happy with the mod. I've tested this method by playing -60dB recordings and they played just fine. This mod has helped to identify other weaknesses in my system which have since been corrected. The resulting perceived sound quality has improved by quite some margin - almost as much as going from I2S mode to simultaneous mode. Total cost of this mod is under $10AUD - why not just give it a shot? If you dont like it its no big loss.

I also attached a pic of a waveform coming out of AOL/AOR comparing with and without attenuation.
Attached Images
File Type: jpg attenuators.jpg (180.6 KB, 42 views)
File Type: jpg With and without attenuation.jpg (166.6 KB, 42 views)

Last edited by ryanj; Today at 11:57 AM.
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