Hi everybody,
this is my first post in this very very very interesting forum.
I'm Stefano, from Italy, 36 y.o.
After designing and building some multichannel tube preamps for guitar (I'm a "musician"), I started to rediscover my old passion for hi-fi gears. In this period I've get caught in the "diy web" another time, this time trying to set up a system for the "liquid music".
I bought a NOS DAC with 8xTDA1543 and so I started to think about modding it to extract the best I can from it: the DAC is sounding very good for the money I spent, but it lacks a bit of dynamics and "sense of space". I think I miss some high freq details, the sound is less "open" with rispect to my modded CD player (Marantz SA7001).
But first I have to understand some things and the first question is:
how can I choose the Rref/Rload in order to optimize the 8 TDA1543s and to get better sound?
or, in other words, wich value of Vout DC (without input signal) must I set?
I found that the Valab has Rload=340 Ohm and a 500k pot for Rref (the res connected to Vref pin). Looking at the datasheet, Vout (DC) must be 1.8 < Vout < Vcc-1.2. I have Vcc = 7.6V so I think that Vout=Vcc/2 could be a good starting point. Right?
With, for example, Vout (DC) = 3.6V, I'll get Rref = 378 Ohm, considering Ibias = 2 * Iref and Vref = 2V. I've read on a website that the best sound can be obtained with Rload = 2*Rref, but in my case I have Ref > Rload. And, just to know: what kind of load resistor (I/V resistor) must I consider to have the best signal? Anti-inductive design, hi temp stability or what else? Some hints about commercial products?
Thanks a lot in advance and...sorry for my english! 😉
Stefano
this is my first post in this very very very interesting forum.
I'm Stefano, from Italy, 36 y.o.
After designing and building some multichannel tube preamps for guitar (I'm a "musician"), I started to rediscover my old passion for hi-fi gears. In this period I've get caught in the "diy web" another time, this time trying to set up a system for the "liquid music".
I bought a NOS DAC with 8xTDA1543 and so I started to think about modding it to extract the best I can from it: the DAC is sounding very good for the money I spent, but it lacks a bit of dynamics and "sense of space". I think I miss some high freq details, the sound is less "open" with rispect to my modded CD player (Marantz SA7001).
But first I have to understand some things and the first question is:
how can I choose the Rref/Rload in order to optimize the 8 TDA1543s and to get better sound?
or, in other words, wich value of Vout DC (without input signal) must I set?
I found that the Valab has Rload=340 Ohm and a 500k pot for Rref (the res connected to Vref pin). Looking at the datasheet, Vout (DC) must be 1.8 < Vout < Vcc-1.2. I have Vcc = 7.6V so I think that Vout=Vcc/2 could be a good starting point. Right?
With, for example, Vout (DC) = 3.6V, I'll get Rref = 378 Ohm, considering Ibias = 2 * Iref and Vref = 2V. I've read on a website that the best sound can be obtained with Rload = 2*Rref, but in my case I have Ref > Rload. And, just to know: what kind of load resistor (I/V resistor) must I consider to have the best signal? Anti-inductive design, hi temp stability or what else? Some hints about commercial products?
Thanks a lot in advance and...sorry for my english! 😉
Stefano
Hi Stefano,
Everything you should know is here http://www.diyaudio.com/forums/digi...g-dac-complementing-cd-pro-14.html#post173483
Everything you should know is here http://www.diyaudio.com/forums/digi...g-dac-complementing-cd-pro-14.html#post173483
Ok, this confirm my previous calculations...with VCC=7.6V -> Vswing=4.6V ->
Vo (0 signal)=4.1V Rl=250Ohm and Rref=180Ohm, with 8xTDA1543.
With 8V -> Vo (0 signal)=5V -> Rl=220Ohm and Rref=180Ohm...
So, could you tell me why I have 340Ohm as Rl and Vo (0 signal) about 6V?
These values seem completely wrong...but I can't hear distortion/clipping or something bad in the sound...in these days I'll measure with the oscilloscope, just to see if there's something "strange".
Thanks
Stefano
PS: any suggestion about type/code for resistors?
PPS: why is always used a resistor to set the Iref? Why not even a simple current sink circuit ( one bjt, some diodes and a resistor...)
Vo (0 signal)=4.1V Rl=250Ohm and Rref=180Ohm, with 8xTDA1543.
With 8V -> Vo (0 signal)=5V -> Rl=220Ohm and Rref=180Ohm...
So, could you tell me why I have 340Ohm as Rl and Vo (0 signal) about 6V?
These values seem completely wrong...but I can't hear distortion/clipping or something bad in the sound...in these days I'll measure with the oscilloscope, just to see if there's something "strange".
Thanks
Stefano
PS: any suggestion about type/code for resistors?
PPS: why is always used a resistor to set the Iref? Why not even a simple current sink circuit ( one bjt, some diodes and a resistor...)
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