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Old 5th March 2012, 04:14 PM   #181
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The HC86 can be thought of as a conditional inverter - with data going into one input, if the other input is 0 then it won't invert, with this second input at 1, it will. Incidentally since the TDA1543 was originally designed to be used with inverting (opamp) I/V, it contains inversion as a matter of course. So to get true phase out of it in passive I/V (as in the Muse) you'd need to run with one input of the HC86 = 1 so that it inverts the digital data. I mentioned this point on the Head-fi (800+ posts long) thread on the Muse
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Old 13th March 2012, 06:25 AM   #182
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hi, sorry for resurrecting an old thread

i have hifiman hm601 portable player which occupies tda1543 in it. from what i can tell, it uses 5v voltage regulator to feed stable supply to the dac chip. the I/V stage is a low pass filter occupied by LM833 and JRC4560

what is the suitable bias resistor value in pin 7? is there any calculation for it? i can't find any useful reference regarding this Rref in the tda1543 datasheet. i want to achieve maximum sound quality and i don't care about the battery life (i can play with the I/V stage & headphone amplifier stage later to achieve longer battery life)

thanks in advance

Last edited by idjoel2000; 13th March 2012 at 06:50 AM.
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Old 13th March 2012, 09:13 AM   #183
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Quote:
Originally Posted by idjoel2000 View Post
hi, sorry for resurrecting an old thread

i have hifiman hm601 portable player which occupies tda1543 in it. from what i can tell, it uses 5v voltage regulator to feed stable supply to the dac chip. the I/V stage is a low pass filter occupied by LM833 and JRC4560

what is the suitable bias resistor value in pin 7? is there any calculation for it? i can't find any useful reference regarding this Rref in the tda1543 datasheet. i want to achieve maximum sound quality and i don't care about the battery life (i can play with the I/V stage & headphone amplifier stage later to achieve longer battery life)

thanks in advance
The standard Vref feeds the voltage reference for the opamp.
To get high quality go passive, then you must load the Vref pin with a resistor and also load the output with a resistor. The values depend on the voltage you have (and the number of parallel units).

It can be done with 5 volt but you get higher quality with about 7 Volt (i have that) without warming the device.

I made a table once of most used values but must look it up.
Anyway, you must have a potmeter for Vref, and a variable Vb too (best is between 6-7.5V) so you can set the operating points. There is a point of equilibrium where the saturation of the top and bottom of a 0 dB sine wave are equally low. (You can see it on a scope).
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Old 13th March 2012, 02:12 PM   #184
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You can find the info how to calculate Rref here: Non Oversampling DAC-complementing CD-PRO
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Old 13th March 2012, 04:23 PM   #185
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peter, sorry to bother again. but i need to ask something

it seems like I/V stage, supply voltage, and Vref are playing key role for calculating the Rref value

but as i mentioned earlier, HM601 uses active I/V stage (2 opamps constructing a low pass filter), and there is no I/V resistor between the dac output and opamp input.

can i calculate the Rref by simply remove the existing Rref and measure the current flowing from the Vref to ground, then simply divide 2.2V with the measured current to obtain the value of Rref?

and why did you suggest using 3R8 ohm for Rref in this post?

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Originally Posted by Peter Daniel View Post
Using Mills is perfectly fine as you are changing other aspects of design anyway.
Please note that for a single DAC chip, the current setting resistor should be 3R8

sorry for the noob questions..

Last edited by idjoel2000; 13th March 2012 at 04:29 PM.
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Old 14th March 2012, 02:18 PM   #186
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Quote:
Originally Posted by idjoel2000 View Post
peter, sorry to bother again. but i need to ask something

it seems like I/V stage, supply voltage, and Vref are playing key role for calculating the Rref value

but as i mentioned earlier, HM601 uses active I/V stage (2 opamps constructing a low pass filter), and there is no I/V resistor between the dac output and opamp input.

can i calculate the Rref by simply remove the existing Rref and measure the current flowing from the Vref to ground, then simply divide 2.2V with the measured current to obtain the value of Rref?

and why did you suggest using 3R8 ohm for Rref in this post?
3R8 is for voltage regulator, not V ref.
As to other question, I'm afraid I can't be much of help.
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Old 14th March 2012, 02:49 PM   #187
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Quote:
Originally Posted by idjoel2000 View Post
what is the suitable bias resistor value in pin 7?
It depends what quiescent output voltage you want from your LM833s. There's a minimum value it can be - 910R (in E24 series), but no maximum.

Quote:
is there any calculation for it?
To come up with an optimum we'd need to know the supply rails to the I/V stage (LM833) and its feedback resistor value. That would allow setting the quiescent output voltage mid-way between the rails.
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Old 15th March 2012, 03:47 AM   #188
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Originally Posted by abraxalito View Post
It depends what quiescent output voltage you want from your LM833s. There's a minimum value it can be - 910R (in E24 series), but no maximum.



To come up with an optimum we'd need to know the supply rails to the I/V stage (LM833) and its feedback resistor value. That would allow setting the quiescent output voltage mid-way between the rails.
i'll look into that later, but as far as i know, the rail to rail supply of LM833 is -5 to +5V. so we need to set the Vref at 2.5V?
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Old 15th March 2012, 04:28 AM   #189
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If by Vref you mean pin7 of the TDA1543, its set internally to 2.2V. Hanging a resistor off that pin, provided its not smaller than 910R won't change the voltage.

Given that the LM833 has balanced supplies we'd want its output to sit at 0V when no music is playing. Are the positive input pins (pin3,5) connected to pin7 of the DAC chip? If they are (even via some series resistance) then the LM's outputs would sit at 2.2V with no current coming out of the DAC.

The mid-scale current for the 1543 is 1.15mA typically, to get the bias current to equal this (for no net current out) needs 0.575mA as the Vref current, meaning Rref=3.8k. However we'd not like 2.2V out of the LM833, rather 0V which is done by increasing the bias (decreasing the Vref resistor below 3k8). The amount depends on the gain of the LM833 stage but I'd make a guess that for 2.8V peak signal the I/V resistor will be 2k4 meaning the bias needs to deliver an extra 1mA roughly to get the output to zero volts. Thus I'd go for a 2k Vref resistor as first stab
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Old 15th March 2012, 05:24 AM   #190
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Originally Posted by abraxalito View Post
If by Vref you mean pin7 of the TDA1543, its set internally to 2.2V. Hanging a resistor off that pin, provided its not smaller than 910R won't change the voltage.

Given that the LM833 has balanced supplies we'd want its output to sit at 0V when no music is playing. Are the positive input pins (pin3,5) connected to pin7 of the DAC chip? If they are (even via some series resistance) then the LM's outputs would sit at 2.2V with no current coming out of the DAC.

The mid-scale current for the 1543 is 1.15mA typically, to get the bias current to equal this (for no net current out) needs 0.575mA as the Vref current, meaning Rref=3.8k. However we'd not like 2.2V out of the LM833, rather 0V which is done by increasing the bias (decreasing the Vref resistor below 3k8). The amount depends on the gain of the LM833 stage but I'd make a guess that for 2.8V peak signal the I/V resistor will be 2k4 meaning the bias needs to deliver an extra 1mA roughly to get the output to zero volts. Thus I'd go for a 2k Vref resistor as first stab
thank you for the very clear explanation abraxalito. i have to check the pcb first with my multimeter to test the connection

to manually set the LM833 output at 0V, can i just play with Rref until i get 0V at the LM833 output? we can measure LM833 output by tapping the red and black probe to pin1 of the LM833 and active filter ground right?

will report back here again after i got something to report. thanks!

Last edited by idjoel2000; 15th March 2012 at 05:31 AM.
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