Building the ultimate NOS DAC using TDA1541A

And there I was, thinking I finally had a good idea!!

There has been a thing about this o/p thing has puzzled me for a while and I'm a bit embarrassed to ask ...

What happened about the 25mV max on the o/p pin of the dac chip?
Or does this only apply to the 1541A chip?

And while I'm asking about this, how is the zero dc offset voltage set for the same o/p pins? - or is that a thing of the past, too?
 
Defective TDA1541A Chip

Hi all,

This is a curiosity only. I have a defective TDA1541A and I've opened it to see the chip. See enclosed. There is the chip in itself and is mounted on a metal piece to disipate heat. In the process I've damaged the chip, sorry.

It's fan.

Best regards, and have a nice weekend
 

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omainik said:
Hi jameshillj,

I already use variable I/V resistor in the input of my preamp. Sound is definitely superior in comparison with R I/V in the DAC.

Resistance switched by a rotary switch sounds in my case better than resistance switched by relays

Ciao
Peter

Hi Peter,

The variable I/V sound is better than the fix resistor, that is very interesting.
I am not sure how that works. I had always thought that there are only a few optimal resistor values for a specific dac.
What range of resistance for the I/V (TDA1543 or 1541)?
Is there a difference in sound below the lower and higher I/V resistance?
Thanks.

...Chuck
 
Hi Chuck,

my expression of the situation was not exact enough. There is no variable Resistor. Different values are achieved by switching fixed value resistors with a 26 pos switch.

The first Version was realized with 8 Relays in parallel. The resulting value is achieved by combination of paralleled fixed resistors.

With the relays I tested the Volume Control in DAC and in the Input of my preamp. The latter was definitely better. In the input of the preamp is a ladder stepped attenuator. In the position for Digital input the input resistor is shorted, so the resistance to ground is switched.

Resistor with switch sounds better than switched resistor with relay.

I use 4 paralleled TDA1541 with output transformer. no resistive load on the primary side (DAC). The transformer is loaded on the secondary winding only with resistance ranging from 100R to 2k2. this is reflected to the dac through the transformer with a step up ratio of 1:19. so the dac sees 0.28 to 6 ohm.
 
tda1541transimpedanceoutput.jpg


V1 is a voltage divider to obtain output at source of J1 almost 0.0mV. I have replaced R1 with jfet CCS but the effect is not significant ( I used 2sk170bL with some source resistor to get about 5mA flowing)

I wonder if this suitable for DC servo or a single ended with negative feedback will do ?
 
I see the familiar current buffer in J1, with source at 0.0V dc to suit the o/p pin of the dac chip, and the JC2 output buffer (the J2 & J3 that you want to add a servo to?)

The only ? thing there is the (almost?) 0volts across that 1uF o/p cap - nearly all caps work better with some dc bias across it - better sonics (IMO again, - plenty of volts - if possible >/= about 70% of capacitor rated voltage ).

ZenMod (poor man's lightspeed thread) has added a small 47R pot between the 2 jfets on this same type of o/p buffer to trim off any dc offset, and no the cap at all (and a bit of local degeneration?) . Simpler, and if you tie the J2 & J3 together, almost zero drift.

(What do the R3 & R4 220R gate resistors do?)

Omainik,
With the 4 x 41A chips in //, o/p current max is 16mA amd this feeds the transformer directly (Sowter number?) - if the reflected impedance at max setting = 6R, dac o/p pin would have about 100 mV on it, yes?

Do you source current for the transformer (to dac o/p pin) from a -ve voltage, or just to 0volt?
 
How to avoid the 1uF capacitors (that's why the idea of DC servo, but that DC was used in folded cascode and not in this configuration).

The 220R resistor is there to prevent oscillation.

There is about 7V just before at the output (before the capacitor). I will try with some resistors. How do I measure the current flowing at J2 at idle?

Actually this is just to experiement. I will be getting the Krell based CAST (Current transmission) amplifier soon. So I hope to make do with the voltage amplification and instead use the folded current source to drive my amp. but that is later.
 
jameshillj said:
Omainik,
With the 4 x 41A chips in //, o/p current max is 16mA amd this feeds the transformer directly (Sowter number?) - if the reflected impedance at max setting = 6R, dac o/p pin would have about 100 mV on it, yes?

Do you source current for the transformer (to dac o/p pin) from a -ve voltage, or just to 0volt? [/B]


Hi,

transformer is 8347
http://www.sowter.co.uk/specs/8347.htm

4mA * 4 DAC = 16mA
0.016 A * 6 R = 0.096 V on the loudest position
in normal use for my system
0.016 A * 0.4 R = 0,0064 V

transformer is connected to 0V
 
Battery Power for TDA1541

Hi John,

I am just about to implement battery power on my D14M, and have sourced 3 x 12v 20Ah SLA batteries. Is it acceptable to directly feed +12v -12v and -24v to the D14M main board and let the LED regulators produce +5, -5 and -15, or would I need to use some kind of pre-regulation before the LED regulators.

I am also looking for 3 x 1f car audio capacitors for each of those voltage rails and it seems a shame to put pre-regulators in if I can get away without them.

Brad
 
Bernhard said:

What does the dV -36.25 mean ?
K2 is -36.25 dB below the fundamental ?

dddac,

I would appreciate your comment.

While I was on my analyzer for another thread, I did a FFT of my DAC with passive I/V @ 1 kHz / 0dB.

As you can see, it is totally clean down to the noise floor of ca. -90 dB.
I was lazy to program averaging to remove the noise floor, it would be clean down to and below the limit of my analyzer = -95 dB also...

Vpp on each leg of the balanced DAC is 395 mV, that combines to 1,3 Vpp after the TVC
The measurement was made on the output of the transformer volume control, thus includes the distortion of the TVC.

dac_fft_0db.jpg
 
omainik said:
transformer is from sowter.

I compared a lot of other possibilities. The sound characteristics I like were only present with the transformer and some tube based output stages with a rather complex psu, so the transformer wins soundwise and is the simpler solution.

Would you mind showing a basic schematic of your output stage.
I got two sowter transformers here that have a 1:19 ratio and I
would really like to compare your solution to my simple passive I/V.

Greets,
Klaus
 
This is such a great post.... John has done a great job of working with us and sharing...providing products on his site.

But is there any way to down the whole thread? Into a word doc or some thing like that....

I would like organize the thread into a bits and pieces that are really meaningful for me....


jk
 
Re: Dynamic jitter attenuator.

I am using 220R-3xBAT43-(to BCK)-154R-499R//220n, I only got 1V at BCK, should I keep it or replace the 499R with a trimmer?

The forwarding volt of BAT43 (VISHAY) from DMM is only 0.27V, is that normal? The datasheet shows 2.7V-3.3V under 2MA, which should be correct. Maybe I need to add another BAT43?

BTW, I am getting 1.2V from WS and 1V from DATA with 1K//3.3K attenuator network. PCM2707 datasheet shows 2.8V output from FUNC1 and 2.4V from DOUT.

Thanks
2A3SET

maxlorenz said:
Thanks EC for your detailed and informative reply about volume control.
Thanks 2A3SET for you tip. I recently saw that ligthspeed attenuator. It sounds interesting and can be driven by 5V PS.

Dear EC, yesterday I made my first attempt with the dynamic jitter attenuator for my D1M. BCK is taken from PCM2707. I put a trimer resistor parallel with 220nf, in series with 150R to ground as per your diagram. The trimer set at 283R (rheostat mode) gave 1,22V DC for BCK. Ripple measured between 150R and 283R (trimer) and ground was around 10mV, even with 230nf or 320nf...is it good enough? Shall I try lower capacitances?

Today I will try to replace the trimer resistor by a better quality fixed R.

Another question> could you advice what tweak would be better for the BCK signals of the multiple DAC chips (DI4 and scrambled versions) converters-> conventional signal attenuator or dynamic jitter attenuator???

Many thanks,
M

PS> the 220R series BCK resistor is place AFTER the bat 85 (in my case) and after the dynamic jitter attenuator. Must I change it?
 

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Hi 2A3SET,

I would recommend using trimer resistors on daughter boards when playing with attenuators and dynamic jitter attenuator (DJA), to set for optimal values and optimal sound, IF you have a scope to check. I would do it just for the fun of learning how the waves move up an down. :D
After that it is easy to measure and replace by better fixed R.

A question> do you get sound coming out?

I report that, even if not optimal, my own version of the DJA made a significant improvement in sonics. :cool:

Another philosophical/technical question to John> do you think using inductors from attenuators R TO GROUND will improve sound???

Good luck,
M