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Building the ultimate NOS DAC using TDA1541A
Building the ultimate NOS DAC using TDA1541A
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Old 11th January 2019, 05:58 PM   #6861
rfbrw is offline rfbrw
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Join Date: Oct 2001
Location: .
Quote:
Originally Posted by poki921 View Post
THANKS!
But What I'm looking for is an ebook about dac and adc
wrote by RUDY JOHA N VAN DE PLASSCHE
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Old 12th January 2019, 12:41 AM   #6862
weissi is offline weissi  Austria
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Join Date: Sep 2002
Location: Austria
Btw, the thing that I like the most with my setup is the incredible Stereo separation / Crosstalk. I've never experienced a more "channel silent" DAC like it is.

Setup:
Foobar(SOX@174kHz) > I2SoverUSB v.III > simultaneous > 2x TDA1541A > opamp I/V (ADA4898)

Reference:
Soekris dam1021 V.1 with Vref Caps increased to ~6000uF
Chi-Fi dual PCM1794A(mono) (all ADA4898)
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Old 12th January 2019, 12:52 AM   #6863
poki921 is offline poki921  Taiwan
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Join Date: Jan 2017
Quote:
Originally Posted by batteryman View Post
I've read the one you mean. Try this:

Found it.
ok!got it!
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Old 12th January 2019, 02:15 AM   #6864
Hanze Khronye is offline Hanze Khronye  Australia
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Join Date: Jan 2018
Quote:
Originally Posted by lcsaszar View Post
My circuit is best suited for balanced DAC output, you drive the ends of the center tapped primary of the transformer in opposite phase, so the -2mA bias currents cancel. One transformer and one tube per channel. The output is low impedance unbalanced.
I can see the appeal as a front and for a balanced system (if that's your preference). Do the 1541As need to be matched for any parameters, and is the 2H cancellation audibly apparent WRT a SE stage?

To run balanced and then recombine to SE seems counterintuitive to me.

I can also see the appeal (probably more than any other scenario involving the additional parts) of running a two way speaker, each driver bi-amped right the way back to independent dedicated HF and LF DACs using PC based software for crossover and DSP, each being optimised and BW limited for optimum performance.

Lots of cool stuff. Is there anything more linear than a resistor as IV ?
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Old 12th January 2019, 08:06 AM   #6865
batteryman is offline batteryman  United Kingdom
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Join Date: Jun 2011
Location: SCOTLAND
Building the ultimate NOS DAC using TDA1541A
Quote:
Originally Posted by lcsaszar View Post
My circuit is best suited for balanced DAC output, you drive the ends of the center tapped primary of the transformer in opposite phase, so the -2mA bias currents cancel. One transformer and one tube per channel. The output is low impedance unbalanced.
You do still have I/V resistors?

Or no resistors and you have grounded the centre tap, in which case DC is flowing through the transformer? (not allowed for the Sowters)

I have tried my balanced setup with the centre tap grounded and not grounded and cannot hear a difference. (I have 100r I/V resistors)
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Old 12th January 2019, 10:04 AM   #6866
Zoran is offline Zoran  Serbia
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Join Date: Jan 2004
Location: Belgrade
For my opinion it is not good to put transformer directly on the current output of the TDA1541A dac chip. When You put the transformer IV conversion acting at the Rdc component of the transformer winding. And it is not common to find transformer with lower Rdc windings for smaller offset than stated in the datas, considering terms of lower distortion. Additionally if the Rdc winding of the transformer is low it could implicating a lower number of turns and leading to lower primary inductance... Can affect bandwidth in low end, and could be less capacitive to secondary, with corresponding lower number of turns. So it could have larger extennsin at the upper end...
.
Alzo should mind the total phase. If You put the +Io at the Riv You will get -Vo. And opposite.
.
The proper way is to use ballanced version. With Current injection of 2mA, and 2 x Riv-s. Connected from Io to GND chip each. THEN go to Inter-stage transformer.
At the Riv-s will be the some small offset BUT it is the same value. Connect now Vouts from Riv taps to the transformer. CT of the transformer leave unconnected. Do not connect CT tap to GND or elsewhere.
The transformer will be acting as isolating passive device, and because of the low value of present signal will have less self distortion. RC snubber network, at the secondary should check and implement if it is needed.
.
After that manage amplification of low level signal, phase at the output of the trafo, filtering of HF component, and output buffer if needed for lower output impedance.
For complete galvanic isolation use separate power supply from the mains point with separate powr transformer. If You have extra space it could be ddual mono 2 x independent PS units for each channel. That is almost ALL and Coul be implemented with all current output dac modules.
...
These higher amplifications gor my opinion should be done with tube of needed higher mju factor, correctly biased. Or JFET for little bit lower amplification result. For my opinion SE topology of amplification stage is better than PP complementary topology...
...
It is not bad idea to Add a for instance low impedance buffer after the IV R, If you want purist approach. That buffer could be supplied with +-15V of TDA1541A power branch. That way You can find more good options for the inter-stage transformer.
.
This is from personal praxis and listening experience.
Cheers

.
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Old 12th January 2019, 10:07 AM   #6867
Zoran is offline Zoran  Serbia
diyAudio Member
 
Join Date: Jan 2004
Location: Belgrade
Check out the ECs non inductive hand made Riv design. In this topic posted earlier. And consider Graphite hand made Riv also, for those lower values of Riv.
.
For the phase path from Riv to end:
+I@Riv, -Vout, SE amplification stage (tube or jfet), +Vout.
-I@Riv, +Vout, SE amplification stage (tube or jfet), -Vout.
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Last edited by Zoran; 12th January 2019 at 10:34 AM.
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Old 12th January 2019, 10:17 AM   #6868
batteryman is offline batteryman  United Kingdom
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Join Date: Jun 2011
Location: SCOTLAND
Building the ultimate NOS DAC using TDA1541A
Quote:
Originally Posted by Zoran View Post
For my opinion it is not good to put transformer directly on the current output of the TDA1541A dac chip. When You put the transformer IV conversion acting at the Rdc component of the transformer winding. And it is not common to find transformer with lower Rdc windings for smaller offset than stated in the datas, considering terms of lower distortion. Additionally if the Rdc winding of the transformer is low it could implicating a lower number of turns and leading to lower primary inductance... Can affect bandwidth in low end, and could be less capacitive to secondary, with corresponding lower number of turns. So it could have larger extennsin at the upper end...
.
Alzo should mind the total phase. If You put the +Io at the Riv You will get -Vo. And opposite.
.
The proper way is to use ballanced version. With Current injection of 2mA, and 2 x Riv-s. Connected from Io to GND chip each. THEN go to Inter-stage transformer.
At the Riv-s will be the some small offset BUT it is the same value. Connect now Vouts from Riv taps to the transformer. CT of the transformer leave unconnected. Do not connect CT tap to GND or elsewhere.
The transformer will be acting as isolating passive device, and because of the low value of present signal will have less self distortion. RC snubber network, at the secondary should check and implement if it is needed.
.
After that manage amplification of low level signal, phase at the output of the trafo, filtering of HF component, and output buffer if needed for lower output impedance.
For complete galvanic isolation use separate power supply from the mains point with separate powr transformer. If You have extra space it could be ddual mono 2 x independent PS units for each channel. That is almost ALL and Coul be implemented with all current output dac modules.
...
These higher amplifications gor my opinion should be done with tube of needed higher mju factor, correctly biased. Or JFET for little bit lower amplification result. For my opinion SE topology of amplification stage is better than PP complementary topology...
...
It is not bad idea to Add a for instance low impedance buffer after the IV R, If you want purist approach. That buffer could be supplied with +-15V of TDA1541A power branch. That way You can find more good options for the inter-stage transformer.
.
This is from personal praxis and listening experience.
Cheers

.
Its not the way I do it, but each to his own.
Yes, balanced is the way to go, but also with an I/V resistor to generate the voltage for the transformers to work without them having DC flowing through. No need for current injection either with this method.

I personally favour no current injection, no additional filtering and definitely no active devices between transformer and power amp volume pot. This way there are far few opportunities to affect the sound otherwise you can spend forever tinkering with designs, component values etc.

You can fine tune the sound with the secondary load resistance. For example I have built an Aleph 5 single ended amp and the bass is much less than my Quad 405, which I put down to the A5 having only 10k input impedance, whilst my vol pot is 50k although I can't be sure its not the amp itself running too high volts and too low current for my 6R speakers.

Of course if your amp is not sensitive enough you will need additional amplification. Or two amps driven from the antiphase transformer outputs with the speakers connected in bridge mode. (would need a 4gang vol pot however)
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Old 12th January 2019, 11:14 AM   #6869
Zoran is offline Zoran  Serbia
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Join Date: Jan 2004
Location: Belgrade
I think that for the passive Riv You have to tap one end to ground - to have any conversion
In the direct Transformer load, You have I/V conversion at the highly reactive element. I listened more implementation like this and personally I was not satisfied. Most of them was from prominent brands. Modifying in this fashion i explained was significantly better. But I must say that was SE typologies? Cant remember now for sure...
.
For the passive IV conversion It is from significance to have "pure" resistive load. Like EC explained earlier on the topic. And give the option for the hand made Isotan wire resistor. I make it may self and it sound very good?
...
How was offset without current inj. and what value of Riv was in Your example please?
Cheers
.
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Last edited by Zoran; 12th January 2019 at 11:18 AM.
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Old 12th January 2019, 11:36 AM   #6870
Zoran is offline Zoran  Serbia
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Join Date: Jan 2004
Location: Belgrade
Quote:
Originally Posted by batteryman View Post
You can fine tune the sound with the secondary load resistance. For example I have built an Aleph 5 single ended amp and the bass is much less than my Quad 405, which I put down to the A5 having only 10k input impedance, whilst my vol pot is 50k although I can't be sure its not the amp itself running too high volts and too low current for my 6R speakers.
If You are changing the value of input pot it can lead to cutting out highs at lower pot levels? Because of conjunction with dynamic capacitance of the stage?
But also, if this amp have C at the output to speaker - maybe should check this value against the load and increase it for lower LF rolloff?
I dont know exactly the case only thinking loudly...
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