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"Reference" TDA1541A DAC with I2S-BUS architecture

Surface Finish for future PCB´s

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Hi,

Right now - I am using just 50 ohm resistors to ground to see if I can just get a voltage sine wave. Although it will be small, I should be able to see it. However, I have measured DC voltages at the AOL and AOR pins and something odd - they are both at -103mV. That does not seem correct, I thought these pins must be at 0V in order to work correctly. Why would I get this voltage at those pins?
Gary

Gary, I am inclined to think that your testing procedure is the problem.

The circuit simply requires that you stuff the board and fire it up.

Other than a component failure, and given you have satisfied yourself that there are both a) correct voltages on the chip AND b) correct i2s signals, you have only one option - the output stage.

...which in your case is a bit of an experiment (that I confess I don't understand!), so if you don't own a proper output stage to try it with, and you want to knock together something both competent and cheap, might I suggest EC designs very simple 2SK170 based design, which as I remember doesn't even require power, and is very simple and cheap to build.

Personally, I think you'll discover that you do have sound after all. I really can't recommend Oliver's Tube-I-Zator board enough for a totally superb output stage. It is the classic lampizator design, and I love it with 6n2p tubes.
 
Hi,

Thanks for your help!
I've verified all parts on the TDA1541A PCB, so no issues there.

The TDA1541A is a current output (source) DAC with a full scale range of +/-4mA. The purpose of the I/V resistor is to convert the current into a voltage of (with a 60 ohm resistor) +/- 240mV. If I'm using a 1KHz sine wave file, it should result in the above described sine wave across the resistor, which should be clearly visible on my scope. The purpose of the Tube-I-Zator, EC Designs or any other amplification stage is to bring that small voltage signal up to drive the input of your preamp or amp. So right now, the output stage is irrelevant.

If this is incorrect, someone please correct me. Otherwise, I still have a problem I cannot identify. On 2 PCBs, nonetheless. I'm beginning to think it's in the USB to I2S Teralink, but the signals all look OK. Clearly a mystery...

Gary
 
Hi Gary,

TDA1541 output has +/- 2mA swing with -2 ma offset, not +/-4ma as you wrote.
So with 60 Ohm and normalised 1kHz signal you should have AC signal which should be between -240 mV and 0 V (with negative 120mv DC offset on digital zero).

If you want to test Teralink's chip for sure, easiest way is to put the TERALINK's optical or RCA SPDIF output back to PC's SPDIF input and check with sofware do you really have that 1kHz signal.


If this is incorrect, someone please correct me. Otherwise, I still have a problem I cannot identify. On 2 PCBs, nonetheless. I'm beginning to think it's in the USB to I2S Teralink, but the signals all look OK. Clearly a mystery...

Gary
 
I connected up the Twister Pear SPDIF to I2S converter - my shop CD player has SPDIF output. I used a test tone on a CD, the same as the USB test. I also ran the signal through Oliver's hi-speed buffer. I now get an analog signal, finally, although very noisy :camoufl:
I confirmed the digital signals entering the DAC were the same levels as the USB.

So now the issue must be the Teralink. I will have to understand why this is not working as it should, perhaps something odd with the timing relationship. I hope it is not broke internally, but it appears it might be.

Noizas, can you please elaborate on the TDA1541A "offset"? Are you saying there should be 120mV of DC at the AOL and AOR pins?

Thank you all who have helped.

Gary
 
Gary, when testing the digital input, test for (K)Hz rather than volts. It's the only way to know you're actually getting the signal.

Oh, and the "correct" I/V resister values are 56 Ohm per channel for a single dac and 27 Ohm per channel for a 2x parallel dac.

These values are the highest safe values before distortion occurs, and recommended.
 
Noizas,

Thanks for the reply.This static DC voltage a result of...what? In addition to the signal, I also observed this at -103mV.
Is it not necessary to null this before sending into the amplification stage (tube or transistor)?

Gary


Yes, if you connect ONLY 60 Ohm resistance on AOL (or AOR) output to ground, here should be negative voltage offset about 120mV (0,002A*60 Ohm).

Saulius
 
Noizas,

Thanks for the reply.This static DC voltage a result of...what? In addition to the signal, I also observed this at -103mV.
Is it not necessary to null this before sending into the amplification stage (tube or transistor)?

Gary

It is recommended to null this offset, but not only because of following amplification stage, but mainly because theoretically best THD can be achieved if output voltage is between ±25mV (reference - TDA1541A datasheet).
50 mV p-p (18mV RMS) is quite weak signal and difficult to amplificate without sensible noise, so many diyers use I/U resistance in 40 - 100 Ohm range, going to achieve 50 - 140 mV RMS before amplification stage.

To null this offset you need inject constant 2mA current by CCS, based on FET (2SK170GR or better BF245A) or by RCR connected to constant voltage source.
Search the DIYaudio threads and you will find schematics for sure.
 
Hi Saulius,

I did recognize this offset as an issue and hence my question, thank you for answering it. I'm going to use the one from Pedja Rogic which is simple and makes sense. And in fact already hacked the board to test.
Now that may parts have been removed from the v2.3 PCB, I am doing a new PCB in Protel beginning this week. However, this time there will be a separate ground plane for both analog and digital, isolated digital sections, and it will contain for both TDA1541A DACs. Reduction of digital noise to the lowest level will be my objective. Also, If I cannot see a strong reason to not put the tube stage on the same PCB, I will do that. Since I work in electronics firm, I can have the board made on one of our weekly board runs for little cost.

Gary
 
Hi Saulius,

I did recognize this offset as an issue and hence my question, thank you for answering it. I'm going to use the one from Pedja Rogic which is simple and makes sense. And in fact already hacked the board to test.
Now that may parts have been removed from the v2.3 PCB, I am doing a new PCB in Protel beginning this week. However, this time there will be a separate ground plane for both analog and digital, isolated digital sections, and it will contain for both TDA1541A DACs. Reduction of digital noise to the lowest level will be my objective. Also, If I cannot see a strong reason to not put the tube stage on the same PCB, I will do that. Since I work in electronics firm, I can have the board made on one of our weekly board runs for little cost.

Gary

I wouldn't mind one of those myself, if you are doing a run Gary....
 
I will post on how it turns out and provide updates. There could be some tweaks to the DEM reclocking circuit - I'll see what it looks like in LT Spice. In fact, I'll likely run a blog on my ISP home page which I'll post later. I've already done the simulation on the tube stage in LT Spice and it's looking phenomenal - about 0.05% distortion. I did not design it, but took a combination of ideas from the web (to which I will acknowledge) made some tweaks and changes to support the overall design. I do have a soft-start in the power supply that enables heater supply for 45 seconds before switching the plate supply, this serves the purpose of stabilizing the tube before allowing the DAC to connect to it - this circuit also controls a reed relay for the signal path into the grid 200ms after tube plate supply is energized. The plate supply to the 6922 is at 250V, and because the plate to heater maximum is exceeded, the heater is referenced to the high voltage supply using the Morgan Jones THINGY.
I appreciate the fact that DIY Audio is a great place to share ideas and projects, but first I need to understand from the DIY moderator how I must contribute back in order to sell PCBs (at cost as dvb-projekt has done), with an amount from each board back to the DIY site.
 
Oliver,

Sorry, I should have done this, thanks for the reminder - I will start a different thread.
Some ideas will be mine, but mostly a combination of existing bits and pieces from many bright people who are already a part of this forum and other websites.

Gary
 
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Now that may parts have been removed from the v2.3 PCB, I am doing a new PCB in Protel beginning this week. However, this time there will be a separate ground plane for both analog and digital, isolated digital sections, and it will contain for both TDA1541A DACs. Reduction of digital noise to the lowest level will be my objective. Also, If I cannot see a strong reason to not put the tube stage on the same PCB, I will do that. Since I work in electronics firm, I can have the board made on one of our weekly board runs for little cost.

Gary

Hi Gary

IMHO, Oliver's reference DAC project is excellent, however it has some small disadvantages to make it perfect set of two TDA1541.
I'm also going to make my own PCB, which main idea is to use two TDA1541 but for balanced connection instead of parallel use.
So if you are going to make your own thread, I'm sure you will find much support from DIY community - here are many crazy lovers of TDA1541.
And I'm one of them...:D


Saulius
 
I'm sure you'll agree that if it were not for Oliver, many DIY people would not have experienced the TDA1541A chip. So I think we should all tip our hats to Oliver for a job well done in bringing his project to life, working with others like Salas and giving many a chance to enjoy the work of the DIY community.:wave2:
 
I'm sure you'll agree that if it were not for Oliver, many DIY people would not have experienced the TDA1541A chip. So I think we should all tip our hats to Oliver for a job well done in bringing his project to life, working with others like Salas and giving many a chance to enjoy the work of the DIY community.:wave2:

Agree without doubt.

I'm going to finish DAC on Oliver's board and only after that will make balanced type DAC, leaving part of system intact, just replacing TDA1541 boards by new one or maybe simply inserting I2S splitting board.

This become possible only because of Oliver's modular :yinyang: approach to this project - all functionally different parts are located on different PCBs :yes::yes::yes:.
Maybe it is not best way for final product, but we are doing DIY project, not commercial device.

Saulius
 
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Joined 2009
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DAC Module V3.0 preview

On many requests for an DAC module update, witch should have a direct shunt voltage input,
here is a preview of my new

DAC Module V3.0


An externally hosted image should be here but it was not working when we last tested it.



The evolution brings the following changes

- Direct shunt voltage inputs with shortest onboard traces
- I2S In-/Outputs with shortest onboard traces
- Upgrades DEM Synchronizer
- Onboard Grounded-Gate MOSFET Current Buffer I/V Stage
(-ecdesigns- MK7 version)
- Compacter design


Still on the module

- Separate GND-Trace for DEM-Synchroinizer
- Master/Slave connectors for parallel DAC module usage
and external I/V Buffer stages e.g.
Tube-I-zator & DDNF Stage
- Groundplane
- no SMD Design

:wave:


The DAC module V2.3 will still be available for those,
who want to use it without the TDA1541A Shunt module!
 
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