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Old 25th May 2011, 12:38 PM   #691
noizas is offline noizas  Lithuania
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Quote:
Originally Posted by roger57 View Post
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.
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Old 25th May 2011, 03:36 PM   #692
roger57 is offline roger57  Canada
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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
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Old 25th May 2011, 04:35 PM   #693
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Quote:
Originally Posted by roger57 View Post
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....
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Old 25th May 2011, 08:15 PM   #694
roger57 is offline roger57  Canada
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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.
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Old 25th May 2011, 08:42 PM   #695
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Hi Gary,

i appreciate your willing to make a own pcb with your ideas, but therefore please start your own thread or come back on topic.

This thread should be for all theme around my Reference TDA1541A DAC project.

Thanks in advance.
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Old 25th May 2011, 09:05 PM   #696
roger57 is offline roger57  Canada
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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

Last edited by roger57; 25th May 2011 at 09:08 PM.
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Old 26th May 2011, 05:00 AM   #697
noizas is offline noizas  Lithuania
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Quote:
Originally Posted by roger57 View Post
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...


Saulius
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Old 26th May 2011, 06:06 AM   #698
roger57 is offline roger57  Canada
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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.
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Old 26th May 2011, 06:31 AM   #699
noizas is offline noizas  Lithuania
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Originally Posted by roger57 View Post
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.
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 approach to this project - all functionally different parts are located on different PCBs .
Maybe it is not best way for final product, but we are doing DIY project, not commercial device.

Saulius
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Old 29th May 2011, 08:10 PM   #700
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Exclamation 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


Click the image to open in full size.


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




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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