Building the ultimate NOS DAC using TDA1541A - Page 362 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 24th February 2011, 10:11 AM   #3611
diyAudio Member
 
Join Date: Mar 2008
This is really GREAT!

maybe an improovement idea:

use optpcouplers on the 3 I2S signal imput to isolate the ground of the transport device (I will use the I2S outpout of a ENVY PCI sound card chip)
  Reply With Quote
Old 24th February 2011, 01:48 PM   #3612
diyAudio Member
 
Join Date: Apr 2003
Location: Eastern Pennsylvania
Quote:
Originally Posted by -ecdesigns- View Post
Hi luxury54,



There is approx. 4V DC on each I/V resistor. So I simply used a 1K potentiometer and suitable decoupling cap to create an adjustable reference voltage. There is a separate reference voltage for L and R channel. This reference voltage now serves as "GND" reference for connected equipment.

By trimming each voltage so it exactly matches DC voltage on the I/V resistor, the DC voltage between I/V resistor and reference becomes zero. In other words, the DC component is removed without using a coupling cap.

The circuit is kept very simple, 1K multiturn trimmer. One side goes to GND, the other to +5V. Suitable decoupling cap is connected between wiper (minus) and +5V (plus). The adjustable reference voltage is now on the wiper.
Hi John,

I once considered such a solution for eliminating the output coupling cap. There are two issues, one minor and one not so minor, that I found.

First, a 'rail-splitting' resistive divider network will substantively increase the circuit output impedance. That's probably a minor concern in a low-level output application. The not so minor concern is that separate left and right offset zero'ing trimmers will be shorted together at the common left and right channel ground of any following amp or preamp input circuit - unless that input is floating or transformer-coupled. This common signal ground connection would equalize the voltage back at the two trimmer wipers inside the DAC, re-creating a D.C. offset there. One can't utilize a common resistive divider to create a single ground reference because the additional impedance on the ground return would be modulated by each channel's signal return current, effectively producing a particularly severe ground-loop.

How did you resolve such issues in your design?
__________________
Ken

Last edited by Ken Newton; 24th February 2011 at 01:56 PM.
  Reply With Quote
Old 25th February 2011, 09:55 AM   #3613
diyAudio Member
 
Join Date: May 2006
Location: Holland
Hi Ken Newton,

Quote:
First, a 'rail-splitting' resistive divider network will substantively increase the circuit output impedance.
The trimmer value equals 1K, when adjusted for 4V DC there will be approx. 200 Ohms between +5V (where the I/V resistor connects) and reference voltage. For ac signals the remaining 800 Ohms will be in parallel (impedance between GND and +5V is almost zero). So added impedance will be 160 Ohms, this increases total output impedance to only 660 Ohms.

I could also use trimmers with lower resistance, 250 Ohm for example. Then the output impedance would only increase from 500 to 540 Ohms.

But since I use 470uF decoupling caps in parallel with this 160 Ohms, increase in output impedance is negligible.


I tested many different semiconductor and tube unity gain buffers to lower output impedance, but the distortion, noise, and loss of (time) resolution doesn't justify their use.

The reason this is so critical is that huge amount of information is left out in digital recordings. Analogue signals have almost infinite bit depth and and infinite sample rate, then one can afford some (time) distortion before perceived sound quality starts to degrade. In other words, when using analogue sources, playback equipment is far less critical as with digital sources.

Suppose we made an approximation by using say 1GHz sample rate and 24 bit resolution. Then we would require 21.6 Terra bytes of information for a 1 hour stereo recording. It would even be doubtful if this information could even be stored and retrieved fast enough for a real-time audio stream.

This still would offer lower resolution compared to the original analogue source. With 44.1/16 we only have 635 Mega bytes at our disposal for 1 hour of music. This should give an impression of the amount of information that was left out.

Digital playback systems can restore fundamentals within the audio spectrum, but they offer very limited time resolution as samples can only change at 22.6us intervals (44.1/16) or 5.1us intervals (192/24).

Practical example, some instruments produce fundamentals that are time shifted at say 11.34223us, 1.02234us, 125.4ns, 881.3442ns and 201.33us.

Digital playback system (44.1/16) would have to force-fit these harmonics into multiples of 22.6 us. So 11.34223us, 1.02234us, 125.4ns, and 881.3442ns translate to zero. Finally 201.33us translates to 181us or 204.084us.

So the playback equipment should be optimized for the time domain in order to preserve whatever time resolution remains after the A/D conversion process. Higher time resolution doesn't result in a day and night difference in perceived sound quality, it does however add more refinement, making the music more realistic.


Quote:
The not so minor concern is that separate left and right offset zero'ing trimmers will be shorted together at the common left and right channel ground of any following amp or preamp input circuit
Since both are decoupled with 470uF, crosstalk between the channels will be remain low. There might be a small DC offset increase that is acceptable in most cases. The DC offset increase depends on channel matching.


Quote:
How did you resolve such issues in your design?
I made sure the channels match very closely.

Split reference was maintained throughout my audio set using separate shunt volume controls and Circlotron monoblocks.
  Reply With Quote
Old 25th February 2011, 04:59 PM   #3614
diyAudio Member
 
Join Date: Feb 2011
Is there any chance you could post a schematic of the MOSFET amplifier circuit? I'm trying to build a small 40 watt/channel amp using the TDA7376B chip but it's quality is not that great. I'd also like to send it optical signals and I'm unsure how to conver the optical signal to line level audio, any advice?
Thank you
  Reply With Quote
Old 28th February 2011, 07:30 AM   #3615
diyAudio Member
 
Join Date: May 2006
Location: Holland
Hi dirtbiker1824


Quote:
Is there any chance you could post a schematic of the MOSFET amplifier circuit?
I already did, photograph of the single-PCB Circlotron power amp is in post #3528

Concept schematics are in post #3539. In the final version a number of modifications were made like using discrete voltage regulators, Honeycomb Mobius wire wound resistors and Honeycomb Mobius purifiers.

Quote:
I'm trying to build a small 40 watt/channel amp using the TDA7376B chip but it's quality is not that great.
This chip was designed for car audio applications, not for high-end audio.

Quote:
I'd also like to send it optical signals and I'm unsure how to conver the optical signal to line level audio, any advice?
This involves signal conversions that are likely to cause further degrading.
  Reply With Quote
Old 1st March 2011, 03:20 PM   #3616
diyAudio Member
 
maxlorenz's Avatar
 
Join Date: Oct 2003
Location: osorno , Chile
Default OT; sort of...

Hi dear -EC-

Since last year I have neglected DIY (but followed your threads) due to job and to my new (and expensive) hobby of playing/enjoying/collecting violins.
My luthier lend me some Dammar gum and I applied as a varnish, diluted on turpentine, on my Audio Nirvana fulrange drivers. I had not listened to them yet. I want them to dry a little more.
With the dammar varnish left I thought about emulating "tube-O-lator":

The Altmann "Tube-o-lator" lacquer

so I put on it powdered graphite from cheap pencils until getting a dark grey matter that I applied to the inexpensive TDA1543 chip, only on the "roof" (I will later put it all around) and waited. Am I getting crazy or the sound changed?

Anybody has experience with this?

Cheers.
M.
  Reply With Quote
Old 1st March 2011, 03:44 PM   #3617
diyAudio Member
 
Bernhard's Avatar
 
Join Date: Apr 2002
Location: Munich
Quote:
Originally Posted by maxlorenz View Post
so I put on it powdered graphite from cheap pencils until getting a dark grey matter that I applied to the inexpensive TDA1543 chip, only on the "roof" (I will later put it all around) and waited.
A much better and well proofed solution is angel dust scattered all over the pcb.
  Reply With Quote
Old 1st March 2011, 03:44 PM   #3618
diyAudio Member
 
QSerraTico_Tico's Avatar
 
Join Date: Oct 2004
Talking Come on!

Quote:
Originally Posted by maxlorenz View Post
Hi dear -EC-

Since last year I have neglected DIY (but followed your threads) due to job and to my new (and expensive) hobby of playing/enjoying/collecting violins.
My luthier lend me some Dammar gum and I applied as a varnish, diluted on turpentine, on my Audio Nirvana fulrange drivers. I had not listened to them yet. I want them to dry a little more.
With the dammar varnish left I thought about emulating "tube-O-lator":

The Altmann "Tube-o-lator" lacquer

so I put on it powdered graphite from cheap pencils until getting a dark grey matter that I applied to the inexpensive TDA1543 chip, only on the "roof" (I will later put it all around) and waited. Am I getting crazy or the sound changed?

Anybody has experience with this?

Cheers.
M.
K-Y Gelly? Come on!
  Reply With Quote
Old 1st March 2011, 05:36 PM   #3619
diyAudio Member
 
maxlorenz's Avatar
 
Join Date: Oct 2003
Location: osorno , Chile
Hi dear,

"Hoc Non Pereo Habebo Fortior Me"

Anybody here knows the meaning of experimentation?
  Reply With Quote
Old 1st March 2011, 08:49 PM   #3620
Sandor is offline Sandor  Italy
diyAudio Member
 
Join Date: Mar 2004
Location: Milan
Hello John,
how does your circlotron amp perform with loads as low as 2 ohms?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 10:17 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2