1865 N-K NOS TUBE DAC (Thorsten-Loesch outputstage) - diyAudio
Go Back   Home > Forums > Commercial Sector > Swap Meet

Swap Meet Sell your stuff here, who knows, some other fanatic might be interested!

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 13th September 2011, 06:11 PM   #1
hebet64 is offline hebet64  Netherlands
diyAudio Member
 
Join Date: Feb 2011
Location: Netherlands
Default 1865 N-K NOS TUBE DAC (Thorsten-Loesch outputstage)

Professionaly built 1865 DAC. As good as no use. Built in 2011 by a techical engineer. At the moment Siemens 6922 in the outputstage. Will deliver with other tubes. Looking for 650.

The tube output board is a UTS board designed by Thorsten Loesch, the designer of the AMR CD-77 TDA1541 CD player. A 200R resistor is used for I/V conversion. The 0.2V (peak) is then amplified 15x by the ECC88 tube to give just over 2V RMS output from the RCA jacks for a full scale digital signal. The ECC88 is loaded with a constant current source (CCS), the 10M45, and instead of the output being taken directly from the tube plate (anode), it is taken from the cathode of the IXYS 10M45. Regardless of the voltage that is being amplified, the current through the tube remains constant, resulting in the best linearity and least distortion, the bonus being that the output impedance is much reduced over taking the output from the plate of the tube. In this case,output impedance is 300R. Downside of using a mu output is that PSRR(rejection of noise from the power supply) is greatly reduced, so the HT power supply needs to be very quiet and clean. Which it is. It is regulated. Also, the 6.3V for the tube heaters is also regulated. The output is coupled to the RCA jacks with an Obbligato film cap.

The digital section of the board is pretty much an exact duplicate of the classic AN design. CS8414 receiver, 74HC02 logic gate/invertor, coupled to the AD1865 DAC chip. SPDIF input is coupled via a pulse transformer and buffered. The DAC chip itself is a 'K', the highest grade

The analogue section of the board is disabled by cutting the +15V/-15V copper traces that supplied power to the output stage and removing the 2 resistors that supplied the signal from the DAC chip to the original output stage. The 15V regulators that are upstream of the 5V regulators have to work harder. Disable the audio part of the circuit that we are not using and the 15V regs only supply a tiny ammount of current to the 5V regs which in turn, supply to the analogue sections on the AD1865 chip. In a perfect design, we would have completely separate circuits for the analogue sections of the AD1865 chip and the analogue output stage. Because the 5V is now double regulated. First by the 15V reg (which used to power the analogue stage) and then by the 5V reg. The reason that the +15V/-15V circuit traces are cut, rather than just removing the regulators, is that as well as supplying +15V/-15V to the transitor output stage, there are also additional +5V/-5V regulators powered from the 15V regulators which are used for the AD1865 chips analogue sections.
Attached Images
File Type: jpg 1865inside.jpg (652.9 KB, 251 views)
File Type: jpg tubes1865.jpg (559.4 KB, 227 views)
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Dac End Boards and 1865 DAC chip boudy Swap Meet 2 30th April 2011 02:23 PM
New??? Dac NOS X8 with Tube output jeffjazz Digital Line Level 0 4th February 2010 06:25 AM
About a I/V tube ouput for a Nos TDA1541A dac gaetan8888 Digital Line Level 1 10th July 2009 08:21 AM
Thorsten Loesch ADAGIO DAC..Help.!! Maurizio Digital Line Level 5 28th April 2009 05:08 AM
what cd-player is a good base for valve-outputstage and is nos neccecary? carburetor Digital Source 0 31st December 2008 02:04 PM


New To Site? Need Help?

All times are GMT. The time now is 04:35 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