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Opinion on Non-oversampling mod for TDA1541 based player?
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Posted on February 17, 2016 at 06:04:30 | ||
Posts: 2515
Location: Brussels Joined: April 27, 2010 |
Hello fellow members, I acquired a ReVox B226 cD player a few weeks ago. It's a 25 or 30 years old player in need of a refresh (altough it sounds surprisingly good as it is now). I've decided on a global recap (all the electrolytics and probably also the output coupling caps) + replacement of the output stage NE5532 opamps with Sparkos Labs SS3602 dual discrete opamps. while I'm at it, as the board will be out and all, it seems to make sense to upgrade the clock as well - as such a thing might be a great leap forward in sound quality, according to internet sources (haven't heard what a proper clock can do). Looking for an affordable clock module I keep bumping on all-in-one, low-jitter reclock and NOS modules that solder in place of the SAA7220 chip found in TDA1541 based players. Those modules are supposed to be "plug and play" and require no further modification of the board, wich sounds appealing. So here are my questions: 1) does it make sense to NOS an existing player designed for 8 times oversampling and sounding quite good that way? 2) is a NOS dac configuration compatible with a tripath-based power amplifier (knowing I'm using a conventional SS preamplifier between the CD player and the power amp), or is there a risk of instability or other problems due to spurious very high frequencies "garbage" that will be left unfiltered at the player output? 3) does NOS modification bring any real upgrade in SQ (in general and on this particular ReVox B226 player) or is it more like a change in flavour and a matter of taste? 4) If I would decide to keep the oversampling, and keep the SAA7220 chip active, wich clock module would you recommend knowing that I need something not too expensive and easy to implement, and if possible reversible (no destruction of board tracks)? Thanks a million! |
RE: Opinion on Non-oversampling mod for TDA1541 based player?, posted on February 17, 2016 at 23:40:15 | |
Posts: 4209
Location: Somewhere nice on planet dirt Joined: September 25, 1999 |
Hi, Service manual here: ftp://ftp.studer.ch/public/Products/Revox/Revox_B226_B126/Revox_B226_Serv.pdf First, the SAA7220 is a first class noise generator. If you keep it, make sure to block off the power supplies seriously to avoid it contaminating everything else. Note that in the B226 all IC's (including DAC) share a common +5V supply! It is probably worthwhile to give the TDA1541 it's own +5V regulator and perhaps something a trifle better than the 317/337 Studer designed in. Same story for the +12V/-6V/-15V lines. Second, if you put in a socket for SAA7220 and a clock, you can very easily try out Non-OS, simply jumper the signals across the Digital filter. If trying Non-OS you need to be aware that the SAA7220 B version in the Revox includes a Treble boost to compensate for the analogue lowpass, so you need to reconfigure that part to get reasonable HF output, especially if you account for Non-OS already dropping the treble by around 3dB @ 20kHz. The fixed outputs of the B226 have only two Op-Amp's in the signal, I might be tempted to skip the second one and just do a simple LC Output filter, with some peaking build in to compensate the treble rolloff of Non-OS... But I guess you can live with the filter as is, I refurbished (and modded) a fair few TDA1541 players and I never did a halfway house mod, I either left the analogue filter or threw all Op-Amp's out. For the I/U conversion Op-Amp use something fast. Personally I had the best success with AD811/LM6181/LM6182 current feedback op-amp's, these are rated at > 1000V/uS. I also rather liked the AD844 in "open-loop" mode as suggested by Pedja Rogic and an OPA637A (135V/uS) with a 10nF cap from inverting input to ground. For the Filter section I tried all sorts and liked the BUF03 Buffer best, BUF634 second, AD811/LM6181/LM6182 with a 1K resistor in the feedback loop also did ok. Sadly all my preferred devices seem deleted and I have not really kept up with what may be good replacements. But AD811/BUF03 was quite magical, followed by OPA637/BUF634 was not much short of this. All the above did way better than NE5532/5534. Properly sorted the old TDA1541 Players and DAC's have a magic little else (IMNSHO nothing else) touches. Hope this helps. PS, I prefer Non-OS with compensation for the drooping treble and tube output stages with TDA1541, but that's just me. As they say on cooking programs - "Here is one I prepared earlier..." http://www.enjoythemusic.com/diy/0310/marantz_cd_mod.htm This machine was also modified for Non-OS (not visible), but the SAA7220 was retained for clock distribution. Thor At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need? |
RE: Opinion on Non-oversampling mod for TDA1541 based player?, posted on February 18, 2016 at 12:40:00 | |
Posts: 15486
Location: Alabama Joined: September 11, 2010 |
post pics of your project! |