Home  |  Hi-Fi Audio Reviews  Audiophile Shows Partner Mags  News       

 

 

 

Enjoy the Music.com Review Magazine

VALVE Magazine

VALVE Magazine Online!

 

Smoothing The Audio Jaggiesan...
Easy CD tube output stage you can build!
From VALVE Volume 2 Number 10

 

  Last week I invited audio buds over at various times to hear the final version of the Super Whamodynes. One of these friends, upon hearing my moaning over my cheapo Onkyo DX-1400 CD player, offered to bring a $900 solid-state output CD player for audition. That was all I needed to light the tweak fire. I had to try the tube output mod for my CD player that had been itching my brains for about a year. First I pulled out the three articles I had seen two from Glass Audio and one from' Positive Feedback, which discussed tube output stages in various CD players and DACs.

Two of the three articles dealt with Burr Brown 28 pin DAC chips, PCM58P's2 and PCM63P's3. I opened my Onkyo to find a pair of PCM61 P's, so I thought I ought to be able to reverse engineer the pinout, even though the PCM61 Pis a 16 pin IC. The Onkyo also contains the same digital filter, a Yamaha YM3433, that the Audio Alchemy DAC-in-a-box uses, so I figured the digital parts quality was probably pretty decent, and therefore, the unit was worth hacking.

First, I had to figure out where to tap into the player. The Norman Tracy article in Glass Audio, as well as the Sheldon Stokes article in Positive Feedbag3 both use a resistor as the 1/V converter which converts the dinky current output at the analog output of the DAC chip to a dinky voltage output. Both articles also run this converted signal directly to the grid of the tube output stage. Shoot, it can't get any easier than that! I took my trusty scope lead and started touching it to DAC pins while I played a CD. At pin 9, I got signal. Whoops, at pin 10 I got signal too. Damn, they were jumpered together!

Well, looking back at the Tracy article, I discovered that the PCM58P did the same thing. One pin was the analog current output, and the other pin was a "bipolar offset point", which sources !mA of current to convert the 0-2 mA current swing of the DAC output to -1 to + 1 mA. This way the voltage conversion swings about 0 volts instead of +.2 volts. Anyway, I knew that I could tie in at this pair of pins and hook up my IIV resistor. I decided to use Sheldon Stokes' output stage fora couple reasons. First I hadn't fooled with an SRPP circuit yet, and, secondly, he offered resistor values for using either 12AT7's or 6DJ8's.

So I pick a couple of sockets, dig out some resistors and a couple of caps, and go looking for an old chassis to build on. Can't find a darned thing, but I turn up a little cardboard box, upon which I glue two ceramic sockets, and build up the circuit using 12AT7WC's. Oh, this is too cool!

I add in and out jacks and attach a Lambda tube regulated power supply and adjustable DC filament supply. I then clip the circuit into the left DAC. I found a 1000 ohm resistor between the DAC and the original I/V converter chip (a 5532) which, when unsoldered at one end, disconnected the 5532 from the left DAC.

In goes a CD. Wow, obvious difference between the solid and vacuum sides. The tube side is way smoother, has much better bass, and seems a bit more transparent. It also has gobs of gain, which I need to drive my passive line stage. Awesome!

I cobble together the other channel about two hours before my friend shows up with the $900 player. We put on the Muddy Waters, Blues Singer CD and compare the two players. With the tube Onkyo Muddy's voice is OBVIOUSLY smoother and the bass is better too. The only plus with the solid stale player is a slightly better leading edge to transients. The next day I altered the circuit to use 6DJ8's, which Sheldon Stokes favors in his DAC. A pair of Telefunken 6DJ8's gave me better transient attack, but bass was a bit lighter. When I switched to early 80's Sylvania 6922's, I got what seemed to be a good compromise between the 12AT7 bass and the Telefunken 6DJ8 transient response. And so they have stayed plugged into the cardboard box.

A good argument for this type of 'in the player' conversion over construction of a whole new outboard DAC is that there's no digital interface between transport and DAC to add jitter. So hacking a medium priced player might sound better than some tube DAC / transport combinations...

    

Lout from pin 9 of BB PCM61 P. For6DJ8,

B+ is 260VDC,. R31- 33.2Q, R32,R33-

680 Ohm, R34- l MOhm, R35-100 Ohm, C109-2.2mF.

 

 

 

1. Painter, Richard, "A Valued Vacuum  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     
 

Quick Links


Premium Audio Review Magazine
High-End Audiophile Equipment Reviews

 

Equipment Review Archives
Turntables, Cartridges, Etc
Digital Source
Do It Yourself (DIY)
Preamplifiers
Amplifiers
Cables, Wires, Etc
Loudspeakers/ Monitors
Headphones, IEMs, Tweaks, Etc
Superior Audio Gear Reviews

 

 


Show Reports
HIGH END Munich 2024
AXPONA 2024 Show Report
Montreal Audiofest 2024 Report

Southwest Audio Fest 2024
Florida Intl. Audio Expo 2024
Capital Audiofest 2023 Report
Toronto Audiofest 2023 Report
UK Audio Show 2023 Report
Pacific Audio Fest 2023 Report
T.H.E. Show 2023 Report
Australian Hi-Fi Show 2023 Report
...More Show Reports

 

Videos
Our Featured Videos

 


Industry & Music News

High-Performance Audio & Music News

 

Partner Print Magazines
audioXpress
Australian Hi-Fi Magazine
hi-fi+ Magazine
Sound Practices
VALVE Magazine

 

For The Press & Industry
About Us
Press Releases
Official Site Graphics

 

 

 

     

Home   |   Hi-Fi Audio Reviews   |   News   |   Press Releases   |   About Us   |   Contact Us

 

All contents copyright©  1995 - 2024  Enjoy the Music.com®
May not be copied or reproduced without permission.  All rights reserved.