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

 

 

Fall 2010

The Blue Velvet Line Preamplifier
An update to an already great design!
Article By Dick Olsher

Difficulty Level

 

Blue Velvet Line Preamplifier  Since its publication in November 2003 (see article here), the Blue Velvet (BV) line preamp design has undergone a couple of modifications; really not bad for a seven-year old design! The intention of this update is to describe these mods, share additional findings, as well as present the updated schematics.

The power supply was modified by the addition of a 1N5406 rectifier diode -- just before the glow tubes. Its purpose is to isolate the 0A2 glow tubes from the large capacitors in the filter network and prevent oscillation. The diode effectively decouples the glow tubes over their entire working current range, and it works like a charm in this application. 

The signal path circuit's output coupling capacitor (C2) was increased in value to a total of 4.7 F. For me that means a Cardas 0.68 uF in parallel with a 4 uF Hovland MusiCap (which I still have on hand from years ago). Since Hovland is now out of business, please feel free to experiment with your favorite types. The increase in capacitance is responsible for enhanced bass extension, especially with low input impedance solid-state amps.

Although not indicated on the schematic, I have by now switched from the original Noble volume pot to a TKD stepped attenuator. The increased levels of clarity and soundstage transparency were quite startling. In hindsight, I can say that the upgrade to a high-quality stepped attenuator is well worth the added expense.

For the past couple of years I have been using almost exclusively Loktal types (7N7 and 7AF7) instead of 6SN7s. They are similar in terms of tube parameters, but because they use a different pinout you'll need to use a 6SN7 to 7N7 adapter if you've already wired the BV for 6SN7 use. Loktal (for Lock-In), was a trademark of Philco-Sylvania. Other manufacturers (e.g., Tung Sol and Raytheon) referred to them as loctals. They are a bit funky looking with a central metal spigot, short pins that are essentially thickened lead out wires, and a metal base shell. The 7N7 has already developed a reputation as an inexpensive yet excellent alternative to vintage 6SN7 types, and I did in fact find it superior to almost all vintage 6SN7s in my collection as far as detail retrieval and spatiality. As good as the 7N7 is, the 7AF7 sounds even sexier, and is currently my top choice for the BV.

Bottom line: I'm still enjoying the BV after all these years. Its convincing tonality, rich colors, and tremendous boogie factor make for an enchanting musical experience. 

Click here for main circuit schematic

Click here for the power supply schematic.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     
 

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.