A Tube Amplifier and HV Switching Power Supply for CAR STEREO

Initial Release 7/28/00

INTRODUCTION

After Building several versions of my Darling SE 1626 amplifier for home use, I wanted to enjoy the same audio "magic" in my long commute to work.
The idea of a Tube Amp in my car had intrigued me for some time. What better way to combine two of my favorite hobbies: Audio and Auto's.
But as an "enthusiast" these could be none other than TUBE audio and ITALIAN sports cars. ;)

My daily driver is a 1978 FIAT X1/9.

Here are a few other photos of the car:
photo 1
photo 2
photo 3
As you can see, this is a *very small* car. So fitting in a TUBE AMP was going to be a real challenge.
Here's a couple shots of the amp in the car:

The Issues

Aside from the real-estate issue, running a Tube Amp in a car presents quite a few technical challenges. Probably the most obvious is the shock and vibration environment (not to mention the lateral G's - after all, the X1/9 is built for tossing around on twisty roads). This isn't as bad as you would think. Although these tubes are made with glass, they are a lot more rugged than they look. The tubes used in this amp are actually "militarized" versions which were originally used in Tanks, Aircraft, and even Submarines.
Additionally, the amp is attached to a platform with shock-absorbing material. The platform is similarly shock-mounted to the rear window sill of the car. The Amp Chassis is internally damped. Even on the roughest roads, i have no evidence of microphonic pick-up. And the amp has securely held its place thru some very spirited driving on twisty mountain roads.

HV Switching Power Supply

The next challenge is producing a decent High Voltage B+ supply to run the amp. Automotive power systems provide between 12 and 14Vdc. The solution was to build a switching power supply to boost the 12V to approx. 275V for B+.
I had already designed and built a few HV switching supplies in the past. One design was even published in Glass Audio (4/99). While this design worked well enough, it was not quite powerful enough to run the amp i had in mind (stereo, parallel SE 1626).
What I ended up with was actually a bit simpler, while providing almost 100W output capability at 200 - 350V. As I find time, I will consider publishing this power supply design. However, because of the specialized magnetics involved, this is not a typical D.I.Y. project. If there is enough interest I may try to make a "kit" available.

The Amplifier

The amplifier is based upon the Darling Stereo 1626 SE amplifier shown HERE . In order to squeeze just a little more power out of it (over 1W), I decided to parallel the output tubes. The parallel single-ended (PSE) Darling provides about 1.5W at clipping. This is plenty for such a small car. It is even loud enough to play above the din of the 1300cc SOHC engine sitting just behind me (yes, it's mid-engine) turning a constant 5000RPM on the highway.
The only other difference is that the 8532 driver tubes were replaced with a pair of 5965 dual triodes in SRPP. This was prompted by the 9-pin sockets already installed in the AMP chassis (i was originally making a PP 6L6 amp out of it).
If i have time, i will include the schematic here.

So Far, So Good

As of this writing, 7/28/00, I've run the amp almost daily (save a couple weeks down time to replace a clutch and transmission) without a problem. I do get some extra-long stares from the State Troopers as I pass them by. Something glowing in the rear window...

Email Bob. D. at robert.m.danielak@lmco.com

This page, and all contents, are Copyright (C) 2000 by Bob. D.