High End Line Driver

The Story:

I visit a local car audio install shop every weekend as I'm friends with the owners and most of the customers. They cater to high end installs mostly in sound quality.

One day, they asked me if I could design for them a line driver as they couldn't find one that fits their requirements mainly: High end components, Minimum parts in the signal path, clipping LED's, independent gain controls/output and minimum alteration of the signal.

I said, No problem. just give me funding and I'll do the rest. And they did.

A month later, I finalized the circuit, sent it to be made with real professional quality PCB's. Three weeks later, I had the boards. A first prototype was made to verify operation and sound quality.

Here is the prototype. That is the complete case I was using for 9 months before the actual prototype enclosure was made.

When the case arrived, it was time to assemble and see if everything fits... The actual RCA connectors for the production has not arrived so I used temporary ones which were ok but not good enough to be called "high end".

Yes, that's a glass top cover.

Top cover is anodized aluminum. We also tried black anodized and even copper plated!

Phoenix pluggable power terminal blocks

Here are some internal shots with the temporary parts:

My prototype unit used Elna Silmic II input caps. and solid core PCOCC teflon insulated wires

Custom wound toroid

Here is where we can separate the PS from the signal boards. Jumpers transfer +/-15V and ground from the PS to the preamp boards

And then the parts arrived! Burr Brown OPA2604 Op amps and the correct RCA connectors...

My 4ch unit updated, op amps changed to AD823 and input caps to Nichicon Muse.

The board can be separated from the SMPS section and joined to another as a host.

That allows the boards to be daisy chained for the 8 channel model.

Basic features:

• Burr Brown Op Amps

• Nichicon Fine Gold input caps

• Panasonic FM powersupply caps

• Independent Bourns Cermet Gain control per channel

• Clipping LED indicator per channel pair

• Balanced output capability

• Bare Essentials - Minimum parts in the signal path

• Heavy duty RCA connectors

• Heavy gauge steel/aluminum/glass enclosure

• Each one is hand built!!!!

Specifications:

• Voltage input: 0.88v - 9.16V

• gain adj range: 0.32dB to 20.68dB

• Voltage output: 9.49V RMS before clipping led lights up

• Signal to noise ratio: 112.84dB

• Channel Separation: 110.14dB (measured between adjacent channels)

• THD+N (JIS-A filter): 0.0025%

• Frequency Response: 20Hz-20kHz +0dB/-0.06dB
  10Hz-100kHz +0dB/-1.2dB

• Input impedance: 22kOhm

• Supply range: 10V-15V

• Supply current: ~150mA (4ch) ~250mA (8ch)

(Specifications above were measured on a bare PCB, no case, so production unit should be better!)

Page created and copyright R.Quan © 23 Jan 2011.