- Posted by AndyN (A) on April 05, 2007 at 07:43:50
I used to run a single ended 6AH4 as the output stage for my pre-amp. Driven by a Sowter TVC and biased thru it via a 12 volt battery, cathode straight to ground, 10K anode load with a 2mfd Copper Paper in Oil Audio Note cap’ driving a Lundahl L1676 set up a 2:1. A good sound, so I thought.But I was reading your article http://www.raleighaudio.com/chapter_4.htm and of course Lynn Olson’s paper and so felt compelled to try a balanced circuit using a 7044, same Lundahl and Audio Note cap. 150R in the joined cathodes and 39K to ground from each grid. Constant current anode loads using cascade DN2540s set to20mA each.
Well the difference is truly amazing. This is not just my view but also the view of two other friends who have listened without me prompting their observations or telling them what I had done.
The slight bass boom is now gone, the sound is more lyrical and the definition is amazing “like moving from the rear of the hall to the front row” said one listener with great space around the instruments and generally far more air. One said he would have been pleased if he had spent $2000 on such an upgrade.
I feel I may now to tempted to try the same concept in other stages of the pre-amp.
Andy
