I think I may be getting it..?? (well something anyway). I have been living happily with the 3w ECL86 amp (current output reigned in by feedback) for some months, and am accustomed to its sound now. A friend has recently returned my Class A hybrid digital amp and I thought I would try it out again. I instantly noticed a sort of grungy ness and colder “transistory” sound, even though this is a no feedback design with a transistor emitter follower output. It is curious how the little IB two way speakers don’t like transistor amps.

I got to thinking about current output amplifiers, I was intrigued a few months ago by some comments on an article in the EE times Consumer audio: Is accurate sound overrated? where the poster "Cookie Jar"  stated “One day on a whim, I hooked up my distortion meters to the actual speaker terminals of my living room stereo, and I was in for a rude awakening. The distortion readings were a couple of orders higher than for...

It seems that random acquisitions seem to precede the direction of my inspirations. This has come in the form of a Technics SU-9011 pre amp and a pair of small infinite baffle 2 way speakers. I have no idea what they are, so please share if you do.

The active sony’s, to be honest have been getting me down, they still have a mushy quality to them. The SU-9011 seems to work but was not the happy match with them either. Enter the little 2 ways and my gain clone. Bad.

So I decided to try and power up a little EL86 record player amp which I acquired a few months ago from a friend. This seems to be a close relation to the Mullard economical 3 watt amplifier. To my slight surprise it is in good working order, so with a bit of drilling fitted some 4mm posts and some phono inputs.

With the little 2 ways and the Technics is a lovely combination, real bloom, very enjoyable, and some nice bass.
Technics has “opamps” in, so that gets...

Had this running for a few weeks now, and the sound coming from the Sonys altogether better, now just a bit bass heavy rather than treble shy. The speakers are mounted right next to the ceiling in the room corners, so not really a surprise.

I have simulated the crossover and equalisation circuit of the preamp section, and realised that I can add a variable resistor to adjust the amount of bass boost the circuit gives, not a horrible mod, just one pot, and a new cap, just need some time to do it.


The not passive pre has no muting circuit in at present, so power sequencing is required. I intend to make it direct coupled at the output. To do this I am planing to do a micro controller servo loop. When I made the Class A digital amplifier, mentioned earlier I used an opamp servo, and I can state that this circuit does definitely have an effect on the sound.


In the interests of minimalism the Not Passive Pre II is already being...

Following my "conversion" that valves really do sound better than transistors:

http://www.diyaudio.com/forums/solid...c-project.html

My home stereo, which is compromised by having to be small person resistant, has been in a state of flux. I worked out that the most economical tube fix was to by a receiver from ebay, so I got a 1967 ish one, 17 tubes, push pull EL84s etc, it is original and it works, but the RIAA is way, out the FM stereo decoder needs re alignment, and all the output tubes share a common cathode resistor, 2 ECC83s in series.... so it went on the bench and has stagnated... also most of my speakers don't really suit it.


So to fill the gap I thought I would drag out a pair of Sony SA H7900 active speakers I acquired about 8 years ago, not just active, motional feedback woofers and electrostatic tweeters no less, and bass reflex(?) what could possibly go wrong?


When...