The Cogent horns use field coil compression drivers patterned after the famous RCA 1428 drivers. The high frequency horn is a conical design from The Acoustic Horn company. For the lower frequencies a 10 foot J horn with an exponential flair is used.
The cogent horns arrived in my listening room with a simple 300 HZ crossover network that had not yet been optimized. I spent more than 6 months refining the crossover design. This turned out to be a major challenge since both drivers have a resonant frequency that is very close to the desired crossover point. After extensive measuring, simulating and listening I ended up first order, 360 HZ crossover. Some gentle impedance correction is used on both drivers. After careful listening to various crossover configurations I have concluded that all crossover components have a detrimental effect on sound. This includes not just the series filter circuits but also impedance correction and attenuation circuits. Adding a crossover circuit is only beneficial if it corrects a problem that is greater than the damage caused by the circuit. I started with a carefully designed and simulated circuit to give flat frequency response. Unfortunately, the sound was a bit lifeless. Backing off on the impedance correction resulted in a much better compromise. It would seem that the art to crossover design is to use a light touch and do plenty of listening. With the refined crossoveres the sound is much more refined with considerable improvement in the spatial presentation.
Now that the crossovers design is completed I will be experimenting with field coil power supplies and adding a super-tweeter. Stay tuned.
For some time my interconnects and speaker cables were DIY solid core
silver. I found that the reasonably priced cables from
The Bolder Cable Company
considerably bettered my DIY silver cables. However, the DIY cables offers
substantially better value due to their dirt cheap price. The
interconnects use 30ga fine silver in Teflon tubing. Both conductors are
closely spaced, placed in a polyester braid and terminated with Cardas
Rhodium RCA plugs. My DIY speaker cables use the same topology as the
interconnects. 16ga silver for the woofers and 18ga for the tweeters.
Like the interconnects the conductors are placed in Teflon tube and then
covered with polyester braid. The speaker cables are unterminated with the
bare wires connecting directly to the binding posts for a simple but
effective connection. These cable far out perform many of the megabuck
commercial cables and are remarkably inexpensive. The cost for the bi-wired
speaker cables was only $6.25/foot and the interconnects came in at
$2.15/foot. I purchased the 18 & 16ga silver wire from
Hoover & Strong.
The 30ga silver, Teflon tube and polyester braid were from Michael Percy Audio.
More than just providing a place to put things, good equipment shelves make a significant sonic contribution. For construction details of the shelves click here.
You analog junkies may be interested in the very effective and inexpensive DIY record cleaner design. Click here for construction details and pictures.
Audio has been a rewarding, long time hobby. I put together my first stereo system when I was 12. It was a cheap mono record player that I added a second amp into and fitted with a stereo cartridge. I built my first, from scratch, stereo amp when I was 16. A 50 watt transistor amp that sounded horrible, but at least it looked nice. Over the years I built a lot of speakers and modified amps and CD players. However, the hobby took a major turn in 1997 when I bought my first tube amps, a pair of EICO HF-22 mono-blocks. This was my first real glimpse of audio nirvana. The EICO's ended up being a wonderful testbed for experimenting with different amplifier topologies. With these amps I was able learn first hand the sonic effects of, negative feedback, triodes vs. pentodes, single ended vs. push pull, etc...
After a lot of experimentation the EICO's ended up being configured for single ended operation with no feedback and using Sovtek 6B4G's for output tubes. A big step forward from the already musical sound of the stock amps. Thats the background. For the rest of the story take a look at the links to my more recent projects.
For some interesting information about modifying tube amplifiers take a look at an article I wrote about modifying a Scott 299-C. In this article I discuss both the sonic and measured performance of a number of mods. Although the article is about a Scott amplifier the concepts apply to any tube amplifier.
