Today was the first time I've taken the time to plug in my amp since CF. So no burn in and no real run time at all!
I'm running a tube preamp that's powered off batteries. Quiet and super smooth. For an amp I've been on a First Watt F1. This makes all comparison kind of unfair as it's a completely different amp in that it's a current source instead of a voltage amp. IE...across the speaker terminals is a steady voltage and it modulates the current. This is exactly what a speaker does anyway so you're leaving out making the speaker convert voltage to current. Speakers are Open Baffle full range crossoverless short line sources that I've put together and are an 8 ohm load.
Gain from the CF amp is a little higher that the F1's listed 14db, which is lower than normal. Had to turn the preamp down a few clicks. Noise floor I'm used to being pretty quiet and the CF amp didn't seem to change much. Good so far!
The first CD I played was new to me and gave the amp a chance to come up to temp. David Lanz is a pianist that I've seen before and have enjoyed many CD's from for years. This one I found in a used CD shop this week and is a 2004 release called "The Good Life". Nice uptempo Sunday morning smooth jazz music! However it seemed unfocused and didn't have a nice soundstage at all.
So I was releaved when I changed to a high rez sampler I've put together of stuff I'm familar with and the sound stage returned and things sounded much better. On DVD-A, this sampler is 26 cuts long and goes through lots of stuff from Beatles, Paul McCartney, Fleetwood Mac, Chicago, Alan Parsons and into some Blues and Bluegrass flavored music and then some nice jazz cuts too. Vocals, both male and female and all kinds of instruments and production styles, but all high resolution and big air, depth and width! The CF amp did pretty well. Not quite as much fluid music presentation, a bit of a shortened sound stage, but no problem with the highs or lows and the frequency response seems smooth.
As a real fair check, I decided to pull out another EL84 amp I built a few years ago. It's based on the Dynaco ST-35 design, the baby brother to the ST-70. It uses a 12AX7 input, 12AU7 phase splitter and then the same EL84 push pull output. On my build, I decided to go with a tube rectifier, which is probably the biggest difference from the CF amp.
You guys that have just built (or are building) will notice right away that the circuit board construction makes building different than point to point. I did this one with the green Euro blocks so that I can completely unplug and remove the PCB in just a minute if I wanted to. This design is fixed bias, which means once in a while you have to meter and reset a voltage for each output tube. I made this simple with test jacks on the top (3 little pin sockets down each side) and access there too to tweek the pots.
Anyway back to the audio amp comparing...I paused the playback and plugged in the Dynaclone, let the tubes come up and went back to play. Immediately a small but noticable difference was there. Just a touch smoother, even before warm up, and a tad more depth. No frequency changes or gain difference. Just a little more music.
I'd lay this at the feet of the power supply. There are other small differences but this is something I've spent a lot of time at. I actually have 4 of these Dynaclones in various configurations. Much of which is power supply. And you can hear this smoothness of a tube power supply over SS diodes represented among them. So this probably belongs over in the mods column, but some small but subtle changes on the power supply might be considered. If others also have slightly high B+ like I do, then there is room to consider adding a second stage of filtering. But probably more important and not much cost and no space really, would be change that pair of rectifier diodes. Some HexFred diodes might do a subtle but nice improvement on imaging in this. Something that may be able to be explored at some future time.
I look forward to more time, as this thing settles in it should get nothing but a little smoother. Tube amps can be really nice sounding and EL84's have always been known for having good dynamics or "pop" to their signature of sound. The CF amp lives...