Fretless wrote: ↑Sun Apr 25, 2021 7:39 am
That is a seriously cool-looking amp, Steve.
antonio66 wrote: ↑Sun Apr 25, 2021 12:36 am
I bet it does sound nice, and if you're happy that's all that counts, looks good by the way
Thanks chaps.
A lot of my amps in the past became more and more complex until they disappeared up their own backsides and got dismantled; the parts awaiting their next outing, and so the cycle carried on. That’s not to say I didn’t learn anything with each project, it’s just that I’m now fed up with the whole cycle thing and need to settle down long term with the system as it is. This is the reason I started to look at simplicity and aesthetics, in that order.
In terms of the simplicity of the audio circuit, I took a leaf out of Richard’s book and removed from the signal path, as much unnecessary clutter as I could get away with, which meant cutting the number of amplification stages. This significantly reduced the component count. There are now only two resistors and two caps in the audio cct signal path.
With a single ended amplifier however, the power supply is also in the signal path and the way you get that out of the way of the music is by using regulators. But the regulators also have a sound, so design choices there are critical if you don’t want the music to be strangled at birth.
Regs are a complex field and folks like Rod Coleman, Guido Tent, Nick Gorham (Lurcher) to name but three, have made the study and implication of them into a huge part of their work in valve electronics. I don’t have that level of expertise and have found that because of that, a simple, unregulated power supply sounds far better in one of my amps, than does one of my incompetent regulated efforts.
Simplicity without using regulators is not an easy undertaking, but help was at hand for me in the form of Duncan Munro’s PSUD computer software
http://www.duncanamps.com/psud2/download.html. This has been available on PCs for years, but has only recently become available on the Mac. It’s a godsend TBH. I wouldn’t be without it now. It has certainly improved my design outcomes.
For example I was using a 10H choke in the power supply and simulated the 4H choke with a stepped current load where I programmed the current through the supply, to suddenly double after a predetermined time period had passed. This tells you how responsive the supply is and whether it rings after the step has occurred. With the 10H choke, the supply rang slightly and I couldn’t get rid of the ringing. With the 4H choke, there was a single overshoot then no ringing after the event. The fact that the 4H choke is potted in a grey box and looks a good deal better than the 10H choke was not allowed to influence the decision about whether or not to use it. The science prevailed of course.
Needless to say, the transient speed and bass response of the amplifier is much improved with the 4H choke, so the PSUD software exercise was well worth the time taken to do it.
One can keep trying different tubes for different sounds until the cows come home, but one has, in the end, to stop somewhere. I love the EL34 valve, and always seem to end up back with them, so I’ve developed this latest version to make the most of them, and to make it stick, I’ve got the aesthetics up to the job too.
