Although I love me VR tubes something fierce, they aren’t in current production and I’d like a simple (or well as simple as possible, I guess) shunt regulator alternative for things like phono preamps or line stages (20mA of load current or thereabouts).
This shunt regulator uses an EL84 for the heavy shunt lifting and a 12AX7 differential amplifier (using non-inverting output) to amplify any ripple on the output (which the EL84 ‘cancels’ across Rs). Quick calculations look like about 100V of headroom would be nice to have so rectified 250Vac with the shunt should be good for about 250Vdc regulated output.
Update: Putting the differential amplifier before the shunt will unload it a bit and provide more B+ headroom for higher gain.
I’ve been doing some reading on tubes in shunt regulator power supplies lately (lots of great articles on TubeCAD including this one). I’m planning to incorporate one in an upcoming build. In operation, this isn’t too different from the VR regulator power supply in my Matemático Phono Preamp, but a shunt regulator with a triode would have an adjustable output and might afford even better ripple rejection.
My recent series regulator project is another example of power supply regulation.
Click here to see the new page on shunt regulators.
What is your opinion on rectification?
Tube vs SS rectification is a hotly contested topic in the audio world and what I tell you will be opinion. That said, I’ve used both and never had a problem (eg here
). When designing from scratch, my choice is dictated by my power transformer, space available on the chassis, and whether a tube rectifier is in the budget. Sound quality is not really a consideration.
Of all the parts in a Class A single-ended amp that contribute to the sound, I think rectification is one of the least important. If you end up with the right B+ voltage and you filter it so that there is no ripple, you’re 99.9% of the way there. The debate about tube vs SS rectification usually focuses on theoretical advantages or disadvantages without respect to whether a supply is well-designed and implemented.
All things being equal, and space and budget allowing, I tend towards tubes because I like the way they look and I like knowing that the high voltage will start up just a little bit slower. All things being equal, others would go for solid state because it has a lower output impedance and allows for larger filter capacitors.
There’s more emotion than measurement in either decision.
274B borrowed from thetubestore.com and 1N5408 borrowed from PartsExpress.com. I claim Fair Use here and anyways they can get bent if they don’t like me linking to them in exchange for the pics.
If someone told me they hiked to the summit of Mt Everest, I’d think they’re pretty amazing. If they told me that their first thought when they got to the top was how much money they spent to get there, I’d probably think they’re not quite so amazing. If they told me they actually took a helicopter to the top instead because it was cheaper, I’d be sure that they’re an idiot.
DIY requires an investment in tools and parts, but more importantly, it requires an investment in time and patience. Your first project is not going to be the Mt Everest of projects, just like a hiker’s first backpacking trip shouldn’t be up the side of the Himalayas. Like every hobby, excellence takes patience and practice.
It’s very tempting to compare the cost of building something yourself to the cost of buying something that’s commercially made. As you’re starting out in DIY, you won’t win this battle. The more you practice, the more you’ll refine your finish and design theory, and the more of a return you’ll see on the time you’ve invested. But price-points still do not capture what DIY is about.
Craftsmanship is what you pay for with high-end, high-dollar, boutique design. The craftsman that wields it didn’t buy his or her experience with money. He or she built experience and knowledge by making mistakes and a lot of crappy products first. When you buy commercial, you are paying for the mistakes it took for the craftsman to become exceptional. DIY is about having the courage to overcome those mistakes yourself instead.
P.S. Yes, I know helicopters don’t fly to the top of Mt Everest.