Amplifier

Would you be surprised to learn that there is a real difference between volume controls and level controls? Unfortunately today, controls which are really “level” controls routinely get tagged with the label “Volume”. But what’s the difference?

Do you ever do a bunch of work on something and then completely forget about it? And it’s only when something else happens that you then remember what you were doing? Well, that’s what happened to me today.

In my last post I discussed what it means to make an amplifier go to 11. But in spite of the issues involved, many amp builders simply can’t help themselves. Even before the first connection is made they start craving more power. However, the truth of the mater is that increasing amplifier power is almost always a fool’s errand. And even the rated power outputs of most commercial amplifiers have nothing to do with listening, and everything to do with marketing.

The year was 1984. The spoof “rockumentary” titled “This Is Spinal Tap” was just released to theaters and it was then that this immortal phrase entered the modern lexicon. I’m referring, of course, to that classic line “These go to 11”.

In the intervening 40 plus years, a million and one jokes have been made about things that go to 11; including amplifiers. As amp builders we would like to know what it takes to make our amp projects go to 11. Unfortunately, the answer is more complicated than you might think.

Today marks five weeks since I hurt my ankle. And this morning I managed to do my full mile plus morning walk without any issues. My dog was happy about this as well. At 18 years old the definition of “walking it off” after such an injury meant maybe a day. I guess now over 40 years later “walking it off” means five weeks. Who knew?

But I’ve also made a slight deviation with the 6V6 Curly Maple amp.

So I’ve been laying low for the last couple of months and not entirely by my own volition. I finished up the Curly Maple amp on the first of June and have not yet gotten the project page posted. But rest assured, the entire write up on the new amplifier is coming soon.

The resistors for which I’ve been waiting to finish the amp showed up in the mail yesterday. Today I got the final resistor installed and did a full check on the amplifier.

After some delay I have managed to finish all the metal work for the Marblewood Upgrade Amplifier. Hereafter referred to as the 6V6 Curly Maple Amplifier.

There are lots of practices in the DIY world that are more than a little out dated. I’m obviously not talking about using vacuum tubes but rather the methods used in building and testing the circuits we build with them. Many of these test methods came about for very good reasons; perfectly applicable at the time. But as technology has advanced the reasons for many of these practices are no longer valid. And there is really no better example of this than the practice of testing audio amplifiers with square wave (or various sawtooth or triangle wave) signals.

This topic comes up a lot! Someone will email me with, “I want to build {insert project here} from your web site. But…”. Sometimes it’s just that part availability varies. Sometimes people want to use parts on hand which are slightly different. Sometimes people want to substitute tubes, transformers, or whole assemblies. And sometimes people want to actually change the topology! So at what point is the amp being built no longer the design on my website?

For anyone who is interested in a little more of the history of feedback development, I have posted an article from the Proceedings of the IEEE from 1999. It’s a relatively quick but informative read about the topic.

This may seem a non-sequitur to some. After all, I don’t post designs on this website that make use of feedback. This is simply because I don’t like the way feedback affects the sound of an audio amplifier. But that doesn’t mean that I don’t understand feedback and make use of it in other applications.

So I’ve been thinking about my next amplifier project. And I thought I had made up my mind. Then things changed… again.

I have been working on the new SET chassis design but that’s not all I’ve been doing. This morning I got a little surprise when I checked on my sump pump under the house. It’s starting the rainy season here and I wanted to make sure everything was ready to go. Unfortunately, I found myself replacing a GFCI outlet and the sump pump that had failed and taken the outlet with it. Since the morning was shot, I decided to finish up a couple of other little projects this afternoon. Last week I mentioned another project, the portable class D amp. We’ll, I took a little time this afternoon to finish off that one.

So it’s been a while since I first grabbed the plank of Zebrawood in my shop and envisioned it wrapped around an amplifier. That was June 13th. Here it is a little over two months later and I now actually have a functioning amplifier. I have to say I’m pretty happy with how it turned out.

As some may already know, I’ve been working on a new version of the 6CY7 amplifier. There is a new chassis specifically designed for this amp and some circuit changes to improve performance. But here’s the issue, I can’t seem to get much done. Let me explain.

Well, the new version of the 6CY7 amp is coming together. The wood for the amp has gone from a raw 11″ x 58″ plank of Zebra Wood {Microberlinia brazzavillensis} into a finished amplifier chassis complete with four coats of Tru-Oil finish. I think it looks pretty good.

So, I was sitting here on this rainy Sunday morning going through some amplifier designs and looking through my stash of tubes and various amplifier building supplies. While standing there looking at the shelves of vacuum tubes, transformers, and various piece-parts, my eyes drifted up to an amplifier sitting on the top shelf. It was my 6AS5 µ-power UL amplifier documented here. But why was the little amp sitting on a shelf collecting dust? Then I remembered.

I keep getting questions about amp grounding so I thought I would consolidate some of my previous notes on the subject. The first is a reprint of a forum post I made back in 2013 on the DIYAudioProjects Forum.

Warning: It has been brought to my attention that some people reading this post mistakenly believe that I am advocating the override, disconnection, or elimination of the safety ground (or bonding) connection in some pieces of equipment. This is not correct! The safety ground or bonding requirement for every piece of equipment is a firm requirement. At no time should any signal cable or independent wire be expected to fulfill the safety ground requirement for any piece of equipment. The process of “ground lift” is simply to provide a different signal ground reference in a piece of equipment.