Tubecube 7: The Amazing Tiny Tube Amp!

Tubecube 7 with Markaudio modified B652 speakers

Tubecube 7 with Markaudio modified B652 speakers

When I first saw this amplifier, I was impressed with the compactness, but noticed that 3.5 Watts from a single EL84 tube would mean pentode mode and some negative feedback. An online review noticed a rolled off high end, which made me think tiny cheap output transformer. But my friend David Still suggested trying it, so I ordered it from Tube Depot. We both tried it and give it two thumbs up!

I knew from past experience that pentode mode can sound pretty good with a little help from some negative feedback. Without large transformers or parafeed, single-ended amps can have poor quality bass, but negative feedback can help that too. In this case, they use the right amount of feedback to cure these problems and still have decent dynamics. My compliments to the designer! Because of the feedback, speakers have the same response as with a transistor amp, so you don’t have the response variation issue that a triode amplifier has.

The roll-off at the top end is there and noticeable in a two-way speaker. The Pioneer BS-22 is already a “warm” sounding speaker and this amplifier makes it favor the lower end even more, not the best match. Most speakers tend to favor the highs and this little amp could help tame the high end and give a better balance to many small speakers. The roll-off is not as obvious in single driver “fullrange” speakers, and these speakers can demonstrate the best qualities of this type of amplifier design:

“Midrange Magic!”  Continue reading

DIY Speakers using Markaudio drivers

After trying out the Fostex 4 inch full-range speakers, I decided to modify my Dayton B652 speakers to use a similar size driver. It may seem like going backwards, taking a 6.5” two-way speaker down to a single 4 inch, but I was not that happy with them and this would be a chance to try out a Markaudio product.chn-70

I ordered a pair of the CHN-70 drivers from Madisound for $54, and some port tubes; Goldwood PT-F415 at 0.90 each. The B652 boxes are the right size (0.2 cubic feet) for a vented box with about a 1.5” diameter by 4” long port to give a low end of 70 Hz. That’s not real deep, but deep enough to sound good. Much deeper would make it harder for this small driver to push enough air, and high high bass levels could cause some distortion in the midrange. However, you could go with a larger box to get more extended bass response; a box above 0.3 cubic feet can get you below 60 Hz where there is more low bass impact. Of course, the vent would have to be resized for the box, and there are online ported box calculators that can tell you what you need.

An advantage to these drivers is the lower frequency response than the Fostex, but a couple dB of efficiency is sacrificed for that. Even better, the overall response is very flat, no capacitors or inductors would be needed to modify the response. However, the box would need to be modified for the smaller driver. I cut some mounting plates out of a left over piece of paneling. These plates would fit into the woofer mounting of the box, and have a hole cut for mounting the CHN-70 driver. The mounting plate was glued and sealed with silicone sealant found at the hardware store.

IMG_0828 Continue reading

Setting up a stereo sound system

Today, when many people talk about sound, they are talking about several channels of sound and many speakers splashed all over the room, plus one or more subs. People are into “Immersive” sound, be it home theater or headphones that put you in the middle of it all. Recordings are usually “mixed” to artificially place sounds in certain directions, and then artificial effects are added for ambience.

When audiophiles talk sound, it is usually about reproducing a stereo “image” of a small band or large orchestra in front of you. We often favor recordings that have little or no effects added, and are recorded in such a way that you can naturally locate where everyone is on the stage, and hear how the room or hall sounds. This is what is meant by the image. Amazingly, it is possible to hear 3 dimensional sound (with depth) while using only 2 speakers and quality recordings. Impossible you say? Your 2 ears do it every day! If that is what you want to achieve, this info is for you.

First, the size of the speakers should match the room. Big speakers should be in a big room where they have room to “breathe”. Small speakers can get lost in a big room and fail to sound full. You may be able to add a subwoofer to help the low bass, but small speakers will still have reduced upper bass and low midrange in a big room. This is one of the main problems with many home theater systems.

The exception to room matching is “near field monitoring”, like your computer speakers when sitting at the desk. As long as you are reasonably close to small speakers, the room does not really matter so much. Continue reading

Checking out the local audio show

It is always good to see what other people are doing in audio, and compare what I see with what I have been learning. My friend David and I decided to meet at the Lone Star Audio Fest in Dallas to see what is going on. This show is a small informal affair between hotel rooms that have both commercial products and guys showing their home-made efforts. This also brings in people who are offering custom items or services to the Do-it-yourself group.

At such a show, you hear a very wide variety of products that shows a wide variety of taste and priorities in audio design and marketing. Here are my observations:

Commercial High End; Impressive to look at with an impressive price tag. One set of speakers had outboard crossover networks in nice wood boxes that were larger than many speakers these days! I saw some really nice speaker woodwork with very fancy cables (some that are held above ground with special supports), massive amplifiers and dramatic looking turntables. These products can be impressive to listen to with their ability hear tiny details and have strong dynamics. Continue reading

What do you expect from your audio system?

We audiophiles like to talk about reproducing the sound of the real thing, but many people have never heard a musical performance that was not played through a PA system, with all the typical distortion. For many, reproducing a “live” sound would require a PA system, or at least 100 Watts to some big Cerwin-Vega speakers (or similar, like Klipsch). It is no accident that C-V looks like PA speakers, they are meant to be similar. I have heard comments from heavy rockers that these speakers are good at recreating that “live” sound experience. This is just as valid a way to experience music, even if it’s not “audiophile” quality.

For those of us who prefer not to attend rock concerts, such a music system would be intolerable and fail to reproduce what we hear at more acoustical performances. Some people don’t think you can experience this outside of classical music halls, and it is becoming more difficult as even a single singer/guitarist seems to think he needs a PA system, even in a small room. Imagine his surprise if he heard someone sing at a large concert hall without using a PA…. and you can actually hear them! I especially enjoy free jazz or classical performances at my local high school…. These kids do great! This is part of what I use as a “live” sound reference of real instruments, unmodified and undistorted by electronics.

There is a third approach that the Japanese came to recognize. Most music is made in a studio, pieced together and mixed down to sound just right on the studio monitors. In this philosophy, the best you can do is to reproduce what the engineer heard in the studio. The better studio monitors are costly, but you can get fairly close using the very cheap Pioneer SP-BS22 with a decent amplifier. Studios seem to be migrating back to higher quality sound these days, so more of this equipment is moving toward the neutral and more natural, full response of the Pioneer and other audiophile speakers. Continue reading

A Cheap Tube Amplifier Kit

You have to be careful when buying a tube amp, not everything is as it seems. There are many hybrid products that are low in cost and use one or two tubes, but have transistor output stages. Some of them even sound pretty good, but they are not true tube amps, and they don’t sound the same. But, except for some Chinese made items on ebay, “real” tube amps are going to cost more than 500 USD. The alternative is a kit made right here in the USA.

K-502 what you get

The K-502 Stereo Tube Amp Kit gets cheap by deleting an enclosure and any other frills. For around 200 USD, you get a circuit board, all the parts that mount on it, and transformers and tubes. Since the transformers and circuit board need to be mounted on something, they give you a piece of pine board and the hardware needed to mount everything. Okay, it’s very basic, but since a finished product sells for a lot more, this is a way to start. Many people use this kit as an easy way to build a complete amp in a nice looking case with whatever features they want, and some upgrades added in.

Warning: Voltages up to 220V are present when this amplifier is on! You must be responsible to follow safety precautions when testing and using this amplifier. For more info, see my Tube Amp page tab above.

K-502 Complete amp Continue reading

Best Cheap Audiophile Headphone Deal

New Info added 25July2014

Cheap audiophile Mike Parente recently asked about headphones and, to be honest, I did not want to go there! But after thinking about it, and realizing that I listen a lot on headphones lately, I have to make a recommendation. Especially since my favorite for personal use is an earbud type that only costs 10 USD and is available not from audiophile shops, but many retail stores. You are skeptical? You have a right to be, but this is no joke.

IMG_0220The Panasonic HJE120 is very cheap, pretty comfortable, and best of all, sounds really good. There are other options for more money, but they often have issues with comfort or sound. I am an old Sennheiser fan, but I like these Panasonics better than my HD280 Pro studio headphones (that cost 10x more). I am not kidding. The HD280 is good with great sound isolation, but like many full size headphones, it is soft in the highs, even when compared to a number of earbuds.

What really struck me about the Panasonic earbuds is their ability to sound natural. Good audiophile systems have a way of making it sound like the voice or instrument is real and in your room. Hi-Fi can sound good, but it does not present an image that can fool your brain.  These earbuds are audiophile quality because they can deliver some of that natural sound. Are there better ones out there? Yes, but for much more money. Continue reading

Fostex Kanspea Speaker Kit Review

Or “Look Ma, no tweeter!”

IMG_0179Can a speaker that has just one 4 inch “full-range” driver really provide a full range of sound? At the end of my last post, I suggested trying these speakers as a way to experience what midrange can sound like when there is no crossover involved. I realized that I needed to try them out for myself, so I bought these at Madisound without the optional amplifier for about 140 USD. I chose the classic FE103 driver that has been popular for a very long time.

I asked my friend David Still to check these out since he uses a larger full-range driver with a Nelson Pass “Zen” amp. He is also a musician and uses the Pioneer BS22 speakers in his home studio. He also has a Crown DC300A amp and Marantz 2230 that he used. I tried the Fostex speakers with my Tripath “Class T” amp, and with a tube amp. The tube amp yielded significantly different and interesting results that is mentioned later. Continue reading

How to hear!

What? Just WHAT do you mean by that?

man playing guitarIf you have been a musician or involved in sound engineering, you know about how a trained ear can be invaluable. It is also a good thing for anyone who wants good quality music playback, especially given the current audio product market. I would like to offer a few suggestions.

This is a tricky subject. There are two camps in the audio universe: the “Objectivist” who goes by the numbers and only believes in science, and the “Subjectivist” that listens for differences and is commonly called the Audiophile community. Both sides can be a bit extreme in their views and, as often happens with anything in the real world, the truth can often be found somewhere in the middle.

Objectivists will try to convince you that all amplifiers will sound the same and are basically perfect, and that double-blind tests by people smarter than you have proved it. Of course, if you have tried different types of amplifierss and listened, you know this is not true. There is even a website out there that tries to “Debunk the Bi-wiring Myth” by showing the math that actually proves that it does make a difference, but then tell you that you could never hear the difference. Seriously, they actually say that! Apparently, they think we are stupid enough to just take their word for it because they are “experts”. Well, even “smart” people act stupid sometimes….

So, my first suggestion is not to take anyone or any theory too seriously, including me. Electronics and acoustics put together makes for a very complex subject that often frustrates any effort at simple conclusions. Things that make a difference in one case don’t always work in another case. My own experiments with Bi-wiring indicate that it can make a significant difference with some speakers, but not so much with others. There is no replacement for experimentation and experience, but don’t allow previous experiences to make conclusions that may not be true under different circumstances. Always be open to try things and learn! Continue reading

It’s a Digital World!

DigaudioMore info added 25May2014

Okay, I am an old guy. When I went to school, computers were still new, and I studied some Boolean algebra for basic digital circuits, and some Fortran…. And I did not care for it. So I tried my best to stay away from it, and became an RF/Analog guy. I loved it! Who knew that computers and digital would come to dominate the electronics world, I sure did not see that coming!

Which brings me to another point: while I have spent some time in this field, I do not consider myself an expert on the audio equipment that’s out there these days (it is hard for one guy to keep up). I have a little experience with Class D amps, more with Class A and A/B, and some speaker design experience, but nowhere near guys like Andrew Jones. I can design a pretty good tube amp now, and speakers that are good enough to impress most people. But I am more known around the net for a practical paper that I wrote on compact antennas for low power applications.

I started this website over a year ago to help steer people to some of the better products that are available at very low prices. I mean dirt cheap, like stuff the audiophile press won’t look at. I included some DIY (do-it-yourself) info since doing mods seemed to be popular and can help save money. Most of the comments I get here are DIY related. So I’m thinking about doing more projects here, or suggesting interesting kits. Continue reading