Friday, September 28, 2007

Degen DE1103 shortwave radio mini review

Can a low-cost digitally controlled radio have the same feel as an analog receiver?

The audio/touch combined feeling that you get while tuning across short wave in the evening on a true analog radio is much more usable than the chop/chop/chop effect experienced on low cost digital radios - until now.

The benefits of a digital radio, accurate frequency read out, full band coverage, and memories are great, but if it's painful to tune around it's just not worth it.

I picked up a Degen DE1103 for AU$159 from the very friendly AV-Comm here in Sydney. Significantly more expensive than I've seen them on eBay, but it came with a local power adapter and a smile on a Saturday morning.

The good:
  • Very sensitive, in fact it overloads on the AM broadcast band (there's a switch for local which must be used).
  • Comes with re-chargeable AA batteries which can be charged in the unit with the supplied power adapter. It has a timed charge system built in.
  • Includes a generous long wire antenna and cloth pouch.
  • Tuning up and down the dial is really smooth, you would think it was an analog system.
  • Direct input of frequencies using the row of number buttons.
  • Remarkably good on single side band.
  • 0xFF memories (255)
  • Short wave broadcast bands for easy finding of the big broadcasters.
The bad:
  • Audio volume is adjusted by pushing a button and then using the tuning knob.
  • Mine doesn't sit flat, there is a pop out stand, otherwise it rocks when laying flat
  • The big digital simulation of a short wave band dial is pretty funny really, tuning is actually continuous.
  • A little cryptic to operate, eg: memories are recalled by pushing a button and spinning the dial. I'd like to store frequencies in those buttons on the front but they just seem to do direct frequency input.
In summary, it's a good little radio. Perfect for travel, with decent sound and great sensitivity. I wish manufacturers would make appliances easy enough to use that you don't need a manual at all - you do with this one.

I wish we had an iPod short wave radio.

Saturday, September 01, 2007

Ultra high quality headphone amplifier

I read Alastair's post about high quality headphones with great interest. 

After finding the excellent Headwize site, I rushed down to Jaycar this morning for bits, and built the cmoy headphone amplifier (in an Altoids tin, with space to spare, as shown above right).

What really got me was the data sheet for the OPA2134 operational amplifier from Burr-Brown which says, in part, "The distortion produced by OPA134 series op amps is below the measurement limit of all known commercially available equipment."

Further: "THD+Noise is below 0.0004% throughout the audio frequency range, 20Hz to 20kHhz".

My experience.. 
  • This is easy to build. I did a hack job, as you can see above, and it worked perfectly first time.
  • I'm driving Sennheiser HD 212Pros.
  • Ripped some CDs at AAC 256kbps as sample content.
  • iPod shuffle has noticeable hiss
  • iPod 30Gb has less noise
  • Switching the headphones between the iPod direct and via the amplifier makes the iPod sound relatively dull.
It's hard to explain, but this little amplifier gives a real sparkle to the sound. It's not artificial or boosted in any way, but things like cymbals sound quite different - better. Sometimes there is too much bass for my liking.

Other notes:
  • Jaycar don't advertise the OPA2134, I went to buy the NE5534AN which is in their catalog and they gave me what I really wanted as a substitute - excellent! (AU$3.95)
  • This chip is broadband, when I touch the input it picks up all sorts of hum, I expect that it will be susceptible to RF from things like mobile phones and will need to be in a well shielded box (Altoids tin for example) with filtering to avoid picking up hash.
  • I used "ugly construction" which works well for RF projects so it's probably pretty stable as it's all ground plane.
  • Didn't bother with gain control as I figure whatever is driving it has it's own volume control. Mine has a bit too much gain for my listening levels.
So, one more thing to carry on the train.. thanks Alastair.

Update

I've spent a very entertaining evening re-importing some of my old favourite CDs at 256Kbs/AAC and of course listening to tracks in different headphones. There is a story around about how your brain works harder listening to music which has been compressed for space (no, not level - that's another topic). Basically masked parts of the audio are removed to reduce the data rate, but in fact you miss those parts of the signal and have to imagine them yourself.

In my youth I was very interested in "hi fi" and well remember the arms race that would follow the upgrade of one component in the system: a new moving coil cartridge would show up the noisy amplifier, upgrading that would show up the speakers, and so on.

Recent years have seen my music move totally on to computers and mostly in to headphones. Loud speakers are always a compromise existing as they do in a room that resonates to some extent. Little computer speakers have advanced tremendously in recent years and work damn well at low level. Headphones can reveal detail and texture in an audio track that will be missed on even the most high end speaker system.

With the falling cost of storage it's now time to re-import my CD collection at a higher bit rate - or perhaps I should just bite the bullet and go loss-less at last.

Update 2

Hmm, not sure if the higher bit rate AAC is worth it for me. I created this test which chops back and forth between 128Kbps and 256Kbps every ten seconds and I can't tell the difference. Of course I'm getting old and probably not listening in the best equipment.