Back in January we had Giveaway #1 and gave away a copy Building Valve Amplifiers by Morgan Jones to Bill in Georgia. Well, with Spring just around the corner we are in a good mood and are having another giveaway. Once again the giveaway will be held on the DIY Audio Projects Forum and you will need to be registered on the forum in order to enter for the giveaway.
The giveaway is for two mono kits (which will make one stereo pair) of the MyRefC LM3886 chipamp. The kits were recently put together by Uriah and Peter as part of a large groupbuy. The groupbuy was a very large effort so thank you very much guys (I got a kit for myself that I will build shortly). Also included in the giveaway are two 160VA (120V primary, dual 24V secondaries) transformers for use with the amplifier modules. This will allow you to build two mono-block amplifiers if you like. To finish off the amplifier kits, you will need to supply your own audio and power hookups (RCA, Speakers, IEC, power switch, wire ...) as well as a suitable heat sink and chassis (or two). A photo of the kit contents is shown below.
The chipamp design is by Mauro Penasa and it has been well received. A schematic of the amplifier is shown below.
In order to enter for the giveaway, you need to post a message in the Giveaway #2 - MyRefC LM3886 Chipamp Kit thread with one or more photos attached and a brief description of the photos. Complete details and giveaway rules are provided in the message thread. The giveaway ends April 10, 2009 at 18:00 (CST) (UTC-6) and the winner will be chosen at random.
The most common questions we get from our website visitors are about the inexpensive and simple K-12 Tube Amplifier Kits by S-5 Electronics. These little tube amp kits have generated a lot of interest over the past few years, but for a little over a year now the question has been ... "The K-12 tube amplifier kit is no longer available - can you suggest a comparable kit?" Back in December 2007, Bruce tried out the new S-5 Electronics K-8LS Tube Amplifier Kit to see if it would make a suitable replacement for the K-12. Unfortunately the performance of the K-8LS was poor. So for over a year, we have not been able to suggest a simple to build and inexpensive tube amplifier available as a kit.
A couple of days back, Lofton posted a message on the DIY Audio Projects Forum letting us know that the S-5 Electronics K-12G Tube Amp Kits are once again available (Thanks Lofton). Well, this is great news and now we have an answer to a very common question that we get.
The photo below shows the contents of the recent K-12G Tube Amplifier Kit.
The contents are very similar to the previous kits which came with the 10GV8 tubes. One thing that I did note is that the power transformer appears to be larger than the one which came with my K-12M Tube Amp Kit. This should be an improvement as my K-12M power transformer runs hot, but in fairness, has not failed even after several years of use. The K-12G kits are modestly priced at $189.95 and available from Tube Depot. Right now (Feb 2009) Tube Depot is offering a free 3.5mm to dual RCA cable that you can use to connect the tube amp to your portable music player. It's not clear if this is a limited time offer.
Please note that these kits do not come with an enclosure. Instead they come with a pine board which will allow you to mount all of the parts and put together a fully functional amplifier. However, this will not be practical and possibly unsafe for most environments. There is high voltage present on the board and the tubes get very hot, so you don't want little fingers or paws poking around the amplifier. So be prepared to construct or buy a suitable enclosure for the kit.
Update March 2009: Here is a finished photo of Lofton's K-12G Tube Amplifier Kit.
If you do pick up one of these simple and fun tube amp kits, here are a few links that will give you some enclosure and modification ideas.
Dan has completed a follow-up project to the Jean Hiraga - "Le Monstre" 8W Class-A Amplifier that he built back in July 2008. Impressed with the result of the 8W Hiraga, Dan set his sights to another Jean Hiraga design - the bigger "Super Class-A 30W" which also had previously appeared in the French magazine "L'Audiophile". The original driver transistors were used, but seeing that the original power transistors are no longer available, Dan opted for Toshiba 2SA1943 and 2SC5200 transistors. The new transistors allowed the use of a higher rail voltages (35V vs 24V), resulting in a measured power output of 58W of Class-A power.
The amplifier enclosure was constructed using aluminum channels and plates. As one would expect with a Class-A amplifier delivering this much power, the heat sinks are huge and so is the power supply (500VA transformer and 1.2 Farads of filter capacitors.
Dan reports good sonic results from this amplifier. "Jean Hiraga's deceptively simple and pure circuit topology once again shines through. The sound seems effortless and gives the impression of a much higher power amplifier yet still being able to produce all the low level details, the sound which Class-A is renowned for."
I've seen some pretty sharp looking diy speaker projects on the net, but these guys take the cake.
The enclosure for these great looking and unique speakers is made out of 20 mm thick black granite. Yup, granite. Once finished, each loudspeaker checks in at about 35 kg so you don't want to drop these. The speakers were put together by Radoslav and his friends in Slovakia. The speaker enclosure is a 15L bass reflex design that is tuned to 45 Hz through a rear firing port. The drivers were sourced from Seas and consist of a G17REX/P woofer and 27 TFFC tweeter. The dividing network is second order at 2500 Hz.
The measured frequency response is very flat and shows surprising low end response despite that enclosure size is relatively small size. Radoslav reports that the finished speakers sound and look great.
See the DIY Granite Speaker project page for full details. Obviously there are very few of you that will have the resources to replicate this project, but it is nice to look at and there is no reason why it should work well using more practical enclosure material like wood.
