12 December 2007

Audio Paradox - S-5 Electronics K-8LS Tube Amp Kit

Bruce Heran writes:

As an avid diyer and fan of the S-5 Electronics K-12 tube amplifiers kits (I have 2) I thought it would be a good idea to get a K-8LS. This tube amp kit is a logical replacement for the S-5 Electronics K-12 and K-502 tube amplifier kits. It is about the same power and is aimed at the same budget tube amp market. The basic amplifier circuit topology of the K-8LS is the same as its predecessors. With the exception of an added preamplifier section, it is not a major redesign, and now uses somewhat more readily available vacuum tubes. The one big plus is that it now comes with a much larger power transformer. The original K-12 ones ran rather warm.

I really want to like this product, but as you will see in the following comments, mine is awful. Sine wave and square wave tests were conducted at several frequencies. The measurements were made at 1 volt output into an 8 ohm non-inductive resistor. This is an easy load for any amplifier. Frequencies checked were from 20 Hz to 40 kHz.

25 Hz Sine Wave

100 Hz Square Wave

There was a significant drop in output (sine wave) below 150 Hz and by 20 Hz there was not much left (about 9 dB down relative to 1000 Hz). The high frequencies were down around 3 dB at 18 kHz. Sine waves at 50 Hz showed clearly visible distortion. Square wave response at 1000 Hz was fair, but with some tilt. By 500 Hz the tilt was significant and below 150 Hz it was excessive. At frequencies below 50 Hz it no longer resembled a square wave at all. On the high side, rounding occurred from about 4 kHz up. By 10 kHz, square waves looked more like a sine wave! To be fair, there was no ringing or overshoot at any checked frequencies.

1 kHz Square Wave

10 kHz Square Wave

Now you can see the paradox. I want to like this product, but it is awful! So rather than jump all over the manufacturer, let’s start a dialogue and see if others have the same or different results. I’d like to give the K-8LS a chance, so let’s hear from you about your experience with this kit.

Good listening,
Bruce Heran

Other DIY Tube Amplifiers by Bruce:

10 December 2007

Ready Made Curved Speaker Enclosures

If you are like me and lack the wood working skills, tools or workspace to build a fine looking pair of speaker enclosures, there is some hope.  Buy some pre-made made enclosures and all you will need is a drill and a hole saw. 

Dayton 0.38 ft³ Pre-made 2-Way Curved Cabinet in Gloss Black
As I want to try another fullrange speaker project over the Christmas holidays, and I don't have the skills or time to build nice looking enclosures, I am going to try out a ready made Dayton 0.38 ft³ Curved Cabinet finished in Gloss Black from Parts Express.

Dayton Ready-made DIY Curved Speaker Cabinet
The ready made speaker cabinet has a great black high gloss piano like finish.  The baffle is 1" MDF and removable.  The grill is secured to the baffle by magnets in line with the machine screws that hold the baffle in place.

Dayton Ready-made DIY Curved Speaker Box
The enclosure is constructed out of 3/4" MDF side and back panels with a 3/4" MDF brace running vertically up the sides and across the top and bottom. The overall dimensions are 14" H x (8" Front, 4.5" Back) W x 11.3" D.  With quality ready made cabinets like this, a finished DIY speaker should only be a few holes away! Somehow, I know it won't be that simple! :)  

LINK - Dayton 0.38 ft³ Curved Cabinet finished in Gloss Black from Parts Express.

UPDATE - 24 March 2008
The cabinets shown above were used to make a pair for Fostex FX120 Bookshelf speakers.  I liked the curved PE cabinets so much I just had to purchase another pair. This time, I opted for the 0.25 ft3 cabinets in a Maple finish. The plan is to house Jordan JX92S Fullrange drivers in the curved maple speaker cabinets.

Dayton 0.25 ft³ Pre-made Curved Maple DIY Speaker Cabinets
LINK - Dayton Audio Pre-made 0.25 cu. ft speaker cabinets with Maple finish 

DIY Bookshelf Speaker Projects using the Dayton Curved Speaker Cabinets:

03 December 2007

DIY Class-T Amplifier Kit (AMP6)

It has been a long while since I added one of my own projects to the diyAudioProjects.com website. I had actually finished this project back in the summer, but never got around to pulling together a web page for it until now. Over the past few years I have read a lot of good things about Class-T Amplifiers (T-Amps). For those who are unfamiliar with T-Amps, the chip manufacturer (Tripath) describes the Class-T amplifier chip as one that can offer both the audio fidelity of Class-AB and the efficiency of Class-D.

DIY Class T Amplifier Kit (T-Amp)
I decided to try a kit from 41hz.com as they are priced very well and I have read several good reviews of their T-Amp kits. I opted for the AMP6 kit which uses the popular Tripath TA2020 chip. The kit was only $39 and fairly simple to put together.

For the enclosure, I used a prefabricated aluminum chassis. The results are a little industrial looking, but heck, I am interested in the sound quality, not the enclosure.

Finished AMP6 T-Amp Kit
A lot of people describe T-Amps as having a "warm tube like sound". I didn't think so. I did not like the sound when mated with high efficiency fullrange speakers. However, with more traditional speakers (2 and 3 way) I was very pleased with the performance of the little AMP6 (about 12W into 4 ohms and only 7W into 8 ohms). It provided accurate tight bass and detailed mids and high. While I prefer the sound from my DIY LM3886 Chipamp (gainclone) Kit, the AMP6 is a solid preforming small amplifier with an excellent price to performance ratio.

Full details of my experience with the AMP6 and additional photographs are available at the AMP6 (T-Amp) - DIY Class-T Amplifier Kit
project page.

What's Playing: New Order -Vanishing Point (instrumental)