Leaderboard

Thank you, I’m kind of also coming to the conclusion I need to learn Illistrator or Inkscape for vector creation. Like guitar, wish I would have picked some of these things up years ago.

RIP, Alto Reed, sax player for the Silver Bullet Band. Boy, if you don't feel the chills when he kicks in here... well, it sure gets me every time.

Looking good, I'm dying over here waiting for mine to show up. Any day now, any day. What CAD/CAM are you using? I've been peeking at Chinese CO2 lasers on Ebay that work with Lightburn, way easier on the pocket book than comparable Epilog/Trotec machines.

I think there are enough of us with turntables to warrant a specific vinyl thread. After all it's not the same as streaming digital. Shirley Bassey: Good, Bad but Beautiful

To see what and how to improve, let's have a look at the original schematic. KSA-5 is designed along the lines of "moderate feedback", that is, it uses very little to no global feedback but lots of local feedback a.k.a degeneration. The pair of input JFET buffers (Q1, red box on the schematic above) run independently of each other and outside of the global feedback loop. With low loop gain, they see very different signal levels, so the differential stage downstream doesn't cancel their distortion. (BTW, because of this JFETs need not be matched. Also, the expensive and hard-to-find JFETs can be easily replaced here with BJTs.) Still, a JFET follower loaded by a current source has 100% degeneration and relatively low distortion, at least at low signal levels, so the buffers are not the biggest problem. The pair of differential stages (Q2+Q3, Q7+Q8, orange box) is heavily degenerated by 680ohm emitter resistors and produce R10/(R1+R2) = 2 = 6dB of gain. The pair of common emitter stages (Q12, Q13, purple box) is also heavily generated by 402ohm emitter resistors and, with the low load of R23 and R24, provides R23/R16 = 9 = 19dB of gain. Since the output stage (blue box) is a double emitter follower with approximately unity gain, the total open loop gain of KSA-5 is 2x9 = 18 = 25dB. The feedback divider (R45-R47) attenuates the output signal by a factor of 9 (19dB), which leaves 18/9 =2 (6dB) of global feedback. That is, the global feedback loop attenuates the distortion of the output stage by a small factor of 1+2 = 3. The output stage, meanwhile, is a large source of distortion. Although Krell claimed that KSA-5 runs in "pure Class A", in reality it can easily slide into Class AB. The output pairs run at only 50mA of quiescent current each and leave Class A (that is, one half of the output stage stops conducting current) when the output current reaches 200mA. The driver quads (Q15-Q22) also run in Class AB (R37 and R38 are connected to the output), which means they stop conducting at that point, too. With a 100ohm load, it would happen at 20V peak output voltage, so the amp never leaves Class A with such a load. However, with 32ohm, KSA-5 leaves Class A at 6.4V peak; with 8ohm, at 1.6V. Even within Class A region, the output stage is not very linear, especially with low impedance loads. It uses paralleled transistors with relatively large emitter resistors to ensure current sharing. The dark side of large emitter resistors is that they make the output impedance of the emitter follower large and nonlinear in the crossover region (see e.g. Douglas Self and his "wingspread" diagrams). Since the output impedance forms a voltage divider with the load, its nonlinearity makes the gain of the emitter follower nonlinear, adding crossover distortion and negating the benefit of the large bias current. Overall, KSA-5 has a nice and linear front end followed by a not-so-linear output stage, with little feedback to let the former help the latter stay linear. The game plan, then, is to improve the output stage and add more feedback.

^^ I almost bought a pair of those some months ago....

Oh, I see, thanks, Steve. I'll wait when it's completed so I can watch at my own pace. Not having to wait for weekly episodes is the best thing these streaming services invented.

Looks great!

I have not, though I probably will now. Feed and speeds are still a bit arcane to me. Easy enough for wood now. But I know the Shapeoko can do softer metals and I intend to do that soon. Even picked up a surplus fridge compressor to kit out as an air assist/mist cooler

I get that. There are 1001 projects in my mind, how many actually will come out...no idea. Have you checked out the cnccookbook? Going to give it a whirl to see if it helps out or is worth while, 30 day free trial.

If either of you ever need something drawn up in CAD and converted to a DXF or even (maybe, haven't tested completely) an SVG I can make pretty quick work of it. I'm shite at 3D stuff, but flat vectors should be no issue.

I’ve reduced power board voltages to +/-12 V. Two Mean Wells 12 V capable to deliver 29 A. Heat sink temperature decreased considerable – of course. My old ears think the sound is as good as with +/-24 V Next step is to make a few more boards to get a balanced set up.

A great Tiny Desk concert (home) by the Iranian-born Sevdaliza. Not much to argue about her 2020 release being one of the best regarded pop albums of the year.

why work at home slows down

Cutting has definitely been an uphill battle with a diode laser in my experience. I have not been paying attention to what rig you are running so I may be in a totally different court. Also Lightburn was worth every penny for laser work. $40 is nothing compared to some of the other CAD/CAM programs out there. Those cutouts look heckin dope! ....if you wouldn't mind sharing the vectors..... I've been doing Arrow of Light plaques for the local cub scout troop. I won't share the finished project because I feel weird sending out names of children but the arrow was cut out with the router then the words cut in with the laser. Arrow was then filled in with yellow paint and the whole thing was stained and varnished.

I built my KSA-5 clone back in 2013 (see my post dated August 9, 2013 in this thread on page 8) but was never quite satisfied with it. I made every effort to make it look good and perform well, and it was well within the original KSA-5's specs. Yet, although it worked well with my 32ohm Grado headphones, it could not compete, in my subjective opinion, with Musical Fidelity's X-CANv8. Connected to a pair of 8ohm speakers, the clone would become rather confused with anything but simplest music. Because of this, the amplifier fell into disuse and was gathering dust on my rack. Until this weekend. This weekend, I finally got around to make KSA-5 work for me. I kept the overall topology and the PCB, only changing some passive parts. The results are quite remarkable: The original KSA-5 was rated for 5W into 8ohm with THD<0.5%. Before modification, my clone gave 5W into 8ohm with THD @1kHz of 0.18%, well within the specs. The revised clone delivers 5W into 8ohm with 0.0015% THD, an improvement of more than two orders of magnitude. The original KSA-5 was advertised to deliver THD<0.03% into 100ohm load, although the brochure did not give the signal level for this performance. Assuming the same output voltage as for 5W into 8ohm, about 6.3Vrms @ 1kHz, my unmodified clone demonstrated THD of 0.02%, again within the specs. The revised clone drives a 100ohm load to the same level with 0.0017% THD, an improvement of more than an order of magnitude. The modified channel sounds very well, clear and transparent. I still need to complete the second channel and do some real listening. I will post the revised schematic with some explanations, as well as additional measurements, in this thread.

I thought my comment was pretty benign, Gene. This isn't really a headphone forum. Most members have been here more than a decade, date back to the earliest days of Headwize, and are friends in real life, despite the thousands of miles, oceans, continents and everything else in between. Are we occasionally rude? Yes. Were we particularly rude here? No. If you'd read around a bit even just in this forum you'd have seen that the top 10 threads are so are either Stax related or about boutique niche headphones. So no, you posting a review of your new AKG K240s was unlikely to generate any sort of stimulating conversation. Most here have probably already owned a pair. Congrats on your new headphones. My advice, spend more time listening to them then writing about them. As the saying goes, sorry about your thin skin.

That's an easy one for me, clearly The Munsters. The Addams weren't even aired here.

A guy on /r/audiophile had a pair of 18" subs for a live PA that he was unable to sell, so he added them to his home theatre. WAF is quite low as it turns out.

Based on my experience, that threshold can be built with only a measly $17k in tool investments. Make sure you buy every accessory as well and the full Woodpecker catalog so everything comes out straight. Easy. 😁

Having someone help you finish is definitely preferred, compared to doing it yourself.