I joined diyaudio.com on Nov 2013 and that's pretty much when i started this hobby. Maybe "restarted" is a better term as i played with diy amps, tin and soldering iron back when in junior high but somehow stopped. That being said, it should be obvious that i am just a beginner and with that:
1. There will be mistakes/misinformation. Feel free to correct me. It will be much appreciated.
2. There is no guarantee any schematic shown works in real life, unless mentioned otherwise. Basically once LTSpice shows that it works, i'm 80-90% sure it should work in real life.
3. There will be updates and revisions as i learn more, hopefully with your help!
4. There will be language barrier. English is not my first language so bear with me!
I'm building a pair of bookshelf speakers for my wife as a gift. Don't worry, it's not one of those bowling ball gifts that's really for me. It will come with a record player and a few records of some of her favorites.
I recently found out my speaker configuration is actually a popular design by Carmody. Which makes me feel good about my choices, but also sets the bar high for me.
The baffle is a 1" thick walnut/maple butcher block look, with 1/2" baltic birch for the rest.
I made the mistake of comparing my PCD7 prediction with his. I noticed they are nothing alike. I got worried so I went back and re did my measurements to make sure I wasn't in a weird spot or getting a reflection. Even moving the mic all over I was pretty impressed with the consistency. The issue was - diffraction. Like 10dB of it. I beveled the corners, but it's still only a 6" wide baffle.
Posted 14th May 2016 at 03:48 AM bygooglyone Updated 14th May 2016 at 03:53 AM bygooglyone
As a kid, which depending on my wives mood could be stated to be "right now" right through to "you have never been a kid", I once made the statement that "if it can't be done with a BC549 it is not worth doing".
this statement was made in jest at the time, and probably stolen from a similar a similar assertion about the NE555. (those of you who are < 30 years old probably haven't seen these used in real anger!)
Here I am travelling, and flying from Adelaide (Australia) to the USA. This is a long, boring flight. In a fit of boredom I set myself a challenge.
So what is the challenge? Something cool and completely different for once. Hmm. Make a power amplifier using BS549's. If you have seem my play room, amplifiers are made to scare speakers and annoy the neighbours. So this can't be a lightweight 100mW job. It must be something that actually works, and is able to make real noise.
The main innovation re. the sapphire circuit is to replace the bias set resistors with diodes made out of the Vbe of transistors Q9 and Q10. This generates more voltage than is ideal, but can be handled by using largish values for the emitter resistors R13 and R14. Since this is a line stage buffer and not a headphone amplifier the output impedance of about 30 ohms and the limited output current swing are not critical flaws. It will drive 600 ohms at 0 dB with 0.001% THD. The whole circuit draws just 150 mW. The input impedance is a very high ~15 Mohms...
I have one First Watt F4 amp, so Iíd be running it stereo unbalanced to drive my speakers.
Since the Impasse debuted, have you or others implemented any revisions that I should know about?
My speakers are at least 94db sensitive, my room is 16 ft x 14 and my ears canít tolerate average SPLs much beyond ~ 60db-at least not much above the lower midrange band (i.e. allowing for the Fletcher-Munson effect). My midwoofers are cut off below 70Hz, where my pair of Rythmik 12" sealed powered subs take over.
Are there certain tube suppliers of specific brands of 6SN7 tubes, or better sounding alternatives, that you would recommend for best performance with my speakers, such as http://www.sophiaelectric.com/ ?
Posted 2nd May 2016 at 12:13 AM byTam Lin Updated 12th July 2016 at 01:38 PM byTam Lin(corrected typo)
With delta-sigma DACs pushing insane clock rates I wondered if a traditional multi-bit DAC could not do better. The fastest multi-bit I know of is the PCM1704, which has a max BCLK rate of 25 MHz. A 32-bit sample frame can run at 768 K samples per second. That is fast but not faster than DSD64.
However, with 32 DACs per channel staggered across the sample period we get 24.576 M. That is better than DSD512. For input at or below the native rate of 768K, the DACs operate in parallel. Below the native rate, inserted nulls stretch the output sample period. Above the native rate, the DACs are staggered and the data at each point is the input sample value minus the sum of the data in the other DACs. Thus, each successive sample is the delta needed to reach the next sample point. This approach has interesting repercussions: I will let you ponder them for the time being.
Listening to headphones creates, on many recordings, an unnaturally wide soundstage. I decided to play with the idea of 'crossfeed' whereby some deliberate crosstalk is introduced between the two channels. With transformers its jolly easy to do - just create an extra winding with the right number of turns then put this winding in series with the main output of the opposite channel.
In the picture I've done this with some EP17 ferrite cores and added a DPDT changeover switch to A/B between the original and crossfed version. The crossfeed factor I've gone for is 25%. It works in practice in that there's a more natural presentation without any 'extreme' stereo effects (almost a kind of phasiness on some recordings). But sometimes I enjoy the 'all around' effect so switchable is the name of the game
Trafo winding details as follows - primary 500T of 0.1mm, two secondaries first 120T 0.21mm, second 40T 0.21mm.