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Posts by wakibaki

Overall distortion (distortion at the transformer output) rose from ~1.425% to ~1.48% when I replaced the diode with a resistor.   This is with the amplifier driven very close to grid current in the second stage, which is the limiting condition governing the power which can be obtained.   Distortion at the output of the first stage is 0.775% with the diode, rising to 0.79% with the resistor.   These are the figures automatically calculated by the program. I...
Yes, you could run the amplifier in the link from the battery in the other link, the reduced supply voltage will not be a big problem, you will get a bit less volume, in fact it may actually make things easier as regards heat.   As you can see though, most people (including me) have concerns about the amplifier overheating, resin is a pretty good thermal insulator.   That said, that particular amplifier probably has the best chance of surviving the experience,...
  I'm still looking at the positioning of the PT, OPTs and Choke for the rebuild. The PCB requires planning, or at least thinking about the whole layout before you start. That's one of the reasons I'm attracted to it, because of the discipline that it enforces, but it's more inflexible than point-to-point. I might go for a combination approach, split the PCB into a number of subcircuit assemblies. I liked the layout I had in the first build, it was just too cramped. I'd...
I generally post schematics of what I do, I just didn't get around to it in the case of the 8-channel volume control. It has some complications anyway because it incorporates the touch-sense functionality.    Towards the end of this thread:- http://www.head-fi.org/t/586042/what-i-did-next-with-texas-headamp-chip-a-digital-control-desktop-portable   ...you will find a schematic for the amplifier using the 7-segment displays, TPA6120 headphone amplifier chip and...
You want an amp that is very efficient if you're going to case it in resin. A class D amp fits the bill, http://www.ebay.com/sch/i.html?_odkw=t+amp&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313&_nkw=ta2024+amp&_sacat=0 I like the Sure electronics boards, I've used them. They call these T-amps because they use a Tripath TA2024 chip.You might like to look on diyaudio.com to see if there are any mods recommended, there used to be when these first became available but Sure...
If you don't get any response to this, have a look at my audio page where you'll find an 8-channel touch sense/remote volume control http://wakibaki.com/audio.php#t5 and further on down, a couple of amps using PGA volume controls. There are sections with circuit diagrams and working code for Microchip PIC to drive 7-segment displays and control digital pots or PGA chips by bit-banging out SPI or other serial protocols.   If you can't get your head round it all you...
  If you change the coupling coefficient of the transformer to 1, the -3dB frequency response goes up to > ~100kHz. The transformer model is primitive, and the 0.95 coupling coefficient is arbitrary. I checked the low frequency rolloff by substituting in progressively smaller caps, you can see things going a bit awry when you put in about a tenth of the capacitance, so I have a bit more confidence that the low end simulation is meaningful, but I don't see much point in...
Turns out I couldn't re-use the CCS bias on the second channel because it makes the current drain assymetric, so it needs to be duplicated at the cost of another 10mA or so...   Good job that the PT and choke are overspecced.   You can see the most recent version of the circuit (arranged for PCB layout) in high detail and save an easy-to-manipulate copy (by right-clicking and selecting 'save image as...') by visiting this...
I'm not familiar with the Pyramid PSU or the V-DAC II, but there is a general procedure for connecting to terminal posts.   You have to make sure that bare copper is showing on the wires to be connected, this means stripping PVC or other insulation back a half-inch or so, or if the wire is magnet wire with a thin varnish-style insulation, scrape this away with a scalpel blade or remove it with sand- or emery paper by grasping the wire tightly in a fold of abrasive...
Hi, people, thanks for the concern.   To answer the question about the LT, first I tried wiring it up to AC. This proved a pain to achieve physically, given that I had to contrive a resistive splitter to connect the ground to and get the soldering iron in through the later wiring to get at the valve bases. So I went back to the DC I had originally intended. I changed the cap in the filament supply to 22,000 uF. This improved the ripple by a factor of 10 to under a...
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