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AlexS

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Everything posted by AlexS

  1. Easter update... a friend of mine has a 3D-Printer: And this is what those parts are for: There will be an additional PCB mounted on top of the volume pot that will also serve as wiring distribution and protection circuit. I will only need tapped holes to the heatsinks, all PCBs are otherwise held in place by the plastic spacers.
  2. After having double checked that the input voltages to the 78/7912 are within limits (max 35V)... measured 31V, I added the remaining 7812 and 7912 to generate the supply voltages for the protection circuit. And modified my prototype so that it no longer needs a individual power supply. The audio 50Hz humm also went away after I no longer crossed the audio input lines with the 230V power cord!!
  3. First testdrive with amps and psus hacked together. Works fine! Input voltage for the 78/7912 dropped to 31V DC. That's great! Did a few hours of listening - no flaws to be heard. Had some great fun there and quite forgot that I was testing a new amp! A tiny bit of 50Hz mains voltage hum to be heard, but that's probably because of no shielding at the moment. Next: integrate the headphone protection board...
  4. For cutting small things I have this cute saw: https://www.proxxon.com/en/micromot/27160.php The soldering pins I source from a German distributor... similar things should be available everywhere: https://www.reichelt.de/de/en/soldering-pins-1-mm-pack-of-100-rtm-1-100-p15321.html The corresponding lugs are these here: https://www.reichelt.de/de/en/solder-lugs-1-mm-tin-plated-pack-of-100-vt-rf-1-100-p231422.html
  5. Hello everyone, it's been a while... busy life, covid, work, supply chains, mouser, jlcpcb, etc... Anyway - the power supplies are finally done and tested: +21,04V and 21,01V. Transformer is a dual 22V/50VA. The rectified and smoothed voltage to the 7812 and 7912 are at +/- 36V DC, that's a hair too much. Hopefully that will drop a little when the amplifiers are connected. That's the next step. Cheerio!
  6. Pretty much on hold until the middle of February. The delivery for the case is delayed and I want to make sure that everything will fit before continuing with ordering the PSUs. The manufacturer has problems with their supply chain for the heatsinks... I will post an update as soon as I receive the case!
  7. Thanks @audiostar! Here's a sneak peak preview of the mechanical design. This is the case that I ordered... not at all cheap, but made by a small company in Germany: https://19zoll.com/en/products/aluminum-cases/19-heatsink-enclosure-series-dsk/ And this will be the inside - Neutrik HP jack and RCAs. Volume pot in the middle. Power via a rotary switch a the rear with a long connecting rod to the front. The toroidal transformer is 50VA and has 2x 22V output windings - that should do for the 21V outputs of the GRLVs.
  8. @ibuskiThanks for the info on the Toshiba alternatives!! Careful if you have size restrictions: those parts have a larger housing: Toshiba specific 2-21F1A: 20.5 x 26.0mm - similar to TO-264 Original parts MJW2119x: 16 x 21mm - TO-247
  9. A happy new year to everyone! The positive part of the power supplies is done: The required PCB dimensions were met, however I had to remove the fine-adjust capability. Everything rather tight! Next step is the negative part and then it's time to order PCBs. These are double sided and I do not have the tools to insert vias underneath large components.
  10. Merry Christmas to everyone here! I hope you had a few days in peace and quiet?! Here is the first half of the power supply (a GRLV with +21V output and a 7812 with +12V output). The PCB area is what I can afford with the current plan for an enclosure - I wonder if it will be possible to place all components!! 🤪 Maybe standing resistors and diodes upright? The big input cap was substituted by 4ea 1000uF/50V. I only have 30mm height for the components.
  11. @audiostarthat's odd... you can also try to directly access my files: https://51two.com/KSA5/PSU
  12. @JoaMatYes - 2mm endmill... does not get into every little space, but saves a lot of time. If I had attempted to rub out the areas with the 0.1mm V-bit, that would have taken forever! @audiostarThis is still to be debated on! The intention is to have a very weak power supply for the protection board, so that the voltage drops fast at mains power off and the relay disengages well before the HT rails of the amplifier come down. If I power the protection circuit off the same rails as the amp, that would obviously not work. So my initial thought was to have a completely separate supply with separate transformer. However, this morning I had the following idea: why not tap the secondary AC from the amplifier transformer and go into a second rectifier? Well the positive part of it. Use the negative half of the existing rectifier for a common ground. That way the heavily buffered DC from the amp will not supply the DC of the protection (diodes block the current path) when the AC is removed. See attached pdf... drawn is a positive channel of a GRLV power supply as per @jamesmking/ @kevin gilmore. I added on a small +12V supply for the protection circuit. Please kindly review this, anyone, and comment? Thanks a lot!!
  13. It's alive 😊 How does it sound? Sounds great - to my ears... whatever thats worth! Seriously: after a short listening session, I am very pleased! Dead silence with no sound input and a very clear sound reproduction. In my opinion the HD-800 are very good in emphasizing any shortcomings in recordings or audio gear for that matter. Is it better or worse than others? I can't really judge. It is what it is and I am having fun during the process of building it - that's the main goal of the project! I will be performing harmonic distortion measurements as soon as I have the PSUs built. That will be the next step! Probably a Goldenreference variant. @kozard happy to share details - wasn't aware that it's of interest: three tools involved here: first is a 0.1mm V-shaped carbide engraving bit. Dirt cheap on eBay. That's for milling the isolation traces at a depth of 0.05mm. I used the same setting for the surround cutout. Only for marking, did the actual cutout with a hacksaw and a file. Then I used a 2mm endmill for clearing out the isolation areas around the 230V traces. Finally I drilled all holes with 0.6mm carbide twist drill. Didn't bother with tool changes for the different hole sizes. Did the ones that needed bigger holes later on manually. Thats really all the magic. I can maybe document the whole process in detail in the future if there is demand?
  14. Finally I got round to getting some time in the workshop: the DC protection circuit is up and running! I decided to do a prototype on my CNC. Converted Gerber files to Gcode with a software called FlatCAM - free, full of features and easy to use! Quite pleased with the result... Assembled and tested: - power on delay ist about 2.5 seconds. I might want to increase that a bit. - The voltage divider for the reference voltages is a bit off: +410mV and -620mV. Not to worry... - Applied a 1 kHz sine wave with 1 Vpp to the inputs and used the DC-offset adjustment on the signal-generator to tease the circuit. The relay clicks off at the exact values as set by the reference voltage divider. Both channels fine! That's it for today - next step is to hook this up with the amplifiers and finally take a listen... looking forward to that!!!
  15. Yes - progress update: I have assembled the second channel and done some measurements. DC offset with OP amp at 1.2mV - happy with that. I didn't get much more done since everything went crazy at work... like every year in December. It's alway interesting when management tells you to use up your annual holiday within the year, you don't really get to take it during the year and then you have to be off for the better part of December. Top management happy, project management... not so much. Anyway... I ordered the parts for the power-up and dc-protection circuits and want to CNC mill the traces of the board in the next couple of days. I want to have that done before I plug in any headphones... call me a chicken!
  16. @kozardsure - send me your email address as private message and I will have the file out to you today.
  17. So, over in the diyAudio forum user Algar_emi from Canada shared a commented schematic of the original clone with a few measurements he made. https://www.diyaudio.com/forums/headphone-systems/109618-krell-ksa5-9.html#post5189211 Turns out that a single channel will draw about 180mA per rail. That's with the voltage across the 2 ohms resistor at 125mV. That works for me. All values from his notes match with my measurements. Strange though, this only seems to work with no heatsink attached! Having only the aluminium L-profile in place, the setup settles at 44°C (100mV). As soon as I connect the big heatsink, obviously the temperature drops and the voltage across the resistor increases to 137mV. (just under 200mA on the input rails). Temperature drops below 30°C. After some ten minutes, temperature is up to 30°C and voltage down to 130mV. So it seems that the thermal capacity of the heatsink has a big effect on the system. Any ideas, anyone? Do away with the big heatsink? Simply live with the increased current through the resistors / transistors?
  18. @kevin gilmoreI use kicad and definitely have forward annotation in place. Funny coincidence, in this case I had two errors for the same part: I had the PNP symbol the wrong way round (Emitter and Collector swapped) AND I had a wrong assignment of the footprint (Q_PNP_BEC - should have been Q_PNP-BCE)... what are the odds?? Anyway - both errors cancel themselves out, leaving me with a layout that is correct - for that part anyway! Then I inserted the OP amp and re-measured the DC Voltage at the output: 1,3mVDC - perfect! Next up: signal generator, dummy load and scope. Set the generator to sine wave with 500mV pp and the load has 250 Ohms on the output. 20Hz ... 2,9V pp 200Hz ... 2,9V pp 2kHz ... 2,9V pp 20kHz ... 2,9V pp 50kHz ... 2,8V pp Seems to be ok - amplification at 5,8. Is that what is to be expected? Removing the load didn't change anything. I still can't figure out why I can't dial in under 110mV across the output resistors. And the heatsink barely goes over 28°C after 1 hour of operation. (19°C ambient) Any ideas what might be wrong? From what I read in the forum posts, 400mA per power rail should be drawn. I have 165mA. Here's a picture of the (still too tidy) workbench:
  19. Right - I found my mistake: swapped the emitter and collectors on the two MJE15031 PNP output transistors... Stupid me! No matter how often you check, re-check and double check something, good old murphy is always lurking somewhere!! It's an easy fix, optically not really pleasing. Lucky for me to have house guests over the weekend, so no time in the workshop. 🙄 @kevin gilmore nice one with the desk! 😂 ... Believe me, my workspace looks like yours from time to time!
  20. Done the first power-on. No magic smoke escaped! But something's not right: Bench power supplies set to 21 Volts. Current draw is 161mA for both the positive and the negative rails. Had to adjust the bias-pot all the way to one side to get a minimum current across the test points of 109mV. I thought that there should be more play here? The power transistors / heatsinks hardly get even warm - after waiting for roughly 10 minutes. DC voltage at the output (with input shorted to ground and no servo OP-amp installed) is at 70mV. Any ideas, anyone? Maybe I will stop for today and have a good look with fresh eyes tomorrow... *frustrated* ?
  21. Yes, I have chosen MPSA06/56. And I should have used the bigger footprints - this one would have been just fine (2.54mm pad spacing): Maybe in a future board revision... And then I fabricated the L-bracket and mounted the five power transistors this evening. The heatsink is for testing purposes only and will be replaced by heatsink sidewalls of the final enclosure. Good that the MJF15030/031 are completely insulated - makes mounting easy, just a dab of heat transfer compound.
  22. Bit of progress here - managed to assemble the first board... Power transistors missing at the moment, I have to manufacture the aluminum angle for the heatsink first. Note to self: next time, use a more suitable footprint for the TO-92 transistors for soldering. The current style is really awful to solder. I needed extremely fine tip and magnification.
  23. Good morning, @audiostar can I share a BOM? Absolutely!! However I do want to actually build and test one of the boards to see if all is good before I post further documentation. I would hate to see someone putting in a lot of effort and money for nothing just because I messed up. After successful testing I will upload the whole lot, including gerbers. I do have all the components already here, but the pcbs got held up in customs for over a week - ah well, I have to be patient! Cheerio, Alex.
  24. Components for two amplifier boards ordered at mouser. Roughly 220 Euros... *outch* But: I got four lsk389A for free as samples from the german distributor!! 😃
  25. So today I finally ordered a batch of five amplifier pcbs at jlcbcb. Total cost of slightly under 60 Euros for 2oz copper and gold plating - that's incredible! Files are here: https://51two.com/KSA5/Amplifier/ Here is the schematic:
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