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AlexS

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Everything posted by AlexS

  1. 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.
  2. @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
  3. 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.
  4. 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.
  5. @audiostarthat's odd... you can also try to directly access my files: https://51two.com/KSA5/PSU
  6. @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!!
  7. 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?
  8. 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!!!
  9. 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!
  10. @kozardsure - send me your email address as private message and I will have the file out to you today.
  11. 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?
  12. @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:
  13. 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!
  14. 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* ?
  15. 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.
  16. 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.
  17. 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.
  18. 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!! 😃
  19. 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:
  20. Good evening everyone - I did a bit of optimization to the amplifier board. Size is now down to 170x100mm ( or 6.7in x 3.9in) Also added DC blocking. I'm experimenting with web-space... try this link: http://51two.com/KSA5/ Cheers, Alex.
  21. This is what the protection board might look like. By the way, does the time delay cap really need to be a bipolar? I somehow cannot figure out why it should be... Any thoughts, anyone? Cheers, Alex.
  22. Great! I think I got the missing diodes... odd, though probably irrelevant: the middle resistor in the reference voltage divider is 500 ohms in your schematic and 1k in the gerber silkscreen.
  23. Thanks Kevin! From the information that I could pull from existing information in the original thread and the google-drive I have tried to compile attached schematic. There were no gerbers or other layout files or images available. The file "protector3.PDF" seems to be missing all the diodes... can you please advise? I had to delete the previous schematic images due to upload file size limitations... sorry for that! Cheers, Alex.
  24. Interresting... This one, right? Unfortumately, I was not able to find any schematic. Do you have a working link? Thanks!
  25. I continued to work on the protection circuit and came across the XEN SHPP Headphone Protection Circuit project: http://xen-audio.com/documents/SHPP/XEN%20SHPP%20V1.pdf Here, a potential flaw in the Epsilon 12 circuit is discussed that might result in the original design not to detect DC offset in certain situations. The outcome is that each channel gets its own DC detector and combines the outputs via diodes to the delay and relay circuitry. Also, in my opinion, the time delay cap C7 does not need to be an non-polarized electrolytic... am I missing something? The last mod is to drive the relay solely from the +12V DC to GND. As I have done away with the virtual ground concept, the rail-to-rail concept of AMBs design is no longer needed. If someone could please have a look at the schematic an comment if I have some bonehead mistake? Sorry about the bad resolution of the schematic - the forum only allows me to post images with a maximum size of 22.87 kB. Does anyone know, why that is? Thanks a lot - cheers, Alex.
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