AlexS

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.

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!!

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...

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

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!

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!

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.

@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

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.

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.

@audiostarthat's odd... you can also try to directly access my files: https://51two.com/KSA5/PSU

@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!!

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?

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!!!

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!