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Huge fan of Mark here. His YouTube and Patreon are a wealth of knowledge for repairing electronics. He’s an expert in everything from electronics to machining a

by crmd 2y ago

Huge fan of Mark here. His YouTube and Patreon are a wealth of knowledge for repairing electronics. He’s an expert in everything from electronics to machining and plastics fabrication. And his demeanor and presentation style is just lovely. I hope this nonsense increases his visibility and he gains some fans. https://youtube.com/@menditmark https://youtube.com/@menditmark https://www.patreon.com/MendItMark https://www.patreon.com/MendItMark I watched the Tom Evans video when it came out, and my guess is that their sham “copyright” claim comes from showing their logo or some written words on one of their PCBs.

rwmj 2y ago
I remember a video he made repairing a very ordinary, mid 90s, cost-reduced Sony Walkman, where he very carefully spent hours reproducing a tiny bit of metal that had worn out in the internal mechanism. Rescuing something that (even when bought) was mostly e-waste. Edit: This one: https://www.youtube.com/watch?v=rxkuOzvHToc https://www.youtube.com/watch?v=rxkuOzvHToc
fuzzfactor 2y ago
Looks like he made his own service manual for this piece of gear and it has the manufacturer's logo on it without their consent. Which he prepared for the client in decent presentation quality. One of the most admirable things to do, above and beyond most repair professionals, looks like Mark really is a cut above and it shows. The top instrument companies have always recognized the advantage of partnering with the rare individual who can service their complex and unique products, and have been the most willing to provide schematics and discounted parts in order to make as many into authorized service centers as possible. To enable field calibration and service, or bench work without having to send their own people or ship the unit back to the main repair depot. The lesser outfits, not so much. If you've got money-making instruments to sell, you really don't want to work against someone who has the talent to fix defects without even having any factory documentation. That's hard to come by, they could be your best ally. Imagine what could happen with full factory support. And Mark prepared his own documentation! How much more respectable can you get? Posting it on Youtube is the only real mistake, unfortunate but true. Obviously, Youtube is not a respectable enough place, oh well, who knew? From the commentary it does look like the circuits are not more innovative than the "generic" guidelines published by the component manufacturers to encourage engineers to adopt their semiconductors for various intended purposes. When these analog devices were first emerging, some of these data sheets were widely published back when some of the example circuits were still under patent. There was every expectation that if you copied one of them, you would have to license it before you could legitimately include it with your own product. For these preamp components, patents have all expired now so that's not a consideration any more. However it's possible that somebody 30 or 40 years ago might have drawn up a PCB of a completely generic circuit that exactly conforms to an example public-domain schematic, no longer under patent by decades, but that pattern on the PCB could easily still be under copyright for decades to come. You create your own original artwork, you own it, even if the circuit is exactly the same. Thus I would say the patterns on the PCBs are only legitimate to reproduce in much less than their entirety, like passages from a book. That could be a pitfall, but I don't think more than a few relevant excerpts were casually shown in the video.
- crmd 2y ago
  The only remotely creative aspect of the preamp was the use of discrete voltage regulators for almost every component in the audio path. It has a comical number of voltage regulator ICs.
  - fuzzfactor 2y ago
    >a comical number of voltage regulator ICs. There hasn't been much commentary about the electronics, but I found it amusing myself about the amount of overkill on the multi-stage voltage regulation scheme. Those components drawing more wasted power from the external supply than the audio circuits themselves. I know overkill is important in some audio circles, but did I say massive external supply for a preamp? This kind of signal handling does not require a high-current audio circuit where there may need to be a very sizable power supply. When that happens it may be the best idea for the power components, especially transformers and other potentially noisy components like voltage regulators to be enclosed in a separate chassis from the sensitive audio semiconductors and their carefully laid out signal connections. You don't have to be an audiophile to recognize when this might be needed, don't ask me how I know ;) What I like to do is make the external supply good enough so that no significant power components are needed inside the instrument chassis, other than ferritics and capacitors for local storage/delivery and filtration of anything that might come in on the (well-shielded) cable like it was an antenna or something. I figure I'm not the only one around here to have designed their own personal phono preamp after looking at numerous opamp datasheets, these are actually not easy. I needed one to work with 78 rpm records, not audiophile material :\ Actual vinyl polymer at 33 1/3 rpm was even more challenging even though the RIAA equalization was standardized by then. I figured might as well, if I'm going to do some serious soldering it would be good to exceed minimal objectives. RIAA is functionally a very steep well-defined mathematical curve[0]. Traditionally implemented using all analog components in a much lower-noise arrangement than usual. It requires quite a high gain preamp to recover the bass from the microgrooves where it has physically been pressed so much more lightly than the other frequencies. I just used one audio circuit board since I was indulging in the opposite approach to overkill. From what I've heard, the fewer active analog components that your signal passes through, the fewer compromises it may be subject to anyway ;) Audiophiles would think I took a lot of short-cuts which is true, I could surely have gotten better channel separation using two boards instead of one. But it did take a little rig about twice as complex just to perform the development experiments on, which was re-architected a number of times, one of the advantages of a non-PCB free-form soldered breadboard. Well I have nothing to brag about the way I cheated on my own power supply for this project. I would say it really does take about as complex a power supply PCB or more than it does for the audio PCB. Screw that, I used batteries :) Needed to be portable anyway like a laptop. Plus batteries have no hiss or hum, that was easy. Actually I got lucky because I was able to achieve my goal of digitizing vinyl at the standard CD format of 44.1 KHz 16-bit, while introducing lower analog noise than a CD can reproduce. IOW transparent for that application, and see what collateral damage there is otherwise :) There was plenty of headroom with two 9V batteries giving 18V peak-to-peak before clipping. Plus the batteries lasted a long time since very few components were on the final board, and it's just a preamp. Now I shouldn't complain about having loads of PCBs stacked in overkill configuration until it almost topples under its own weight, using blank copper boards for shielding within a plastic enclosure. Not when mine sits on a teflon sheet inside a mere small cookie tin, and the shielding is still usually OK when the top is removed :) For a while there you could even still smell the cookies. [0] Here's some good info for vinyl heads: https://hifisonix.com/wp-content/uploads/2010/10/RIAA-Equalization-Amplifiers-Part-One.pdf https://hifisonix.com/wp-content/uploads/2010/10/RIAA-Equali... http://waynestegall.com/audio/riaa.htm http://waynestegall.com/audio/riaa.htm and a single-board amateur project to learn from where it looks like there are some power components on the PCB, probably not much more complex than my lab effort otherwise. They cover using a single 9V battery during their prototyping as well as the migration to A/C adapter and virtual ground for the opamps. I used a pair of batteries wired for true bipolar +/- 9VDC and stopped there. Also notice how much bigger the plastic caps are than tantalum would be: https://www.instructables.com/RIAA-Equalization-with-analog-electronics/ https://www.instructables.com/RIAA-Equalization-with-analog-... Edit: Left out the part where I would use a Dremel to cut out the RIAA section from the populated PCB of cheap scrap record players that people were once discarding quite commonly. These were small little "partial" PCBs too and quite dissimilar, but made them work on their own before building to my final specs.

by crmd 2y ago

rwmj 2y ago

I remember a video he made repairing a very ordinary, mid 90s, cost-reduced Sony Walkman, where he very carefully spent hours reproducing a tiny bit of metal that had worn out in the internal mechanism. Rescuing something that (even when bought) was mostly e-waste. Edit: This one: https://www.youtube.com/watch?v=rxkuOzvHToc https://www.youtube.com/watch?v=rxkuOzvHToc

fuzzfactor 2y ago

Looks like he made his own service manual for this piece of gear and it has the manufacturer's logo on it without their consent. Which he prepared for the client in decent presentation quality. One of the most admirable things to do, above and beyond most repair professionals, looks like Mark really is a cut above and it shows. The top instrument companies have always recognized the advantage of partnering with the rare individual who can service their complex and unique products, and have been the most willing to provide schematics and discounted parts in order to make as many into authorized service centers as possible. To enable field calibration and service, or bench work without having to send their own people or ship the unit back to the main repair depot. The lesser outfits, not so much. If you've got money-making instruments to sell, you really don't want to work against someone who has the talent to fix defects without even having any factory documentation. That's hard to come by, they could be your best ally. Imagine what could happen with full factory support. And Mark prepared his own documentation! How much more respectable can you get? Posting it on Youtube is the only real mistake, unfortunate but true. Obviously, Youtube is not a respectable enough place, oh well, who knew? From the commentary it does look like the circuits are not more innovative than the "generic" guidelines published by the component manufacturers to encourage engineers to adopt their semiconductors for various intended purposes. When these analog devices were first emerging, some of these data sheets were widely published back when some of the example circuits were still under patent. There was every expectation that if you copied one of them, you would have to license it before you could legitimately include it with your own product. For these preamp components, patents have all expired now so that's not a consideration any more. However it's possible that somebody 30 or 40 years ago might have drawn up a PCB of a completely generic circuit that exactly conforms to an example public-domain schematic, no longer under patent by decades, but that pattern on the PCB could easily still be under copyright for decades to come. You create your own original artwork, you own it, even if the circuit is exactly the same. Thus I would say the patterns on the PCBs are only legitimate to reproduce in much less than their entirety, like passages from a book. That could be a pitfall, but I don't think more than a few relevant excerpts were casually shown in the video.

crmd 2y ago
The only remotely creative aspect of the preamp was the use of discrete voltage regulators for almost every component in the audio path. It has a comical number of voltage regulator ICs.
- fuzzfactor 2y ago
  >a comical number of voltage regulator ICs. There hasn't been much commentary about the electronics, but I found it amusing myself about the amount of overkill on the multi-stage voltage regulation scheme. Those components drawing more wasted power from the external supply than the audio circuits themselves. I know overkill is important in some audio circles, but did I say massive external supply for a preamp? This kind of signal handling does not require a high-current audio circuit where there may need to be a very sizable power supply. When that happens it may be the best idea for the power components, especially transformers and other potentially noisy components like voltage regulators to be enclosed in a separate chassis from the sensitive audio semiconductors and their carefully laid out signal connections. You don't have to be an audiophile to recognize when this might be needed, don't ask me how I know ;) What I like to do is make the external supply good enough so that no significant power components are needed inside the instrument chassis, other than ferritics and capacitors for local storage/delivery and filtration of anything that might come in on the (well-shielded) cable like it was an antenna or something. I figure I'm not the only one around here to have designed their own personal phono preamp after looking at numerous opamp datasheets, these are actually not easy. I needed one to work with 78 rpm records, not audiophile material :\ Actual vinyl polymer at 33 1/3 rpm was even more challenging even though the RIAA equalization was standardized by then. I figured might as well, if I'm going to do some serious soldering it would be good to exceed minimal objectives. RIAA is functionally a very steep well-defined mathematical curve[0]. Traditionally implemented using all analog components in a much lower-noise arrangement than usual. It requires quite a high gain preamp to recover the bass from the microgrooves where it has physically been pressed so much more lightly than the other frequencies. I just used one audio circuit board since I was indulging in the opposite approach to overkill. From what I've heard, the fewer active analog components that your signal passes through, the fewer compromises it may be subject to anyway ;) Audiophiles would think I took a lot of short-cuts which is true, I could surely have gotten better channel separation using two boards instead of one. But it did take a little rig about twice as complex just to perform the development experiments on, which was re-architected a number of times, one of the advantages of a non-PCB free-form soldered breadboard. Well I have nothing to brag about the way I cheated on my own power supply for this project. I would say it really does take about as complex a power supply PCB or more than it does for the audio PCB. Screw that, I used batteries :) Needed to be portable anyway like a laptop. Plus batteries have no hiss or hum, that was easy. Actually I got lucky because I was able to achieve my goal of digitizing vinyl at the standard CD format of 44.1 KHz 16-bit, while introducing lower analog noise than a CD can reproduce. IOW transparent for that application, and see what collateral damage there is otherwise :) There was plenty of headroom with two 9V batteries giving 18V peak-to-peak before clipping. Plus the batteries lasted a long time since very few components were on the final board, and it's just a preamp. Now I shouldn't complain about having loads of PCBs stacked in overkill configuration until it almost topples under its own weight, using blank copper boards for shielding within a plastic enclosure. Not when mine sits on a teflon sheet inside a mere small cookie tin, and the shielding is still usually OK when the top is removed :) For a while there you could even still smell the cookies. [0] Here's some good info for vinyl heads: https://hifisonix.com/wp-content/uploads/2010/10/RIAA-Equalization-Amplifiers-Part-One.pdf https://hifisonix.com/wp-content/uploads/2010/10/RIAA-Equali... http://waynestegall.com/audio/riaa.htm http://waynestegall.com/audio/riaa.htm and a single-board amateur project to learn from where it looks like there are some power components on the PCB, probably not much more complex than my lab effort otherwise. They cover using a single 9V battery during their prototyping as well as the migration to A/C adapter and virtual ground for the opamps. I used a pair of batteries wired for true bipolar +/- 9VDC and stopped there. Also notice how much bigger the plastic caps are than tantalum would be: https://www.instructables.com/RIAA-Equalization-with-analog-electronics/ https://www.instructables.com/RIAA-Equalization-with-analog-... Edit: Left out the part where I would use a Dremel to cut out the RIAA section from the populated PCB of cheap scrap record players that people were once discarding quite commonly. These were small little "partial" PCBs too and quite dissimilar, but made them work on their own before building to my final specs.