I had the platter off my Micro Seiki BL-91 earlier today doing some cleaning so thought I'd take a picture of some of the normally hidden DIY parts. I posted previously about the tonearm builds. I have some neodymium ring magnets around the bearing to mostly unload the spindle bearing. There's one magnet on the platter underside and two on top of the bearing housing. The ones on top of the bearing housing also form a small oil well I use to keep the top of the bearing shaft well lubricated. The platter is filled with epoxy up to the level of the magnet and weighs around 10 pounds. There are also ten evenly spaced small neodymium magnets around the platter circumference and a corresponding hall effect probe (see red arrow) in the plinth to run the speed tachometer (just one of those inexpensive $10 Chinese things, but I repackaged it), or I can plug it into my DMM and use the frequency function for even more precision, though it is a pretty stable circuit and doesn't really need any regular adjustments ...
Slick. @Davey what sort of improvement in speed did you see with that upgrade, do you have any before/after?
Well, with the magnetic unloading, the spindown time from 45 rpm is about 4 minutes, but unfortunately I didn't time it when stock (I know it's much longer now but not by how much). I added the magnets when I first took apart the bearing to clean and change the oil, with first just one magnet epoxied to bearing housing top (as shown below when I had it apart), then maybe 6 months ago I added the second. I didn't really do it for better speed performance, though it may have improved, it is primarily to prolong the bearing life, and maybe reduce bearing noise. I also changed the bearing to a silicon nitride ceramic ball when I had it apart, it's the black one next to the stock silver one in picture below ... I made a similar magnetic bearing update on my Micro Seiki DD-40 direct drive after I added the additional 1/2" think aluminum platter on top of the stock platter ... top picture with motor cover removed showing 300 slot optical sensor, middle picture with motor cover installed with magnet and bottom of platter with magnet, and then bottom of table in last picture ...
Hehe, it's just a few magnets, doesn't everyone here like to play with magnets? It's not just me, is it? I have a stack of leftover small neodymium magnets I'm using for a little isolation platform under my turntable, not sure yet how it's gonna turn out, may show up here one day in the near future, or maybe not Magnets are fun. Have you seen this little magnetizing video .... I'm playing with my Sojourner box today, just got it a couple days ago, finally out on vinyl, real pine box and all, love it, no DIY content yet but maybe I can think of something to modify
4 minutes is impressive. Have you ever been tempted to compare the spin-down time with various styli running the same VTF? There was a paper where they did that to determine friction coefficients but I don't think ML was available at that time. Very impressive work.
It's been a long time coming but the boards have finally arrived! A little bittersweet in that they messed up the number of snubber boards. I am optimistic in the end all will be good though. This is the top of the main amp board. The bottom of the main amp board. The top of the regulator board (left) and the top of a snubber board (right) The bottom of the regulator board and the snubber board. Let the fun begin!!
The tube regulator boards for the heaters were done by PCBWay a number of months ago. The main amp board, input/driver regulator board and the snubbers were done by JLCPCB.
The PCBWay boards took around 30 days. This was due to the Chinese post handing off to the US post. They shipped them like 5 days after I ordered them. The JLCPCB boards would have been here in about a week but they had a few questions and because of the time difference (I was responding in their middle of the night and they were responding in my middle of the night, I lost 2 days). They also shipped them via FedEx which was like 3-4 days. Very fast. The quality and accuracy of the JLCPCB boards appear to be at a whole other level as well. The weight of the JLCPCB board vs the similar sized PCBWay board was night and day different as well. My first thought was the gold on the ENIG (JLCPCB) made that board a good deal heavier but there isn't really that much gold on the ENIG board so I don't know.
Here is the completed HV regulator board. I figured I would start with something small and easy. Took a break after I finished it and when I fired the soldering iron back up.....it wouldn't get hot any more. Lights up, just no heat. Off to the hardware store I go.....
Thank you so much! I honestly thought people would find it to be a bit ugly. It was intended to be part of its charm. I've fixed the speaker hum issue, so now I am enjoying it a whole lot more. For anyone that hasn't seen it, the design and build process was appended to my original Aikido preamp thread, starting at this post: Building A Tube Preamp: The Aikido It co-stars @Jaytor & @bluezee3228, with special guest appearances from @Davey, @jfeldt and others.
I was thinking about this project again earlier today and it reminded me of a simple gain-stage I had built, complete with on-board power supply. After reading through a couple of online articles and some opamp datasheets, creating this board really demystified a component that always looked more complicated than it actually was. Anyway, my reason for bringing it up is that I was taken aback to find that different opamps sounded different in the circuit. I'd always been extremely skeptical of 'opamp-rolling' but in the future it's something I may experiment more in. Just thought it might be worth mentioning.
I've been skeptical of rolling op amps as well, but never tried. This board is designed to accommodate rolling. The extra decoupling caps from each rail to ground and rail to rail should allow me to try different op amps hopefully without concern of oscillation, so I look forward to experimenting.
The problem with op-amp rolling is that they always use rather massive amounts of negative feedback. The self-correcting nature of feedback would cover up any potential sound quality differences. Running them without negative feedback is not an option.
Can't argue with that. I guess some theorize the difference others can hear may be due to oscillating op amps due to a lack of local decoupling. So I'm building-in the flexibility without any expectation of return, because all it takes is three 0.1uf capacitors. The worst case scenario is I spend $20 or $30 on op amps and decide I can't hear a difference.
Nice progress. I hope it ends up working well. Interesting that you found the JLCPCB boards better. I've been happy with the ones they have made for me so far.
I was kind of surprised as well considering they were on the inexpensive end of the spectrum. My son, who is becoming a machinist, was the first one to pickup on the precision of the boards. I was also very pleased with what I saw from them, not that I thought the PCBWay boards were bad. Quite the opposite. Just in comparison the JLCPCB seemed much nicer. Having spent quite a bit of time with the JLCPCB boards the last two days, my opinion of the boards has only gone up. Everything fit PERFECTLY except the 4 Clarity TC4 caps. This was definitely due to the imprecision of the Clarity Cap leads, not the boards. I have adjusted the EasyEDA file for more leeway with the holes. Why.....I don't know...maybe OCD. Placed an order for more snubber caps (for the regulated heater boards) since they were somewhat of an afterthought. The snubber circuit for the main amp board was already baked into the big board. Next up will be to put the finishing touches on the Front Panel Express files. My son may be able to turn my amp chassis into one of his mandatory projects. Even if he can't he still wants to machine the panels for me.
To be honest, even I doubt that one experience. It wasn't any deliberate test; more of a 'oh, this sounds different than yesterday' thing. I was looking to insert a low-gain op-amp stage before my then unity-gain tube preamp, but it sounded pretty awful. Obviously one has to use op-amps that are circuit compatible, and I would take a guess that a lot of claimed differences found while rolling could be due to people just bunging any old thing in. From memory I chose op-amps that could optimally be run at +/- 15V with the correct decoupling on the board. They were the NE5532, OPA2134, LM4562 & NJM2068. It was the NJM that surprised me.
