Converting mains to 24V AC with variable frequency - Page 1
Forum section: electronics / beginners

author: aeberbach
author_rank: Regular Contributor
timestamp: June 22, 2025, 11:09:30 pm
content: There's a series of turntables from Rega that runs on a 24V AC synchronous motor, 250rpm at 50Hz, 300rpm at 60Hz. Power supply is by plugpack. The basic configuration has you taking the platter off and switching the belt to a different pulley position for 33 1/3 or 45rpm depending on the disc you want to play. Rega sell a variable frequency power supply for about $600 locally which allows switching record speeds electronically. If this power supply was world voltage/frequency that would solve my problem but it doesn't appear to be.I'm moving to a 60Hz country for a few years, then I will be back here. I'd like to play records without buying a new motor or a speed control box that I can't use in a few years, so I need to do what the Rega box does and run it from a switching power supply. I definitely don't want a frequency and voltage conversion box, they are not really any cheaper. I'm not really concerned that involving a switching regulator will destroy the sound coming out of the speakers.The motor is hard to pinpoint exactly but it appears to be 9904 111 31511 on this datasheet:https://www.farnell.com/datasheets/1765731.pdf. (150mA) There is a Rega sticker covering up any part number in any pictures I can find.What I am thinking of is a a PSU module (Mean Well etc), a DDS signal generator and an amplifier to power the motor. The few discussions I can find talk about using a subwoofer amp module - is this sensible?

author: Psi
author_rank: Super Contributor
timestamp: June 22, 2025, 11:14:28 pm
content: Be good to know what current the motor needs. but yes, sine wave sig-gen into car subwoofer amp should work.Might not even need a car subwoofer amp, might be able to use a small indoor class D amp, but car amps are easy to get 2ndhand.Might also be worth looking around for any signal generators with high power outputs. Maybe you can find one that can drive directly.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: June 23, 2025, 12:45:32 am
content: You need 50Hz in a box. What Ivor Tiefenbrunn introduced with Valhalla to run his LP12 in 60Hz world. CD4060 followed by 2 stages of 4013 (Divider by 2) to obtain a precise 50Hz square. Active LPF and final stage. If you are doubling the output stage and fetching the 90deg atthe cheap capacitor phase shifter at second winding can be elimninated. Adding a switchable second crystal w PAL frequency (4,433) the platter spins very close to 45rpm. Tiefenbrunn named his similar improovement Lingo. As PA i would prefer Class-B circuits (eg TDA2020 (obsolete)) with minimal additional external components. U4a, 4b are power_on_reset circuit & power switch

author: Andy Chee
author_rank: Super Contributor
timestamp: June 23, 2025, 01:24:06 am
content: For a belt drive turntable, check for a pulley that allows you to change between 50Hz & 60Hz (in addition to swapping between 33.3 & 45 rpm).Essentially you should be capable of four combinations of platter speed and mains frequency.If you don’t have one, 3D print one.

author: Seekonk
author_rank: Super Contributor
timestamp: June 23, 2025, 01:52:23 pm
content: I went thru the golden age of audio in the 70's, even knew Saul Marantz. So, I know how particular some people can be. If it were me, I would just use a IR2153 in a half bridge driven thru a capacitor. There used to be these 300W inverter boards from China which could easily be converted to half bridge. Wouldn't be hard to get it to resonate nicely. Trouble is you never know what they will send you. I used to have a Weathers turntable with two synchronous motors. Beautiful table I should have never sold. Don't think you need anything like a sub woofer amp at that power.

author: aeberbach
author_rank: Regular Contributor
timestamp: June 23, 2025, 11:01:53 pm
content: Thanks everyone! There are some very economical modules out of China now, in fact the most expensive part will be a transformer and case to put it all together.

author: aeberbach
author_rank: Regular Contributor
timestamp: June 25, 2025, 11:39:06 pm
content: Thanks for the tip - the table in the IRF2153 datasheet shows the frequency range I want (50-60Hz) is right at the edge of what that chip can do. A higher frequency might be easier to achieve and then use a divider... then a hall sensor to detect speed at the platter for feedback - but maybe this is getting harder than something like an AVR driving a AD9833 and adjusting frequency via SPI?

author: MathWizard
author_rank: Super Contributor
timestamp: June 26, 2025, 01:23:06 pm
content: How easy is it to just replace AC motor, and use a small DC supply, and brushed DC motor ?

author: ejeffrey
author_rank: Super Contributor
timestamp: June 29, 2025, 03:01:13 pm
content: Quote from: MathWizard on June 26, 2025, 01:23:06 pmBecause a brushed DC motor won't have the necessary speed control.A "modern" design would use a brushless DC motor and driver but that's more work to retrofit than generating a 50 Hz sine wave and amplifying it.

author: aeberbach
author_rank: Regular Contributor
timestamp: June 30, 2025, 03:21:52 am
content: In the longer term I am thinking of trying a BLDC motor, but:- all the slow BLDC motors I have seen are pretty expensive, they have many more poles than the fast ones- cheaper BLDC motors tend to be for radio control and drones and have a kV rating somewhere above 1000, rpm in the thousands!- these cheap and fast motors can't be run slowly because they "cog" at lower speeds- the cheaper ones also can come with cheap noisy bearings - too much motor noise would be very badSome turntable manufacturers, Technics for example, do use brushless motors for turntables and the arrangement is very like CD/HD/Floppy drives where a series of coils is mounted on the PCB and some kind of magnet-bearing flywheel spins the drive. The stray magnetism doesn't seem to be an issue even with a phono cartridge fairly close.Maybe it could work to get a very small and cheap drone motor and gear it down with multiple belts, and drive it with something like Allegro A4963. Some PID control from a cheap micro using a hall effect sensor on the platter?Easiest solution first. The first goal is not to buy a Rega replacement motor kit for $300+.

author: Andy Chee
author_rank: Super Contributor
timestamp: June 30, 2025, 03:40:25 am
content: Quote from: aeberbach on June 30, 2025, 03:21:52 amThe easiest solution is a new pulley to suit 60Hz.

author: aeberbach
author_rank: Regular Contributor
timestamp: July 01, 2025, 12:02:11 pm
content: What I'll probably do first is print a ring to make the subplatter larger rather than the motor pulley smaller.

author: Andy Chee
author_rank: Super Contributor
timestamp: July 02, 2025, 03:46:02 am
content: Quote from: aeberbach on July 01, 2025, 12:02:11 pmWhen you do the math, you will probably find the addition of the increased thickness of your ring, will make the platter no longer fit inside the turntable.

author: aeberbach
author_rank: Regular Contributor
timestamp: July 02, 2025, 06:05:57 am
content: You're right. Tons of room under the platter but the motor sits too close by about 4mm. Spindle it is.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 02, 2025, 06:35:08 am
content: If you can't buy a new belt kit why not use a cots DC-AC converter?We have meanwell TS-200-112 with one of their AC/DC power supplies to provide a reference voltage for production testing, and this voltage/frequency is very stable. Perhaps amazon's cheaper house brand is also clean an stable, ymmv.Turntables don't use much power, so you can easily do this without also needing a 200W AC/DC psu, if I guess 30 Watt is plenty.They even have an open frame one now: NTS-250PNot to be too audiofoolery, but:Don't use BLDC motors, they will introduce additional vibrations.You also do not want an approximate sinewave as the harmonics will translate into torque pulses on the motor.

author: Zero999
author_rank: Super Contributor
timestamp: July 02, 2025, 10:29:22 am
content: Quote from: aeberbach on June 22, 2025, 11:09:30 pmI bet that power supply doesn't care about the input frequency, just the voltage, since it'll be an inverter which first converts the input to DC. All you need it to buy it, plus a suitable transformer.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 02, 2025, 12:51:50 pm
content: Quote from: Zero999 on July 02, 2025, 10:29:22 amLooks like it, it comes with an transformer wall-wart (not smps) for audiophoolery reasons it seems. But a smps ~30v unit will probably work fine if it see this:https://www.thefactoryaudio.com/blog/2017/11/2/the-rega-buzz-and-how-to-kill-ithttps://forums.stevehoffman.tv/threads/rega-power-supply-unit.907212/But you'd still need to buy the 600 box though.You can also buy this:https://nl.aliexpress.com/item/1005006286524824.htmland a 1:1 transformer for filtering?

author: Seekonk
author_rank: Super Contributor
timestamp: July 02, 2025, 08:08:20 pm
content: Ebay right now has several meanwell TS-200-112 in scuffed up boxes for $55US shipped!

author: aeberbach
author_rank: Regular Contributor
timestamp: July 03, 2025, 12:09:06 am
content: Looks like there is no reason the Rega PSU will not work on 60Hz AC - I found this:https://www.turntablepsu.com/images/Neo%20Schematic.pdf- I think the distributor meant to say that the plugpack they supply won't work, instead they just said "the Neo PSU won't work". In fact I have found that Rega sell turntables like the RP8 with 50Hz spindles around the world - it's just different plugpacks. And if you bought a turntable in a 60Hz country and have the 60Hz spindle, the Rega PSU has a jumper to choose 60Hz-spindle output.So getting the Rega supply might be the go. It costs too much but what about turntables doesn't? And at least I'll be able to play some music while making my own.Rega's PSU-turntable connection uses 4-position power DIN likehttps://www.sameskydevices.com/product/interconnect/connectors/dc-power-connectors/din/pd-40s.If I print a new motor cover with one of those wired up and the the power supply than I will have the works-anywhere turntable. Just I like I could have had if I had bought something from Technics

author: Jeroen3
author_rank: Super Contributor
timestamp: July 03, 2025, 05:57:23 am
content: That schematic.... Wait what.The 33/45 rpm switch only changes the amplitude of the output of the AD9837 waveform generator chip?What am I missing here?Also why is there even an waveform generator chip if there is a dac in the PIC16F1826?

author: Seekonk
author_rank: Super Contributor
timestamp: July 03, 2025, 11:24:07 am
content: Always amazed what some threads lead you to. Searching that Meanwell TS-200-112 on ebay found a new in box 42-60V version for $38 shipped. How can you pass that up. This will work with my off grid shop and use DC directly from my PV panels with no battery.

author: Zero999
author_rank: Super Contributor
timestamp: July 03, 2025, 12:54:34 pm
content: Definitely go with the Meanwell inverter. All you need is a decent universal input switched mode power supply. Job done.