60 Hz Yamaha C-80 vintage preamplifier in 50 Hz country - Page 1
Forum section: electronics / general

author: conductivity
author_rank: Contributor
timestamp: May 19, 2022, 10:47:43 pm
content: Does core saturation or related problems matter if my hi-fi preamplifier from the US only has a 30 W rating, and I want to use it in my 50 Hz country with a NEDIS 230 V to 110 V AC converter?I have read the section called "Operation at Frequencies Lower than Normal" here:https://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/practical-considerations-transformers/I have read on hi-fi forums, but people often don't know about electronics engineering there.The service manual is also online with schematics.

author: james_s
author_rank: Super Contributor
timestamp: May 19, 2022, 10:57:04 pm
content: It depends on how much iron is in the core of the power transformer. Any 50Hz transformer will work fine on 60Hz but a 60Hz transformer may start to saturate on 50Hz. If it isn't labeled as such then the easiest way is probably to power it up while monitoring the current, if you hear an unusually loud buzzing or the current draw is excessive then you'll need to drop the voltage a bit to prevent saturation. If it all seems normal then let it run for a while and see if the transformer gets unusually hot.

author: bob91343
author_rank: Super Contributor
timestamp: May 19, 2022, 11:32:59 pm
content: Another idea would be to reduce the line voltage. Look at the nameplate to see what the highest 60 Hz mains voltage rating is and then make sure the source is no more than 5/6 of that voltage.Having said that, there is still the issue of filtering; it will have more power supply ripple. In addition, if there is a clock in the unit, it may run slow, depending on its time standard. Further, the maximum output audio power will be lower.

author: james_s
author_rank: Super Contributor
timestamp: May 20, 2022, 12:11:24 am
content: It's a preamplifier so output power should not be an issue, and I really doubt it contains a clock. The filtering is unlikely to be a problem either as there is typically plenty of margin.

author: taste_tester
author_rank: Regular Contributor
timestamp: May 20, 2022, 11:13:37 pm
content: You might want to check that the transformer really can accept 50hz or not. Often times a transformer was used that could do 50hz or 60hz despite the label saying only one or the other, especially if it can be wired to output either 110v or 220v. Sometimes the transformer really is specific to a frequency as well as a voltage.

author: conductivity
author_rank: Contributor
timestamp: May 21, 2022, 01:21:34 am
content: I don't mind touching the transformer seen in the picture after it has been used for a while. But do you think it will heat up more if a music signal is being played than just idling? And is there any concern about electric shock, so that I should unplug the power cord and check the place on the transformer, where I want to touch with a multimeter?

author: TimFox
author_rank: Super Contributor
timestamp: May 21, 2022, 03:38:19 am
content: Assuming that device was also sold in Japan, half of that country is 50 Hz (including the Tokyo area) and the other is 60 Hz (including the Osaka area). The standard single-phase voltage is 100 V rms (not 120).I assume that all the transformers used in Japanese equipment can handle both frequencies.

author: conductivity
author_rank: Contributor
timestamp: May 21, 2022, 04:03:24 am
content: Now that you mention it, I looked at the service manual again: I have the U.S.A. & Canadian model with a caution on the back that says "use only with the indicated load". There is also a general model with 110 to 240 V and 50 to 60 Hz input with a voltage selector on the back.I would say that I should send this preamplifier home, I probably don't need it as modern audio interfaces can deliver the correct line level straight from a computer to a power amplifier.

author: David_AVD
author_rank: Super Contributor
timestamp: May 21, 2022, 06:35:13 am
content: I've never seen an issue with using an audio device on 50Hz even when it was from a 60Hz region.Just plug it in (with any voltage converter if required) and move on with your life.

author: james_s
author_rank: Super Contributor
timestamp: May 21, 2022, 05:57:43 pm
content: Quote from: conductivity on May 21, 2022, 01:21:34 amThere is no shock hazard so long as you don't touch live connections but you can unplug it if you want to be extra safe. Saturation is actually more likely to occur when there is less load on a transformer, although for a preamplifier the amount of power involved is tiny so it's not likely to make a difference.

author: conductivity
author_rank: Contributor
timestamp: May 23, 2022, 04:04:50 pm
content: After 15 hours of continuous operation, the transformer enclosure causes a burning sensation that is way too undesirable to endure for more than 2 to 3 seconds. The same for some transistor heatsinks in the middle of the circuit board. I will couple the enclosure and heatsinks to the preamplifier chassis with Arctic TP-2 thermal pads that are not electrically conductive.Comments on whether you think this transformer is safe to run on 50 Hz are still appreciated though.

author: bdunham7
author_rank: Super Contributor
timestamp: May 23, 2022, 04:35:33 pm
content: Quote from: conductivity on May 23, 2022, 04:04:50 pmA metal part at 70C will be too hot to hold onto, but is still a perfectly safe temperature for a transformer and most certainly a transistor.

author: james_s
author_rank: Super Contributor
timestamp: May 24, 2022, 01:30:49 am
content: Have you measured the input current draw? If the transformer is saturating the current will be higher than rated. If you have a variac you could slowly raise the voltage while watching the current and see if there's a point at which it begins to rise quickly.

author: conductivity
author_rank: Contributor
timestamp: May 27, 2022, 04:26:58 am
content: How exactly would you connect a multimeter to the circuit seen in the picture, both for testing polarity of the power cord and operating current after the live wire has been identified? The preamplifier has a 2x16AWG power cord with the original US plug, where polarity is not visible (the two black wires in the picture). From what I understand, the live wire must be disconnected inside the device, and then the circuit must be closed again by connecting the multimeter in series for current measurements.I realize the brown wire is likely live, but am still curious exactly how you would connect a multimeter for verifying the polarity.

author: james_s
author_rank: Super Contributor
timestamp: May 27, 2022, 06:13:05 pm
content: Polarity is irrelevant, it's AC, just break the circuit somewhere and place the meter in series using the current jacks and it will measure the current. Polarity only matters from a safety standpoint, ideally you want the power switch on the live wire, but it will work the same either way.

author: bdunham7
author_rank: Super Contributor
timestamp: May 27, 2022, 07:08:37 pm
content: Quote from: conductivity on May 27, 2022, 04:26:58 amThe literal answer is that to check for "polarity" in a ground-referenced mains AC circuit, one probe of the multimeter goes to an earth ground and other to a wire. If you get line voltage, that wire is 'hot' and if you don't it is neutral.In and older US-style device where the plug has two identical prongs, polarity isn't a big deal except maybe for buzz/hum situations in audio equipment where reversing the plug often helps.

author: conductivity
author_rank: Contributor
timestamp: May 27, 2022, 11:23:25 pm
content: Quote from: bdunham7 on May 27, 2022, 07:08:37 pmDoes neutral work for this, so that RCA jacks could be used as a "ground reference" or does it have to be a real ground wire?

author: bdunham7
author_rank: Super Contributor
timestamp: May 27, 2022, 11:42:53 pm
content: Quote from: conductivity on May 27, 2022, 11:23:25 pmIf it is a two-prong plug, everything external should be isolated from the main power, so no. In normal usage in a system, the chassis and RCA jack shells do usually end up grounded, but you shouldn't count on it.