A few days ago I suddenly noticed 'something' was humming noticeably in my set up and that something turned out to be my Sony MDS-JE480 Minidisc recorder which was in use at the time. Switch to standby and the noise vanished. Hmmm, well hummmm actually and from the transformer. Examination of the PSU shows that it uses two transformers, one for standby and one to power the main unit. Kind of unbelievable really for a budget model although it was and is ranked as one of the very best sounding of all due to its use of the very last generation of ATRAC which is the data compression system.
For curiosity I measured the mains and it is was high(ish) at 247 to 248 volt. Was that playing a part I wondered. The mains here is often in the 242 volt region but this was right at the top end. We also have something that is a kind of active voltage control system in this area where mains voltage is dynamically controlled and optimised in real time according to overall demand. It obviously has to keep within legal limits but the idea is to reduce voltage when demand is high to reduce loading on the grid which is sort of counter intuitive when you think of all the SMPS as lowering line voltage will increase current draw... however...
Back to the Minidisc. I wondered if doing the unthinkable would be possible... adding a series dropper resistor to the mains transformer.
The power supply is shown here. You can see the little standby supply at the top of the schematic and the larger (but in reality still pretty small) main transformer at the bottom. The PCB layout lends itself well to trying this as there are two wire links (arrowed) are fitted in the feed to the larger transformer primary. I removed these wire links and fitted two 56 ohm flameproof resistors in their place.
Results seem really good. Operation is now silent and the two resistors drop around 3 volts each and run essentially cold. The drop seems very constant and does not change under any operating conditions such as when the mech is loading. So regulation is essentially unaffected.
I wouldn't normally recommend anything like this but in this instance it seems to be a viable and workable solution. The PSU regulated supplies have a lot of headroom and even at lower mains voltage near the lower legal limit (not that we ever come close to that here) there should not be an issue.
Totally unrelated to this and something I only noticed with studying the PSU diagram is that the analogue opamp stages are fed from a 100% unregulated supply (arrowed). How audiophile is that? Perhaps very! because it certainly works extremely well on these budget machines and which as mentioned are reckoned to be one of the best sounding.
Also of interest is the 0.0022uF cap shown across the relay contacts in the PSU schematic. I measured an AC voltage of around 17 volts AC across the primary in standby, quite high really and due to the reactance of the cap. Is that of consequence? Maybe it plays a part in muting and silent power on and off as it means some voltage will be present on the rails (particularly the unregulated ones) even in standby. This is one of those times where you have to think that the designers really knew what they were doing.
The analogue stages fed from the unregulated supply:
For curiosity I measured the mains and it is was high(ish) at 247 to 248 volt. Was that playing a part I wondered. The mains here is often in the 242 volt region but this was right at the top end. We also have something that is a kind of active voltage control system in this area where mains voltage is dynamically controlled and optimised in real time according to overall demand. It obviously has to keep within legal limits but the idea is to reduce voltage when demand is high to reduce loading on the grid which is sort of counter intuitive when you think of all the SMPS as lowering line voltage will increase current draw... however...
Back to the Minidisc. I wondered if doing the unthinkable would be possible... adding a series dropper resistor to the mains transformer.
The power supply is shown here. You can see the little standby supply at the top of the schematic and the larger (but in reality still pretty small) main transformer at the bottom. The PCB layout lends itself well to trying this as there are two wire links (arrowed) are fitted in the feed to the larger transformer primary. I removed these wire links and fitted two 56 ohm flameproof resistors in their place.
Results seem really good. Operation is now silent and the two resistors drop around 3 volts each and run essentially cold. The drop seems very constant and does not change under any operating conditions such as when the mech is loading. So regulation is essentially unaffected.
I wouldn't normally recommend anything like this but in this instance it seems to be a viable and workable solution. The PSU regulated supplies have a lot of headroom and even at lower mains voltage near the lower legal limit (not that we ever come close to that here) there should not be an issue.
Totally unrelated to this and something I only noticed with studying the PSU diagram is that the analogue opamp stages are fed from a 100% unregulated supply (arrowed). How audiophile is that? Perhaps very! because it certainly works extremely well on these budget machines and which as mentioned are reckoned to be one of the best sounding.
Also of interest is the 0.0022uF cap shown across the relay contacts in the PSU schematic. I measured an AC voltage of around 17 volts AC across the primary in standby, quite high really and due to the reactance of the cap. Is that of consequence? Maybe it plays a part in muting and silent power on and off as it means some voltage will be present on the rails (particularly the unregulated ones) even in standby. This is one of those times where you have to think that the designers really knew what they were doing.
The analogue stages fed from the unregulated supply:
This definately shows that supply rejection of opamps ( typically 100dB, min 80dB ) is no BS.
No wonder, "it extremely works well."
Power supply regulators with extraordinary PSRR are most of the time not required. It doesn’t hurt, but likely useless aiming at lower than 80dB.
On the other end, decent concern about supply rejection is part of correct circuit design.
Many years ago, we sold electronic crossovers etc using op-amps and a raw supply. No one ever noticed any supply noise unless the grounding was done wrong. I suspect that is the actual reason you see regulators used for op-amps. If you "need" a super clean supply, the real problem is probably your ground paths. You need a sense of what ground currents go where and avoid mixing them in any conductor. Note that 10mA from a 1000uF cap is about 83mV ripple, -100dB is less than a uV.
Last edited:
Not OK as the modifications of that time were to add extra transformer boards with regulators. Also with higher voltages as some types had too low voltages.
Placed those but did not see the practical value of the medium and players.
Placed those but did not see the practical value of the medium and players.
Why choose resistor values that drop only 3 volts? Why not 7 or 8 volts of drop instead? Doesn't this passage offer solace that everything will be okay when dropping 7-8 volts?
This is so true and it can often pay to think in terms of grounding issues as a DC problem and just ask yourself 'what happens if the output delivers 1amp' and to look at how that might alter DC conditions. Also what happens if I pull 1amp from the PSU with an external load. How does that alter the DC voltages in the circuit at a mv level.
Honest answer is that 56 ohm 1watt flameproof types were all I had and it seemed enough in practice. It would only be a minutes work to change them to something different. I'm sure it would work fine dropping far more. In fact I also tried the theory on an old Sony CD player first and had no operational issues with a 270 ohm 2 watt carbon type in series with the mains.
Good point when it is a 240V tap. Ironically green technology like solar and wind energy will let die out transformer based 230/240V gear sooner than many wish. Mains voltage is going up and up because of all those fine inverters. It does make sense today to have custom wound (if one needs such anyway) transformers having a 250V primary winding.
Accept it or not but SMPS will eventually be the standard anyway in the "green" world.
Accept it or not but SMPS will eventually be the standard anyway in the "green" world.
Last edited:
Its a good question 🙂 and tbh I didn't investigate the other tapping.
The manual shows only two voltage variants available and each with a different part number for the transformer. You would think they might use one with tapping's for 120/230 vac but apparently not.
Also unusual is that the thermal fuse seems to be able to be bypassed (never do this in anything) as both sides of the fuse are brought at as separate pins.
The manual shows only two voltage variants available and each with a different part number for the transformer. You would think they might use one with tapping's for 120/230 vac but apparently not.
Also unusual is that the thermal fuse seems to be able to be bypassed (never do this in anything) as both sides of the fuse are brought at as separate pins.
It would be very funny if it does have a 240V tap. That was not uncommon then. UK was officially on 240V versus 230V in the EU. Later it was "harmonized" as fiddling with numbers was called.
Bypassing a thermal fuse is not a thing of beauty but often there is no other way when having multi winding transformers as found in Japanese devices. The cause often being cooking electrolytic caps. When these are replaced the heat is gone as well. Besides that a technically orientated person likely switches off the mains distributor when leaving stuff unattended.
Bypassing a thermal fuse is not a thing of beauty but often there is no other way when having multi winding transformers as found in Japanese devices. The cause often being cooking electrolytic caps. When these are replaced the heat is gone as well. Besides that a technically orientated person likely switches off the mains distributor when leaving stuff unattended.
Last edited:
Nowadays it is (un)officially 240V as nothing really changed, only the tolerance on paper. Just measured it this minute at 246V
And even today one finds vintage measuring equipment with voltage choice switch set to ...220V...(while having a 240V position).
This was interesting reading.
Before i moved to devon, i worked at the FCDO in London for 15 years, and while i was there they lowered all of the voltages to the main equipment from 415v to 380v,using something called 'power perfector units' without any effect on the plant.I know this is 3 phase and proberbly isnt related to the above directly, but i did prove that the original tolerence of 409v to 415v for the kit proved to be underestimated, as it worked just as well, and proved to save energy.
you may find this interesting.
https://powerperfector.com/over-voltage-is-wasted-energy/
That sounds similar to what was supposedly done in this area to manage power demand but this was an active thing that could change constantly as needed. Domestic electricity cable supplies in the road are three phase but each individual property is connected to one phase and neutral which gives the nominal 230 (or 240) volt AC. Root 3 multiplied by 230 gives 400 volt which is the line voltage between phases. Each phase is 120 degrees phase shifted from the next.
Reducing voltage will save energy for resistive type loads and motors/lighting and all that kind of thing but it will actually increase current demand in applications using SMPS. As voltage goes down with an SMPS the current draw rises to maintain the load voltage and power delivered to the load.
Its very scary when electricity contractors cut through the neutral in the road as then puts each house 'between phases' and they get the full 400 volts rather than 230. I've seen that happen many many times as we used to repair all the brown goods for such incidents over a large geographical area.
Reducing voltage will save energy for resistive type loads and motors/lighting and all that kind of thing but it will actually increase current demand in applications using SMPS. As voltage goes down with an SMPS the current draw rises to maintain the load voltage and power delivered to the load.
Its very scary when electricity contractors cut through the neutral in the road as then puts each house 'between phases' and they get the full 400 volts rather than 230. I've seen that happen many many times as we used to repair all the brown goods for such incidents over a large geographical area.
🙂 I was guilty of similar defects more than a few times testing cables in habited areas with 1.5 kV test equipment. An intermittent error was blasted to a dead short with 1.5 kV high current pulses. We visited all houses but when no one was there ... always the darn videorecorder.
The place where the dead short occurred could be felt when walking on the ground there. We "shot" the 3 and 6 kV distribution cables with a "cable guillotine" in case there was high voltage still on them. The cable guillotine of then was with a pull wire... Needless to say that was also a time of too many incidents. The director of the energy company often being the one that was responsible for switching etc. Many technicians and just 1 responsible manager. Today that has changed but now there are 1 technician, 8 security officers, 1 diversity officer (!?!) and 24 managers 🙂
The place where the dead short occurred could be felt when walking on the ground there. We "shot" the 3 and 6 kV distribution cables with a "cable guillotine" in case there was high voltage still on them. The cable guillotine of then was with a pull wire... Needless to say that was also a time of too many incidents. The director of the energy company often being the one that was responsible for switching etc. Many technicians and just 1 responsible manager. Today that has changed but now there are 1 technician, 8 security officers, 1 diversity officer (!?!) and 24 managers 🙂
Last edited:
there was one downside to it though we found out and that it affected the power factor correction units in the main panels.I left while this was going on so i never found out why they didnt work correctly with the power perfector units
The company already lies on their web page with "you should be at 220V". Anyway their units likely will have an influence on cos phi possibly because capacitive or inductive parts internally. One has a hard time finding information on what their stuff looks like. Probably a niche sector. Having some experience I noticed similar equipment to have very large 3 phase coils, switches, fuses and not much else...
Normally the process is to discuss too high mains voltage with the energy company which will then choose another tap on the distribution transformer but governments are easy targets with more than enough budget. Since the green wave developed and less and less new technicians are educated they tend to believe anything.
What do you think when you read this?
Normally the process is to discuss too high mains voltage with the energy company which will then choose another tap on the distribution transformer but governments are easy targets with more than enough budget. Since the green wave developed and less and less new technicians are educated they tend to believe anything.
What do you think when you read this?
- 100% reliability record
- No moving parts
- Hand-wound components
- 15-year warranty
- Expected lifespan over 100 years
Last edited: