Modern PSU
Hello everyone,
I'm looking for a modern PSU for my Spectrums and my dual set of 3.5'' floppy drive+HxC floppy emulator. The one for Spectrum should be 9v @ 2A and the one for the dual set should be 5v @ 3A (2A should be enough, but I've experienced power drop-downs especially in long diskette to diskette copies when I temporarly replace the HxC with a second 3.5'' floppy drive).
I want the best for my equipment. What should I look for? Can you give me an explanation of isolated vs regulated? Is it the same? How about switching? Does switching mean by default that it is also regulated/isolated? Or switching simply means that it is of the type that have a switch on it to select between different voltages?
Also wouldn't over voltage and over current protections actually protect my Spectrums better?
Could you give me a link (ebay?) of quality PSUs with the above characteristics?By the way, I don't worry about the plugs, I can change the both for the floppy drives and the Spectrum which needs a center negative connection. What I would like is that the are of the EU main connector type and preferably not cheap from China if you think those are of very low quality (I have one for another device and you can't listen to a radio in the same room...).
Thank you everyone!
I'm looking for a modern PSU for my Spectrums and my dual set of 3.5'' floppy drive+HxC floppy emulator. The one for Spectrum should be 9v @ 2A and the one for the dual set should be 5v @ 3A (2A should be enough, but I've experienced power drop-downs especially in long diskette to diskette copies when I temporarly replace the HxC with a second 3.5'' floppy drive).
I want the best for my equipment. What should I look for? Can you give me an explanation of isolated vs regulated? Is it the same? How about switching? Does switching mean by default that it is also regulated/isolated? Or switching simply means that it is of the type that have a switch on it to select between different voltages?
Also wouldn't over voltage and over current protections actually protect my Spectrums better?
Could you give me a link (ebay?) of quality PSUs with the above characteristics?By the way, I don't worry about the plugs, I can change the both for the floppy drives and the Spectrum which needs a center negative connection. What I would like is that the are of the EU main connector type and preferably not cheap from China if you think those are of very low quality (I have one for another device and you can't listen to a radio in the same room...).
Thank you everyone!
Post edited by geosiou on
Comments
There are some PSUs (I have a shredder that uses one like this) which are transformerless, and should be avoided at all costs. You are unlikely to find a low voltage one though.
Regulated means it has some mechanism (usually a linear voltage regulator) to maintain a stable voltage up to its rated current. Unregulated means it doesn't, and might read 12V with no load on it, 9V under load, and drop below 9V as it gets closer to its maximum current output.
Voltage regulation usually requires a higher voltage to work, so a 9V regulator usually requires at least 10V, and will get rid of the excess current as heat. If you've opened up a 48K, you'll have noticed the huge heatsink attached to the regulator inside.
The 128K toastrack has it's heatsink for it's VR on the side.
Switched is another mechanism for voltage regulation, but works much more efficiently than a linear voltage regulator. Rather than burning the excess current off as heat, it turns the output rapidly on and off, so the averaged output is the regulated voltage.
Switch mode PSUs are the most efficient, your PC will be using one. If you want to spend the least amount of money on electricity, then a switch mode psu is the way to go.
The downside of switch mode devices is the rapid turning on and off can create interference in power lines, and RF frequencies. But I wouldn't worry about that unless you are working with very sensitive test equipment.
As for ebay... look for a switched mode PSU that has enough current for your needs. And beware that it isn't uncommon for chinese products to claim way more than they deliver.
Isolated means that there are no connection between the mains power and the output of the PSU. Most power supplies are isolated when you have a transformer inside, there is no common earth wire and without any feedback circuit between the primary and secondary. Mains isolation is normally achieved with a 1:1 transformer at the input. With the feedback circuit you can use optical feedback to isolate the primary and secondary circuitry.
Regulated means that the output power is regulated at a specified voltage within a specified current range.
Switch mode power supplies works as follows: The AC power is rectified and then switched at a high frequency. This high frequency AC is then fed into a transformer and the output of the transformers if fed to a regulation circuit. The advantage is that the output of the PSU is well regulated and the size of the power supply is very small. When you use high frequency AC, then the size of the transformer is very small because the transformer can be a solid core instead of a laminated core as with low frequencies. They do however produce a lot a RF noise if they are not well screened which can be a problem in some areas.
Over voltage yes, but not over current. Short circuit protection will be an added benefit. Over current and voltage power supplies are also much more expensive due to the sensing circuits that he PSU needs.
Just seach for a power supply for your specifications
No need to apologise! It's always good to have multiple explanations, people often say things in different ways which can make it easier for others to understand.
For ZX Spectrum 16k/48k/+/128k+ and Grey +2 machines, these all have internal voltage regulator circuitry. They are designed to be operated from a nominal 9V DC unregulated external power supply unit (PSU). So if you are going to use an unregulated type, select a 9V rated unit. The computer does not care, and it makes no difference to the operation if it is being supplied by a unregulated or a regulated PSU.
For most uses, they will run quite happily from a regulated supply with an output voltage of 8V to 11V. If you wish to reduce the amount of heat that the internal 5V regulator has to dissipate, go for an 8V rated PSU.
For use with disk drives where the PSU has to provide a 5V supply, you must use a regulated type.
Additional protection features are nice, but not essential. With some regulated designs, current limiting (over current/overload/short circuit protection) is part of the design and comes as standard. Over-voltage (also called crowbar protection) will always bump up the price, as it means extra circuitry and is a rare feature on consumer electronics.
Most (but not all) switch mode type PSU are regulated.
Also a warning, if you are after a regulated type, but an advert does not say "regulated" or "stabilized", assume that the PSU is an unregulated type.
Mark
Repair Guides. Spanish Hardware site.
WoS - can't download? Info here...
former Meulie Spectrum Archive but no longer available :-(
Spectranet: the TNFS directory thread
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
I don't know why, but I feel safer with a regulated PSU... I clearly understood Mark's answer that the Spectrum won't notice the difference, but since I have to use a regulated one for the disk drives...
As I understood, the advantage of switched PSUs is their size. But what about that RF noise? Will it affect Spectrum at all? Display noise maybe? Or the SD card reading/writings of HxC floppy emulator? Or the floppy disks?
Would it be better to use just a non switched regulated PSU (the money on electricity is the think I mind less with Spectrum!)?
Also do you think it's a good idea to use one PSU (with more than enough 3A current) for the disk drives or should I prefer two seperate? Would it be more stable for those times of long sector to sector copies between the two disks, where they are costantly starting and stopping?...
Personally with a Spectrum I prefer a standard PSU with only a transformer, Diode Bridge and a capacitor. Every Spectrum user will have their own preferred solution for a PSU and regulation. The Spectrum is very forgiving with the input voltage as discussed in many posts on this forum. I have used a PC Power Supply a few years ago with the Spectrum as all the supply voltages are there (+12, +5, -5Vetc.) I used the PSU board out of the PSU case and the RF noise introduced a lot of interference on the TV picture. If you go for a standard PSU, I would however suggest that you regulate the output of the standard PSU with a regulator to about 9V. This will lower the voltage drop on the internal regulator and thus dissipate less heat. There are quite a few posts also on the forums with regards to use better regulators in the Spectrum (changing the 7805 to a new switch mode model). This mod lowers the heat caused by the voltage drop over the regulator.
I do not know what will be the best in your case with one or two power supplies. I know with my one setup I have a Spectrum Issue two board with a floppy disk drive interface. I have one standard power 12V supply with a 9v regulator which feeds the Spectrum and a 5V and 12 V Regulator which feeds the floppy drive. Sometimes my drive does not initialise, but that is due to the disk interface which gets powered a few milli seconds before the floppy drive is initialised. It is a timing issue. In my case the floppy drives should be powered on first and then the Spectrum with the interface.
Pierre
A well designed switch mode power supply unit (SMPSU) should not emit significant levels of RF noise, so there should be no interference. However, this does mean that you have to pay extra compared to the cheaper types.
Examples of computers that used good SMPSU are Acorn BBC Micro, Atari ST and all modern desktop / tower PC's (admittedly all these have internal PSU's).
Small "plug-in" plug top PSU's, as used for a lot of modern gadgets are also often of the switch mode type. You can often tell because they are very light compared to a heavy transformer type of PSU.
If using modern 3.5 inch floppy drives, 2A should be enough, but some older designs may be more power hungry I suppose.
My advice is to buy from a trader you trust and buy what you suits you. Just stay clear of the really cheap imported PSU's, as the quality is poor.
Mark
Repair Guides. Spanish Hardware site.
WoS - can't download? Info here...
former Meulie Spectrum Archive but no longer available :-(
Spectranet: the TNFS directory thread
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
The speccy isn't forgiving about too high a voltage. I've made a mess of a speccy with a 14v supply. (Melted traces and everything).
The 5v regulation inside the speccy is fine up a silly voltage, (Although it would still fail because it has inadequate heat-sinking for anything much above 14v), but the 12v DC-DC conversion section is notoriously sensitive to.. Well... everything really, and when it goes it usually takes a ram chip or two.
Keep your unregulated voltage between 8 and 12v...
Second choice would be a 9V linear regulated supply.
Worth pointing out the difference between off-load and on-load outputs when referencing the Sinclair unregulated PSU's. Off load, between 13-14v output is fine, although your figures are right for on-load measurements taken at the regulator.
Personally I used to use a PSU from a grey +2 to power all except my +2A and +3. I've since switched to using a 9v 2A regulated supply.
B
zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
The circuit for the internal DC-DC converter / inverter was improved in later issue boards (some issue 4 variants and issue 5 and later), also some earlier boards had their circuitry upgraded when serviced. Boards that have this improved circuitry should not be damaged by a DC input of between 12V and 14V. Also the heatsink on issue 3 and later boards is slightly bigger. However, it will get a lot hotter if running at a higher input voltage, and so is not recommended.
Unless you know what to look for, assume your ZX Spectrum 16k/48k/+ does not have the improved internal power circuitry and don't use any power supply that has a on-load output voltage of 12V or more.
Mark
Repair Guides. Spanish Hardware site.
WoS - can't download? Info here...
former Meulie Spectrum Archive but no longer available :-(
Spectranet: the TNFS directory thread
! Standby alert !
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb!
Looking forward to summer in Somerset later in the year :)
I power my Speccy from a switched mode supply purchased from RS.