It's a bit high, there's a voltage regulator inside these but it's usually a 7805. It requires, depending on the datasheet, 2 to 2.5 volts drop to properly regulate. And IIRC there is a diode as well to prevent reversed polarity. So to be on the safe side and account for possible grid dips the power supply must provide about 9V - and since the PSU doesn't need to be well regulated the voltage will be somewhat higher without a load. But it should not be this high IMHO. The PSU for my CM-64 (which is two boards so it draws more current) measures about 11.7V unloaded.

7805 will tolerate this but will run hotter which is not good. Is that a genuine ACB-220? Or some cheap copy? The original is a transformer based design, not a switching-mode PSU that many sellers offer. You might want to look for a different PSU, just keep in mind it needs to have center pin negative.

This is normal for unregulated transformer based power supplies. Usually the equipment from that era is able to deal with it. It never hurts to upgrade to a modern electronic power supply if you are worried, but ironically the transformers from yesteryear last decades without issues

Deunan wrote on 2024-12-27, 22:14:

It's a bit high, there's a voltage regulator inside these but it's usually a 7805. It requires, depending on the datasheet, 2 to 2.5 volts drop to properly regulate. And IIRC there is a diode as well to prevent reversed polarity. So to be on the safe side and account for possible grid dips the power supply must provide about 9V - and since the PSU doesn't need to be well regulated the voltage will be somewhat higher without a load. But it should not be this high IMHO. The PSU for my CM-64 (which is two boards so it draws more current) measures about 11.7V unloaded.

7805 will tolerate this but will run hotter which is not good. Is that a genuine ACB-220? Or some cheap copy? The original is a transformer based design, not a switching-mode PSU that many sellers offer. You might want to look for a different PSU, just keep in mind it needs to have center pin negative.

Hi,
it's original ACB-220. I was also worried about that voltage, but comment under Yours says different?!?

bertrammatrix wrote on 2024-12-28, 01:17:

This is normal for unregulated transformer based power supplies. Usually the equipment from that era is able to deal with it. It never hurts to upgrade to a modern electronic power supply if you are worried, but ironically the transformers from yesteryear last decades without issues

Hi,
so it is ok to try it and check voltage under load?
I've changed 3300uf 16V cap for new one, but of course, that didn't changed anything. There are few diodes there, and one disk cap... Don't know if the changing diodes would change anything?

It is 11,25V when i check on the ac adapter jack inside Roland, when turned on?!? Is this ok or too high, or do i need to check after some chip, not on the adapter jack?
Thanks

My power supply is not the original ACB-220. Also it's for 230V, unlike the original which is for 220V. All in all less than 12V when plugged in is acceptable. Not optimal but it should work fine. 7805 regulators are known to fail if run hot for years so preferably don't leave your MT-32 powered on all the time when you are not using it.

I've seen this with a number of older adaptors - it's because they're basic unregulated supplies - they have a big AC transformer in them which puts out a what seems like a high number of AC volts - I've seen anything up to 16V. This is the passed through a full bridge rectifier to convert it to a somewhat noisy but usable DC voltage. The majority of these old devices then have regulators inside them - usually 7805s that regulate down to a noise free 5V DC line. The more voltage you put into them, the more heat is generated by the regulator. These devices usually have decent heat sinking so they're fine. So they are designed to take that kind of voltage input.

Modern switched mode supplies can directly put out cleaner DC direct from the adapter. This can still be regulated by a 7805 etc without issue. But in theory you can put a lower amount of voltage into these devices and less heat will be generated.

I didn't see 7805 nowhere on Roland or on adapter?!? Shouldn't inside this adapter (or roland itself) be 7809, not 7805? It is a 9V adapter...

Inside the device itself - in your case, the MT-32. The adapter outputs a 'rough' DC voltage and the device itself has the regulator which then regulates the voltage.

Exactly, the power supply is called "9V" but that's the voltage it will output at full load (which is 1.2A), in fact it will still be a little over. The 7805, or equivalent, is inside the MT-32. Since it works with such high unregulated supply it will be bolted to a big chunk of metal to dissipate the heat. Probably the case since it should be metal on MT-32 (unlike my CMs).

Thanks, i've just ordered new caps for mt-32, and i will change 7805 when i will change caps.

Truetone 9v (NW1-US) replacement adapters works very well with Roland devices.

I prefer to use them instead of old transformer design adapter, even if it's genuine.

Where in Croatia are you?

oldhighgerman wrote on 2025-02-23, 03:24:

Where in Croatia are you?

Kutina 😀

I forgot to add to this post that i replaced all the capacitors (and 7805 of course) for a high quality audio grade new ones, and it work perfect!!! Like Deunan said, it is a little bit over 11V when Roland is turned on, but it doesn't matter because it sounds like a charm - Monkey Island on Roland steroids is awesome 😀

butjer1010 wrote on 2025-02-23, 17:17:

oldhighgerman wrote on 2025-02-23, 03:24:

Where in Croatia are you?

Kutina 😀

My momma was born near Senj, south of Rijeka.

Do they have McDonald's in Croatia? I hope not, the schnitzel is disgusting. Just had it for the first time in weeks. I think it likely I'll keel over soon. Ah but ain't that America! You and me! 🤣 🤣 🤣

oldhighgerman wrote on 2025-02-24, 04:14:

butjer1010 wrote on 2025-02-23, 17:17:

oldhighgerman wrote on 2025-02-23, 03:24:

Where in Croatia are you?

Kutina 😀

My momma was born near Senj, south of Rijeka.

Do they have McDonald's in Croatia? I hope not, the schnitzel is disgusting. Just had it for the first time in weeks. I think it likely I'll keel over soon. Ah but ain't that America! You and me! 🤣 🤣 🤣

Yes of course we have MCD in Croatia! I don't eat anything there, but my kids are (like all youngsters) mad about it. I cannot explain them what is "the income" of eating this shit 🙁
My grandmother lived in Rijeka for 30 Years, so i was every summer there for at least 2 months. Know every corner of the town 😀
Do You ever come to Croatia?

Many years ago. It's a little weird, because due to the language barrier I've never kept in contact, which is a deplorable situation. AND my mother passed in 2017, and none of us (4 siblings, eldest was born in Croatia) have taken it up on themself to write them. Seems like a scary thing now!! My cousin, 1 year younger, wrote me a letter once, in Croatian. I'm not even sure I was told she did. I have a digital copy. I need to dig it out and run it through a translator.

Would love to go back. The thing is the last time I was there, it was hot, and we didn't do anything. Except once took a ferry to Rab and walked along some cobble stone paths that may have been built by the Romans for all I know!

oldhighgerman wrote on 2025-02-25, 09:39:

Many years ago. It's a little weird, because due to the language barrier I've never kept in contact, which is a deplorable situation. AND my mother passed in 2017, and none of us (4 siblings, eldest was born in Croatia) have taken it up on themself to write them. Seems like a scary thing now!! My cousin, 1 year younger, wrote me a letter once, in Croatian. I'm not even sure I was told she did. I have a digital copy. I need to dig it out and run it through a translator.

Would love to go back. The thing is the last time I was there, it was hot, and we didn't do anything. Except once took a ferry to Rab and walked along some cobble stone paths that may have been built by the Romans for all I know!

In this era we live now, language barrier is smallest problem. We all have translator, and most important thing, here in Croatia, we all learn English in school, so, anybody younger than 50 probably knows to speak English language 😀 It would be great to connect with Your cousins here. As You probably know, Croatia is beautiful country (to see at summer, not for living), and its a shame not to come here. High temperature can be a problem, but there is a enormous sea to solve this 😀