[sdiy] [AH] Roland CMU-800R transformer (again, 2 years later)

[Roman Sowa]

$10 in tariffs is not bad at all. I pay much more just for the customs 
fee, and then comes duty (you call it tariff) and VAT.
But what's more important, now the $800 limit of "we don't care what's 
inside" limit is gone, so every small order sent to US, which previously 
was delivered free of charge, is now more expensive for the recipient.

Roman

W dniu 2025-02-06 o 02:03, Todd Sines via Synth-diy pisze:
> Hi Ben, Bob, Florian, and Marvin,
> Thanks for the tips!
> I ordered the Triad VPT30-830
> https://mou.sr/42IFATi <https://mou.sr/42IFATi>
> although I wonder if I should have gotten the VPT36-690 instead
> https://mou.sr/41R8TSY <https://mou.sr/41R8TSY>
> Plus a few CUI P7805B-1000 5V regulators. will report back tomorrow night.
> 
> PS. These tariffs are no joke, even on an order of $59, it's an 
> additional $10 in tariffs. I really feel for those who are reevaluating 
> their business model altogether right now (Retroaktiv specifically, but 
> just about everyone else). There should be a tariff exemption until the 
> completed module/synth/device ships, not just every step of the way.
> Going to be a GREAT next 4 years. 😭
> 
> Todd
> 
> 
> On Feb 4 2025, at 5:33 pm, Ben Stuyts <ben at stuyts.nl> wrote:
> 
>     (Sorry, just saw that the Recom has quite a bit of noise on its
>     output. The CUI P7805B-1000 is a better choice.)
> 
>>     On 4 Feb 2025, at 23:26, Ben Stuyts <ben at stuyts.nl> wrote:
>>
>>     One more thought:
>>
>>     There are DC/DC converters with the same pinout as a 7805. So what
>>     you could do is:
>>
>>     - remove the 7805 and rectifier for the 5V section.
>>     - Put a DC/DC converter in it’s place, e.g. a Recom R-78E5.0-1.0
>>     (input is 8-28V, output is 5V, 1A max)
>>     - Wire the input to the +20V input of the 15V section.
>>
>>     DC/DC converters are very efficient and can handle the drop from
>>     20 to 5V easily without breaking a sweat. An analog part like the
>>     7805 would dissipate a ton of heat.
>>
>>     Ben
>>
>>>     On 4 Feb 2025, at 23:15, Ben Stuyts <ben at stuyts.nl
>>>     <mailto:ben at stuyts.nl>> wrote:
>>>
>>>     Yes, that should work for the lower part, the +/- 15V section. It
>>>     can deliver 1.67A when the windings are in series, not 3.34A. But
>>>     that is more than plenty for this application.
>>>
>>>     For the 5V you need a separate winding, for the reasons Bob
>>>     explained. You can use a separate transformer for this, it
>>>     doesn’t need to come from the same transformer. Looking at the
>>>     schematic, a 5VA or 10VA type should be sufficient.
>>>
>>>     Another possibility without an added winding is to add a small
>>>     DC/DC converter on the +20V line, and pre-regulate it to 8V. A 5W
>>>     type is probably enough. Feed this into the input of 7805. You
>>>     could even take out the 7805 and use a DC/DC converter which
>>>     outputs 5V directly, depending how purist you are. ;-)
>>>
>>>     Ben
>>>
>>>
>>>>     On 4 Feb 2025, at 23:05, Todd Sines <sines_list at scale.la> wrote:
>>>>
>>>>     I have a Triad VPT30-1670, which is a dual 15V output toroidal
>>>>     transformer at 3.34 A.
>>>>     I would think that would work, but maybe I'm missing something?
>>>>
>>>>     The schematic is here:
>>>>     Roland-CMU-800-Compu-Music-Schematic.pdf
>>>>     <https://www.synthxl.com/wp-content/uploads/2020/01/Roland-CMU-800-Compu-Music-Schematic.pdf>
>>>>
>>>
>>
>>
> 
> 
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