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

[Ben Stuyts]

(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>
>> 
> 
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20250204/392db837/attachment.htm>