yeah... the plain link only works on steempeak.com though

the steemit.com frontend and tribes like sonicgroove.net want to see the iframe embed code like this:

<iframe width="100%" height="166" scrolling="no" frameborder="no" allow="autoplay" src="https://w.soundcloud.com/player/?url=https%3A//api.soundcloud.com/tracks/735943411&color=%23ff5500&auto_play=true&hide_related=false&show_comments=true&show_user=true&show_reposts=false&show_teaser=true"></iframe>

the original comment above had both in the text, so steempeak.com actually showed two players there

you can get the iframe code on souncloud via "share" and "embed"