Halakhah su Salmi 51:17

Before saying, Tehillos le'eil elyon,⁴“Praises to the most high Almighty.” you should stand and prepare yourself for the prayer of Shemoneh Esrei [Amidah]. You should rid yourself of phlegm and saliva, and anything that may distract your thoughts; then walk back three steps and say: tehillos le'eil elyon, and continue till [Ga'al Yisrael],⁵“Who redeemed Israel.” then return [to your position] by walking three steps forward in the manner of one approaching a king. You should not make any interruption between Ga'al Yisrael and Shemoneh Esrei, not even [in response] to Kaddish, Kedusha, or Barechu, because [the prayer of] redemption must be joined to the [Amidah] prayer. It is best to be precise in concluding the berachah of Ga'al Yisrael simultaneously with the chazzan, because should you finish first and the chazzan afterwards, there is a question whether to answer Amein to the berachah of the chazzan;⁶However if you finished before the chazzan you should answer Amein to his berachah. but when you conclude the berachah with him, you are certainly not required to answer Amein, because you do not answer Amein to your own berachah. (See Chapter Six, paragraph eleven.) In the ma'ariv service, since the berachah preceding the Shemoneh Esrei [does not] end with Ga'al Yisrael, an interruption is permitted, as it is permitted at any place between one chapter and another. [See Chapter 16 paragraph 2] Before praying Shemoneh Esrei, we say the verse: "Hashem, sefasai tiftach" [My Master open my lips]⁷Psalms 51:17.. This is not [considered] an interruption because it is relevant to the prayer; but the verse: "Ki Sheim Hashem ekra," etc.⁸“When I proclaim Hashem’s Name.” Deuteronomy 32:3. should not be said [before the Amidah], except at musaf and minchah prayers, before saying, Hashem, sefasai tiftach.

The Law of Juxtaposing "Redemption" to "Prayer". Containing 3 Seifim:
One needs to juxtapose “redemption” [i.e. the last blessing of the Sh'ma - "Ga-al Yisrael"] to “prayer” [i.e. the Amidah]. And one should not interrupt between them, even with "Amen" after “Ga-al Yisrael”, and not for any verse other than “Hashem Sefatai” [Psalms 51:17, the introductory verse for the Amidah]. Gloss: And there are those who say that it is permitted to respond Amen after “Ga-al Yisrael”, and so we practice (Tur). And there are those who say that this requirement to juxtapose “redemption” to “prayer” is only on a weekday or Yom Tov, but on Shabbat one does not need to. (Meaning, that the reason that we require to juxtapose “redemption” to “prayer” [during the week] is because it is written “God will answer you in a day of distress,” [Psalms 20:2] and juxtaposed to it [is written], “Let the words of my mouth be desire … and my redeemer.” [Psalms 19:15], but Shabbat is not a time of distress. And in my humble opinion, it seems [that the reason] this is not so on Yom Tov is because they are days of judgement, as we learned in Mishnah Rosh Hashanah 1:2, “On Passover [the world is judged] on grain…”) (Hagahot Ashir"i [Rabbi Yisrael MiKrems] on Chapter 1 of Berachot; and Kol Bo, Laws of Shabbat; and Mahari"l, the Laws of Yom Tov) And it is good to be stringent unless in a place that needs to do such (Tur).