As commented above, the two sentences don't have the same meaning. In order to understand what the passive voice is, you need to understand the followings.

1. There should be an agent (that performs an action) and patient (that receives an action). The definition of patient is as follows:

the semantic role of a noun phrase denoting something that is affected or acted upon by the action of a verb.

In the passive voice, the agent is almost always placed after the preposition by. The reason the preposition to is used in your example is "known" is not a past participle, but an adjective meaning:

recognized, familiar, or within the scope of knowledge.

In "I know him", "I" is an agent and "him" is a patient (object). However, "He is known to me", "He" is not an patient in a sense that it doesn't receive any action. "He" is just a subject which is described by the adjective "known". If you replace "known" with "familiar", it would be easier to understand.

He is familiar to me.

It is not a passive voice sentence.

2. Not all the past participles are used in the passive voice. Sometimes they function as an adjective. There is no hard-and-fast rule, but for example,

He was surprised at the news.

This sentence is not in the passive voice. "Surprised" is just an adjective meaning feeling or showing surprise. "At the news" is a prepositional phrase that complements the adjective.

The news surprised him.

is an active voice. The passive voice of the above sentence should be

He was surprised by the news. (He is the patient, the news is the agent)

The below sentence is in the passive voice of "A baseball broke the window".

The window was broken by a baseball.

However, the below sentence is not in the passive voice. There is no agent.

The window was broken and a strong wind came through it (the broken window).

3. To know is classified as a stative verb rather than a dynamic (action) verb. The main characteristics of the stative verb are:

(1) you don't make a progressive sentence with it (there are some exceptions),

(2) Constructing a passive voice of the stative verbs don't work very well and the passive voice sentences don't sound natural.

?He is known by me (I know him). ?A car is had by me (I have a car). ?He is believed by me (I believe him).

This link has a list of stative verbs. Learning what they are and how they typically work is very important.

Conclusion: "He is known to me" is not in the passive voice. "Known" is an adjective, not a past participle. If you contrast your example with "He is well-known to me", it becomes clearer. It is not the passive voice of "I know him well".

The verb to feel is a special verb.  In your example, it's both ergative and copular. 

Some languages have a voice that is different from both the active and the passive voices, called the middle voice.  English doesn't, or at least English grammar doesn't have a separate form or structure to mark the middle voice.  Ergative verbs in English use active voice constructions. 

This farmer grows wheat. 
Wheat is grown in the Great Plains. 
Wildflowers grow in my back yard. 

The first sentence above uses the transitive sense of to grow in an active voice construction.  The subject is a semantic actor, and the direct object is a semantic patient.  The second sentence uses the same sense of the verb to grow in a passive voice construction.  There is no actor or agent required (although a prepositional phrase can supply one), and the subject is the patient. 

The third sentence uses the ergative sense of to grow.  The subject of this sentence isn't simply an actor or a patient.  It's something like actor and patient combined. 

Suzie smelled the roses. 
The roses smelled wonderful. 

In this pair of sentences we see the transitive and ergative senses of the verb to smell.  In the first, we have subject as actor and direct object as theme.  In the second, we have subject as agent and theme combined and a predicate adjective subject complement. 

Most copular verbs allow either a predicate adjective complement or a predicate nominative complement.  These copular ergatives do not allow predicate nominatives. 

The roses were wonderful.  The roses were a delight.
The roses smelled wonderful.  *The roses smelled a delight.

That last sentence doesn't work with the ergative sense of to smell because "a delight" looks like a direct object instead of a subject complement -- which forces to smell into its transitive rather than ergative sense. 

I feel good. 
Hanging out feels good. 

Both of these have the same grammatical structure as "the roses smelled wonderful."  We have subjects that combine the roles of actor or agent and patient or theme, and a predicate adjective subject complement.  These are both copular ergative structures with predicate adjective subject complements.

Despite the identical grammar, they don't carry the same semantics.  In the first, the subject "I" is able to perceive things.  It makes sense to assign a semantic role of perceiver or experiencer to the subject of the first sentence.  An activity like "hanging out" isn't a sensible perceiver, and we simply assume that someone not mentioned in the sentence experiences the good feeling. 

There is no change in voice between "I feel good" and "hanging out feels good".  There is only a change in what semantic roles those subjects can fill.