Грамматика русского языка. Часть 3. Различие согласных звуков по глухости / звонкости. Глава 1. Звонкие и глухие согласные (Продолжение (2)). Russian Grammar. Part 3. Voicing and Devoicing of Consonants. Unit 1. Voiced and Voiceless Consonants (Continued (2)).

Voicing before a Voiced Consonant

The opposite holds true. If a voiced consonant (other than л, м, и, or р) follows a voiceless consonant, the voiceless consonant becomes voiced.

For example:
сделать [zd'eh-luht'] to have done

Compare:

просить [pruh-s'eet'] to ask and просьба [prawz'-buh] request
сажать [ suh-zhaht'] to seat and сжать [zzhaht'] to squeeze
собрать [suhb-raht'] to gather and сбор [zbawr] collection

Грамматика русского языка. Часть 3. Различие согласных звуков по глухости / звонкости. Глава 1. Звонкие и глухие согласные (Продолжение). Russian Grammar. Part 3. Voicing and Devoicing of Consonants. Unit 1. Voiced and Voiceless Consonants (Continued).

Devoicing at the End of a Word

Let´s take up the sounds that change when they are at the end of a word. The voiced consonants б, в, г, д, ж, and з - when they come at the end of a word - lose their sharpness; that is, they become voiceless.

The б sounds almost like п;
The в sounds almost like ф;
The г sounds almost like к or х;
The д sounds almost like т;
The ж sounds almost like ш;
The з sounds almost like с;

Грамматика русского языка. Часть 3. Различие согласных звуков по глухости / звонкости. Глава 1. Звонкие и глухие согласные. Russian Grammar. Part 3. Voicing and Devoicing of Consonants. Unit 1. Voiced and Voiceless Consonants.

You've learnt how the soft vowels and the soft and hard signs affect the sounds around them. Now you'll see how the position of the consonant in the word affects its sound.

Voiced and Voiceless Consonants

Russian consonants are divided not only into hard and soft sounds, but also into voiced and voiceless consonants. Voiced consonants are produced with the aid of the vocal chords, which give to the consonants a buzzing sound; in the production of voiceless consonants, however, the vocal chords remain inactive.

Грамматика русского языка. Часть 2. Изменение звуков. Глава 1. Действие мягкого знака. Russian Grammar. Part 2. Sound Variations. Unit 1. Action of The Soft Sign.

You have now learnt to pronounce all the Russian letters when they are true to their sound in the alphabet. However, as in English, the sound of a Russian letter is affected by: the sounds of the letters that surround it, by its position in the word, and by its position in the sentence. First, let's study how a consonant is affected by the sounds that surround it.

Грамматика русского языка. Часть 1. Русский алфавит. Глава 5. Согласные Ж, Ц, Ч, Ш, Щ. Russian Grammar. Part 1. Russian Alphabet. Unit 5. The Consonants Ж, Ц, Ч, Ш, Щ.

The following Russian letters are quite easy to pronounce because there are similar sounds in English. However, in English, it is necessary to use several letters to represent these sounds; in Russian, each of these sounds has its own special letter. These letters are: ж [zheh], ц [tseh], ч [cheh], ш [shah], щ [shchah]. The letters sound harsher than in English. 

The letter Ж ж [transcribed zh]
The letter ж [zheh] sounds even harsher than in pleasure or vision.
Examples:
жук  [zhook] beetle
жажда  [zhahzh-duh] thirst
кожа [kaw-zhuh] skin

Грамматика русского языка. Часть 1. Глава 4. Русский алфавит. Согласные К, П, Т. Russian Grammar. Part 1. Russian Alphabet. Unit 4. The Consonants К, П, Т.

Now let us take up some sounds that will require a little practice - first, the letters п [peh], т [teh], and к [kah].

Attention!

Aspiration occurs when a short puff of breath is released after another sound, giving the effect of a slight hesitation or h-sound. It can be heard after the p in pie, the t in tie, and the k in kind. By contrast, the h-sound should not be heard after the p in please, the t in try, or after the hard c in clean.
Before you proceed to work intensively on the letters к, п, т, practice on the English words please, try, and clean so that you may be sure to avoid any aspiration when you pronounce the Russian к, п, т.

The letter К к [transcribed k]
The letter к [kah] sounds like the k-sound in clean. Once more, the aspiration heard after the k in English words like key and kind never occurs in Russian.
Examples:
как [kahk] how
кот [kawt] cat
класс [klahss] class

Грамматика русского языка. Часть 1. Русский алфавит. Глава 3. Согласные Д, З, Л, Н, С. Russian Grammar. Part 1. Russian Alphabet. Unit 3. The Consonants Д, З, Л, Н, С.

The letter Д д [transcribed d]
Examples:
дом [dawm] house
два [dvah] two
дама [dah-muh] lady

Грамматика русского языка. Часть 1. Русский алфавит. Глава 2. Согласные Б, В, Г, М, Ф. Russian Grammar. Part 1. Russian Alphabet. Unit 2. The Consonants Б, В, Г, М, Ф.

Now let me introduce to you some Russian consonants that also sound much as they do in English. They are the letters: б [beh], в [veh], г [geh], м [emm], and ф [eff].

The letter Б б [transcribed b]
Examples:
бак [bahk] tank (receptacle)
бум [boom] boom
бок [bawk] side