Page 16
Page 1 4
A m is p la cem en t c an not h ap p en e x cep t b y a p re v io us c are le ss s e rv ic e w ork o r b y u n sc re w in g o r d is m an tli n g
o f t h e m ag n et. T he l e ft " e n d t h re ad o n t h e m ag n et e n su re s t h at t h is c an n ot u n sc re w i ts e lf . O n t h e o th er h an d,
i t c a n h ap pen w hen t h e a d ju stm en t m en tio ned a b o ve h as b ee n m ad e a n d t h e m ag n et i n su ffic ie n tl y w ell
s e cu re d . I n p ra ctic e, i t s h ould b e t ig h te n ed u p s e c u re ly b efo re r e -a d ju stm en t.
I f t h e d if f e re n ce i s s m all, r e p la ce t h e b ru sh es w here t h ey w ere b ecau se t h e d if f e re n ce i s p ro b ab ly a n e rr o r i n
m easu re m en t. O ur f a cto ry -a d ju stm en t m ad e b y t h e a id o f a s p ecia l m ach in e i s m uch m ore a ccu ra te t h an t h at
m ad e b y a d ju sti n g t o m in im um c u rre n t.
PR EC A UTIO NS A GA IN ST I N TER N AL N O IS E
A s w ith a ll t a p e r e co rd ers , t h e N ag ra I II h as s o m e r e sid u al n ois e . W e m ust d is tin gu is h :
1 ) N ois e i n t h e m ic ro phon e p re am plif ie r
2 ) N ois e i n t h e r e co rd a m plif ie r ( o utp ut a m plif ie r)
3 ) N ois e i n r e c o rd in g o n t h e m ag n etic t r a ck
4 ) N ois e i n t h e p la y b ack a m plif ie r
5 ) N ois e i n t h e s w it c h in g d io des o f t h e s p eed s ta n dard s e le c to r
6 ) N ois e i n t h e p la y b ack a m plif ie r
7 ) F or t h e s e co nd t im e n ois e i n t h e o u tp ut a m plif ie r
D is c u ss in g t h e n atu re o f t h ese n ois e s, w e h av e:
a ) His s
T his i s a p pro xim ate ly w hite n ois e , t h at i s t o s a y c o m pose d o f a ll f re q uen cie s i n t h e s p ec tr u m . I t r e se m ble s
t h e n ois e o f a j e t o f a ir o r d ry s te am . I t i s q uit e c le ar b ut a l i tt le l e ss t h an t h e p ro no un cia tio n o f t h e l e tte r " S ".
H is s i s e sse n tia ll y p ro duced b y t h erm al a g ita tio n a n d h as a l im itin g m in im um v alu e f ix ed f o r a g iv en
t e m pera tu re a n d a g iv en i m ped an ce . S im ila rly t h e n ois e f o llo w in g t h e b re ak ag e o f a c o nnecti o n o n t h e i n put
c ir c u it i s o f t h is t y p e.
b ) Sem ic o nducto r N ois e ( F li c k er N ois e )
T his i s s im ila r t o t h e p re c ed in g n ois e . b ut i n clu des m ore l o w f r e q u en cie s. O ur e a rs a re a lw ay s l e ss s e n sit iv e
t o l o w f re q uen cie s a t l o w l e v el, a n d s e m ic o nducto r n o is e i s d is ti n gu is h ed b y t h e f a c t t h at i t i s m odula te d b y
t h ese l o w f re q uen cie s. T he s o und w hic h m ost n ea rly d esc rib es t h is t y p e o f n ois e i s t h at o f a j e t o f v ap our
c o nta in in g d ro ps o f l iq u id , f o r e x am ple a n e x pre sso c o ffe e m ach in e. T he n ois e i s p ro duce d b oth b y d efe ctiv e
r e sis ta n ce s c a rr y in g c o ntin uo us c u rre n t. I n c ase s 1 , 2 , 4 , 6 a n d 7 t h e t r a n sis to rs s h ou ld b e f ir s t s u sp ect, t h en
t h e b ase d iv id in g r e sis ta n ces a n d t h e c o ll e cto r r e sis ta n ce s.
S PE C IA L W A RN IN G
D o n ot d is m an tle y o ur N ag ra b ecau se o f t h e r e su lt s o bta in ed w ith a d ou btf u l t a p e. A
b ad t a p e c a n p ro duce s u ch n ois e o n a p erf e ct m ach in e.
c ) R esid ual N ois e a t 1 0 00, 2 000 a n d 4 000 c . p . s .
T he s p ee d s ta b ili s a ti o n s y ste m o f t h e N ag ra u se s t h ese f re q u en cie s a n d i t c an h ap pen t h at t h ey m ay b re ak
t h ro ugh a n d b eco m e a u dib le a t t h e s p ee d o f 3 3 /4 " p er s e co nd w hic h w e d o n ot c o n sid er " p ro fe ssio nal" . A
p erc e p ti b le r e sid ual s ig n al i s a ll o w ed . O n t h e o th er h an d , i t s h ould n ot b e p oss ib le t o h ea r s u ch
