amplifier attempt #1

[name773]

virtual ground. although i think i'm going to go for a wall supply instead on this one. good battery chargers are more expensive than i thought

 

[name773]

here's how i decided i'd like to build this amp. are the resistor values ok? R12/13 in particular i am not sure about, R3 too but less uncertainty. i'm fairly certain about the rest.

R1 15k
R2 150k
R3 6k8
R4 47R
R5 47R
R6 33k
R7 150k
R8 33k
R9 47R
R10 4k7
R11 470R
R12 470R
R13 470R
R14 4R7 5W
R15 4R7 5W
R16 10R

VR1 10k

C1 1.33uf film
C2 100uf non-polar
C3 150uf non-polar
C4 100nf mlcc
C5 100pf mlcc
C6 100nf mlcc
C7 100pf mlcc

Q1 BC239
Q2 BC239
Q3 BC560
Q4 BC550
Q5 BD139
Q6 BD140

(MLCC -> monolithic multilayer ceramic capacitor)

 

[name773]

and here is the psu

the empty triangle thing is a less noisy ground used in the amplifier section

is it ok to put ferrites on the power line? or should i wait until after the transformer

 

[edl]

a few comments, my friend:

-the RMS power of the amp will be about 1W (why are you using so big mains transformer?).
so the output current will be 0,5A (4ohm speaker) or 0,35A (8ohm speaker)
let's say, that the gain of the output transistors is 30 (in the worth case.) so the current that sourced need to be 0,5/30*2=33mA. if the rails are 8V, than R13 and 12 need to be 120R.

-C7 need to be between the base of Q1 and the ground.

-R6 is 33K. so the current flowing in the LTP will be about 250uA! that too low. you need 1-3mA. so let R6 be 3K9. than R3 need to be 680R.
if you use 33K in tha place of R6, than R3 need to be rated about 5K6, so the 6K8 will be good, I think.
if the offset (DC on the output) will be higher than +/-100mV, than you need to change R3 to minimalize this voltage.

-C3 is not need to be non-polar. let's use 22uF, 47uF or even 100uF elko here.

-R8 is rated 33K. so C2 is too high. only 3,3uF will be enough. or you can use lower. 1uF will be just good (for example an 1uF foil cap)

-R14 and R15 need to be 2R2. 5W not needed, let's use 0,4W resistors here.

-if you not decrase R13 and R12 from 470R, than R9 need to be 100R. if you decrase R12 and 13 to 120R, than R9 need to be 22R.

-470nF for C1 willl be enough.

-R10, VR1, R11 depends on R12 and R13.

I hope my comments will help you.

all the best, good luck!

 

[name773]

very helpful, thank you

i've got 32 ohm headphones in mind for the load on this amp. good point on the oversized trafo, i might put in a 12.6vct 1A
i've read that the dc voltage output from a rectified transformer is sqrt(2) * the ac voltage. does this happen right at the rectifier diodes or after the filter caps?

some new values

R1 4k7
R2 47k
R3 820R (edit: off by 10x the first time)
R4 47R
R5 47R
R6 6k8
R7 47k
R8 10k
R9 33R
R10 1k8
R11 150R
R12 150R
R13 150R
R14 2R2 .5W
R15 2R2 .5W
R16 10R .25W (current rating ok?)

VR1 2k

C1 .82uf poly
C2 10uf poly
C3 100uf el

better? thanks for all the help

 

[name773]

ok, so i looked the caps over again and i'll go with C1 .47uf and C2 3uf like you said

can't wait to build

here's the updated power supply

cheers