Bias of AX-14
Solved. Solution is in post #191
Test it with +/- 24volts 3amp for one channel with 10000uf each rail.
The sonic was fantastic you can hear crystal clear and also the bass you can hear separate the bass guitar and the bass drum.
its dead silent even if you go near the speaker you cant hear any sounds.
burned it test last night for 2 hrs and this morning for 4 hrs.
Now, how to bias this amp? This is my first amp build that needs of biasing. please help with procedure.
when i measure the 0R33 resistor with load the value is not constant. if there is no load in the input 0volt that i can measure across 0.33 resistor.
for biasing...
if i want to have a bias of 50mA...
V=IR; ohm law
V=50mA*0.33Ohm
V=16.5mvolts
is this correct? please enlighten. Thanks
Solved. Solution is in post #191
Test it with +/- 24volts 3amp for one channel with 10000uf each rail.
The sonic was fantastic you can hear crystal clear and also the bass you can hear separate the bass guitar and the bass drum.
its dead silent even if you go near the speaker you cant hear any sounds.
burned it test last night for 2 hrs and this morning for 4 hrs.
Now, how to bias this amp? This is my first amp build that needs of biasing. please help with procedure.
when i measure the 0R33 resistor with load the value is not constant. if there is no load in the input 0volt that i can measure across 0.33 resistor.
for biasing...
if i want to have a bias of 50mA...
V=IR; ohm law
V=50mA*0.33Ohm
V=16.5mvolts
is this correct? please enlighten. Thanks
Last edited:
congrats!
calculation is correct.
it's normal to have a fluctuating voltage across the 0R33 resistor when there input load.
to set the bias, short circuit the input terminals. turn the pot at a VERY SMALL increment while observing voltage reading on any 0R33 resistor.
as per suggestion, the bias is between 15mV to 20mV (50mA to 60mA bias).
edit: if you have trouble setting the bias, you may need to change R16 from 1k to 1.5k.
if you have unstable bias, you may need to install zobel network on output, that is connect output and ground with 4.7R/2W resistor in series with 100nF/100V capacitor.
Last edited:
Hope this helps.
With this, you get two(2) Zobel networks. I think either one can be removed.
Attachments
ax11 is first amp i assembled and it gives me a hard time but interesting. i replaced bd139 and i got 200mv at amp out but 2sa1943 have mv in all its pin, i will replace bd140 tomorrow and maybe amp will work. i am lucky with those defective transistor.
joeyt
joeyt
What audio amplifier?
Hi Mr Mile!
Which audio amplifier you recommend for making the MJ15003/MJ15004.
I have a 250VA transformer of the second hand 2x27V.
Amplifier I need for home use.
Thanks for your help!
G-ne Mile, posto slabo stojim sa engleskim, evo ovako:
Hocu da izradim pojacalo za kucnu upotrebu sa izlaznim komplementarnim tranzistorima MJ15003/MJ15004.
Inace za ovo pojacalo imam trafo od 250VA sa sekundarom 2x27V.
Mile, molimte preporuci neko pojacalo od tvojih projekata koje dobar zvuk (saund) daje.
Jel tvoje pojacalo AX11-MK2 bez ikakvi izmena moze dobro raditi sa napajanjem Ucc=+/-36V ?
Hvala na pomoci!
Hi Mr Mile!
Which audio amplifier you recommend for making the MJ15003/MJ15004.
I have a 250VA transformer of the second hand 2x27V.
Amplifier I need for home use.
Thanks for your help!
G-ne Mile, posto slabo stojim sa engleskim, evo ovako:
Hocu da izradim pojacalo za kucnu upotrebu sa izlaznim komplementarnim tranzistorima MJ15003/MJ15004.
Inace za ovo pojacalo imam trafo od 250VA sa sekundarom 2x27V.
Mile, molimte preporuci neko pojacalo od tvojih projekata koje dobar zvuk (saund) daje.
Jel tvoje pojacalo AX11-MK2 bez ikakvi izmena moze dobro raditi sa napajanjem Ucc=+/-36V ?
Hvala na pomoci!
Last edited:
busted fuse in -35v is the reason why 2sa1943 is not working,forgot to change the temporary fuse i used. now amp out got 5mv and ax11 is working right now.
have a good bass and its fun to listen with this kind of amp. very quiet amp. 2nd ax11 is coming up.
thanks apex for this amp, and willy for pcb layout
joeyt
hello apex,
what is your recommended replacement for mpsa92?
and i used 10k potentiometer for ax11 is this good enough or i go for 20k
thanks
joeyt
what is your recommended replacement for mpsa92?
and i used 10k potentiometer for ax11 is this good enough or i go for 20k
thanks
joeyt
Use AX11, you have pcb on this thread with MJ15003/4 in OS, with +/-36V no need for any change.
Regards
AX11 is my new favorite amp...running at 400mA with monster heat sinks. Very tube like and warm sounding...almost single ended but with much more bass.
hello apex
im testing right now ax11 at full power, at full power 0.22r resistor has a pluctuating from 45mv to 65mv and mpsa13 vce=2mv and output transistors are hot.using fan to cool them. what is your suggestion to decrease the voltage across the 0.22r? and to keep this amp to warm?
thanks
joeyt
im testing right now ax11 at full power, at full power 0.22r resistor has a pluctuating from 45mv to 65mv and mpsa13 vce=2mv and output transistors are hot.using fan to cool them. what is your suggestion to decrease the voltage across the 0.22r? and to keep this amp to warm?
thanks
joeyt
Has anyone attempted the HX 11, i cant find BAV21, but according to data sheets its a general purpose diode, can i replace it with 1n4148