Explendid amplifier designed by Michael Bittner, our MikeB

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#2,241
MikeB said:
Hi dytln_02, sorry, i did not check pinout of sc2240, it's not an option...
Your psu with 31v 5a and 2x15.000uf is good, this should give ~45watts into 8 ohm.
Have you tried to swap q1 with q2 in one board to check if the matching is the problem ? Matching is not only necessary for dc-offset, it's also important for quality. This would be the easiest way to finally find out if this is the problem.

Mike
Click to expand...


mike swap it's not working it's the same
 
#2,245
In first board with hfe +40mV (using BC547B) yesterday I maching it
I don't remember what hfe

First board
Voltage across R14 -84mV and R29 -89mV
Second Board
Voltage across R14 -35mV and R29 -40mV

It's the same differences is about -5mV

May be I must remove 4.7uF to see if it's interferences with DMM
 
#2,247
MikeB said:
I thought these readings were to ground ?
Can you give me readings from the base of q1/2 to ground AND voltage across r14/29 ?

Mike
Click to expand...


Voltage Accros r14 = -35mv
Voltage Accros R29= -64mV
Voltage Base to ground Q1 = -35mV
Voltage Base to ground Q2 = -40mV

I try to remove input caps 4.7uF it's give the same reading

edit :

mike -64mV still drop may be this is dc offset ~20 to 30mv
 
#2,251
MikeB said:
Okay, now you completely confused me, can you give me the values in one part ?
Like:
Voltage Accros r14 = xx mV
Voltage Accros R29= xx mV
Voltage Base to ground Q1 = xx mV
Voltage Base to ground Q2 = xx mV

r29 to ground would be either output to ground or base of q2 to ground.

Mike
Click to expand...
Sory R29 to ground = Base Q2 to ground
not output to ground


Voltage Accros r14 = 35 mV
Voltage Accros R29= 64 mV
Voltage Base to ground Q1 = 35 mV
Voltage Base to ground Q2 = 40 mV
 
#2,256
This thread is one of the longest so its becoming difficult
to find specific items of information. I apologise then, if these questions have been answered before.

There are several options for output transistors, among them
mjl 3281/1302
mjl 0281/0302
2SA1943/2SC5200

Ive seen Pavel's recommendations for the cap changes needed to keep the amp stable if using the 2SC5200 combination.

If mjl 0281/0302 is used what changes to the circuit are necessary ?
Can I use Pavel's recommendations for these semis as well?

Some components are difficult to find;

C1 = 10uf WIMA , mjl0281/0302 especially here in Australia. In fact put MJL 0281 into google and nothing turns up.

If there is no dc on the input is C1 necessary?

Where have others found their diificult to find bits ?

Thanks
 
#2,259
Hi Sandro600, C1 is necessary not for keeping DC-outside, it's mainly to keep DC inside. You can't skip it. Wima seems difficult to get outside europe, it's a german manufacturer. (of course easy to get here) Maybe time for a group buy ?

You see MJL0281/0302 here:
http://www.onsemi.com/PowerSolutions/product.do?id=MJL0281A

The MJW version is available at digikey: http://www.digikey.com/

The MJL0281/0302 seems still only available as samples ?

The MJL0281/0302 is used as the others, c14 = 10pf and c3/4 = 330pf.

Dytln_02, these values are fine, they are way below 1%.

Mike
 
#2,260
mike My DMM give Similar Result

I have done test hfe with your hfe schematic.
In first transistor :
v1=2.95
V2=0.88
hfe=(2.95/0.95)*100=335.2
my dmm give 326
in second transistor
v1=2.95
V2=0.88
hfe=(2.95/0.95)*100=335.2
my dmm give 322

it' seem there is nothing wrong with my dmm :h_ache:

Can I change MJ150030/MJ150031 with bd911/912
may be from this transistor....
 
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