Arcam A60

[GEirin]

Hi all.
I need your help. What is the funtion of R51//C27 and C30.
Thank.
Geirin.

[jaycee]

R51/C27 is compensation for the VAS transistor Q13.

Every time I look at that schematic, looking at R50 makes me shudder

[GEirin]

Thank Jaycee.
And C30?

[ppa]

Hi,


regarding c30 it look like that it's a simple compensation cap..........but the its function is more complex:

Arcam c60 has a quasi-complementary final stage because it uses
a npn bjt Q21 (a very slow 2n3055) instead of a pnp.
Mr. Curtis (the designer), for giving a functionality near to a fully-complementary design, has put D3 in the schematics.
Q19 , D3 and the 82 ohm resistor near it should recreate (in theory...) the Q20 and q16 series Vbe non-linearity.
The q20 and q16 darlintong has the q20 velocity (velocity ? ........
velocity is a big word for an 2n3055 !) , the complementary pair for the negative side has the velocity (hem....slowing) of Q21 (an other 2n3055).
When Q21 is on C30 isn't necessary (but helps.......) because the velocity near to the darlintong is given by D3, but when Q21 is off (for positive output voltages) C30 is very important because , in this case, D3 is off (the D3's current is complemetary to q20 base junction current.........) and C30 gives a velocity to the reopen Q21 near to Q20 velocity.

Kind regards,
ppa


PS: Hi guys ! I have some old 2n3055 , I give you for free...............(only shipping cost).........I joke.........I have just given they to my friend............................................ .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. ..............................................for free!

[ppa]

Hi,

I repeat with correct typing

regarding c30 it look like that it's a simple compensation cap..........but the its function is more complex:

Arcam c60 has a quasi-complementary final stage because it uses
a npn bjt Q21 (a very slow 2n3055) instead of a pnp.
Mr. Curtis (the designer), for giving a functionality near to a
fully-complementary design, has put D3 in the schematics.
Q19 , D3 and the 82 ohm resistor near it should recreate
(in theory...) the Q20 and q16 series Vbe non-linearity.

The q20 and q16 darlintong has the q20 velocity (velocity ? ......
velocity is a big word for an 2n3055 !) , the complementary pair for the negative side has the velocity (hem....slowing) of Q21 (an
other 2n3055).
When Q21 is on C30 isn't necessary (but helps.......) because the
velocity near to the darlintong is given by D3, but when Q21 is off
(for positive output voltages) C30 is very important because , in
this case, D3 is off (the D3's current is complemetary to q20 base junction current.........) and C30 gives a velocity to the reopen
Q21 near to Q20 velocity.

Kind regards,
ppa


PS: Hi guys ! I have some old 2n3055 , I give you for free...............(only shipping cost).........I joke.........I have just
given they to a my
friend.................for free!

[GEirin]

Ciao.

Thank you ppa. Because for the important information.

Grazir. Gracias

Guillermo.

[GEirin]

Grazie ppa.

[ppa]

don't thank me,

I think that arcam a60 It's a good way for using two 2n3055.

If you want I can council you some modification for it.

Cheer,
ppa

[GEirin]

Ciao.
Thank you.
My idea is to improve my amplifier 50W (circuit philips 197..).
Vas and Output stage is similar at Arcam A60.
What is your opinion?
Cheer
Guillermo

[big jim]

hi all i have one or two points to make about the A60.
1 jaycee. Every time i look at R50 i shudder.[ WHY ] the resistor keeps the base.s of the drivers 2.1 volts apart.
And as the A60 was designed in 1976 and proven to very reliable
Why shudder.
2 To the best of my knowledge john dawson and chris evans
designed the A60.

jim