Shehantha
On the original SR series amplifiers C Audio set the bias by measuring the current between the emitters of Q2 and Q3. In practice you will find the correct bias is obtained by varying VR1 to get 525mv between the emitters of Q2 and Q3. VR1 will be at about 450ohm setting.
The drivers do not need to be on a heat sink but the output fets do need to be on a heat sink that is fan cooled.
I own a number of the C Audio SR series and I have repaired and rebuilt a number of them. If you set the voltage between the emitters of Q2 and Q3 at 525mv you will find that the amplifier runs slightly hot when running fan cooled in the original case with no signal.
If you can not find the original parts for Q2 and Q3 then the C Audio recommended replacements are TIP50 and MJE5731A.
The transistor manufacturers replacement for the original 2sc2238 and2sa968 are 2sc4739 and 2sa1837 ( both available) However these are only rated at 1amp as against 1.5amp for the originals so I use them piggy backed.
If I was building an SR series amp from scratch I would pick the SR606 or SR404 which are more forgiving than the SR707; but then you will need to adjust some resistors in the protection, driver and feedback circuits to suit the lower rail voltage.
The circuit was designed to suit the characteristics of the original Hitachi 2SK135 and 2SJ50 ( up to series e from memory ). Later Hitachi fets need a different protection circuit ( I do not have details ) and other lateral fets are slightly different again. I have found that the of the latest and current fets the profusion ones sound best in this circuit and seem to work ok.
Don
On the original SR series amplifiers C Audio set the bias by measuring the current between the emitters of Q2 and Q3. In practice you will find the correct bias is obtained by varying VR1 to get 525mv between the emitters of Q2 and Q3. VR1 will be at about 450ohm setting.
The drivers do not need to be on a heat sink but the output fets do need to be on a heat sink that is fan cooled.
I own a number of the C Audio SR series and I have repaired and rebuilt a number of them. If you set the voltage between the emitters of Q2 and Q3 at 525mv you will find that the amplifier runs slightly hot when running fan cooled in the original case with no signal.
If you can not find the original parts for Q2 and Q3 then the C Audio recommended replacements are TIP50 and MJE5731A.
The transistor manufacturers replacement for the original 2sc2238 and2sa968 are 2sc4739 and 2sa1837 ( both available) However these are only rated at 1amp as against 1.5amp for the originals so I use them piggy backed.
If I was building an SR series amp from scratch I would pick the SR606 or SR404 which are more forgiving than the SR707; but then you will need to adjust some resistors in the protection, driver and feedback circuits to suit the lower rail voltage.
The circuit was designed to suit the characteristics of the original Hitachi 2SK135 and 2SJ50 ( up to series e from memory ). Later Hitachi fets need a different protection circuit ( I do not have details ) and other lateral fets are slightly different again. I have found that the of the latest and current fets the profusion ones sound best in this circuit and seem to work ok.
Don
Dear Mr. vzaichenko
Hope you remember me. Again i need a valuable help from you. Couldyou please tell me the actual values of C30, C31, C22, C17 and the capacitor which is near R51. One ofmy friend said though the schematic mention those values actual original c audio sr707 have used 25pf instead of C30, C31 / 25pf for C22, C17 and 56pf for the cap which is near R51.
Also could you please tell me what is the real impact if we lower the values as above mention. means instead of 220pf if we use 25pf for C31 and C30, can i increase the Bass or can I increase the Trebles.
hope you will help me
Once I send you the C Audio Sr707 schematic. Hope you have it if not i can re send it to You Sir.
Thanks
dinesh
Hope you remember me. Again i need a valuable help from you. Couldyou please tell me the actual values of C30, C31, C22, C17 and the capacitor which is near R51. One ofmy friend said though the schematic mention those values actual original c audio sr707 have used 25pf instead of C30, C31 / 25pf for C22, C17 and 56pf for the cap which is near R51.
Also could you please tell me what is the real impact if we lower the values as above mention. means instead of 220pf if we use 25pf for C31 and C30, can i increase the Bass or can I increase the Trebles.
hope you will help me
Once I send you the C Audio Sr707 schematic. Hope you have it if not i can re send it to You Sir.
Thanks
dinesh
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