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Old 5th September 2011, 07:25 AM   #1
radio is offline radio  Macedonia
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Unhappy 100W Hi-Fi amplifier-Help!?

Hi all!
I designed this amplifier under this schematic (Figure 1). Now I want to do some changes to the schematic because we need your help!
For the output transistor want to use of komplementary a pair 2SC2922/2SA1216, because you have to change the schematic?
What else should I change the schematic to improve the characteristics of this amplifier?
thanks and cheers!!
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File Type: pdf Figure 1 (For).pdf (86.1 KB, 177 views)
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Old 5th September 2011, 08:50 AM   #2
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Looks good from here. You could change the VAS (T5) to a Darlington.
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Old 5th September 2011, 09:33 AM   #3
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Quote:
Originally Posted by ingenieus View Post
Looks good from here. You could change the VAS (T5) to a Darlington.
OK I try will,...
Otherwise, the amplifier works fine like this, but the sound is soft Valve/Tube!!
I want to get one really defined the sound of solid-state!?
Is a good replacement for the T5 (BC517 or BD678 or,....) Darlinkton?!
Thanks and cheers

Last edited by radio; 5th September 2011 at 09:42 AM.
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Old 5th September 2011, 09:36 AM   #4
AndrewT is online now AndrewT  Scotland
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Well done.
the ratio of R4:R1 gives good symmetry of current balance in the LTP.
Change the emitter resistor Vr in the LTP to two accurately matched 51r resistors.

Add a trimmer (try5k) in parallel to R4 and use this to exactly balance the LTP emitter currents. The remaining offset will be the error in matching the LTP transistors Vbe + the error in LTP transistor hFE at the quiescent current times the difference in the base source resistances. You can reduce all of these to very low levels by selecting before assembly.

If the voltage across the LTP bjts are matched and the currents through the LTP bjts are matched then the two LTP transistors dissipate the same heat. Couple these two transistors thermally and the drift in output offset with warm up becomes quite low.

If protection T8 is triggered then T5 will be destroyed.
For the time being, do not fit any of the protection circuits. Learn how they work first.

Read up Baxandall's diode for a quasi output stage.
Then read about JLH's capacitor modification for the quasi. Leave space on the PCB for these few extra components.
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regards Andrew T.

Last edited by AndrewT; 5th September 2011 at 09:54 AM.
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Old 5th September 2011, 09:58 AM   #5
radio is offline radio  Macedonia
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Quote:
Originally Posted by AndrewT View Post
Well done.
the ratio of R4:R1 gives good symmetry of current balance in the LTP.
Change the emitter resistor Vr in the LTP to two accurately matched 51r resistors.

Add a trimmer (try5k) in parallel to R4 and use this to exactly balance the LTP emitter currents. The remaining offset will be the error in matching the LTP transistors Vbe + the error in LTP transistor hFE at the quiescent current times the difference in the base source resistances. You can reduce all of these to very low levels by selecting before assembly.

If the voltage across the LTP bjts are matched and the currents through the LTP bjts are matched then the two LTP transistors dissipate the same heat. Couple these two transistors thermally and the drift in output offset with warm up becomes quite low.

If protection T8 is triggered then T5 will be destroyed.
For the time being, do not fit any of the protection circuits. Learn how they work first.

Read up Baxandall's diode for a quasi output stage.
Then read about JLH's capacitor modification for the quasi. Leave space on the PCB for these few extra components.
I must admit I go weak English, .. so please all show the schematic (Figure 1).
Thanks for your help and cheers!
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Old 7th September 2011, 06:14 AM   #6
radio is offline radio  Macedonia
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Hi all!
If someone who has the possibility of a simulation done for this amplifier (according to the schematic) I'll be very grateful?!
I expect the other comments, do not worry they can be negative and criticizing!
In the end, what changes to the schematic need to do to connect the output instead of quasi-complementary pair of a complementary pair with 2SC2922/2SA1216?
thanks

Last edited by radio; 7th September 2011 at 06:21 AM.
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