120W amplifier

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#21
Thank you all for the ideas and suggestions you gave me. My next project will be some new design that`s more reliable. But still I will finish this project ... it is not so expensive and still I have the transformer and power supply circuits ready.
I was curious about T3 and T4 - are they powerful enough to empower the end stage transistor or it is better to change them with some of these: BD139/140, MJE340/350, MJE15032/MJE15033 or MJE15030/MJE15031

Kind regards
 
#23
is this your recommendations .... to a beginner ? so far it seems that he hasn't got the ability to evaluate the existing circuit and operations and benefits of darlington or not what makes you think that he is able to actually compose a circuit from scratch adding all the things you describe ?

Lets be realistic here .... Dear word ..skip anything that works with darlington then if you wana keep it simple go for a DX amplifier or a P3A both of them way too well documented

If you go for something more complex a leach style amp is the next step

Kind regards
sakis
 
#25
🙂 I was asking about the driver transistors. Nothing more. Just want to finish it - I hate trowing away something that I already have began.
I have stopped reading technical literature long time ago (it was at high school). Now I am working as a pharmacist.
I would like to thank to Tekko for his attention to my project and would like to ask, can you provide me with pcb for your version of this amplifier?
Best regards
 
#27
Sorry I think there is some misunderstanding. I really appreciate you (Tekko) willing to help me. Just the modification you have shown me is too sophisticated for me and have to rebuilt the PCB ... I don`t have so much time to learn my self how to work on the different programs capable to draw the PCB. At school I had time to read more and to spend more hours experimenting. Now I am working and trying to have some social live in the rest of the day, but still want to get my project finalized.
Regards
 
#29
So is there are big difference between original T3 - T4 transistor and the ones you suggest me to use - unless the power. I am asking because I think transistors from original schematic are not powerful enough to run the final stage transistors. In my previous tests they (T3-T4) got little worm after 15 minutes working with normal 8 Ohm speakers.
Regards
 
#30
_world_ said:
So is there are big difference between original T3 - T4 transistor and the ones you suggest me to use
Click to expand...

Due to the way the output driver is permanently connected to the output transistor, packaged darlington transistors (and circuits they are in) are very unique. Changing even with similar darlington, the result is often like sky and earth, sometimes even does not work at all. And especially the Philips parts are hard to find the substitute (if available at all).

Changing the parts is similar like designing a new amp. And you will have difficulty to find the model if you want to simulate it. Do you use sim software?
 
#32
Sorry I got lost 🙂 What does mean IPS, VAS ? I saw three transistors on the heatsink ... is this all circuit or there is more that you didn`t show on the video? And I do not understand the lines in the osciloscope .... please translate to me what was the purpose of the video. You mean this is the original design with just little bit lower voltage?
Regards
 
#33
IPS = InPut Stage, these are the two transistors with the emitters joined together and mounted face to face. VAS = Voltage Amplification Stage and is the transistor tucked between Base and Collector of the lower output transistor with the 56pF cap on it.

The oscilloscope is showing the audio output from the amp. The third transistor on the heatsink is the thermal compensation bias transistor.
 
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