SYMEF amplifier

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#1,241
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#1,242
Hi everyone,
On,
I really like this amplifier, and I would to finish it. Let me start by saying that I've finished schematic just now by Kicad, and then moving on to create the PCB : primarily because I am passionate about CAD, I have never developed PCBs for audio power amplifiers and this is the opportunity to learn many things for me; then because I recovered an old enclose with limited internal spaces, for which I will have to develop two PCBs with required dimensions. The questions I would to ask:

- in the circuit I have 2 gnd type: power gnd and signal gnd: how should I connect them?
1) together at the star center of the chassis ( so let them separate in the scheme);
2) directly short-circuited in the schematic > in the same pcb; ( I think so )
3) in the scheme by an RC parallel group (I've seen recently some schematics with this type of connection, or connected them by one low value resistor. In case: values?) ;

- what is the maximum power supply voltage? Can I supply with + - 55Volt? ( I think it's possible)

- It’s ok for you mount toshiba final bjts 5200 / 1943 ? ( other brands are obsolete and hard to find )?: excellent subustitutes?

- can I substitute NPN 2N5551 and PNP 2N5401 with other low noise bjts( maybe I have them at home) ?

- I’ve to match pairs bjt of differential stage and current mirror ( same specifics ) ?; (I think so)

- I've to join physically the schematic critical parts ? I mean for example: joining by heat shrinkable sheath ( or another way) input differential bjt Q18 and Q19…other example: joining by heat shrinkable sheath the mirror current Q13 and Q15 bjt …and so on...). ( I think yes)

Thanks in advanced. Un saluto ! Ros
 
#1,244
Within the pcb where the ground lands can be the local pcb star ground from where you source low current ground and high current ground. The purpose of the ground raise resistor is for discouraging high currents from using that path, sometimes the resistor isn't even necessary
 
#1,245
good morning guys, ciao On, thanks so much for your replies . The gnd star center configuration you reproduced above is exactly what I have always foreseen and implemented in my equipment, to avoid noise and ground loops risks. I must say that it has always well worked: they are very silent. I see that you haven't provided any answers about the union of bjts, so it's reasonable to think that it's not that crtitical.
Last question as a newbie:
I started routing the PCB just yesterday, and I have a dubt:
Q12 (MJE340), bjt dedicated to Vbias, is it mandatory mount it on the same heatsink of driver/final bjts ? What's up if I mount it stand alone on its heatsink, in the center of the PCB ? (certainly nicer and tidier to the eye ) . Thanks again , hand (have a nice day) 🙂
 
#1,246
Matching isn't all that critical for this circuit. The vbias bjt provides thermal feedback. The output stage isnt cfp. for fun you could have an experimental proof of concept pcb where its on its own heatsink, add board fuses and see how much bias and how long the output stage lasts before going quiet.
 
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