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DETAILED DESCRIPTION
WebPage for original schema and project: https://sound-au.com/project68.htm
Tested with 3 pairs SC5200 / SC1943 at 50+50V DC, at 4 ohms resistence, 100Hz, I get:
- 250W RMS at output (with 3 pairs of SC / SA).
- Up to 400W RMS drained (about 150W heat dissipatio).
I used an small heatsink, protected by 90ºC thermal switch to disconnect input signal.
With no fan, after ~5 minutes at full power, transistors get 100ºC and protection is enebled.
But with 120cm fan at up of heatsink, temperature become stable at 80/90ºC.
Changes from original projetc:
- Replaced R2 22k for 50k trimpot, to provide fine adjust (increase or decrease input signal).
- Original project uses 2 diodes between driver trasnsisitors MJE. But this causes excess of bias, getting them hot. So, one of this is removed in this project, with no difference in sound quality or signal continuity when sound is changing from NPN to PNP.
- Removed Q7 and Q8 power transistor drivers. Q5 and Q6 8A MJE becomes output drivers, with 100R to output.
- Add 4R7 in base of each power transistor.
- Changed output transistor resistors (R18-R21) to 0R22 - 5W.
Obs.:
There are 4 jumpers (A, B, C and D), all for low current.
This module needs high input signal voltage. So, need an good pre-amp to delivery at least 6vpp.
All power transistors and drivers are at same heatsink. Only driver Q4 I used at isolated small heatsink. Teperature stay normal, slightly warm at full load (250W output).
Output inductor is not in use. Its jumped in the board I´m using. After I project, I see this is not necessary. Use this if you consider necessary (ex: long cable to speaker).
Scheme and pcb is for 2 pairs of output transistor. Need much space for 6 power transistors plus 2 drivers in line. I'm usin 3 pairs at output, where one pair is off board, up others in same heatsink and with parallel connection. There are extra outputs in PCB for 2 more pairs (4 pairs in total).
When there are +49v / -49v power supply input, output maximum is +46v / -46v (92vpp) @ 4 ohms.
With results observed and using 4R7 in base of each output transistor, I suppose can be used up to 6 pairs of SC/SA. This would result in aprox. 900W drained from power source at 67+67v @ 4 ohms, and 500W RMS output power.
With 2 pairs SC / SA, use at maximum 200W RMS. Because each transistor will be near maximum dissipation capacity when hit 100ºC (60W is red line at 100ºC).
In general rule for genuine 150W transistors, use at maximum 100W RMS output for each pair.
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