Hi Mooly
up to which rail voltage are the source resistors(0,22R) okay with 3W rating?
kr
chris
up to which rail voltage are the source resistors(0,22R) okay with 3W rating?
kr
chris
around -/+45v was the design target for the rails and delivering around 75wrms/8ohm the resistors see just over 1 watt dissipation. The series output series sees around 2 watt dissipation. These figures are worst case sine testing, music won't come anywhere near those levels.
hello，Mr mooly. I want to amplify the voltage and supply it separately, what happens if the ± is different? I think it should work, but will the metrics be lowered? Can you simulate it?
If you increase the positive rail above +45V, Q3 is likely going to be above its derated thermal limits. It already runs right on the edge with +45V rails. Consider replacing with KSA1381E. It works in simulations and will handle the dissipation better. However, it is untested and not pin compatible with 2N5401.
May we ask what the reason is for running different rail voltages?
May we ask what the reason is for running different rail voltages?
Maybe this will help having a dual power supply. Just a thought.
If you don't feel like winding transformers I have another schematic for you with discreet components only. But this is going beyond the scope of this thread.
I'm all in favour of SMPS for many things rather than big bulky linear supplies. Simple designs running 'open loop' without complex feedback should be fine for power amps. That one kind of reminds me slightly of the old Sony Pulse Locked Power Supply although they ran at a low frequency compared to modern designs and used all discrete bjt's.
I'm thinking of the really early ones like the TA-F6B
http://www.thevintageknob.org/sony-TA-F6B.html
http://www.thevintageknob.org/sony-TA-F6B.html
We are deviating from the subject again Mooly. Someone amongst the police is going to block me again. I suppose if you outrank him I am okay.
I thought it might help some to show the calculations for the thermal limitations of the 2N5551/2N5401 devices.
We can start with the device dissipation in the VAS (Q5) and VAS-CCS (Q3) positions. The design runs with a VAS current of 6.2mA on ±49V rails.
There is a voltage drops from R5 and R12, but it is small. We will ignore it for simplicity. This puts our dissipation at:
49V x 6.2mA = 304mW
We can can consult the datasheet for 2N5551/2N5401 for the following specifications
Total Device Dissipation @ TA = 25°C: 625mW
Derate above 25°C: 5mW/°C
Thermal Resistance, Junction−to−Ambient: 200°C/W
Based on this, temperature rise will be:
304mW x 200°C/W = +61°C
And our de-rated power rating is:
625mW - (61°C x 5mW/°C) = 321mW
From this we can see there is very little margin to increase the rail voltages above 49V. Additionally, an argument can be made that 49V leaves too little safety margin for worse case mains/PSU regulation. For example, if the rails run 10% high, we get the following:
Dissipation: (49V x 110%) x 6.2mA = 334mW
Junction Temp Rise: 334mW x 200°C/W = +67°C
De-rated Power Rating: 625mW - (67°C x 5mW/°C) = 290mW
If this were a new design, this might be a concern. However, Mooly has had his build in steady use for many years without issue. Safe to say it is a proven design, if built to the his stated specs.
We can start with the device dissipation in the VAS (Q5) and VAS-CCS (Q3) positions. The design runs with a VAS current of 6.2mA on ±49V rails.
There is a voltage drops from R5 and R12, but it is small. We will ignore it for simplicity. This puts our dissipation at:
49V x 6.2mA = 304mW
We can can consult the datasheet for 2N5551/2N5401 for the following specifications
Total Device Dissipation @ TA = 25°C: 625mW
Derate above 25°C: 5mW/°C
Thermal Resistance, Junction−to−Ambient: 200°C/W
Based on this, temperature rise will be:
304mW x 200°C/W = +61°C
And our de-rated power rating is:
625mW - (61°C x 5mW/°C) = 321mW
From this we can see there is very little margin to increase the rail voltages above 49V. Additionally, an argument can be made that 49V leaves too little safety margin for worse case mains/PSU regulation. For example, if the rails run 10% high, we get the following:
Dissipation: (49V x 110%) x 6.2mA = 334mW
Junction Temp Rise: 334mW x 200°C/W = +67°C
De-rated Power Rating: 625mW - (67°C x 5mW/°C) = 290mW
If this were a new design, this might be a concern. However, Mooly has had his build in steady use for many years without issue. Safe to say it is a proven design, if built to the his stated specs.
Maybe it is a bold statement, but if you feel that doubling up on the output devices is feasible and no space constraints, then that would be a solution.
That's great Brian 👍 very nicely set out
-/+45V was really the target value for the original design and yes they do run quite/very warm but there have been no reliability issues whatever in all the years and thousands of hours it must have on the clock. The only 'failure' in all that time has been the 'tarnished relay syndrome' and the relays were replaced with solid state versions.
The green illuminated mains rocker switch (an RS part) is pretty dim compared to how it should be. It uses a neon and resistor internally.
-/+45V was really the target value for the original design and yes they do run quite/very warm but there have been no reliability issues whatever in all the years and thousands of hours it must have on the clock. The only 'failure' in all that time has been the 'tarnished relay syndrome' and the relays were replaced with solid state versions.
The green illuminated mains rocker switch (an RS part) is pretty dim compared to how it should be. It uses a neon and resistor internally.
Hi Mooly - I agree that 45V is probably a safer voltage for 2N5551/2N5401 VAS/CCS devices and a single output pair. But like you said, a long history of use says 49V works in practice.
Thanks
It is planned to use "voltage multiplier", but the load is different, ±voltages is unbalanced。
Voltage amplification The voltage is higher than the current amplification, and the independent power supply is good for sn, I want to try it