I found more about it here: https://exclusive-audio.jp/en/produ...ucts-class-a-single-no-return-power-amplifier
.. Including a price tag...
.. Including a price tag...
Nice to meet you, I'm using translation software so I'm not sure if my message will be conveyed well.
I borrowed an AMP-8510A and listened to it in my listening room.
Unfortunately, GaN has not been completed and is not currently for sale.
It can output up to 3W, but it seems to die at any output higher than that.
The other MOS-FETs, SiC ULI-MOS-FETs, had very good sound quality.
The ULI-MOS in particular had outstanding sound quality, and it was my first experience with an amplifier of such quality.
I'm not familiar with circuits so I can't answer technical questions, but I can get in touch with the designer and seller of this amplifier.
It may take some time, but I think I can act as an intermediary for questions and answers.
I borrowed an AMP-8510A and listened to it in my listening room.
Unfortunately, GaN has not been completed and is not currently for sale.
It can output up to 3W, but it seems to die at any output higher than that.
The other MOS-FETs, SiC ULI-MOS-FETs, had very good sound quality.
The ULI-MOS in particular had outstanding sound quality, and it was my first experience with an amplifier of such quality.
I'm not familiar with circuits so I can't answer technical questions, but I can get in touch with the designer and seller of this amplifier.
It may take some time, but I think I can act as an intermediary for questions and answers.
"Circuit Consideration: Protection Circuit
I had seen some examples online that said GaN analog amplifiers had stability issues, so I was proceeding with the project carefully, but I have blown GaN FETs twice myself (excluding careless damage during measurement and manufacturing). In addition to thermal runaway due to insufficient heat dissipation, GaN also seemed to be damaged by surge voltages (?) that seemed to occur when the power was turned on and off. When damaged, an abnormal through current flows through the upper and lower GaN-FETs, damaging the source resistor as well. With a power supply voltage of ±180V, there were several times when I had to rebuild the entire output board because it would take the surrounding circuitry with it.
Therefore, we also considered protection circuits to reduce the failure rate.
Heat generation was dealt with by suppressing the bias current, etc., but for the GaN-FET, which was still unusually susceptible to damage, we added overvoltage protection (gate input protection) against surge voltages, etc. Although we still do not know the detailed mechanism by which the damage occurs, we believe that adding the protection circuits below has prevented it from occurring.
- Conventionally
(see diagram below), the MOS-FET gate resistance was R1 and the source resistance was R2. However, since the impedance of electrostatic headphones is large, about 145kΩ , the source resistance of an electrostatic headphone amplifier can be increased to several tens of ohms to several hundred ohms.
- GaN-FET protection
(1) Vgs limiting Zener diodes DP31 and DP32 , and (2) gate input protection (clamp diodes) DP11 and DP12 are assumed to be effective. (3) Surge voltage absorption: The body diode equivalent DP21 was added because it is present in MOS-FETs but not in GaN-FETs, but to be honest, its effectiveness is unclear.
(When I looked up literature on the Internet, I found that these external diodes are used in protection circuits for switching power supplies, so they may have been essential when using GaN FETs. I just didn't study enough.)"
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"Power supply abnormal voltage protection
If an abnormal power supply is applied due to output GaN FET damage or power supply trouble, both the upper and lower boards of the driver will be damaged (I have experienced this once). In order to reduce this as much as possible, we have considered adding protective diodes DP1 and DP2 near the power connector to reduce abnormal voltage . In this case (on the primary side of the power transformer), we are assuming protection by blowing the power supply fuse , so it is necessary to select an appropriate fuse. (If the holding current is too large, it will not blow, and if it is too small, the inrush current when the power is turned on will exceed the fusing current.)
Power supply inrush current protection
Prevention of inrush current when the power is turned on is not implemented in this subproject. It can be easily configured using a solid-state timer (relay), but there is also a track record of building it using a relay and a discrete delay-on circuit. We will prepare it if necessary in the future.
Output overcurrent protection circuit
As for output FET overcurrent protection , we have not found any examples of successful prevention of GaN FET damage in the online DIY articles, so we have put it on hold. In addition, electrostatic headphone amplifiers have a high resistance ( R70 ) for output protection and electric shock prevention, so some protection is actually built in. However, it is not effective in preventing damage to GaN-FETs.
I really like the sound output from GaN FETs, but I think the protection circuit needs to be improved in order to continue using them safely.
That being said, I would like to continue using them as they are for the time being and see how stable they are over the course of a year."
If an abnormal power supply is applied due to output GaN FET damage or power supply trouble, both the upper and lower boards of the driver will be damaged (I have experienced this once). In order to reduce this as much as possible, we have considered adding protective diodes DP1 and DP2 near the power connector to reduce abnormal voltage . In this case (on the primary side of the power transformer), we are assuming protection by blowing the power supply fuse , so it is necessary to select an appropriate fuse. (If the holding current is too large, it will not blow, and if it is too small, the inrush current when the power is turned on will exceed the fusing current.)
Power supply inrush current protection
Prevention of inrush current when the power is turned on is not implemented in this subproject. It can be easily configured using a solid-state timer (relay), but there is also a track record of building it using a relay and a discrete delay-on circuit. We will prepare it if necessary in the future.
Output overcurrent protection circuit
As for output FET overcurrent protection , we have not found any examples of successful prevention of GaN FET damage in the online DIY articles, so we have put it on hold. In addition, electrostatic headphone amplifiers have a high resistance ( R70 ) for output protection and electric shock prevention, so some protection is actually built in. However, it is not effective in preventing damage to GaN-FETs.
I really like the sound output from GaN FETs, but I think the protection circuit needs to be improved in order to continue using them safely.
That being said, I would like to continue using them as they are for the time being and see how stable they are over the course of a year."
This is the answer from the designer.
I looked at the data sheets for GaN devices that seem to be usable, but the protection circuit listed is a switching protection circuit, not a DC protection circuit.
In fact, in the first prototype, the 3W GaN single works without any problems.
The reason it breaks at the 10W output setting is the drop in maximum loss due to the rise in chip temperature.
It may be possible if the chip temperature can be kept at 25 degrees with air or water cooling, but I don't think the sound is worth the cost of going that far.
Considering that devices with low ON resistance also have low output impedance and are highly rated, I don't think there is any point in trying GaN, which has a relatively high output impedance, and taking the risk.
GaN will be compatible if a compatible device is released, but at the moment I can't find any device that can support DC operation.
At the moment, there are no compatible devices, so I can't say anything.
I will test a device that supports 30V 10A DC operation at a device temperature of 25 degrees.
Does anyone know?
For now, it seems the maximum is 30V3A.
If I can find an element that can withstand DC operation, I'll try making a prototype.
I looked at the data sheets for GaN devices that seem to be usable, but the protection circuit listed is a switching protection circuit, not a DC protection circuit.
In fact, in the first prototype, the 3W GaN single works without any problems.
The reason it breaks at the 10W output setting is the drop in maximum loss due to the rise in chip temperature.
It may be possible if the chip temperature can be kept at 25 degrees with air or water cooling, but I don't think the sound is worth the cost of going that far.
Considering that devices with low ON resistance also have low output impedance and are highly rated, I don't think there is any point in trying GaN, which has a relatively high output impedance, and taking the risk.
GaN will be compatible if a compatible device is released, but at the moment I can't find any device that can support DC operation.
At the moment, there are no compatible devices, so I can't say anything.
I will test a device that supports 30V 10A DC operation at a device temperature of 25 degrees.
Does anyone know?
For now, it seems the maximum is 30V3A.
If I can find an element that can withstand DC operation, I'll try making a prototype.