I'm thinking of building a Rod Elliott Lateral MOSFET Power Amplifier and in the power supply section of the article he specs. the transformers that are usable as:
"AC Volts DC Volts VA Power (8Ω)
20-0-20 ±28V 100 40 Probably too low for most applications,
25-0-25 ±35V 100 50 Fine for use in a biamped hi-fi system
30-0-30 ±42V 160 80 Maximum voltage for low power version
40-0-40 ±56V 200 150 Recommended supply voltage for high power
50-0-50 ±70V 300 240 Absolute maximum. Can be used, but not recommended - aim for a lower voltage if possible"
I have a 30-0-30 300VA transformer that I would like to use so it is almost double the VA that Rod specifies, any chance that someone would please let me know if this is usable?
Project 101 - High Fidelity Lateral MOSFET power amplifier
Thanks.
"AC Volts DC Volts VA Power (8Ω)
20-0-20 ±28V 100 40 Probably too low for most applications,
25-0-25 ±35V 100 50 Fine for use in a biamped hi-fi system
30-0-30 ±42V 160 80 Maximum voltage for low power version
40-0-40 ±56V 200 150 Recommended supply voltage for high power
50-0-50 ±70V 300 240 Absolute maximum. Can be used, but not recommended - aim for a lower voltage if possible"
I have a 30-0-30 300VA transformer that I would like to use so it is almost double the VA that Rod specifies, any chance that someone would please let me know if this is usable?
Project 101 - High Fidelity Lateral MOSFET power amplifier
Thanks.
Thanks suzyj,
I'm building a two way active system and I have it on good authority that the Elliott mosfet amplifier is very good indeed.
I'm building a two way active system and I have it on good authority that the Elliott mosfet amplifier is very good indeed.
I see little in P101 that would qualify it as "very good indeed", although it should be easily good enough for a plate amp (not the very most demanding application in terms of distortion or damping factor anyway, simply because you are running into driver limitations first and there generally is no passive crossover to contend with to speak of, a dropper resistor for the tweeter aside).
No provisions are made for an output inductor, making for a worse tradeoff between slew rate and stability (via Miller capacitor C3) than it could be.
I am guessing he kept the bootstrapped resistor thing for the VAS in order to have more voltage swing for driving the MOSFETs. This generally comes with a hit in load immunity though.
The input stage is guaranteed to be unbalanced because current mirror currents do not equal input transistor currents (VAS base current is added to one side in between). Beta for an MJE350 at 10 mA is about 90, so that would be a ~110 µA imbalance.
If the tweeter section is going to have a dropper resistor in series anyway (significant bringing up load impedance), some adjustments to its amplifier section should be considered. Swap MJE350 for e.g. KSA1220(A) at ~3 mA or so, reduce C3 (maybe ~47 pF?), wind a ~1.5 µH air-core output inductor and add a 4.7 ohm 3 W parallel resistor to it.
No provisions are made for an output inductor, making for a worse tradeoff between slew rate and stability (via Miller capacitor C3) than it could be.
I am guessing he kept the bootstrapped resistor thing for the VAS in order to have more voltage swing for driving the MOSFETs. This generally comes with a hit in load immunity though.
The input stage is guaranteed to be unbalanced because current mirror currents do not equal input transistor currents (VAS base current is added to one side in between). Beta for an MJE350 at 10 mA is about 90, so that would be a ~110 µA imbalance.
If the tweeter section is going to have a dropper resistor in series anyway (significant bringing up load impedance), some adjustments to its amplifier section should be considered. Swap MJE350 for e.g. KSA1220(A) at ~3 mA or so, reduce C3 (maybe ~47 pF?), wind a ~1.5 µH air-core output inductor and add a 4.7 ohm 3 W parallel resistor to it.
sgrossklass, thanks for the reply. I appreciate your technical review/critique of the 101c. Have you listened to this amplifier in a Hifi set up?
P101 sounds great don't listen to bashers
I’m not going to critique Rod’s amplifier, as I think it’s a reasonable compromise between performance and complexity.
Why would you use a dropper resistor in an active 2 way setup? Surely that’s just burning power needlessly. Instead, just decrease the gain appropriately such that the tweeter and woofer are matched in level. You could even do that right on the power amp board, by varying Rf.
That’s certainly what I do with my own 2 way setups, and it works quite well.
OP: There’s no need to go for the full 100W for your tweeter amp, so you could run that with just one pair of lateral MOSFETs.
True, just remember to feed it from a lower voltage supply, not the higher voltage woofer amplifier.
Why so? I run my tweets off the same voltage as the woofer amps. There’s no way a pair of lateral MOSFETs on +/-56 is going to expire before the tweeter they’re driving.
That´s the point.
I worry about the tweeter, not the power devices.
With an unneccessarily powerful amplifier driving them , any pop or click can TOAST them.
How many output devices you use is irrelevant, short time full output from your tweeter amp is same as of the woofer one, if fed from same supply, and long enough to damage.
Just look at 99% of biamped power cabinets out there: they use a sensibly smaller amp for tweeters, from 50% to even 10% of main power amp rating.
Not to save money, making an extra power supply always will cost more than plain using available power rails.
Maybe they know something you don´t?
A couple of points to consider.
With this amplifier there are a couple of points you might like to consider:
The PCB is only available from Rod Elliot. You will have to order it directly from him. Refer to ESP - Complete Price List for instructions. His prices are reasonable.
It is likely that you will want to order Exicon ECX10N20 and ECX10P20 lateral mosfets from Profusion (See ECX10N20 Plastic Lateral MOSFET | Profusion). There may be delivery issues given the current state of the UK with COVID, BREXIT and BORIS. You will need to check with Profusion.
It might be a good idea to include some sort of speaker protection. Rod has options available at his web site.
Regards
Mr Tibouchina.
With this amplifier there are a couple of points you might like to consider:
The PCB is only available from Rod Elliot. You will have to order it directly from him. Refer to ESP - Complete Price List for instructions. His prices are reasonable.
It is likely that you will want to order Exicon ECX10N20 and ECX10P20 lateral mosfets from Profusion (See ECX10N20 Plastic Lateral MOSFET | Profusion). There may be delivery issues given the current state of the UK with COVID, BREXIT and BORIS. You will need to check with Profusion.
It might be a good idea to include some sort of speaker protection. Rod has options available at his web site.
Regards
Mr Tibouchina.
Renesas 2SJ162/2SK1058 latfets are available from Germany (Reichelt). The ones I got from them are originals.
Tibouchina said:
("It might be a good idea to include some sort of speaker protection. Rod has options available at his web site")
Thank you for that advice, are there issues specific to the P101 that cause you to say that?
("It might be a good idea to include some sort of speaker protection. Rod has options available at his web site")
Thank you for that advice, are there issues specific to the P101 that cause you to say that?
Speaker Protection
The amplifier is robust and the probability of failure is just as low as other lateral MOSFET amplifiers. But, it is likely that you want to protect your investment in speakers. So speaker protection is generally a good idea for most of us.
The amplifier is robust and the probability of failure is just as low as other lateral MOSFET amplifiers. But, it is likely that you want to protect your investment in speakers. So speaker protection is generally a good idea for most of us.
@Tony D.
Speak to Rod directly. He is extremely helpful, and will give you straight answers; there is no BS with him.
Speak to Rod directly. He is extremely helpful, and will give you straight answers; there is no BS with him.
The picture of the FET's on Reichelt's web page looks different from original Hitachi/Renesas, could you perhaps show pictures of what you received from Reichelt?
Latfets: Renesas on the left and Exicon on the right for reference.
