Is it your plan to convert this prototype to a "cleaner" prototype with a higher WAF?
I am somewhere in between that. I don't think my MoFo setup with BA3-pre has a high WAF but high enough for me…….at least for the moment
Nice setup there Meper, this is purely a prototype setup and as such, has been great for testing. Installing the amp PCB and MOSFET into the heatsink CPU cooler is a 30 second operation with a hex screw driver. I can’t imagine how slow this would have been had I used a traditional case for development.
Next step is for a proper amp PCB and single rail cap Mx layout. Then it can be beautified and put in some sort of chassis. The open air extruded rails look quite nice.
I am planning on using a new compact cap Mx (MrEvil type) with a new integrated active bridge using LT4320 and a pair of SMT dual N channel MOSFETs that will allow up to 5amps with almost no heat output (no heatsink needed).
I have "only" 3A bias. With 26 VDC this is about 80W in heat. It is what the heatsink can take (approx. 54 C). The choke can take much more but I am very satisfied so far with the sound and the BA3-pre is a good match. It takes 1/2 - 1 hour of heating up before the sound quality is at maximum. Good to hear that your plan is to make a final version of the MoFo!
I salvaged 3 of these heat sinks quite a while ago. What are the chances? I can just remove all other devices except one and solder on to what is remaining of the leads. I believe the IRFP250 devices are OK. Hopefully the heat sink is large enough.
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Finally up and running in full stereo with MOAMOFO. Currently operating at 36Vdc rail, 4.35A bias current, and driven by Melbourne Preamp. Once I upgrade the power supply trafo on the Melbourne to +/-28v (currently 24.5v), should be good for almost 50w into 6.8ohms. Right now in main listening room and driving very inefficient (82.4dB sensitive) but superb sounding transient perfect ScanSpeak 10F/Dayton RS225 FAST speakers. There is an abundance of power and no sense of strain. Sounds wonderful.
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If you are adventurous, you could cut all three heat sinks in half, screw 3 of them vertically into an aluminum plate at least 5mm thick of equal dimensions,
to use like a traditional case as you see in the store.
This would work well if you are using external laptop power supplies.
to use like a traditional case as you see in the store.
This would work well if you are using external laptop power supplies.
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This is 36V ~10A SMPS by Meanwell and is $37 but has a small fan. If replaced by Noctua, could be made very quiet. Ideally needs to be about 39v to allow 2v drop through cap Mx for soft start and cleanup.
LRS-350-36 MEAN WELL USA Inc. | Power Supplies - External/Internal (Off-Board) | DigiKey
LRS-350-36 MEAN WELL USA Inc. | Power Supplies - External/Internal (Off-Board) | DigiKey
There are several cap Mx threads. The ones that work well with a big Class A amp need to have adjustable voltage drop of circa 1.3v to 2.5v. Using a simple MOSFET like the standard Juma Easy Peasy one has 4v drop and that is just too much excess heat burned off.
The ones I have tried and work include the JasonKeutermann MrEvil cap Mx, and the Mark Johnson / Prasi BJT cap Mx.
They are in these threads.
Simplified MrEvil / PMI Capacitance Multiplier
Juma's Easy-Peasy Capacitance Multiplier
The ones I have tried and work include the JasonKeutermann MrEvil cap Mx, and the Mark Johnson / Prasi BJT cap Mx.
They are in these threads.
Simplified MrEvil / PMI Capacitance Multiplier
Juma's Easy-Peasy Capacitance Multiplier
I have a problem. I have constructed two amps as per the recommended boards, components including the 193T's. I am using a same spec Dell power supply.
I have biased them as recommended. Voltage across the inductor is 1.10 vdc
Problem is no sound output. I have done some basic measurements. DC voltage in is 19.75 vdc. Voltage across the transistor is as follows. Gate 5.41 vdc, Drain 19.75 vdc, Source 1.10 vdc.
Suggestions please
I have biased them as recommended. Voltage across the inductor is 1.10 vdc
Problem is no sound output. I have done some basic measurements. DC voltage in is 19.75 vdc. Voltage across the transistor is as follows. Gate 5.41 vdc, Drain 19.75 vdc, Source 1.10 vdc.
Suggestions please