Hi guys,
I am looking for a quick build power amp with little effort. RTR kits seem to fit the bill to drive a pair of DIY , 3 way inefficient bookshelf speakers that are a bit power hungry. I was initially looking at class D kits to power them, but since I have zero experience with class d builds, this kit caught my eye. Looks like a great price, its dual channel and quite versatile in operating voltages. Seems to have speaker protection built in and uses sanken outputs similar to the Denon/ Luxman designs of the late 80's.
Here is the link: https://www.ebay.com/itm/222529950811
Has anyone used it or know what amplifier its based on?
With much appreciation
K-Amps
I am looking for a quick build power amp with little effort. RTR kits seem to fit the bill to drive a pair of DIY , 3 way inefficient bookshelf speakers that are a bit power hungry. I was initially looking at class D kits to power them, but since I have zero experience with class d builds, this kit caught my eye. Looks like a great price, its dual channel and quite versatile in operating voltages. Seems to have speaker protection built in and uses sanken outputs similar to the Denon/ Luxman designs of the late 80's.
Here is the link: https://www.ebay.com/itm/222529950811
Has anyone used it or know what amplifier its based on?
With much appreciation
K-Amps
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the 2sa1494 are 200W devices that are down to 125W @ 60Vce and down to 80W @ 80Vce
I would not use +-80Vdc supply rails for these devices.
If you use +-60Vdc supplies, then you might get 160W into 8ohms (50.6Vpk) from the two pair output stage. (2pr @ 200W = 800W/5 = 160W of maximum output into severe reactance speakers.)
I would not use +-80Vdc supply rails for these devices.
If you use +-60Vdc supplies, then you might get 160W into 8ohms (50.6Vpk) from the two pair output stage. (2pr @ 200W = 800W/5 = 160W of maximum output into severe reactance speakers.)
Thanks Andrew. Having interacted with you for over a decade, I knew I could count on you, to ensure the OP stage was adequately sized, specifically with thermal deration. 
I was planning to replace the 2 Sanken pairs with 8 pairs of njw0281/0302's and running it with 92v supplies. What I cant say is if the drivers supplied will be able to drive the mod.
I was planning to replace the 2 Sanken pairs with 8 pairs of njw0281/0302's and running it with 92v supplies. What I cant say is if the drivers supplied will be able to drive the mod.
Beta droop needs to be examined when peak transient currents into the load are passing.
4ohm resistive sounds like a test load for an 8ohms capable amplifier.
I suggest that you analyse the output current requirement for speakers that can demand transient currents approaching and even exceeding three times the peak current into a resistive equivalent load.
that would require your 92Vdc supply rail to push current around the load circuit with a 2r67 resistor in there.
Assuming the maximum output voltage were ~80Vpk, then the peak curent would be 30Apk
If the drivers see an output transistor hFE of 80 at that loading, then they have to pass a transient of ~ 0.375Apk and each output is passing ~3.8Apk.
Many driver transistors of around 1A to 2A rating can manage that and their droop should not be too bad to become a severe loading on the pre-driver or VAS stage.
What driver quiescent current is required to bias the 8pr output stage? and how big would their heatsink/s need to be?
4ohm resistive sounds like a test load for an 8ohms capable amplifier.
I suggest that you analyse the output current requirement for speakers that can demand transient currents approaching and even exceeding three times the peak current into a resistive equivalent load.
that would require your 92Vdc supply rail to push current around the load circuit with a 2r67 resistor in there.
Assuming the maximum output voltage were ~80Vpk, then the peak curent would be 30Apk
If the drivers see an output transistor hFE of 80 at that loading, then they have to pass a transient of ~ 0.375Apk and each output is passing ~3.8Apk.
Many driver transistors of around 1A to 2A rating can manage that and their droop should not be too bad to become a severe loading on the pre-driver or VAS stage.
What driver quiescent current is required to bias the 8pr output stage? and how big would their heatsink/s need to be?
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And thats where lies the rub, I don't know what bias current requirements are for the driver. Adding more output pairs reduces beta droop, but since the driver needs to supply bias to all OP devices, it will get loaded a bit, so under what conditions will it be better or worse for the driver stage?
I'll give you a starter.
With a double EF output stage: single driver and 8 outputs.
Re = 0r22, Vre = 24mVre, then Ibias = 109mA
@ hFE = 100 then Ib = 1.09mA
driver output = 8times 1.09mA = 8.7mA
driver bias ~10times = 87mA, leaving Iedriver=~78mA
Driver Pq = ~92*0.087 = 8W = mighty big heatsink
Low value base stoppers will allow you to check some of these currents during testing.
With a double EF output stage: single driver and 8 outputs.
Re = 0r22, Vre = 24mVre, then Ibias = 109mA
@ hFE = 100 then Ib = 1.09mA
driver output = 8times 1.09mA = 8.7mA
driver bias ~10times = 87mA, leaving Iedriver=~78mA
Driver Pq = ~92*0.087 = 8W = mighty big heatsink
Low value base stoppers will allow you to check some of these currents during testing.
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Andrew,
It wasn't a nice answer.
I can project my own amplifier, but a nice and cheap one is always welcome.
If I have schematics I can SIM and see if it is really good.
Have you any money gain promoting this amplifier?
Thank you for your answer.
I also asked schematics from other seller as the one you appointed finished their sale.
If I got schematics I will post here with simulations files to other see.
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