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Wanted: DIY amplifier builder with experience. I need a 0.7 ohm stable amplifier

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Audiophilenoob

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Joined 2005
soundsolutionsaudio.com/forum/index.php?showforum=44
#1
Hello all,

I need an amplifier to power a pair of DIY ribbons... final load should be around 1 ohm... but I'm going to say 0.7 to be safe

Any amp type will do, though class A is preferred (I know that this design is tough)... don't worry if Class A is too complicated

Linesource on here had posted several schematics to make this amp...

but again... design doesn't matter

Optimially I would like it to have as low of distortion as possible...

Requirements:
>0.01% THD
Stable daily at 0.7 ohms
2 channel amplifier
gain control knob
input and output RCAs/XLR/.25" microphone (any of these... not all)
35-55 watts per channel (ideally on the high end)

mosfets are fine, as all are topographies... no need to build the amp case... you can just supply the put together PCB board...

Here's linesources schematic:
http://www.diyaudio.com/forums/attachment.php?s=&postid=448463&stamp=1091084434

Quote me prices people 😀 and thank you in advance
 
#4
ACD said:
You can use this good old amp...Just have the person making it for you to add lots of output devices 😉
Click to expand...

I currently have three devices per rail. I'll see how low I can drive it later this week!

What sort of power do you need? I imagine 5-10w should be more than enough if your sensitivity is that good. That means the rail voltage can be dropped significantly from the 35-40V used in the current prototypes.

Board orders will be taken soon.
 
#5
pinkmouse said:


I currently have three devices per rail. I'll see how low I can drive it later this week!

What sort of power do you need? I imagine 5-10w should be more than enough if your sensitivity is that good. That means the rail voltage can be dropped significantly from the 35-40V used in the current prototypes.

Board orders will be taken soon.
Click to expand...


10 watts would work... but I would like 25-35 for overhead...

are you willing to make me one?

I understand all those schematics I don't know if I have the skills to make it.... I can try I guess
 
#7
#11
Hi Audiophilenoob,

You may want to build your ribbons first and have your ears decide if this is true love, or just infatuation with a 150 lb Heavy Metal sculpture.

There are many amps that are stable into 2 ohms. You can buy or make a non-inductive 1 ohm resistor to put in series with your 1 ohm tweeter ribbon to trade-off 50% of the amp's power for transformer-free direct drive. A 100db/watt speaker only needs a few watts, but the first watt must have very low noise and distortion.

Many amplifier topologies can be adapted to drive a 1 ohm ribbon by dropping the output power supply to about 8 volts. There are high current 12V CT and 12.6V CT filiment transformers availble. The low driver stage voltages allow simple topologies with very low noise transistors to be used. The low output voltages make it simple to keep Class-A bipolar output transistors in the safe operating area.
 
#13
LineSource said:
Hi Audiophilenoob,

You may want to build your ribbons first and have your ears decide if this is true love, or just infatuation with a 150 lb Heavy Metal sculpture.

There are many amps that are stable into 2 ohms. You can buy or make a non-inductive 1 ohm resistor to put in series with your 1 ohm tweeter ribbon to trade-off 50% of the amp's power for transformer-free direct drive. A 100db/watt speaker only needs a few watts, but the first watt must have very low noise and distortion.

Many amplifier topologies can be adapted to drive a 1 ohm ribbon by dropping the output power supply to about 8 volts. There are high current 12V CT and 12.6V CT filiment transformers availble. The low driver stage voltages allow simple topologies with very low noise transistors to be used. The low output voltages make it simple to keep Class-A bipolar output transistors in the safe operating area.
Click to expand...


true I should wait and make sure this is ideal for me...

I don't want to add a resistor.. it is not the ideal solution and since I will have to purchase SOME amp for these I figured it might as well be the best one possible
 
#15
It's hard to argue when your right!

There are many amps that are stable into 2 ohms. You can buy or make a non-inductive 1 ohm resistor to put in series with your 1 ohm tweeter ribbon to trade-off 50% of the amp's power for transformer-free direct drive. A 100db/watt speaker only needs a few watts, but the first watt must have very low noise and distortion
Click to expand...

This is the simplest method and most likely the cheapest. A properly paralleled number of LM3886 could even do this!

Mark

Allways willing to add flies to the ointment😉
 
#17
LineSource said:
Hi Audiophilenoob,

You may want to build your ribbons first and have your ears decide if this is true love, or just infatuation with a 150 lb Heavy Metal sculpture.

There are many amps that are stable into 2 ohms. You can buy or make a non-inductive 1 ohm resistor to put in series with your 1 ohm tweeter ribbon to trade-off 50% of the amp's power for transformer-free direct drive. A 100db/watt speaker only needs a few watts, but the first watt must have very low noise and distortion.

Many amplifier topologies can be adapted to drive a 1 ohm ribbon by dropping the output power supply to about 8 volts. There are high current 12V CT and 12.6V CT filiment transformers availble. The low driver stage voltages allow simple topologies with very low noise transistors to be used. The low output voltages make it simple to keep Class-A bipolar output transistors in the safe operating area.
Click to expand...

ideally for a resistor a non-inductive 1 ohm with 1% tolerances?

any certain types that I should pick up for testing?
 
#19
Hi,
I'm not a valve head so I'm talking out the top of my hat.
Most valve amps are transformer coupled to the load and they use a fixed turns ratio to determine the nominal load value.
It seems to me that you specify the turns ratio to suit 0r5, 0r7, 1r0 instead of the usual 4r & 8r.
When setting it up the designer will ensure it is stable.
 
#20
Can tubes be stable into .7 ohms?
Well if the output transformer is wound for a 1ohm output probably they can - but I thought you were trying to avoid a transformer...

Seems in the distant past I have seen a transformer coupled amp with 2 and maybe 1 ohm taps, but it might have been one of those McIntosh transistor amps with output transformers.

Bill

Edit: Andrew beat me to the cooment🙂
 
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