300VA 2 x 18v trafo - which Class A?

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gilera

Member
Joined 2020
#1
After ditching the idea of using a my higher voltage transformer for a Class A build, a friend of mine has kindly given me a toroidal 300VA 18+18VAC transformer which he no longer needs.

I was planning on starting by building a low noise regulated power supply while sourcing the transistors and other bits for the amp.

Can anyone suggest some options for a Class A design which will match a transformer of this size and output? Primary focus is on the best quality sound, but also preferably something reasonable simple and without really hard to source matched transistors.

Hirage Le Monstre usually calls for 12-14V I think. Would this be too high?

JLH?

Hiraga Le Classe A 20W?

One of the Pass Labs designs?
 
#3
Linear regulated power supply requires its own heat sink. From the load current, select a bridge (with a margin). Taking into account ripple, the capacitance of the filter capacitor. Usually 10000 mf or more. The regulator must compensate for voltage fluctuations (20-30%). We take into account the minimum voltage on the regulating element.
You can get 35 V of stabilized voltage (or 2 * 18 V bipolar).
By complexity, the power supply circuit corresponds to the amplifier circuit JLH1969))).
Does your transformer have separate or connected secondary windings?
 
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#5
OldDIY said:
Does your transformer have separate or connected secondary windings?
Click to expand...

There are 4 wires coming of the secondary side. Do I guess you'd describe as 2 separate windings? It is described as 18 + 18.

My speakers are 8 ohms and I only require about 8-10W but am happy to scale up a bit to get the best use of the transformer.
 
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#6
You can make a separate unstabilized unipolar 24 V power supply per channel. This will give an amplifier output of 6-8 watts / 8 ohms.
Ready-made boards or kits can be bought cheaply in online stores (but wait a long time))).
You can assemble from parts on the breadboard quickly)))
 
#8
You think this transformer is best suited to JLH 1969?

Would it work with the 1996 version. It looks like bipolar 22V power supply, or can I not do this with my transformer? I have heard that this 1996 version is much better than original and easier to get transistors.
 
#9
1996 is done mainly as a headphone amplifier.
2003 (bipolar) make for more power.
1969 do to understand: "Do you need it"?
You can make bipolar unstabilized 2 * 24 v or stabilized 2 * 18 v.
All transistors are bought in one place (or in several)))
 
#12
gilera said:
After ditching the idea of using a my higher voltage transformer for a Class A build, a friend of mine has kindly given me a toroidal 300VA 18+18VAC transformer which he no longer needs.

I was planning on starting by building a low noise regulated power supply while sourcing the transistors and other bits for the amp.

Can anyone suggest some options for a Class A design which will match a transformer of this size and output? Primary focus is on the best quality sound, but also preferably something reasonable simple and without really hard to source matched transistors.

Hirage Le Monstre usually calls for 12-14V I think. Would this be too high?

JLH?

Hiraga Le Classe A 20W?

One of the Pass Labs designs?
Click to expand...
That transformer will fit nice for most First watt amps. F5, F6, M2X, aleph J +++. all this amps are 25W class A.
 
#13
Pass Aleph3 or Aleph30 are perfect for this trafo. No hard to get parts or need for complementary pairs. MOSFET matching is done easily on a breadboard. The bass control and detail on these Pass Aleph designs are just fantastic and the circuits are nice and simple.
 
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