Hiraga The Monster...

[chrille]

Anyone built this amp? Having problems finding the transistors...
Does the PSU have to be so big, I think it is over 0,5F/ch!
It looks like a very fine amplifier.

http://www.gmweb.btinternet.co.uk/monster31.htm

[halojoy]

Originally posted by chrille
Anyone built this amp? Having problems finding the transistors...
Does the PSU have to be so big, I think it is over 0,5F/ch!
It looks like a very fine amplifier.

http://www.gmweb.btinternet.co.uk/monster31.htm

It is a Class A amplifier.
Do you know how much idle Current it is?
It is also a Current feedback amplifier,(fb goes to emitter of input transistors)
and they are a little more demanding on Power Supply things/disturbance.
In this amplifier it is also not possible to decouple
the pre- and output power supply from eachother.

But you are right. It is a great amplifier!
Only 8 watts.
But those 8 watts will be of very high quality

Like first 8 watts of a 100-200 watts normal class AB amp, maybe.

/halo

[P.Lacombe]

In this amplifier it is also not possible to decouple
the pre- and output power supply from eachother

Halojoy

This is the reason why monstrous capacitors are needed.

This amplifier can give very superior sound quality, but is now very difficult to build, because of the very hard to find transistors. Substitutes are not possible without audible degradation of the sound quality.

Regards, Pierre Lacombe.

[Nelson Pass]

I don't think there's a conceptual reason you can't
substitute devices on this amplifier without degradation.
There was nothing particularly magic about these parts
and you might be able to find better in later chips.

[halojoy]

Originally posted by Nelson Pass
I don't think there's a conceptual reason you can't
substitute devices on this amplifier without degradation.
There was nothing particularly magic about these parts
and you might be able to find better in later chips.

I agree with Nelson.
There are even better substitutes of transistors.
Not to mention low voltages high uF Electrolytic Caps.
And toroid trafos.

Regarding power supply to suit this amplifier,
there is a lot to find in Pass Sites and Forum.
This class A amplifier is a bit like some Pass Amplifiers
when it comes to what is needed in a pure and well filtered supply.

An alternative to big cap bank is
a cap-inductor-cap filter (CLC) that the Pass-builder-guys
sometimes uses and Nelson recommends.
A big selfmade air-inductor is a lot cheaper
then those big high quality electrolytes, like RIFA and those.

The good thing regarding the Caps to this amp is
the low voltage. 25 volts caps are half the price of 50 volts.

/halo

[SvErD]

Originally posted by P.Lacombe
This amplifier can give very superior sound quality, but is now very difficult to build, because of the very hard to find transistors. Substitutes are not possible without audible degradation of the sound quality.

Here are some suggested replacement transistors

http://www.gmweb.btinternet.co.uk/hiragatrans.htm

[RobPhill33]

When substituting transistors is it imparative that the maximum current and voltage ratings are the same as the original?

[halojoy]

Originally posted by RobPhill33
When substituting transistors is it imparative that the maximum current and voltage ratings are the same as the original?

The important is not that it is same,
but that the substitute can take and work well
at the current and the voltage that is in the circuit.
Of course if you have ratings same or higher than the original
it is never any problems.

But if you in a circuit with 24 max voltage,
substitute the original transistor, 45 max volt,
with a transistor with max 30 volt,
it is perfectly okay.
As the circuit only demands 24 volt.

There are other data that can be more important.
Ft= the speed of the transistor MHz
the noise and and the gain, hfe.
---------------------------------------
In Class A amplifier where a lot of current and heat is involved
there is also important how well the transistor
can cool itself down.
This is the data C/W.
It is related to the Max Power data.
It is good if C/W is as low (or lower) than the original
output transistor.
If it is higher you might need a bigger heatsink,
and heatsinks cost more money than a transistor
with good data.
And if C/W is too high there is a limit, where not even
the biggest heatsink will be enough.
---------------------------------------

The circuit sets the demands on the transistor.
The max data sets a limit for, IF transistor can do the job
without breakdown.
And secondly HOW WELL it will do the job.

/halo

[Nelson Pass]

Not usually. In this case, for example, the outputs
have much more voltage and current rating than
the amp will subject them to.

[fdegrove]

Hi,

I think it is over 0,5F/ch!

Make that > 1F/channel on the one I heard in Paris 15 years ago.

8W of pure class A....impressive thingie.

Cheers,