[gerado]

If I were to multiamp my LF100 amp/amps is there any way , or any point in optimising the amplifier for better performance in the frequency range it will be used for.
That is, is there a tweak to make so the one used for low frequencies is optimised for this frequency band and the one used for high frequencies/midrange  sound sweeter, detailed, softer, harder what ever your preference might be.

The power supply has so much impact on the nice sound of these amps it is logical to assume one could start here someway? After all what might be ideal for base might be a compromise for the top end and vice versa and a middle ground might be the "factory setting" Hugh has chosen.

Go easy if this is silly question- Im only learning!

[netaron]

I will try to help with my basic understanding of things. I know that certain caps have a better high or low end response depending on the type of cap. So you could try to modify an amp slightly for better upper or lower response by choosing different parts.

The other method would be to use an active cross over to filter out what you don't need and feed that signal to the amp, so the amp only has to work with the frequency it is fed. I'm sure this is how the multi amped systems with electronic cross overs work right now and keeps the amp from amplifying unwanted signals.

One las thing I would like to mention is that "only the simplest can accommodate the most complex" (credit here given to either Dr. Harvey "Gizmo" or 47 labs) trying to keep with the less is more approach.

haron 

[AKSA]

Theo,

There are certain optimisations with the AKSA/LF output stage which can be made for different frequency bands.  For HF amps, for example, you can use the super expensive teflon caps for charge suckout.  This costs bass, but enhances top end, so this is one change you could gainfully make!

Cheers,

Hugh

[andyr]

The other method would be to use an active cross over to filter out what you don't need and feed that signal to the amp, so the amp only has to work with the frequency it is fed. I'm sure this is how the multi amped systems with electronic cross overs work right now and keeps the amp from amplifying unwanted signals.

haron 

Hi haron,

The issue which Theo asked about is this ... if you are using an active XO and so feeding, say:
* low signals to a bass-driver amp
* mid signals to a mid-driver amp, and
* high signals to a tweeter amp

... then is it possible to optimise the behaviour of each amp for the band of frequencies which it is reproducing?

For instance, if an input coupling cap is known to lose base, then certainly don't use it for the bass amp.  And as Hugh has explained, if a teflon cap enhances the top end then certainly use it in the tweeter amp - but not in the bass amp.

Along similar lines, tweeters don't generally need as much power as mid-range drivers.  So I have a LF55 modified to become a "LF25" to drive my Maggie ribbons (by reducing the +/- DC rail voltage) as this makes it sound much sweeter in the top end than the "normal" LF55.

Regards,

Andy

[Jens]

So I have a LF55 modified to become a "LF25" to drive my Maggie ribbons (by reducing the +/- DC rail voltage) as this makes it sound much sweeter in the top end than the "normal" LF55.

Hi Andy,

Interesting. I am considering a second, low-power Lifeforce amp for the tweeter section as well. What changes were made compared to the "original" LF55?

[MikeC]

Hi Gerardo

Running three AKSA N+'s into Orions, these are my modifications. Bear in mind these are still Nirvana Plus amps, I haven't got around to Life Forces yet 

100 N+ on Bass - increased transformer size to 500VA and reduced PS rails to 42 V to optimise current delivery. The capacitance in the power supply is increased by 50% and the rectifier diodes are upgraded for increased current.
55N+ on Mids - Mundorf ZN polyprop film & foil input cap. I can't remember the value now, but it is lower than standard, so low frequencies are rolled off prematurely. This is not a problem as the crossover rolls this driver off at 120Hz. The rectifier diodes are IR Schottky's.
25N+ on Tweeters - TFT Teflon input cap (I think it's 0.33uF) and TFT charge suck out cap. The rectifier diodes are IR Schottky's, the transformer is a 75VA laminated type, supplying a lower rail voltage, and PS caps are bypassed with 47uF Black Gates and small value polyprops.

I have put small (0.1uF) BG's as bypasses on several of the smaller electrolytics on the mid and tweeter amps as well as replacing some of the electrolytics with equivalent value BG's.

Regards

Mike

[andyr]

Hi Andy,

Interesting. I am considering a second, low-power Lifeforce amp for the tweeter section as well. What changes were made compared to the "original" LF55?

Hi Jens,

The transformers are 80VA, 18v-0-18v secondaries which turn it into a LF25 which supports my 3 ohm ribbons with no problems (I was running the same configuration on my AKSA amps before the upgrade).  This means the DC rails are +/- 25v instead of +/-36v for a standard AKSA/LF 55.

Hugh changes a resistor in the circuit as well, to match the lower DC voltage (R3 on the AKSA).

Regards,

Andy

[gerado]

Thank you for all your responses

I would need help doing some of these because I do not even know what a rail is let alone where it is