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Shahriar 14th March 2007 10:11 AM

Redesign Elektor gigant2000 Amplifier

I Love Accuphase Amplifier topology very much and it is long time I am trying
to find a good schematic.
I found Elektor gigant2000 design very similar to Accuphase. But I Need a Lower power
Can Anybody tell me how is possible to redesign it for 50 to 60Watt.

I Know some what to do, But I affraid to Miss something and can't get the result.

Here a link to German Site which contains the schematcs


consort_ee_um 14th March 2007 12:26 PM

The link did not work but I went to the basic site and clicked on the "elektronik" menu which took me to the circuit diagram.
Basically you do not need so many output transistor pairs perhaps one or two will do. Also you can cut down the supply voltage.
The detailed answer Fotios gave me in this thread should be a guide:

Shahriar 16th March 2007 09:50 AM

Dear consort_ee_um

I can Reduce the 70V Line (i.e. to 35V) on Power Transitors and reduce them to 2.

But What about the Regulated 78V Line.
I think If I reduce it (i.e. 40V) then the Circuit bios WIll be corrupted although I can't Understand what the designer has done in that stage. I just guess :D
In the Elektor Magazine is written

"The amplifier has been designed in
such a manner that its output is ‘programmable’
as it were"

But it didn't point to anything else.


consort_ee_um 16th March 2007 11:41 AM

The 78V regulated supplies are to provide "headroom" for the 70V output stages. You could reduce the regulated supplies down to +/-40V for a +/-35V output stage. the voltage across R22 would be lower of course.
A simplification would be to use a high voltage version of the LM317 to replace the regulators.
The drivers are based on current sources so providing the regulated supply "tracks" the output supply by being ~5V above the output supply no other changes are necessary (I think!). Hence the power output is programmable by what you set the supplies at.

Shahriar 17th March 2007 02:24 PM

Tell me if I am right:

I want to decrease The 78V regulated supply to 30V and 70V Unregulated to 25V.

1- I will reduce R22, R23 (3K3) to 680ohm.
2- I will reduce R19, R21 (10K) to 2K2

But I have No Idea about Which Transistor to remove among T15-T26 and T29-T34 If I use Just Two Output transistor (i.e T35 & T39)

ThanX in advance

consort_ee_um 17th March 2007 04:01 PM

Hi Shariar,
Yes, it looks as though they want to pass 10mA constant current through R22 and R23 so you need to reduce the value otherwise excessive voltage would be across the resistor. Also it looks as though they want to pass 5mA through R19 and R21 so again the value needs reducing.
I think you could have just one driver pair ie T15 and T21 for 2 output devices but then you not do need so much current down R22!
Also R63 and R72 potential dividers need to be changed to get the power supplies right.

Shahriar 17th March 2007 09:37 PM

ThanK you very much
But what about T29-T34 for 2 Output devices.
is two of them enough. i.e. T29 & T32


consort_ee_um 18th March 2007 10:06 AM

Yes again you can just use T29 and T32. Since you are lowering the voltages the power dissipation in the devices is not so much of an issue. Do you use Spice? It would be worth modelling the proposed design. Possible difficult pieces are the BF256 Fets used as current sources. I would use current sources for modelling these.

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