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Old 21st February 2012, 12:50 PM   #821
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Quote:
Originally Posted by triode_al View Post
I remember now why the power supply bounced and oscillated heavily: I had as section after the supply, 56.000 muF capacitors. That is why they were completely opened up to maximum conductivity. The schema has 8 muF and a formal stopper resistor even to reduce the output current. I should try it again that way!
albert
That's not to limit the output current. It prevents the supply from high frequency oscillation.

I've built many of these power supplies, all buffered by high capacities at their regulated exits. None ever showed oscillation.
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Old 24th March 2012, 09:33 AM   #822
Duco is offline Duco  Netherlands
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Dear all,

I got myself a le monste kit from ebay.
But I found that the amplifier board has a 9V DC-Offset without speaker connected and 4.9V with a 6Ohm speaker connected.

Using Click the image to open in full size. these pcbs. I solderd a 1.2K as R1 (input resistor) and 1K on R2 and R3.

I also tried: R1=1k and R2=R3=470 and R2=R3=235.

The other components are the same as these: Click the image to open in full size.

I can't think of another solution. Can you please help me?

As power supply I'm using a: 2x22V 300VA transformer with a rectifier bridge and a 4x(15000uF @ 63V) capacitor bank.

Hope you can give me some advise,
Duco
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Old 24th March 2012, 10:38 AM   #823
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How are you using that 2x22v transformer to get the required + and - 12v and
are those TO3 bolts insulated from the heat sink?
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Old 24th March 2012, 10:59 AM   #824
Duco is offline Duco  Netherlands
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Thanks for the reply. Gives one hope

To be precise It's based on le monstre. This is the design that came with the pcb: Click the image to open in full size.

Bots are insulated. I measured them with a multimeter.
Weird, I can't figure it out


-Duco
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Old 24th March 2012, 11:53 AM   #825
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Quote:
Originally Posted by Duco View Post
Dear all,

I got myself a le monste kit from ebay.
But I found that the amplifier board has a 9V DC-Offset without speaker connected and 4.9V with a 6Ohm speaker connected.

Using Click the image to open in full size. these pcbs. I solderd a 1.2K as R1 (input resistor) and 1K on R2 and R3.

I tried: R1=1k and R2=R3=470 and R2=R3=235.

Duco
Duco, the transistors and selected FETS deviate from the originals (a lot) so indeed you should change the resistors value.

Having a DC value means that you have too little 'room' in the potmeter to accomodate for this DC point.

No problem:.
I suggest a potmeter of 2K5 parallel of the R2R3's. Then you can bias the unit just like is written in the F5 thread in the Pass sections (the Le Monstre works just like the F5; only difference is the other type of output configuration: MosFET versus inverted Darlington).

I bought my devices at the shop of Hiraga (lucky) and ititially went for 910 ohms; but I reimplemented it various times. As I lowered the powerline from 14 volts to 13 volts and reduced the current too I found it necessary to reduce the original value from 1 k to below 900 ohms; and all the time inserting new values drove me mad.
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Old 24th March 2012, 12:02 PM   #826
Duco is offline Duco  Netherlands
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@triode_al
Thanks for your comment

You say, mount in addition a 2k5 potmeter parallel to the R2=1k and one parallel to the R3=1K?

This way a have 3 potmeters and I'll be able to adjust the bias the a proper value?

Yours,
Duco
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Old 24th March 2012, 01:08 PM   #827
Duco is offline Duco  Netherlands
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Is it problem that my Working DC is around +31V and -31V? instead of +22V and -22V?

-Duco
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Old 24th March 2012, 01:44 PM   #828
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Originally Posted by Duco View Post
@triode_al
Thanks for your comment

You say, mount in addition a 2k5 potmeter parallel to the R2=1k and one parallel to the R3=1K?

This way a have 3 potmeters and I'll be able to adjust the bias the a proper value?

Yours,
Duco
Put your P1 (on the sources) in the mid position; then you can select the DC bias current on both halves independently (call them P2 and P3 now).
When you have the correct bias and about the correct DC point you can leave it like that.

As I see it: Having 31 V rails on this MONSTRUM SUPERBUS is no problem (as long as the output pairs can handle this voltage and the heat).
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Old 24th March 2012, 01:50 PM   #829
Duco is offline Duco  Netherlands
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All right. Thanks! I will get some of these pot meters. If I'm lucky today.

So i can vary the resistance between (1000^-1 + Rpot^-1)^-1 where Rpot can very between just above 0 and 2k5?
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Old 24th March 2012, 02:02 PM   #830
Duco is offline Duco  Netherlands
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Is it problem that my Working DC is around +31V and -31V? instead of +22V and -22V?

-Duco
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