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Old 28th March 2007, 03:02 AM   #601
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Default Here is RAJ revised board in PDF format


Thank you RAJ.

regards,

Carlos
Attached Files
File Type: pdf dxamp.pdf (40.9 KB, 311 views)
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Old 28th March 2007, 03:20 AM   #602
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Default Dx amplifier...now guaranteed against ressonances and all kind of very

low frequency disturbances.

Life is very interesting and exciting...when we have good friends.

regards,

Carlos
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Old 28th March 2007, 08:07 AM   #603
Nordic is offline Nordic  South Africa
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What are you doing up at 5 my dear uncle Carlos?

Finaly managed to source 4 2SA1943 transistors yipee!!!!
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Old 28th March 2007, 08:44 AM   #604
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Hi Carlos,

The RAJ board has electrolytics on the PCB, but what I would describe as a 'snake-earth'.

In my own final 'star-earth' design my ground was a genuine star, like the one being worked on by Greg.
I have one large electrolytic per channel rail at the PCB, but this is on the amplifier side of the fuses. Fuses can drop up to one volt peak at signal frequency under full power load, and this is not decoupled at the output devices on the RAJ board.
I also feel that fuses should be on the rear panel of an amplifier chassis, not inside so that a serviceman needs to dismantle and locate simply to replace them.

Cheers ......... Graham.
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Old 28th March 2007, 08:53 AM   #605
kvholio is offline kvholio  Netherlands
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Carlos, here's a picture of my changes. I've given different traces different colours.
It's still far from perfect imo, zobel-return should go back straight to main ps-caps (now 10.000 uF per rail).
Also local ps-caps could go back to main ps-caps.
There is now short piece of wire between signal-gnd and central gnd-connection on pcb, a lifting-resistor could be fitted here.
Click the image to open in full size.

Bigger picture here =>
Explanation of colours:
Red are signal-gnd traces
Black wire(s) are gnd-connection of ps-caps of output-stage.
Light-blue is gnd-traces that were removed
Yellow is zobel-return
Dark-blue is gnd-return of ps-caps for front-end.

Everything is now tied to central gnd-point on left of pcb, from there a single connection to gnd between main ps-caps.
Speaker-gnd is running straight to gnd between main ps-caps.

Greetings from sunny Holland (spring has arrived :-) )

Klaas
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Old 28th March 2007, 09:26 AM   #606
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Default hehe... the way i have imagined..slowly Dx amplifier go loosing it's own character,

personality...and changes beeing made are making it less and less different from the perfect Aksa 55.

Now the lifted ground..... also used by my friend Hugh Dean...as something very needed...i was avoiding not to make the amplifier with too much things alike.

But friends have perceived better stability this way.

That effect, called reverberation...or sonic body...solid sound that came from low end bass could be found into an Aussie amplifier too, and not only in Aussie unit i have...many amplifier has that sonics characteristic...hard to perceive.... this guy...Klaas, may have a very special speakers and trained years to perceive that.

This sounds good, as i told before in this forum evaluating an Aussie amplifier with lateral fets at the output....this will give you the idea of longer bass...... and this effect i like.

Do not worry about that.... happens in very deep bass...very low frequencies..those not normally founded in normal music...and not a sonic disadvantage, as others amplifiers have much more "effects" than this one...for sure they have... some famous ones have mufled sonics (not too much)..others have harsh sonics (intermitent)..others have not good focus, nor resolution...explaining what i mean:

Two women singing...voices turns mixed in such way that you cannot concentrated in one of the voices to listen it separatelly related other ....brain work of course..but information not too much mixed must be there in the signal source and not destroyed by the amplifier....so...small problems as triangle wave over the audible spectrum are not really defects...are effects.

Of course it is more precise now, without ground problems.... using lift ground (10 ohms) that Greg will include in the last board that is cooking.

You are rigth about fuses Graham....because of that i will sugest people to use a very thin wire soldered in parallel with their fuses...to have a guarantee that resistance there will be keep as low as possible.

Also... condensers, with increase values may be needed to be soldered under the board...or over the board if possible to avoid problems if someone forget to solder those "low resistance auxiliary fuses" there.

Many thanks by your researches guys....RAJ and Klaas...in special Klaas that have constructed and accepted that modification during listening tests....and perceive that klaas have the excelent amplifier...that Krell is in his home..so..he knows what is quality of sound reproduction

I am waiting your news dear nephew Nordic...happy with your progress.

regards,

Carlos
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Old 28th March 2007, 09:44 AM   #607
Nordic is offline Nordic  South Africa
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Just a quick question, it would be pretty simple and easy to cut the groundplane into a star (just did it in photoshop), but do you think it is realy needed to avoid hum... ?

I ******* hate 50/100hz hum.

Carlos 1 resistor extra is no big deal, we won't invoice you for the 10c...

Uncle Charlie, you should try all these mods and let us know which SOUNDS the best.

Don't get hung up on morals, this is not the Moral Amp, make it the Best Practices amp... i.e. use bests solutions, not most humble and kind methods...

Your ears allready know the answer.
I am a little worried that there was a small issue with subsonics, you knew about and was not comfortable telling us...

And you know that I am not someone, to qoute a Carlosism, one who goes looking for snake legs.

But I am human too and have those same weaknesses.

You must have a fun day uncle Charlie, I am going to fetch my parts later today, depending on how many hours I have to que for my car licence renewal.

I also looked at transformer datasheets
250va is 26VAC x5A x 2

I know this provides 26 x 2 SQRT 2 Volts DC minus diode losses, which I assume to be closer to 2V at these currents.

But does it provide the full 5A - losses on the DC side of the rectifier, or what? Even if I divide the 5A by 1.414 again I still get about 3.5A, but I guess the drop is not so bad...

ABOUT THE FUSES....

You said earlier that the onboard fuses where not needed, or did you mean fuses on the output?

I will die lrolling and laughin on the floor when this amp finishes up with mosfets on the outputs...
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Old 28th March 2007, 10:29 AM   #608
kvholio is offline kvholio  Netherlands
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Nordic, i don't think this grounding-discussion is about hum.
When grounding-problems cause hum, you have a HUGE problem in grounding (mostly loop(s) ).
This is about 'perfect' grounding.
Improving your grounding-layout improves sonic quality of equipment.

But to put this in perspective: If i would get a dollar for each GOOD sounding amp (diy or commercial) that had 'imperfect' grounding i could retire today.

About the fuses: They are at the worst possible place on Raj's pcb. An option would be to put them in the ps-rails between
rectifier and pcb, and use a wire-bridge on the pcb to bypass the place where fuses go on pcb.

Carlos, i always listen to well-known music, demanding in midrange and/or low-end.
The krell is good, but not unbeatable. It's a good benchmark to have. Also i have lived with the krell and speakers (acoustic energy ae-509's) for many years, knowing their strongnesses/weaknesses.

One example of a track i use is 'sail on' by Commodores.
Two male voices should be completely separate entities.
If it sounds good, it raises the hairs in my neck.
When not satisfied, it's time to heat up the soldering-iron

With best regards,

Klaas
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Old 28th March 2007, 10:36 AM   #609
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Default I am very satisfied Klaas...i hope you too..not only with Krell but also with Dx amp

hehe

regards,

Carlos
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Old 28th March 2007, 10:49 AM   #610
kvholio is offline kvholio  Netherlands
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Carlos, if the sound-quality of your dx-amp wouldn't be so good, i wouldn't be motivated to squeeze even better performance out if it

It has the ability to give you goosebumps, i like the midrange better than the krell

With kind regards,

Klaas
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