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Old 2nd July 2007, 03:17 PM   #2071
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Location: Bucharest
After a couple of days of listening (with some friends also),
I come back with the impressions:

First of all, the DX amplifier IS REALLY GOOD!

The only other amplifier that stood next without shame was a 600E
amplifier!

Overall, DX has:
- Nice trebles
- Lots of details
- Quite warm voices; I have not encountered sibilance etc
- Bass is there (here is the only doubt I remain with, it seemed to
me a little, very little boommy in the lower extension - anyway, nothing
to really disturb the listening experience)

The first impression is always of a "full and rich" sound, that covers
all frequencies, that is not metallic/fatigue/etc. Somehow, is like
having a "loudness" in it, if you understand what I mean!

Remember, all tests were made with quite a low bias setup.
I have some plans to operate on DX, so the experience will
continue!

CONGRATULATIONS, Carlos!
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Old 2nd July 2007, 04:36 PM   #2072
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Default Oh!.... fit wheels and engine.... oh!...do not remember dear Nordic


That i made him construct an enormous huge supply that needs a truck to carry...he is already nervous against me.

Do not talk his heatsinks are bigger than the needed size....he will be nervous with me once more.

Not so big dear Nordic...not so big the way people is thinking.

It is dear Graham that is kidding...

See the image Graham suggested.

ahahahahah

Carlos
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Old 2nd July 2007, 04:39 PM   #2073
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Hi Usernamex,

Carlos, I hope you won't mind me coming in here.

When I have studied the bass response of amplifiers, I have found that not only do a pair of substantial electrolytics need to be connected between the PCB rails and ground *at the PCB*, (as you have already mentioned above) but the series input capacitor needs to be much larger than is normally considered suitable when looking at it purely from its input resistor loaded forward response point of view.

The DX uses 2.2uF and 39k. However the base of the input transistor uses this junction as its NFB reference (for loudspeaker load output damping) potential, and I have heard bass control weakness due to such low values when a bipolar input stage has NFB on its emitter. Audible as opposed to measurable !

This would be an ideal time to try say 22uF in parallel on the PCB underneath the 2.2uF. It might firm up the bass; but the PSU rails need extra capacitance first to ensure there is no weakness here.

Maybe Usernamex could try this ?

There is another possibility here. Many amps over-react at bass frequencies and can sound too punchy ! The DX should not be like this, though anyone used to the punchy sound might then think the DX is lacking, when actually it is okay.


Cheers .......... Graham.
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Old 2nd July 2007, 04:42 PM   #2074
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Default Thank you very much Usernamex...also my thanks to Charlie-fd


Pictures, high resolution ones, will be needed to the Dx Corporation history.

Data bank is starting to be big!

Send, please, pictures ...from yourself and Charlie_fd...also inform is images can be used...if can be posted or not.

The amplifier, higher resolution pictures will be welcome.

Also images of your country and those things.

But place them directly to me:

panzertoo@yahoo.com

To the forum..... amplifier images and only one personal..... not to bother our moderators (they hate the mess i use to make.... some of them complain a little...in a very charming and educated way always)

Thank you!

Made my day.

Now pay Big Fat Happy Charles sending me informs about Rumania...also picture...those ones direct to me, please.

Dx Corporation thanks you by the preference and will include you into the Member list.

regards,

Carlos
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Old 2nd July 2007, 04:45 PM   #2075
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Default You are welcome Graham...one of my best cooperators


Permanent Member of the Council of Dx Corporation.

You can say whatever you want.... just do not atract theorists as they will stole the thread to talk about picovolts!

Dx amplifier produces sound!...not data!

regards,

Carlos
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Old 2nd July 2007, 04:57 PM   #2076
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Default I am waiting dear Microp to play his Dx amplifier


His nice daugther will smile this way listening to Dx amplifier.

Nice sonics.....not perfect...not the best one in this earth..but very good!

regards,

Carlos
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Old 2nd July 2007, 05:52 PM   #2077
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Thanks, Graham! You read my mind! ... I already purchased a couple
of days ago WIMA 10uF MKP to replace the 2.2uF...
I will also replace the rail capacitors with 2200/50v, good quality...
Another tweaks are on the way:
- replace 10k variable pot with fixed resistor+1k var pot
- ferrite-beads on the rails cables
- Ball-bearings for the coolers (noise reduction desired to be lower than 20db)
- bias increase to 800/80mA


Carlos, high quality pictures are a promise!

In the mean time, here are some pictures of the
Mountains Marathon that took place in Romania last weekend:

http://www.maratondhl.ro/dhl/?lang=r...allery&an=2007

Our team (that included me and charlie_fd, and other teammates,
both runners and supporters finished a little under 4 hours...)

We hope to finish "the DX marathon" also...
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Old 2nd July 2007, 05:54 PM   #2078
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Default Good Marathon to you.


thanks by images and informs.

Also, please, inform and attach, if possible, this 600E amplifier schematic...or picture.

Good "Rezultatte Maratonul"

regards,

Carlos
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Old 2nd July 2007, 06:34 PM   #2079
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Schematic it is difficult, I would have to do reverse engineering...

But pictures (of the first version - not really much different of the
version I have) and reviews can be found here:

http://www.tnt-audio.com/ampli/nlf_amp02.html
and
http://www.suono.it/pdf/Garage_NLF_AMP_02.pdf

In these links the (old) price is 460E... The actual price is 600...

P.S. Some similarities to DX are: no output protection, simple
schematic, dual mono etc... as for the schematic, it would
take some time...
Anyway, the output uses BD139/BD140 (good sonic, like SC/SA)

As I said before, only this one stood next to the DX...

P.S. Other amplifiers used for comparison:
Opera Audio Consonance
LM Gainclone

Source: Sony CDP-XB970 QS (digital output)
Xindak Dac 3

Preamplifier: Vacuum tubes Aeron AP-120

Speakers: Cath Victory, Visaton Couplet, Mosquito StudioLab HES B10
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Old 2nd July 2007, 06:41 PM   #2080
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Hi usernamex.

800mA is a whopping current for class-AB.
It will make your amplifier class-A for most low listening levels, but it might degrade the treble response !!!
Hence you might not gain the quality you think this change should produce because the crossover capabilities are slowed and the NFB maintenance of accuracy is degraded.

Ball bearings on coolers !
Try not to use more than one fan per cabinet. Split the airflow for one fan rather than have two producing speed hunting induced beat effects.
Also do not have any guides or grilles close to the rotating blades, for the variations in pressure as the fan edges rotate close to another edge causes a sharp increase in 'noise dB'.

Potentiometer. By all means reduce its value. This maintains reproduction quality IF your source is capable of driving the potentiometer resistance without loss of quality or bass.
Sometimes it can be hard to find a logarithmic potentiometer of low value, so by using say a 1k resistor connected to the slider of a 5k linear component you can get a good range of level variation through the centre range of adjustment, again IF the source output resistance is low.

Generally connecting the DX direct to a CD or DAC output via a potentiometer should be fine, but many tube pre-amplifiers do NOT have a sufficiently low output impedance.

Ferrite beads on cables. Which cables and why ?

Cheers .......... Graham.
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