Another Aleph-X coming up!

[grataku]

Originally posted by Netlist

Bit off topic:
Buy the IRFP140 at RS. There, they are much cheaper than the IRFP240.

/Hugo

Sorry, what's RS?

[cHoc]

http://www.rscomponents.com/

[Edwin Dorre]

Originally posted by grataku


Edwin
I haven't thought about it much but I was puzzled by the values of source resistors you have chosen. Basically I come up with a much higher value for bias current than what you declared. I 'll try that again later.

Hmmm...

0.5V / 0.56 = 0.893A each * 4 * 2 = 7.144A total

I cheat a bit and drove them down to 0.470 / 0.56 = 6.7A total!

I only could get 0.56 ohm or 0.47 or 0.68 ohm. So 0.56 was the next best thing to get around 7A of bias.

Am I missing something? My power meter (a plug-in thing into a power socket) and the measurements on the source resistors and the voltage over my CRCRC resistors tell me the thruth...

Edwin

P.S. Also the heat of the heatsinks

[grataku]

Edwin,
I guess my head isn't a good enough calculator.
I will use .75 ohms for my 6 parallel mosftet at 27 volts rails, 8amps, ~425w dissipated/chn.

Yeeee-haaaa!

[Edwin Dorre]

oh boy, oh boy...

I have listened for a few hours now with two channels of my new Aleph-X... The transients, the violins, , the air around the drums, the slamm, the air around everything... *WOW* And I am spoiled with an Aleph-4 for more than a year now!

Sorry have to leave now! The music is waiting! I have to try the over 600 cd's!!!!

Even with some zipcords between the amps and my speakers; *WOW* again,

Edwin

--- Sony CDP-XA50ES, Aleph-P, Aleph-X (25-0-25, 7A bias), B&W Nautilus 802 ---

[Netlist]

Originally posted by Edwin Dorre

Sorry have to leave now! The music is waiting! I have to try the over 600 cd's!!!!

You must be a lucky man now.



/Hugo

[Edwin Dorre]

Originally posted by Netlist


You must be a lucky man now.

/Hugo

YEP! *bigest smile available*

Still some little things to decide and solve:

a) One channel has 15-20mV diff DC offset, and one channel has 30-35mV diff offset. However when I connect my Aleph P balanced I get; 30-40mV and 60-70mV . I do not like the 60-70 it is too high. So I can use input caps so the 30mV will not double into 60mV, or try to solve the 30mV problem.

Strangely;

The 392 ohm (I used 390) diff pair resistors of the 'bad' channel has an even 4.51, 451. The 'good' channel has 4.48, 4.52 ... hmmm... Both use 0.1% resistors!

The 9610 pair in the 'bad' channel is very good matched! It took me some time!

Any new ideas about this?


b) Channel 1 has 4k7 Ian resistor and 96ohm to ground (-250mV to 250mV and slower at warm to low values)

Channel 2 has 2k2 and 47ohm to ground (-50mV to 50mV and fast to low values during warm up) .

Channel 2 behaves absolute DC offset wise better, so I can either move to 2k2,47ohm or try 4k7,47ohm or just forget about it and put both channels at ... Nelson says that you better can stay at 4k7 and use resistors.. What do you think?


But it is still one hack of an amp! Nick Drake on 180grams Simply Vinyl! Amazing!

Edwin

[Nelson Pass]

Originally posted by Edwin Dorre
I do not like the 60-70 it is too high

I'd rather have the 60-70 than a cap. Besides, you can
trim that out easily enough.

[grataku]

Edwin I guess you like it!
Is it better than the aleph or just more powerful? I went directly to the AX never known the aleph sound.

you can trim that out easily enough

gotta love NP! How would you get that done?

In the single mosfet prototype I ended up swapping a couple of output mosfets around to get it down to ~10mV from about 75mv. In the case of multiple parallel mosfets it sounds a lot more complicated.
I never tried anything other than 4k7 to the differential and 100 to gnd. I figured if it works for Nelson should work for me.

[Edwin Dorre]

Originally posted by grataku
Edwin I guess you like it!
Is it better than the aleph or just more powerful? I went directly to the AX never known the aleph sound.


gotta love NP! How would you get that done?

In the single mosfet prototype I ended up swapping a couple of output mosfets around to get it down to ~10mV from about 75mv. In the case of multiple parallel mosfets it sounds a lot more complicated.
I never tried anything other than 4k7 to the differential and 100 to gnd. I figured if it works for Nelson should work for me.

I had to smile when I read Nelson's answer *THANKS* . However I have at this moment not a clue what to do. I tried the CSS trimpots, with this I can get the diff DC offset down, but the amout of the amps running through 'left' and 'right' side is way off when I hit 0V .

I swapped IRFP9610's but a perfect match pair did not do the job. Tonight I will swap 0.56 resistors to see if my unbalance in the voltage over the source resisors are because of the mosfet or resistors. This morning I did a recheck on some of my unused IRFP240's but my matching was ok, mosfets which where the same two weeks ago when I did the matching are still the same now. Because I was in doubt of the start temperature of the mosfet when I did the first matching. My voltages over the resistors are a bit off, when I compare the 4 voltages I get something like 0.456, 0.472, 0.472, 0.485 or something like this. I will swap the resistor of the 0.456 and 0.485 to see if the voltage moves with the resistor...

Let you know,

Edwin

P.S. Nelson matches his output mosfet to a staggering 0.3% ! I do not dare to ask what kind of tolerance percentage he usages for his source resistors ...