grataku said:
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 😎
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!
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!
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 ---
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 said:
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
Edwin Dorre said:
I'd rather have the 60-70 than a cap. Besides, you can
trim that out easily enough.
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.
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.
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.
grataku said:
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 ... 😉
Edwin
I did swap resistors and things got a little bit better. The change wasn't very dramatic like when I swapped mosfets.
I would swap the 4.85 mosftet or the 4.56 mosfet with something from you stash of mosfets that is a little bit lower and higher Vgs, respectively.
I wouldn't be too worried about a dc offset within 50mV when the amp is in the actual system playing music.
Why do I care so much? 😉
I did swap resistors and things got a little bit better. The change wasn't very dramatic like when I swapped mosfets.
I would swap the 4.85 mosftet or the 4.56 mosfet with something from you stash of mosfets that is a little bit lower and higher Vgs, respectively.
I wouldn't be too worried about a dc offset within 50mV when the amp is in the actual system playing music.
Why do I care so much? 😉
Try a 20K ohm in parallel with the differential pair load resistor (392 ohm on yours?) that is on the side with the output with the more positive voltage. This should reduce it by around 60 millivolts. Or, you could put a bigger pot (100k) on and null it out completely.
You may also have to adjust your current source to get the overall offset back down.
Steve
YEAH!!!!
I got the diff DC offset down! I swapped some of the mosfets around, specialy the negative mosfets. I made sure the negative mosfets of the two sides of a channel are the closest together with Vgs and this helps alot. It seems the Vgs's of the two sides of a channel of the CCS do not care that much, as long as the mosfet are 'working' together.
My 2% resistor seem to be very good. With 15V and 12ohm I put about 1.1A through a few of them and each dropped between 0.660V and 0.663V so the tolerance looks quit ok (I only checked 6 of them and all where ok). Swapping the resistors did not help that much as I have found out.
Drums please 😉 ; I have now about 15-20mV without something connected and 35-42mV with my Aleph P connected... And I did not have to trim the CCS's alot, both sides are more or less putting out the same amount of current! YEAH!!! I will bring my expensive 4.7uf input caps back to the shop, as I do not need them 🙂
Next stage; removing ACS gain trimpots, equal the two channels with the 4k7 and 97ohm to ground... and making an enclosere!
Tomorrow I will post a picture of both channels together!
Time to go to bed,
Edwin
I got the diff DC offset down! I swapped some of the mosfets around, specialy the negative mosfets. I made sure the negative mosfets of the two sides of a channel are the closest together with Vgs and this helps alot. It seems the Vgs's of the two sides of a channel of the CCS do not care that much, as long as the mosfet are 'working' together.
My 2% resistor seem to be very good. With 15V and 12ohm I put about 1.1A through a few of them and each dropped between 0.660V and 0.663V so the tolerance looks quit ok (I only checked 6 of them and all where ok). Swapping the resistors did not help that much as I have found out.
Drums please 😉 ; I have now about 15-20mV without something connected and 35-42mV with my Aleph P connected... And I did not have to trim the CCS's alot, both sides are more or less putting out the same amount of current! YEAH!!! I will bring my expensive 4.7uf input caps back to the shop, as I do not need them 🙂
Next stage; removing ACS gain trimpots, equal the two channels with the 4k7 and 97ohm to ground... and making an enclosere!
Tomorrow I will post a picture of both channels together!
Time to go to bed,
Edwin
Edwin Dorre said:
Thank you, this house is now clean!
😉Just in case update the resistors first then re-check the gain before removing the pots, it shouldn't make a difference but you never know. Also things that should never need to be adjusted again are V1 and V3 once you are sure that the same current flows on both sides of the circuit. I don't see a reason to have the additional variable. Fixed resistors would be more stable than pots.
Did you make a final adjustment of the absolute dc two or 3 hours after turn on usinv V2? It maybe beneficial to make the adjustment permanent or at least narrow its range.
Edwin Dorre said:
If you didn't make enclosure yet and the amp is not in a permanent chassiss, I wouldn't rush with replacing trimpots with fixed resistors. The chassiss (or enclosure) will change thermal heat distibution inside the amp and I can almost guarantee that you will have to readjust everything again. This is also one reason, the amp wasn't very stable with DC offsets. When I lift the cover of my AlephX, DC can run 30mV one way or another in a first minute. That's why also, in my A75 amp I made holes in a chassis to adjust DC and bias without having to remove the top panel.
Somehow it slipped my attention that you were runing the amp without enclosure.😉
Peter Daniel said:
That is a _very_ excellent point Peter, and I didn't notice the lack of enclosure either. One thing I have learned from the prototype is that I am going to mount the board horizontally and on top
to have ready access to the ccs trimpot. However, V2 is really the only thing that needs tweaking in situ to trim the absolute DC when everything is at the steady state. V1, 3 and the current gain stay the same.
==============================================
So many projects, so little money
grataku said:
Thank you, this house is now clean!
Just in case update the resistors first then re-check the gain before removing the pots, it shouldn't make a difference but you never know. Also things that should never need to be adjusted again are V1 and V3 once you are sure that the same current flows on both sides of the circuit. I don't see a reason to have the additional variable. Fixed resistors would be more stable than pots.
Did you make a final adjustment of the absolute dc two or 3 hours after turn on usinv V2? It maybe beneficial to make the adjustment permanent or at least narrow its range.
Thanks Grataku,
You have been (and ofcourse Netlist and others!) a great help. I will now start on the enclosure. I have drawn the panels and will order them this weekend. Hopefully they will arive in 1 or 2 weeks.
For the time being I will keep my v1,v2,v3 trimpots in there. I have build in the possibilty to get to the back side of the PCB because I use movable distance thingies (I do not know the word) which angle at 45 degrees. So at anytime I can remove the trimpots without dismanteling the amp!
Both amps now react exactly the same. Same diff DC offset, same absolute DC offset, same bias... I run about 6.7A and my amp runs about 60 degrees celcius (Nelson calls this &#*%*$ hot!) . But my old Aleph 4 has been running on 65 for a year now, no problem!
Final picture before it will be in an enclosure!
An externally hosted image should be here but it was not working when we last tested it.
Thanks you all, and ofcourse, TWO THUMBS UP for Nelson and GRollins!!!
I am so proud 🙂 ,
Edwin
P.S. Oyes, the amp makes almost non-existing hiss and absolutely no hum whatsoever in the loudspeaker.
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