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Old 1st December 2005, 07:02 PM   #1001
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It is not mandatory to have caps at the inputs. All that is required is a source with no (or very, very small) DC offset at the output. All healthy tube preamps will meet this criterion. Many solid state preamps will also. The user will be in the best position to determine how much--if any--DC offset will be present at the inputs of the amplifier.
When in doubt, put 'em in, but anyone who owns a decent meter should be able to puzzle this one out for themselves.

Grey
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Old 1st December 2005, 07:17 PM   #1002
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Well I tried my amp without input caps because I didn't know any different. I had like 2.5vdc offset when the preamp was hooked up. Without the pre it was 24mV offset. My Pre is a Bryston .4B. It doesn't put out that much dc so the A-X is amplifying it. The input caps cured it.

Blessings, Terry
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Old 1st December 2005, 07:55 PM   #1003
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Thanks to everyone for their input.

Graeme
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Old 1st December 2005, 09:49 PM   #1004
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Hi Guys,

If this has been already answered please forgive me.


I've been wondering what the advantage the X design is. Is it supposed to be better sounding than the regular Aleph? Less distortion? Just what is the benefit from it?

Thanks, Terry
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Old 1st December 2005, 11:11 PM   #1005
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The idea is to minimize distortion and noise with minimal
circuitry. This is easy enough to do without X in small Class A
amps, but harder in high power amps. The first X example,
the X1000, managed a kilowatt with good specs and did it
with 2 stages - a differential input and complementary
followers.
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Old 22nd December 2005, 07:14 PM   #1006
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OK guys, I've had mine up and running for a while now. As stated before I used the Onsemi MOSFETs so my findings may not apply to the masses but here is what I'm experiencing. First, I get a small hum when I connect the preamp. (Bryson .4B) None of my other amps have a problem with this preamp. With nothing plugged in there is no noticeable hum. The high and mids sound nice but low mids and bass are little weak. It sounds nice with a sub going but if I switch to my other amps I can hear things that were missing with the A-X.

I have a switch installed that connects the #1 & #3 pins on the XLR inputs for use with the RCA jacks. I have not tried it with a balanced input yet. I should probably do that to see if the hum goes away. I have the input caps connected in series between the XLR input and the PCB. 1 for the #2 pin and 1 for the #3 pin, nothing between the #1 and the PCB. I am using a shielded cable with two leads to connect the XLR and the PCB. I used Orange Drops for the input caps.

Any suggestions, will of course, be greatly appreciated.

Blessings, Terry
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Old 23rd December 2005, 01:43 PM   #1007
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Hi Terry,

what value are the orange drops? If they are too small this could cause a drop in bass combined with the lowisch input impedance.

I can´t complain of weak bass with my Aleph-X. It goes very deep and is much more controlled than the bass from my Aleph5 or Crescendo amps (on a pair of Thiel CS6).

William
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Old 23rd December 2005, 03:52 PM   #1008
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Although I have not seen a schematic for Nelson's real XA amps, I wouldn't be surprised to find that he was using 10uF for DC blocking caps. He may have said something about this in a post, but I can't remember at the moment.
I have some 1uF Orange Drops in a parts bin down in the dungeon, but don't recall ever seeing a larger value. Something on the order of, say, .1 to .47uF will seriously limit the bottom end response of a stock Aleph-X.
The fact that the hum is not present when the preamp is not plugged in suggests to me that it's not the amp, per se, that is humming. I'd start thinking in terms of a ground loop.
I doubt that the Motorola/OnSemi outputs have much bearing on these two problems.

Grey
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Old 23rd December 2005, 05:21 PM   #1009
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The orange drops are 10uf, or so I was told. I don't have a way to test them. They are fairly large in size. I used an electro at first because that's what I had. The bass was about the same with the electro. Actually, when I first had the amp running I wasn’t using any blocking caps. Sounded pretty much the same then as well. The amp has a nice sound it's just not near as dynamic as the other amps I've built. It is definitely weaker in the low end than my Krell, P101 & Leach.

I suppose the hum could be from a loop but it starts as soon as I plug in either lead from the preamp. I had a loop in the first KSA50 but both channels had to be plugged in before it would hum. This does it as soon as I plug in either channel. I will try to remember to plug in a balanced input and see if it goes away. That may tell me something.

With nothing plugged in there is no hum with the switch in balanced position but a pretty loud buzz with it in unbalanced position. With the pre plugged in to the RCA jack, there is a slight him no matter which position the switch is in.


Plugging in both channels doesn't seem to cause any more hum than with only one plugged in.

Blessings, Terry
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Old 6th January 2006, 03:15 AM   #1010
lgreen is offline lgreen  United States
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Default Hello A-X Builders

Hello Aleph-X builders!

I am starting my attempt at the A-X and seek your guidance.

Many of you have already helped me out with Parts, so its already a group effort.

Anyway, this link shows an idea of my case, transformers and soft start.

You see that I'm using 3 MOSFETs (thank you Kilowattski) where 1 goes on the hifizen boards, that the pair of transformers (which will sit atop another like my Krell clone) are 700 VA with 17VAC secondaries, that there will be a 3rd xformer for my soft start circuit with a relay to bypass the ss after a few seconds.

So I am going through the massive thread and build guide, and while I am at it hows about a few tips-

1. I don't want to stretch the envelope re the heat. You see the size of my heatsinks (8.7" high, 8" long, 1.5" deep x 4) how much pwr should I go for? I'm not looking to run this on the edge of thermal capacity, 40-60 WPC is fine.

2. Any special values I should use to populate the boards other than the standard ones on the spreadsheet? I see notes for "high power" versions, and I am reading those now.

3. What value of R should I use in my Power supply, CRC filter? Per rail it will be 60,000uF --- R --- 60,000 uF. 8x60,0000 uf Caps total. I've simulated the PS on the PSU designer but not sure of the load etc... I am not going to attempt a CLC filter.

I already have a bunch of .6 and .5 ohm aluminum clad dales if that helps.

4. i'm thinking of mounting the boards as shown, rather than the more intuitative vertical mounting right at the heatsinks, so that I can probe and test the boards easier. My last few projects were so jam packed with stuff that it will be a nice luxury to have access to all the circuits for testing. Tell me now if this is an idiotic idea.

5. how the heck does one connect big wires to the spikes on my diode bridges (shown in the pic at the far ends)? is there a std connector for this?

This is only the beginning....... but thanks.
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