Aleph-X builder's thread.

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
 
The one and only
Joined 2001
Paid Member
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.
 
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
 
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
 
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
 
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
 
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.
 
The one and only
Joined 2001
Paid Member
Re: Hello A-X Builders

lgreen said:
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.

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.

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?

1) If these sinks are 2 per channel, then I don't see any problem
with the 60W figure.

3) .5 ohm is a typical figure, but you want it in the 10+ wattage
size.

5) Bend the wire around the spike and solder it.

:cool:
 
Re: Re: Hello A-X Builders

Nelson Pass said:


1) If these sinks are 2 per channel, then I don't see any problem
with the 60W figure.

3) .5 ohm is a typical figure, but you want it in the 10+ wattage
size.

5) Bend the wire around the spike and solder it.

:cool:


Nelson? thanks! Hey, shouldn't you be at the CES? If so see you Saturday if I'm not too hung over!
 
wuffwaff said:
Graeme,

I never tried the amp without input caps after reading Peter Daniels reports quite a long time ago.

When you use unbalanced dc-coupled connections you will load both inputs differently.

Since I wanted to mate it to an X-BOSOZ wich has a small amount of dc-output depending on the input (thanks to the X-resistors wich are dc-coupled) I never further investigated.

William

JENSEN TRANSFORMERS (look on their site white paper etc)have an interesting but simple way to create a balanced output from a single ended pre with only an addition of a resistor and a cap.You could add these to the output of your preamp or even the input of the ax.
I find the sound with this mod much better in my system.There should nor really be a difference but there is.
I am using an aikido pre and it is a huge difference from the bosoz/bls even xbls.It gives all the advantages of tubed sound but with the power of the ax .I was also using before a well designed opamp pre with AD8610 /current sources/output buffers etc but only with the aikido did I get the excellent mid/high transparency that is similar to good set amp.To my ears the bosoz and opamp pre although pretty good were too colored in the long run and I found I was always reverting back to my set amp for most listening.
 
Output "hum" AlephX

Hi Gent's,

I'm one of the proud owners of a AX but when i put my ear in the bass speaker i hear some hum. It's not much and normally you don't hear it but i don't like it.
When i measure with a scope at the output i see a few millivolt 100 hz products(see picture; timebase 2ms/div and input 10mv/div).
When i measure the rail voltage i see 30mv tt ripple.

The ax's are monoblocks with CLC filtering(44.000uF-2,2mH-44.000uF per rail, so 176.000uF total per monoamp)
Rail voltage is around 19 volts and the idle current is 6,6A

I read something about turning the transformer and i try this a bit but it's almost impossible with 4x2,5mm secondary.
B.t.w. it's no input hum and in low power mode(2,2A idle current) i need a stethoscope to hear it.

Is it usual to have some hum under these conditions?
More capacitors? or inductive problems?

Gr.
Johan.
 

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Johan,

Mine acts the same way but I don't bother since I can't hear it when the music plays. It seems to be a common problem with many AX's and I suspect that only meticulous design, component choice and layout as in the stock Aleph's can cure the problem. I still wonder how Nelson manages to get a hum level in the µV range.

/Hugo
 
hum in ax output

Netlist said:
Johan,

Mine acts the same way ... I still wonder how Nelson manages to get a hum level in the µV range.

/Hugo

Hi Hugo,

I'm "happy" you have the same"problem". I wonder too how Nelson solve this item.

The strange thing is that i have a "remarkeble" difference between the two monoamps while their contruction is the same and the one with the lowest hum level has the highest ripple.
Strange isn't it ???
I played with the wiring but nothing is sensitive.

The ax-design has not much feedback so it's not amazing that there is some hum but that difference between the two monoamps is still playing around in my mind.

I also read reports of other ax-owners who say that their amp is as quiet as a mouse so what do we wrong??? Or they didn't put a ear in the bass speaker.

Gr.
Johan.
 

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You could do a regulator if the filtering is insufficient. However, maybe it is hum being induced from the power supply. A couple of things to try:
1) Shield unshielded transformers with a high nickel content alloy.
2) Use a separate chassis for the power supply, or at least partition the amplifier.
3) Solid state rectifiers create ringing which is far above audio frequency, but it is modulated by the power line frequency, so you have a sort of high frequency carrier RF being induced into your audio circuits, and you hear the 60 Hz modulation in an analogy to AM radio. This is best solved with a snubber; see this article.