AX100 100W Aleph-X Monoblocks

[gl]

Hi Dave,

Here are the answers to your questions,

1. You are right. Good call. R11 and R33 set the CCS current to allow 115W out.

2. The main SuSy "feedback" resistors are R16 and R30. The gain of the amp is set by R16 divided by R18 on one side and R30 divided by R28 on the other.

R46 and R47 provide a different feedback path that is used to reduce absolute DC offset. I am still using the 10K value and am no hurry to experiment further.

Cheers,
Graeme

[daly2k]

What size power supply inductors did you use? I am thinking about using 1-2mh devices that can handle the current of 3.6 amps per side assuming 12 devices at 300ma of bias current each.

I am guessing this is the bias current based on the source resistors of 1 ohm that you are using with about a +/- 30volt rail.

The Bias on these resistors for the Aleph 1.2 is also 300ma. dave

[gl]

Hi Dave,

I used 1mH Sledgehammers from Madisound. They are made from 15ga wire and the steel core is not huge but seems adequate. When the amps are running and I touch the ends of the cores with a small steel screwdriver it's attracted but not really strongly. That very unscientific analysis tells me that the inductors aren't saturating.

They have a DC resistance of .1 ohms IIRC. So the calculation on heat dissipation would be I*I*R = W. For the AX100 this is 5.4*5.4*.1 = 2.9W. They get noticably warm to the touch. The people that use air core inductors, which have larger resistances, report that those get quite hot. Keeping the heat level down is the trick for these components.

The sledghammers come with tape wrapped around the coil and an assortment of labeling. I removed all that and wiped down the winding with naptha or paint thinner to get the residual glue off.

There are a number of places selling air core inductors for speaker crossovers. These should all work well. Hammond also has some good looking EI inductors. I think they're 156 or 157 series parts. The trade-offs are size, money and heat.

I think you should re-check your calculations regarding the bias. The 300ma for the 1.2 doesn't really compare to the Aleph-X which is more of a bridged type of topology. If you take the AX100 and increase the voltage to 30V and add one more transistor per quadrant for a total of 24, you will have a total bias requirement of 12 times 540ma or 6.48A not 3.6A. 3.6A of bias will limit your output to much less than the specified 100W. There's a huge amount of background on this in the big Aleph-X thread.

Cheers,
Graeme

[daly41k]

GL-sorry for the delayed feedback, I have been on vacation and then I couldn't get back in the forum as it wouldn't recognize my password and I couldn't get a response from the site so I had to re-register.

Regarding eliminating some residual noise (120hz hum) from my Aleph 1.2's, I purchased some 1 mh-.1dcr inductors custom made from Meniscus Audio. They have a rating of 1000 watts before saturating. I already have some air core inductors in the power supply and this worked for 6 years until I built my line array loudspeakers which are 90 to 92 db efficient. Now with my ear against the grill cover I can hear (barely audible) some hum and buzzing. I have noise filters at the input of the amp for emi and rfi. My question is where to attach this second set of inductors?

I have two places:

a. immediately following the hexfred diodes to the first set of caps.
b. immediately after the first set of caps followed by the next pair.

I have 8-15,000 uf caps per mono block with politically correct PP bypass caps.

Idea A would give me l-c-c-l-c-c
Idea B would give me c-l-c-l-c-c

How do you have your inductors connected? My big 2kva transformers buzz and this might be causing the noise in the speakers but I won't know until I try this fix. That noise is by far the loudest as I don't hear any noise from my listening position.
The original Aleph's are vertically constructed, mine are the more traditional horizontal box with heat sinks on the side. This of course means longer wiring runs especially with 8 caps per side.

I also measured the ohms across the CL-60 thermistor in series with the AC switch and Fuse. Cold the thermistor measures 14 ohms but after 30 seconds after turn on it still close to an ohm.

These amps draw 5 amps ac continuous from the wall which means a 5volt drop across the thermistor. I have two time delay ac relays left over from a tube amp project and I will use these to by pass the thermistor after a 5 second delay. My voltage rails on my Aleph's are +/- 60volts. Are you using thermistors for turn on surge protection on your amps? Happy Holidays, dave

[gl]

Hi Dave,

Wecome back. I trust your vacation was enjoyable. I'm sorry to hear about your login problems.

First off here's this one mans humble opinion on your L-C connection question: - option "b". If you use option "a." then your power supply output voltage will drop considerably. Rather than me go on and on here and possibly mislead you I would refer you to Rod Elliots website or a good text book.

I have a 68,000uf cap connected to the output of the diode bridges and the inductor. The other end of the inductor is attached to a second 68,000uf cap and the signal circuitry.

It sounds like you've knocked your hum problem down to a minimum. With a 2KVA transformer you will have to really tweak the locations of your wiring and input circuitry to keep out hum generated by the leakage flux.

Yes, I am using CL-60's on the AX100's. I am using one in series with the hot lead of the 120V mains and another to separate the frame and signal grounds. Very much like the ZEN schematics on the passdiy site.

1000W inductors? Does this mean they can dissipate 1000W or that Meniscus says they can be used in a loudspeaker crossover that can be used with up to 1000W of input power?. I used 1mh .1 ohm sledgehammers because I could get them easily and because they were relatively cheap. There's no magic in the numbers. If I hadn't been able to get those I probably would have used the Solen 14ga air core units and put up with the higher voltage drop and resulting heat. Can you post more info on the your new inductors? How big are they and how are they constructed?

Anyway, glad to hear you're making good progress on your amps.

Cheers,
Graeme

[daly41k]

The weather here is the remains of the tropical storm and it is lousy outside so I was working in the "lab". The inductors are iron core types wound for me and they probalbly are very similiar to your sledgehammers. I remember reading in an old issue of Audio electronics that if you put a small cap in parallel with/to the inductors that you can reduce the ripple even further. I am searching back through the years of magazines to see if I can find that article because it had the formulas for sizing the cap as well as Inductors in general.

Also, I am aware that you have to align the inductors by 90 degrees etc to prevent the fields from coupling etc. I am not sure if it matters but I have my inductor axis placed 90 degrees with respect to the transformer. I know in tube amps manufacturers may align their transformers for the same reason. there have been articles in Audio Electronics about this issue.

Thanks, I will keep in touch from time to time. dave

[daly41k]

HI Gl--it has been a long time since I responed regarding building 4 XA100's. I bought a DEQX unit so I can actively biamp the line array speakers that I finished a few months ago. I want to crossover at 2600 hz to the ribbon tweeters using a 96db digital crossover. The Midbasses will handle 2600 down to 50hz.

How have your XA100's sounded over the last few months, are they still pumping out the music? When you crossed over to your tweeters in you biamp mode where you concerned about the DC offset from the XA100's messing with your tweeters? I do intend to put a 40uf PP cap in front of my ribbons to protect them since I probably won't put a dc protection relay on the outputs since this is a push/pull bridged amp.

I am just curious if you made anyother changes, I have copied your published schematic and will attempt to bread board it over the next few months. As always the chasis and heatsinks are the biggest obstacles to overcome. My Aleph 1.2's are still singing away and it will be interesting to AB them against the XA100 for comparison. I have to be fool to build four of these but they are so different from anything else it should be fun. dave

PS--I used to be daly21k but forgot my password so I had to reregister as daly41k. dave

[gl]

Hi Dave,

It's good to hear from you. I'm glad to hear that you Aleph 1.2's are still singing and that you are still planning to build AX100's. I think you'll be pleased with the result.

My two AX100's are doing fine and are in regular use. The amp they replaced is now packed away in storage. The AX100's are keepers.

I've done nothing to the amps since I last posted, except use them constantly. They have been left on by accident for several days on two occasions with no harm done. Once was in the middle of summer.

That being said, I have gathered up the components to make several minor upgrades. These are:

1) I am replacing the 68,000uf PS caps with new 56,000uf Sprague units. The 68K caps were surplus parts that I have come to view with suspicion.

2) I am replacing the output binding posts with nice Cardas units and the SE input jack with a Vampire. Yeah, it's a splurge but it's my way of acknowledging these amplifiers as keepers.

3) I will finally install the previously discussed snubbers on the PS caps.

4) I am going to try removing the input caps to see if I hear an improvement. My pre-amp has output coupling caps.

Other than that I have become interested in what NP has done to the XA100 in upgrading it to be an XA100.5. He has stated that the output bias current has been increased but I think there's more to the upgrade. In essence I suspect that he's taken the Aleph J, expanded the output section to put out 30 watts into 4 ohms, then made a SuSy connection between two of them. I'm sure that there must be some other finagling like cascoding etc to keep dissipation down on certain parts but I don't there's too much more to the whole thing. Kind of makes me think about turning on my soldering iron.

Keep me posted on your AX100 progress! By the way - if you lived closer I'd invite you over for a listen.

Cheers,
Graeme

[moe29]

When did the XA series get upgraded to XA .5s?

Did i miss something? Did they show them at CES?

[gl]

Look here:

http://www.diyaudio.com/forums/showt...65#post1119565

Graeme