AX100 100W Aleph-X Monoblocks

[jacco vermeulen]

Tad,

count yourself lucky, consider how much people elsewhere have to pay for Magnepan or any other US gear.
For example, a set of 3.6 Maggies retails for $10k overhere.

If i could get an MG3.6 set at US rate, use it for 15 years and then trade it in for $1k end value, then the annual write-off of my LSP system would be less than what i pay for a pair of shoes.

Money talk Off.

[daly41k]

Hi GL it has been a long time since I posted but I have recently retired and I now have more time to spend on Audio projects. I don't have to be on an airplane all the time.

I was thinking that I would like to re bias my XA100 to a new bias point reducing it down from about 5.5amps to 3.5 or so as I don't need this much class A power and it might help quiet down my trannies. I am thinking that a simple adjustment is all that is needed without any component changes. The voltages from the PS would remain the same. I want to use them on my ribbon tweeters which are crossed over at between 2100 to 2500khz at 60db using my DEQX digital crossover. I measured using my scope about 10volts p to p during a normal level listening session which is just a few watts. Let's say with some safety I could get by normally on 20watts class A with maybe peaks of 50watts (hard to imagine in less I got into the wine stock a little too much). I probably would use a 40uf caps on the outputs for tweeter protection (12 5" ribbon tweeters per side at over $100 bucks each is a reason to at least think about protecting them). Builiding a protection relay scheme is not to interesting. What do you think?

I was also considering building an F3. I remember that they may put out about 10 watts and this could be enough. I can't find the schematic on the F3 thread but it must be somewhere. I also thought about trying to build the Jan Didden design in the recent Audio express but it is not a balanced input.

Hope all is well with you and yours in this new year. dave

[gl]

Hi Dave,

It's good to hear from you. Congratulations on your retirement. It's a condition I look forward to in another 5 years or so if all goes well. It's also good to hear that your system continues to serve you well.

As far as the bias reduction goes, I would be inclined to remove output transistors rather than turn the bias down on the whole output section. Turning the overall bias down and keeping the current gain percentage where you have it set will require changing a number of resistor values.

The more elegant overall approach would be to build an F3 as you suggest. The schematic is on the Firstwatt site here:

http://www.firstwatt.com/downloads/F...-manual-sm.pdf

Things are going well here although 2009 was very brutal to my business. Things are turning up with the start of 2010. I hope my comments are helpful.

Cheers,
Graeme

[daly41k]

GL thanks for your comments, after reflecting on this you are right and if things are working well leave enough alone. Noisy trannies irritate me and I have put caps across the hexfreds in the PS and added the chokes but still they wine. I found out that the avel lindberg trannies are made in China. This can be hit or miss on quality. I worked in China for a number of years and their quality is all over the place. This is why avel trannies are cheaper.
I even put in a dc blocking circuit in the ac input on the primary side but nothing has stopped it. Talking to Avel they say "oh welll stuff happens".

Thanks for the schematic, I will go back through my audio x press mags and find the old Nelson articles and read up on current source amps.

I should tell you that my dream retirement job is to be an tasting consultant and organizer at one of the big NAPA Valley vineyards. Hey I could ** all day and work on audio at night. The music would definetly sound better.

Or I could volunteer as a listening consultant at Pass Labs and help them all day by listening to their equipment and giving opinions. Just have to sell my house first. dave

[chchyong89]

sorry to bringing this topic top again, can i know AX100 = XA100? XA100.5 = revision of XA100 ?

[gl]

Back in 2006 when this thread started and the Aleph-X was all the rage, everybody would have known the answer to this question. Some things do get lost in the mists of time.

It's a reasonable question however, so here goes.

AX100 - This is a 100W version of Grey Rollins original 38W Aleph-X project that is documented in the thread of the same name. In general all amplifiers here in this forum whose names start with the letters AX derive in some way from GR's original. In the case of the AX100 numerous changes have been made to bring it closer to the factory version. Most of these changes come from hints dropped by NP himself.

XA100 - This is a Pass commercial product. When referring to the XA series one usually uses that term or the term 'X Aleph'. The owners manual for this product is on the Pass website.

XA100.5 - This product replaced the XA100 and is a very different design. There are a number of threads discussing this amp.

There.

Graeme

[Andy5112405]

I'm intrigued by the heat dissipation conversation.

Mathematically the alluminium plates should be capable of 1.7 K/Watt which is far too small for a 100W Class A design. Such a design would be looking for 0.7 K/Watt to run at a hot 40-45 Degrees above ambient.

[gl]

Well for starters the first post in this thread states that the amplifiers run at 21 degrees C above ambient - not 45 to 50.

Second, you state in so many words that the mathematics indicate that the amplifiers shouldn't work. Yet you provide only a couple thermal resistance coefficients without stating where you found them or showing how you derived them.

And finally, the amplifiers work fine and have done so for over four years.

Here's some math: Taking one heat sink plate we have two transistors which input 12 watts of heat each for a total of 24 watts, and a temperature rise of 21 degrees C at the edge of the plate. So we have 21/24 = a T.R.C. of .87 (at the edge of the plate). Not that far away from your number of .7 actually. At the transistor the temperature measures about 7 or 8 degrees C higher.

However, the thermal gradient of the plate is quite poor. The key to success is keeping the heat dissipation on each transistor low, using lots of transistors, and spreading them out physically. Works like glue.

Graeme

[Andy5112405]

Sorry, I did not mean to offend.

I did the maths using two sides of each plate this time and your results are then very close.

The equation that I normally use is Tha = 50 / (Square root of Area (cm2))

So for a plate that is 17" x 8"; Area = 1745cm2

50 / (Square root 1745)) = 1.2 K/Watt

I'm planning on building an Aleph 4 but the cost of heatsinks is beating me. The Aleph 4 dissipates nearly 300W / Channel. This is spread over 12 devices so 24W / Device.

All 12 devices on one heatsink would require a heatsink of less than 0.15 K/Watt - ENORMOUS.

[jacco vermeulen]

Dirty Harry's quicky isn't exactly what i'd call mathematical and a fool's approach for a 2 times 300W dissipation project.