I noticed some postings in which pictures were shown from PCB that were obviously not made with permission of Nelson Pass. It resulted in forum members refusing to help with questions about building an amp with these boards. As far as I know/could find, there is no list of approved boards other than in the DIYaudio store. Because I am not an experienced builder the possibility is very real I need help with some problems I encounter when I decide to build an Aleph X. It would be dissapointing for me if I could not post my questions on this board.
Salomon, I hope you understand my question was not to attack you in any way.
OneplusTwo: I guess Nelson would understand
To continue with the Aleph X: As far as I understand these boards ARE approved: ALEPH-X - Pass Labs Clone Class-A amplifier PCB & schematic
Anyone experience with these?
Well, did some research and since Kristijans boards and web-adress are mentioned several times on the passdiy site, I guess they are approved although the discussions on DIYA sound different. (Or am I making this issue "bigger" than I should?)
@ Solomon: during my reading I found your Aleph X. Beautiful! Sorry to see your website is down.
Another question: I saw a lot of builders are using Macmillan resistors. I googled but no result. What are, where are Macmillan resistors.
@ Solomon: during my reading I found your Aleph X. Beautiful! Sorry to see your website is down.
Another question: I saw a lot of builders are using Macmillan resistors. I googled but no result. What are, where are Macmillan resistors.
Now you find more pictures and several infomations about my Aleph-X here on this website:
Class A monster: Aleph-X by Horst Wolf Audio Tweak
My own Website with more infomation about my projects will be ready again in a few weeks.
That is not difficult. But it would be nice if someone with better English knowledge then I could write the answer.
I will try and answer your question.
The MacMillan resistors are named after Ian MacMillan, a member of this forum. On the large Aleph-X thread NP challenged the forum to discover a second method that he had employed to reduce absolute DC offset in the factory XA circuit. Ian won the contest by proposing the resistors that are now named after him.
My most recently published Aleph-X schematic is attached to the following post. The MacMillan resistors are labeled R46 and R47.
http://www.diyaudio.com/forums/pass-labs/73543-ax100-100w-aleph-x-monoblocks-37.html#post1404235
This next post includes a discussion of my own experiments to find an optimum value for them. There is valuable follow on discussion and results from other builders.
http://www.diyaudio.com/forums/pass-labs/73543-ax100-100w-aleph-x-monoblocks-2.html#post856975
Please note that there is a large amount of inaccurate information around on Aleph-X circuit values. KK's site for instance is not high on my list of accurate information sources.
Graeme
His PCB's may be fine. They look nice. It's some of his schematics I question. KK is a layout guy. There is no evidence that he has ever actually built any of the projects embodied in his PCB's.
Graeme
I can confirm his PCB's are fine. I have build an Aleph 5 with his boards a couple of years ago. Sold the Aleph 5 and bought UCD400AD's. Now I'm looking for something wit a bit more power and it has to have balanced inputs. The 100W Alpeh-X seems like a good option. Now I have to find PCB's (with a bit of documentation since I'm not an electronics engineer) which seems to be a bit more difficult than I thought it would be...
Hi Salomon,
very nice amp!
On the website you mention a "special thermal offset correction"
Would you care to tell a bit more about it? I would be very interested.
William
Hello William,
sorry for the long wait!
I don’t know the exact values of my modification because it was more than two years ago and I did not make a documentation of it.
I think I have made the following thinks:
You have to take two pieces of the PTC KTY81-110 and solder in both parts parallel instead of the 475 R source resistor of the constant current source.
Be sure to make a good thermal coupling of both parts (per channel) to the heat sink. Now you have to re-adjust the offset with V2 (200R)
You will get a low offset in a much shorter time than with a normal 475R Resistor. The two PTC have soldered parallel in cold state a value of 500R.
I use this modification since more than two years together with modified DC-protection boards (see the pictures in the left and right back side of the amp) who are switching the output pins to ground and at the same time switch completely off the amp.
I do not use relays in the signal path, because they reduce the sound quality.
The protection boards are controlling each of the four output Pins of the Aleph-X amp separately.
It has not been necessary to re-adjust the amp since building the amp.
sorry for the long wait!
I don’t know the exact values of my modification because it was more than two years ago and I did not make a documentation of it.
I think I have made the following thinks:
You have to take two pieces of the PTC KTY81-110 and solder in both parts parallel instead of the 475 R source resistor of the constant current source.
Be sure to make a good thermal coupling of both parts (per channel) to the heat sink. Now you have to re-adjust the offset with V2 (200R)
You will get a low offset in a much shorter time than with a normal 475R Resistor. The two PTC have soldered parallel in cold state a value of 500R.
I use this modification since more than two years together with modified DC-protection boards (see the pictures in the left and right back side of the amp) who are switching the output pins to ground and at the same time switch completely off the amp.
I do not use relays in the signal path, because they reduce the sound quality.
The protection boards are controlling each of the four output Pins of the Aleph-X amp separately.
It has not been necessary to re-adjust the amp since building the amp.
Pass DIY Addict
Joined 2000
Paid Member
Looks like an interesting solution to offset! I'll have to give this a try. Currently, my amps live in an unfinished section of my basement that ranges from a low temp of 13c during winter to 20c during summer. As a result, my DC offset drifts as much as 2.5v on the completed amps. Heat sinks show a 35c temp rise.
I wonder if this will keep offset under better control...
I wonder if this will keep offset under better control...
Hi Eric,
it should. I did a few calculation on which resistors to use (R24/26 and VR2) to get the best result. Will try this when I get back home. Will report as soon as I have tried it. Now the bias through the diff pair in my amp changes almost 3% from cold to warm. With the PTC it becomes more like 0,2% (theoretically).
William
it should. I did a few calculation on which resistors to use (R24/26 and VR2) to get the best result. Will try this when I get back home. Will report as soon as I have tried it. Now the bias through the diff pair in my amp changes almost 3% from cold to warm. With the PTC it becomes more like 0,2% (theoretically).
William
Pass DIY Addict
Joined 2000
Paid Member
Hi Eric,
maybe it would be better to replace the 9610's first as my changes and values will be based upon a Jfet input......
But I will try to create a sort of spreadsheet to calculate the resistor values (R24/26 and VR2) based upon the PTC, bias through the input pair and Vgs over Temp of the current source Fet.
William
maybe it would be better to replace the 9610's first as my changes and values will be based upon a Jfet input......
But I will try to create a sort of spreadsheet to calculate the resistor values (R24/26 and VR2) based upon the PTC, bias through the input pair and Vgs over Temp of the current source Fet.
William
Pass DIY Addict
Joined 2000
Paid Member
Hi Eric,
Here you go. I have since removed the 15 ohm JFET source resistors. Matched 2SJ74's will do just fine in place of the 2SJ109's.
http://www.diyaudio.com/forums/pass-labs/73543-ax100-100w-aleph-x-monoblocks-37.html#post1404235?
You will be very pleased with the improvement in the sound of your amps.
Graeme
P.S. Please note NP's follow-on post and comment.
Here you go. I have since removed the 15 ohm JFET source resistors. Matched 2SJ74's will do just fine in place of the 2SJ109's.
http://www.diyaudio.com/forums/pass-labs/73543-ax100-100w-aleph-x-monoblocks-37.html#post1404235?
You will be very pleased with the improvement in the sound of your amps.
Graeme
P.S. Please note NP's follow-on post and comment.
Last edited: