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Old 5th November 2007, 10:55 PM   #1511
JBL4435 is offline JBL4435  Germany
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Thanks to macka.

Changed R24 from 470 to 320 ohms and can now adjust abs. DC to around 0V.

Nice
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Old 11th December 2007, 10:42 PM   #1512
tenderland is offline tenderland  United States
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Default back home again

Hello,

After a brief "break in" period in a new job I am ready to resume my
Aleph project. Get ready for some rather dumb questions.



j
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Old 18th December 2007, 05:46 AM   #1513
Chois˘â is offline Chois˘â  South Korea
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Hi,
I made aleph-x few months ago.
It works well except minor problem.
Absolute DC voltage changes with temperature increases.
I thought that temperature-free(?) constant current will help this
minor problem. But I wonder it works.
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Old 18th December 2007, 06:38 PM   #1514
Nelson Pass is offline Nelson Pass  United States
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Aleph-X builder's thread.
As an alternative you could use a thermistor in the CCS
circuit to compensate. Try a high value, maybe 10Kohm in
parallel with either the 50 or 100 ohm resistor and see what
happens.

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Old 21st December 2007, 12:32 AM   #1515
Chois˘â is offline Chois˘â  South Korea
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Thanks Pass,
I'll try.
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Old 1st January 2008, 02:00 PM   #1516
D_o_S is offline D_o_S  Czech Republic
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Where can I find a PCB for the Aleph-X? Looking to build the 150W@4ohm version...
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Old 6th February 2008, 10:15 PM   #1517
noisefree is offline noisefree  Germany
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Hello altogether…

Since half a year I wanne built an AX.5 design but had absolutely no time to work on it.
Last week I have finished the output board and UGS layouts and the matching of the output mosfets.
Now my main problem is the bias voltage circuit:
The amplifier should have a stand by circuit (because of the monster inrush current and the electricity bill) which leave the output stage in a small conducting state while the front end is shut down.
I have done a long catalog of questions. Hope that Mr. Pass or one of the experts out there would answer to it.

1) What is the power consumption of one mono block of a commercial AX100.5 in stand by mode?

2) Are there bootstrapping capacitors implemented to get more voltage swing out of the front end? Is that generally possible?

3) Does it make sense to modulate the front end cascode devices?
(I am searching an application for the two elcaps in the original bias circuit)
4) Mr. Pass / You told me for half a year that the output of the front end is loaded by 10k resistors to each rail. Are these 3W power resistors?
5) Is the thermistor in the voltage bias circuit for faster warm up / less bias drift or current limiting for the output stage?
6) How can I drop down the dissipation of a TL431 voltage reference? My calculations show a dissipation of about 200mW when it is driven by the UGS module. Isn`t this a bit to much for a TO-92?
7) For what is the third cable (blue) in the screw clamp beside the two extern turn on cables on the mainboard?
8) Are there any plans on Passlabs for an INT-30A? (Same topology / circuit and case like an INT-150 but only 30W@8Ohm class A)


Best regards
Dirk

Forgot: There is a pass consulting internet side. They use exactly the same PASS logo as you on your new equipment - just google pass!!!???
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Old 7th February 2008, 05:06 AM   #1518
Luke is offline Luke  New Zealand
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Quote:
Forgot: There is a pass consulting internet side. They use exactly the same PASS logo as you on your new equipment - just google pass!!!???
Dirk its first hit on google.de not co.nz or probably other sites.

they are travel management consultants, but
i think closet pass labs freaks like many of us:-)

http://www.pass-consulting.com/internet/index.html
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Old 8th February 2008, 09:28 AM   #1519
Ian Macmillan is offline Ian Macmillan
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Quote:
Originally posted by noisefree
Now my main problem is the bias voltage circuit:
The amplifier should have a stand by circuit (because of the monster inrush current and the electricity bill) which leave the output stage in a small conducting state while the front end is shut down.
1) What is the power consumption of one mono block of a commercial AX100.5 in stand by mode?
2) Are there bootstrapping capacitors implemented to get more voltage swing out of the front end? Is that generally possible?
3) Does it make sense to modulate the front end cascode devices?
(I am searching an application for the two elcaps in the original bias circuit)
4) Mr. Pass / You told me for half a year that the output of the front end is loaded by 10k resistors to each rail. Are these 3W power resistors?
5) Is the thermistor in the voltage bias circuit for faster warm up / less bias drift or current limiting for the output stage?
6) How can I drop down the dissipation of a TL431 voltage reference? My calculations show a dissipation of about 200mW when it is driven by the UGS module. Isn`t this a bit to much for a TO-92?
7) For what is the third cable (blue) in the screw clamp beside the two extern turn on cables on the mainboard?
8) Are there any plans on Passlabs for an INT-30A? (Same topology / circuit and case like an INT-150 but only 30W@8Ohm class A)
Dirk,
Do you really expect NP to help you in what amounts to a micro reverse engineering of his shipping product? I think not and it is not really in the spirit of DIY experimentation, i.e. learning for one’s self.

That said, you raise some interesting points which I will try and answer although I should say that I do not have access to an AX100.5 and these are just my opinions.

You say that you think the standby circuit exists mainly to limit the large inrush on switch on. Are you sure? This is something that has to be handled anyway as switching on from cold will cause a large inrush due to the charging of the PS capacitors. I suspect that it might be more to do with getting the amp to warm up more quickly and reach optimal performance.

1) I’m afraid I have no idea but I would hazard a guess of something around 5-10mA per output device, i.e. a total of 5-10W.
2) I doubt it. More likely the front end (UGS) is using a higher voltage PS to fully drive the output stage.
3) Unlikely in this application and with the typical FETs used.
4) Why does it matter if the 10k resistors are 3W or not? They will typically see about 20v across them (assuming you connect to the output PS), i.e. about 40mW so I don’t see why they would need to be 3W.
5) I didn’t know there was a thermistor in the bias circuit but perhaps it has something to do with the standby arrangement. Have you considered how this might work?
6) I too have wondered about this, always assuming it is a TL431 that is used. The only way to reduce the dissipation of which I am aware, would be to use a resistor in parallel to take some of the current.

I’m in no position to answer the last two questions.

I’m also in the process of (slowly) building my interpretation of this amplifier but I haven’t given any thought to a standby option so far. Even so, it would be interesting to speculate on how this might be achieved and what benefit it might provide.

Ian.
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Old 8th February 2008, 04:03 PM   #1520
Ian Macmillan is offline Ian Macmillan
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Dirk,

Just noticed this in the XA.5 information on the Passlabs web site:

"New bias circuit – A newly developed bias generator has eliminated three sources of variation in bias current in the output stage. It also allows approximately 20% greater power output for a given supply voltage"

so perhaps you are on to something with your thermistor idea. Certainlly worth thinking about.

Ian.
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