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Old 15th April 2009, 06:30 PM   #1751
xcel is offline xcel  Netherlands
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Talking Regulated supplies for my Aleph-X

Jason,

I'm currently building an Aleph-X with a partially regulated power supply i.e. the front-end of the amp receives a regulated voltage while the output stages are connected to an unregulated voltage.

The unregulated voltage comes from the main power supply which is passively filtered by means of a CRCRC configuration. The amp draws a 4A bias current from this supply, which results in a ripple of 10 mVpeak. This makes for a pretty quiet supply to start with. Not entirely satisfied though, I decided to use this allready clean voltage as an input for a voltage regulator stage for the low power front end (the diff amp). Again this voltage is passively filtered, followed by a regulator which in turn is followed by yet another passive filter. I've just finished building it but I've built similar supplies for my preamp and we're looking at a 90-110 dB suppression with this circuit.

I haven't tested it thoroughly and the amp hasn't played yet so I can't tell you anything about the sonic advantages in this particular amp. I can tell you however that I've built and designed numerous pre- and power amps and each and every one of them have increased their sonic capabilities with improved power supplies. I can't tell you when it's finished so if you want to know send me a message somewhere in the near future.

Regards,

Xcel

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Old 15th April 2009, 06:52 PM   #1752
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The Aleph X schematics that I have seen all have the differential
pair directly driving the Gates of the negative half of the output
stages. If this is the case, the Drains of the input FETs will want
to connect to the same supply (through the resistors) that the
negative half of the output stage sees, otherwise the difference
between a regulated (-) supply for the front end and the output
stage (-) supply will be amplified. a lot.

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Old 15th April 2009, 08:08 PM   #1753
xcel is offline xcel  Netherlands
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Nelson,

Thanks for the usefull comment.

Suppose I trim the regulated voltage at the same value of the unregulated voltage (just for the sake of presenting a regulated voltage to the diff amp), this problem wouldn't occur, right ?

In your white paper on power supplies you presented this approach to achieve a significant amount of the advantages the goals of fully active regulation, at reduced complexity and costs.

Correct me if I'm wrong, but from detailed photos of the insides of various XA.5's I made out that you're currently using this approach.

What do you consider as the particular sonic benefits of this approach ?

Greetz,

Xcel

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Old 15th April 2009, 08:21 PM   #1754
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Hi,

just look at the unregulated voltage of your amp. It is changing all the time just as the mains voltage is. Therefore it will be very difficult to set a voltage.

It will also be difficult to get a regulated voltage with the same value as the unregulated one without using a seperate power supply

William
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Old 15th April 2009, 08:22 PM   #1755
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by xcel
.....

Suppose I trim the regulated voltage at the same value of the unregulated voltage (......


difference in ripple between smoothed one and non-smoothed supply will transpose directly at output mosfet's gates as signal .

conclusion - try to better entire PSU ....... symmetrically , off course .

if you want - search any possible benefit for input stage - in bettering his CCS ......... but will that be audible ....... that's the question
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Old 19th April 2009, 09:20 PM   #1756
Jozua is offline Jozua  South Africa
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Default Any New PCB for sale

Hi

Does anybody have a spare set of the latest version PCB for sale?

Please e-mail me.

Thanks

Jozua
South Africa
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Old 19th April 2009, 10:30 PM   #1757
labjr is offline labjr  United States
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Default Re: Any New PCB for sale

Quote:
Originally posted by Jozua
Hi

Does anybody have a spare set of the latest version PCB for sale?

Please e-mail me.

Thanks

Jozua
South Africa
I have an extra pair of version one boards if you are interested.
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Old 20th April 2009, 01:21 PM   #1758
Jozua is offline Jozua  South Africa
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labjr

Thanks for replying.

I have a set of the green the version 1 boards already but I want to rebuild the amp with the latest board.


Regards


Jozua
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Old 6th May 2009, 02:33 PM   #1759
sftw is offline sftw  China
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Default good

good
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Old 11th May 2009, 01:04 AM   #1760
lgreen is offline lgreen  United States
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Default shorted MOSFETs

I never finished my A-X....its been I hate to say how many years ago that I started!

I am going to get it working in the next few months. Heck its amost done. I think I made a mistake by using arctic silver thermal compond with mica insulators under the MOSFETs, I think the devices were under sufficient pressure that the grease become conductive.

Anyway I have measured the resistance between MOSFET terminals.

My A-X uses 4 banks of MOSFETs, each bank has 3 MOSFETs; these are connected to Grey's green Aleph-X boards.

One bank of 3 MOSFETs measures short-circuit between the pins. I know that the MOSFETs are supposed to be matched but I forget what you are supposed to match to what?

Question 1: How many transistors do I need to buy and match? and what is supposed to match what? Should I start over with a complete new set of 12 matched transistors for the channel or can I get 3 matched to each other? Putting in 12 matched devices is going to be pain! Maybe 24, have not looked at the other channel yet.

Question 2: I recovered some sil-pads from a 1998 receiver. Have these worn out or can I use them? I didn't think that it was possible for these to wear out but I could be wrong.
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