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Old 9th April 2002, 04:27 PM   #1
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Default Aleph's front end separate power supply

I was wondering if it would make much of an improvement to use separate regulated power supplies for front end of Aleph power amps. I have some custom transformers from Plitron (I was using them for A75) with separate windings for that purpose.

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Old 9th April 2002, 04:41 PM   #2
jam is offline jam  United States
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Peter,

You can only regulate the tail of the differential of the Aleph(positive rail). This might have some sonic benefits the negative rail cannot be regulated.

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Old 9th April 2002, 05:56 PM   #3
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Why not regulate the negative rail?
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Old 9th April 2002, 06:13 PM   #4
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I see no reason that you cannot regulate the negative rail. If you look at the Balenced Zen Preamp power supply schematic, the positive and negative rails are regulated.

I see no reason to run seperate power supplies for each. As noted in the below post, this possibly cause problems.

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Old 9th April 2002, 06:14 PM   #5
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Default Regulated supplies for Aleph

The current source for the front end of the Aleph must come up at the same time as the rest of the circuit or you will get a big turn on thump. I lost some tweeters in a biamp setup this way by putting a Cap across the zener reference. Messing with the decoupling caps for the Dynanic current source in the output will most likely get you in the same trouble. Getting a power amp to power up without a transient on the output is a challenge. But if the 9.1V zener was replace by a couple of series LM329 and the source resistor increased to give the same current you would have better regulation of the reference for the current source. They can be biased by a current source for even greater Power supply rejection You also could bias the zener with a 5 ma current source for the same effect. A larger source resistor for the current source will give a higher output impedance for the Mosfet current source as will cascoding. I have 5 series green LEDs bypassed by a small cap in place of the zener in my Aleph 3.
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Old 9th April 2002, 06:43 PM   #6
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From my past experiences I have learned that the more separate power supplies you have the better the sound: better defined bass and more texture overall. One way to avoid turn on thump would be to leave the amp on all the time and disconnecting output stage from PS only, avoiding inrush currents as well.

I was hoping that maybe someone has already experimented with supplying separate voltage to amp's front end and would share his observations.

Harry, this is tweaking at it's best. BTW does your Aleph has a thump at turn on? My A75 doesn't.

Peter
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Old 9th April 2002, 06:46 PM   #7
BrianGT is offline BrianGT  United States
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Doesn't the Pass Labs X series keep the input stage on during standby mode and turn off the output stage?

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Old 9th April 2002, 06:49 PM   #8
jam is offline jam  United States
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Peter,Brian,

If you look at the drain resistor of the differential you will see that the output mosfets are turned on by the voltage drop across this resistor. Now if you regulate the front end how is the output mosfet going to track the voltage across the drain resistor when the outputs rail falls or rises. The only solution would be to regulate the whole supply.

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Jam
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Old 9th April 2002, 06:51 PM   #9
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Brian,

In standby mode the amplifier stays on the input is muted and the bias to the outputs is shut off.

Jam
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Old 9th April 2002, 06:55 PM   #10
BrianGT is offline BrianGT  United States
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I was initially referring to regulating the entire supply. I see now what was initially meant that you could not regulate the negative cannot be regulated. Would any benefit be obtained from regulating the entire supply?

Also, as far as a standby mode, could you place relays on the rails between the input and output stage, to turn off the biasing of the output stage, on the Aleph 2? Would this be all that is needed for standby mode?

Thanks for you input,

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