Aleph 30 Supply Voltage

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Hi,

My first post here... Thanks to Nelson for being one of the coolest guys in audio allowing us to play with his designs.

I have a completed Aleph 30 board set, but my spare power supply transformer yields +-30v when rectified. Can I run the Aleph at this voltage level, approx. 5v higher than specified? The capacitors etc. can take the extra voltage, but I'm not sure if running +-30v is ok otherwise.

Maybe a dropper resitor to lose a few volts is a good idea. How many amps does the Aleph 30 draw? I read 4A somewhere but would like to confirm to calculate the R value accurately.

Any input is appreciated.

Thanks,
 
I run mine higher than that. It will dissipate more heat with the higher voltage, so as long as your heat sinks can take it you'll be OK.

If you want to lower the voltage, consider an inductor instead of a resistor before the caps. The inductor will let less noise in and won't dissipate as much power as a resistor. I have some inductors I can switch in mine (shorting them out) to go from high to low voltage.
 
You should be able to calculate the amp draw from the resistors in line with output devices.

The bipolar transistor in the current source allows a roughly .65 voltage drop across each one. Multiply by the total number of output devices.

Then Zen articles are good reading --- it is explained in the third or fourth article in the series.

JJ
 
Running it at 5V higher rails is not a big deal with the A30 having 6 output devices, 2 more than the Aleph-3.

Both Aleph-3 and Aleph-30 are biased at 2 amps, +/-25V rails, aka 100W dissipation per channel.
2 Amps makes 32 Watts in 8 Ohms, means that at 30 watts output power both top and bottom sides are still conducting/open.
To fully profit from 30 Volt rails, the quiescent current should be biased up from 2 to 2.5 Amps.
30 Volt rails and 2.5 Amps makes 150 watt dissipation, which sets the minimum requirement for the heatsinks at 0.20 C/W per channel.

Biased at 2 Amps, it's much more preferable to use the 5 spare Volts for a CRC/CLC, Single-Ended amps benefit most from the cleanest power.
To drop the rail voltage, it makes no difference whether CLC or CRC is used because Ohms law remains the same : 5 Volts times 2 Amps is 10 Watts dissipation.
Dissipating the 10 watts with a thick metal sinked power resistor is a whole lot cheaper than an aircoil, and cheaper than bigger heatsinks for the output stage.
(the benefit of an aircoil is that it reduces the ripple much more than a CRC arrangement for an identical voltage drop)
 
jacco vermeulen said:

To drop the rail voltage, it makes no difference whether CLC or CRC is used because Ohms law remains the same : 5 Volts times 2 Amps is 10 Watts dissipation.
Dissipating the 10 watts with a thick metal sinked power resistor is a whole lot cheaper than an aircoil, and cheaper than bigger heatsinks for the output stage.

Clarification: If you were referring to what I wrote, I was talking about a LC arrangement, not a CLC. The inductance rather than the DCR of the coil drops most of the voltage in a LC power supply, hence, less power dissipated.
 
Thanks to all of you for the advice!

The amp modules are mounted on a heat tunnel with a fan for active cooling. Should dissipate enough I hope.

Will calculate a dropper resistor to lose a volt or two and gain some filtering. If this sounds good (I'm a tube guy trying to convert) a choke should be better. Any suggestion on the right inductor to think about?

Wanted to hear the Pass sound for a while now... I've tried Class D (not enough tonal color for my ears), Chipamps, and Class A/B (SKA 150, nice sounding amp and the SS I like best so far), but have yet to hear a full on Class A SS amp so I'm really looking forward to hearing this classic design of Nelson's.

Thanks to your helpful input I have a project for this weekend finishing off the power supply and getting everything connected. This is gonna be fun!

Happy listening :)
 
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Joined 2005
TV Man,

just wondering if you had hooked up the PSU to the amp boards to see what +/- rail V's you are getting under load? Or is the +/-30V the PSU unloaded?

i'm running 2R dropper resistors in a CRC config in Aleph30 monoblocs and get slightly over +/-32V unloaded, which drops to +/-26V when loaded by the amp boards.

cheers
Paul
 
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