passive + Active Aleph L?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
According to this website : http://www.high-endaudio.com/RC-Linestages.html on Aleph L

"The most original feature of this preamplifier, never duplicated or imitated by anyone else, including Pass Labs themselves, is its automatic Passive/Active signal routing. If the audio system doesn't need more gain than the signal source provides, the Pass will not further amplify the signal. This is achieved by a unique volume control."

I try to look at Aleph L Service manual, but can't find the circuitry which can do the passive to Active mode change. Any idea?


This product also claim to have passive to active changeover feature :

http://www.ciaudio.com/ PA1 preamp

Does anyone know how this is done? To get the best of both passive and active in on pre.

Regards.





:D
 
Pls see the attachement of simplified Aleph L diagram . Is this correct?

When volume is set beyong 3 o'clock, output is taken in between Rf1 and Rf2 and does the gain is determine by Rf1/Rin? Does Rf2 contribute to the output impedance of the opamp since it is in series with the opamp?

Pls advise. :confused:

Thanks.
 

Attachments

  • simplified aleph l.jpg
    simplified aleph l.jpg
    14.7 KB · Views: 356
The one and only
Joined 2001
Paid Member
No, that is not correct. Imagine a non-inverting gain stage
driving the top of an attentuating ladder (selector switch with
resistors between the pins). The bottom of the ladder goes to
ground, and the wiper goes to output. Ordinary output volume
control, right?

Now take the input to the gain stage and also connect it to one
of the pins toward the middle. Too high, and the system
will oscillate without a load (or maybe even with one). Now
you have an output attenuator where it starts out at the CCW
bottom in "passive" mode, at one point the output is directly
connected to the input, and above that, the system has active
gain.

:cool:
 
Member
Joined 2004
Paid Member
Not surprisingly, you folks are operating at a level far beyond the understanding of this newbie. Let me ask a simple question: has anyone implemented a clone of the attenuator in Mr. Pass's Aleph P? I am considering building an Aleph P using Kristijan's PCBs, but they do not incorporate volume control or source selection. One option is to try the Dantimax products, but I don't know whether they measure up sonically to the Aleph P. If there is another option available to beginners like me, I'd love to hear about it.

Regards,
Scott
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.