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Old 29th October 2010, 12:49 AM   #3631
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Quote:
Originally Posted by georgehifi View Post
Me thinks it time for the moderators to step in, before this thread ends up in the gutter.

Cheers George
What do you think needs moderating?
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Old 29th October 2010, 12:53 AM   #3632
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Your system is compatible for a Lightspeed without buffer, you may enjoy it even more, as it will not have an transistor preamp thinness to it, as in a "hot" shot at you type transients. The transients the Lightspeed have has more body to them and sound more relaxed yet it will extend higher and lower than your tube pre.
If you feel the need for a tube buffer after it, this is the one that sounded best to me tube or transistor
Cheers George
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File Type: jpg SLCF Super Linear Cathode Follower.jpg (31.3 KB, 400 views)
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Old 29th October 2010, 01:34 AM   #3633
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Quote:
Originally Posted by georgehifi View Post
Your system is compatible for a Lightspeed without buffer, you may enjoy it even more, as it will not have an transistor preamp thinness to it, as in a "hot" shot at you type transients. The transients the Lightspeed have has more body to them and sound more relaxed yet it will extend higher and lower than your tube pre.
If you feel the need for a tube buffer after it, this is the one that sounded best to me tube or transistor
Cheers George
I'm assuming this is in response to my post. Thanks George.
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Old 29th October 2010, 12:42 PM   #3634
AndrewT is offline AndrewT  Scotland
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post3632
George,
is that the schematic that was converted to mosFETs by one of our Members in Europe?
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Old 29th October 2010, 01:34 PM   #3635
maximus is offline maximus  Scotland
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Hi Andrew,

I posted a mosfet circuit, that is very similar in operation to the tube buffer, in post 1742 on page 175 if this helps.

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paul
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Last edited by maximus; 29th October 2010 at 01:37 PM.
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Old 29th October 2010, 02:02 PM   #3636
markusA is offline markusA  Sweden
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I've started work on my clone again.
Hopefully I'll have it up and running within a month or so. It's been collecting dust for too long.
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Old 29th October 2010, 08:09 PM   #3637
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Quote:
Originally Posted by AndrewT View Post
post3632
George,
is that the schematic that was converted to mosFETs by one of our Members in Europe?
It is a buffer that Tektronics used in their top tier tube Occilloscope of yester year and called the "SLCF" Super Linear Cathode Follower, and yes it was reborn. For a tube buffer it has a nice low 100ohms output impedance, shame about the coupling cap thou.

Cheers George
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Old 2nd November 2010, 10:34 AM   #3638
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Default rise and decay times

Hi all

I don't doubt that the lightspeed attenuator works well and like the concept but am struggling to understand how the optocouplers with a rise and decay time of 5 and 80ms respectively can follow an audio signal of 20kHz-can someone please help me with this...I'm but a mechanical engineer dabbling in electronics...

Thanks
Chris
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Old 2nd November 2010, 10:43 AM   #3639
AndrewT is offline AndrewT  Scotland
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the operator sets the "volume" by adjusting the current fed to the LEDs.
The LDRs adjust their resistance (slowly) to follow the light output of the LEDs.
After your time constant or seven have passed the LDRs have reached their final resistances.
These final resistances attenuate the Audio Signal that passes through the LDRs.
The Audio Signal does not pass through the LEDs.

If the design can hold the LEDs light output more constant then the resistances of the LDRs will be more constant. That's where regulation and capacitors come to our aid. To help fix the LED currents.
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Old 2nd November 2010, 10:45 AM   #3640
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That rise and decay time - isn't that only relevant to the speed with which the volume control adjusts? In other words, isn't it the case that if you turn the volume up, that is the response time of the opto-coupled led to ldr, and not the response time of the ldr to the music signal?
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