lighspeed attenuator w/Simple SE AMP

[Salsero]

The research continues before I plunge into building my first tube amp. I am looking into an attenuator to set it up as an integrated amp.
Is the Simple SE AMP compatible with the lightspeed attenuator shown in diyaudioprojects.com ? It is a highly praised attenuator (hopefully not overhyped).
Has anyone tried a TVC attenuator with the simple SE - its flat frequency response should lead to a great balanced sound.
Your input is appreciated in advance.
Thanks
Salsero

[Fenris]

There's a whole thread in the Solid State forum on the Lightspeed. I'm building one into a tube amp of my own design (if I can ever stop working 12 hour days). It shouldn't present a problem.

[tubelab.com]

I looked at the plans for the Lightspeed attenuator. It looks like a good idea, and is a fairly low impedance device (10K ohms). The input impedance of the Simple SE is much higher so it should not be a problem as long as your source can drive it. I am using a relay based attenuator with my Simple SE and it works fine. I have not tried a TVC.

[rknize]

Wow...audio through an LDR. Never would have crossed my mind. Pretty clever.

[tubelab.com]

Wow...audio through an LDR

They was pretty common in guitar volume pedals back in the 60's. LDR's have been used in audio and video compressors and auto leveling controls for ever as well.

LDR's kind of fell off the radar screen when better technology appeared. The originals used incandescent bulbs which resulted in a finite life time. The new ones use an LED which means that the power supply for the LED must be very clean or the hum and noise will directly modulate your audio signal.


There is a whole counter culture revolving around the use of these things. A popular brand of light - LDR pair from the 1960's was Vactrol. That term now seems to be used in a generic manner to represent any form of LDR. Google Vactrol or "circuit bending".

[rknize]

Yeah the term Vactrol is used for optoisolators in general and I've used them for digital stuff. Guess I'm just not that clued-in to professional audio. I was starting to have thoughts of digital control, but you make a valid point about introducing noise via the LED. Looks like matching is an issue too.

[pchw]

Originally posted by rknize
Looks like matching is an issue too.

It is just labor intensive and like hell. No kidding, the Silonex LDR's don't settle down until they are powered up for a few hours!! I have 50 of them, and they all have the characteristic - the resistance continues to drift (up to 20+%) from powered up to 6 hours later, and they are very sensitive to temp. If LS is used as the volume control, I strongly suggest to use 2 mono pot instead of one dual gang. That way you can relax the matching because you can balance the 2 channels individually.