LDR Active Preamp - does it exist?

I am using passive LDR (Light Dependent Resistor) volume control LightSpeed Attenuator. As much as clarity and all the good stuff about this little preamp, I wish I can have some gain for my low sensitivity amplifiers. Is there any existing active preamp using LDR volume control?

Showing 10 responses by nguyen787

I already owned the amp which input sensitivity at 4V. These amps practically eliminate the use of passive pre, even using Tekton Lore speaker rated at 98 dB, still does not provide enough loudness and dynamic. It would be a surprise to me that no other commercially available active preamp (tube preferred) that utilized LDR volume control.
I have three questions here regarding using of buffer:

1.) My understanding is buffer provide no gain, it is rather impedance mismatch correction device. Burson website does not indicate 6dB gain nor voltage gain. I sent them an email today to inquire about gain will let you know about that.

2.) Does Burson use LDR for volume control?

3.) What are the main differences between Burson Buffer and other buffer such as Dodd Audio.

You see, I like Goeorge's Lightspeed so much and my amp is not a good match due to low sensitivity (4V input). Another way is to add gain into my amp via mod, but that is beyond my skill level :)
CD/BluRay player is Oppo BDP-103. I dont know what are the output impedance nor voltage. I asked them the output voltage and impedance, but their answer was abit vague "designed to work with receiving equipment which is expecting an input impedance between 10K and 40K"

Amps are monoblocks Shuguang S845 MKII, which is 845 output tube.
Using Lightspeed, I can get the sound level at average 90 dB with high sensitive speaker 98 dB. The dial is near to max, position between 2 PM - 3 PM. Low volume tracks are the problem.

In anycase, I would like to optimize our system using the amps that I have in hand. It seems that these amps are not best choice. The main reason I am going with 845 output tube is the power 27 Watt that 300B SET can not provide. It seem low sensitivity defeats the purposes.

The Truth is an interesting concept. It does not seem to be popular in audiophile community.
What do you think - One alternative to solve the issue is to buy a match preamp. The match preamp specification is a bit worrysome for me because it output voltage is minimum 3V and max at 10V. I guess the reason it matches with the amp 4V input is because the preamp can deliver high voltage. The potential caveat is the preamp is less likely to compatible with most of other amplifiers. Preamp output at minimum 3V seems too high that may cause damage if the amp input voltage less than 3V?
Thanks George. I asked Grant Fidelity but did not get the answer I want to hear.

It is suggested that the amp Shuguang S845MK need to match with preamp Shuguang S200MK. The preamp spec is kinda freaky:

Input impedance: 100kohm
Input Power Voltage: ≤150mV
Output Voltage: more than 3V, maximum 10V
Output impedance: less than 10k ohm

George - the OPA627 DIY is too hard for me. Is there another version that easier.... :))
George - to your understanding, is a battery significantly improve sonic quality over wallwart to power Lightspeed?
I think I will keep the Lightspeed - sorry Steve SCM. Burson buffer sounds like a good idea. The cost is around $700 which is not cheap for what it is but if it is truly solve the high voltage input issue with my amp, that may be worth it.

I looked a bit deeper and learn that Decware offers two buffers and one of those "ZSTAGE" model is adjustable output voltage using single ended triode gain stage. It can adjust from 0 to 5 V :)


Consider that my amp input is 4V, it seems that it dials to between 4V to 5V would be ideal for my amps. If everything else being equal, SET gain stage is more of my liking than solid stage base Burson.

Have anyone using the ZSTAGE buffer before?
4hannons - how do you set up the Lightspeed and Burson.

Source --> Lightspeed --> Burson --> Amp


Source --> Burson --> Lightspeed --> Amp

Have you tried between those two configurations and what sonic results different between those two configurations.