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?
It's not LDR, but I think a preamp like the W4S STP-SE is what you're looking for. If it isn't everything you hoped for, well, they take returns.
Your best bet is to deal with your gain issue at the amp. Choose one with higher input sensitivity and a passive line stage will match just fine, no extra gain needed.

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.
Pretty much any balanced or single-ended tube preamp with a volume control of up to 100K impedance can be retrofitted to a DIY LDR shunt volume control. I made the modification to an AtmaSphere MP-1 balanced preamp and am pleased with the improvement.

I believe the only commercial preamps with LDR controls were the top Melos models of the late '90s and current darTZeel.

Commercial use in an active preamp is problematic insofar as even closely-matched LDRs don't track each other very closely above 15K. L/R channel balance shifts with changes in volume. This doesn't bother me, but may test the patience of a couch potato.
4v? Wow, I have never heard of any amp that was over 2.5v.

Higher Input sensitivity means a lower number. For example a 1V sensitivity is better than 2V. A 700mV sensitivity is better than 1V. Gain was exactly the reason I chose the Parasound A21 over others, when using my TVC which is a passive component.
Nguyen787 Hi, 4v sensitivity for your amp means it needs 4 v in to get it to go to full level, that means when using a passive you need a source cdp or dac that gives out 4v or greater. It would be far better if the amp were changed to two 2v sensitivity. What is the name and model of this amp so I can check to see if it is possible.?

Cheers George
Also please give the source name and model as this may be configured to give out more.
Cheers George
"Better"...for use with a passive preamp.
Maybe use the Burson Buffer?


6db of gain, or about 2V. Not ideal, although it solves potential future impedance mismatch problems too.
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.
Nguyen hi, I had a look to see in the user manual what the output of the oppo is at full volume, but it's not stated, hopefully it must be above the standard of 2v. I've been told from a guy who mods them that it is 2.5v.

Your amp says on this main page that it is <1v input sensitivity
Yet when I downloaded the manual it says 4v as you say
Your impedance matching to and from the Lightspeed is great from the Oppo's 100ohm and into the S845's 100kohm.
My question to you is do you have enough volume when the Lightspeed is almost at full up?

As "GOD" Nelson Pass and I both state:
QUOTE: "Nelson Pass,we’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp. Nelson Pass"

Cheers George

The Burson has a 6db gain, although it isn't obvious from the literature. It also has no volume control, so you would continue to use the Lightspeed LDR.

It's called out here:


And also implied by looking at the specs for maximum input voltage and maximum output voltage. Somehow it got more out than in, so it has to add it in between.

It is different than the Dodd Buffer Preamp which has no gain, does buffer, and has a volume control.
The only one I know of that's not $40k is the old Melos SHA Gold. There's one on listed here now if it hasn't been sold. I've had an LDR for years. Wouldn't swap it for anything. I'd change amps first. Also, you may want to check with Uriah Dailey on the DIY Audio forum to see if he can offer a solution.
Check out Hornshoppe's 'The Truth'. Active. No gain. Sounds astonishing.
Great idea, except gain is exactly what he's looking for.
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.
Nguyen787 if you feel like you need to move off of the Lightspeed I`d be very interested in it.
Nguyen, the amps 4v sensitivity is the problem, try this, email the manufacturer and ask is there any way of getting the amps sensitivity to 2v or even 3v will do. It may be a simple thing like change the input tube for a higher gain one.
If not you could get someone to build this simple buffer that has gain, parts would be around $10 http://www.diyaudio.com/forums/attachments/analog-line-level/341197d1365395103-preamp-buffers-simple-idea-buffers.gif

I Just looked at you input tube 6SN7 it is a very low gain tube of 20. A tube tech should be able to reconfigure this for a higher gain tube of say 40 or so with a different input tube.

Cheers George
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

The Lightspeed LDR is wonderful provided your source and amplifier are appropriate for a zero gain, zero buffering preamp.

Either find a source that outputs closer to 4V, find an amp whose sensitivity is closer to whatever output voltage of your source, find another way to either add gain or lower sensitivity, or get an active.

I happen to think the Burson Buffer is a reasonable try to add gain to your system. It's actually what you're looking for, isn't it? An active, with gain and LDR volume control. The Burson Buffer adds 6db gain, and your Lightspeed LDR acts as volume control.

Having said that, an LDR is not the only means to deliver great sound, I happen to think the Coincident Statement Linestage and TRL Dude are better than the Lightspeed. But if your source and amplifiers are appropriate, I'd agree that there may be nothing better at the price point of the Lightspeed LDR.
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?
After lightly reading this thread I thought I would comment on it. I have the Burson buffer and the Lightspeed LDR. It is a outstanding combo. It would solve your high input voltage issue. Just put it before the Lightspeed and after your source. I think you would be extremely happy with it, but each one has his own preferences. I got my buffer from Chris Johnson at Parts Connecxion and he told me that this Burson is the Cadillac of buffers. Have fun.
The Burson Buffer is your other option, but your are introducing it's sound into the mix. I would use it after the Lightspeed, between it and the amp. As your Oppo has great output impedance and it would do more good after than before the Lightspeed.

Cheers George
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?
You would want to use the ZStage between your source and the Lightspeed. If your source is 2V you can use the buffer to add another 2 or 3V to the signal. Then use the Lightspeed to attenuate.

The idea of such a device that adds voltage to the signal is not unheard of. We actually make one using all passive parts and it also has a built in attenuator.
This would be better, only use the first half it has 4 x gain, change the NE5534 for a better OPA627. It has 100k input impedance and 100ohm output impedance, put it after the Lightspeed. (Forget about the back stage with the NE5532) This would be far better than the ZStage.


Cheers George
And there's this one also,even better, already has a OPA627 and gain can be changed 7 or 2 And it has a discrete match fet output stage, I would omit R1 as the output of the Lightspeed will take it's place.


Cheers George
Burson Buffer is $550, not $700.


I have not much to say about the Decware. At the risk of being impolite, when people talk about buffers, Burson usually comes up first. I'd go with the more well known manufacturer in this case.
+1 for Burson with LDA. A great match, been happy with this combo. Also, the people at Burson are friendly and accommodating.
George - the OPA627 DIY is too hard for me. Is there another version that easier.... :))
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.
If you think the OPA627 is a little hard then an OP275 is for you, but I think it's a dual, there maybe a OP175 single.
As for Burson buffer in the system position, I would put it after the Lightspeed as the Lightspeed is fine with the standard output of 2v from cd it's has .01% second harmonic distortion, but when it gets over 4v into it, the second harmonic distortion rises, not bad, but enough, to start giving that typical second harmonic distortion sound that tubes give, some even like this.
Also the Burson has a lower output impedance than the Lightspeed so it can drive lower input impedance poweramps and longer interconnects.

Cheers George
Source-->Burson-->Lightspeed --> Amp

Tried both ways and settled on the above config being slightly better.
May be you prefer the sound of a little second harmonic distortion, nothing wrong with that, adds a little ease to the presentation if needed, and may cover the sound of the Burson a little, that's what tube amps do.
But if everything is spot on in the system, then the Burson after the Lightspeed will be a more precise presentation, and give warts and all, and not be kind to bad recordings, and let the sound of the Burson through as well. This could be a good or bad thing, I'm not sure how the Burson sounds, but anything active has a sound signature of it's own.

Cheers George
George - to your understanding, is a battery significantly improve sonic quality over wallwart to power Lightspeed?
Thank you George, you nailed it. That's exactly how I would describe the difference between having the Burson before LDA or after, except I couldn't describe it well as you.

BTW, I purchased an empty Burson case to house the LDA and they look great together as a matching pair. The empty Burson case was just about a perfect fit for the LDA to fit inside. The Burson folks are very nice. Typical Aussie's.
The battery is not a significant improvement. There is a difference in the sound but I cannot precisely pinpoint what it is. I swap the power supplies around every so often, but could live with either one.
Same as what Clio09 said, very hard to pick the difference between battery and wall wart.
Even the highly critical listener/reviewer Sam Tellig of Stereophile has memory lapses to what he has on powering his Lightspeed Attenuator when he's using it, as he has both battery and wall wart, and has to look to see which one he last put on, they are so close, same with his guitar teacher son and his Lightspeed I believe.

Cheers George
I've had both a battery and an AC version of the Lighter Note, which is based on George's design, at the same time. I found that the AC version is better but only if you keep it on all the time. I don't know why, but it sounds better after being on for 48+ hours. I've confirmed this a number of times and also in two different homes. The AC version has better dynamics and more sparkle up top than the battery version does.