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?
nguyen787

Showing 10 responses by georgehifi

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
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
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
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.

http://www.ebay.com/itm/OPA627-K170-J74-2SK170-2SJ74-Audio-preamp-DIY-KIT-/320840215695?pt=US_Amplifier_Parts_Components&hash=item4ab3912c8f

Cheers George
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
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
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
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.

http://www.ebay.com/itm/HI-FI-STEREO-NE5534-NE5532-CLASS-AA-OUTPUT-STAGE-LINE-LEVEL-PREAMPLIFIER-/261127345717?pt=US_Home_Audio_Amplifiers_Preamps&hash=item3ccc671635

Cheers George
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
http://shop.grantfidelity.com/Shuguang-Classic-S845MK-Tube-Power-Amplifier-pair.html
Yet when I downloaded the manual it says 4v as you say
https://shop.grantfidelity.com/files/s845mk%20manual.pdf
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