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Lightspeed Attenuator a new passive preamp
Lightspeed Attenuator a new passive preamp
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Old 19th January 2007, 07:20 PM   #271
georgehifi is offline georgehifi  Australia
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Sorry to have to post this up, but I find it necessary with the amount of emails that I'm getting bombarded with.

I will not sell the separate parts, if I do it for one I have to do it for all, and that's just impossible for me to do

I've given all the info on how where and why to DIY the Lightspeed Attenuator yourself in these threads, for a little of your own time you can Do It Yourself, I only sell the completed product.

I hope all understand and don't think that I'm a big nasty Ausie Oger who won't help them.
Thanks for your understanding, hopefully.

Cheers George
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Old 20th January 2007, 12:37 AM   #272
Audionutz is offline Audionutz  Australia
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As a relatively long term user of the Lightspeed (L.A. ?) I can offer a couple of insights as to what I have found with this little marvel of Georges.

I purchased a completed model from George, single input/output and have used it with over 10 different pairs of speakers, about the same number amps, both Valve and SS.

A wise old (sorry Pete) audiophile once said to me that it helps to have one truly blameless component in your system from which to build from and to evaluate other components. For me, that's been the Lightspeed. Although it has come and gone out of my system over the last 12 months, it has always been my preamp of choice when I change anything else in the system. It has allowed me to evaluate and judge speakers, amps and sources very accurately, as it just gets out of the way, adding no colouration or sonic signature of its own. To me, that's its greatest strength - the ability to do it's job and allow whatever is playing to come through cleanly and clearly. I might not always like what I hear with the Lightspeed inline, but at least I know I'm hearing the truth !

This can be a double edged sword though, as components and tracks that were previous favourites are now ruthlessly revealed in all their glory (or not as the case may be !) However, I firmly believe that my system is better for having had the Lightspeed involved in it's growth.

I'm not one for getting into the technical aspects of circuit design etc and only have a rudimentary knowledge at best of how the Lightspeed works - but I can vouch for the fact that it has beat almost everything else I've tried. Occassionally I have wanted to add a certain sound to my system and that's the only time I have swapped it out for a Valve pre or something else. Otherwise, it's usually in there.

For such an innexpensive component, comparatively, the Lightspeeds' a true audiphile addition to any system - something proven by the number of big dollar preamps I know are now languishing unused in systems around Australia.

I hope that this helps those that are still pondering the wisdom of inserting something this "low key" into their mega-dollar rigs, but at the price and performance of this unit, you'd be mad not to give it a try.

Current System.

Teac Esoteric P500/D500 Transport and Dac Modified.
Lighstpeed
Peter Gay 50wpc Class A SS Power Amp
Altec Barcelonas with Piezzo Twin Diaphram Supper Tweeters

Alternate Amps

Sonic Impact T-Amp
Beam Echo/Avantic SPA21
UCD180 Digital Monblocks
Melody 2A3 Integrated
ME850
ME55
Melody KT88 Monoblocks
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Old 20th January 2007, 06:56 AM   #273
Nordic is offline Nordic  South Africa
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Sorry, I'm still working my way through this long thread, but I have a question.

You said you use $2 pots... now what would be the point of carefully matching LDRs it the pot is messing up the tracking between 2 channels?

Very interesting what you said about the wipers being bounced...
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Old 20th January 2007, 07:23 AM   #274
georgehifi is offline georgehifi  Australia
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All the pot does is vary the voltage to the LED's of all 4 LDR's, it does not work in stereo mode.
One side of the pot takes the voltage up to both channels of the series LDR's and the other side of the pot takes the voltage down to both channels of the shunt LDR's.
If you can get your head around this, you will then realize that the quality of the pot has no bearing on the sound quality of the LDR's.
It's one of those weird things that you have to do a double take on to understand whats happening. The pot has no bearing on the channel balance of the output and is not connected in any way to the input signal or output signal.

Cheers George
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Old 20th January 2007, 10:26 AM   #275
Nordic is offline Nordic  South Africa
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Thanks!
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Old 23rd January 2007, 07:41 AM   #276
Lostcause is offline Lostcause  United Kingdom
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Hi chaps, been lurking for some time now whilst building my new amp and wondered if I could integrate one of these puppies?
From my schematic below you can see that I love to keep it simple (KIS as George puts it)!
I have put everything in one box to reduce the parts count and keep the amount of joints/connections to a minimum. Thatís why I love the thought of using this idea.
Looking at the schematic of the ĎLightspeedí it appears to work in shunt mode, which will affect the gate resistor on my FET whenever the dial is turned. So, my question isÖ can it be used as a regular volume pot with a fixed grounding resistor and only the LDRís on the signal line?
I donít want another Cap in there before the attenuator as Iím just multiplying the number of parts and caps certainly have a sound. I canít put the cap before the attenuator because the T-amp has 2.5V bias on the input.
Iím only a beginner here so if Iím talking complete hogwash then please correct me!
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File Type: gif ps1 buffer to ta2020.gif (17.7 KB, 1998 views)
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Old 23rd January 2007, 10:41 AM   #277
Panelhead is offline Panelhead
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Default Do not bother

Using just a fixed shunt and variable series element will not give much range in attenuation. You need to vary both to keep impedance fairly constant.
A better place for the attenuator is in front of the jfet buffer. And use it close to the design GeorgeHIFI has kindly posted. This works, and works real well.
Took mine to a Bottlehead meet last weekend. Never got to do any preamp swaps to compare, but hooked to my old My_Ref everyone was complimentary of how it sounded. I am biased, but thought the pair sounded better than any of the other amps listened to that day. There were some kits, a couple commercial, and a tweaked out vintage tube unit to compare.
How does the chip amp handle the 4.7 ufd input cap? I found them to pop on power up when the input cap was 2.2 ufd and larger. Bigger cap gave bigger pops.


George
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Old 23rd January 2007, 11:10 AM   #278
Lostcause is offline Lostcause  United Kingdom
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Hi George, thanks for the reply although I'm not sure that I can put it in front of the buffer due to it using the 2.5V offset from the PS1 DAC as it's input bias.?
To get rid of the turn on pop I implimented Nick's soft start circuit:
Delay circuit
Works a treat.

Lee
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Old 23rd January 2007, 12:01 PM   #279
georgehifi is offline georgehifi  Australia
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Not knowing this chip amp, but looking at your circuit I would just sub the 50k pot (which is series shunt anyway) for the Lightspeed as I've designed it, the only thing is how much dc offset is present on the output of your buffer? if over say 10mv then i would have another 4.7uf before the lightspeed, with it's input of around 7k this then will give a -3db point of 4.8hz which is fine, use a good polypropylyne or Blackgate NX though. same for your existing 4.7uf after the Lightspeed.

Cheers George
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Old 23rd January 2007, 12:22 PM   #280
Lostcause is offline Lostcause  United Kingdom
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Quote:
Originally posted by georgehifi
Not knowing this chip amp, but looking at your circuit I would just sub the 50k pot (which is series shunt anyway) for the Lightspeed as I've designed it, the only thing is how much dc offset is present on the output of your buffer? if over say 10mv then i would have another 4.7uf before the lightspeed, with it's input of around 7k this then will give a -3db point of 4.8hz which is fine, use a good polypropylyne or Blackgate NX though. same for your existing 4.7uf after the Lightspeed.

Cheers George
Thanks for the reply George, the LDR's don't like DC then?

No issues on the caps, I have some very nice polys
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