Lightspeed Attenuator a new passive preamp

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georgehifi

georgehifi

Member
Joined 2003
lightspeedattenuator.com
alexkosha said:
No shipping to US. :mad:
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This item 2508662482 is from our Extended Range
http://au.rs-online.com/web/generalDisplay.html?id=services/extended-range

•This element of your order is supplied from our US company and forms part of the RS Extended Range. •Please ensure you have selected the correct product as once your order has been placed it cannot be cancelled or returned•RS will aim to deliver Extended Range products in accordance with the lead times published on the website but such lead time are approximate only.•Extended Range products are only visible on our website but can be purchased via any channel


UK has them as well

Cheers George
 
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gdlen1

Member
Joined 2010
udailey said:
Changing gain is pretty easy. Can be done with one resistor. There are a lot of Dynaco buffs on the site. Im sure you can manage it. Other than that you can adapt your lightspeed to your situation by forcing series ldrs to stay high resistance and shunts to move slowly.
I suspect you also have efficient speakers. Efficient speakers and high gain dont work well with a lightspeed because of the minimum value you can achieve on the shunt ldrs.
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If it only takes one resistor to change the gain of the Dynaco circuit , then that I will try that, and my speakers are only 89db
 
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gdlen1

Member
Joined 2010
Vincent77 said:
Are you sure you need a preamp? The PAS 2 is a pretty horrible design by today's standards, anyway, and has quite a lot of gain (20 dB), so if your DAC outputs a 1 volt signal, after the preamp you'll have 10 volts, which is way too much for any amplifier input.
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As good as the lightspeed is by itself, it wasn't really better that the dynaco, just different, and I preferred the tone that the dynaco added to the sound, more bass and slightly warmer, not by much though. my VTL ST-125 poweramp has an 140k input impedance so it should have been working well

the stock Dynaco pas circuit is not horrible, I see people claim that all the time, I don't get it.
I have tried several modern upgrades including the famed Aikido circuit, and they at best sounded no better, but I still think the Dynaco sounded slightly more punchy and spacious, it never sounded bad from the day I got it, even before I modded anything, if it aint broke, don't fix it:)
Just for kicks, I tried a Perreaux SM6 preamp (I think about NZ$6000 when new) with my VTL ST-125, sounded horrible, overly bright and harsh, must have been and impedance mismatch some where, either that or it was rubbish:D
 
alexkosha

alexkosha

Member
Joined 2013
Guys, I have tube preamp and it is 100K Alps there now. Would like to go and to try Opto-LDR, but not sure how to rich 100K as an original Alps has. Please advise.
 

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gdlen1

Member
Joined 2010
udailey said:
Gdlen thats because of the system gain not the value of a pot/lightspeed. Were just dividing voltage and we could do that with a one ohm pot if we wanted. A buffer solves the issue like Andrew said.
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I know that my pre has about 20dB of gain, but why does my alps "blue velvet" work fine with a normal range of adjustment?

does it have anything to do with linear vs logarithmic?
 
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udailey

Member
Joined 2008
picasaweb.google.com/udailey/MyRef#
The ldrs may be changing value faster than the tracks on a log pot would. You could build a shunt attenuator with ldrs as the series elements. You set them where you want them then never change them. Use the pot as shunt element. Ive used this several time and it really works well. Better than I expected and sounds fantastic. Impedance varies but if you do the math it doesn't change much til the highest volume levels. No ldr matching required. Using a log pot means slow volume change.
20db is a lot of gain going into an amp. Huge really. Thats the kind of gain you need going into a power buffer like the F4 and not an amp with even more gain. I would try getting rid of the pre and just using the lightspeed into the amp.
 
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gdlen1

Member
Joined 2010
udailey said:
The ldrs may be changing value faster than the tracks on a log pot would. You could build a shunt attenuator with ldrs as the series elements. You set them where you want them then never change them. Use the pot as shunt element. Ive used this several time and it really works well. Better than I expected and sounds fantastic. Impedance varies but if you do the math it doesn't change much til the highest volume levels. No ldr matching required. Using a log pot means slow volume change.
20db is a lot of gain going into an amp. Huge really. Thats the kind of gain you need going into a power buffer like the F4 and not an amp with even more gain. I would try getting rid of the pre and just using the lightspeed into the amp.
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Hi, I think I'd rather not change the Lightspeed if I can, as I do like to listen to it every now and then when the mood takes me, and it works fine going straight into the power amp. I am going to get a higher quality pot of some kind for the Dynaco, connecting the Lightspeed made me realize just how much a quality attenuator affects the sound.
20db is a lot, I'm going to try some 5751 tubes which should drop it down a couple of db, but I've never run into any problems as it is, 1 volt of actual music out of the preamp is deafening anyway.

thanks
 
alexkosha

alexkosha

Member
Joined 2013
udailey said:
I used to sell them but you can build your own. Its not hard. Do not breathe the fumes. It hurts and is reaaly bad as in giving you asthma etc.
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:D I made one for my DCB 1. Took me about 2 hours total. Not bad...
But then.. I saw these professionally made and I like to acquire one if you still have it for sale.
 

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