Lightspeed Attenuator a new passive preamp - Page 15

Ronnie_Ericsson · 7th August 2006, 10:09 AM

Yes. 7K is a quite fine value for between two amplifiers.

On the other hand it would be nice to be able to put them everywhere... For example between 2k to 250k units in active crossovers.
On each input of 6 channel amps for gain-matching (making the load 7k/3 because they're in parallell. And so on...

I'm thinking that if they don't drift much, then very exact attenuators could be built.
To make it really messy but possible to fine-calibrate:

a 24 or why not >100-position switch with a trimpot at each position replaces the 100kohm pot.
Each step would be fine tuned for resistance in the series and shunt element, and the channels could have better matching than with 1% tolerance resistor ladder-attenuators...

A lot of trimming, but the leds and the LDR would not have to be matched at all, right?

What do you think? Are there reliable LDRs with higher resistance than the ones your using, for such a circuit?

Panelhead · 7th August 2006, 10:10 AM

At first I was using two stereo 50K linear pots. Measured around 8K. The sonics were great, but the volume control for low level listening was very touchy.
Replaced the two 50K pots with a pair of stereo 100K linears. Now the impedances measure about 25k. At first I did not like the resulting sound as much. Semed to color the sonics and slow things down.
Swapping back and forth, decided the sound was not worse, just different. The 100K pots allow great low level control. Since mine uses two controls. the series resistors are now 200 ohms.
I get a little different measurements compared to a real Lightspeed. The Lightspeed uses a single stereo pot and it is a 100K log. But mine tracks real well and I like the taper.
I have used mono volumes controls since 1989. It takes a little time to get used to. Also if you wire the source selector with a mute inbetween every source it minimizes opening and closing the volume controls.

George

SamL · 9th August 2006, 01:54 AM

Reading this post with great interest. I am currently using DACT ct2 as passive attenuators with my aksa100n power amp. The power amp input impedance is 47K. Will I get better sound switching from DACT to lightspeed? All the nice amp kit that I come across have below 100K input impedance. The Simple Killer Amp's GB150 power input impedance is 27K. Aussie Amplifier NX150 is 34K.

Far out!! Just realise that those I listed plus George are all Aussie.
Must be something in the water

Sam

georgehifi · 9th August 2006, 04:19 AM

Quote:

Originally posted by SamL
Reading this post with great interest. I am currently using DACT ct2 as passive attenuators with my aksa100n power amp. The power amp input impedance is 47K. Will I get better sound switching from DACT to lightspeed? All the nice amp kit that I come across have below 100K input impedance. The Simple Killer Amp's GB150 power input impedance is 27K. Aussie Amplifier NX150 is 34K.

Far out!! Just realise that those I listed plus George are all Aussie.
Must be something in the water

Sam

If you have a good strong source, (cd player or dac) there is no problems with the Lightspeed Attenuator driving the 47k Aska, and yes it will absolutely flog the Dact, done that comparsion and there is no comparison.

Cheers George

jeff mai · 14th August 2006, 05:24 AM

What's the noise performance of this attenuator like?

The reason I ask is that the spot where it makes the most sense in my system is right after I/V conversion in my DAC where the signal is only around 40mV RMS. The output impedance at this point is 50 ohms. A further 30db of amplification is needed to get near line level. Since I want to use valves for this gain, getting low impedance is going to cost something - a step down transformer or cathode follower.

georgehifi · 14th August 2006, 05:45 AM

On my Tektronix scope at .2mv per division there is a straight line, with no noise at all, in other words it's noiseless.

Cheers George

flyboi · 14th August 2006, 11:32 PM

Hi guys!

I'm one of the lightspeed owner. I bought the unit on my recent trip to Sydney after reading about it in this forum n met the man himself. Nice chap. So far, here is my findings. First, I'm a very happy owner of the unit. Basically the good points has been discussed here in the forum. For me, this pre has the best dynamics compare to the other passive pre's(tvc,step). N it has speed too. Resolution is first class. Other than that, I've managed to play with power source other than the walwart. Coz getting a bit itchy. Wonder how is the sound if I push it further. But what the heck, no harm for trying. So what I did, I swapped the walwart with battery power supply. Initially I was a bit sceptical that it will change the sound. But OMG! The improvement is tremendous! Night n day difference! It is very quiet. The sound is even more sweeter n transparent n improve all the other positive areas as well. Dunno why this happened. Probably it makes the led quieter thus reducing the inteference in the optocoupler. Or maybe bcoz the grounding scheme is a common ground between the signal ground n psu ground n the battery makes the psu quieter. I only can speculate but the result speak for itself. So far, I'm very satisfied with this pre. So guys, start to heat up your soldering iron. Gud stuff George! Thumbs up for the man!

Cheers!

Eddy.

jleaman · 15th August 2006, 12:35 AM

So all this talk about these pre-amp's and yet not one picture.. HUMM!!

breguetphile · 15th August 2006, 01:12 AM

Quote:

Originally posted by jleaman
So all this talk about these pre-amp's and yet not one picture.. HUMM!!

posts 48,49,86 ??

1543 · 15th August 2006, 06:19 AM

Hi,

finished my Lightspeed Pre yesterday. Im am also very satisfied with the results. Very good detail resulation and absolute noiseless. As far as I can say after short testing: Better than my 24 step attenuator.
G o o d w o r k G e o r g e !!! THX!

@flyboi
Instead of batteries you can also use two voltage regulators in series to reduce ripple to minumim. The ripple will be under noise
level of the regulator.

Arne

7th August 2006, 10:09 AM	#141
Ronnie_Ericsson diyAudio Member Join Date: Jan 2005 Location: Stockholm	Pot applications Yes. 7K is a quite fine value for between two amplifiers. On the other hand it would be nice to be able to put them everywhere... For example between 2k to 250k units in active crossovers. On each input of 6 channel amps for gain-matching (making the load 7k/3 because they're in parallell. And so on... I'm thinking that if they don't drift much, then very exact attenuators could be built. To make it really messy but possible to fine-calibrate: a 24 or why not >100-position switch with a trimpot at each position replaces the 100kohm pot. Each step would be fine tuned for resistance in the series and shunt element, and the channels could have better matching than with 1% tolerance resistor ladder-attenuators... A lot of trimming, but the leds and the LDR would not have to be matched at all, right? What do you think? Are there reliable LDRs with higher resistance than the ones your using, for such a circuit?

7th August 2006, 10:10 AM	#142
Panelhead diyAudio Member Join Date: Dec 2002 Location: Houston	Changed value of voltage control pot At first I was using two stereo 50K linear pots. Measured around 8K. The sonics were great, but the volume control for low level listening was very touchy. Replaced the two 50K pots with a pair of stereo 100K linears. Now the impedances measure about 25k. At first I did not like the resulting sound as much. Semed to color the sonics and slow things down. Swapping back and forth, decided the sound was not worse, just different. The 100K pots allow great low level control. Since mine uses two controls. the series resistors are now 200 ohms. I get a little different measurements compared to a real Lightspeed. The Lightspeed uses a single stereo pot and it is a 100K log. But mine tracks real well and I like the taper. I have used mono volumes controls since 1989. It takes a little time to get used to. Also if you wire the source selector with a mute inbetween every source it minimizes opening and closing the volume controls. George

14th August 2006, 05:45 AM	#146
georgehifi diyAudio Member Join Date: Sep 2003 Location: Manly Australia (Jewel of the Pacific)	On my Tektronix scope at .2mv per division there is a straight line, with no noise at all, in other words it's noiseless. Cheers George __________________ Avatar : Production Lightspeed Attenuator www.lightspeedattenuator.com

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9th August 2006, 01:54 AM	#143
SamL diyAudio Member Join Date: Jun 2004 Location: Wgtn	Reading this post with great interest. I am currently using DACT ct2 as passive attenuators with my aksa100n power amp. The power amp input impedance is 47K. Will I get better sound switching from DACT to lightspeed? All the nice amp kit that I come across have below 100K input impedance. The Simple Killer Amp's GB150 power input impedance is 27K. Aussie Amplifier NX150 is 34K. Far out!! Just realise that those I listed plus George are all Aussie. Must be something in the water Sam

14th August 2006, 05:24 AM	#145
jeff mai diyAudio Member Join Date: Aug 2002 Location: Melbourne	What's the noise performance of this attenuator like? The reason I ask is that the spot where it makes the most sense in my system is right after I/V conversion in my DAC where the signal is only around 40mV RMS. The output impedance at this point is 50 ohms. A further 30db of amplification is needed to get near line level. Since I want to use valves for this gain, getting low impedance is going to cost something - a step down transformer or cathode follower.

14th August 2006, 11:32 PM	#147
flyboi diyAudio Member Join Date: Dec 2004 Location: .	Hi guys! I'm one of the lightspeed owner. I bought the unit on my recent trip to Sydney after reading about it in this forum n met the man himself. Nice chap. So far, here is my findings. First, I'm a very happy owner of the unit. Basically the good points has been discussed here in the forum. For me, this pre has the best dynamics compare to the other passive pre's(tvc,step). N it has speed too. Resolution is first class. Other than that, I've managed to play with power source other than the walwart. Coz getting a bit itchy. Wonder how is the sound if I push it further. But what the heck, no harm for trying. So what I did, I swapped the walwart with battery power supply. Initially I was a bit sceptical that it will change the sound. But OMG! The improvement is tremendous! Night n day difference! It is very quiet. The sound is even more sweeter n transparent n improve all the other positive areas as well. Dunno why this happened. Probably it makes the led quieter thus reducing the inteference in the optocoupler. Or maybe bcoz the grounding scheme is a common ground between the signal ground n psu ground n the battery makes the psu quieter. I only can speculate but the result speak for itself. So far, I'm very satisfied with this pre. So guys, start to heat up your soldering iron. Gud stuff George! Thumbs up for the man! Cheers! Eddy.

15th August 2006, 12:35 AM	#148
jleaman Banned Join Date: Apr 2002	So all this talk about these pre-amp's and yet not one picture.. HUMM!!

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