Lightspeed Attenuator a new passive preamp

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#1,521
Tolu said:
Have you tried input switching with one optocoupler in series and a relais that switches ground in shunt configuration?

It's a shame that the Silonex parts can't be used in the EU by high end firms because of WEEE and RoHS!!!:smash:
Click to expand...

To me input switching (attached) would slightly compromise the sound quality with 2 ldr's in series with the signal and it's permanent.
I'll keep to my purest production single input version, if someone wants to have input switching there are numerous switch boxes out there, QED make one that I recommend, as it has silver contact Alps dual leaf switcher, and silver wired, it adds some degradation to the sound quality but bearable, and then if you want to hear the Lightspeed Attenuator for all it's glory, then you can still use it direct as single input and disconnect the QED.

And the ROHS thing hasn't affected me yet, one day it may, and that will be the end of it, unless Silonex get their act together and produce an ROHS compliant NSL32sr2s. As all the others brands are far behind the Silonex LDR for this type of product.

BTW those who haven't done so yet, please vote for our own "Passive Preamp" forum if you want one, here.
http://www.diyaudio.com/request/

Cheers George
 

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#1,525
Hi James

great job!

I just have to add an issue regarding matching sr2s. The high temperature dependancy.

Before measuring let the 10 minutes "glow". Then you must have a thermometer that controlls the room temperature (better would be the optp-coupler temp). Do any measuring at constant (same) temperature that will be same than later real use environment.

I matched many with a DAC and a PC. There you can do random values and see how they react. I mostly do pair comparisons for fine matching!
 
#1,526
Thanks Thomas,
I was so confused about the variations, but when I had to read the whole thread all together, (over and over), I gradually got the hang of it.
With a bit of luck, some good feedback , we'll end up with a short well organised manual.
I had forgotten the temperature effect when testing - will add to the update. Couldn't find any info about tolerances with the LDR matching.

I see that your dac control system is working well - looking foreward to the "unveiling".

I was hoping that "Blues" was doing well with his AD420 dac system - it sounded really interesting. Good to see Paul's is going so well - we'll call it the "Maxi-Mote"!
 
#1,529
another happy user!!

Finally had some time off last week to put mine together....

12v SMPS (just for testing, will change to linear) -> 5V regulator -> Lightspeed Mk2 circuit.

Matching took some time but I just did each one in the circuit, and out of 10 sorted LDRs, there were 2x very close matched pairs, 2x fairly close matched pairs, and 2x way out there.

Soldered in the close matched pairs and it works.

Signal chain is:

Laptop -> DDDac USB/2 tower [90 ohm output impedance] -> Lightspeed -> ESP P09 Actice Xover [100k input impedance] -> 2x stereo mini Alephs -> 2-way speakers [Scanspeak 8545/9700]

+ tested direct into Mini Aleph amp and frugel horns.

compared to Alps RK40 'black beauty' (10K + 50K) and RK27 'blue' (10K + 50K).... (only using croc clips so far)... Extremely happy! 😀 The ALPS sound extremely mushy in comparison and I'm surprised at the difference.

George: MANY MANY THANKS for sharing this concept and circuit!

Question: haven't tried caps across the LDRs -- I've a few 0.1uf in the parts bin -- would these be worthwhile?
 
#1,530
Your welcome Smithy, gad you like it as well.
You know of the 100's of emails I've had, not one has been negative, goes to prove with no contacts or preamps it's a done deal, nothing can match it, wait till you get your linear supply on it, that SMP is putting out all types of crap.
Give the caps a go tell us what you think.
Don't forget to vote for the Passive Preamp forum
http://www.diyaudio.com/request/

Cheers George
 
#1,534
georgehifi said:
Your welcome Smithy, gad you like it as well.
You know of the 100's of emails I've had, not one has been negative, goes to prove with no contacts or preamps it's a done deal, nothing can match it, wait till you get your linear supply on it, that SMP is putting out all types of crap.
Give the caps a go tell us what you think.
Don't forget to vote for the Passive Preamp forum
http://www.diyaudio.com/request/

Cheers George
Click to expand...

I do look forward to trying the linear PSU. But even testing with cheapo crocodile clips in the signal path, spread out naked over the living room floor, the Lightspeed is dead quiet and extremely clean. I'm afraid I only have the Alps pots to compare it to -- no dacts or transformers or whatever. I also have no measuring equipment to back up what my ears tell me -- the Lightspeed is significantly better. Reminded me of the really positive change I heard when I switched to biamping.

The difference between the Lightspeed and the Alps pots is huge. In comparison, the Alps pots are junk. No other word for it. I'm not surprised the response has been so positive.

I haven't yet compared it to controlling volume in software (i'm using FLACs by the way), which in any case I never liked anyway because of both practical reasons and the fact that in my system it results in a higher noise floor.

Will experiment with bypassing. Have already voted for the passive forum.

Thanks again!
 
#1,538
How do they sound with Hypex UCD amp?

Hi LS users,

Does anyone use the LS - Hypex UCD combination?

I do need new amps and would love to build the LS in the monoblocks.

Only problem would be to build a receiver / remote control combination that allows for volume control on two amps simultaniously.
Alternative is an extra lead in the cable (I will go balanced) and use a central pot!!

Some one done this before?

Thanks

Peter
 
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