Lightspeed Attenuator a new passive preamp

[georgehifi]

Originally posted by jkeny
Hi all,
I'm about to pop for 10 of these LDRs from Allied and I'm just looking for some feedback before I do.

Firstly, is the part of choice the NSL-32SR2S matched part?

Yes



Would 10 be about right for a stereo control or should I go to 12 & hope to get 2 controls?

For two Lightspeeds I would go 20



These are the sorted part - has anybody managed to get parts from the same batch or same grade? I emailed Silonex but was told to go through distributors with no guarantee of same grade.

Yes they are the sorted ones



Allied sell them for $24.50 for 10 (€18) but don't give shipping costs until completing the order. I'm not sure if they ship internationally but if they do I doubt shipping could be more than $20 or am I wrong? Ahs anybody shiiped from Allied to Ireland or UK?

Tell them they are miniscule and can be posted in the smallest jiffy bag and sent standard air, and do your homework with usps web site to find out how much, then quote it to them, so they don't rip you off.


Thanks
John

Cheers George

[Dr.H]

John,

Those are the right ones. However, be warned that Allied can be VERY expensive on the shipping costs. Ask them to commit to a range so that you have an idea.

In my case, they delayed with the order, eventually (about 3 weeks after I placed the order) saying that they did not have stock. When I queried this with Silonex (Mary), Allied changed their tune and shipped the stock, but, given the delays they had incurred in dealing with my order, chose the fastest way to get them to me (without my prior consent) and I ended up paying Euro60 for 10! I guess the cost was exacerbated by the fact that I live in South Africa.

Ryan

[zarate]

Sorry GeorgeHifi, too much of a Newbie to be allowed to PM.
Perhaps you could PM me.......

Obviously a security risk....

[georgehifi]

Originally posted by zarate
Sorry GeorgeHifi, too much of a Newbie to be allowed to PM.
Perhaps you could PM me.......

Obviously a security risk....

You have your PM turned off.

Going to catch some zzzz's now, will have to wait till morning.

Cheers George

[ssmith]

Originally posted by jkeny
Ahs anybody shiiped from Allied to Ireland or UK?

I always get a relative in the US to do digikey/allied/mouser/allied purchases for me (usually lots of things in one go) and then forward them in the regular post. Saves a fortune on shipping/customs and I've never lost anything. You must have a good friend/relative stateside -- we (the irish) are everywhere...

[mikelm]

I think the cap across the LED mod will always improve the sound regardless of how good the regulators are.

This is based on the theory that the LEDs themselves are inherently noisy. Even if the regulators a totally silent, if the load ( the LED ) is noisy, you will get noise. ( unless you redesign the cct and have a pair of variable regs directly across the led's ) With the cct as it is, the resistance of the pots will always give the LED's the freedom to express there inherent noisiness

However, I still think that it will be best to use the quietest regulators available because the there are plenty of other noise sources - mains, diodes etc - that can mess up the sound and with these noise sources reduced to a minimum the LED caps ( mostly ) only have to cope with the LED and pot noise.

mike

[Panelhead]

I went all out on both of mine. Dual regs to start with. Then series resistors inline on the + line and ground feeding the first reg.
Next was a series 1 mH choke on the +5 and ground going to the pots. Finally slapped some Silmic II caps across the LED's.
Got to think all this helped the sonics some. But it was very small in my system. The Lightspeed was very good with just the regs and no chokes or caps. Guess I could remove them to see, but am too happy to fiddle with it.
Overall I think it is audionervoso, the effect is small if any. But maybe my chokes are too small, or the caps too high ESR to address the noise. Or it could be my 51 year old ears are shot. Or the rest of my system is so crap that it is not evident.
What did make a big difference was playing around with the value of the pots. The pot value is what really sets the impedance of the LDR circuit. Initially it was set at about 22K. Then subbed some lower valued pots to get it down to 9 - 11K.
The lower impedance is a big improvement. But I think the Lightspeed commercail units are about 10K to start with. If you have a diy job, check the impedance to see what it is as the pot is rotated.
I think there is posibility that George might add bypass caps to the commercial Lightspeed attenuators. If the buyers realy feel they need them, it is simple to add while building up the boards. The addded cost should not be more than 10% or so at most.
Either way, I removed the PEC carbon pots from both of my linestages after listening to the LDR circuit. It is that good, bypassed with caps or not.
And I do not think it is the contacts. Most systems have lots of contacts. Maybe it is the disimiliar materials between the wiper and resistive track.

George

[Dr.H]

Hello George,

I am using a 100k DACT pot. Are you saying that there is benefit in reducing that to a say 10-15k pot?

Ryan

[georgehifi]

Originally posted by Dr.H
Hello George,

I am using a 100k DACT pot. Are you saying that there is benefit in reducing that to a say 10-15k pot?

Ryan

Are you using the 100k dact as a stand alone passive volume control? if you are, then Yes
A 100k pot would have an output impedance of 50k at half level, that into say a standard power amps input impedance of 50k is a 1 to 1 ratio, a far cry of my minimum ratio of 1 to 10 or better, for your pot to have the minimum ratio of 1 to 10, the poweramp would have to be 500k input impedance, virtually impossible to reach except on a tube amps.

My Lightpeed Attenuator led control pot is 100k log using the
NSL-32sr2s, this has the best feel, smooth gradual increases from 7am to around 2pm then progressivly stronger from then on 5pm

Cheers George

[Panelhead]

Terry,
Measure from input to ground. This will measure the series and shunt leg in series. In the passive unit, 10K sounded faster, punchier, more dynamic.
Somehow I ordered the wrong parts from Allied. Mine are R3, not R2. This means I get different impedance than most. A 100K pot ended up as 22 - 24k impedance as the pot is rotated. 50K pot measues 9 - 11K for the Lightspeed. But most have said the R2 give 10K with a 100K.
Since you are using the LDR's as a volume control in front of an active preamp this may not be as critical. With a passive line stage this is much more critical. Driving the cables and input of the amp is demanding. With your 27K input amp, the lower value would be more important.
The amps I use have 100K input impedance. And the cables from amp to Lightspeed clone are very short. The passive works great with them. In fact better than my line with an AD815 and LDR volume controls.

George