Lightspeed Attenuator a new passive preamp

[metal]

Thanks for the reply George, good you pointed it out here, I re-enabled this setting, funny ;- )

albertli, after you correctly balanced the LDRs, can you ensure that the LDRs always track at different levels? I mean, is volume the same for both channels spanning the whole range?

[albertli]

Originally Posted by metal

Thanks for the reply George, good you pointed it out here, I re-enabled this setting, funny ;- )

albertli, after you correctly balanced the LDRs, can you ensure that the LDRs always track at different levels? I mean, is volume the same for both channels spanning the whole range?

I would say yes,a t least for 75% of its range. Dont forget I never have it turn over 40%, about 10-11 oclock position. My power amp is 25w, with my speaker around 90 db.

[macm75]

Hello George,
First of all, thank you so much for sharing your design with all who care about amplifier building. I recently got my first lightspeed up and running and floored with the new level of detail, clarity, and liquidity. I was sold from note one.
Originally I powered it with a 9V battery which was fed to a small LM317 circuit. After changing from battery to small 12V SMPS (still using the LM317 circuit) I found I lost some fullness and fluidity to the sound.
You recommended a 12V Li-ion Rechargeable battery from ebay in some past posts. Was not sure the capacity of the battery - is 1800mAh adequate or do I need something like 6800mAh?
Thank Again, Joe

[georgehifi]

Thanks for the pat on the back. As for battery use this is the one I have used, good for weeks of use before a recharge. But there's not much in it when compared to a linear regulated 12v wall wart of >300mA. Portable 12V DC 6800mAh Rechargeable Li ion Battery CCTV Camera MP3 with Switch | eBay

Cheers George

[ntropy]

Hello George,

I really think your idea with using LDR as a volume control is fantastic.

I have read about 200 pages of this thread but I still fail to understand why the LSA sounds better than a high quality potentiometer or a resistor ladder. You say it's the absence of mechanical contacts with different materials which make the LSA better, did I get this right?

If this is the case, everytime I use solder I'm connecting at least 2 different materials together. If I plug in a RCA, then again I have a contact.

For me, I can't logicaly understand this.

I have seen that the LDR has rather high 2nd order THD numbers which are pleasant to the ear. Maybe that's the main reason why the LSA sounds so great?

Don't get me wrong, I think the LSA is a great design. Only the explanation is for me a bit to exotic

[bambadoo]

I bought 2 lightspeed kits some time ago. (And 2 lighter notes - still unused, unsoldered)..
I never could get the tracking right and the signal level was to high with my Audio Note preamp.. So I left the "project".

Well - a couple of weeks ago I found the lightspeeds again. Did some homework. Made a dcb1 buffer.
Used 68ohm and 750ohm (instead of 1k) resistors. Used 4Vdc as power (regulated lm338) . Readjusted everything. Hooked it up to the dcb1 and to the amplifier..

This was much better than earlier. Channel balance - perfect. Volume settings perfect. Seems I can use from 0 to 100 with no problem.

Question: How important is the quality of the 5v PSU for these? (Well mine is 4Vdc - but I guess just average in quality)

[georgehifi]

Originally Posted by ntropy

Hello George,

I really think your idea with using LDR as a volume control is fantastic Thank you

I have read about 200 pages of this thread but I still fail to understand why the LSA sounds better than a high quality potentiometer or a resistor ladder. You say it's the absence of mechanical contacts with different materials which make the LSA better, did I get this right?There are no light pin point touch contacts of dissimilar metals and track substances, have you ever wondered why all different make pots sound different to each other?

If this is the case, everytime I use solder I'm connecting at least 2 different materials together. At least they are both metalic, and a fixed together contact, not a plastic or carbon track with a metal wiper touching lightly on it.
If I plug in a RCA, then again I have a contact. A massive tight metal to metal contact area, but still have you ever cleaned your rca's with contact cleaner? you will hear a difference.
For me, I can't logicaly understand this.

I have seen that the LDR has rather high 2nd order THD numbers which are pleasant to the ear. Maybe that's the main reason why the LSA sounds so great?This 2hd at cd source level input is only .01% speakers and tube amps give out far more than that.

Don't get me wrong, I think the LSA is a great design. Only the explanation is for me a bit to exotic

Each to his own, have you listened to one??
Cheers George

[georgehifi]

Originally Posted by bambadoo

I bought 2 lightspeed kits some time ago. (And 2 lighter notes - still unused, unsoldered)..
I never could get the tracking right and the signal level was to high with my Audio Note preamp.. So I left the "project".

Well - a couple of weeks ago I found the lightspeeds again. Did some homework. Made a dcb1 buffer.
Used 68ohm and 750ohm (instead of 1k) resistors. Used 4Vdc as power (regulated lm338) . Readjusted everything. Hooked it up to the dcb1 and to the amplifier..

This was much better than earlier. Channel balance - perfect. Volume settings perfect. Seems I can use from 0 to 100 with no problem.

Question: How important is the quality of the 5v PSU for these? (Well mine is 4Vdc - but I guess just average in quality)

Get yourself one of these led testers and a cheap digital multimeter that way you can match your own ldr's from 1-20mA at 5 different levels.
As for using only 4v insted of 5v naturaly the 100ohm current resistor on all the + legs of the NSL32SR2S's of my circuit would have to be smaller otherwise you won't get enough sweep (low volume).

Cheers George

[studiostevus]

I have been using the lsa in my aikido preamp for a year now, but i am getting increasingly frustrated with tracking. I had ordered ldrs from uriah (2 matched pairs) but always had channel imbalance.

Yea, the lsa is in the same cabinets as the tubes (maybe 15 cm away). But i would assume the ambient temperature is the same for each ldr.

In your experience:
1. Is it possible to get perfect tracking channels?
2. How many Ldr's does roughly one need to buy to get a perfectly matching quartet (not 2 pairs)? (in your experience)

[AudioLapDance]

Here's a super cheapie but it starts at 2ma (do you need the 1ma?):

Mini Handy 2 150mA LED Bulb Light Lamp Tester Test Meter Box Tool w 9V Battery | eBay

This one's a bit more upscale and does the 1ma:

Precision LEDs Tester Light Emitting Diode Test Box | eBay



Oh, and how many LDRs to get a good match for simple single-ended stereo? Was it 15?

http://www.alliedelec.com/search/pro...x?SKU=70136789