Lightspeed Attenuator a new passive preamp

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#681
What LDR were you using?
Click to expand...

Yes, I'm very curious to know.

In my mind, I flirted with the idea of replacing the pot in my Acurus L10 with a device like this, however I know the issue of I/O impedances is going to come up, as I haven't really measured anything inside the unit.

Has anybody thought about replacing the pot in a minimalist preamp with a lightspeed? Seems like it wouldn't be too difficult, desolder the pot, flip it upside down, solder leads in its place to a secondary circuit with the lightspeed parts, and then use the pot in its place to drive the LED's...
 
#683
DrDyna said:
[B

Has anybody thought about replacing the pot in a minimalist preamp with a lightspeed? Seems like it wouldn't be too difficult, desolder the pot, flip it upside down, solder leads in its place to a secondary circuit with the lightspeed parts, and then use the pot in its place to drive the LED's... [/B]
Click to expand...

It is not a minimalist preamp, but I use a "Lightspeed clone" as a volume pot in front of an active unit. So do several others.
Works great. It might give better results as a passive. The reason I have an active is to drive amplifiers with input impedances on the low side. This 10 - 25K.
If you only use one source, email Goeorgehifi about one of his commercial units. It will surprise you.

George
 
#686
Hey guys, I'm having to post this up again as I'm getting too many emails wanting to buy the matched LED/LDR parts off me, it is hard to say it with cador and remorse in email form but I cannot do it, as it is there is a 1 week wait for a completed Lightspeed from the time of ordering. For me to spend additional time matching up LED/LDR packages for spare part sales would effect the waiting time even more for complete units to be shipped, so please stop begging some of you it won't help. And you wouldn't like what I would charge anyway, as they are 50% of the labour and parts costing of a complete unit.

On a softer note, don't forget to do this:

I believe we need a PASSIVE PREAMP forum of our own, not to be stuck here in the solid state (yuk) forum. To get our own PASSIVE PREAMP forum you should vote here.

http://www.diyaudio.com/request/

Under the Passive Preamp Heading section that I have started with the first vote.

Please take the time to do this and get us out out limbo.

Cheers George
 
#688
The darTZeel NHB-18NS pre would address the matching problem of LDR's.
http://www.dartzeel.com/pages_E/NHB18_info_E.html
http://www.6moons.com/audioreviews/dartzeel2/preamp_4.html

Yes that would be take the matching problem of the LED/LDR units out of the equation for me, but looking into it, it could escalate the cost of my unit 5 fold to implement the circuitry into my Lightspeed Attenuator, and not gain anything extra in sound quality.
And I'm not sure if the detectors for this circuit hanging off my signal output wouldn't influence the sound at all, I think maybe it will. I'll just stick to the simple way thanks of the laborious machining of the ldr's

Cheers George
 
#691
he never said what he was or is applying for. Or if it exactly applies to the volume. Melos was doing this nearly 20 years ago. All he could apply for at this juncture, that I can easily see... is a process patent, or an applications patent. But not a basic 'fundamental' patent.

Half the time patents are only there to distract and turn away casual abusers. If someone is serious about screwing you or coming after one's ideas, they are going to do so -- regardless.

Patents are pretty frilly little things to put on the shelf, like an award or ceramic doll. Not much use beyond that.
 
#692
I can say with confidence that it cannot be patented, as I did this system over 30 years ago with proof, and that is all it takes to stop a patent
Not to mention that Mark Porzilli of Melos used it also 10 years ago, he didn't try to patent it because of my efforts prior to that.

He's just fishing with the patent pending statment as it will never be granted, if it does I will then speak up and show that it has been done before.

Cheers George
 
#695
serengetiplains said:
Guys, pardon my ignorance, but does the Dartzeel pre use an LDR as the attenuating device?
Click to expand...


Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light. However, until all the patents are in place, I would prefer not to specify the details.

Above: This is a direct quote from the interview with the designer


You know what's funny is the specs of the darTZeel NHB-18NS at ($23,000us), are comprehensively thrashed by the standard Lightspeed Attenuator at ($410us) and maybe the sound too!

Cheers George
 
#696
georgehifi said:

You know what's funny is the specs of the darTZeel NHB-18NS at ($23,000us), are comprehensively thrashed by the standard Lightspeed Attenuator at ($410us) and maybe the sound too!

Cheers George
Click to expand...

I wouldn't be surprised. Take away the 1200(!) components and the uber fancy case and I guess you are left with something very similar to the Lightspeed. Thank you for sharing the circuit. I hadn't heard of using LDR's until I saw this thread. I look forward to trying it.
 
#697
LOL @ that pre

Just looking at that dartzeel thing makes me feel uncomfortable. I've always lived by the rule that less = more in the hifi world. That thing has about 1500 too many parts to be a really good sounding preamp, LDR's or not.

You can't polish a turd.
 
#698
This is a long thread!! I just read it through very quickly so sorry if this has been covered before.

When I read about people buying several optocouplers and going trough the trouble of matching them I would like to ask if it would be better to use several optocouplers in a series/parallel arrangement?

This would have two potential benefits:
1. Component mismatches will average each other out.
2. Distortion is voltage dependent. With many resistive elements there will be less voltage per optocoupler -> less distortion.

For example instead of using 2+2 matched it might be possible to use 8+8 unmatched optocouplers for a stereo attenuator (or 4+4 with a halved or doubled impedance). Or are the components usually so badly off spec that this wouldn't work?

I hope you understand what kind of arrangement I mean.

-thomas
 
#699
serengetiplains said:
Guys, pardon my ignorance, but does the Dartzeel pre use an LDR as the attenuating device?
Click to expand...


georgehifi said:
Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light. However, until all the patents are in place, I would prefer not to specify the details.

Above: This is a direct quote from the interview with the designer
Click to expand...

It looks like they switch resistors using light:

Q: I am fascinated by the mysterious volume control light system.
A: Mark Levinson, for example, uses a chip with trim resistors in a ladder configuration and they switch them with FET transistors. The problem with FETs is that you have a silicon junction and the signal is altered by the switch. You can use relays but the contact remains the problem. There is an electrical potential difference between two contacts so here we use a similar resistor ladder but we switch using our light system instead of relays.
 
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