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PostPosted: 03 Feb 2009, 16:13 
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Location: Australia
RiGuy wrote:
So do you think its possible to make the equivalent of a 100k pot with these?
I have been considering using the LDRs to build an equalizer. Anythoughts or past experiences?

marc brown wrote:
I've had a similar thought -- because I need more input impedance than the PSMLS or the LS provides. I might try putting some high quality caddocks before the LDR attenuators.

Marc you must have a tube output cd player to ask this?
I'm afraid your fighting a loosing battle, as if you introduce more resistance into the circuit with resistors you will nullify your volume control range as well, the best way is to make the output impedance of your source (CD) lower,
Here is a very good tube (sub 100ohm output) circuit that I found works very well with the Lightspeed Attenuator the way I designed it, and is maybe the best tube output buffer I've heard.
Cheers George
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Low out Z tube buffer.jpg


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PostPosted: 03 Feb 2009, 16:17 
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Well, they are supposed to go all the way to 1megohm so we can do it, but I have no clue as to how to get there short of, which wouldnt be so hard, getting a huge resistance pot to vary the juice going to the LDRs. I suppose this is something I will have to try out to find out. It is just puzzling to me that George stopped at around 7k but I think he had his reasons.
Ri

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PostPosted: 04 Feb 2009, 23:48 
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If built MkII (series & shunt ldr's) as I posted (diagram) on page 3, you will get an average mean of around 7-10kohm impedance (with good usable volume range). If additional series resistances are added to either the shunt or series ldr's you will get into trouble with the volume range.

My production Lightspeed Attenuator runs the ldr's at a max of 75% of their rating, this way if the level (current) control to the ldr's is at max or minimum volume, their life expectancy is around 20 years, if you leave the volume (current) control at half level (12o'clock) their life expectancy doubles to around 40 years.
I have now about 110 current MkII Lightspeed Attenuators around the world, not one failure yet over the 5 years it's been out, and 99% of these are powered on 24/7
You must remember, I been doing these for over 30 years, I've tried just about everything.
The original Mk1 was the simpler series resistor with a shunt ldr, it was easy to build, no ldr matching headaches, trouble was the volume did not go down low enough and the in/out impedance was all over the shop. The MkII simply kill it for sound quality, more dynamic, tighter and stronger in the bass, and a much more even impedance match for the source and power amp. I recalled all the Mk1's and converted them to MkII.
Cheers George

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PostPosted: 05 Feb 2009, 11:54 
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georgehifi wrote:
Marc you must have a tube output cd player to ask this?
I'm afraid your fighting a loosing battle, as if you introduce more resistance into the circuit with resistors you will nullify your volume control range as well, the best way is to make the output impedance of your source (CD) lower,
Here is a very good tube (sub 100ohm output) circuit that I found works very well with the Lightspeed Attenuator the way I designed it, and is maybe the best tube output buffer I've heard.

Thanks for the tip about the buffer George. I've been researching tubed buffers and tubed NOS DAC's this week. All look fun to try out. :)


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PostPosted: 16 Mar 2009, 10:29 
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I want to try the tube buffer. Not necessary but it will give that tube sound, right?
Questions then.. Are the Tesla actually the best sounding here. This website claims they are the best E88C
Is this buffer before or after the Lightspeed?
Is the +/-85 V a DC or AC current. Sorry, I am lost in tubes. How many mA do I need to power the buffer?
Guess I am looking at this and saying, is this the whole circuit? Is this all I have to do except find a power transformer or is there extras in the circuit that are assumed?
Uriah

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PostPosted: 16 Mar 2009, 10:53 
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Hi, I'm interested in more info on the Lightspeed attenuator. I was going to email you but your profile doesn't have an email address attached to it.

Where do you find matched optocouplers? How would you go about matching them?

Thanks,
JG


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PostPosted: 16 Mar 2009, 12:40 
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RiGuy wrote:
I want to try the tube buffer. Not necessary but it will give that tube sound, right?
Questions then.. Are the Tesla actually the best sounding here. This website claims they are the best E88C
Is this buffer before or after the Lightspeed?
Is the +/-85 V a DC or AC current. Sorry, I am lost in tubes. How many mA do I need to power the buffer?
Guess I am looking at this and saying, is this the whole circuit? Is this all I have to do except find a power transformer or is there extras in the circuit that are assumed?

Hi Uriah, Which tube sounds best is subjective. I have never tried a E88C, but I have some extra 6DJ8 / ECC88 / 6922 tubes I could send. You only need one tube for a stereo buffer. Current draw will be tiny, less than 10mA so you won't need much of a transformer. The technical name for a "buffer" is a "cathode follower", so you can search for that as well. It is very simple. You can use a number of inexpensive tubes to test it out. The buffer would go after the attenuator.

EDIT: I just noticed you were referring to the circuit above, so ignore my single tube comment. But a cathode follower can be built with one tube.

merlin2049er wrote:
Hi, I'm interested in more info on the Lightspeed attenuator. I was going to email you but your profile doesn't have an email address attached to it.

Where do you find matched optocouplers? How would you go about matching them?

Hi merlin2049er, I got a matched set of LDRs from RiGuy. You should be able to send him a private message by clicking the "pm" button under his posts.

Cheers,
Gio

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PostPosted: 13 May 2009, 16:25 
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Joined: 11 Dec 2008, 10:23
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Location: Austin, TX
Aaaargh, I've got to stop browsing through here. :x

Uriah, this is just something else I MUST build. Congrats on your successful build and now I've got this on my 2010 build list along with the PassDIY F5. If it hasn't been mentioned before, Uriah really liked this combo.

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PostPosted: 13 May 2009, 17:05 
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2010???!!!?
Look, this can be built in one hour or less :)
Send your wife to the mall with the girls. Get this done and cook dinner. She will be thrilled and so will you! :)
Uriah

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PostPosted: 13 May 2009, 21:30 
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RiGuy wrote:
Send your wife to the mall with the girls. Get this done and cook dinner. She will be thrilled and so will you! :)

That really depends on how good he cooks! ;)

BTW - here are some detailed instructions that Ri put together for a DIY Lightspeed Passive Attenuator. It is simple to build and it really is great.

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