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Old 18th March 2008, 12:18 AM   #1241
wlowes is offline wlowes  Canada
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Default Matching LDR pairs

One way I sped up the matching job was to test 6 at a time. Basically, I took an IC socket and soldered a wire down each side of the pins. Then you can stick 6 ldr's into the socket and power the whole lot thru the pot. That way you warm up 6 all at once. Set the pot to 9 oclock and measure all six. then 12oclock and measure again etc. With 4 measurements and ldr's all from the same sorted lot, really close pairs emerged quickly. The measuring just took a few mins once the rig was set up.
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Old 18th March 2008, 03:27 AM   #1242
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Default Re: Matching LDR pairs

[QUOTE]Originally posted by wlowes
One way I sped up the matching job was to test 6 at a time. Basically, I took an IC socket and soldered a wire down each side of the pins. Then you can stick 6 ldr's into the socket and power the whole lot thru the pot. That way you warm up 6 all at once. Set the pot to 9 oclock and measure all six. then 12oclock and measure again etc. With 4 measurements and ldr's all from the same sorted lot, really close pairs emerged quickly. The measuring just took a few mins once the rig was set up. [



If you are testing more than six LDR's, this method does not yield very consistant results. You might consider using four discrete resistors as the current limiting device. This gives repeatable results if trying to match up lots of the LDR's.


George
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Old 18th March 2008, 10:10 AM   #1243
Harry3 is offline Harry3  Australia
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Hi Georgehifi,
Thanks for all the info. Great thread.
I have a curiosity question. What do you use for a phono amp?
Regards
Harry
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Old 18th March 2008, 02:50 PM   #1244
DeepSea is offline DeepSea  Hong Kong
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Quote:
Originally posted by georgehifi

Hi DeepSea, welcome to diyaudio forums, you can reach me on

georgehifi @ optusnet.com.au

delete the spaces before and after @


Cheers George
Hi George,

Please read the E-mail.


Thank You!
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Old 18th March 2008, 09:17 PM   #1245
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Quote:
Originally posted by Harry3
Hi Georgehifi,
Thanks for all the info. Great thread.
I have a curiosity question. What do you use for a phono amp?
Regards
Harry

My sources:
Are Transport/DAC, Tentlabs clocked Teac VRDS-25 as a transport, (I'm the Tenlabs agent in Australia)
My own heavily moded Harman HD970 with discrete Transimpedance I/V stage and pure class A discrete output stage all dc coupled as the dac, and a stunning Tandberg 3001 FM tuner.

My preamp:
That's obvious, the Lightspeed Attenuator

My speakers:
Bi-amped Martin Logan Monoliths III Electrostatics
<100hz they have a 12" driver now tuned to -3db @ 28hz actively bi-amped with my own designed active xover and a revamped SV12 12" bass unit in the Monoliths, the Eminence one was a cheap sad driver, and badly implemented.

My amps:
Were my own 805 SET tube monoblocks for the stats,
now a moded heavily biased (50 watts) class A ME850 for the Stats and a stock ME850 for the bass, (modded inputs on both amps to 200k) also DC coupled.

This system is now dc coupled from dac chip (AD1955) output to the speakers, I have found that any coupling cap anywhere in this system no matter how good or esoteric is detrimental to the sound.

As for phono, from the dozen or so of my customers that use them, two of them use the Dynavector phono stages, and one uses his own design based around an opamp, the others I cannot remember, Lehman rings a bell though.

Cheers George
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Old 31st March 2008, 10:29 PM   #1246
Tolu is offline Tolu  Germany
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Hi George,

I wan't to add more inputs to my Lightspeed (3 or 4) because only CD is too less.

What would be best for switching? Reed relay, "normal" relays like Takamisawa or Omron 6k or some electronic switches?
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Old 1st April 2008, 12:34 AM   #1247
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This is the best I've seen, one of the members here thought it up, no signal degradation at all. Going to be a b***h to build, but all others are a compromise, no matter which one you use.
If you don't want to use this, then your better off using a QED input switch box in front of the Lightspeed, then when your serious about showing off your system, go back to direct and forget the QED.

Cheers George
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Old 1st April 2008, 11:04 AM   #1248
Tolu is offline Tolu  Germany
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Has the member just thought or has he built it? If I understand this circuit right there is much attenuation of the active source in comparison to a relay (0,1 Ohm vs. 80 Ohm). I think it isn't the Silonex 2R part but what is it (with 1k)?

What is the mysterious of the QED device? I can't see nothing out of the box.
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Old 1st April 2008, 12:20 PM   #1249
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Default LDR for channel switching

Tolu,

Whilst the LDR produces a higher in series resistance than a relay or switch this should not be a problem with most devices today.

usually they have enough signal level to support this increased resistance (i.e voltgae drop) and if you add some additional circuitry to this circuity it is relatively easy to add channel level matching too (either manual or through software).
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Old 1st April 2008, 02:03 PM   #1250
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Is anyone using this pre-amp on the outputs from a DCX2496?

I think it would be ideal as you could control all 6 channels at once but I'm sure if the output impedance of the dcx would be ok....
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