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Old 17th January 2011, 01:07 PM   #3921
udailey is offline udailey  United States
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Could you please try a 12V battery instead of your wallwart? You may have something going on that none of us can know in your wallwart or in the power feeding the wallwart.
It truly is odd what you are experiencing and something wonderful can be attained with LDRs. Maybe together we can all figure out the problem.
Uriah
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Old 17th January 2011, 01:53 PM   #3922
Alexiss is offline Alexiss  Sweden
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Originally Posted by udailey View Post
Could you please try a 12V battery instead of your wallwart? You may have something going on that none of us can know in your wallwart or in the power feeding the wallwart.
This is a great idea. Something latent seems to be the problem.

It is encouraging to hear that this seems to be an isolated incident. Of all the info there is to read about this great design, nothing has been found to confirm my observations.

As stated earlier, this is a very straight forward and innovative design.

What is more puzzling to me is that two identical units of the original Lightspeed design were assembled, with identical, pre-described PSU's and both exhibit the same sonic signature. Therefore your argument for possible contamination via the PSU/AC adapter is a valid one and quite an excellent idea.

I will try this and inform you on the outcome. It is good to know that no one else seems to have had similar experiences.

Thanks
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Old 19th January 2011, 12:13 PM   #3923
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Originally Posted by Nelson Pass View Post
OK, this would be the last manual version that you are
likely to see. It has all the pieces, and allows pretty complete
adjustment of input impedance and range, top to bottom.

As a 2 channel piece, LDR1 and LDR3 should be matched to
each other, and LDR2 and LDR4 should also be matched.
The match should take place around the 5 Kohm resistance
value. LDR1 and 3 do not have to match LDR2 and 4.
Sorry to change the subject here, but I'm new to this thread, having just finished my first LDR attenuator just recently. It sounds lovely in my secondary system, but less so in my primary system due to the tube output stage of my DAC. Sooooo....I'm thinking of building Mr. Pass's buffered version (p137 of this thread - I thought the picture would appear in the quote, but I guess not). Before I go to the trouble of learning how to match complementary JFETs (not a prospect I'm relishing) - is there any reason that the 2SJ74/2SK170 pairs can't be replaced by an LM394 supermatched pair? Would any adjustments to the circuit be necessary? I know they're obsolete but they're still readily available on ebay. Thanks to anyone who can provide guidance!
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Old 22nd January 2011, 12:57 AM   #3924
alazira is offline alazira  United States
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Quote:
Originally Posted by schubert View Post
Sorry to change the subject here, but I'm new to this thread, having just finished my first LDR attenuator just recently. It sounds lovely in my secondary system, but less so in my primary system due to the tube output stage of my DAC. Sooooo....I'm thinking of building Mr. Pass's buffered version (p137 of this thread - I thought the picture would appear in the quote, but I guess not). Before I go to the trouble of learning how to match complementary JFETs (not a prospect I'm relishing) - is there any reason that the 2SJ74/2SK170 pairs can't be replaced by an LM394 supermatched pair? Would any adjustments to the circuit be necessary? I know they're obsolete but they're still readily available on ebay. Thanks to anyone who can provide guidance!
It would be easier to buy matched jFets from Blues or Spencer here on the forum as the 2SJ74 are difficult to source nowdays. If you really want to match yourself:
Short the gate and source legs of the 2SK170. Connect these to the neg of a 9V. Connect the drain to the pos side with a 10ohm resistor. Use a DMM to measure voltage across the resistor. 0.1V=10mA Idss
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Old 22nd January 2011, 01:37 AM   #3925
udailey is offline udailey  United States
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THAT Corporation sells a 300 series that I have been thinking to try out. Its not expensive and it includes 4 transistors. Can get 4 matched PNP, 4 matched NPN or 2 PNP and 2NPN matched. Not saying you shouldnt try 2sj74 but man they are hard to come by and expensive, specially if doing your own matching.
ITs not hard at all to match the transistors by the way. Super simple. Go to pass' site and look up his articles. http://www.firstwatt.com/pdf/art_matching.pdf
You can literally get it done in 20 minutes. Including building the jig.
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Old 22nd January 2011, 09:56 AM   #3926
AndrewT is offline AndrewT  Scotland
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Originally Posted by udailey View Post
........... try 2sj74 but man they are hard to come by and expensive, specially if doing your own matching.
It's not hard at all to match the transistors by the way.
if "matching" means selecting jFETs with the same or very similar Idss then the "selecting" process is very simple and very quick. And a smallish batch of devices will yield a fair number of selected pairs, triples, quads.

Matching transconductance is all together much slower. Yield of matched pairs is much lower. I have not tried to find matched triples nor matched quads. I know how much work would be involved to find a tiny proportion of triples or quads. From a 200batch I'd guess I might get one matched quad to better than 1% of Id over a range of Id from 25% to 100% of Idss.
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Old 22nd January 2011, 12:50 PM   #3927
udailey is offline udailey  United States
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In the B1 paper Nelson specifies that they only need Idss matched so it should be very simple. Now that I think about it I have not looked back at that LDR circuit Nelson designed in a long time. Maybe it does have PNP, but if you just need a buffer the B1 is cheap and easy.
If I recall the B1 does not need the PNP version, only the NPN.
Also, I think AndrewT sells matched devices and his prices are better than anyone else. I think you have to ask him because I have never seen him advertise it. But anyway, if I were buying matched devices it would be from Andrew. We all know how particular he is about things being just right and thats the way I would want my matching.
Uriah
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Old 22nd January 2011, 06:32 PM   #3928
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Thanks gentlemen for your responses. A source of matched sets sounds like just the thing. But does anyone know for sure that LM394s won't work?
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Old 22nd January 2011, 06:40 PM   #3929
udailey is offline udailey  United States
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Well, I dont know that they will or not. I am working up a board to play with for the THAT devices right now. Dont know how these will work but its worth a shot. Yours are nice metal cans. I like that idea but pricey!! OMG Besides being out of production the cheapest I can find is 6.99 each plus 5 shipping. THAT is expensive to but at least you get 4 per package and can buy from Mouser when you get the rest of your parts. I think your idea with those cans will work but you might have different resistor values. Its worth playing with I think if you dont mind stuffing them into a protoboard and testing different combos.
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Old 22nd January 2011, 06:46 PM   #3930
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Hmmm....that is a little expensive for a "maybe". I'll check out the souces for matched sets of 2SJ74 and 2SK170 first.

By the way, Uriah, the Lightspeed I put together using your board, LDRs and instructions sounds marvelous with my reclocked Sony CDP-710, Rotel RB-980BX and Cambridge Soundworks speakers. Thanks for making this possible.
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