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Old 9th February 2011, 01:50 PM   #3991
Blues is offline Blues  United States
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Quote:
Originally Posted by Zen Mod View Post
boyz - isn't this George's thread ?

I can understand and support process of searching for even better alternatives , but something is fishy smelling here

cordially

ZM
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Originally Posted by soongsc View Post
I agree, if there are technical issues regarding the Lightspeeds, they can present data. With no data, I think other products are really should have their own thread.
In my case I just replied to what I think is wrong analysis about the design and optocouplers...and yes there is already a Thread and data.
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Old 9th February 2011, 02:14 PM   #3992
ua100k is offline ua100k  United States
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Originally Posted by Bernhard View Post
Diameter of each plate is 22mm.

If you can get a hp 3420b cheap somewhere...

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Agilent HP 3420B




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Last time it was running about USD$500.
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Old 9th February 2011, 02:19 PM   #3993
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by Blues View Post
In my case I just replied to what I think is wrong analysis about the design and optocouplers...and yes there is already a Thread and data.
I don't agree, but am interested in this thread you talk about. If you have subscribed to it as well, I'd appreciate the info since I keep track of only a few threads.
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Old 9th February 2011, 06:05 PM   #3994
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Originally Posted by udailey View Post
Sometimes, when they are so sensitive you may consider finding a way to keep the shunt LDRs at a lower max resistance or a way to keep series at a higher min resistance. This way you do not get incredibly loud volume on accident with touchy LDRs. It may be your pot and it may be the taper of your pot as well. Since all LDRs have a different resistance taper to them you may have a pair that increase in resistance faster than most in shunt or the opposite in series.
Anyway.
Here is the things to try
100k pot dual gang log. This will help for sure.
10k-30k resistors in place of the 100R resistors that are feeding your Series LDRs. You will NOT get max volume this way and your resistance curve will change a lot, but it will help with your immediate problem.
5k-20k resistors in parallel with the resistor side of your Shunt LDRs. This will keep shunt from increasing in value to fast and will also have negative side effects as mentioned above with series fix.

Probably your only problem is that you are not using 100k dual log pot. However if you have high gain amp and you have super efficient speakers sometimes the normal LS setup can be tuned to work better with that sort of system in these ways. There are other options like different voltage to drive them or series 10R pot before 100k pot.
Try 100k first and let us know.
Uriah

Thanks alot for the information.
I am using 68r resistors for the series ldrs (according to the manual) and 1k for shunt.
My preamp is Audio Note, poweramps are Quad II's (low gain) . Speakers are diy 15" coax with approx 96dB effiency.

In fact when volume pot is at its lowest the sound is "normal listening level".
An alps 100k log pot is in order. I have a noble pot 100k also I think so I may test it tonight..

Also changing the series resistors.



One more question. Would it be possible to change the 100k pot with for instance a pga2311 kit?
I am not sure.
http://cgi.ebay.com/PGA2311-Volume-c...item3a631ddf75

Thinking about a remote option. Or should I go for motorized alps solution?

Sincerely

Last edited by bambadoo; 9th February 2011 at 06:14 PM.
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Old 9th February 2011, 06:44 PM   #3995
udailey is offline udailey  United States
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Hi,
The PGA2311 wont work like you want it to. It could be a preamp all by itself but it does not work the same as a pot. Its actually an opamp with programmable gain.
The 100k pot is going to help you a lot. Right now your series LDRs are very very low resistance at their max resistance compared to what they would be with a 100k pot. If you have normal volume at min with a 50k then I think you will be fine with the 100k.
Another Lightspeed builder has had success with those motoroized pots but make sure that you check the pinout of the motorized pot as its not typical. Also be careful with those motorized pots. They might work for a while and then die. They can only handle about .05W, not .5W. That said, I know one is successfully in use and probably more. They might be underrated.
Make sure your 100k is DUAL LOG. Try that noble if its a dual log.
Dont worry about changing any resistors until you try a 100k pot. Seriously. Those are just bandages to fix it when your entire system has to much gain for the 100k pot version. Try 100k, then decide if you need to replace any resistors.
Uriah
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Old 9th February 2011, 07:53 PM   #3996
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The 100k dual log did not make any difference.
I will try increasing the series resistors.
I built the module after the manual
https://docs.google.com/fileview?id=...OTNjMzdm&hl=en
from buildanamp.com

It says
68R for R2 and R4 (in series with the shunt ldr)
1K for R1 and R3 (in series with the series ldr)
This is what I am using. Now with a 100k dual log pot.

So increasing the series resistance will be tested..
I made a typo in an earlier post. I said 68r for series. 1k for series is correct.

Sincerely

Last edited by bambadoo; 9th February 2011 at 07:59 PM.
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Old 9th February 2011, 08:23 PM   #3997
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Tried 68k and 9k in series and the same. A bit lower minimum level but still extremely sensitive with the knob.

Last edited by bambadoo; 9th February 2011 at 08:35 PM.
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Old 9th February 2011, 11:23 PM   #3998
udailey is offline udailey  United States
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I know this sounds nuts, but try a bigger knob. I wonder if its just to hard to dial it slowly while the shunts rise quickly in resistance. A larger diameter knob will make it much easier to dial small amounts than a small diameter knob. Now, if you tell me you are using some 2" diameter knob already I wont know what to do. Well, I will have some suggestions such as limiting the shunts ability to raise quickly by paralleling a resistor with the shunt side of your 100k pot. Very odd that a 68,000R resistor and then another 9,000R didnt help much.
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Old 10th February 2011, 10:20 AM   #3999
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Originally Posted by udailey View Post
I know this sounds nuts, but try a bigger knob.
It's not nuts at all. I fitted a larger knob on my Lightspeed for the same reason and it worked a treat.

Slightly off topic but other tricks are (1) to squirt the likes of Deoxit onto the tracks of the pot and work it in a couple of times on successive days and (2) to cover the back and front (i.e. not near the solder joints) with as much BlueTak as you can comfortably fit.

No, neither tweak makes any difference to the sound but they do make that $2 pot feel smoooooth and serrfistykated.

(Squidging Bluetak over a stepped attenuator does make it mechanically quieter.)
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Old 10th February 2011, 11:52 AM   #4000
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I have a big knob

Approx 2" in diameter....

I will build the other set of lightspeed that I have on hand and see if it behaves the same.

Sincerely
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