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Old 11th December 2010, 05:57 PM   #41
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Default Balanced LDR

Hi Ondesx,
The pdf shows the shunt connected to + and -. How will that change the sound of the balanced ldr pre? Is the shunt controlled by the pot? That doesnt make sense to me. I am looking for circuits to improve the ps of the ldr preamp. The 2 posts you point to do not have any circuit info. I am not that knowledgable about this stuff but am willing to learn. I find the single end ldr pre I made sounds very good and would like to finish the balanced one someday soon.
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Old 11th December 2010, 06:23 PM   #42
ondesx is offline ondesx  France
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Originally Posted by bikerboy View Post
The pdf shows the shunt connected to + and -. How will that change the sound of the balanced ldr pre? Is the shunt controlled by the pot? That doesnt make sense to me. ...
Well, there are two different ways to go balanced. One is the schematics you already have, the second is the so-called "floating balanced" which is represented on my figure.

The two series and the shunt are controlled as they are in your own circuit, i. e. series in one polarization and shunt in another. In this approach not only you'll save 2 "matched" components but it is easier to control.

You have to "imagine" that "a virtual ground" is somewhere in between the bridge figured by the shunt LDR.

Perhaps to help you understand the things in a very simplistic way, please go do it with "fixed resistor values" (not LDRs) for a given attenuation factor... You'll see that the voltage of the +/- input side is really attenuated by the expected value at the output side...

The best way to understand is to experiment...
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Old 11th December 2010, 06:43 PM   #43
ondesx is offline ondesx  France
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Originally Posted by bikerboy View Post
The 2 posts you point to do not have any circuit info...
I'm afraid that even if I provided the circuit this wouldn't help you unfortunately, because the heart of this attenuator is something not easy to deal with in fact...

Suffice to say that the "linearity" and "stability" of LDRs are far from to be the "better parameters" of these components. As you probably are aware, it's necessary to always give an adapted current to the LDRs for ALL the attenuation steps. There is no "analog method" which delivers "continuously" the correct currents for all the working range (this is what was tempted through the potentiometer method...). Then you must either "manually" or "automatically" determine these values. Last, all these data are stored and used for each required attenuation.

It'll be near impossible to derive a correct working balanced device for all the attenuation range by the use of a good potentiometer, even a very good one and even by the use of the "floating balanced" approach... Unfortunately.
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Old 11th December 2010, 07:40 PM   #44
Blues is offline Blues  United States
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Originally Posted by bikerboy View Post
Hi Blues,
I use a single ended lighter note ldr preamp that I got as a kit from Uriah. I love it. The sweetest sound for a preamp I have ever heard. Build An Amp
I have a set of 8 matched ldrs from Uriah to build a balanced ldr lightspeed type preamp. I also have a wireless remote kit I got from diyclub. the pot is a 6 gang 100k type. If I'm lucky and the seattle weather continues I will have a rough build this weekend. I had planned on a basic ps for the ldrs but your warpspeed ps looks nice. Whats the chance it would work in a light speed type circuit.

http://www.diyaudio.com/forums/attac...ii-circuit.gif
Hi bikerboy,

I have not tried the balanced version of the Warpspeed as I don't have a balanced source and amp to really go fully balanced. I can't find any reason though that it won't work as presented on the simplified schematic. The Warpsquid can source enough current and will work with just one along with one precision pot. You probably can use the matched LDRs you have, as these are what are common to all the designs, but not sure if these are matched at the Warpspeed's listening range (response curves on article). If you really want to try I can provide just the Warpspeed and the control pot. Please pm me if you do.

Yeah, it's only late fall we have already ran the full gauntlet of winter weather here in the PNW...including thunder and lightning!
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Old 11th December 2010, 07:41 PM   #45
Blues is offline Blues  United States
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Quote:
Originally Posted by ondesx View Post
A much better schematics for balanced LDR use in audio is presented on the following figure... Then you just need 6 instead ! A working high precision stereo balanced LDR based on this circuit is presented in the LS thread posts #3703 and #3705.

Hope this helps !
Could you please start your own Thread so we can discuss your designs separately. Thanks...
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Old 11th December 2010, 07:47 PM   #46
ondesx is offline ondesx  France
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Originally Posted by Blues View Post
Could you please start your own Thread so we can discuss your designs separately. Thanks...
Oh sorry I didn't realize it's a "private thread". And the circuit I suggested isn't "my own design" but a well known balanced design. Anyway...
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Old 13th December 2010, 03:00 AM   #47
Blues is offline Blues  United States
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Btw, this is already up...Warpspeed Optocoupler Volume Control Kit
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Old 13th December 2010, 09:09 AM   #48
markusA is offline markusA  Sweden
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It's nice to see people experimenting.
Could we please have a summation and update?
Where are we at?
Did you solve the issues?
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Old 13th December 2010, 03:38 PM   #49
Blues is offline Blues  United States
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Thanks! The attached on post #3 has more info...
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Old 13th December 2010, 10:33 PM   #50
markusA is offline markusA  Sweden
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Ok, I looked at the pdf.
Now please explain to me what's so special about it?
To me it looks like standard series/shunt configuration with current sources?
I'm doing current sources as well, I have a big knob (well actually two since I have balance as well) and distortion due to a psu shouldn't be a problem if you know how to design a psu?

It's possible I'm missing something here but I'm just not seeing anything special?
I don't want to be a bad sport, I'm just not seeing it? Please explain?
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