New LDR6 Passive Preamp using light dependent resistors - Page 2 - diyAudio
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Old 17th January 2013, 01:27 PM   #11
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Quote:
Originally Posted by Speedskater View Post
Remember to connect each XLR pin #1, directly to the chassis and not to the audio circuit ground.
Hi Kevin,

Thanks for your comment.

I agree that grounding pin #1 is considered best practice these days with balanced connectors between primary components with active circuitry. Perhaps the best overview of this can be found in Rane's technical note on Sound System Interconnection which can be found at: http://www.rane.com/pdf/ranenotes/So...connection.pdf

Rane's recommended approach (the best approach!) is summarized in the following pic.

Click the image to open in full size.

That said, when it comes to placing a passive attenuator (unbalanced or balanced) between a source and power amp, I submit that the cleanest (least noise) approach is to not ground the common if it isn't needed.

In its simplest form, a balanced attenuator is a variation on the conventional L-Pad attenuator typified by a potentiometer per the diagram below.

Click the image to open in full size.

In our passive preamps, the audio signal pathways are optically isolated from the DC power supply via the LDRs - signal and power commons are not joined. Nor is the chassis itself grounded since neither the power nor the signal touch the box - they just pass through via the printed circuit board and some wire (which are also electrically isolated from the chassis). As far as the audio signal is concerned, the preamp is just a wire with a built in variable voltage divider.

Hence, at least as things stand right now, the plan is to not tie pin #1 to the chassis. We shall see if this approach survives the prototype testing but I'm reasonably sure it will.

Of course feel free to comment.

Cheers,
Morten
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Old 17th January 2013, 07:15 PM   #12
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Default Good reference

Hi Morten,

Just a quick note say that I admire your "purist" design philosophy.
Your volume control will make a great reference point to ensure that digital volume is being implemented in a totally non decimating manor.

Personally I use a dedicated PC or lap top as my high quality music source and run everything else through an AV amp.

What price is your volume control?

Thanks
Derek.
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Old 17th January 2013, 09:18 PM   #13
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Quote:
Originally Posted by Overkill Audio View Post
Hi Morten,

Just a quick note say that I admire your "purist" design philosophy.
Your volume control will make a great reference point to ensure that digital volume is being implemented in a totally non decimating manor.

Personally I use a dedicated PC or lap top as my high quality music source and run everything else through an AV amp.

What price is your volume control?

Thanks
Derek.
Hi Derek,

Thanks. But just to avoid any misunderstanding by people reading this, the LDR Passive Preamp is a digitally controlled "analog" volume control.

Aside from vinyl, all of my music is now ripped and resident on a PC in my office/shop with backup to a network server plus a synced copy to a cheap laptop in my living room where my big rig is located. I'm a big fan of using GoodSync for backup/syncing.

In fact I've dumped all my CD cases years ago and have parked all the CDs/inserts in big flippers that are collecting dust on a shelf. I've literally not looked at my archived CD's in over a year. Hi-rez digital is the future in my view - vinyl notwithstanding.

The single input/dual output LDR1 is $1195 and the six input/single output LDR6 is $1475. Note that these are both unbalanced RCA I/O. More info at: Products/Pricing |

Pricing on the Balanced LDR3B Preamp hasn't been settled yet. I'm targeting around $1800 and want to keep it under $2k worst case. Won't know until more of the development work is completed.

Best,

Morten
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Old 18th January 2013, 11:36 AM   #14
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Thanks Morten, sounds like a good value product, I can see that you spend a lot of time and effort on R&D as well as assembly.
Cheers
D.
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Old 31st January 2013, 04:18 PM   #15
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Default Potential DIY LDR board including IR remote function

As we continue to evolve the LDRx Preamp product line, it's been suggested that the DIY community may be interested in a DIY LDR volume control board.

Without going too far into the spec weeds, the LDR board could have the following characteristics:

1) Digitally controlled single ended volume control using matched LDRs
2) Microcontroller with embedded proprietary software including customized matching curves for the LDRs installed on the board
3) Accommodates 2-3 different selectable inputs
4) Input switching would be via LDRs working as switches in lieu of relays
5) Includes IR receiver with the following control functionally via external remote:
a) power on/off toggle
b) raise/lower volume
c) left/right channel adjust
d) channel balance adjust reset
e) input select
f) mute
6) Most, if not all, of the IR remote functionality listed above would be duplicated via digital or analog inputs. For example, volume could be controllable via either a 0-5 VDC input (from an external pot) or via an external encoder A/B leg inputs. On/Off could be via an external push button switch etc.
7) No on board power supply - would require external 5 VDC supply

I'd be very interested in hearing from forum members on their interest level and welcome any comments or suggestions.

Cheers,
Morten
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Old 31st January 2013, 05:34 PM   #16
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I would be very interested as long as it had balanced inputs/outputs.
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Old 15th February 2013, 02:26 PM   #17
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I would also be very interested in a DIY balanced input/output LDR volume control board.
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Old 15th February 2013, 09:47 PM   #18
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I've started another thread on the topic of a DIY LDR preamp control board.

Here's the link to the thread: Tortuga Audio LDR3x DIY Preamp Controller w/ Remote
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Old 2nd March 2013, 04:42 PM   #19
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Default New Design/Look For Balanced Passive Preamp

Here's a preview of the new look of our upcoming LDR3B Balanced Passive Preamp (and other products). Anodized brushed aluminum with carbonized bamboo sides. More info here: Update On Balanced LDR3B Passive Preamp (rev 3.2) | Tortuga Audio

Click the image to open in full size.
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