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Old 11th August 2009, 01:57 PM   #11
udailey is offline udailey  United States
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If you use a dual gang pot this is how to do it.
This is an older drawing and I leave it as is but suggest changes.
The 100Ohm resistors can be replaced with one 1k resistor in front of the pot in series with 5VDC just like in the picture in the last post. This is to protect your pot from burning out in the long run. I have not had any problem and I have not had any reported problems, but its just a precaution.
Also, this pic shows how to insert trimmer pots if there is a reason you want to change the balance of the passive pre. You can leave them out or use just one on the channel with the least resistance or replace it with a chassis mount pot so you can adjust from the outside of the chassis.
Uriah
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Old 12th August 2009, 12:56 PM   #12
deandob is offline deandob  Australia
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Uriah,

I am doing a single LDR shunt circuit for a 6 channel amplifier attached to my home theater PC but I want to use the R3 LDRs not the R2 as the distortion is lower for the R3. I intend driving each LDR individually from a 6 channel programmable potentiometer, the DS1806, which will be connected to the serial port of a PC for control (toggling the Tx, RTS and DTR lines to send the serial bits to the Ds1806 using a .NET program). To get sufficient current to drive the LED I will be using a high current opamp per LDR in a constant current source configuration (MAX4167 single supply high current opamp to keep it simple). This setup will allow me to measure each LDR individually and create a lookup table in .NET to balance the response curve out across all 6 LDRs, as finding 6 perfectly matching R3 LDRs will be pretty hard. The .NET software will keep the volume control level between reboots and will also address each LDR separately for real time fine tuning when changing volume.

So I'm wondering if you would sell 6 "moderately" matched R3 LDRs as I can do the fine tuning matchup in software. If so, how much?

I can share the circuit and software if anyone is interested.

Regards.
Dean
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Old 13th August 2009, 03:54 AM   #13
tinitus is offline tinitus  Europe
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Quote:
Originally posted by deandob
Uriah,

So I'm wondering if you would sell 6 "moderately" matched R3 LDRs as I can do the fine tuning matchup in software. If so, how much?


Im not sure, but isnt the careful matching to make sure all LDR reacts the same at any SPL levels ?
Or else the difference between them would change at every SPL change ?
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Old 20th August 2009, 06:18 AM   #14
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Hi Uriah

Would it be possible to buy two stereo sets please?

Thanks

Richard
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Old 20th August 2009, 11:17 AM   #15
deandob is offline deandob  Australia
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Quote:
Originally Posted by tinitus View Post
Im not sure, but isnt the careful matching to make sure all LDR reacts the same at any SPL levels ?
Or else the difference between them would change at every SPL change ?
I will be using a lookup table on the computer to real time adjust the current levels of the LEDs according to the volume level (not signal level). However this will only work for fine tuning, the devices will still need to be somewhat matched (eg. +- 3db) and have the same curve characteristics.

Uriah, are you still selling unmatched batches? Given that I have to take measurements to build the lookup table, I might as well do the matching myself. I wanted to use the R3 LDRs however after doing modelling I need more low on resistance than the R3 can give (and less of the off resistance range) - so will go for R2s. Let me know how much for 25? Thanks!
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Old 23rd August 2009, 10:36 PM   #16
udailey is offline udailey  United States
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Have been getting emails for orders but no posts. Wanted to bump this thread. Remember, if you order LDRs you will get tech support from me to help you build. No problem, even phone help.
Uriah
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Old 24th August 2009, 09:46 AM   #17
deandob is offline deandob  Australia
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Uriah, no need to answer my request for an unmatched batch - I found another source of the R3's from another DIY enthusiast. Thanks.
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Old 24th August 2009, 01:31 PM   #18
udailey is offline udailey  United States
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deandob, I have tried to respond to you, there is no way to contact you as your email has not been available.
Uriah
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Old 24th August 2009, 09:03 PM   #19
SRMcGee is offline SRMcGee  United States
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Uriah:

What's the range of attenuation for the Lightspeed Attenuator?

Thank you,
Scott
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Old 24th August 2009, 09:20 PM   #20
deandob is offline deandob  Australia
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Uriah, sorry, not sure what is wrong, the personal messages work and I have had others send me email. Did you try personal message or email? I checked my profile and it is setup correctly. Possibly an issue with the new site?
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