Cool idea! I need to think about this one. Surely though, it changes the Zo by quite a lot. How does the downstream amplifier like this?
Karl
The attenuation for the T attenuator at Zo=6k tops out at 88dB when R2=0. I need to rewrite the spreadsheet to allow different resistor values that would result in higher attenuation, even if the price is a higher Zo. But I'm guessing that 88dB is practically silent, isn't it?
Karl
Thanks for the explaination.
I want to use a digital pot to control the LDR but can't get a log one that is the right value so would there be any problem with using a 100k linear digital pot with a resistor across the input like this?
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Hmm, what would the ultimate curve look like after you combine the S-curve with the non-linear curve of the LDR module? Have you tried graphing the composite?
Karl
Not sure, only ordered my LDRs yesterday! I'll have a play when they arrive. With a 256 step digital pot there would be room to adjust the resulting curve in software. I'll be controlling the digital pot via I2C from an ardunio.
Remote control for the "Lightspeed" LDR configuration designed by George
Hello maxw
That's why I designed the Voltage Controlled Current Source (VCCS) module with an Infra Red interface for remote control. It can be configured to deliver up to 20ma to the LDR LEDs. It has volume and balance control from the use of front panel push button switches on your preamp, or an Infra Red remote controller and one VCCS user has also interfaced a microcontroller to the serial ports on the DS1802. It can also be set up to run LDRs in balanced signal mode by modifying the voltage relationships in the voltage bias chain.
I can now supply very low noise discrete replacements for the TL431 shunt regs in the bias chain and for the 12 volt series reg powering the 12 volt supply.
Regards
Paul
Hello maxw
That's why I designed the Voltage Controlled Current Source (VCCS) module with an Infra Red interface for remote control. It can be configured to deliver up to 20ma to the LDR LEDs. It has volume and balance control from the use of front panel push button switches on your preamp, or an Infra Red remote controller and one VCCS user has also interfaced a microcontroller to the serial ports on the DS1802. It can also be set up to run LDRs in balanced signal mode by modifying the voltage relationships in the voltage bias chain.
I can now supply very low noise discrete replacements for the TL431 shunt regs in the bias chain and for the 12 volt series reg powering the 12 volt supply.
Regards
Paul
Got my VCCS LDR running...
I can recommend maximus's VCCS LDR control boards with the infrared remote- very well thought out and pcb's are top notch.
I have been using it for a 8 months now- works like a charm! Even with matched LDR's, I get a slight shift of image to the left on low volume. Having the balance controls on the remote has been very useful to compensate. I'm using a small Lamdba 15V power supply I found at a surplus shop.
pre>VCCS LDR>amp.
A big thanks to George, udaily and maximus. The most transparent volume control I've ever had!
-Kent
I can recommend maximus's VCCS LDR control boards with the infrared remote- very well thought out and pcb's are top notch.
I have been using it for a 8 months now- works like a charm! Even with matched LDR's, I get a slight shift of image to the left on low volume. Having the balance controls on the remote has been very useful to compensate. I'm using a small Lamdba 15V power supply I found at a surplus shop.
pre>VCCS LDR>amp.
A big thanks to George, udaily and maximus. The most transparent volume control I've ever had!
-Kent
Attachments
LDR Imp curves
Hi,
as I´m driving a fairly low impedance amp (10k7) with those LDRs, I wonder if it would be better to lower the total impedance of the LDR attenuator by paralleling LDRs in the signal path, e.g. paralleling the serial LDR. Or , maybe paralleling serial and shunt LDRs (total of 8 LDRs i.s.o. 4)
I tried to predict the impedances (see below) . What would be most important to look for ? eg.flat curves (=constant impedance at the amp or source over the attenuation range), or equal number of shunt/series LDRs to compensate distortion ?.....
Cheers, Frank
Hi,
as I´m driving a fairly low impedance amp (10k7) with those LDRs, I wonder if it would be better to lower the total impedance of the LDR attenuator by paralleling LDRs in the signal path, e.g. paralleling the serial LDR. Or , maybe paralleling serial and shunt LDRs (total of 8 LDRs i.s.o. 4)
I tried to predict the impedances (see below) . What would be most important to look for ? eg.flat curves (=constant impedance at the amp or source over the attenuation range), or equal number of shunt/series LDRs to compensate distortion ?.....
Cheers, Frank
Hi James,
yeah, already envisaged the DCB1.
But as George mentioned, "no buffer" should be desirable, maybe I have to try different things:
yeah, already envisaged the DCB1.
But as George mentioned, "no buffer" should be desirable, maybe I have to try different things:
- Leave the classic 4 LDR setup (alredy sounds great) or
- Modify the input imp from 10k7 to ca. 50k and/or
- Modify the LDR Att total impedance by paralleling LDRs or
- use a DCB1 (without capacitor in the signal path