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Old 15th June 2009, 04:26 PM   #2261
2A3SET is offline 2A3SET  Canada
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Default VCCS with constant Zin

Original VCCS has variable Zin, it reaches lowest Zin in the middle of the wipe and higher when moving away from middle.

Hopefully this design would work to get constant Zin.

Adjust CCS for Zin range, with 0.1ma, the current over LDR is around 0.02-1ma, so for SR2 it's aournd 5-7K, for SR3 around 20-30K.

Maximus, any comment? I think 0.1ma should be fine for DS1802 and 1ma output fine for OPAMP direct drive.
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Old 15th June 2009, 05:16 PM   #2262
maximus is offline maximus  Scotland
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Default Lightspeed remote control

Hi Folks,

I am running behind schedule with business commitments because I had to take time off this last month to refurbish my workshop and computer systems to cope with the increased demand for power supply products. I had reached the point where there was not enough workspace and storage space to deal with all the business requirements. I have several consultancy contracts in operation at present that are requiring a lot of attention and I am afraid these consultancy obligations are not helping the situation.

Please accept my apologies for the delay in answering your questions. I will be very busy this week catching up with outstanding orders for PHD so it will be Saturday before I can look at any questions on the Lightspeed remote control.

For those looking for boards and modules I will continue to make them available as long as interest continues.

Regards
Paul
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Old 16th June 2009, 02:10 PM   #2263
2A3SET is offline 2A3SET  Canada
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Default VCCS with constant Zin

Diagram in #2262 is wrong, should use Volt ref instead of CCS, current range over LDR is 0.03-3ma.

The idea is to keep current over DS1802 wiper lower than 1ma, and use OPAMP to get 3X current output.

Say R is the resistance between W and L of DS1802, the current over LDR shunt is in ratio of 0.6V/(R+680) and over LDR serial is in ratio of 0.6V/(45000-R+680). Expect in certain range resistance/current over LDR is linear, so Zin should be in the ratio of (R+680)/0.6+(45000-R+680)/0.6 which is a constant value.

Any better idea to get a 0.6V or lower volt reference?
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Old 17th June 2009, 07:31 AM   #2264
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Default Passive Preamp forum

Time to do some more recruiting for our own Passive Preamp forum/heading, please vote here.

http://www.diyaudio.com/request/

Cheers George
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Old 18th June 2009, 02:07 AM   #2265
udailey is offline udailey  United States
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Default Re: VCCS with constant Zin

Quote:
Originally posted by 2A3SET
Diagram in #2262 is wrong, should use Volt ref instead of CCS, current range over LDR is 0.03-3ma.

The idea is to keep current over DS1802 wiper lower than 1ma, and use OPAMP to get 3X current output.

Say R is the resistance between W and L of DS1802, the current over LDR shunt is in ratio of 0.6V/(R+680) and over LDR serial is in ratio of 0.6V/(45000-R+680). Expect in certain range resistance/current over LDR is linear, so Zin should be in the ratio of (R+680)/0.6+(45000-R+680)/0.6 which is a constant value.

Any better idea to get a 0.6V or lower volt reference?
Have you tried this?
Here are my naive comments.
I get approx a 1.5V drop over the LED. I dont know how .6V would get the LED to flicker. Maybe though I havent tried it.
.03mA may be to high. I get them to work with .00001A and less but I cant measure lower. Anyway, sure it would work but you might not get as much resistance as you could. I have an odd batch of LDRs that are reacting to extremely low current and this is not the norm but my last batches were tested with .000125A which was only at 40k in series with the voltage.
What if you switched it around a bit and ran the current output of the opamps into the DS1802 instead of through the DS1802 first? You could get high and extremely low current.
Also, you get lowest distortion with 2.5V over the LED. Thats somewhere on the Silonex website. Distortion is low anyway though.
Just comments let me know if I am full of it.
Uriah
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Old 18th June 2009, 01:56 PM   #2266
2A3SET is offline 2A3SET  Canada
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Default VCCS with constant Zin

0.6V is to make current over DS1802 less than 1ma (maximum according to datasheet), the OPAMP control the current over LDR (amplify 3x times) by adjust the voltage over LDR, I am gonna use 0.03ma-3ma to get 20K pot with 40-50db.
By the way, I just got 3 pair match perfectly and another 2 pair matched in 10% from 16 SR3.
I am using CCS to test the LDR, with LM334 and 10K variable resistor.
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Old 18th June 2009, 03:42 PM   #2267
udailey is offline udailey  United States
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Two of your pairs would be great, one of them would not make it into my pairs, but I am super picky and that is a great percentage out of 16. Well, if I wast testing out of 16 I would definitely take them all Awesome percentages. I have to build an LM334 circuit when I get home. On vacation right now.
So are you testing one at a time or how many?
I have to build one with SR3 to hear the sound. I wonder if its the same resistive material as the SR2.
Uriah
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Old 18th June 2009, 04:51 PM   #2268
2A3SET is offline 2A3SET  Canada
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Default Combine VCCS and CCS version

I was testing 4 pairs at each time with 15V supply, 1K resistor in series to monitor the current (only get one DMM), should test 16 together as it's a pain. Have to pick up close pair from excel chart, then match together again as even 0.001ma can make pretty big difference.

Here is another diagram I am thinking, the 250R can be lowered to make the adjustment range bigger, with 250R it's around 44DB, with 680R it's 37DB. Adjust the 1K pot for Zin.

I am going to build the CCS version first then this one as it's more complicate. I like the DS1802 balance control so I can use those 10% pair (1db difference?) as well.
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Old 23rd June 2009, 03:29 PM   #2269
maximus is offline maximus  Scotland
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Default Lightspeed remote control

Hi Dave G, post 2260,

1. The VCCS and IR boards are still available.
2. I have provided circuit diagrams and board layouts for the ‘Lightspeed’ remote control. This is enough information for a reasonably experienced constructor to copy my application of a single ended, IR remote controlled/chassis push button controlled, LDR volume control using either MKI or MKII ‘lightspeed’ LDR configuration based on George’s passive volume control. I am too busy at present to write out an application note for every option that is possible with the VCCS module. Alternative application configurations can be discussed on the forum thread.
3. The easiest and cheapest solution for balanced operation retaining the left/right balance control function is to wire a second set of LDRs for the anti-phase signals with their LEDs wired in series with the single ended set. You will need to have reasonably well matched quads for the series LDRs and the Shunt LDRs to do this successfully. To ensure enough headroom for the op-amps to drive the series connected LEDs you will also have to raise the voltage of the 3v3 TL431 shunt reg in bias chain to 5 volts and change the 12 volt 3 terminal power supply regulator for a 15 volt reg (it may even need to be slightly higher depending on the LED forward voltage) with a corresponding increase to the raw supply voltage to ensure the 15 volt reg does not drop out of regulation.
4. You will probably need to select different LDR types to achieve 25K.

Sorry no time for any more right now. I will try to get some time on the thread tomorrow.

Regards
Paul
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Old 24th June 2009, 01:42 AM   #2270
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Default IR remote +v supply

Hi Paul-

First, thanks for such nicely made boards! Starting to put mine together.
Is it critical to use +5V for the remote? Would 4.5V (3 cells in series) be enough?

Thanks- Kent
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