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Old 15th May 2013, 08:35 PM   #5041
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Quote:
Originally Posted by wapo54001 View Post
Rudi, I am looking at your photograph and the MCP602x datasheet. I guess the 8 pin DIP in the upper right corner is your 6021, but I can't visualize the function of a single op-amp in a circuit where there are two pot sections and four legs to be controlled. If the purpose was to offload managing the current from the pot onto the op-amp, I would think you'd use a 6022 or 6024 with two or four amps, so that can't be it. Could you tell me what that single op-amp does, please?
It serves as a buffer for the voltage across one of the LDR's LED in order to measure actual volume attenuation. Its output is connected to ADC input of the PIC.

Last edited by metal; 15th May 2013 at 09:04 PM.
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Old 23rd May 2013, 05:53 PM   #5042
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It serves as a buffer for the voltage across one of the LDR's LED in order to measure actual volume attenuation. Its output is connected to ADC input of the PIC.
Thank you for that enlightenment. I thought it was part of the current control circuit.
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Old 2nd June 2013, 12:42 PM   #5043
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George, I'd like to ask your opinion about using metal-film resistors at the output of an LDR potentiometer as pictured.

I understand that they will affect the response curve of the pot; however, I'm mainly interested to know if you believe that they would adversely affect the sound of the LDR pair. What do you think?
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Old 2nd June 2013, 03:09 PM   #5044
acumos is offline acumos  Italy
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hi guys, I'm building my new f5 with lightspeed and speaker protector by diyaudio. Can you tell me if I can use a single toroidal 12v to power these two circuits?
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Old 3rd June 2013, 12:51 AM   #5045
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Quote:
Originally Posted by wapo54001 View Post
George, I'd like to ask your opinion about using metal-film resistors at the output of an LDR potentiometer as pictured.

I understand that they will affect the response curve of the pot; however, I'm mainly interested to know if you believe that they would adversely affect the sound of the LDR pair. What do you think?
Not only the respones curve but also the min volume achievable, and the nice log feel to the progression of the level control, this is why it is as I have found always better to quad match all the LDR's and not try to short cut with buffering ressitors.
As for the sound of resistors, some think they all sound different when in circuit, and some believe that the unique sound of the Lightspeed is due to the composition of the LDR itself, as well as no contacts in the signal path.


Quote:
Originally Posted by acumos View Post
hi guys, I'm building my new f5 with lightspeed and speaker protector by diyaudio. Can you tell me if I can use a single toroidal 12v to power these two circuits?
I cannot see why not as the Lightspeed is powered after the toroidal with it's own 5v regulated power supply, so long as there is no sag in the the toroidals voltage it should be fine to power both from it.
Just be careful that there is no temp swings inside the F5 if you plan on putting it inside it that the Lightspeed circuit will see, or you will get channel imbalance drift.
Cheers George
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Old 14th June 2013, 12:40 AM   #5046
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Lightspeed Attenuators owners and diyer's, I've just been informed again by Stereophile, and you'll be happy to know that your Lightspeed has just made it again into the Recommended Components with the highest 3 x $$$ rating for sound and value for money in the next issue.
You can download it free via Apple Ipod from the Stereophile website or wait for the hard copy to come out.

Cheers George
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Old 15th June 2013, 12:05 AM   #5047
soongsc is offline soongsc  Taiwan
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I downloaded the app, but not sure what to make of it. Have not found the light speed on it.
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Old 15th June 2013, 12:20 AM   #5048
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I downloaded the app, but not sure what to make of it. Have not found the light speed on it.
Someone who downloaded the app sent this to me, as I don't do Apple myself.

Cheers George
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Old 15th June 2013, 02:25 AM   #5049
gootee is offline gootee  United States
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Originally Posted by metal View Post
It serves as a buffer for the voltage across one of the LDR's LED in order to measure actual volume attenuation. Its output is connected to ADC input of the PIC.
That would measure the commanded attenuation, not the actual attenuation.

Actually, it would only measure the commanded resistance of only one of the LDRs (photocell), if you only measured across one LED.

To measure the actual attenuation, you would need to measure the voltages across BOTH of the photocells (i.e. the LDRs, not the LEDs), and then do some arithmetic involving the two measurements; at least one ADD and one DIVIDE, I think.
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Old 18th June 2013, 03:03 PM   #5050
soongsc is offline soongsc  Taiwan
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Originally Posted by georgehifi View Post
Someone who downloaded the app sent this to me, as I don't do Apple myself.

Cheers George
Even the layout of the app looks different.
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