µController-based contactless passive pre/front-end...
Hi Thomas,
as you may have already read here some posts ago, we're trying to do that (also including remote control) here:
http://www.audiofaidate.it/forum/topic.asp?TOPIC_ID=2576
(sorry, it's in Italian language... but I and Andy can give you whatever info you'd like to know about it in English).
We are still in a "brainstorming" pre-design phase, thus we have not built anything yet. If you're planning to do just about the same, please let' join our efforts!
Hi Thomas,
Tolu said:
as you may have already read here some posts ago, we're trying to do that (also including remote control) here:
http://www.audiofaidate.it/forum/topic.asp?TOPIC_ID=2576
(sorry, it's in Italian language... but I and Andy can give you whatever info you'd like to know about it in English).
We are still in a "brainstorming" pre-design phase, thus we have not built anything yet. If you're planning to do just about the same, please let' join our efforts!
beau2317 said:
Many years ago when I was in conversations with Mesa, the
guitar amp guys, and they were using the Eg&G parts. Their
concerns were not distortion, but tracking.
I worked up a servo system which used a small amount of DC
to measure the resistance of the Cadmium Sulfide cells and this
fed back to the light drive circuit, with a large time constant.
It worked fine - the disadvantage being that it slows down the
response of the attenuator and that you must capacitively
couple the signal path.
No doubt some of the bright boys on this forum could work up
an example, if there is an interest.
Nelson,
Obviously you are keeping an eye on this thread.
I am curious whether you have taken another look into LDRs again or perhaps all the discussions here are not sufficient to motivate you to give it another trial ?
Or if you have, whether you would share with us what you think about PDRs ?
Patrick
Obviously you are keeping an eye on this thread.
I am curious whether you have taken another look into LDRs again or perhaps all the discussions here are not sufficient to motivate you to give it another trial ?
Or if you have, whether you would share with us what you think about PDRs ?
Patrick
The EG&G (Perkin Elmer) LDR's may well be higher in distortion than the Silonex NSL32SR2S LDR's.
At CD highest playback level <2v the Silonex LDR's are still below .01% and that is 2nd harmonic in nature, which if anything is pleasing to the ear, ask any tube guru.
And then we have the speaker itself >1% in distortion, so if anyone can hear .01% of 2H in a system I'll kiss his feet, as he is the LORD.
Cheers George
At CD highest playback level <2v the Silonex LDR's are still below .01% and that is 2nd harmonic in nature, which if anything is pleasing to the ear, ask any tube guru.
And then we have the speaker itself >1% in distortion, so if anyone can hear .01% of 2H in a system I'll kiss his feet, as he is the LORD.
Cheers George
LDR control loop
Nelson, something like this? Just a quick sketch of mine:
When the LDR decides to go down in resistance or the user increases the resistance control voltage, the node's DC potential falls with respect to that voltage. Then the error amp's output goes positive in an integrating fashion and that in turn decreases the LED current, increasing the LDR's resistance. Some bias current to the LED is required to keep the V->I converter in a closed loop condition.
Regards, Klaus
Nelson, something like this? Just a quick sketch of mine:
An externally hosted image should be here but it was not working when we last tested it.
When the LDR decides to go down in resistance or the user increases the resistance control voltage, the node's DC potential falls with respect to that voltage. Then the error amp's output goes positive in an integrating fashion and that in turn decreases the LED current, increasing the LDR's resistance. Some bias current to the LED is required to keep the V->I converter in a closed loop condition.
Regards, Klaus
Channel selector
Tolu asked:
Tolu asked:
I don't know how it sounds, but here is my idea how it could be done:
An externally hosted image should be here but it was not working when we last tested it.
Another selector possibility
Here is a data sheet: http://www.farnell.com/datasheets/1160.pdf
One problem could be that the series resistance of the LDR is too high when it is ON. Combining selector and attenuator by using fewer optocouplers could be reasonable.
I thought also that this could be one possible solution:
Here is a data sheet: http://www.farnell.com/datasheets/1160.pdf
One problem could be that the series resistance of the LDR is too high when it is ON. Combining selector and attenuator by using fewer optocouplers could be reasonable.
I thought also that this could be one possible solution:
An externally hosted image should be here but it was not working when we last tested it.
If you buffer the output(s) with a high input impedance circuit, there is little problem with the LDR on-resistance and distortion.
Regards, Klaus (uh, we are sort of threadjacking here, BTW)
Regards, Klaus (uh, we are sort of threadjacking here, BTW)
An externally hosted image should be here but it was not working when we last tested it.
Nelson Pass said:
Many years ago when I was in conversations with Mesa, the
guitar amp guys, and they were using the Eg&G parts. Their
concerns were not distortion, but tracking.
I worked up a servo system which used a small amount of DC
to measure the resistance of the Cadmium Sulfide cells and this
fed back to the light drive circuit, with a large time constant.
It worked fine - the disadvantage being that it slows down the
response of the attenuator and that you must capacitively
couple the signal path.
No doubt some of the bright boys on this forum could work up
an example, if there is an interest.
Either this or a calibration circuit which looks at the LDR
at switch on, or when asked to, adjusts and disconnects.
Kinda like Dan Lavry's mega expensive multi bit DAC which
re calibrates all the bits every time you switch it on with low
bit digital servos.
Terry
georgehifi said:
George,
On a good system you can hear 0.01% H2.
We made a power amp that had incremental H2/H3 addition.
I was surprised at how low levels you could hear.
However at these levels it doesn't sound like distortion. It just
changes the 'mood' of the music slightly.
In fact we found adding very small amount of H3/H2, in ways,
sounded like there was less distortion because without the
distortion the sound was slightly less pleasing and engaging - so it
could push you away slightly.
It's a very complex subject that needs much more understanding.
Terry
Once more!
I developed the idea a little bit:
Do I need to explain? Now there is also the volume control.
I developed the idea a little bit:
An externally hosted image should be here but it was not working when we last tested it.
Do I need to explain? Now there is also the volume control.
@Nicolas
what I don't get in mind is the meaning of the relay! Is it just for absoulte quietness when source is off?
I think the chosen optocoupler has too much Ron resistance when you use it only at series resistant. The last circuit will work better but therefore you won't get it with this optocoupler because resistance range is too wide so channel deviation is the main problem. I also don't know the distortion characteristics of that device.
Next week I'll get some NSL-32SR2S and NSL-32SR3 devices, some µCs, DACs, pots etc. for testing purposes. I will examine in the next weeks four sorts of preamps with the only goal: which one sounds best.
1. Opamp solution (active)
2. Optocoupler (passive)
3. Relay attenuator (passive)
4. Alps pot (passive)
Then theory becomes hard reality
I'll stay on the ball!
Regards
Thomas
what I don't get in mind is the meaning of the relay! Is it just for absoulte quietness when source is off?
I think the chosen optocoupler has too much Ron resistance when you use it only at series resistant. The last circuit will work better but therefore you won't get it with this optocoupler because resistance range is too wide so channel deviation is the main problem. I also don't know the distortion characteristics of that device.
Next week I'll get some NSL-32SR2S and NSL-32SR3 devices, some µCs, DACs, pots etc. for testing purposes. I will examine in the next weeks four sorts of preamps with the only goal: which one sounds best.
1. Opamp solution (active)
2. Optocoupler (passive)
3. Relay attenuator (passive)
4. Alps pot (passive)
Then theory becomes hard reality
I'll stay on the ball!
Regards
Thomas
10Megs at DC sounds fine, but capacitive coupling might be an issue. I measured some LDR cell dark state capacitances on the order of 300pF and more (if I can trust the LCR-meter).
One might use another LDR for the GND shunt (no mechanical parts), that should do enough isolation in a T-circuit. I'd say the tracking/aging problem has been adressed, at least with a basic proposal how this could be handled.
Regards, Klaus
One might use another LDR for the GND shunt (no mechanical parts), that should do enough isolation in a T-circuit. I'd say the tracking/aging problem has been adressed, at least with a basic proposal how this could be handled.
Regards, Klaus