Hi Rellum,
How much more work would it take to include an auto calibration feature in your set-up? i.e something that applied a series of currents to each LDR & recorded the resistance for each current. I read through your posts quickly but didn't really understand where the table lookup for each LDR was being stored & how it was created & used? I'll have another read
How much more work would it take to include an auto calibration feature in your set-up? i.e something that applied a series of currents to each LDR & recorded the resistance for each current. I read through your posts quickly but didn't really understand where the table lookup for each LDR was being stored & how it was created & used? I'll have another read
Silonex Data Sheet
Per the data sheet for part numbers with the "S" suffix:
"Packaged in ranges. Printed with part number, R2
followed by a letter. Individual ranges not available
separately. Range distribution is not guaranteed."
R2A 100 110 IF = 1 mA (guaranteed +/- 1 range)
R2B 110 122
R2C 122 135
R2D 135 149
R2E 149 164
R2F 164 181
R2G 181 200
Assume it's still not tight enough but a start?
jkeny said:
Per the data sheet for part numbers with the "S" suffix:
"Packaged in ranges. Printed with part number, R2
followed by a letter. Individual ranges not available
separately. Range distribution is not guaranteed."
R2A 100 110 IF = 1 mA (guaranteed +/- 1 range)
R2B 110 122
R2C 122 135
R2D 135 149
R2E 149 164
R2F 164 181
R2G 181 200
Assume it's still not tight enough but a start?
Re: Silonex Data Sheet
This is where I got kind of ticked off at Silonex and Allied. They wanted 3.79 each for these. I talked to Silonex technical support about how they end up grading these. They apply a certain milliamps for a few seconds and make one single measurement then they feel like they can apply a grade to it. You can have 4 come in at grade "e" lets say and then end up with 4 that have wildly different measurements at other amounts of current. You have to do more than one measurement and 3 is a minimum. You also have to test them for a long time under the applied current so that the entire encapsulation comes up to a temperature that becomes steady in ambient. This is not just fiddly techno/audiophile freakiness. It really is necessary and for them to grade them based on one single test for only a few seconds is really ridiculous. If you bought all graded ones you would have a slightly better chance at getting matches. I buy ungraded and grade them myself as their grading standards are poor at best.
If youre not going to buy them already matched then at least buy a large handful of ungraded and try to buy enough that you get a price discount. Maybe someone will buy your extras so they dont have to buy so many to get more matches.
Its true that with many of the near matches the resistance at the same milliamps will pass each other back and forth on a curve. This will result in the image wavering left to right and is annoying.
Uriah
ps some type of autocalibration would be really really nice and would be a great help so that more people can make these attenuators. Of course it would cost so maybe it would be a draw as to whether to match or autocalibrate but I think it would be really neat to have a microprocessor do it.
jimbo51 said:
This is where I got kind of ticked off at Silonex and Allied. They wanted 3.79 each for these. I talked to Silonex technical support about how they end up grading these. They apply a certain milliamps for a few seconds and make one single measurement then they feel like they can apply a grade to it. You can have 4 come in at grade "e" lets say and then end up with 4 that have wildly different measurements at other amounts of current. You have to do more than one measurement and 3 is a minimum. You also have to test them for a long time under the applied current so that the entire encapsulation comes up to a temperature that becomes steady in ambient. This is not just fiddly techno/audiophile freakiness. It really is necessary and for them to grade them based on one single test for only a few seconds is really ridiculous. If you bought all graded ones you would have a slightly better chance at getting matches. I buy ungraded and grade them myself as their grading standards are poor at best.
If youre not going to buy them already matched then at least buy a large handful of ungraded and try to buy enough that you get a price discount. Maybe someone will buy your extras so they dont have to buy so many to get more matches.
Its true that with many of the near matches the resistance at the same milliamps will pass each other back and forth on a curve. This will result in the image wavering left to right and is annoying.
Uriah
ps some type of autocalibration would be really really nice and would be a great help so that more people can make these attenuators. Of course it would cost so maybe it would be a draw as to whether to match or autocalibrate but I think it would be really neat to have a microprocessor do it.
Auto calibration isn't possible I think!
The optocouplers are very temperature sensitive. You have the evironment temperature that has an influence and the part temperature that differs very much.
I did very much attempts with a 16bit DAC and the SR2S. Manual matching is the way to go. You can get 0.1 dB channel matching over the whole range! But it is the hell!
Try thermal coupling with a constant heat source of about 40° C.
The optocouplers are very temperature sensitive. You have the evironment temperature that has an influence and the part temperature that differs very much.
I did very much attempts with a 16bit DAC and the SR2S. Manual matching is the way to go. You can get 0.1 dB channel matching over the whole range! But it is the hell!
Try thermal coupling with a constant heat source of about 40° C.
Udailey,
When I spoke to them they wouldn't even pick from the same batch run either so their "matched" premium prices are a joke - just another way to gouge the public
Tolu,
Why is auto calibration not feasible? Surely if the can be hand matched they can be machine matched? I'm talking about juts putting in any two LDRs into their working environment & letting a PIC processor build a lookup table for each which would give the correct current needed to produce a certain resistance and thereby a certain dB.
When I spoke to them they wouldn't even pick from the same batch run either so their "matched" premium prices are a joke - just another way to gouge the public
Tolu,
Why is auto calibration not feasible? Surely if the can be hand matched they can be machine matched? I'm talking about juts putting in any two LDRs into their working environment & letting a PIC processor build a lookup table for each which would give the correct current needed to produce a certain resistance and thereby a certain dB.
It would be cool if you could drop any two into one channel and then use your volume pot to change volume on that one channel. Then put two others in for the other channel and have a pic microcontroller measure resistance on all 4 then alter the current to the 2nd channel LEDs so that the resistance of both channel's Series resistors match and the Shunt match as well.
Uriah
Uriah
No problem. If you go back and order another dozen of the cheap ones you will surely find a suitable stereo setup when combined with the ones you have.
It might take a week or so if you measure one by one and dont try real hard
Just use a 3V battery and a pot and never move the pot til you measure each one then another setting etc. Or use a few different resistors in series with the + from the battery. Give them time to warm up and then measure and put it in a spreadsheet. Then when all done graph it out and "look" for the best match.
Uriah
It might take a week or so if you measure one by one and dont try real hard
Just use a 3V battery and a pot and never move the pot til you measure each one then another setting etc. Or use a few different resistors in series with the + from the battery. Give them time to warm up and then measure and put it in a spreadsheet. Then when all done graph it out and "look" for the best match.Uriah
Hi JKeny
About the actual code, the dac words are manualy stored in a long list of RETLW xxxx instructions. Storing them in the program memory is the only method provided by this chip to create an easy acces to a lookup table. I've got the values by connecting a DMM across each LDR in ohmmeter mode and activating a part of code called "setup mode". With my handy remote control, I can select whatever 16 bit word wich is then instantly transmitted to the dac by the pic. When the correct resistor values are found and not wandering too much, I read both 16 bit values on the preamp display (in hexa mode) and put them on paper. It took hours to complete for 57 steps.
Auto calibration would require an extra AD converter and a DC reference voltage. Vref would be applied at the audio inputs and the ADC at attenuator's mid points. Relays should be used to keep isolation between analog and digital side in play mode. That way, knowing Vref value and the desired attenuation, we could measure the appropriate voltage at each mid point. An iterative programming method would vary led's currents to reach the perfect dac word and store it in eeprom for each step.
The PIC I'm using (16F628), has no inbuilt ADC and too less memory. Some bigger ones of the same family have ADC and Vref capabilities, but with only 10 bits of resolution. This is short if high levels of attenuation must be reached. Vref should be of low value and only applied during measuring to minimize temperature effect, wich is really a problem with those LDRs.
This is for an R-LDR attenuator. For an LDR-LDR one with constant input resistor value, Vref should be replaced by a precise constant current source and the voltage measured at the mid point AND input point.
For me, that would imply an entire redesign of my pic card and added relays on the analogue board.
What Tolu tried to tell you is that even if feasible, the end result, precision wise wouldn't give better results than a good simple hand matched process, probably even worse at low attenuation settings. What you think about is nice but I find it highly overkill.
When it comes to ageing, I always turn my hifi off when not in use and don't feel concerned.
And nowadays, such projects take too much of my time.
I still didn't find some to compare my pre with an ptivol/SKPre combo that a friend of mine seems to like a lot.
Cheers
Francis
About the actual code, the dac words are manualy stored in a long list of RETLW xxxx instructions. Storing them in the program memory is the only method provided by this chip to create an easy acces to a lookup table. I've got the values by connecting a DMM across each LDR in ohmmeter mode and activating a part of code called "setup mode". With my handy remote control, I can select whatever 16 bit word wich is then instantly transmitted to the dac by the pic. When the correct resistor values are found and not wandering too much, I read both 16 bit values on the preamp display (in hexa mode) and put them on paper. It took hours to complete for 57 steps.
Auto calibration would require an extra AD converter and a DC reference voltage. Vref would be applied at the audio inputs and the ADC at attenuator's mid points. Relays should be used to keep isolation between analog and digital side in play mode. That way, knowing Vref value and the desired attenuation, we could measure the appropriate voltage at each mid point. An iterative programming method would vary led's currents to reach the perfect dac word and store it in eeprom for each step.
The PIC I'm using (16F628), has no inbuilt ADC and too less memory. Some bigger ones of the same family have ADC and Vref capabilities, but with only 10 bits of resolution. This is short if high levels of attenuation must be reached. Vref should be of low value and only applied during measuring to minimize temperature effect, wich is really a problem with those LDRs.
This is for an R-LDR attenuator. For an LDR-LDR one with constant input resistor value, Vref should be replaced by a precise constant current source and the voltage measured at the mid point AND input point.
For me, that would imply an entire redesign of my pic card and added relays on the analogue board.
What Tolu tried to tell you is that even if feasible, the end result, precision wise wouldn't give better results than a good simple hand matched process, probably even worse at low attenuation settings. What you think about is nice but I find it highly overkill.
When it comes to ageing, I always turn my hifi off when not in use and don't feel concerned.
And nowadays, such projects take too much of my time.
I still didn't find some to compare my pre with an ptivol/SKPre combo that a friend of mine seems to like a lot.
Cheers
Francis
Tolu said:
I have an idea for cooking the LDR's to the same temperature -- you can mount each on an a pair of LM317's, in series, set up as CCS -- I would affix the LDR to the tab of the LM317 with a dab of epoxy. You can work out all the equations to optimize the amount of heat you need to generate on 2 LM317's. I've done the same thing with the some of the elderly RCA transistor matrices to maintain constant temperature, an idea which goes back into the 1980's at least.
I spent yesterday afternoon working with some Perkin Elmer LDR's -- the problem with measurement of any of these devices is hysteresis -- the potted body of the emitter/receptor is such that it takes quite a bit of time to get the body temperature to stabilize. You can measure temperatures to a fraction of a degree, but there seems to be quite a bit of variability between the surface (ambient) and that which is extant on the diode emitter.
I tried these with an HV adjustable regulator and abandoned the idea as you couldn't (easily) tame the beast.
jackinnj said:
I don't know why there is so much talk about temperature drift as it is a not an issue, I get none. As I've said before, in the production "Lightspeed Attenuator" I manufacture they are matched and calibrated, then all 4 Silonex NSL32SR2S's are then (this is the secrete) potted together in hard wax, then a final calibration done, and they never drift even with age, or even with big changes in ambient temperature. My original MKII prototype is still perfect after being on now 24/7 for over 5 years. (Maybe the Perkin Elmer ones you are using do drift.)
I have had two customers only out of more than a hundred that have sent their Lightspeed Attenuators back to me for checking, not knowing it was other components in their system that were actually playing up and faulty, I have checked them, and they are still as per originally calibrated, not needing to be touched and sent back.
Cheers George
As far as my drifting comments go its more for matching and I have to say that after they warm up I dont have any problems with the Lightspeed that is driving my MyReFC amps. It never even has the top on and it could drift like mad if it wanted to but it stays after warming up. Also, for the most part I leave it on all the time as well.
For matching, as I want it as tight and accurate as possible, I try to keep the room the same exact temp with no airflow. When I test its small movements and never grab the LDR by the body only by the resistor leads with my DMM clips. Otherwise the numbers start to change fast.
Last night I was putting together a test fixture that will test dozens at a time using trimpots. So I dont have to buy .01% resistors to make sure I am testing the LDRs under the same current. The .01% are expensive. Trimpots are not cheap but they are less anyway. Plus I can dial them in very accurately. What was befuddling me last night was that I would set the trimpots all at 40k for a test and then come back 10 minutes later and retest a few trimpots.... They would all read 39.9k ARGHH. What could be the problem? But then I remembered that I had turned up the thermostat in the house and the heat was on. So even the resistors are quite sensitive. (of course the LDRs are resistors to so its no wonder that the trimpots and LDRs both drift) Guess I dont mind as long as they all drift together I will still get accurate tests on the LDRs. So thats my drifting story for the day
Uriah
For matching, as I want it as tight and accurate as possible, I try to keep the room the same exact temp with no airflow. When I test its small movements and never grab the LDR by the body only by the resistor leads with my DMM clips. Otherwise the numbers start to change fast.
Last night I was putting together a test fixture that will test dozens at a time using trimpots. So I dont have to buy .01% resistors to make sure I am testing the LDRs under the same current. The .01% are expensive. Trimpots are not cheap but they are less anyway. Plus I can dial them in very accurately. What was befuddling me last night was that I would set the trimpots all at 40k for a test and then come back 10 minutes later and retest a few trimpots.... They would all read 39.9k ARGHH. What could be the problem? But then I remembered that I had turned up the thermostat in the house and the heat was on. So even the resistors are quite sensitive. (of course the LDRs are resistors to so its no wonder that the trimpots and LDRs both drift) Guess I dont mind as long as they all drift together I will still get accurate tests on the LDRs. So thats my drifting story for the day
Uriah
Lightspeed remote control
Hi folks,
Sorry about the tardy reply. We had an electrical storm on Saturday, which took out the telephone/broadband line, and the engineer has only just fixed it.
Hi jkeny,
According to the Dallas DS1802 data sheet it is possible to cascade DS1802 chips to form multiple volume controls.
Hi Alan,
The quoted postage in post 1706 should cover a set of VCCS, IR transmitter and IR receiver boards. The additional weight does not take the postage into the next price band.
General discussion,
I have not thermally coupled the LDRs in my Lightspeed and I am not finding any annoying drift problems. They are even open to the surrounding atmosphere. The LDRs were matched up with precision current sources at three different current levels. All the LEDs were wired in series so exactly the same current passed through each one.
The DS1802 has 65 wiper positions with balance control. In practise this is fine as far as I am concerned. I do not find myself wishing for an intermediate step or constantly adjusting balance. I would suggest that too much attention is being paid to absolute precision (which is extremely difficult to achieve with these devices) when the rest of the items in the system are worse regarding absolute balance, particularly loudspeakers and even listening room, which vary with frequency as well as level balance. You could be listening to music instead of worrying about this.
Regards
Paul
Hi folks,
Sorry about the tardy reply. We had an electrical storm on Saturday, which took out the telephone/broadband line, and the engineer has only just fixed it.
Hi jkeny,
According to the Dallas DS1802 data sheet it is possible to cascade DS1802 chips to form multiple volume controls.
Hi Alan,
The quoted postage in post 1706 should cover a set of VCCS, IR transmitter and IR receiver boards. The additional weight does not take the postage into the next price band.
General discussion,
I have not thermally coupled the LDRs in my Lightspeed and I am not finding any annoying drift problems. They are even open to the surrounding atmosphere. The LDRs were matched up with precision current sources at three different current levels. All the LEDs were wired in series so exactly the same current passed through each one.
The DS1802 has 65 wiper positions with balance control. In practise this is fine as far as I am concerned. I do not find myself wishing for an intermediate step or constantly adjusting balance. I would suggest that too much attention is being paid to absolute precision (which is extremely difficult to achieve with these devices) when the rest of the items in the system are worse regarding absolute balance, particularly loudspeakers and even listening room, which vary with frequency as well as level balance. You could be listening to music instead of worrying about this.
Regards
Paul
Hi Paul,
It's not that I'm looking for absolute precision in all this just the ability to buy any 2 LDRs and use them without having to pre-grade from a batch. I also saw the uC method as a way of making balanced and/or multi channel operation possible. I don't think a multi channel LDR vol control has been done yet, has it? The fact that the LDRs would be precisely matched is just a by-product of these aims.
It's not that I'm looking for absolute precision in all this just the ability to buy any 2 LDRs and use them without having to pre-grade from a batch. I also saw the uC method as a way of making balanced and/or multi channel operation possible. I don't think a multi channel LDR vol control has been done yet, has it? The fact that the LDRs would be precisely matched is just a by-product of these aims.
Re: Lightspeed remote control
Paul, thanks for getting all of this together and thanks so much for the detailed explanation for those of use that were in a bit of a fog regarding how to pull this together.
I just sent you money for the IR boards. I'd previously sent you money for an assembled VCCS module and associated carriage. I mentioned this in my PayPal note as I'm sure you have a lot of things to keep straight.
regards,
Marc
maximus said:
Paul, thanks for getting all of this together and thanks so much for the detailed explanation for those of use that were in a bit of a fog regarding how to pull this together.
I just sent you money for the IR boards. I'd previously sent you money for an assembled VCCS module and associated carriage. I mentioned this in my PayPal note as I'm sure you have a lot of things to keep straight.
regards,
Marc
Lightspeed remote control
Hi jkeny,
It would be nice to pick a pair at random without the hassle of matching. The same could be said for FETs, transistors etc.
In theory the Dallas DS1802 should allow a multi-channel volume control to be built. Also the VCCS board can be adapted for use with a balanced lightspeed.
Regards
Paul
Hi jkeny,
It would be nice to pick a pair at random without the hassle of matching. The same could be said for FETs, transistors etc.
In theory the Dallas DS1802 should allow a multi-channel volume control to be built. Also the VCCS board can be adapted for use with a balanced lightspeed.
Regards
Paul