on the LDR matching: I remembered this post, sorry if its old
http://dropmix.xs4all.nl/pipermail/synth-diy/2008-March/006197.html
http://dropmix.xs4all.nl/pipermail/synth-diy/2008-March/006197.html
Lightspeed remote control
Hi Folks,
I am getting a lot of e-mail about technical issues relating to the VCCS and the IR boards/modules. I have already asked people to confine these technical questions to the thread so everyone can benefit from the discussion. Answering these e-mails is interfering with my work schedule, and it is apparent, that the same questions are being repeated. I know the thread is now rather long but people are just not bothering to read the forum thread. I do not wish to be unhelpful and will be pleased to answer questions on the forum thread but only once.
Regards
Paul
Hi Folks,
I am getting a lot of e-mail about technical issues relating to the VCCS and the IR boards/modules. I have already asked people to confine these technical questions to the thread so everyone can benefit from the discussion. Answering these e-mails is interfering with my work schedule, and it is apparent, that the same questions are being repeated. I know the thread is now rather long but people are just not bothering to read the forum thread. I do not wish to be unhelpful and will be pleased to answer questions on the forum thread but only once.
Regards
Paul
Why don't we split the thread off and do a construction thread?
Or even a wiki chronicling the details of the thread and the relevant pages / posts.
I have LDR's waiting for PCB's. Once I have the parts, then the questions will come. I would rather do the research and get the facts / knowledge before construction rather than during.
Or even a wiki chronicling the details of the thread and the relevant pages / posts.
I have LDR's waiting for PCB's. Once I have the parts, then the questions will come. I would rather do the research and get the facts / knowledge before construction rather than during.
Lightspeed remote control
Hi Troy,
I would rather not divorce the project from George. He started the thread, and enthusiasts, who do not have the ability to build their own unit, or the time, go to him for ready built and tested “Lightspeed” preamps.
A wiki would be ok, as it will keep the basic stuff together.
I do understand that it is hard waiting around for things to happen, but please bear with me, as I have to prepare everything in my spare time. There are other demands on this time besides the Lightspeed. I will get the application notes and materials lists ready as quickly as possible.
Regards
Paul
Hi Troy,
I would rather not divorce the project from George. He started the thread, and enthusiasts, who do not have the ability to build their own unit, or the time, go to him for ready built and tested “Lightspeed” preamps.
A wiki would be ok, as it will keep the basic stuff together.
I do understand that it is hard waiting around for things to happen, but please bear with me, as I have to prepare everything in my spare time. There are other demands on this time besides the Lightspeed. I will get the application notes and materials lists ready as quickly as possible.
Regards
Paul
Paul-
When I said the following:
"I have LDR's waiting for PCB's. Once I have the parts, then the questions will come. I would rather do the research and get the facts / knowledge before construction rather than during."
Meant I would rather do the preparations now, IE a new thread or Wiki, so when the PCBs do ship we have a base for constructing them.
It was in NO WAY to push, rush, or hurry you or the GB.
I appreciate what you are doing and I can certainly wait.
My suggestion and statement were solely intended to just help with the slew of questions that I'm sure will come once the PCB's ship.
When I said the following:
"I have LDR's waiting for PCB's. Once I have the parts, then the questions will come. I would rather do the research and get the facts / knowledge before construction rather than during."
Meant I would rather do the preparations now, IE a new thread or Wiki, so when the PCBs do ship we have a base for constructing them.
It was in NO WAY to push, rush, or hurry you or the GB.
I appreciate what you are doing and I can certainly wait.
My suggestion and statement were solely intended to just help with the slew of questions that I'm sure will come once the PCB's ship.
Lightspeed remote control
Hi Troy,
Do not think I was carping at you. I was just illuminating the situation.
I have already discussed the splitting of the thread with George and we both felt it would be better for the thread to stay intact and stay busy as the additional activity could help achieve the upgrading of the thread to the "passive preamp forum".
To everyone else,
I do not mind answering any questions about the VCCS and the IR boards/modules as long as they are placed on the thread and I can look in when I get a spare moment. What is concerning me is that my business e-mail address is getting a lot of the tech questions that should be on the thread. I sometimes end up spending over an hour a day answering them and this stops me building power supplies or doing consultancy work during this time.
Regards
Paul
Hi Troy,
Do not think I was carping at you. I was just illuminating the situation.
I have already discussed the splitting of the thread with George and we both felt it would be better for the thread to stay intact and stay busy as the additional activity could help achieve the upgrading of the thread to the "passive preamp forum".
To everyone else,
I do not mind answering any questions about the VCCS and the IR boards/modules as long as they are placed on the thread and I can look in when I get a spare moment. What is concerning me is that my business e-mail address is getting a lot of the tech questions that should be on the thread. I sometimes end up spending over an hour a day answering them and this stops me building power supplies or doing consultancy work during this time.
Regards
Paul
Matching LDRs
Perhaps could someone clear up, what I don't understand (Georges basic-circuit): The Amp is always "looking" at the resistive side of the LDRs. So every channel has the same resistance, if the both serials and the both shunts have the same resistance. So why matching so much, if it is only necessary to bring every of this two pairs to the same value: Adjusting the 4 (actually 3) 100 Ohm resistors (or i.e. using a trimpot at the serials and at the shunts).
Serials and shunts should have constant resistance-overall-values at all volume-steps...
Perhaps could someone clear up, what I don't understand (Georges basic-circuit): The Amp is always "looking" at the resistive side of the LDRs. So every channel has the same resistance, if the both serials and the both shunts have the same resistance. So why matching so much, if it is only necessary to bring every of this two pairs to the same value: Adjusting the 4 (actually 3) 100 Ohm resistors (or i.e. using a trimpot at the serials and at the shunts).
Serials and shunts should have constant resistance-overall-values at all volume-steps...
But they dont have a constant value cuz the manufacturing of the LDRs is a bunch of junk. They sound great but they could be cut with lasers rather then the apparent hack saws. You might read 2k ohms with a 40k resistor in series with a LDR or with another LDR you might read 7k so you have to keep working till you get two with the same reading over many resistances in series with it and then you can start to build. The trimpots will take care of small differences but not 1k differences or even close to that.
Uriah
Uriah
You've got to remember TJF, the NSL32SR2S is what I use in the production Lightspeed Attenuator, this is the only one in my view that works with a good low level minimum volume, it's full power resistance is 40ohm which gives it that low level minimum volume. It's high level maximum volume is up to 5megohm!! It is this 125000-to-1 difference that makes matching so hard but mandatory.
This is just one of the reasons why I don't sell kits, as I've been constantly asked, as ham fisted solderers that heat up the matched NSL32SR2S's to much will destroy the matching and render them useless.
Cheeers George
This is just one of the reasons why I don't sell kits, as I've been constantly asked, as ham fisted solderers that heat up the matched NSL32SR2S's to much will destroy the matching and render them useless.
Cheeers George
Attachments
TJF said:
Yes they do. I have looked for other sources and pretty much its Silonex or Perkins Elmer who sells an LDR they call a Vactrol. They have one that has apparently 2 resistors in it. WOW this must be the holy grail, right? Nope, the single package has two resistors and they are guaranteed to be within 20 percent of each other.... Who wants that?
TJF, I know I am talking negative but in all truth this is by far the best pot I have ever heard. It never fails to impress and OMG when you listen to really well recorded music through it its mind blowing. Build one and keep it forever.
Uriah
That's a word Uriah! Thank you. Couldn't get a feeling for the dimensions until the right parts arrive
Nevertheless: There are Trimmpotis from 100Ohm to 1MOhm... so it should be possible to regulate the circuit (only with 3 Trimmpotis instead of hundred of measured LDRs).
I don't want to displease anybody, I only want to understand, why it is necessary to order hundred or thousands of LDRs to get the things work in one or two houses ... Perhaps I don't understand anything at all up to now - I am shure I will do ...
Regards
Thomas
No no. I was selling them. Thats why so many for me. Pretty cleaned out at the moment but when I get to Texas in a month or so I might buy a few hundred more.
You dont need that many. Buy 25 and you will for sure get a good match. Dont buy the sorted ones. There is no advantage. Get them as cheap as possible and put a call in to Allied and ask for a discount off of the regular price.
Uriah
You dont need that many. Buy 25 and you will for sure get a good match. Dont buy the sorted ones. There is no advantage. Get them as cheap as possible and put a call in to Allied and ask for a discount off of the regular price.
Uriah
Wow, I've just built one of those cheap rotary stepped ladder attenuators - it works great, but I wish I'd seen this first, great concept!
I've read for hours, but can't seem to find any actual circuits, or projects, other than George's originals (thanks George!). Particularly, I'm thinking multi-channel, and I'm not sure it's so easy to match that many LDRs The LDRs drift with temperature, but do they also drift with age, etc? I'm thinking in any case, a DAC approach might be best.
Maximus, am I right in thinking your remote circuit still requires matched LDRs, ie the DS1802 does not have the resolution to balance the LDRs?
I'm a complete novice, but always wanted to do a microcontroller project, maybe now's a chance, but I don't want to re-invent the wheel.
I think I saw a post that had some links to various projects, but I can't find it again now - I really wish these forum threads had updateable header pages for this kind of stuff.
I've read for hours, but can't seem to find any actual circuits, or projects, other than George's originals (thanks George!). Particularly, I'm thinking multi-channel, and I'm not sure it's so easy to match that many LDRs The LDRs drift with temperature, but do they also drift with age, etc? I'm thinking in any case, a DAC approach might be best.
Maximus, am I right in thinking your remote circuit still requires matched LDRs, ie the DS1802 does not have the resolution to balance the LDRs?
I'm a complete novice, but always wanted to do a microcontroller project, maybe now's a chance, but I don't want to re-invent the wheel.
I think I saw a post that had some links to various projects, but I can't find it again now - I really wish these forum threads had updateable header pages for this kind of stuff.
Hi Jackpipe, no drift with age, I still have my oringinal prototype MkII running in my system, and it's still perfectly in balance, even after being on now 24/7 for over 5 years.jackpipe said:
Also temperature drift is a non issue if you pot them together in hard wax like I do in the production Lightspeed Attenuator.
Cheers George
Ooh, what I need is a temperature calibrated digipot...
http://www2.electronicproducts.com/...eter_features-article-maxim-may2005-HTML.aspx
"Parts are available that include an internal EEPROM that stores thermal calibration lookup data in temperature increments. A temperature sensor within these devices measures the ambient temperature. The digipot then adjusts the variable resistor using the modifier in the lookup table that corresponds to the measured temperature. Thermal-lookup-table-based digipots typically either correct for a nonlinear temperature response of a circuit element, such as a laser or a photodiode, or intentionally create a precise, nonlinear resistive temperature response that is specific to an application."
I wonder if you can hook up an external "temperature" sensor.
http://www2.electronicproducts.com/...eter_features-article-maxim-may2005-HTML.aspx
"Parts are available that include an internal EEPROM that stores thermal calibration lookup data in temperature increments. A temperature sensor within these devices measures the ambient temperature. The digipot then adjusts the variable resistor using the modifier in the lookup table that corresponds to the measured temperature. Thermal-lookup-table-based digipots typically either correct for a nonlinear temperature response of a circuit element, such as a laser or a photodiode, or intentionally create a precise, nonlinear resistive temperature response that is specific to an application."
I wonder if you can hook up an external "temperature" sensor.