Hi BFNY
Thanks, but your breadboard misses out on using current steer NPN transistors BC547 recommended, rather appears to have substituted resistors, and has not current limited the supply with LM317 1.25/60R as required, and provided on the test schematic.
But Thanks, that is good of you for trying. 🙂
Cheers / Chris
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I will say something for Chris Daly: he is persistent and is not put off by minor setbacks like inconvenient facts of circuit theory.
I have another theory: it is a Gnirut test - a real person is trying to convince us he is a bot by giving barmy answers. Or it could be a Lakos hoax.
I have another theory: it is a Gnirut test - a real person is trying to convince us he is a bot by giving barmy answers. Or it could be a Lakos hoax.
There are worse cases to pursue for audio delights that cost a lot and do nothing.
From what I can see from testing, the circuit works. It will control volume via LED LDRs. It is not efficient, or optimized, or most certainly not elegant. It may not be the best way. But it appears to actually fulfill the stated function.
It does not eliminate the need for matching.
How does it sound?
Probably like any other LED/LDR series / shunt control. Are people overpaying? Well, that's up to them. There's at least 2 or 3 other solutions out there for $500ish, are people that buy those also overpaying?
The transistor/diodes could be eliminated by using the proper type of op-amp in a single supply mode. Way more than half the parts could be eliminated. But why go there...
The fact the person behind it has no idea why it works is not in question. Certainly there is a language translation barrier, and deep lack of electronics at play.
Sort of a .01% inspiration, 99.99% perspiration approach.
What *is wrong* is misrepresenting how it works, over and over again. If someone said, "I have no idea how it works, I just played around with parts until it did. Can someone tell me why this works?" there would be a lot less friction here.
From what I can see from testing, the circuit works. It will control volume via LED LDRs. It is not efficient, or optimized, or most certainly not elegant. It may not be the best way. But it appears to actually fulfill the stated function.
It does not eliminate the need for matching.
How does it sound?
Probably like any other LED/LDR series / shunt control. Are people overpaying? Well, that's up to them. There's at least 2 or 3 other solutions out there for $500ish, are people that buy those also overpaying?
The transistor/diodes could be eliminated by using the proper type of op-amp in a single supply mode. Way more than half the parts could be eliminated. But why go there...
The fact the person behind it has no idea why it works is not in question. Certainly there is a language translation barrier, and deep lack of electronics at play.
Sort of a .01% inspiration, 99.99% perspiration approach.
What *is wrong* is misrepresenting how it works, over and over again. If someone said, "I have no idea how it works, I just played around with parts until it did. Can someone tell me why this works?" there would be a lot less friction here.
if only.
This has become the problem. But at least some can say "it's not my problem".
I have deleted a few recent posts which could be potentially have legal implications. Please stay away from this line of discussion.Hi guys,
I have started to follow this topic with great interest and I am now working on building my own LDR volume pot. I have simulated some stuff in spice and I think I have found a circuit that might be of interest.
I have designed the circuit to control the current through the LDR's with only one pot because this would make multi-channel volume control possible. I started out with a long-tailed pair of BC547's (Q1 & Q3) with a constant current source (Q2), the current for this is set to 65mA. I have added Q4 in order to prevent as much DC current as possible from the volume pot-part of the circuit. The LDR's can be matched with R5 and the volume level can be set with R6.
In the simulation it seems to work pretty well and I am now thinking of ordering the parts. Do you guys think this circuit will work in real life as well?
I have started to follow this topic with great interest and I am now working on building my own LDR volume pot. I have simulated some stuff in spice and I think I have found a circuit that might be of interest.
I have designed the circuit to control the current through the LDR's with only one pot because this would make multi-channel volume control possible. I started out with a long-tailed pair of BC547's (Q1 & Q3) with a constant current source (Q2), the current for this is set to 65mA. I have added Q4 in order to prevent as much DC current as possible from the volume pot-part of the circuit. The LDR's can be matched with R5 and the volume level can be set with R6.
In the simulation it seems to work pretty well and I am now thinking of ordering the parts. Do you guys think this circuit will work in real life as well?
An externally hosted image should be here but it was not working when we last tested it.
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It certainly looks more sensible than the OP's circuit, but then I guess you understand electronics.
Don't worry, you'll see it for sale soon. Not by lechuck... (where is the "cynical" emoticon?)
It strikes me that if you're going to do something like this, a VCCS is the way to go, with a differential adjustment for balance.
Don't worry, you'll see it for sale soon. Not by lechuck...
It strikes me that if you're going to do something like this, a VCCS is the way to go, with a differential adjustment for balance.
I would not allow commercial usage of my schematics. People (DIY-ers) are free to try and build it for themselves. If some one would commercialize my work without asking for my permission they would be in for a lot of trouble.
However, since this is a DIY forum I would sincerely appreciate it if we could think outside of the commercial box and simply help each other with sharing our ideas and experiments.
Now on topic 🙂
I am a self learned vacuum tube enthusiastic which means that I sometimes have difficulties with abbreviations that I am not familiar with, so please forgive me in my noob-ness 😀
With a VCCS (Voltage Constant Current Control if I googled it correctly), do you mean an addition of a voltage regulator? If this is so then I can only agree, spice showed me that the stability of the voltages (+5v and -5v) are important to the operation of the circuit. I am thinking of building a PSU with a voltage doubler and a 7805/7905 combo to get the proper voltages.
I am planning to throw some parts on a breadboard tonight to see how the circuit operates in real life. I still need to order the LDR's, but for now I will build it with 2 LED's to see if the switching is working how it is supposed to do.
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Hi Andrew,
The current is divided over the LED's. The amount of current flow trough the LED's is dependent on the setting of R6. If R6 is in it's middle position the current flow through the LED's would be Iccs/2. If R6 is at an end point one LED will get almost the full 65mA, and the other LED will receive 1.565uA (according to spice). In other words, one would be conducting fully and the other one would be switched completely off in that situation.
@ lechuck:
I think a fundamental problem with your circuit is that the sum of the LED currents is constant. When the volume pot is 1/2 way, they will each have 1/2 of the maximum current, resulting in both photocells having very low resistance.
A better approach may be to control the 2 currents separately, making use of the exponential nature of transistor's collector current vs base-emitter voltage. Then, for example, if it's set up for 0.1mA per LED when centered, then increasing Vbe on on side by 60mV and decreasing it on the other side by 60mV will result in currents of about 0.01mA and 1mA.
It should be possible to track quite accurately if a well matched transistor array is used (and opamps with low input offset voltage for the control circuitry).
I think a fundamental problem with your circuit is that the sum of the LED currents is constant. When the volume pot is 1/2 way, they will each have 1/2 of the maximum current, resulting in both photocells having very low resistance.
A better approach may be to control the 2 currents separately, making use of the exponential nature of transistor's collector current vs base-emitter voltage. Then, for example, if it's set up for 0.1mA per LED when centered, then increasing Vbe on on side by 60mV and decreasing it on the other side by 60mV will result in currents of about 0.01mA and 1mA.
It should be possible to track quite accurately if a well matched transistor array is used (and opamps with low input offset voltage for the control circuitry).
Thinking top down, there are a few points to consider:
1. Constant total current through all channels.
2. Constant distribution of current to each channel.
3. Gain control shaping.
4. Temperature variation effects.
5. Interfacing impedance.
Some people like a balance control, I think that the need should be eliminated through adequate design.
1. Constant total current through all channels.
2. Constant distribution of current to each channel.
3. Gain control shaping.
4. Temperature variation effects.
5. Interfacing impedance.
Some people like a balance control, I think that the need should be eliminated through adequate design.
Good luck with that!
VCCS = Voltage-Controlled Current Source
Go to national.com and look in application notes AN-20, AN-31, and AN-1515 .
Hi Godfrey,
Thank you for your reply. I will experiment with this circuit first. Dividing the current has been the first stage that I started the design with, making it the fundament of the design. If you are correct, which I am about to find out in a few days, then I guess a complete new circuit would be needed.
Not really. Unless you have a patent, once you post it here (or anywhere else), anyone can use it. And unfortunately, there are people who like to use members to get free design work since they are incapable of it themselves. That's one reason I don't do design on threads where commercial guys ask for help.
Publishing an idea here ought to, in theory, prevent someone else from patenting it. Stopping someone else exploiting it would be down to the author making a claim in a civil court against the copier. That could get expensive. Even large manufacturers have difficulty policing their designs against Chinese copies.
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