purchase of lightspeed
Hi George,
Since I am new at the DiY Audio, i am not permitted to send direct mail, nor was I able to find any URL that leads to your products.
Therefore, kindly let me know how i can get in contact with you and purchase the ready made product.
Best regards
Patrik a.k.a Gizmologic
gizmologic@gmail.com
Hi George,
Since I am new at the DiY Audio, i am not permitted to send direct mail, nor was I able to find any URL that leads to your products.
Therefore, kindly let me know how i can get in contact with you and purchase the ready made product.
Best regards
Patrik a.k.a Gizmologic
gizmologic@gmail.com
Greyskale said:
That was what my first Mk1 Lightspeed Attenuator was. But it was quickly learnt that series/shunt (2 LDR's) sounded superior to (one LDR), it also gave a much more constant input impedance and output impedance.
So all the Mk1's that I manufactured and sold, got recalled and modified up to Mk2 status (2 LDR's), with every owner saying it was far better when they got it back.
Cheers George
Well, I'm taking the plunge on your design... I've designed a PCB and had it set off to be fabricated and all parts have been ordered. I added a small filter cap just before each NSL-32SR2S in such a way to keep them optional (testing time 
) but I figure it might add a little extra stability. I'll post some pics and impressions when it's all put together and tested.
) but I figure it might add a little extra stability. I'll post some pics and impressions when it's all put together and tested.I would love to use a n optocoupler volume control to control MIDI instruments. Yet, since both hands are busy playing the keyboard I need to find another way to vary the volume levels for vibrato and overall dynamics (like used by flute/ accordion players etc).
A foot pedal isn't good enough, because with the foot I can't vary vibrato intensity accurately as needed. Any suggestions on how to solve this problem??
A foot pedal isn't good enough, because with the foot I can't vary vibrato intensity accurately as needed. Any suggestions on how to solve this problem??
jjj333, it sound as though you want an accurate instant control over the volume continuously, the Lightspeed may not be suitable for you, as it has a slight delay from when the volume is turned up or down, kind of like steering a barge or very large boat, it responds after the fact.
This is not a problem when using it as a volume control for audio, because when you turn the control it has found it's level before you have sat back down to listen. But to use it up and down constantly, I could see some delay factors being a problem for you.
This is a time vs level setting distortion which many have totally misconstrued as sound distortion, (lost souls) and in no way affects listening to audio but with your way of wanting to use it constantly, you will have a problem.
Cheers George
This is not a problem when using it as a volume control for audio, because when you turn the control it has found it's level before you have sat back down to listen. But to use it up and down constantly, I could see some delay factors being a problem for you.
This is a time vs level setting distortion which many have totally misconstrued as sound distortion, (lost souls) and in no way affects listening to audio but with your way of wanting to use it constantly, you will have a problem.
Cheers George
Obviously the suggested method of sorting LDRs for matching curves at constant voltage works to everyone's satisfaction. But in the spirit of great mousetrap designers everywhere, I would like to ask this dumb question:
Why not drive the LEDs with current instead of voltage, as suggested by Silonex? There are LED driver chips available which will drive LEDs to variable current with precision. Like these app note from Maxim.
Any thoughts?
Thanks
Rich
Why not drive the LEDs with current instead of voltage, as suggested by Silonex? There are LED driver chips available which will drive LEDs to variable current with precision. Like these app note from Maxim.
Any thoughts?
Thanks
Rich
That is exactly what I was thinking for some time! Couldn’t get rid of that idea in my head so I made a test setup to be able to compare between the original Lightspeed and a constant current source (CCS) version, as a volume control for my pre-amp. I connected the LED’s of the NSL-32SR2S by a connector to be able to switch between the two versions in a few seconds.
To make a long story short……the current source version is sounding MUCH better!! I am not talking about small differences here!
There is one problem to cope with. In my design the constant current also flows through the potentiometer (100k) which sets the current through the LED’s. That gave some severe crackling at the highest volume settings. Potentiometers don’t like DC voltage and with constant current things even get worse. So I used my DACT stepped attenuator, which was already in my pre-amp, to control the current sources. With the DACT everything is dead silent.
There is one other topic here in this thread that pops up from time to time, and that is the question what is best sounding: series LDR / parallel LDR or series resistor / parallel LDR. I did some additional listening tests to cover this topic as well. In my tube pre-amp I have some gain to waste, so the series resistor is no problem. I tested with the famous Shinkoh 47k tatalum resistors. The series LDR / parallel LDR combination sounds so spatial (also due to the CCS) that in my system it is to much sometimes. I also missed some of the focus and directness that the resistor / LDR version has. And voices and instruments have a more natural timbre with the resistor version. So I prefer the series resistor / parallel LDR version in my setup. That is to say, in my system and with my ears. Someone else could judge different because both sound very good.
The overall sonic difference between the DACT volume control (in a shunt configuration in my case) I used before and CCS LDR volume control is phenomenal.
Thanks for the tipp Andrea.
I wonder whether you have any practical experience of using that iver 3 decades of current range.
I mean if you take a JFET, for example, it would be find from 2mA to 20mA, but below 2mA it runs into noise problems, and one would have to use another device type for lower current, etc.
I have yet to find an active device / circuit that would operate equally well over 3 decades.
Patrick
I wonder whether you have any practical experience of using that iver 3 decades of current range.
I mean if you take a JFET, for example, it would be find from 2mA to 20mA, but below 2mA it runs into noise problems, and one would have to use another device type for lower current, etc.
I have yet to find an active device / circuit that would operate equally well over 3 decades.
Patrick
Currrent Drive
Hi Patrick,
My approach to current drive is using AD420 16 bit DACs. Ignoring inaccuracies for the moment you have a potential resolution of just over 3uA when using the 0 to 20mA range.
It is taking longer than I would like (!) due to other pressures and the desire to make a multi-channel PC based version from the outset.
Good luck
www.analog.com/UploadedFiles/Data_Sheets/AD420.pdf
Hi Patrick,
My approach to current drive is using AD420 16 bit DACs. Ignoring inaccuracies for the moment you have a potential resolution of just over 3uA when using the 0 to 20mA range.
It is taking longer than I would like (!) due to other pressures and the desire to make a multi-channel PC based version from the outset.
Good luck
www.analog.com/UploadedFiles/Data_Sheets/AD420.pdf
The datasheet did not show any information on output current noise.
While I can understand your motivation of using a DAC if you were to go multi-channel and digital remote, etc., I have my doubts as to whether this is a better alternative than a variable resistor (in whatever form) driven by constant voltage, in pure performance terms.
So I hope pietjers would still be kind enough to share some more details of his implementation.
Regards,
Patrick
While I can understand your motivation of using a DAC if you were to go multi-channel and digital remote, etc., I have my doubts as to whether this is a better alternative than a variable resistor (in whatever form) driven by constant voltage, in pure performance terms.
So I hope pietjers would still be kind enough to share some more details of his implementation.
Regards,
Patrick
Hey guys, now that this thread has kicked again, how about putting in your vote for a Passive Pre-amp forum?
Vote here http://www.diyaudio.com/request/
Cheers George
Vote here http://www.diyaudio.com/request/
Cheers George
Icss for Lightspeed
If you are going to use remote controls with dac chips, ROMS, etc, voltage control via "normal" series/shunt stepped attenuators and CCS or perhaps fet gain stage systems, and maybe Maxim ICs to dial in the individual currents to save matching the LDRs, then why not add some i/p and o/p buffers to reduce the effects of impedance loading with a power supply from the "Blowtorch" to finish it off!
Sorry George, couldn't resist!
If you are going to use remote controls with dac chips, ROMS, etc, voltage control via "normal" series/shunt stepped attenuators and CCS or perhaps fet gain stage systems, and maybe Maxim ICs to dial in the individual currents to save matching the LDRs, then why not add some i/p and o/p buffers to reduce the effects of impedance loading with a power supply from the "Blowtorch" to finish it off!
Sorry George, couldn't resist!
Re: Icss for Lightspeed
Hope that was said tongue in cheek, that's all we need more active crap in the signal path, hey this is the 1000th post got to be an Omen. for what I don't know, maybe now we can have a Passive Pre-amp forum?
Vote here http://www.diyaudio.com/request/
Cheers George
jameshillj said:
Hope that was said tongue in cheek, that's all we need more active crap in the signal path, hey this is the 1000th post got to be an Omen. for what I don't know, maybe now we can have a Passive Pre-amp forum?
Vote here http://www.diyaudio.com/request/
Cheers George
This is how I did it!!
The current source is built round a voltage reference. In this case a TLV431, which has an internal reference voltage of 1.24V. But it is also possible to use other references such as TL431 (2.45V) or LM336-2.5 (2.5V) or others. To get an even more stable reference voltage, I used a LM317 current source to bias the TLV431.
The current range of this current source depends on the reference voltage of the chosen device, the potentiometer value and set resistor R2/R4 value. With the set resistor you can set the maximum value of the current source: I = Vref / R2. In this example 10.3 mA. And by turning the attenuator (I use a DACT stepped attenuator) fully clockwise this value drops to I = 1.24 / 100k = 12.4uA. This gives on de LDR side a range of about 48 Ohm to 20 kOhm. But you can of course choose other values for the reference or the attenuator to get the desired range. When you are using a 2 pin reference it is also possible to influence the range by using a darlington transistor instead of a normal transistor, because the Vbe is subtracted from the reference voltage.
The optional 2 Meg potentiometers are for calibration purposes. With these pots you can shunt a small amount of current to get perfectly matched channels.
The sound of this CCS volume control is really great and outperforms the original design with ease (see also my previous post).
Cheers,
Peter
The current source is built round a voltage reference. In this case a TLV431, which has an internal reference voltage of 1.24V. But it is also possible to use other references such as TL431 (2.45V) or LM336-2.5 (2.5V) or others. To get an even more stable reference voltage, I used a LM317 current source to bias the TLV431.
The current range of this current source depends on the reference voltage of the chosen device, the potentiometer value and set resistor R2/R4 value. With the set resistor you can set the maximum value of the current source: I = Vref / R2. In this example 10.3 mA. And by turning the attenuator (I use a DACT stepped attenuator) fully clockwise this value drops to I = 1.24 / 100k = 12.4uA. This gives on de LDR side a range of about 48 Ohm to 20 kOhm. But you can of course choose other values for the reference or the attenuator to get the desired range. When you are using a 2 pin reference it is also possible to influence the range by using a darlington transistor instead of a normal transistor, because the Vbe is subtracted from the reference voltage.
The optional 2 Meg potentiometers are for calibration purposes. With these pots you can shunt a small amount of current to get perfectly matched channels.
The sound of this CCS volume control is really great and outperforms the original design with ease (see also my previous post).
Cheers,
Peter
