Im looking to design an attenuator to serve as a link between my computer and
active studio monitors, with the -6Db setting I have about 6 Db`s of headroom left. So im guessing with the lengths of wire im using there won`t be any problem with the capacitance. So im going passive attenuator.
pricewise the LDR seems reasonable and the things i have heard about it seem excelent. But what id like to do is to compare it to a pre made Mini-V trimmer.
(on a t bridge).
Wich one would yield the best sound quality?
active studio monitors, with the -6Db setting I have about 6 Db`s of headroom left. So im guessing with the lengths of wire im using there won`t be any problem with the capacitance. So im going passive attenuator.
pricewise the LDR seems reasonable and the things i have heard about it seem excelent. But what id like to do is to compare it to a pre made Mini-V trimmer.
(on a t bridge).
Wich one would yield the best sound quality?
Hi,
you could measure the frequency response of your attenuator and cable and power amp combination.
Or you could assume a range of output impedances for the attenuator and using data for the cable and the Power amplifier model the frequency response of the combination.
Or, you could place the pot inside the power amp to remove the cable affect and just have to model the attenuator output impedance combined with the Power amplifier.
Source impedances exceeding 1k and cables are not a good combination for flat frequency response.
you could measure the frequency response of your attenuator and cable and power amp combination.
Or you could assume a range of output impedances for the attenuator and using data for the cable and the Power amplifier model the frequency response of the combination.
Or, you could place the pot inside the power amp to remove the cable affect and just have to model the attenuator output impedance combined with the Power amplifier.
Source impedances exceeding 1k and cables are not a good combination for flat frequency response.
I'm not sure what you were implying, but the resistive (photocell) part of the LDR is basically a pure resistance. The DC current through the semiconductor part, the LED, is held more-or-less constant unless the user is changing the attenuation level. So although the attenuation versus the DC control-current response is very much not linear, the pure-resistance photocell parts that the music goes through are about as linear as anything can get, with electronics.
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I must be missing something here as i thought at line levels these things distorted like crazy. Ok, 0.1% may not be exactly crazy if you're listening through a SET amp and the positives may well outweigh the thd but it is still hard to justify such an amount of distortion.
You wanted general statements about LDR volume controls.
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Most people who use them report very good sound quality.
They are deemed to sound better when used without buffering.
Without buffering there are issues arising from the interaction with the input impedance of the following component.
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The last statement is where most of the problems arise.If these devices could drive any impedance with no change in sound quality,they would be universally praised and far more widely adopted.
They may be adopted into a circuit as an attenuator,and good results have been reported in both transistor and tube designs.So can we say that should the input impedance of one's components not pose a problem for an LDR based attenuator,by all reports it should be a success.Otherwise use a buffer.Otherwise ditch the LDR.
I got curious about these devices,bought a Lightspeed,used it for 8 months and went back to an active preamp.The Lightspeed improved on all of the active preamps that I had(at hand,nothing high-end)however it wasn't optimum in my system due to the impedance interaction situation.I'm using an active preamp currently.
To the LDR fans out there
on't lynch me.I haven't criticised their sound(for good reason,they are very good).They are not however for everyone,if used without a buffer.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Most people who use them report very good sound quality.
They are deemed to sound better when used without buffering.
Without buffering there are issues arising from the interaction with the input impedance of the following component.
-------------------------------------------------------------------------------------------------------------------------------------------------------------
The last statement is where most of the problems arise.If these devices could drive any impedance with no change in sound quality,they would be universally praised and far more widely adopted.
They may be adopted into a circuit as an attenuator,and good results have been reported in both transistor and tube designs.So can we say that should the input impedance of one's components not pose a problem for an LDR based attenuator,by all reports it should be a success.Otherwise use a buffer.Otherwise ditch the LDR.
I got curious about these devices,bought a Lightspeed,used it for 8 months and went back to an active preamp.The Lightspeed improved on all of the active preamps that I had(at hand,nothing high-end)however it wasn't optimum in my system due to the impedance interaction situation.I'm using an active preamp currently.
To the LDR fans out there
on't lynch me.I haven't criticised their sound(for good reason,they are very good).They are not however for everyone,if used without a buffer.The cadmium sulphide that makes up the resistive track in an LDR is a semiconductor and therefore subject to non-linear voltage dependent behavior. There are 2 ways to determine if that is going to be a problem for your particular application.
A/ Do your homework or B/ do the necessary experiments perhaps with a distortion meter or other careful measurements. Of course you can build something anyway and if it sounds ok then ok who's asking.
A/ Do your homework or B/ do the necessary experiments perhaps with a distortion meter or other careful measurements. Of course you can build something anyway and if it sounds ok then ok who's asking.
What's better no contacts in the signal path with a Cadmium Sulphide cell that at cd levels 2v produce no more than .1% 2HD, even less at cd playing levels.
Or the "diode" effect from the feather weight contact between wiper and track (two dissimilar materials, metal and carbon or conductive plastic) that all potentiometers give, even single leaf switch pots.
No two different manufactured pots sound the same they are all flawed, that's why they all sound different, except for double sided dual leaf switched pots they seemed to be getting there.
Cheers George
Or the "diode" effect from the feather weight contact between wiper and track (two dissimilar materials, metal and carbon or conductive plastic) that all potentiometers give, even single leaf switch pots.
No two different manufactured pots sound the same they are all flawed, that's why they all sound different, except for double sided dual leaf switched pots they seemed to be getting there.
Cheers George
I am interested in a balanced bridge solution, perhaps with a wheat grain incandescent bulb in one leg of the bridge and resistors in the other 3 legs. I would say you could feed current into the bridge using a constant current source. That would heat up the bulb filament and make the bridge unbalanced. Some arrangement like that could be nice. I would imagine the distortion levels would be very low but there could be some slight concern about thermal noise from the hot filament. Now look what you have done, I have to go and search for the Christmas tree lights.
Tracking problems with "wheat grain incandescent bulb" as they emmit heat, this is the LRD's worst enemy for calibration between channels, the Mk1 Lightspeeds I did back in the 70's used this setup and they were a nightmare to keep the channels tracking. Led's are the only way.
Cheers George
Cheers George
a comparision.......
Hi all,
I built a LDR series shunt,a 1% resistive ladder switch ,and a used a vishay 1% resistor,Now I replaced my volume controls with each one and played the same song same levels and listened,no test equipment other than my ears,lol 2 big floppie ones,
Results,I could tell a difference between the resistor and the ladder ,maybe contacts? in the ladder,sonics were different a little closed in,ok.
The ldr's I have one (set) series ,shunt per side,I like 2 volume controls one for each channel, I do hear better highs,midrange is more open and I did notice a bass increase,IF thier is distortion in this setup It's ok! It sounds good to me,I can't silence the volume but it's low enought to be a background when I'm doing other things.
I have a display with db's into active 3way system into gain clone amps,no special caps or resistors,or power supplies,maybe These change later ,but for now I listen for a while !
My audiences like the system so I am not trying to upset anyone's opinion this is only mine and my 2 cents,but I like the LDR improvement for now.
I have listen to some very expensive equipment, I live in a large city,
lots of high end stereo stores here,I'll stick with building from this GREAT site,
I come out alot better and cheaper!
Hi all,
I built a LDR series shunt,a 1% resistive ladder switch ,and a used a vishay 1% resistor,Now I replaced my volume controls with each one and played the same song same levels and listened,no test equipment other than my ears,lol 2 big floppie ones,
Results,I could tell a difference between the resistor and the ladder ,maybe contacts? in the ladder,sonics were different a little closed in,ok.
The ldr's I have one (set) series ,shunt per side,I like 2 volume controls one for each channel, I do hear better highs,midrange is more open and I did notice a bass increase,IF thier is distortion in this setup It's ok! It sounds good to me,I can't silence the volume but it's low enought to be a background when I'm doing other things.
I have a display with db's into active 3way system into gain clone amps,no special caps or resistors,or power supplies,maybe These change later ,but for now I listen for a while !
My audiences like the system so I am not trying to upset anyone's opinion this is only mine and my 2 cents,but I like the LDR improvement for now.
I have listen to some very expensive equipment, I live in a large city,
lots of high end stereo stores here,I'll stick with building from this GREAT site,
I come out alot better and cheaper!
one can use a stepped attenuator to send control currents to the LDRs. This can be trimmed at every step to ensure balance throughout the whole range of steps.
The stepped attenuator also allows experimentation with a very wide range of control currents, thus achieving small steps in volume adjustment wherever in the volume range you need small steps and can achieve accurate balance at very high attenuation levels.
The stepped attenuator also allows experimentation with a very wide range of control currents, thus achieving small steps in volume adjustment wherever in the volume range you need small steps and can achieve accurate balance at very high attenuation levels.
A voice of sanity in the midst of confusion.
Did everyone get that this applies to LDRs just in much the same way as any other resistive pot ?
Just the shape of the curve will be different.
I decided to take a shot at making a ldr,so far so good ,I made some with just a drop of SG and the led to the photocell,it works better to flatten the tip of the led ,the whole assembly fits better,I checked the 2 I had made up and they were exactly the same, I made the circuit to test and only changed the ldr when testing,I made 4 more I will test and try them out tomorrow,BTW I cover the LDR when testing,when I finish them I will cover them with Black heat shrink and blk tape if the shrink bleeds light.
I found these parts on ebay 50 photocell $7.00 and 100 White LED's /resistors were $4.00. I did find some after I bought these that have a flat top,lol,my luck!
so if they hit 20 cents it's a keeper,
I like the test circuit I think Nelson put that up for us,THANKS ! I used push on monetary switches ,as all the rotary I had on hand where 1 to 6 ers,lol.
I am thinking about a touch up down control for these anyone made one yet?
Regards,
NS
I found these parts on ebay 50 photocell $7.00 and 100 White LED's /resistors were $4.00. I did find some after I bought these that have a flat top,lol,my luck!
so if they hit 20 cents it's a keeper,
I like the test circuit I think Nelson put that up for us,THANKS ! I used push on monetary switches ,as all the rotary I had on hand where 1 to 6 ers,lol.
I am thinking about a touch up down control for these anyone made one yet?
Regards,
NS
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