It's a voltage divider. So, as you turn the pot, the voltage to one set of LDRs (say, the Series pair) increases at the same time the voltage to the other set of LDRs (Shunt pair) decreases.
try matching the "lean" by leaning in the opposite direction.
Seriously,
read the adjustment procedure for your purchased version. In it, it should tell you how to balance the image at the most used volume setting.
If it doesn't say how, then you bought from someone who does not give adequate support to their customers.
BTW,
there could be gain errors in the source or in the pre-amp or in the amplifiers or in the sensitivity of the speakers.
Maybe you should actually check the overall gain & sensitivity of the supply chain rather than assume it is correctable in the volume control.
Wushuliu
Dont know if you bought from me or not. If its from me then you can use either the 200R pot or the 5k pot to adjust balance. If its the Oliver board then ... man I gotta go back and look.. I forget if the trimmers are on series or shunt supply.. okay its on series. On the channel that is loud you want to let less current in, on the channel thats not loud enough you want more current so you trim accordingly. I guess that doesnt help because it depends which direction you turn the pots so just listen as you turn and the image will adjust to center.
Dont know if you bought from me or not. If its from me then you can use either the 200R pot or the 5k pot to adjust balance. If its the Oliver board then ... man I gotta go back and look.. I forget if the trimmers are on series or shunt supply.. okay its on series. On the channel that is loud you want to let less current in, on the channel thats not loud enough you want more current so you trim accordingly. I guess that doesnt help because it depends which direction you turn the pots so just listen as you turn and the image will adjust to center.
Has anybody tried paralleling LDRs in an attenuator? I am constructing a 100K shunt volume control for a tube preamp. The volume control will have a fixed series resistor with an LDR shunt. I'm a little concerned that an LDR failure will cause a bump in volume to zero attenuation that could damage a speaker. Two LDRs in parallel would moderate the bump and might even sound good, as has been sometimes observed when paralleling conventional resistors.
David
It will also give you lower min volume as min NSL32SR2 resistance should be set at 40R.
To address your concern over LDR failure you would also wire their power parallel, not series.
Any particular reason you like using such high resistance pots to control tubes? I know a lot of people do it but that doesnt make it right
I have used much lower values on tube pre's and if you are designing your own you might consider as low as possible which will allow for lower noise and less filtering of the high frequencies.
On your pre you may want to put a fixed resistor from signal to ground, which would set the input impedance and also perform part of the function you were concerned about losing if an LDR went south.
You wont get very reliable operation from ~22k-100k with the LDRs either. Best to design for max resistance on the LDR of 22k. Past 22k and on average the matched LDRs will begin to take their own path which will not match the other. This is not a hard/fast rule but I see it to be true on more LDRs than not.
Build your circuit so that the LDRs turn off AFTER the PreAmp or you will have dramatic increase in volume very very quickly. Perhaps putting a bleeder resistor on the PreAmps power supply caps and extra capacitance with no bleeder on the LDRs power supply will help you.
Uriah
It will also give you lower min volume as min NSL32SR2 resistance should be set at 40R.
To address your concern over LDR failure you would also wire their power parallel, not series.
Any particular reason you like using such high resistance pots to control tubes? I know a lot of people do it but that doesnt make it right
I have used much lower values on tube pre's and if you are designing your own you might consider as low as possible which will allow for lower noise and less filtering of the high frequencies. On your pre you may want to put a fixed resistor from signal to ground, which would set the input impedance and also perform part of the function you were concerned about losing if an LDR went south.
You wont get very reliable operation from ~22k-100k with the LDRs either. Best to design for max resistance on the LDR of 22k. Past 22k and on average the matched LDRs will begin to take their own path which will not match the other. This is not a hard/fast rule but I see it to be true on more LDRs than not.
Build your circuit so that the LDRs turn off AFTER the PreAmp or you will have dramatic increase in volume very very quickly. Perhaps putting a bleeder resistor on the PreAmps power supply caps and extra capacitance with no bleeder on the LDRs power supply will help you.
Uriah
Thinking about it some more and if you parallel you will have to take the LDRs up to 200k each to get your 100k and that will be so crazy as far as trying to get anything similar at all in their resistance curves. Seriously, these LDRs that match at 22k might be as crazy as 200k and 500k with same min current through them.
Anyway, paralleling is still great idea for low volume and I have had it working in my house for quite some time. I removed it recently just to use different circuit and have turned up resistance on my series LDR to compensate for the 40R min of shunts. I am probably running 10k-12k as max which gives me respectable low volume. I would prefer 6k but then I am back to paralleling and it looks like I would rather peruse DIYaudio than parallel another LDR
Anyway, paralleling is still great idea for low volume and I have had it working in my house for quite some time. I removed it recently just to use different circuit and have turned up resistance on my series LDR to compensate for the 40R min of shunts. I am probably running 10k-12k as max which gives me respectable low volume. I would prefer 6k but then I am back to paralleling and it looks like I would rather peruse DIYaudio than parallel another LDR
Uriah, This preamp has an integral phono section with an output impedance of around 2K. Thus I probably need at least a 50K volume control. I'll use TX2575 for fixed series resistors, and control the shunt LDR for each channel with a separate pot-- or possibly one dual pot for master volume, with separate low-value trim pots on the front panel to trim any imbalances. With this approach tracking should not be a problem.
Also, this is a balanced circuit, so for each channel there will be a TX2575 series resistor on each signal phase(each with R= 1/2 the nominal value of the attenuator). The variable LDR shunt will connect between the +/- signal phases.
I will leave the LDRs constantly powered up to minimize temperature drift.
Perhaps when left powered up constantly at low resistance as needed for high attenuation , two LDRs in parallel in the shunt position might last longer than one.
Dave
Also, this is a balanced circuit, so for each channel there will be a TX2575 series resistor on each signal phase(each with R= 1/2 the nominal value of the attenuator). The variable LDR shunt will connect between the +/- signal phases.
I will leave the LDRs constantly powered up to minimize temperature drift.
Perhaps when left powered up constantly at low resistance as needed for high attenuation , two LDRs in parallel in the shunt position might last longer than one.
Dave
Last edited:
David
Different than I had imagined. However I believe you will have issues with matching LDRs at the resistances you are talking about. Nice series resistors!
Can you put the LDRs on the input of the preamp? I have not acquainted myself with phono designs at all so I am unsure what you would have available to drive the LDRs on that side.
Uriah
Different than I had imagined. However I believe you will have issues with matching LDRs at the resistances you are talking about. Nice series resistors!
Can you put the LDRs on the input of the preamp? I have not acquainted myself with phono designs at all so I am unsure what you would have available to drive the LDRs on that side.
Uriah
Lightspeed combined with Pass B1 buffer
I wonder if there could be dc or other kinds of issues if using Lightspeed powerswitch as a mute function
apart from being a mute function, it would solve at least two other problems,
having LDR's on for too long set on low SPL, where its known to put more wear on the LDR's
and the mute function switch is not part of the signal chain
any issues doing so ?
I wonder if there could be dc or other kinds of issues if using Lightspeed powerswitch as a mute function
apart from being a mute function, it would solve at least two other problems,
having LDR's on for too long set on low SPL, where its known to put more wear on the LDR's
and the mute function switch is not part of the signal chain
any issues doing so ?
Uriah, I am currently running LDRs 35R-150K as variable load resistors at phono input. It requires a 1meg pot on 5Vdc PS to obtain this wide a range-- with a 25K pot in series for accurate adjustments in the 35R-1K range. That application doesn't require close L/R tracking, as an RCA or XLR patch cable between the input jack to an ohmmeter can be employed to set resistance.
A 50K volume control with a fixed series resistor and a variable shunt resistor that attenuates -10db to -63db, requires LDR shunt resistance up to around 25K. This is inside the range of reasonably close tracking for matched LDRs.
A 50K volume control with a fixed series resistor and a variable shunt resistor that attenuates -10db to -63db, requires LDR shunt resistance up to around 25K. This is inside the range of reasonably close tracking for matched LDRs.
Last edited:
Tinitus
Problem is only that the shunt LDRs will gain resistance very quickly and volume will go loud BEFORE mute. So give extra capacitance on Shunts power after the 100k pot but problem might be that 100k pot might burn if caps draw a large amount of power quickly so I would choose carefully the size of the caps for shunt LDRs. It will only allow a very small amount of time but the series LDRs will be hitting megohms before shunt gets close to catching up if you have a bit of capacitance feeding shunts. I dont know what value is best or what value would burn the pot, but its something to consider.
David
If you need only 25k then this is perfect and good application for LDRs. If paralleling two LDRs to get 25k then you will obviously have 50k on each and like I said will have matching problems. However, since resistance to ground will be averaged out I think this has a real good chance of working and I wonder if several in parallel would ever give better matching than just one since their averages would begin to produce a resistance that is closer to a 'norm' than individual curves. I dont believe this would work well with values up over 100k since they are so odd at those values that the lowest LDR would basically control the resistance but at values like 50k I think it has merit.
Uriah
Problem is only that the shunt LDRs will gain resistance very quickly and volume will go loud BEFORE mute. So give extra capacitance on Shunts power after the 100k pot but problem might be that 100k pot might burn if caps draw a large amount of power quickly so I would choose carefully the size of the caps for shunt LDRs. It will only allow a very small amount of time but the series LDRs will be hitting megohms before shunt gets close to catching up if you have a bit of capacitance feeding shunts. I dont know what value is best or what value would burn the pot, but its something to consider.
David
If you need only 25k then this is perfect and good application for LDRs. If paralleling two LDRs to get 25k then you will obviously have 50k on each and like I said will have matching problems. However, since resistance to ground will be averaged out I think this has a real good chance of working and I wonder if several in parallel would ever give better matching than just one since their averages would begin to produce a resistance that is closer to a 'norm' than individual curves. I dont believe this would work well with values up over 100k since they are so odd at those values that the lowest LDR would basically control the resistance but at values like 50k I think it has merit.
Uriah