Peter, any idea how they'd implement a ladder scheme using an LDR as the switching device? I read the 6M + Stereophile Dartzeel reviews and descriptions on Dartzeel's website, which read to my eye not inconsistent with their using an LDR as the attenuating device---hence the balance control, which can be implemented with an LDR without any sonic penalty. Mind you, the same can be implemented using a ladder resistor if switching increments are fine enough.
serengetiplains said:
if they are actually using some sort of switched resistors network, I guess they may/should have used "Opto-FET" (Bilateral Analog FET Output Optocoupler) rather tha the LED/LDR. I mean, something like these:
http://www.fairchildsemi.com/pf/H1/H11F1.html
UnixMan said:
My sources tell me that it not a resistor ladder network as it is continuously variable (that is no increment volume db steps) and this is also not stated in the specs. It sounds very much to me like a Lightspeed with an active stage after it.
You could use the term resistance ladder for the series/shunt LDR system in the Lightspeed, but I think it would be better to call it a continuously variable resistance ladder network.
Anyway I've searched the European and USA patents offices and all I came up with was one for Herve Deletraz was his power amp circuit (posted below) no sign of an application for the LDR volume control.
His expalation of how the power amp works:
Apparently the same circuit is for the preamp also.
Abstract not available for CH695431
Abstract of corresponding document: WO03043185
The invention concerns a power amplifier consisting of three stages: a first feedback-free stage amplifying the input signal in current; a second stage amplifying in voltage the signal output from the first stage and comprising two direct current feedback half-circuits symmetrically implanted and operating over the whole frequency spectrum; a third feedback-free stage amplifying the current derived from the second stage and powering a loudspeaker.
Cheers George
Attachments
Lightspeed Attenuator
Hi George,
The amplifier topology shown in the thumbnail (post 704) is a basic current feedback topology with the feedback taken from before the output stage instead of the output node. The input stage would normally be out of the overall loop feedback. This sort of topology has been around for a while now so whether this would be valid grounds for granting a patent would be debatable.
Regarding commercial use of the LDR volume control, a further prior use example is the Audio Synthesis Passion Ultimate preamp, which has been around for over five years. It uses a fixed series resistor and an LDR shunt element with microprocessor control.
Like you, I have been using LDR volume controls for a while now (since 1996) in custom preamplifiers for my customers. They are my preferred choice for volume control, although I ended up with a more complex control system, with voltage controlled current sources to allow easy balancing and remote control operation. Also I use a fixed series resistor and a shunt LDR. You are to be commended for your design, which is very elegant in it’s simplicity.
Regards
Paul
Hi George,
The amplifier topology shown in the thumbnail (post 704) is a basic current feedback topology with the feedback taken from before the output stage instead of the output node. The input stage would normally be out of the overall loop feedback. This sort of topology has been around for a while now so whether this would be valid grounds for granting a patent would be debatable.
Regarding commercial use of the LDR volume control, a further prior use example is the Audio Synthesis Passion Ultimate preamp, which has been around for over five years. It uses a fixed series resistor and an LDR shunt element with microprocessor control.
Like you, I have been using LDR volume controls for a while now (since 1996) in custom preamplifiers for my customers. They are my preferred choice for volume control, although I ended up with a more complex control system, with voltage controlled current sources to allow easy balancing and remote control operation. Also I use a fixed series resistor and a shunt LDR. You are to be commended for your design, which is very elegant in it’s simplicity.
Regards
Paul
maximus: Thank you for your commendation Paul, are you sure about the Audiosynthesis Ultimate having shunt LDR's have you physically seen them, as it has 1db per step switched levels X 60 and they only mention Vishay Bulk-Foil resistors as the passive component in the volume control circuit.
Series LDR/Shunt LDR vs Fixed Series resistor/Shunt LDR
I also in the Mk1 model of the Lightspeed used a high quality series resistor with a shunt LDR, but luckily I only had a few sent out before I found that using the LDR's in series and shunt mode sounded so much better in the MkII version, I recalled all the Mk1 and modded them up to MkII status.
Let me say I wish the Mk1 sound was close to the MkII because the matching of the Ldr's was soooo much easier when there was only one per channel to worry about, but the MkII was the only way to go, it was streets ahead but a PITA to build.
Also the MkII input/output impedance stays much more constant at different volume settings than the Mk1, this keeps the subjective sound quality the same at different volume settings.
Mind you the Mk1 Lightspeed, series resistor with shunt LDR still sounded better than any other form of passive or active.
Cheers George
Series LDR/Shunt LDR vs Fixed Series resistor/Shunt LDR
I also in the Mk1 model of the Lightspeed used a high quality series resistor with a shunt LDR, but luckily I only had a few sent out before I found that using the LDR's in series and shunt mode sounded so much better in the MkII version, I recalled all the Mk1 and modded them up to MkII status.
Let me say I wish the Mk1 sound was close to the MkII because the matching of the Ldr's was soooo much easier when there was only one per channel to worry about, but the MkII was the only way to go, it was streets ahead but a PITA to build.
Also the MkII input/output impedance stays much more constant at different volume settings than the Mk1, this keeps the subjective sound quality the same at different volume settings.
Mind you the Mk1 Lightspeed, series resistor with shunt LDR still sounded better than any other form of passive or active.
Cheers George
Good stuff. You have convinced me (long ago) to attempt to make one. If I find anything interesting and new, I'll certainly share. I was going to make one when the Melos came out (it gave the idea popular recognition), but it was put on the back burner..as is usual.
Even more interesting, would be a ........XXXXX strike that. I'll keep it to myself for the moment...
Even more interesting, would be a ........XXXXX strike that. I'll keep it to myself for the moment...
Thought this might be of interest:
Programmable controls for vacuum tube preamplifier
US Patent 5,208,548 Messa Boogie
Digital vol. adjustment circuit for audio amplifier - has photoresistor as vol. adjuster in input circuit of inverting operational amplifier
DE3933657 THOMSON BRANDT GMBH
Hafler Cyberoptic audio level control system
Strickland; James C. Rockford Corporation
Regards
James
Programmable controls for vacuum tube preamplifier
US Patent 5,208,548 Messa Boogie
Digital vol. adjustment circuit for audio amplifier - has photoresistor as vol. adjuster in input circuit of inverting operational amplifier
DE3933657 THOMSON BRANDT GMBH
Hafler Cyberoptic audio level control system
Strickland; James C. Rockford Corporation
Regards
James
Re: Lightspeed Attenuator
Hi Paul,
What series resistor value and the volume pot resistance did you use ? I was having the same thought about doing this because I'm wanting to build a simple and compact 6 channel volume control inside my Behringer DCX2496. My initial calculations showed that I needed only 1K in the series resistance, and with a volume pot of 100Kohm should be sufficient to enable a -40dB attenuation.
thanks.
will
maximus said:
Hi Paul,
What series resistor value and the volume pot resistance did you use ? I was having the same thought about doing this because I'm wanting to build a simple and compact 6 channel volume control inside my Behringer DCX2496. My initial calculations showed that I needed only 1K in the series resistance, and with a volume pot of 100Kohm should be sufficient to enable a -40dB attenuation.
thanks.
will
Hi George,
Good work deserves commendation. I also like your no bull-hype approach. The industry could do with more people like you in it.
I am sure about the Audio Synthesis Ultimate. It was me who originally recommended the LDR for volume control, to David Heaton at Audio Synthesis, after my early trials. Initially he liked the sonic qualities of the LDR but was not happy with their poor matching so he developed a switched current source system (1dB x 60) with microprocessor control. The Bulk Foil is the series element of the volume control.
The series resistor type makes a large difference to the sonic quality in the series resistor/shunt LDR volume control. Which series resistor types did you try in your MkI. I can see that the MkII impedance characteristic could be an advantage over the MkI. I would like to try this for my own personal use, if you have no objections (I would not use this commercially without your permission), however it will have to wait for a few months as my consultancy work is rather busy at the moment. I will have to redesign my control board to accommodate the MkII topology drive requirements.
Regards
Paul
Good work deserves commendation. I also like your no bull-hype approach. The industry could do with more people like you in it.
I am sure about the Audio Synthesis Ultimate. It was me who originally recommended the LDR for volume control, to David Heaton at Audio Synthesis, after my early trials. Initially he liked the sonic qualities of the LDR but was not happy with their poor matching so he developed a switched current source system (1dB x 60) with microprocessor control. The Bulk Foil is the series element of the volume control.
The series resistor type makes a large difference to the sonic quality in the series resistor/shunt LDR volume control. Which series resistor types did you try in your MkI. I can see that the MkII impedance characteristic could be an advantage over the MkI. I would like to try this for my own personal use, if you have no objections (I would not use this commercially without your permission), however it will have to wait for a few months as my consultancy work is rather busy at the moment. I will have to redesign my control board to accommodate the MkII topology drive requirements.
Regards
Paul
maximus said:
Thanks for that visual conformation on the Audio Synthesis, then for sure they are using the Mk1 version, (series resistor and shunt LDR)
The resistors I tried for the MK1 were Beschlag, Vishay, Rodenstien, and a few others, I found the Beschlag to be the cleanest but it was close. However the MKII configuration is clearly discernable, it's that good.
Imagine if Audio Synthesis and Dartzeel used the MkII version then they could charge $5000 and $50,000 for their units. They are only a MkII version away from audio nirvana.
Paul, I have no problem with you using the MkII version as you are a gentleman for asking and you will be quite stunned at the outcome, though you will curse me for the extra labour of matching the LDR's.
I have a small problem with Audio Synthesis for using the system and not disclosing it because they would know that Melos and I have done it, and probally want to be seen as innovators and not copiers of a new system, why else keep it quiet.
And with Dartzeel trying to give the impression that they are innovators of this LDR system as well and giving the impression that they will get a patent for it.
Cheers George
Hi George,
I think you may be judging Audio Synthesis too harshly. I have known David for a long time and I am pretty certain it is a case of independent development, from manufacturers data, rather than copying.
Let me give you a little history from my knowledge of their usage. In the early nineties I developed an acoustic instrument valve preamplifier for use by touring folk musicians. Folk/blues musicians Isaac Guillory and John Renbourn used two of these units on tour, with Isaac giving me further design suggestions to enable me to improve the operational aspects of the preamplifier. The dynamic range and scale of the preamp was quite awesome (it used my high speed, wideband regulators in the power supply), and in some circumstances, with wide dynamic range songs, it could be a little tricky to handle, as his acoustic guitar was also quite dynamic (he had chosen it because it was the most dynamic guitar he had found at that time and this suited his style). I suggested a switchable compressor for the difficult songs and proceeded to develop a FET circuit to achieve this. I wasn’t entirely happy with this circuit and had heard that Vactrols (analog optoisolators by EG&G VACTEC) could be used as the active element for a compressor so I contacted them for information and samples. They sent me a data book with applications information, which defined various methods of use for various functions. One of these functions was series resistor/shunt vactrol volume control, which I decided to try in my hifi system early in 1996. I was very impressed with the resultant sound as it bettered all other methods that I had previously used. I found they were a little tricky to match just as you had found. Initially I used two separate potentiometers to drive them from the valve heater supply, which was fine in operation, but there is market resistance to two separate volume controls in the UK, so I had to consider other ways of dealing with the control aspects. Also, because of slight drift problems, I wanted to develop remote control and balance functions.
I told David how good the sound quality was and he tried them out for himself. I suppose the matching problems bugged him and he worked out his own solution to this. At this time I was not aware of any prior volume control use in commercial hifi products and in fact it’s only since finding your forum thread earlier this year that I have become aware of other users. This shows how much of a hermit I am. I don’t generally pay any attention to what others are doing, but just do my own thing. I’m pretty sure that David wasn’t aware of other users either or he would have said so at the time. Incidentally, David ceased production of his Passion Ultimate model last January.
For general information the Vactrol data/applications book is dated October 1991 and they claim to have been manufacturing these devices for over 20 years previously to this date. I suspect that any attempts to patent LDR volume controls would be aimed more at control methods rather than their actual use as they have been around for a while.
I am nearly out of stock of the resistors that I use. They are Russian non-magnetic carbon film types with silver plated leads that I bought in 1972. Sadly they are no longer available so I will have to do some more trials I suppose.
Regarding your MKII volume control, I shall certainly give it a try as soon as I get some time to sort out the control circuit. The balance function of my control circuit works over a rather wide range, which should help relax the matching requirements a little. I will let you know how this goes.
Got to go prepare the barbeque and air the wine now.
Regards
Paul
I think you may be judging Audio Synthesis too harshly. I have known David for a long time and I am pretty certain it is a case of independent development, from manufacturers data, rather than copying.
Let me give you a little history from my knowledge of their usage. In the early nineties I developed an acoustic instrument valve preamplifier for use by touring folk musicians. Folk/blues musicians Isaac Guillory and John Renbourn used two of these units on tour, with Isaac giving me further design suggestions to enable me to improve the operational aspects of the preamplifier. The dynamic range and scale of the preamp was quite awesome (it used my high speed, wideband regulators in the power supply), and in some circumstances, with wide dynamic range songs, it could be a little tricky to handle, as his acoustic guitar was also quite dynamic (he had chosen it because it was the most dynamic guitar he had found at that time and this suited his style). I suggested a switchable compressor for the difficult songs and proceeded to develop a FET circuit to achieve this. I wasn’t entirely happy with this circuit and had heard that Vactrols (analog optoisolators by EG&G VACTEC) could be used as the active element for a compressor so I contacted them for information and samples. They sent me a data book with applications information, which defined various methods of use for various functions. One of these functions was series resistor/shunt vactrol volume control, which I decided to try in my hifi system early in 1996. I was very impressed with the resultant sound as it bettered all other methods that I had previously used. I found they were a little tricky to match just as you had found. Initially I used two separate potentiometers to drive them from the valve heater supply, which was fine in operation, but there is market resistance to two separate volume controls in the UK, so I had to consider other ways of dealing with the control aspects. Also, because of slight drift problems, I wanted to develop remote control and balance functions.
I told David how good the sound quality was and he tried them out for himself. I suppose the matching problems bugged him and he worked out his own solution to this. At this time I was not aware of any prior volume control use in commercial hifi products and in fact it’s only since finding your forum thread earlier this year that I have become aware of other users. This shows how much of a hermit I am. I don’t generally pay any attention to what others are doing, but just do my own thing. I’m pretty sure that David wasn’t aware of other users either or he would have said so at the time. Incidentally, David ceased production of his Passion Ultimate model last January.
For general information the Vactrol data/applications book is dated October 1991 and they claim to have been manufacturing these devices for over 20 years previously to this date. I suspect that any attempts to patent LDR volume controls would be aimed more at control methods rather than their actual use as they have been around for a while.
I am nearly out of stock of the resistors that I use. They are Russian non-magnetic carbon film types with silver plated leads that I bought in 1972. Sadly they are no longer available so I will have to do some more trials I suppose.
Regarding your MKII volume control, I shall certainly give it a try as soon as I get some time to sort out the control circuit. The balance function of my control circuit works over a rather wide range, which should help relax the matching requirements a little. I will let you know how this goes.
Got to go prepare the barbeque and air the wine now.
Regards
Paul
serengetiplains said:
No idea what Dartzeel are using but Peter's idea is easy to implement in a shunt volume control. A resistor for each position needs to be grounded so you connects an LDR with a low "light on" resistance in series. Some types go below 50 ohms so if the shunt resistors are sufficiently bigger it will work. Of course this means an LDR for each volume position but no matching is required.
I guess you can do source switching the same way. This may explain why "the ultimate" has poor source crosstalk.
maximus said:
Ok Paul, I'll bite my tongue regarding David, especially seeing he ceased production, I can understand that for full scale production like him, doing series/shunt LDR's would not have been commercially viable with the labour of matching involved.
I hope you are drinking one of our great Aussie Reds?
We have a glut over here of great wine and the world is reaping the benefits, but us Aussies are not getting it any cheaper, the rest of the world is though.
But I still am p----- off about the Dartzeel and their patent application, I will, as soon as something appears at the patent offices, have a little to say regarding approving it goes.
Cheers George
Hi George,
firstly, thanks for all the informatiom you have provided.
I purchase six 32SR2S from RS recently. To my surprise I recieve three R2A's which were very closely matched to each other and three R2E's which were also very closely matched.
As I need four matched for a stereo setup, I am one short. To resolve this this problem, can I use two of the matched devices (R2A) in series which have lower resistance and the other two matched devices (R2E) which have a higher resistance in the shunt part of the circuit?
Regards
Harry
firstly, thanks for all the informatiom you have provided.
I purchase six 32SR2S from RS recently. To my surprise I recieve three R2A's which were very closely matched to each other and three R2E's which were also very closely matched.
As I need four matched for a stereo setup, I am one short. To resolve this this problem, can I use two of the matched devices (R2A) in series which have lower resistance and the other two matched devices (R2E) which have a higher resistance in the shunt part of the circuit?
Regards
Harry
Harry3 said:
Yes Harry use 2 matched for the series LDR's, for each channel.
And another 2 matched for the shunt LDR's for each channel.
All this will do is give a weird (different) gain progression when turning up the volume, but the channels will stay balanced if the pairs are matched.
Cheers George
Hi George,
When Dartzeel file their application all should be revealed. If they are claiming priority on applications for LDRs that have already been used you will have an ally here.
D’Arenberg High Trellis Cabernet Sauvignon at just less than a tenner (sterling). This is good drinking. Unfortunately good wine from anywhere is expensive here, due to heavy government taxation. They tax you when you earn a little money, they tax you when you spend a little money, they tax your house and they tax you when you die. If you were born with a gold sovereign in your hand they would tax that as well. It’s why everything is so expensive in this country and wage demands are so high because we lose so much in tax. It’s only the everyday plonk (the battery acid gut rot that wine producing countries can’t sell to their own people) that gets offered at low prices as a loss leader.
Regards
Paul
When Dartzeel file their application all should be revealed. If they are claiming priority on applications for LDRs that have already been used you will have an ally here.
D’Arenberg High Trellis Cabernet Sauvignon at just less than a tenner (sterling). This is good drinking. Unfortunately good wine from anywhere is expensive here, due to heavy government taxation. They tax you when you earn a little money, they tax you when you spend a little money, they tax your house and they tax you when you die. If you were born with a gold sovereign in your hand they would tax that as well. It’s why everything is so expensive in this country and wage demands are so high because we lose so much in tax. It’s only the everyday plonk (the battery acid gut rot that wine producing countries can’t sell to their own people) that gets offered at low prices as a loss leader.
Regards
Paul