LDR Volume Control Hot-Mod
Printed From: Graham Slee Hifi System Components
Category: DIY AUDIO
Forum Name: Owner's Hot-Mods
Forum Description: Tell us how and why you hot-modded your audio gear
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=843
Printed Date: 27 Mar 2026 at 3:31am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: LDR Volume Control Hot-Mod
Posted By: jonclancy
Subject: LDR Volume Control Hot-Mod
Date Posted: 06 Apr 2010 at 10:49am
I'll kick off by outlining an idea for integrating a Light-Dependant Resistor volume control upgrade for the Solo series of headphone amplifiers. I'll flesh out the details over the next few days when I've committed my ramblings to notepaper and edited from gibberish to English!  This will work a treat with the new PSU1 as well. Why? 1. There is room in the Solo case for the LDR board. 2. There is already a volume pot in the Solo. 3. There is room to for a small regulator board to power the LDRs. 4. You could either draw power from the secondary supply on the new PSU1, or tap into the pre-regged 24VDC as it enters the Solo (or after the second reg for less voltage drop). Parts are easily available and the LDR circuit can be made up on perfboard or even etched as a simple PCB. The whole mod should only take a couple of hours to put together and fit. Discuss!!  |
Replies:
Posted By: Graham Slee
Date Posted: 06 Apr 2010 at 11:54pm
Can't Wait! 
------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 07 Apr 2010 at 10:10am
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What I would envisage if asked how I thought it works is... An LED as light source (or array of LEDs) requiring the regulator board such that the light intensity didn't change with power supply fluctuations. A fixed resistor in series with a light dependent resistor, input and ground either end and "wiper" taken from the junction of the two. Dark resistance is usually in Meg Ohms. Lit resistance 50k - 100k Ohms according to this http://www.farnell.com/datasheets/44006.pdf - data sheet (the only one I could easily find that is RoHS compliant). Are there quite a few in parallel? Jon, it will be interesting to see and read about this novel idea. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: jonclancy
Date Posted: 07 Apr 2010 at 2:25pm
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Hi Graham, You're very near!  Yes, a separate regulator board for the LED side of things. I use an ALW Super-Reg at 5V in mine. Overkill, probably, but in theory a clean supply is IMHO essential.Fixed resistor in series, but also a trim-pot to adjust balance. I use the O'scope for getting mine completely balanced in real time, at the listening volume position. The best way is to use the circuit based on George Stantscheff's Lightspeed MkII attenuator - i.e. two LDRs per channel in series / shunt configuration. Details in a nutshell in Uriah Dailey's contribution here: http://diyaudioprojects.com/Solid/DIY-Lightspeed-Passive-Attenuator/ Uriah can also supply matched sets of LDRs for this project. George's unveliling of his product to the DIY world here (first 5 pages are most relevant): http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html RoHS wouldn't matter for the hobbyist. I tried my Lightspeed with the SCHA when I was comparing with the SRG II. I noticed that the Lightspeed appeared, during the short time I listened, to be very similar in quality to the £100++ TKD stepped attenuator I was also testing. Having created an EAGLE LDR device, and laid my own attenuator out on perf-board, it struck me that a really compact board could be built to go in the Solo. Desolder the pot and use the holes for signal etc from the LDR board and use a suitable 100K dual pot (inverted for access) for controlling the 5VDC supply. I was thinking of something like a Teddy Regulator board for the 5VDC, as they are very compact, but boast good performance. http://www.pinkfishmedia.net/forum/showthread.php?t=39990 If you have a spare Solo board at Slee towers, I can try this out and return it to you for comparison with a stock unit. Doesn't matter if it's an older version, as it's just the difference in SQ that we're looking for. George holds the IP for this idea, but for an individual to mod their own gear, I think it presents an interesting alternative to other pots or stepped attenuators. Cheers Jon |
Posted By: jonclancy
Date Posted: 07 Apr 2010 at 2:29pm
Re-reading my original post, it might appear that this is my idea. It is NOT! I'm enjoying this vol-co, though, and thought it sounded great through a headphone amp. It's compact and simple nature immediately stuck me as being a good candidate for modding commerical headphone amps. Sorry if it appeared I had invented something...  |
Posted By: Graham Slee
Date Posted: 15 Aug 2010 at 2:20pm
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Just to kick this thread off again, Jon kindly sent me his prototype ages ago and only just today did I get round to putting it in the "Slee Towers" system. Will report back when I get a long enough listen. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: Graham Slee
Date Posted: 16 Aug 2010 at 6:17am
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Whilst waiting for the lightspeed attenuator to warm up I uncovered something quite interesting... European RoHS makes it impossible to sell such a product in European Union countries and other versions of RoHS in other countries probably have the same effect. This is possibly why it became "open-resource"??? But why? One of the hazardous substances RoHS identifies is cadmium and the light dependent resistor elements (LDRs) which the lightspeed attenuator uses are CdS - cadmium sulphide. All LDRs are. Such a pity as so far I find this attenuator completely "invisible", revealing musical information I never heard before. I was very surprised! So where from here? The only other way I can think of making such an attenuator is using analogue transistor output opto-couplers. I'll take a look into this and see what I think is possible. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: mrarroyo
Date Posted: 16 Aug 2010 at 11:42am
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Could you offer the entire kit except the LDR which would have to be sourced and installed by the buyer? ------------- Miguel |
Posted By: Graham Slee
Date Posted: 16 Aug 2010 at 1:31pm
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Hi Miguel, I don't think I can do that because the project says "George has chosen to share his Lightspeed Attenuator with the DIY community provided that it is only used for personal use only" and I feel that in doing a kit I will be breaking his copyright. Having said that there are possibly other ways of making a similar attenuator. I have read articles where solid state analogue switches are used (cmos/fet logic controlled switches) and there is a possibility of using opto-isolators with analogue outputs - these use a transistor which could be used to pull down a resistor (a shunt) whilst another un-shunts another resistor. All quite mind bending at the moment but I'm sure we will find an equivalent we here can make as a kit, it also being RoHS. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: less
Date Posted: 18 Aug 2010 at 12:53pm
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I am also quite interested in this idea and look forward to what you might come up with Graham.
One point though, if all LDRs contain cadmium is not illegal to even sell or import this component in the EU? Regards Les ------------- I don't do mediocrity! Les Sutherland |
Posted By: Graham Slee
Date Posted: 18 Aug 2010 at 9:37pm
It is not illegal to bring in such a component into the EU, but it is illegal for a manufacturer to incorporate it into a product for sale within the EU. So why do they bring the parts in? Spares for repair of existing products, educational, infrastructure communications and control equipment, airframe electronics or engineering projects not covered by RoHS - these are the few exceptions. Unfair? We think so, but the Holy Roman Empire - oops! I mean the EU is the boss! ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
less wrote:Posted By: jonclancy
Date Posted: 24 Aug 2010 at 9:43am
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Hi All, Just back from our hols and saw the thread. A couple of thoughts... George still sells the original Lightspeed in Aus, so I'm assuming they don't have RoHS there! As Graham said, these LDRs are quite easily obtainable in the UK, but would have to be manufactured into an exempt device. But, it is a global village. I still hold that a board might be made available, and a simple email/PayPal transaction will see matched devices winging their way to your door. This would not be a kit, or a manufactured item. The board design could be made to drop into your existing Solo and seeing as there are only about a dozen components involved, it would be withing the reach of all but the most novice builders.I was going to design such a board, but Uriah has an offer on at the moment that would see you with a set of four matched LDRs and a PCB for 30USD. Bargain! Would probably fit in the case fine. http://www.buildanamp.com/ Of course, the custom version would just be better for fitment..... Finally, I'm really chuffed you like the sound of the attenuator, Graham. I was impressed myself, but I do wonder if I'm getting a bit cloth-eared as I get a (bit) older! Cheers Jon |
Posted By: Graham Slee
Date Posted: 26 Aug 2010 at 8:33am
Cooped up in that noisy cabin at work probably doesn't help.... Having said that and as you noticed the difference with the lightspeed your lug holes seem to be in tip-top condition! ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: jonclancy
Date Posted: 26 Aug 2010 at 1:55pm
I wish!! My top range is down to about 12.5KHz on both sides. Most likely as a result of non-noise-cancelling hearing protection in my old work environment.At least I can annoy my daughter with 18KHz tones..... |