Tortuga Audio LDR6 Attenuator

AlanAlan
edited October 2012 in Amplifiers
This discussion was created from comments split from: passive pre with seca.

Comments

  • tortugatortuga
    You might want to check out our new 6 input passive preamp with remote designed around light dependent resistors (LDRs). Since it's digitally controlled it overcomes some of the challenges designing with LDRs. Like any passive preamp it's not a universal fit with every source and every amp combination but most DACs/CDs coupled with reasonable high impedance solid state amps (and most any tube amp) will work nicely. We decided to design/offer our LDR6 preamp because we were so impressed with the sonic quality of LDRs. 
    www.tortugaaudio.com  
    Cheers, 
    Morten
  • Brain_DeadBrain_Dead
    edited October 2012
    Hi Morten,

    A good analog engineer can design a stable control circuit around LDR with out to much problem, but your method I suspect uses clocks and crystals and a whole manor on non audio products that produce noise.
    So how have you over come that problem, and even most remotes add signals across in to audio signal when operated.

    Interesting web site, a few odd things I see.
    LDR do wear out, after 50K hours the value have changed by 20% or more with the same light levels, oh so do LED,s

    You state a pure sound is better from a LDR , Maybe in a active circuit but passive the internal capacitance may effect the top end roll off ( that will help filter the digital noise clocking about)

    In the UK and Europe we have a thing call RhoS this present a problem has most LDR's are cadmium based, nasty stuff, so how do will handle end of life disposal?

    I do like the Hammond Chassis, we started to use them but found the fixing screw to be crap, and the styling did not make the electronics look stylish and designed.

    I used one for the Alps Pot Passive I made for Chris, but used soft glue to keep screws in tight.
    And keeping signal return paths separate in a pot type is easy, so no problem there, and cross modulation interference is zero no digital crap bouncing about.

    So for me you  would have to make a analog version with no remote control, and no nasty SMPSU to drive it.
    Oh and no toxic metals too.

    Nice idea but not for me, sorry.

    Cheers Col
  • tortugatortuga
    Hi Morten,

    A good analog engineer can design a stable control circuit around LDR with out to much problem, but your method I suspect uses clocks and crystals and a whole manor on non audio products that produce noise.
    So how have you over come that problem, and even most remotes add signals across in to audio signal when operated.

    Cheers Col
    True, the microprocessor uses a crystal/clock which in this instance runs at 16 MHZ and is undoubtedly "seen" by the control (LED) side of the LDRs. I can see it on a scope. Hearing that on the other side of an LDR coming out of a speaker is something else again. I worried about that but I can't detect it within the audio band with a scope and especially not with my ears which I concede roll off at around 14 khz these days. 

    The remote carrier runs at 38khz and then is only present when you push a button to say raise/lower volume or any other momentary command otherwise it isn't in the picture. Even when the remote is "on" (button pushed) I frankly can't hear it in the audio signal. I agree that if you could hear it it would be unsatisfactory.  

    Other than to handle the remote decoding, digital control provides a great deal of flexibility in dealing with the nonlinear and non-matching aspects of LDR behavior and makes possible near perfect left-right channel matching throughout the entire attenuation range which improves imaging. In addition to testing each LDR individually, each LDR6 preamp is tested after assembly and the test results are used to fine tune the attenuation curve of each channel with the results loaded into the final software. In this way each LDR6 has its own customized code that is unique to the set of attenuation LDRs in that unit. In addition to all that, the design also allows for traditional fine turning of the left-right channel balance via both the encoder knob or the remote. 

    And yes of course LDRs have been made to work in a purely analog configuration without digital control. 

    Best, 

    Morten
  • Brain_DeadBrain_Dead
    Hi Morten,

    A good analog engineer can design a stable control circuit around LDR with out to much problem, but your method I suspect uses clocks and crystals and a whole manor on non audio products that produce noise.
    So how have you over come that problem, and even most remotes add signals across in to audio signal when operated.

    Cheers Col
    True, the microprocessor uses a crystal/clock which in this instance runs at 16 MHZ and is undoubtedly "seen" by the control (LED) side of the LDRs. I can see it on a scope. Hearing that on the other side of an LDR coming out of a speaker is something else again. I worried about that but I can't detect it within the audio band with a scope and especially not with my ears which I concede roll off at around 14 khz these days. 

    The remote carrier runs at 38khz and then is only present when you push a button to say raise/lower volume or any other momentary command otherwise it isn't in the picture. Even when the remote is "on" (button pushed) I frankly can't hear it in the audio signal. I agree that if you could hear it it would be unsatisfactory.  

    Other than to handle the remote decoding, digital control provides a great deal of flexibility in dealing with the nonlinear and non-matching aspects of LDR behavior and makes possible near perfect left-right channel matching throughout the entire attenuation range which improves imaging. In addition to testing each LDR individually, each LDR6 preamp is tested after assembly and the test results are used to fine tune the attenuation curve of each channel with the results loaded into the final software. In this way each LDR6 has its own customized code that is unique to the set of attenuation LDRs in that unit. In addition to all that, the design also allows for traditional fine turning of the left-right channel balance via both the encoder knob or the remote. 

    And yes of course LDRs have been made to work in a purely analog configuration without digital control. 

    Best, 

    Morten
    Hi Morten,

    How about harmonics from 16MHz and the 38KHz how do they if at all interfere with the audio, oh just a wee thought what colour are the LED's as you will be aware the light spectrum of the LDR is very narrow say 650nm .

    Best

    Col
  • AlanAlan
    edited October 2012
    Hi Morten

    Thanks for joining Chews to let us know about your LDR6, I thought it deserves a topic of it's own seeing as Colin designed both the SECA and the passive pre in the other thread.

    The LDR6 is a nice looking product, and looks to be a high-end version of the EVA2. It's a little rich for my blood, I'm afraid, but I bet I would like it very much.

    Do you plan to offer variations of the LDR6? Less inputs, no remote, or perhaps more usefully, more outputs? For those who Bi-amp or Tri-amp (passively) that would be essential.
  • tortugatortuga
    Hi Morten,

    A good analog engineer can design a stable control circuit around LDR with out to much problem, but your method I suspect uses clocks and crystals and a whole manor on non audio products that produce noise.
    So how have you over come that problem, and even most remotes add signals across in to audio signal when operated.

    Interesting web site, a few odd things I see.
    LDR do wear out, after 50K hours the value have changed by 20% or more with the same light levels, oh so do LED,s

    You state a pure sound is better from a LDR , Maybe in a active circuit but passive the internal capacitance may effect the top end roll off ( that will help filter the digital noise clocking about)

    In the UK and Europe we have a thing call RhoS this present a problem has most LDR's are cadmium based, nasty stuff, so how do will handle end of life disposal?

    I do like the Hammond Chassis, we started to use them but found the fixing screw to be crap, and the styling did not make the electronics look stylish and designed.

    I used one for the Alps Pot Passive I made for Chris, but used soft glue to keep screws in tight.
    And keeping signal return paths separate in a pot type is easy, so no problem there, and cross modulation interference is zero no digital crap bouncing about.

    So for me you  would have to make a analog version with no remote control, and no nasty SMPSU to drive it.
    Oh and no toxic metals too.

    Nice idea but not for me, sorry.

    Cheers Col
    50,000 hours - 20% drift:  I've not heard this before and so far haven't seen evidence of it with the LDRs we're using (Silonex). Have had a prototype unit running "hot" for just over 3 years now with no tangible change. That's 3 x 8760 hrs = 26,280 hours give or take. So far so good. On the other hand if LDRs were only "on" while listening to music and let's say you listened to music 2 hours each day every day then 50,000 hours of listening would be 50,000/2/365 = 68.5 years. I'd say you'd have gotten your money's worth. 

    Roll-Off:  The top-end RC roll-off question comes up often enough with passive preamps generally but usually with regards to higher capacitance (or very long) connectors between preamp and amp. Simply put, we've seen no evidence of roll-off from the LDRs themselves but then again haven't looked beyond 20 khz. 

    RoHS:  Well aware of RoHS and yes the Silonex LDRs use very small amounts of Cadmium. Silonex has applied for an exemption based on numerous criteria but I don't know where all that stands. One criteria is the Cadmium represents less than 0.01% by weight. Some suppliers of Silonex LDRs claim they're RoHS compliant and some do not. After checking, our supplier states they are not compliant. If unequivocal RoHS compliance is your bright line test for product acceptance then there you have it. 

    Chassis:  The chassis is not manufactured by Hammond. It's a very robust one-piece extruded aluminum unit. Not that I'll ever test this to confirm but I suspect I could run a car over a fully assembled LDR6 unit and it wouldn't get crushed. 

    Remote Adding Noise To Audio:  I fear this is one of those red herrings. Even accepting for a moment that a momentary press of a button on a remote could actually be heard (I can't hear it myself) it's arguably irrelevant to normal listening when you're not pressing the remote. And when you're not pressing the remote, it's inactive and can't possibly influence the audio in and of itself. I concede that I may not fully grasp something here but we've not been able to measure or hear the 38khz IR receiver in the audio. IR receivers have become common place in audio and even hi-end audio without adversely impacting the sound. Personally, being able to control my gear via a remote is a must but I understand that a "purist" view towards the superiority of manual/analog control is not to be trifled with. Rock on! 

    Switch Mode Power Supply:  Yes, SWPSU's are not ideal and it's on our target list for an upgrade to a cleaner linear supply. That said, while I can see the noise on the control side of the LDR's I'm completely convinced I can't hear it on the audio side. LDR's are effective filters in their own right. 


  • tortugatortuga
    Hi Morten

    Thanks for joining Chews to let us know about your LDR6, I thought it deserves a topic of it's own seeing as Colin designed both the SECA and the passive pre in the other thread.

    The LDR6 is a nice looking product, and looks to be a high-end version of the EVA2. It's a little rich for my blood, I'm afraid, but I bet I would like it very much.

    Do you plan to offer variations of the LDR6? Less inputs, no remote, or perhaps more usefully, more outputs? For those who Bi-amp or Tri-amp (passively) that would be essential.
    Alan, 

    No plans to offer a variation without a remote. Someone has to strike a blow for civilization and getting off my duff to adjust volume just doesn't cut it. :) 

    Are considering a simplified and less costly single input but would retain remote along with on/off, mute and channel balance adjustment functions. 

    Would be very interested in getting more feedback on optimum mix of inputs/outputs etc. 

    Cheers, 
    Morten
  • Brain_DeadBrain_Dead
    50,000 hours - 20% drift:  I've not heard this before and so far haven't seen evidence of it with the LDRs we're using (Silonex). Have had a prototype unit running "hot" for just over 3 years now with no tangible change. That's 3 x 8760 hrs = 26,280 hours give or take. So far so good. On the other hand if LDRs were only "on" while listening to music and let's say you listened to music 2 hours each day every day then 50,000 hours of listening would be 50,000/2/365 = 68.5 years. I'd say you'd have gotten your money's worth. 

    All the LED's manufature are aware of it, our eye will not see small brightness changes, but CdS/CdSe will and control of this will need to be compensated for.

    Roll-Off:  The top-end RC roll-off question comes up often enough with passive preamps generally but usually with regards to higher capacitance (or very long) connectors between preamp and amp. Simply put, we've seen no evidence of roll-off from the LDRs themselves but then again haven't looked beyond 20 khz. 

    You and I and most people who will read this 20KHz may or may not be your upper limit of hearing, but we understand that harmonic content above this will effect lower frequency and phase,.

    RoHS:  Well aware of RoHS and yes the Silonex LDRs use very small amounts of Cadmium. Silonex has applied for an exemption based on numerous criteria but I don't know where all that stands. One criteria is the Cadmium represents less than 0.01% by weight. Some suppliers of Silonex LDRs claim they're RoHS compliant and some do not. After checking, our supplier states they are not compliant. If unequivocal RoHS compliance is your bright line test for product acceptance then there you have it. 

    Having read this:- http://www.silonex.com/announcements/RoHS_Letter.pdf   it suggests you the manufacture will have to apply not them, which makes sense as they would not want there LDR with a radioactive wrist watch that dim at night.
    So you will need to look at that again sorry.

    Chassis:  The chassis is not manufactured by Hammond. It's a very robust one-piece extruded aluminum unit. Not that I'll ever test this to confirm but I suspect I could run a car over a fully assembled LDR6 unit and it wouldn't get crushed. 

    Remote Adding Noise To Audio:  I fear this is one of those red herrings. Even accepting for a moment that a momentary press of a button on a remote could actually be heard (I can't hear it myself) it's arguably irrelevant to normal listening when you're not pressing the remote. And when you're not pressing the remote, it's inactive and can't possibly influence the audio in and of itself. I concede that I may not fully grasp something here but we've not been able to measure or hear the 38khz IR receiver in the audio. IR receivers have become common place in audio and even hi-end audio without adversely impacting the sound. Personally, being able to control my gear via a remote is a must but I understand that a "purist" view towards the superiority of manual/analog control is not to be trifled with. Rock on! 

    Now this will depend surely on the chosen PIC you have, and the crystal you have running it, an then when this "High" frequency carrier is pick up by the optical sensor sub carrier of 38KHz  are you saying (that with your limited B/W scope) this will not produce cross-talk to the high impedance audio signal on your LDR  and harmonic and phase changes, clever.

    Switch Mode Power Supply:  Yes, SWPSU's a:- 

    Not so fast, lets make this clear.
    There are many types of SMPSU some are ideal for purpose Fly-Back are good cheap for PC, lights, but not Audio and since most people want to save money then cheap Fly-Back wins.
    The Forward Converter nice solid more cost less nasty harmonics but it does like a constant load like it's brother the Fly Back. So for audio unless it a SECA design do not bother.
    Bridge and Push-Pull monsters in the norm many version but cost , nice for audio, and D Class Amps.
    Full Bridge Resonant type Nice Sine wave  output very good for dynamic loads and NASA Space Stations, X Ray machine up to 150KW size to power ratio small  and efficient up to 95% and 97% low harmonics, BUT the COST help.

    Morten the basic thing that worries me is the use of Cd law suit cost to much so please be sure you are covered, we at "Tellurium Q Ltd" have a Amanda that does that for us, on all our products and we have already dumps or scraped tons of "Toxic" products and some expensive connectors when tested used a CdAlMg alloy gold  plated and sold to us as RHoS compliant but we send all bits to be tested for nasties.
    You can never be to safe, OK and boring.

    Best of luck Morten

    Kind regards

    Colin
  • MaxMax
    hi, I like this attenuator ! Has anyone actually got one here and could share some personal experience ? From the reviews it is supposed to be very good.

    Best


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