Jump to content

stereo coffee ldr

Members
  • Content Count

    18
  • Joined

  • Last visited

Community Reputation

3 Neutral

About stereo coffee ldr

  • Rank
    10+ Post Club

Profile Fields

  • Location
    North island

Recent Profile Visitors

545 profile views
  1. Hi I am Chris , hi to everyone. Listening to Keith Jarrett today, his Paris concert and Vienna concerts
  2. Hi Owen My main interest was simply whether (i) output impedance varies with volume & (ii) how high does it get? Yes output impedance varies with volume as the Java is a passive stereo L Pad signal side circuit, in this case using LDR's , impedance across the series LDR pair when volume is least on the input selected is just above 80k , and when fully on 60-100 ohms ( depends on the actual matched individual LDR, hence 100 ohms has been specified ) The LDR in its OFF state ie no current to its anode or cathode, has typically 25 mega ohm resistance. A data sheet here, gives the devices specifications: http://logosfoundation.org/instrum_gwr/tinti/datasheets/Silonex_NSL-32SR2_60721.pdf The relationship of impedance series LDR pair vs shunt LDR pair shows fairly close mimic of a 20k passive. Cheers / Chris
  3. Hi With LDR's like NSL32SR2s they never bottom out to zero ohms, rather they exhibit 40 ohms upward. The NSL32SR3 60 ohms upward. See data sheet Typically our circuit has them at 90 ohms on L and 90 ohms on R when volume is at minimum , inferring our implementation is very kind to the LDR, not stressing it with current.
  4. At what volume setting ? You appear to be asking for input and output impedance that relates to fixed pads or fixed resistances, confusing a variable passive element with active circuits. At low volume where audio commences the input impedance is very high typically 80k as the series placed LDR has little current , whereas the output impedance is low as the shunt LDR has more current. At lowest volume where there is no audio present our circuit provides the typical 40 ohms across the shunt LDR which is then in parallel with the load, no harm its just- no audio typical with volume being zero. As the volume increases then the shunt LDR starts to lose current and the series starts to gain that same current, accordingly the series input impedance starts to reduce and the load shunt impedance increases. An average where some answer can be given of this variable activity, shows our circuit resembles a 15k -20k potentiometer.
  5. Hi Owen We use a simple L pad made for each stereo channel of a pair of NSL32SR2s for shunt and the same for series, so no not multiple LDR's, just what is required, a pair for series and a pair for shunts. Very careful matching proceeds and we usually get the quad of LDR's within 1-2% Left to Right channel difference. we have though achieved 0.25% channel difference on occasion and identical resistances has occurred, of course subject to temperature variation. Our most recent control board assists these excellent figures. Cheers / Chris
  6. Hi The signal side of a LDR based attenuator is a stereo L pad, hence it attenuates by varying series and shunt resistances however of course coupled by light rather than switching one surface arranged with varying resistance against another. the attached diagram shows a Audiohm LDR Asking as to impedances has comparison to asking the impedance of a potentiometer, however LDR's behave differently as they approximate a potentiometer. There is choice in design to choose the LDR to have lower resistance for shunt, thereby encouraging a log response. Similarly for series the resistance can be chosen to provide adequate coupling to the source. Inviting active current regulation however provides another level of control, whereby high resistance can be used with a potentiometer to provide modest gain, and therefore control of the LED. Matching of LDR's is not rocket science its just patience and observation of how series and shunt provide resistance in this case so Left is ideally the same as Right. Mr W will not rest of course until a impedance figure is provided, so we usually set up resistance to approximate a 15k-20k potentiometer with a log response. So by all means measure a 20k log pot, and let us know input and output impedances. Moreover moving ahead LDR's provide excellent isolation as it is a medium without comparison to switches and wiped surfaces where signal paths are always degraded. Are LDR's the ultimate attenuator well they are very very good indeed, until something else comes along. However they are only as good as your source can provide, ideally the source where buffers etc can be used should have low impedance capability. Comparison to other LDR products is not valid, the one mentioned in question uses a fixed voltage into a high resistance potentiometer and calls upon stopper trim pots so the device maximum ratings are not exceeded. Our circuit in comparison uses a Vref/r where there is sensing of the LDR Every edition of LDR we have done has provided ability to have no audio apparent at nil volume, as well as ability to turn the series LDR's off and achieve input switching such as 3 stereo inputs. I hope this clarifies some of the mystery with LDR's I am happy to answer any questions you may have. Cheers / Chris
  7. Whilst audio systems in the 1960's and 1970's had source components attached to them like phono cartridges radios and tape players having driver stages catering for each source component back then, yes made sense. Today however CD players outboard DAC's and dedicated phono stage preamps have more than enough drive to simply be attenuated.
  8. Hi AudioEnz Members Just letting you know some nice reviews and comparisons took place here see post 1, 19, and 28 being the persons other than one who were present. http://theartofsound.net/forum/showthread.php?33176-Pre-Amp-bake-off-What-Happened and some DIY building here: http://theartofsound.net/forum/showthread.php?32977-Macca-s-Stereo-coffee-LDR-Build DIY kits proudly made in NZ. Cheers / Chris
  9. Hi System plans for 2014 are already well underway. Firstly the three code digital transfer I invented and had published in 1997 in Electronics World is up and running via Sony CX555ES, so with that excellent front end along with DBX Type 1 via a 150x, I am busy rerecording all my Cd's and LP's to Yamaha Hard Disc recorders CDRHD1500 which will take until about August. may also do a backup as flac files to my little Linux Mint Box Pro and optimize it for audio. The little stereo coffee ldr preamp is running very nicely so I will get to building myself a 5 or 6 input model to assist all the inputs Will probably do a service on the 1961 ESL 57 and build some better crossovers for my Gale 401a. Also fit a stereo Coffee LDR board replacing its variable out to my Yamaha CT1010 easily the best tuner I have heard. So a busy year ahead - but off to a great start. Chris
  10. Hi We have a policy with our Stereo Coffee LDR products to update our customers where any new development occurs, at no cost to our customers. We are based in Masterton. There have been three revisions to our control board, A, B, and C. Whilst we had all the circuit values correct at model A, as our first Stereo coffee LDR preamp sounded excellent. There is far more to getting an LDR product sounding amazing, and we are very confident revision C2 is it. We are back at our workshop this week and our present 5 NZ customers can all expect revision C2 in their mail week ending 10/01/14, so please await review until then. A brief explanation of Light Dependant Resistors's may help to clarify some of the mystery. LDR's used for audio have to meet ability to go to low resistance typically 40 ohms. Another criteria is there be No volume when the potentiometer is off, and most importantly that the LDR's are matched. We use the NSL32SR2S which is an expensive part, and our 3 input model uses 6 matched LDR's for the series devices and 2 LDR's for the shunt as it is an L pad circuit. To get 3 inputs there is NO signal switching, rather we turn the anode on for the next input and the prior anode off- we are using the LDR both as a switch and a variable resistor. another requirement is that volume be gradual similar to other volume controls. Light Dependant Resistors are on one side a LED, and on the other a variable resistor, separated by nothing more than light that activates and changes that resistance. They are a far better device for audio than switched attenuators as there is no contact. Their current and voltage requirements dictate how they should be connected. To supply the LED for the LDR ,whilst you can get a result with supplying a regulated voltage into a high resistance potentiometer and placing some resistors at the other end so the current is not exceeded, this is not the method we use. Our circuit has a patent application pending, and is quite different to former methods of controlling LDR's Happy to answer any questions you may have. Cheers Chris and Dorothy
  11. Whilst 75 ohm cable will be good, you have not informed anything about your antenna. Broadcast transmission is at 50 ohms, and many antenna are designed to that impedance rather than 75 ohm. If you were using a Discone antenna, it is a 50 ohm type and for instance you would use RG58 for short lengths, or long lengths Belden 9913 or its cheaper cousin RG213 - these are RG8 type cables which can assist in lower loss per metre but not very domestic friendly. You may ask what is the difference between 75 ohm and 50 ohm coax ? the difference is the distance between the inner conductor to the outer shield, a 50 ohm is slightly closer Aside from radio reception RG58 is an excellent cable, although a little awkward for audio use. RG174 also 50 ohm represents a good choice for all round audio use. Cheers / Chris
  12. PCB boards are the best looking and professional way to do it. The cost of PCB manufacture is mainly in the setting up. With first hand experience of now 2 designs of board, you may want to think about higher production numbers than one. We used Fritzing on a Linux Mint 15 xfce platform for schematic placing and layout design and to generate the gerber files for our LDR kit circuit boards. It is best to simulate test, and actual component test your schematic design. we like Oregano for schematic drawing, and we used Tina using a virtual box in Linux Mint for simulation. Cheers / Chris Stereo Coffee Kits Masterton NZ
  13. Hi Stereo Net Looking forward to sharing info on hifi Thanks / Chris
  14. Hi Michael You are quite wrong about DBX Type 1. Typified by the 150x it offers a genuine improvement over straight CD when partnered with the Yamaha Hard Disk Recorder. If you have not heard it you should. My offer is there to hear it for yourself. My guess is you will be very pleasantly surprised. No I never explored Type C, Type B was bad enough.:rolleyes: Chris
×
×
  • Create New...