shaky Posted January 8, 2013 Share Posted January 8, 2013 (edited) I am currently building some 3way speakers. For xover (slope and frequency) duties I have a processor that will handle this (also does time correction too). It has 8ch outputs so has room for two subs too and a great pc interface to program it through. It runs off 12VDC so I need to make a supply for it as well. Details for processor: http://www.audison.eu/index.php?page=product&id=49 Now, to expand on the idea, I want to make a preamp to send signal to the processor. I came across the Lightspeed Attenuator mentioned in the preamp thread in 2ch area and am considering using that for my volume control, placed between the pre and pro. Where I need help is in the input switching area for the preamp. I'm loathe to use switches or relays if I can help it, unless there is a good noise free viable solution here, so was looking at a microprocessor based design. So far I have been told to look at the Picaxe range of processor chips to start with. If anyone can give me ideas on where to look for appropriate processing, circuit design, products out there or similar projects they have done, any help really, that would be greatly appreciated. Edited January 8, 2013 by shaky Link to comment Share on other sites More sharing options...
Owen Y Posted January 8, 2013 Share Posted January 8, 2013 FWIW I found that relay preamp signal switching signif degrades fidelity (dynamics esp), compared with a decent contact switch. (I did not try other than a Omron 5v small signal relay.) Your setup should be nicely user-controllable, user-convenient, when complete Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted January 8, 2013 Share Posted January 8, 2013 FWIW I found that relay preamp signal switching signif degrades fidelity (dynamics esp), compared with a decent contact switch. (I did not try other than a Omron 5v small signal relay.) Your setup should be nicely user-controllable, user-convenient, when complete That's because you need a hermetically sealed, precious metal contact relay. Such relays are as good as switches get. Link to comment Share on other sites More sharing options...
ArthurDent Posted January 8, 2013 Share Posted January 8, 2013 (edited) I came across the Lightspeed Attenuator mentioned in the preamp thread in 2ch area and am considering using that for my volume control, placed between the pre and pro. Not going to work as the input impedance of the processor is only 20k (high level) and 5k (low) and the output impedance of the LS is rather high. ZB can no doubt take it from here. Edit: How much is this thing? Spec wise it sounds like it's very similar to the MiniDSP 2x4. Edited January 8, 2013 by KenTripp Link to comment Share on other sites More sharing options...
shaky Posted January 8, 2013 Author Share Posted January 8, 2013 Thanks so far. I already have the processor so will make use of it. Link to comment Share on other sites More sharing options...
ArthurDent Posted January 8, 2013 Share Posted January 8, 2013 Thanks so far. I already have the processor so will make use of it. Aware of that and wasn't suggesting you use something else, just curious about the cost. Link to comment Share on other sites More sharing options...
shaky Posted January 8, 2013 Author Share Posted January 8, 2013 Not sure of the cost now but when I got it 3-4yrs ago it was around $1k mark. In reality it is designed for car audio use (hence the 12V) but I figure I've got it now so may as well use it. The build of a PSU to power it doesn't concern me at all. Link to comment Share on other sites More sharing options...
Owen Y Posted January 9, 2013 Share Posted January 9, 2013 Sealed w silver/palladium/gold contacts, etc...? Yup. That's my hands on experience anyway. YMMV of course. That's because you need a hermetically sealed, precious metal contact relay. Such relays are as good as switches get. Link to comment Share on other sites More sharing options...
georgehifi Posted January 11, 2013 Share Posted January 11, 2013 Lightspeed Attenuator mentioned in the preamp thread in 2ch area and am considering using that for my volume control, placed between the pre and pro. Where I need help is in the input switching area for the preamp. I'm loathe to use switches or relays if I can help it. Hi Shaky, I manufacture the Lightspeed Attenuator and what it is all about and the reason for it's transparency is not to have any contacts in the signal path. I recommend owners if they want multiple inputs is to get a separate source switching unit, such as the Decware http://www.decware.com/newsite/rotary.htm that way when you really want to listen or show how good the system can sound without contacts in the signal path you simply plug your source you want to hear in direct to the Lightspeed and not use to source switcher. If I were to ever offer a Lightspeed Attenuator with multiple input switching, the only thing I would comprimise on (my no contact in the signal path rule) would be to use Mercury Wetted Relays, http://www.smtnet.com/company/index.cfm?fuseaction=view_company&company_id=53660&component=catalog&catalog_id=17803 but these are costly and maybe becomming illegal soon to buy. Cheers George Link to comment Share on other sites More sharing options...
shaky Posted January 11, 2013 Author Share Posted January 11, 2013 George, thank you for the informative reply. Yes, I understand the LSA is yours and have read up about it and how it operates, an ingenious method of volume control. From what has been explained here though my processor has an unsuitable input impedance for it. I have read though of people using your attenuator successfully even outside of recommended impedance matches. Could this be possible here or is there some sort of buffer that can be employed between the two items? As for the switching side of things I can see your point in regards to no contacts in the signal path but would also like the convenience of multiple inputs. There is the added bonus of two aux inputs into my processor that could be used though. However three inputs would not be enough for my gear. Other than the manual method of removing the switching from between the LSA and processor that you suggested, trying to setup a 'bypass' for the LSA to get around the switching section might be tricky too but perhaps manageable. It's obviously early days in my planning here so thankyou for the step in the right direction. Any further help I can get would be appreciated. Link to comment Share on other sites More sharing options...
georgehifi Posted January 11, 2013 Share Posted January 11, 2013 George, thank you for the informative reply. Yes, I understand the LSA is yours and have read up about it and how it operates, an ingenious method of volume control. From what has been explained here though my processor has an unsuitable input impedance for it. I have read though of people using your attenuator successfully even outside of recommended impedance matches. Could this be possible here or is there some sort of buffer that can be employed between the two items? As for the switching side of things I can see your point in regards to no contacts in the signal path but would also like the convenience of multiple inputs. There is the added bonus of two aux inputs into my processor that could be used though. However three inputs would not be enough for my gear. Other than the manual method of removing the switching from between the LSA and processor that you suggested, trying to setup a 'bypass' for the LSA to get around the switching section might be tricky too but perhaps manageable. It's obviously early days in my planning here so thankyou for the step in the right direction. Any further help I can get would be appreciated. Hi Shaky, if you have a source that is below 100ohms output impedance then your processor's input impedance can come down to as low as 20kohms as it is up to the source to drive both Lightspeed and processor input impdance combind, just keep the interconnects from Lightspeed to processor at 1mt or less. As for mulitple inputs I suggest one of these that way you can still go direct when you want to hear you system at it's best when you want, or just do what I do and manualy change them. http://www.decware.com/newsite/rotary.htm Cheers George Link to comment Share on other sites More sharing options...
brownemi Posted January 11, 2013 Share Posted January 11, 2013 Hi Shaky, if you have a source that is below 100ohms output impedance then your processor's input impedance can come down to as low as 20kohms as it is up to the source to drive both Lightspeed and processor input impdance combind, just keep the interconnects from Lightspeed to processor at 1mt or less.As for mulitple inputs I suggest one of these that way you can still go direct when you want to hear you system at it's best when you want, or just do what I do and manualy change them. http://www.decware.com/newsite/rotary.htm Cheers George George. When manually switching over should you turn the LS, source and power amp off? I do this but find it slow and annoying waiting for everything including valves to come up to full steam again. Cheers Michael. Btw the LS arrived yesterday. Great service thanks. Link to comment Share on other sites More sharing options...
georgehifi Posted January 11, 2013 Share Posted January 11, 2013 (edited) George. When manually switching over should you turn the LS, source and power amp off? I do this but find it slow and annoying waiting for everything including valves to come up to full steam again. Cheers Michael. Btw the LS arrived yesterday. Great service thanks. Hi Michael that was quick Aus post rules. If manually changing the inputs, you should turn everything off, but you can do it if you turn the volume down to minimum with it all powered up which is what I do, you may get a very small bump from the speakers as the Lightspeed Attenuator cannot go to absolute zero even when it's at it's minimum setting, you just have to try it and see, it's a system gain thing. BTW: change one channel at a time so there is always at least one thing on the input when changing sources, so the earth stays referenced BTW BTW Michael, just looked at your gear complement, bet your getting some kind of good sound with that setup? Cheers George Edited January 11, 2013 by georgehifi Link to comment Share on other sites More sharing options...
shaky Posted January 12, 2013 Author Share Posted January 12, 2013 (edited) Hi Shaky, if you have a source that is below 100ohms output impedance then your processor's input impedance can come down to as low as 20kohms as it is up to the source to drive both Lightspeed and processor input impdance combind, just keep the interconnects from Lightspeed to processor at 1mt or less.As for mulitple inputs I suggest one of these that way you can still go direct when you want to hear you system at it's best when you want, or just do what I do and manualy change them. http://www.decware.com/newsite/rotary.htm]http://www.decware.com/newsite/rotary.htm[/url] Cheers George George, you are a legend!!! Seems as though with my cdp having an output impedance of only 42 ohms, and my pros input impedance of 20k, the LSA should work ok according to you. The length of IC shouldn't be a drama as they will be right next to each other. Tim Edited January 12, 2013 by shaky Link to comment Share on other sites More sharing options...
georgehifi Posted January 13, 2013 Share Posted January 13, 2013 Correct, your source of 42ohms will see the combined load of processor and Lightspeed of 6.6kohm (6,6000hms) it won't even know it's there. Cheers George Link to comment Share on other sites More sharing options...
Addicted to music Posted January 13, 2013 Share Posted January 13, 2013 Correct, your source of 42ohms will see the combined load of processor and Lightspeed of 6.6kohm (6,6000hms) it won't even know it's there. Cheers George Hi George, when you google lightspeed attenuator, there is a black box with the digital read out 18, and what look like an apple remote control, is this your product as well? BTW, nice product, zero physical mechanical contact is the way to go. If you had to spend a $1K for a volume pot this is the way to go and there is still change left! Link to comment Share on other sites More sharing options...
shaky Posted January 13, 2013 Author Share Posted January 13, 2013 Can I sorta answer that for you? The exact name of it escapes me at the moment but its not George's product. According to a review I found in all my searching about the LSA, it uses the similar LDR based volume control but also incorporates switching in it which as George has stated is one of his objectives with the LSA that has been removed. In this review it was noted that the switching is to the detriment of this particular boxes output and so the reviewer preferred the LSA alone. Link to comment Share on other sites More sharing options...
georgehifi Posted January 13, 2013 Share Posted January 13, 2013 (edited) Hi George, when you google lightspeed attenuator, there is a black box with the digital read out 18, and what look like an apple remote control, is this your product as well? BTW, nice product, zero physical mechanical contact is the way to go. If you had to spend a $1K for a volume pot this is the way to go and there is still change left! No that is a clone that does not used QUAD matched NSL32SR2S ("s" stands for "sorted" matched) from what I've can gather it only uses NSL32SR2 and pair matched and I believe it's configured the way my MKI Lightspeed was done years ago. The current MKII Lightspeed Attenuator has vastly superior sound with lower min level and better logarithmic feel to the progression of the volume (led) control. It is also much more costly to make, and the matching process is exponentially more time consuming to do . All MkI I made were recalled and converted to MKII and customers were very happy with the sound and usability improvements. So any S/H on the market of mine are up to date MKII status. Mind you a MKI configured clone will still sound better that any other passive or active pre. Cheers George Edited January 14, 2013 by georgehifi Link to comment Share on other sites More sharing options...
shaky Posted January 14, 2013 Author Share Posted January 14, 2013 You have email George! Link to comment Share on other sites More sharing options...
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