Having done some audition in this regard (we 'switched', if you will pardon the pun, to our custom Shallco part about 15 years ago as a result of some of these auditions), the difference in contacts that George is describing above is clearly audible.
Its my opinion that the volume control is what shoots many preamps down (especially preamps with remote control) before they can even get off the runway. One of the consequences is that the majority of line stage technologies are in a deplorable state- I don't fault anyone for thinking that a passive might be better. |
We are on the same wave length, like I've said on the Lightspeed Attenuator web site. The diode effect with contacts (potentiometers or single leaf switches) is a fact, and I would go further to say, that they are probably the worst component in the signal path.
Even rca's have this problem also, even with their much larger contact areas and tighter fitment, ever wonder why your system sounds better after a good clean up of all your interconnects rca plugs and sockets? Same deal, "diode effect" because of bad contact area contamination.
Cheers George |
Here's an interesting snippet from the latest Stereophile review of the DCS Debussy Dac which has volume control in the digital domain. Yet two stage adjustable analogue level output stage 2v or 6v, this means you can use it straight into a poweramp and only use the top 25% of the digital volume control, this way you should not be "bit striping".
Quote: The differences in sound between the Debussy into a preamplifier and the Debussy directly driving a power amplifier will depend on the preamp's transparency, dynamic capabilities, and overall quality. Sending signals directly to my Musical Fidelity Titan amp from the Debussy or through my reference preamp, a darTZeel NHB-18NS, I heard minimal differences. Given the darTZeel's price of $29,500, that's what you should expect. :Quote
Guess what the Dartzeel uses as a volume control? you guessed it. A Lightspeed setup, they tried to patent when they first released it but I quickly put a stop to it showing proof to the patent offices in Eu and USA that I first did the LDR volume control back in early 1974.
Cheers George
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Interesting comparison between running direct to amp and then via preamp. It appears darTZeel has done a good job implementing LDR technology into their peamp. |
"I quickly put a stop to it showing proof to the patent offices in Eu and USA that I first did the LDR volume control back in early 1974."
Good! |
Quote from the Stereophile Review of the darTZeel NHB-18NS
"For the first time in all audio history," said Delétraz, "the signal path does not pass through any physical switch, relay, or even transistor switch." Instead, inputs are enabled or disabled using electro-optical analog components. Because there is no physical input switch or FET-based analog switch, there is no "diode effect," either electrical or chemical (electrovalence differential), to alter the signal, he explained in an e-mail. Quote
Someone else has found the "diode effect", funny that?
Cheers George |
Apparently not the first time in all audio history:) |
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Lightspeeders, with George's permission I'll be starting a Lightspeed Owner forum on a web site I'm putting up. As soon as I create the forum I'd like for a few of us to run it through the paces to check for bugs. Anyone interested in being a beta tester? Email me offline if you are. |
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I'll email you details on how to sign up. Hopefully, I've configured this thing to be pretty bug free, but it is software so I expect a few hiccups. |
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Sent you an email with instructions. look forward to getting things started. I'll be posting some stuff on their tomorrow. |
Please count me in.
Thanks |
Anthony, did you get my info? |
Just a quick note. Those of you who requested access to the site should have received a confirmation email from me. If you didn't ping me and let me know. All that requested have accounts set-up with the user name and passwords they specified. Have at the forum. |
I really like the thread interface you have on the site, very easy to ride, follow, and edit or preview before finalizing. |
Oh, and congratulations and good luck on the Electra-Fidelity venture ... seems like you will at least have a good time with it, and beyond that, who knows...... |
I'm using a content management tool for the layout and publishing. The forum module was very easy to work with. Not as robust as some other third-party options, but since this is the only forum that will be on the site and I don't expect heavy traffic it works for me.
Electa-Fidelity is a playground. I don't expect much from it. Just wanted to do something fun and interesting with my spare time, as well as try to help a few friends out. Now I guess on occasion I'm going to have to add disclaimers on my posts here. What a PITA. |
I asked this elsewhere but wanted to move this discussion here since it concerns adding an LSA to my system.
I've read a lot here about DAC output impedance and power amp input impedance but less about sensitivity. To give an example, my DAC has an output voltage of 1.75v and my power amp has an input voltage of 2.1v. So that isn't an ideal relationship for passive preamp purposes but my power amp has a continuous rated output of over 500w which I never fully max out. At what point does the difference in the DAC output voltage and power amp input sensitivity become a problem? How does this problem affect the sound? And if you never push your amp to the outerbounds of its volume capabilities, does it really matter?
Interconnects would be pretty short and impedance out (100ohms) and amp impedance in (62k ohms) shouldn't present a problem.
In the other thread, Almarg responded with some good information and estimated that the output/input voltage discrepancy of 0.35v represented a reduction in volume anywhere from 1.3-3.0db, which effectively means reducing my power amp to maybe the 200-400w category, which is undesirable. What are your thoughts? |
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Pubul - Magnepan MMGs. Why does this matter? |
If your speaker are 92db and you have 500 watts, loosing 75% of that power would not be very noticeable even if never driven to max ouput. |
I don't think the output, input shortfall would be heard in your case. I think Anthony was running the Atma-sphere S30 which are not very sensitive for full about, maybe 2.8v - with no apparent gain issues. |
Pubul - I see. So you are saying that I would indeed lose some of the amps output potential due to the mismatch between the voltage output/input gap. Is there a solution to the mismatch other then changing to a different amp or DAC? Can DAC output voltage be increased? (I know it can be decreased by installing a resistor.) |
That is above my pay grade:) I think George could answer the DAC question later today (he is in Australia) - mine has a 2v or 4v switch, but that seems to be fairly uncommon. Yes I do think you would loose some ouput potential, but with your kind of power and your current speaker I'm not sure you would be able to hear any difference. I assume you have a SS amp, I would think the impedance match might be more of an issue than sensitivity (with most, not all SS amps). |
Paul, I'm not certain but I suspect that the reason for the Atma-Sphere S30's high sensitivity number may be that it reflects the voltage DIFFERENCE between the + and - signals at its balanced input, which would be twice the amplitude of either signal. Not sure how its rca input is configured, or if the 3V sensitivity spec is meant to apply to that input as well as to its balanced input.
Also, although I realize you were referring to a 92db speaker just in answer to Jult52's question about "why does it matter," it's worth noting that the MMG's sensitivity is spec'd at 86db/2.83 volts/1 meter, which for its 4 ohm nominal impedance is only 83db/1 watt/1 meter. Although as a planar speaker its acoustic output will fall off relatively slowly as listening distance increases.
Jult52, the only ways that occur to me for stepping up the dac's output voltage would be:
1)Putting an active gain stage somewhere in the path between the dac and the power amp, but of course that would defeat your purpose in using a passive preamp.
2)Modifying the dac internally -- lots of potential issues there.
3)Using some sort of audio step-up transformer -- lots of issues there as well.
Best regards,
-- Al |
Almarg, I suspect you are right, Ralph's spec sheets don't specify single-ended sensitivity specs. So, given a 3db loss, or a 50% reduction in wattage, assuming a worse case scenario, it will seems Jult52 more than sufficient power to drive his speakers VERY loud in most rooms, I assume Maggies are not for headbangers. So, yes there is a slight loss in max power, but do you think it would be relevant? But then again I come from drive my Merlin VSMs with 27-60 watts amps. |
So, yes there is a slight loss in max power, but do you think it would be relevant? My guess is that it would not be a problem, especially considering this statement by Jult52 in the other thread: My power amp has a continuous rated output of over 500w which I never fully max out being a law-abiding middle-aged person :) I like the power for the instantaneous peaks, especially at the onset of sounds and for the feeling of headroom. BTW, my rough estimate of 3db as the amount of the amp's power capability that would become unusable was based on the following: 1)1.3db due to the disparity between dac output voltage and amp input sensitivity. 2)0.5 to 1.0db due to tolerances or possible inaccuracies in those specs. 3)0.5 to 1.0db estimated margin in the recording, between the highest musical peaks and digital full scale. That's what I've actually seen on a number of commercial cd's, that I've analyzed with an audio editing program called Sound Forge. Best regards, -- Al |
All this is not an issue, most amps/speakers are fine.
If you have an amp that is .5 or 1v input for full output sensitivity and 110db speakers, then you my have a problem with having to use the Lightspeed way down on the volume and never being able to go past 8 o'clock on the volume. And an active pre would be even worse in this situation. But this is very rare as most amps are 1.5 to 2v sensitive and most speakers are 93db below.
Cheers George |
I think you'll be fine. Your CD has a good amount of output voltage and your amp isn't too insensitive. You should definitely be able to swing the volume knob past 12 o'clock which is ideal.
I do use my LSA with the S-30 single ended inputs. I've also removed two of the driver tubes and shorted the tube sockets, effectively lowering the gain of the amp 12db. In each case the LSA worked fine. My speakers are rated 92db, but that is conservative. 94 or 95db is probably more accurate. Had they been under 90db I doubt the LSA would have worked well with the S-30. |
George, note that the issue is not whether or not the volume control will have to be used too close to the bottom of its range. The issue is that even with the volume control set to its maximum position, a substantial fraction of the power capability of the amp (perhaps half) will not be able to be utilized. And keep in mind that the gentleman's speakers are relatively insensitive, at 83db/1W/1m.
I doubt it will be a problem, as I indicated, but that is the issue.
Best regards,
-- Al
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Jult52, you have no worries, in fact this is more of an ideal situation (so long as you can get the amp to make satisfying power)- you *want* the amp to have less sensitivity than the maximum level of your source, as this allows you to run the passive volume control at higher levels. The math works more in your favor in this case- you are less likely to loose bass and impact since you will not be running the volume control at a lower level.
When the amp has higher sensitivity, so that your source makes more voltage than you need, then the math works against you; with any passive as you turn the control down more, the more bass and impact is reduced. |
Thanks Ralph is a very important bit of information and affects the advice given for ideal matching, especially since there seems to be a phobia, or worry that turning the volume control to high is somehow stressing the system in some way. As this relates to the M60s, does that suggest that it is best to set their gain at minimum settings based on the same reasoning whether using the LSA or MP-3? |
George, this may have been asked elsewhere in the thread, but I can't find it, is it possible to make a balanced version of the LSA? |
I would say that with this low 83db speaker, your amps input sensivtity would have to be between 1-1.5v to have compatibility with the Lightspeed Design.
But then seeing your amp is beastly 500watt rms, you would never use all this into (I take it their Maggies), so you could afford to loose some., I doubt you would even hit 250watt into them.
Cheers George |
Thank you for the responses and information, gentlemen. It's very much appreciated. To clarify, I have modded Maggies with a sensitivity of about 89 or 90dbs. |
Pubul57, it could well be that there could be some advantage to that, if your speakers have higher efficiency and your sources have plenty of voltage. |
A balanced version could be built and George has a schematic for the design, but he has made it known to me that it is very difficult to properly match the LDRs for operation in balanced mode and the unit would not be as stable. |
thank you Ralph, thank you Anthony. |
any suggestions for a readily available power supply? |
Circuit-Test Electronics RP-1240R-P |
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This is the best battery, it's Lithium-Ion, rechargable (no memory problems) lasts about 12hrs on the Lightspeed before recharge got all the right leads, on/off switch for the Lightspeed an neat sits on top. And cheap.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=320645701036&ssPageName=STRK:MEWAX:IT
Cheers George
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G, have you come to believe that a battery approach sounds battery in some way to walwart? |
Everyone who has bought one, including Sam Tellig from Stereophile has said they think the battery is better than the wall wart I supply with the Lightspeed Attenuator. But it's a small difference, and they cannot say what the differences are, this also includes myself. I think maybe it's psychological perhaps. It cannot be noise as the supplied wall wart into the Lightspeed measures 200uV of noise on the output, that's not mV (millivolt) but uV (microvolt) this is undetectable.
Cheers George |
Well, I'm going to have to try it, Anthony has a link for the battery at his electra-fidelity site. |
The battery I use is the same one the designer of my turntable supplies for the motor pod of the table. It can go days without having to be recharged. In fact I actually went and bought the next model up because it allowed me to run two pieces of equipment on battery power (I have a preamp that could be connected to it too). So far with just the LSA connected I haven't had to recharge it once, and its been 45 days. |
The one on your site is the next model up? |
Oh I forgot. I agree with George. I sensed the sound was different using the battery power supply, but can't really pinpoint exactly what it is except to say that I felt the lower frequencies were affected. I know there was no difference in noise level, at least from what I could tell by just placing my ear next to the speaker. With my Music Reference RM-10 it was dead silent either way. |
