georgehifi said:
George,
You said you can be a "hot head" and I guess that is true given your somewhat angry tone. Calm down.
You seem to feel that every comment is directed as an attack aimed at YOU? My comments are directed at the thread, and the circuit/idea/implementation. The only issue that was directly focused on your posts in specific is the advertising issue.
Now:
1. Addressed? Dunno, having read more of the thread, no matter who started the original thread, you have given a specific commercial pitch, offering to sell product for a specific price... I thought that was not permitted here, but I am not a moderator and only am commenting on that point.
As I said, if this is permitted, I'll perhaps try the same thing and see if I can sell some product too... 😉
2. Obviously the response is not flat to Ghz., if it was I'd be shocked. And my comment on that is not trivial, IF there is some sort of harmonic distortion present, especially if it is non-linear (changing in structure with level) then the response is not "flat" per se, as any deviation in amplitude is actually distortion.
2a. I suggested simple ways to test the response using just a scope and a test signal. Are you going to do that?? Show the results?
Anyone else gonna do it?
3. If yourself and others have tested it, why not put up some data/pix etc?? I have an open mind.
4. I guess we agree about the use of a buffer, but it seems like it might be necessary in many cases to preserve the performance of the LDR unit??
5. George I have not heard any LDRs in an audio circuit since the very early 70s. Have you heard of Lumitron Pots?? 😀 Know what they are?? Very little is new.
If you would like me to hear your product, I'd be happy to audition it and return it in a timely manner, in clean condition. Also, I'd be more than pleased to make truthful comments here or in any other forum or venue about it. If I thought it was wonderful, I'd be more than happy to say so.
Personally, I do not have a predjudiced position on things of this nature, because if I did, I'd never learn or find new things and end up being stuck in the past and static in my life. Over the years I've changed my mind 180 degrees about something audio in quite a few notable cases. Horns are one of them, for example - until I heard a SUPERIOR compression driver I thought that the sound I heard from horns was the horns, it wasn't. Changed my mind completely. So, show me is my approach, back it up, and then I'm happy to adjust my views. If it doesn't stand up to scrutiny... Bah!
I know, you're going to tell me to make one up and report back... which is something I'm giving some thought to - but first we're chatting about it! 😀
Oh, and finally, no matter what people hear - which is all well and good, and important - you've knocked all other means of attenuation, so I want to know what the difference between the LDR and two MF resistors measures! It's fine with me what anyone wants to then use, but at least be accurate and truthful about the existence or lack thereof between the LDR and an objectively reasonable alternative. (if you object to the use of two MF resistors, saying that they don't have a switch or contacts, then your complaint is about the switch (or other contact point) and then we need to examine the switch issue more fully - which you alluded to and made some claims about early on - and see what the significance of that really is or is not. A good direction, imho)
So, George, you may in fact be "on to something" but it is important to separate the underlying problem from a proposed solution/alternative. <--- I think this is the main thrust of my comments so far.
_-_-bear
I had a thought that might be helpful.
For controlling the brightness of LEDs, current control is frequently a better way to go than voltage control...
Consider using a 3pin vreg as a current regulator and keeping the voltage constant?
Fwiw, I suspect that the purity of the LED's control voltage, assuming that the LED can change intensity at high rates (which apparently they do well) will have an effect on the "noise floor" of the LDR attenuator - eventhough the LDR tends to change slowly. Once could test this without too much difficulty using a FFT program and a good soundcard.
Anyone got such a thing?
_-_-bear
For controlling the brightness of LEDs, current control is frequently a better way to go than voltage control...
Consider using a 3pin vreg as a current regulator and keeping the voltage constant?
Fwiw, I suspect that the purity of the LED's control voltage, assuming that the LED can change intensity at high rates (which apparently they do well) will have an effect on the "noise floor" of the LDR attenuator - eventhough the LDR tends to change slowly. Once could test this without too much difficulty using a FFT program and a good soundcard.
Anyone got such a thing?
_-_-bear
Bear you obviously have not read all of this thread, but as for your idea about current control this is one thing at has some merit, and has crossed my mind before, I'm just waiting for a quite time to impliment it to see how it goes, as for now it works perfect as such, but as with anything there is always room for improvment.
As far as the 2nd harmonic distortion goes you need to read some more of the thread, as it is stated that these LDR's I use have a 2H distortion of .1% at the (CD) levels we are using them at, but yes the 1% to 2% 2h can be got, but that is at 50v-100v input, I never said it should be driven with that sort of input, a cd player is lucky to give out 2v peak at the loudest Telarc 1812th canon shot, at this it would be .1% 2h, I challenge you to be able to detect this with your ear.
Cheers George
As far as the 2nd harmonic distortion goes you need to read some more of the thread, as it is stated that these LDR's I use have a 2H distortion of .1% at the (CD) levels we are using them at, but yes the 1% to 2% 2h can be got, but that is at 50v-100v input, I never said it should be driven with that sort of input, a cd player is lucky to give out 2v peak at the loudest Telarc 1812th canon shot, at this it would be .1% 2h, I challenge you to be able to detect this with your ear.
Cheers George
dear George,
No, I have not read every post in the thread.
Most of the posts seem to be questions about implementation details and obtaining parts, and matching them.
If there was a post that addressed the points I raised, I am sure someone would point me to that post. So, it is safe to conclude that none do?
Now, I am thinking more about what you claim to have found in terms of "ringing" with certain switches?
If I recall you stated that you put a very very high speed (rise time) square wave into various switches and found "ringing" on the leading edge. Something about this bothered me, and it festered in the back of my soft gummy head for a while.
What my suspicion is: I think you are are seeing not "ringing" from the switch, but a reflection due to an impedance mismatch - a common occurance with extremely high speed signals.
I don't think that the "switch contacts" are actually doing anything at all except presenting a mismatched load at some VHF or UHF frequency.
Given that my DAC presents absolutely NOTHING above 100kHz for certain (we can debate out of band noise below that frequency if you wish), the possibility of this being an issue is lowered to next to zip?
Oh... and if it is a VHF or UHF "ringing" of this low level, how pray tell does that effect anything in the audio band?? Just wondering.
Dear George, as far as "detecting" 0.1% distortion - I think you'd be rather flabbergasted and flustered if you came here an listened to my system by what you can detect without difficulty. There is little difficulty detecting differences in amplifiers for example. DACs, transports no problem. Level matched, and all that, blah blah blah...
That's not to say that I could or one could definitely detect ur LDR attenuator or not. I do not know until it is tried.
You also avoided mentioning if you know about Lumitron Pots or not?? Yes? No?
Regardless, there is nothing wrong with people trying and working with these LDRs. If they add some nice even order harmonics, that is a neat feature which will help many systems be more enjoyable to listen to.
However the assertion that high quality stepped attenuators are lower in quality than ur LDR for the reasons you gave needs to be addressed. I do not think that this assertion can stand. (btw, I agree (for other reasons) that single point contacts are not good.)
_-_-bear
No, I have not read every post in the thread.
Most of the posts seem to be questions about implementation details and obtaining parts, and matching them.
If there was a post that addressed the points I raised, I am sure someone would point me to that post. So, it is safe to conclude that none do?
Now, I am thinking more about what you claim to have found in terms of "ringing" with certain switches?
If I recall you stated that you put a very very high speed (rise time) square wave into various switches and found "ringing" on the leading edge. Something about this bothered me, and it festered in the back of my soft gummy head for a while.
What my suspicion is: I think you are are seeing not "ringing" from the switch, but a reflection due to an impedance mismatch - a common occurance with extremely high speed signals.
I don't think that the "switch contacts" are actually doing anything at all except presenting a mismatched load at some VHF or UHF frequency.
Given that my DAC presents absolutely NOTHING above 100kHz for certain (we can debate out of band noise below that frequency if you wish), the possibility of this being an issue is lowered to next to zip?
Oh... and if it is a VHF or UHF "ringing" of this low level, how pray tell does that effect anything in the audio band?? Just wondering.
Dear George, as far as "detecting" 0.1% distortion - I think you'd be rather flabbergasted and flustered if you came here an listened to my system by what you can detect without difficulty. There is little difficulty detecting differences in amplifiers for example. DACs, transports no problem. Level matched, and all that, blah blah blah...
That's not to say that I could or one could definitely detect ur LDR attenuator or not. I do not know until it is tried.
You also avoided mentioning if you know about Lumitron Pots or not?? Yes? No?
Regardless, there is nothing wrong with people trying and working with these LDRs. If they add some nice even order harmonics, that is a neat feature which will help many systems be more enjoyable to listen to.
However the assertion that high quality stepped attenuators are lower in quality than ur LDR for the reasons you gave needs to be addressed. I do not think that this assertion can stand. (btw, I agree (for other reasons) that single point contacts are not good.)
_-_-bear
Sorry, say what?
I presume that is meant as some sort of insult... nice.
What is ur position on the alleged switch "non-linearities" that were reported in this thread?
Let's let all assertions of "magic" and causality go unchallenged?
Is that ur position, serengetiplains?
hmmmm...
_-_-bear
I presume that is meant as some sort of insult... nice.
What is ur position on the alleged switch "non-linearities" that were reported in this thread?
Let's let all assertions of "magic" and causality go unchallenged?
Is that ur position, serengetiplains?
hmmmm...
_-_-bear
Contacts
Bear,
I got to agree with you here on the contacts. The Lightspeed has none, this to me limits my sources to one.
I switched to 4 pole selectors a while back. This way there is are paralleled contacts. May not be as good as none, but a whole lot better than just one.
You might like the shunt stepped attenuators you are using. But the LDR's are very good also. The distortion levels mentioned are only at peak levels. Most loudspeakers are running a couple orders of magnitude higher distortions and non linearities once things start to get LOUD.
My suggestion, try a set of LDR's inplace of the SA. I think you will find them just as good, maybe better.
As far as supply voltage for LED's. The light source has a slow time constant. I think a good 3 pin reg with decoupling on output is fine. But I will try adding an inductor to see if it smoothes things out. This will kill any hf nastries.
George
Bear,
I got to agree with you here on the contacts. The Lightspeed has none, this to me limits my sources to one.
I switched to 4 pole selectors a while back. This way there is are paralleled contacts. May not be as good as none, but a whole lot better than just one.
You might like the shunt stepped attenuators you are using. But the LDR's are very good also. The distortion levels mentioned are only at peak levels. Most loudspeakers are running a couple orders of magnitude higher distortions and non linearities once things start to get LOUD.
My suggestion, try a set of LDR's inplace of the SA. I think you will find them just as good, maybe better.
As far as supply voltage for LED's. The light source has a slow time constant. I think a good 3 pin reg with decoupling on output is fine. But I will try adding an inductor to see if it smoothes things out. This will kill any hf nastries.
George
Let me just thank George again for offering this design here. I have built one and am enjoying it. I also have a Promethius transformer based passive. They both have very good clarity, imaging, and stage. But the LDR pre is head and shoulders above it by having dynamics. A heart and soul if you will. It actually reminds me of a very good tube preamp with better definition. Just my personal observations.
Hi Bear,
your technical queries may have some technical merit
but generally I think if you appear to critisise a device that you have not heard then you may well attract critisism to you.
I am not critisicing you but also I am not paying much attention to your viewpoint because you have not heard Georges product and so for me your words do not have much authority.
If you bought or made one of these items it may be you think it is the best volume control u ever heard or you may not like it. But before you hear it, the truth is, you just don't really know
cheers
mike
your technical queries may have some technical merit
but generally I think if you appear to critisise a device that you have not heard then you may well attract critisism to you.
I am not critisicing you but also I am not paying much attention to your viewpoint because you have not heard Georges product and so for me your words do not have much authority.
If you bought or made one of these items it may be you think it is the best volume control u ever heard or you may not like it. But before you hear it, the truth is, you just don't really know
cheers
mike
serengetiplains said:
serengetiplains said:
Bear your going off half cocked again, do a bit of research first, take the time do a search on the diode effect on ac music signal of contacts by many well regarded people like the above Herve Deletraz, and the very knowledgable Frank de Grove a highly respected Aussie Peter Stein of ME Electronics and Mark Porzilli of Melos who made the Lightspeed a commercial concern in their top pre the SHA-Gold Reference in the 90's.
Then make one for yourself and judge it, then you will have the right to criticise it, until then you have no right.
Cheers George
georgehifi said:
george,
I've had enough at this point.
You've ignored the focus of my comments.
Refused direct inquiry about the facts and measurements of your "Lightspeed a new passive preamp". Which apparently isn't new at all.
Ignored my inquiry about your knowledge of the existence of the Lumitron pot which predates your "new" passive volume control by ummm almost 50 years??
And now you make false assumptions about what I said about contacts and call me going off "half cocked"??
I said that I agreed with you about point contacts, didn't I?
Perhaps you failed to read that - so I have restated it.
I asked about YOUR claims of testing and seeing a "ringing" at what you - iirc- claimed was a very high frequency.
Over and over you've attributed things to causalities that may or may not be correct. All that I have done is to suggest that some despositive tests would be in order before making such claims. Or to offer alternitive thesis.
Something wrong with that??
Fwiw, the "switches" that I use for my descrete stepped L attenuator and for the "function/selector" switch are of the LARGE surface area/ CONTACT WIPING TYPE. These are not point contact switches and if used at all, will have nil oxide build up. They are designed that way.
I have NOT at any time "criticized" the sound of your commercial product - I have asked specific questions about the design, the theory, the claims and the measurements, as well as the causalities that you attribute to all other switches being inferior. So get off it.
Now, I started to read the thread because of the provocative claim explicit in the title of the thread itself: "Lightspeed Attenuator a new passive preamp" Instead I find something that is NOT new, and perhaps problematic in some regards. So I ask questions.
Apparently you prefer people to follow religiously, and you do not take well to answering reasonable and specific questions.
Thus ends productive discussion, I regret.
_-_-bear
PS. for the others participating in the thread, I have "no dog in this fight" - if you wish to build something, build it. I have not criticized the SOUND of the unit - per above. I don't know about the sound. Personally I want an attenuator that is invisible, no sound. You are free to chose what you wish. I am free to question claims that sound dubious. That's the nature of a technical forum, even one for Diyers.
It is perfectly reasonable to engage in an informed discussion of a design without building it - if eveyone had to build something before discussion takes place here, precious few would be participating and much quality and useful information and ideas would never surface. Please read what I write, and don't read into it something that is not on the page. Thank you.
Alright then, back to unproductive discussion about this rather old technology.
One of the first things I noticed about this unit's sound is the reduced HF edge. Has anyone else had a similar experience? Prior to using the Lightspeed, my best guess at pinpointing the source of that edge was thinking it might be jitter or line noise. I'd made considerable progress on both fronts, but the Lightspeed opened a new window in reducing edge.
One of the first things I noticed about this unit's sound is the reduced HF edge. Has anyone else had a similar experience? Prior to using the Lightspeed, my best guess at pinpointing the source of that edge was thinking it might be jitter or line noise. I'd made considerable progress on both fronts, but the Lightspeed opened a new window in reducing edge.
serengetiplains said:
sorry if I missed it earlier but what was your previous pre-amp arrangment ?
cheers
mike
serengetiplains said:
Tom that's the imedeate thing that stikes you first off when you hear it for the first time, it's as though the digital glare has been removed in the high frequencies and the top end has become more transparent and natural. But then after that the rest of the frequency range also is noticable, but the highs are the first thing you hear.
I did proved on the bench with the megabuck digital/storage cro that I borowed, the contact bounce (rectification) is more pronouced at high frequency transients (faster vpms rise time) on pots and cheap switches, that this is why most people that hear it say the highs are so clean and transparent, they didn't think it possible digital could have top end like it gives with the Lightspeed.
(watch Bear jump on this one)
Cheers George
mikelm said:
Mike, I've been playing around with several preamps over the years including a Placette Vishay unit. My references pre Lightspeed were an Audio Consulting TVC and an Emm Labs Switchman modified to excellent effect by adding a Schottky bridge, Black Gate storage caps and large value (many uF) teflon bypa$$es.
I was hoping Bear would come back, start a thread and share his "secret circuit tricks" for his Super Phono Stage.🙄
georgehifi said:
That makes only sense if you don't use source selector, do you?
serengetiplains said:
I don't know about your Placette, but mine was not using Vishay resistors but Alpha resistors. I've built a version of Placette with nude Vishays and it sounded completely different that the original Placette, but still not completely transparent.
I use S&B TX102 and it does not have any "HF edge" which I cannot say was the same with silver version of that passive attenuator.
Peter, the Placette was Vishay and the AC TVC was less edgy than a copper TVC I tried, that's for sure. As to a TVC (or any component whatever, for that matter) that "does not have any HF edge," let's define our terms. By "edge" I mean that grating sound of a poorly recorded CD, which grate I hear on even the best of my recordings, but now markedly attenuated with the LDR unit in place.
George, the Lightspeed handily beat the Switchman, in my musicworld. The Switchman, despite its naming, *has no switches.* Meitner, for his part, thought switches and line level signals do not mix, so specifically designed the preamp (including his DCC2, which I owned) around a switchless volume control. The problem, I always felt, was that pesky cord that connected the unit to the wall.
George, the Lightspeed handily beat the Switchman, in my musicworld. The Switchman, despite its naming, *has no switches.* Meitner, for his part, thought switches and line level signals do not mix, so specifically designed the preamp (including his DCC2, which I owned) around a switchless volume control. The problem, I always felt, was that pesky cord that connected the unit to the wall.
Peter Daniel said:
Hi, Pete
Guilty as charged, I do use a 2 input source switch on my Lightpseed prototype, it's a DPDT 2A 240v toggle with gold plated contacts. Yet when I put on the production Lightspeed's that have no input switching for final listening tests before being shipped, you can always detect that they seam cleaner again.
This is why I say to customers it's better to have a QED 3 or 5 source switch box that has a silver plated alps rotary switch for source switching, then if you want to get serious disconect the QED and go direct into the Lightspeed.
Cheers George