Looking for passive volume regulator (passive preamp) recommendations - AVS Forum
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post #1 of 63 Old 03-31-2012, 07:03 AM - Thread Starter
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Would be interesting to know what audiophiles use for any kind of passive volume regulator-passive preamp to connect source directly to power amp inputs.
I have read about Lightspeed, Axiom Audio Luminous, Goldpoint SA series, Akustyk, NVA (nene valley audio), Tisbury Audio, not sure which would make sense keeping in mind their differences/limitations.
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post #2 of 63 Old 03-31-2012, 08:25 AM
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The George HI-Fi Lightspeed Attenuator may be what you are referring to; good one.

There are a lot of technical issues to be considered, of course. One of the major functions of a preamplifier is to provide impedance matching and isolation between the source and amplifier, which a passive unit does not do. A passive unit changes the loading on the source and the impedance matching every time you adjust the volume setting which is not ideal. Using one these is a bad idea without very carefully considering the impedances of the source and amplifier and analyzing the interaction.

In general, they usually do not work out very well for those reasons. You really need to look at the precise internal design of each one and consider the input impedance of your amplifier and output impedance of each source in relation to that.

Among the less expensive decent preamps on the market are the Vincent SA-31, which is only $700 and quite good, and the Conrad-Johnson Classic for $2000. You may want to consider them.

I can also highly recommend the Audio Research LS-17 preamp which is Excellent, and the LS-27 (I have the LS-26, which is basically the same), which is the best-sounding preamp I have ever heard for under $10k.



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Originally Posted by bordo32 View Post

Would be interesting to know what audiophiles use for any kind of passive volume regulator-passive preamp to connect source directly to power amp inputs.
I have read about Lightspeed, Axiom Audio Luminous, Goldpoint SA series, Akustyk, NVA (nene valley audio), Tisbury Audio, not sure which would make sense keeping in mind their differences/limitations.

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post #3 of 63 Old 03-31-2012, 10:03 AM
 
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Originally Posted by bordo32 View Post

Would be interesting to know what audiophiles use for any kind of passive volume regulator-passive preamp to connect source directly to power amp inputs.
I have read about Lightspeed, Axiom Audio Luminous, Goldpoint SA series, Akustyk, NVA (nene valley audio), Tisbury Audio, not sure which would make sense keeping in mind their differences/limitations.

You don't have to spend a lot to get this function.
http://www.smproaudio.com/index.php/...lers/nanopatch
http://www.smproaudio.com/index.php/...ollers/mpatch2
http://adesignsaudio.com/products/at...eo-attenuator/
http://www.audioplex.com/ISV1.htm
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post #4 of 63 Old 03-31-2012, 11:43 AM
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I've used most styles of passive attenuator except the Lightspeed - simple pots, stepped switch, stepped relay (several variants of both) and transformers (S&B TX102). Properly designed and implemented, they should all be transparent, but depending upon what you're putting them between and what and how you use to attenuate, they can (doesn't mean they will though) cause audible effect.

In all honesty, I see no reason not to use a simple buffer like the Pass B1 as it neatly sidesteps any issues. If interested in DIY or electronics this would make a great first project and probably could be made in a nice case for under $250 and some sweat.
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post #5 of 63 Old 04-01-2012, 07:03 AM
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One of the major functions of a preamplifier is to provide impedance matching and isolation between the source and amplifier,

We stopped impedance matching in pro audio over 40 years ago, consumer audio systems have never been impedance matched. A preamp doesn't do this, nor is it meant to.
It doesn't provide isolation either, it actually connects your source to the amplifier, otherwise you wouldn't hear anything.

Quote:


A passive unit changes the loading on the source and the impedance matching every time you adjust the volume setting which is not ideal.

A variable voltage divider, or volume control, presents a fixed impedance to the source.

Quote:


Using one these is a bad idea without very carefully considering the impedances of the source and amplifier and analyzing the interaction.

You don't have to consider impedance at all, there is no matching.

Quote:


In general, they usually do not work out very well for those reasons. You really need to look at the precise internal design of each one and consider the input impedance of your amplifier and output impedance of each source in relation to that.

You need to read up on modern audio equipment, you're hung up on something that doesn't exist.
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post #6 of 63 Old 04-01-2012, 07:55 AM - Thread Starter
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Thanks for your comments, a lot of interesting info.
Based on my system components input/output signal levels and impedances, I think I have a good chance to have good matching approach for passive volume regulator. Need to find out what is better, shunt resistor approach, or regulator potentiometer/switch based three pin divider as in many systems.

Commsysman, your recommend preamps or tube based, are not allowing to pass an audio without adding distortions. I agree that they sound nice, working as a harmonizers as well. My goal is to have as minimal as possible processing and keep an audio signal as neutral as passible. In that way it sounds the best on my system. I tried this already.
I am using tube based DAC (Paul’s designed PreDAC, and I feel sorry, Paul has passed last week, so big loss) with passive volume regulator running outputs straight to power amp. So I know how tube based preamps affecting the sound.

As Pass B,1 recommend by A9X-308 could be a very good option, even would still require a passive volume regulator and all my questions above would apply. The problem with this, as well as with it’s clones, that it is DIY project. This preamp is not available to buy in a nice looking case as finished product. It is rare to find on audiogon or other places. I can go for DIY, have extensive experience doing that, but I want a shorter path, find what is already available. But if nothing will be avaiolbe I will need to get on to DIY path, starting from finding a good, decent looking case and smooth motion multi position switch.

Diomania, thanks for point in to several interesting options, I will research them more.
Can you share your experience trying a passive regulator, which model?

SAM64, thanks for good comments. In case of shunt resistor based regulator, the load impedance to source would change, especially if I would need to keep low resistance of shunt regulator in order to have low impedance, acting as volume regulator output impedance applied to power amp input.
But in my case, when the audio source output impedance is in 50 Ohms range and input impedance of power amp of 25 kOhms, I may get a matching solution if shunt regulator would have 2.5 kOhms resistance or so.
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post #7 of 63 Old 04-01-2012, 10:09 AM
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Quote:
Originally Posted by bordo32 View Post

Would be interesting to know what audiophiles use for any kind of passive volume regulator-passive preamp to connect source directly to power amp inputs.
I have read about Lightspeed, Axiom Audio Luminous, Goldpoint SA series, Akustyk, NVA (nene valley audio), Tisbury Audio, not sure which would make sense keeping in mind their differences/limitations.

I like the placette passive line stage. I moved to this from my old preamp (a DIY bottlehead with Mullard cv4003 tubes and stepped attenuators). Love the way it sounds.
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post #8 of 63 Old 04-01-2012, 10:12 AM
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Those are some breathtakingly incorrect statements, as any audio engineer is well aware.

When you get your Master's degree in electrical engineering and have 40 years of teaching and circuit design experience, as I have, we can have a nice talk about this. Until then YOU have a very long way to go before you even understand the fundamentals of the subject at hand; your comments make that quite clear.






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Originally Posted by SAM64 View Post

We stopped impedance matching in pro audio over 40 years ago, consumer audio systems have never been impedance matched. A preamp doesn't do this, nor is it meant to.
It doesn't provide isolation either, it actually connects your source to the amplifier, otherwise you wouldn't hear anything.
A variable voltage divider, or volume control, presents a fixed impedance to the source.
You don't have to consider impedance at all, there is no matching.
You need to read up on modern audio equipment, you're hung up on something that doesn't exist.

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post #9 of 63 Old 04-01-2012, 11:01 AM
 
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Quote:
Originally Posted by bordo32 View Post

Can you share your experience trying a passive regulator, which model?

I did a diy version using Alps 100K potentiometer. I put a 10K Ohm resistor in front of it in series and it works well for me.
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post #10 of 63 Old 04-01-2012, 01:12 PM
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Quote:
Originally Posted by bordo32 View Post

Would be interesting to know what audiophiles use for any kind of passive volume regulator-passive preamp to connect source directly to power amp inputs.
I have read about Lightspeed, Axiom Audio Luminous, Goldpoint SA series, Akustyk, NVA (nene valley audio), Tisbury Audio, not sure which would make sense keeping in mind their differences/limitations.


Hi Bordo,
I was in your shoes about 1yr ago looking for a passive preamp to connect my CD to my tube amp. I wanted the most transparent sounding passive preamp as possible. After doing some research I found that the Lightspeed from Australia uses light rather than physical contacts to change the amount of attenuation. This places fewer parts in the signal path and as a result it is a fabulous device. You order it directly from the manufacturer in Australia who takes PayPal, costs about $450, comes with 1 pair of RCA inputs and outputs, and usually takes 2-4 weeks wait. You might wish to learn more here:
http://forum.audiogon.com/cgi-bin/fr...up&1181&4#1181

For a good match in a system, the Lightspeed Attenuator should see:
1) A CD player or DAC that has an output impedance of less than <1kohm (1,000 Ohms)
2) The poweramp should have an input impedance of more than >47kohms (47,000 Ohms)
3) Interconnect cable with a low capacitance (below around 150pf [picofarad] per foot )

Hope this helps . . .
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post #11 of 63 Old 04-01-2012, 03:33 PM
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Quote:
Originally Posted by commsysman View Post

Those are some breathtakingly incorrect statements, as any audio engineer is well aware.

When you get your Master's degree in electrical engineering and have 40 years of teaching and circuit design experience, as I have, we can have a nice talk about this. Until then YOU have a very long way to go before you even understand the fundamentals of the subject at hand; your comments make that quite clear.

False, false, and false.

For every new thing I learn, I forget two things I used to know.
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post #12 of 63 Old 04-01-2012, 04:14 PM
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Quote:
Originally Posted by commsysman View Post

Those are some breathtakingly incorrect statements, as any audio engineer is well aware.

When you get your Master's degree in electrical engineering and have 40 years of teaching and circuit design experience, as I have, we can have a nice talk about this. Until then YOU have a very long way to go before you even understand the fundamentals of the subject at hand; your comments make that quite clear.


Breathtaking, indeed.
You cannot refute my statements, instead you wave you're 'internet credentials' around, LOL.
You're 'internet credentials' are worth nothing, and your statements about impedance indicate that you've been out of the loop for decades.
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post #13 of 63 Old 04-01-2012, 05:28 PM
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Quote:
Originally Posted by bordo32 View Post

TI am using tube based DAC (Paul's designed PreDAC) with passive volume regulator running outputs straight to power amp.
[snip]
But in my case, when the audio source output impedance is in 50 Ohms range and input impedance of power amp of 25 kOhms, I may get a matching solution if shunt regulator would have 2.5 kOhms resistance or so.

Is this your source? Says it's got a VC already, so why are you asking now?

Very dubious if so about the 50R Zout, as even with a parallel 12AU7 cathode follower you'd be 3 times that, and it definitely isn't going to like a 2k5 AC load.
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post #14 of 63 Old 04-01-2012, 07:40 PM
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You want Bent Audio, they have modular approach with nice casing and remote.
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post #15 of 63 Old 04-01-2012, 07:43 PM - Thread Starter
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No, my sources are Cambridge Azure 840C CD player and Oppo 95 universal player. I have mentioned PreDAC as an example that I am familiar with the simple tube based preamp and passive reagulators. It was regarding Commsysman's recommendations on tube based pre amps. Sorry for confussion.
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post #16 of 63 Old 04-01-2012, 08:24 PM
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Quote:
Originally Posted by bordo32 View Post

No, my sources are Cambridge Azure 840C CD player and Oppo 95 universal player. I have mentioned PreDAC as an example that I am familiar with the simple tube based preamp and passive reagulators. It was regarding Commsysman's recommendations on tube based pre amps. Sorry for confussion.

Hi Bordo,
I mentioned the Placette Passive Line Stage a few posts ago. I am also using the dedicated stereo output of the Oppo 95 with the placette and very pleased. The amps are Citation 7.1. I was initially worried about the impedance matching and it has turned out to be a non-issue. Hope this helps.
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post #17 of 63 Old 04-01-2012, 10:09 PM
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Quote:
Originally Posted by SAM64 View Post

...
You don't have to consider impedance at all, there is no matching.
....

While that is correct, no impedance matching, output and input impedance must be considered if a passive preamp or such a device is used.

Hayward, James 'Beating the Bafflegab & Filtering the FooFooDust,' Part 1- Marshall's Audio Ideas Guide(Canada) Summer/Fall 94

Very interesting analysis of what an interconnect can do when the passive output impedance is, let's say about 63kOhms. A low capacitance speaker cable can roll off your high frequencies at 18kHz by 3 dB and a high cap cable will do this as low as 2.7 kHz. Maybe that is why some like passive preamps?
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post #18 of 63 Old 04-02-2012, 05:24 AM
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Originally Posted by commsysman View Post

When you get your Master's degree in electrical engineering and have 40 years of teaching and circuit design experience, as I have, we can have a nice talk about this. Until then YOU have a very long way to go before you even understand the fundamentals of the subject at hand; your comments make that quite clear.

I've got similar educational credentials, and 52 years experience of designing and building audio gear, some of which has been marketed.

I think my following comments have useful weight in this discussion. ;-)

Here are the statements that you took exception to:

Quote:
Originally Posted by SAM64 View Post


(1) We stopped impedance matching in pro audio over 40 years ago, consumer audio systems have never been impedance matched. A preamp doesn't do this, nor is it meant to.

(2) It doesn't provide isolation either, it actually connects your source to the amplifier, otherwise you wouldn't hear anything.

(3) A variable voltage divider, or volume control, presents a fixed impedance to the source.

(4) You don't have to consider impedance at all, there is no matching.

(5) You need to read up on modern audio equipment, you're hung up on something that doesn't exist.

(1) is true as far as it goes. However, tubed equipment is a different animal than SS equipment. You don't need to match impedances with it, but as its source impedance is generally high by modern standards, you have to take it into account. So while impedance matching is obsolete even for tubed equipment, considering the high source impedance is very relevant.

(2) Looks like hair splitting to me. A preamp does isolate the source from the load, even though it doesn't isolate the load from the source if the volume setting results in passing any signal at all.

(3) Is mostly true unless the load impedance is on the same order or smaller than the impedance of the attenuator. Unfortunately, with high source impedances, the load may have the same or lower impedance than the attenuator, in which case it can load down the source for the attenuator when the attenuation less than about 10 dB.

(4) may be wrong in this particular case because we are dealing with sources that are tubed equipment. Note that it is possible to build tubed equipment with decently low source impedances - often its as simple as one of the simplest circuits in the world - the cathode follower.

(5) Unfortunately, we're not dealing with modern equipment.

That all said, unless we find that the tubed equipment that is part of this system is designed to drive low impedances, which may or may not be true, it is best to be very wary of using modern attenuators that are designed to work with SS equipment.
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post #19 of 63 Old 04-02-2012, 06:03 AM
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(5) Unfortunately, we're not dealing with modern equipment.

Are we dealing with 600 Ohm, impedance matched, +8dBm equipment here?
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post #20 of 63 Old 04-02-2012, 06:11 AM
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What I was trying to point out was that a preamplifier has a fixed high input impedance, typically 50k ohms, regardless of the volume setting, and thus puts a fixed high impedance across the the source component, isolating it from the amplifier input impedance.

It also typically has a fixed low output impedance, typically 600 ohms or so, enabling it to put out a relatively constant voltage to the amplifier regardless of whether the input impedance of the amplifier is 1.5K ohms or 47K ohms (both of which I have had in my amplifiers).

This is what I meant by "impedance matching"; a high input impedance input and a low output impedance, appropriate to the connected circuits. I was not implying the sort of true impedance matching that is done when matching an amplifier to a speaker (for maximum power transfer), or a transmitter to an antenna.

A fixed attenuator does not provide this sort of high input impedance and isolation, and there are pitfalls and problems that do occur when using them. This has been discussed over and over in articles in the audio press where these devices have been tested and reviewed, and I assumed some of this knowledge was common and did not need to be explained in detail. I did not realize I was speaking to some people with such a limited knowledge base, or I would have been more detailed and explicit to prevent misunderstandings.

BTW; As far as I can tell, the Cambridge 840 and OPPO BDP-95 players are still being sold, so why aren't we dealing with modern equipment here??

Also, as an aside, IMO the OPPO-BDP-95 has redefined the state-of-the-art in CD and SACD playback. My Ayre C5xe/MP, which WAS the gold standard for CD playback (and costs $6k), is noticeably surpassed by its performance. I personally think that it makes every player over $1000 obsolete. The companies that make those expensive units must be in a state of shock.





Quote:
Originally Posted by arnyk View Post

I've got similar educational credentials, and 52 years experience of designing and building audio gear, some of which has been marketed.

I think my following comments have useful weight in this discussion. ;-)

Here are the statements that you took exception to:



(1) is true as far as it goes. However, tubed equipment is a different animal than SS equipment. You don't need to match impedances with it, but as its source impedance is generally high by modern standards, you have to take it into account. So while impedance matching is obsolete even for tubed equipment, considering the high source impedance is very relevant.

(2) Looks like hair splitting to me. A preamp does isolate the source from the load, even though it doesn't isolate the load from the source if the volume setting results in passing any signal at all.

(3) Is mostly true unless the load impedance is on the same order or smaller than the impedance of the attenuator. Unfortunately, with high source impedances, the load may have the same or lower impedance than the attenuator, in which case it can load down the source for the attenuator when the attenuation less than about 10 dB.

(4) may be wrong in this particular case because we are dealing with sources that are tubed equipment. Note that it is possible to build tubed equipment with decently low source impedances - often its as simple as one of the simplest circuits in the world - the cathode follower.

(5) Unfortunately, we're not dealing with modern equipment.

That all said, unless we find that the tubed equipment that is part of this system is designed to drive low impedances, which may or may not be true, it is best to be very wary of using modern attenuators that are designed to work with SS equipment.

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post #21 of 63 Old 04-02-2012, 06:25 AM
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This is what I meant by "impedance matching"; a high input impedance input and a low output impedance, appropriate to the connected circuits.

I would have hoped that someone with such great internet credentials, and over 45 years of teaching experience would be familiar with the correct terminology.
What you described is called 'bridging'....this has been common for the past 40 years or more.

Quote:


I did not realize I was dealing with people with such a limited knowledge base, or I would have been more detailed and explicit.

LOL...I didn't realise you were so arrogant....yet uninformed.
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post #22 of 63 Old 04-02-2012, 06:47 AM
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If you use the term "bridging" around here, I don't think you will be properly understood by most people; that's why I didn't use it. It can be used in several different contexts in electronics, all of which I am quite familiar with, since I have lectured on them in my engineering courses for many years.

It is nice that you have an opinion; I will just let the knowledgeable sort out who is right and who is wrong. I think that will take care of it.





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Originally Posted by SAM64 View Post

I would have hoped that someone with such great internet credentials, and over 45 years of teaching experience would be familiar with the correct terminology.
What you described is called 'bridging'....this has been common for the past 40 years or more.



LOL...I didn't realise you were so arrogant....yet uninformed.

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post #23 of 63 Old 04-02-2012, 08:00 AM
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If you use the term "bridging" around here, I don't think you will be properly understood by most people; that's why I didn't use it.

So, you used the wrong terminology out of fear of being misunderstood?

You're back peddling

Quote:


It is nice that you have an opinion; I will just let the knowledgeable sort out who is right and who is wrong. I think that will take care of it.

I think so too, sorry to have embarrassed you.
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post #24 of 63 Old 04-02-2012, 02:41 PM
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I used a DIFFERENT terminology to communicate more clearly, not the "wrong' terminology. When a word can be interpreted several ways, it is often better to choose a different terminology that is clear and unambiguous. There is nothing "wrong" about choosing the best words for effective communication. As I clearly stated, the term "bridging" can refer to several different things and its ambiguity therefore makes it a poor choice for effective communication.

Educated people spell it "pedaling" ...as in "pedaling" a bicycle (which is where that expression "back-pedaling" came from; it refers to moving the pedals backwards to activate the "coaster brake" that bicycles used to have).

"Peddling" is selling something on the street or door-to-door etc.

I am not embarrassed at all, and have no reason to be, so don't concern yourself.

Don't worry about spelling words wrong all the time either; literacy is a rare thing these days, it seems.




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So, you used the wrong terminology out of fear of being misunderstood?

You're back peddling



I think so too, sorry to have embarrassed you.

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post #25 of 63 Old 04-02-2012, 02:58 PM - Thread Starter
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jmcomp124, thanks for your recommendations. Well even Placette is a very nice -fine piece of equipment, my system upgrade philosophy does follows the rule that the volume regulator, price wise, should not be close to the source equipment price. It is a bit out of my price range (more than $1000 or so).

I am still looking for other here proposed options, communicating with Axiom Audio Luminous designer to understand what would be proposed resistor/shunt volume regulator values for my system, to understand if I have enough headroom to have input/output resistance in a good matching ratio.
I do not want to load my source outputs too much and have elevated distortions; as well I want to have low enough volume regulator output resistance to guarantee good low frequency range.
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post #26 of 63 Old 04-02-2012, 05:27 PM
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Originally Posted by bordo32 View Post

jmcomp124, thanks for your recommendations. Well even Placette is a very nice -fine piece of equipment, my system upgrade philosophy does follows the rule that the volume regulator, price wise, should not be close to the source equipment price. It is a bit out of my price range (more than $1000 or so).

I am still looking for other here proposed options, communicating with Axiom Audio Luminous designer to understand what would be proposed resistor/shunt volume regulator values for my system, to understand if I have enough headroom to have input/output resistance in a good matching ratio.
I do not want to load my source outputs too much and have elevated distortions; as well I want to have low enough volume regulator output resistance to guarantee good low frequency range.

Lightspeed again. It's purer than a resistor-based vol and costs less than the Placette. Have you looked it up?
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post #27 of 63 Old 04-02-2012, 07:10 PM - Thread Starter
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Kevinzoe, thanks for pointing out the Lightspeed.
I looked already in to it. Few things are worrying me.
The design of the case/chassis, overall how it looks, not so attractive design (it could be just my preference) at least what I see on the pictures. No XLR in/outs, no few inputs switching capabilities.
I have read on silonex dooth com that the opto resistors based attenuators have some distortions; they are not completely passive and linear devices. It appears that the opto cell variable resistance, which is dependent of the light intensity from LEDs, is not linear. Its resistance could be modulated by the voltage drop across it. The non-linearity is proportional to the voltage. It is discussed on diyAudio doth com forums, where the Lightspeed designer George is aware about this and admits the distortion existence.

At the very last point I may need to go ahead, order the decent looking box/case and build it as DIY volume regulator.
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post #28 of 63 Old 04-02-2012, 11:06 PM
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Quote:
Originally Posted by bordo32 View Post

jmcomp124, thanks for your recommendations. Well even Placette is a very nice -fine piece of equipment, my system upgrade philosophy does follows the rule that the volume regulator, price wise, should not be close to the source equipment price. It is a bit out of my price range (more than $1000 or so).

I am still looking for other here proposed options, communicating with Axiom Audio Luminous designer to understand what would be proposed resistor/shunt volume regulator values for my system, to understand if I have enough headroom to have input/output resistance in a good matching ratio.
I do not want to load my source outputs too much and have elevated distortions; as well I want to have low enough volume regulator output resistance to guarantee good low frequency range.

The Placette with the BDP-95 is a combo I hope to keep for a long time. I can reassure you, this is a beutiful combo. If you watch audiogon there are used ones that come up for under $1K.
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post #29 of 63 Old 04-03-2012, 05:31 AM
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Originally Posted by kevinzoe View Post

Lightspeed again. It's purer than a resistor-based vol and costs less than the Placette. Have you looked it up?

I'm curious about the sense in which a LDR-based attenuator would be purer than one based on plain old ordinary resistors.

I can tell you for sure that when it comes to nonlinear distortion in the audio range, LDR's are pretty dirty.

I've worked with them extensively. Once upon a time (30 years ago) they were used in audio for things like compressors or limiters but they were replaced by active solutions (VCAs) in the interest of lower distortion.

Resistors have no peers or superiors other than copper (or other highly linear, conductive metal) wire.

Looks to me like yet another audiophiel myth!
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post #30 of 63 Old 04-03-2012, 05:33 AM
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Quote:
Originally Posted by bordo32 View Post

I have read on silonex dooth com that the opto resistors based attenuators have some distortions; they are not completely passive and linear devices. It appears that the opto cell variable resistance, which is dependent of the light intensity from LEDs, is not linear. Its resistance could be modulated by the voltage drop across it. The non-linearity is proportional to the voltage. It is discussed on diyAudio doth com forums, where the Lightspeed designer George is aware about this and admits the distortion existence.

Congratulations on discovering a number of relevant facts that are well known to good audio designers. LDRs were replaced by VCAs in the interest of improved perofrmance including vastly lower distoriton decades ago.
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