The other possibility that you didn't explicitly state is an active preamp that has unity gain, i.e. gain = 1, which might be thought of as "no gain".
As a side note, "having gain" would be a little ambiguous, in one sense, because it doesn't really imply an active preamp as opposed to passive/resistive, since those have gain, too, but it's just less than 1. And an active preamp could have a gain of less than 1, too, if desired, not to mention a negative gain (i.e. inverting the signal).
Anyway, one advantage that AndrewT didn't mention, for active preamps (i.e. a preamp with one or more powered electronic amplifiers, e.g. opamps, transistors, tubes), which is also there even if their gain is one, or less than one, or more than one, is that their input impedance can be almost whatever you want, and unchanging, and their output impedance can be very, very low, and unchanging, independent of the fixed or variable gain that they have.
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AndrewT covered this very well but I wanted to mention that the LDRs are typically made by encapsulating an LED in a light-tight enclosure with a Cadmium Sulfide photocell, and a CdS photocell does present a "pure resistance" that looks just like a regular resistor, to the circuit.
Regarding the line "The best buffer is no buffer at all.", it would be very nice to be able to agree with that for all cases. But it would be unrealistic. There are many situations where using a buffer or two, or a preamp with a gain of more than one, would result in a system with more-faithful sound reproduction. It's simply not always true that "the fewer components the better". As Einstein said, "Everything should be made as simple as possible, but no simpler.". So a good goal might be to use as few components as possible, but no fewer.
(Continuing from the post above: )
My main goal in audio is the truest reproduction of the input source. There are usually many trade-offs to consider. It's a classic optimization problem. In this "one-off"-oriented DIY world, there are a lot of ideas about the tendencies of things to have certain effects, many of which are basically correct. But there's often not a lot of real analysis done as to how significant each of those effects might be, in a given situation. But in order to correctly solve an optimization problem, that is exactly what is needed. i.e. You have to have the correct weighting factior for each component of the whole (especially when some of the effects might be miniscule). Otherwise correct decisions can't be made. In layman's terms, "It's complicated.". That's why I tend to not like generalizations such as "The best buffer is no buffer.".
I could just as easily say something like "The frequency response characteristics of the system must not change when I move the volume knob on my LDR (or passive resistive) attenuator and therefore buffers are absolutely required and anyone who doesn't use them has a crappy system." But that would likely be wrong something like 97.4% of the time, because even though "technically" the frequency response WOULD change as the volume knob is moved (because the input or output impedance would change), in most systems that effect would be so miniscule that it would never be noticed. However, a competently-implemented buffer would also never be noticed, except possibly for the improvements it would provide if it were needed.
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in the true spirit of "High Fidelity"
Yes, a buffer cannot be avoided if the source/transmitter cannot adequately drive the receiver and whatever comes between the two.
Wow, this thread has really heated up
gootee
Thanks for the awesome links on page 2 of this thread. I know that attenuation schemes apply to any amp not just the MyRef but I tried to focus the discussion to that amp only when I started this thread. The optical sensor attenuation schemes seem to be a little too fussy to me. The designs I've seen seem prone to drift and misalign over time.
AndrewT
It's always good to see your no-nonsense technical input.
soongsc
Your recommendation to use the lowest value range the source can drive jibes with the links provided by gootee. I interpreted flatter to mean less affected by input frequency as the signal length shortens. Is this due to the parasitics on a longer cable interconnect?
bmcbob
Cool link on bi-amping but let's try to keep on topic. I know bi-amping and active speakers/crossovers are related to an attenuation scheme discussion but my concern is that it will dilute what I hope to be a very focussed discussion.
gootee
Thanks for the awesome links on page 2 of this thread. I know that attenuation schemes apply to any amp not just the MyRef but I tried to focus the discussion to that amp only when I started this thread. The optical sensor attenuation schemes seem to be a little too fussy to me. The designs I've seen seem prone to drift and misalign over time.
AndrewT
It's always good to see your no-nonsense technical input.
soongsc
Your recommendation to use the lowest value range the source can drive jibes with the links provided by gootee. I interpreted flatter to mean less affected by input frequency as the signal length shortens. Is this due to the parasitics on a longer cable interconnect?
bmcbob
Cool link on bi-amping but let's try to keep on topic. I know bi-amping and active speakers/crossovers are related to an attenuation scheme discussion but my concern is that it will dilute what I hope to be a very focussed discussion.
My inclusion of the bi-amping link may have been misunderstood. It was intended as pure background theory. The reason I feel it relevant is as stated, I am very impressed with Uriah's Lighter Note attenuator in the general "less is more" or as posted above "as little as is necessary" approach offered by that unit. Andrew's definition of a preamp/attenuator or whatever one names it, as a core with input and output elements on either side is still how I see a system. Bi-ampimg as a concept and an active crossover (or maybe a passive network) as a physical element, in my mind, combine as the input side of the "receiver/transmitter" role mentioned again by Andrew.
If I see the attenuator-MyRef-speaker side from the "if it ain't broke, don't fix it" view, what's fed into the other side is my only variable. If something much simpler than the entire -biamp/actv cross- package maintains the quality of the volume control I have and adds a bit of a bump up in power - I'm all ears. (Pun Intended) 🙂
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A point of clarification may be needed - I am working with two MyRef systems. One is comprised of Siva's V1.3 kits combined with the Lighter Note. Pure, simple and stable.
The second is the experimental bi-amp group with TP v1.2 amps and two BPA-150 offerings from Jim's Audio on eBay. So I'm not taking an either/or approach, more accurately - "what else can I try and learn from?".
The second is the experimental bi-amp group with TP v1.2 amps and two BPA-150 offerings from Jim's Audio on eBay. So I'm not taking an either/or approach, more accurately - "what else can I try and learn from?".
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bcmbob
Noted. How long have you been using the lighter note? What value range is the resistive element? Have you noticed any drift or warble? Please describe the improvement over a standard switch attenuator.
Noted. How long have you been using the lighter note? What value range is the resistive element? Have you noticed any drift or warble? Please describe the improvement over a standard switch attenuator.
From communications with Uriah 03/09/2011........
"Well I got everything dialed in perfectly to 10K – 10K
V at Max/Balance at full right - L Series = 225.8 ohm
V at Max/Balance at full left - L Series = 60.7 ohm
V at Max/Balance at full right - R Series = 226.8 ohm
V at Max/Balance at full left - R Series = 63.3 ohm
Here is the other end:
V at Min/Balance at full right - L Series = 21.6K
V at Min /Balance at full left - L Series = 4.9K
V at Min /Balance at full right - R Series = 4.5K
V at Min /Balance at full left - R Series = 22.2K"
I have not experienced any inconsistencies with either the Lightspeed or Lighter Note kits from Uriah. However - one must remember that by design and as stated in the documentation, there is a lot of interactivity between ALL the adjustments in this approach. Particularly with the LN it is important to find the settings that are best for a given system, the users ears and even the listener's general position (balance pot).
In my case, based on my personal concept of realistic levels, the size of my room and fairly inefficient speakers, I often find full rotation of the volume pot necessary. At that point the balance pot has little or no effect. Backing the volume off a tad (from 5:00 to 4:50) brings balance control back in correctly. I attribute this more to what I'm feeding the unit (power) and not a flaw or problem with the attenuators.
If one is looking for an absolute, out of the box perfect device for volume control I would guess LDR is not a good choice. If the ability to tailor and match the components of a system (without the use of a soldering iron) is what your after, IMHO, there is nothing more flexible and unobtrusive than the Lighter Note. Uriah's new offerings with remote control should bring all this together in a very user friendly manner.
It dawned on me this past weekend that I have never used anything other than LDR attenuators with any of my LM3886 projects - including the BrianGT mono-blocks. I have a Carver C-1, a Sanyo top end pre and a modified Dynaco PAT-4A that I plan to audition in the next few days. In my mind, any of these or the use of a multi-resistor pot is a step backward from the Lighter Note - but I'm open to all the suggestions and recommendations posted on this forum.
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Test Report
I found the Carver C-1 very good with the MyRef. The other two are not in the same league. The Carver gave me all the gain I needed but also compromised/cluttered the airy-pristine nature when compared to the Lighter Note. Not by much but definitely there. I would still like to find a solution without adding a complete multi-function pre.
From what I read above, it sounds like a buffer or a switchable gain stage is all I need as there already is a pot on the LN for finer variations. A couple questions:
1. Is it proper/necessary to combine a gain stage with a buffer or is that redundant?
2. Is placing either between the source (eg: CD player) and the MyRef the only option?
3. Has anyone applied this approach with the MyRef/Lighter Note combination?
4. Is there a thread or link where one can learn more about these subjects?
I found the Carver C-1 very good with the MyRef. The other two are not in the same league. The Carver gave me all the gain I needed but also compromised/cluttered the airy-pristine nature when compared to the Lighter Note. Not by much but definitely there. I would still like to find a solution without adding a complete multi-function pre.
From what I read above, it sounds like a buffer or a switchable gain stage is all I need as there already is a pot on the LN for finer variations. A couple questions:
1. Is it proper/necessary to combine a gain stage with a buffer or is that redundant?
2. Is placing either between the source (eg: CD player) and the MyRef the only option?
3. Has anyone applied this approach with the MyRef/Lighter Note combination?
4. Is there a thread or link where one can learn more about these subjects?
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ESP has a lot worth reading.
Decibel dungeon is also good.
We have an article on the Forum all about system gain. Sounds like you have not read it !!!!
If some sources need more system gain then you cannot (never ever) get the quiet sources as loud as the loud sources without adding in an appropriate amount of extra system gain.
That is equivalent to saying that buffer and gain stage complement each other.
Decibel dungeon is also good.
We have an article on the Forum all about system gain. Sounds like you have not read it !!!!
If some sources need more system gain then you cannot (never ever) get the quiet sources as loud as the loud sources without adding in an appropriate amount of extra system gain.
That is equivalent to saying that buffer and gain stage complement each other.
bcmbob,
1, Again, "EVERYTHING" has "gain". It might be a gain of 1 (unity), i.e. "no gain", like a unity-gain active buffer amplifier, or it might be LESS than 1 ( < 1), like a passive attenuator, or it might be > 1 (greater than 1), like an active booster amplifier (but active amplifiers CAN also have gains of less than or equal to one (<= 1), if you want).
"Gain" is just the ratio of the output amplitude divided by the input amplitude, for a two-port system. A system's "having gain" does NOT necessarily imply an active booster amplifier type of system.
But, to try to answer what I think your question must have been: Any active amplifier stage, whatever the gain is, would also act as a buffer, in the sense that its input impedance could be made very high, so it would be "stiff enough" to not have to lose any significant portion of the input signal level, and its output impedance could be made very low, so it would provide the best conditions for the input of any following stage.
So you wouldn't need BOTH an active buffer AND an active booster amplifier, in series with each other. (However, you might want an active stage both before and after a passive stage, sometimes (or maybe usually, in my opinion).)
2. The only option? No. You could use a passive stage, like a passive attenuator. But if your source's output level is "too low", you might find it desirable to use either an active buffer or an active amplifier with gain > 1.
3. Probably.
4. Yes.
Tom
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Tom, I'm following you except for "unity-gain active buffer amplifier". That sounds like a pass-through to me. If so, what does the "active" refer to? The word oxymoron comes to mind. 😕
Thanks
Tom,
I have a Mackie mixer that has "u" for unity on both rotary(12:00) and slide(mid point) pots and I understand that function/concept. That is a setting or effect in my mind, not a device. Is that closer to what you are trying to convey?
I have a Mackie mixer that has "u" for unity on both rotary(12:00) and slide(mid point) pots and I understand that function/concept. That is a setting or effect in my mind, not a device. Is that closer to what you are trying to convey?
No, there really is such a thing as a "buffer", which, for analog circuits, usually means an amplifier with a gain of 1. "Active" just means it is powered and uses some type of active device, such as opamps, transistors, or tubes (as opposed to only passive devices such as resistors, capacitors, inductors, diodes, etc).
Very often, a buffer is made with a single opamp, by connecting the opamp's output to its negative input. Then the output voltage will try to always stay equal to the voltage that is applied at the positive input pin.
You might wonder why anyone would want "an amplifier that doesn't amplify"! But they are extremely useful and very common. It's often to prevent some part of a circuit from being "loaded down" by the circuitry that comes after it. i.e. It makes it so you don't have to worry about incompatible output and input impedances, or losing too much of your signal level due to "hidden" voltage dividers, or not having enough current to sustain the desired voltage (i.e. not having enough power available to drive a low impedance that follows).
The circuits before the buffer only see the very high input impedance of the buffer, which is very easy to drive since it needs almost no current no matter what voltage is across it. They can no longer be significantly affected by whatever is on the other side of the buffer.
The buffer transfers an (theoretically) exact copy of its input voltage to its output, but with a very low output impedance (which basically gives a minimum of unwanted effects on the operation of whatever circuitry follows). And the output is POWERED. So up to some limit it can also supply whatever additional current is needed to sustain the desired output voltage across the impedance of whatever comes next.
It is probably quite typical to place a buffer amplifier after every passive stage, in every kind of analog signal-processing circuit.
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Got it. Makes sense now. Great explanation. Thanks
The more I learn the more I'm convinced I should just go back to my 1958 Sony 9V 9 transistor radio. Life was simple then.
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The more I learn the more I'm convinced I should just go back to my 1958 Sony 9V 9 transistor radio. Life was simple then.
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