Passive Balanced Preamp

[jlafrenz]

As far as having smaller increment adjustments, it is still going to be depended on the things we have already discussed. A lot of volume pots are wiper style where there is not a specific spot on the volume control. It is smooth from start to finish. The level is purely where you turn the knob too. Think of your speedometer. As you push on the gas it gradually increases until you get to the desired level. Giving it more or less gas the gauge will change where the needle is. That needle would be the wiper part. Alps is a very popular volume pot of this style.

Your other option is a stepped attenuator. This has specific steps and locks into each position. There can be a different number of steps with this style. It depends on the manufacturer. If you are looking for small precise adjustments this would be your best option. The Goldpoint I have is a stepped attenuator. You may also look at this

http://www.dact.com/html/attenuators.html

The volume pot or attenuator is only pieces of the puzzle along with your voltage and input sensitivity. You will also want to know what the input impedance of your amp and output impedance of your source will be.

Here is some reading on that.

http://www.kpsec.freeuk.com/imped.htm

http://whirlwindusa.com/support/tech...dance-signals/

[WiWavelength]

Josh, is there a reason why you seem to be focused on ~500 W/ch amps? That limits your amp choices, increases your amp budget, and could easily be five times the power that you realistically require.

AJ

[WiWavelength]

Originally Posted by jlafrenz

The volume pot or attenuator is only pieces of the puzzle along with your voltage and input sensitivity. You will also want to know what the input impedance of your amp and output impedance of your source will be.

That is a good point. With an active preamp, you really need not worry about impedance compatibility. But with a passive preamp, you do. And that is another reason why I would not recommend that Josh go the passive preamp route. Instead, use the digital volume control on the Oppo, and find an amp with an input sensitivity that is a good match.

AJ

[Josh]

Originally Posted by jlafrenz

Your other option is a stepped attenuator. This has specific steps and locks into each position. There can be a different number of steps with this style. It depends on the manufacturer. If you are looking for small precise adjustments this would be your best option. The Goldpoint I have is a stepped attenuator. You may also look at this

http://www.dact.com/html/attenuators.html

The volume pot or attenuator is only pieces of the puzzle along with your voltage and input sensitivity. You will also want to know what the input impedance of your amp and output impedance of your source will be.

Here is some reading on that.

http://www.kpsec.freeuk.com/imped.htm

http://whirlwindusa.com/support/tech...dance-signals/

I think this is what I'm thinking about. Not optimal, but a possible solution.

Originally Posted by WiWavelength

Josh, is there a reason why you seem to be focused on ~500 W/ch amps? That limits your amp choices, increases your amp budget, and could easily be five times the power that you realistically require.

AJ

The currect plan is to get the Focal Chorus floor standing speakers which run 250-300 watts depending on the model. I did read Big Daddy's post regarding have twice the amp of what the speakers are driven RMS which is why I am looking at 500 watts. Do I not need that much?

Originally Posted by WiWavelength

That is a good point. With an active preamp, you really need not worry about impedance compatibility. But with a passive preamp, you do. And that is another reason why I would not recommend that Josh go the passive preamp route. Instead, use the digital volume control on the Oppo, and find an amp with an input sensitivity that is a good match.

AJ

I'm leaning towards that since I want to get as close to a direct signal as possible to the speakers. My budget and availability of product will greatly influence that. I want to avoid an active preamp if at all possible.

[WiWavelength]

Originally Posted by Josh

The currect plan is to get the Focal Chorus floor standing speakers which run 250-300 watts depending on the model. I did read Big Daddy's post regarding have twice the amp of what the speakers are driven RMS which is why I am looking at 500 watts. Do I not need that much?

That 250-300 W figure is power handling. It is not a requirement but rather what is a safe amount of power that the speakers can handle.

I seriously doubt that you need 300 W, let alone 500 W. As I noted the other day, the Focal speakers that you are considering all have sensitivities of ~92 dB/W/m. Thus, at a distance of 1 m, you already get a quite loud 92 dB output from a single speaker with only a 1 W input. For each 3 dB increase, double the power output. As such, a full 500 W input would get you 119 dB at 1 m -- and it might destroy the speakers.

Unless you have a large, absorbent room and/or like to listen at outrageous levels, you probably do not require greater than 100 W, not even for peak signals. Using the same math as above, with 100 W, you can still hit 112 dB at 1 m.

AJ

[Josh]

Originally Posted by WiWavelength

That 250-300 W figure is power handling. It is not a requirement but rather what is a safe amount of power that the speakers can handle.

I seriously doubt that you need 300 W, let alone 500 W. As I noted the other day, the Focal speakers that you are considering all have sensitivities of ~92 dB/W/m. Thus, at a distance of 1 m, you already get a quite loud 92 dB output from a single speaker with only a 1 W input. For each 3 dB increase, double the power output. As such, a full 500 W input would get you 119 dB at 1 m -- and it might destroy the speakers.

Unless you have a large, absorbent room and/or like to listen at outrageous levels, you probably do not require greater than 100 W, not even for peak signals. Using the same math as above, with 100 W, you can still hit 112 dB at 1 m.

AJ

Ideally the max I would push the amp is 50%, as Big Daddy suggested, leaving plenty of headroom for spikes. That would be 116dB. It's a ton more than I would probably need, nice to have if I want it.

So really, a 250-300 watt amp would get me 113dB at 50%? That might be a compromise I'd be willing to consider.

I currently have an unbalanced Acurus 3x100 watt amp. Maybe I need to focus more on the speakers at this point?

[WiWavelength]

Originally Posted by Josh

I currently have an unbalanced Acurus 3x100 watt amp. Maybe I need to focus more on the speakers at this point?

Yes, I would suggest making the speakers your focal point (pun intended). Speakers/acoustics will make a far greater audible difference than will anything else.

I would also suggest that you do some listening with an SPL meter handy. Using slow response, get an idea of your highest average listening level. Then, using fast response, do the same for your highest peak listening level. That info can be used to calculate how much power you really need.

AJ

[Josh]

Originally Posted by WiWavelength

Yes, I would suggest making the speakers your focal point (pun intended). Speakers/acoustics will make a far greater audible difference than will anything else.

I would also suggest that you do some listening with an SPL meter handy. Using slow response, get an idea of your highest average listening level. Then, using fast response, do the same for your highest peak listening level. That info can be used to calculate how much power you really need.

AJ

I will definitely do that, thanks. I keep reading how easy the Focals are to drive (like you said), and a lot of people are using pretty small amps. I guess I need to bring my expectations down to a more realistic level.

So I didn't realize Acurus was reborn, so I better be more specific. I have an Acurus A-100x3 which has input sensitivity of 1.1V via RCA. The Oppo puts out 2.1Vrms via RCA. Am I going to have to exercise the same level of caution as you warned me about using XLR? Is that too much of a gap?

[WiWavelength]

Originally Posted by Josh

I have an Acurus A-100x3 which has input sensitivity of 1.1V via RCA. The Oppo puts out 2.1Vrms via RCA. Am I going to have to exercise the same level of caution as you warned me about using XLR? Is that too much of a gap?

I am familiar with that amp. I like three channel amps, so I have thought of picking up a used one myself. That said, I do not know its input sensitivity off the top of my head. But if your quoted spec is accurate, then you need to bring the Oppo digital volume control down to -6 dB to avoid potential clipping.

AJ

[Josh]

Originally Posted by WiWavelength

I am familiar with that amp. I like three channel amps, so I have thought of picking up a used one myself. That said, I do not know its input sensitivity off the top of my head. But if your quoted spec is accurate, then you need to bring the Oppo digital volume control down to -6 dB to avoid potential clipping.

AJ

Thanks!

I picked up the Acurus years ago to run the front sound stage of my theater. I then picked up an Acurus A80 to run the rears, but the left channel went bad. I'm trying to sell it for parts since its been in storage for so long. I'll try to remember you went I get ready to sell the A100x3. I think I'd like to replace it with a McIntosh MC352. More amp than I need, but fully balanced to the speakers.

[WiWavelength]

Josh...

Just to be clear, if you do any testing in the coming days, the digital volume control attenuation settings that we discussed are just the maximums that you should ever use.

For example, if you set the BDP-95 at -6 dB, run unbalanced RCA into your Acurus amp, and play some highly compressed pop/rock, that could drive your amp straight to 100 W and probably drive you from the room.

So, be conservative. With almost any player/amp/speaker combo, a good starting point would be -30 dB. Then, increase the digital volume control as needed, but do not exceed the aforementioned maximum settings.

AJ

[Big Daddy]

Josh,

Have you seen The Truth Preamp? It is sold by The Horn Shoppe.

• It has an input impedance too high to measure, output impedance is a couple ohms, bandwidth is to 60Mhz, slew rate is a couple hundred V/microsecond.
  
• There are no capacitors or resistors in the signal path. There is no potentiometer in the signal path.
  
• It uses photo cells to control the volume. It does not use optocouplers.
  
• It is an "active" device and suffers none of the "problems" that "passive volume control/pre amps" have. It can drive long (30 feet) cables with ease.
  
• I've had parts of this circuit run for >10 years without failure.
  
• As far as I know there is nothing like it available for any price.....I could be wrong but I doubt it. I looked "pretty hard and long".
  
• The price in a painted Aluminum enclosure is $975 shipping included. Extra inputs are 40 dollars. Remote adds 250 dollars.
  
• Please call me with any questions........also, there are a couple threads on my forum which may be of interest.

[Josh]

Originally Posted by WiWavelength

Josh...

Just to be clear, if you do any testing in the coming days, the digital volume control attenuation settings that we discussed are just the maximums that you should ever use.

For example, if you set the BDP-95 at -6 dB, run unbalanced RCA into your Acurus amp, and play some highly compressed pop/rock, that could drive your amp straight to 100 W and probably drive you from the room.

So, be conservative. With almost any player/amp/speaker combo, a good starting point would be -30 dB. Then, increase the digital volume control as needed, but do not exceed the aforementioned maximum settings.

AJ

I received the Oppo on Tuesday and after I hooked it up, I started by putting in Dire Straits - Brothers in Arms SACD. The player went right at it and fortunately I had put the volume at zero. I say fortunately, because as soon as I went up to 1, it was already at a level that I wouldn't want to exceed much as my son was already asleep. As "So Far Away from Me" started playing, I immediately thought, even at this low volume, that the added clarity was shocking. What a change just with the transport. I can't wait to crank the system this weekend.

So my question relates to the volume. Going back to what Big Daddy said about digital volume control, at what level on the player am I starting to lose fidelity? In other words, how high does the volume have to be (1-100 on this player) where I'm getting all the fidelity? I download an SPL meter ap for my iPhone (which is supposed to be within 1-2dB of the professional stuff) and I should have measured the sound level for reference, but I forgot. But going back to a previous post, I calculated a theoredical 78dB level as a minimum, so am i just going to have to break out the SPL meter and keep raising the volume until I hit 78dB?

I'm starting to get more concerned that the stereo is going to have to be at too high of a level for me to get 100% of the fidelity.

Originally Posted by Big Daddy

Josh,

Have you seen The Truth Preamp? It is sold by The Horn Shoppe.

I'm going to need some help translating what all that means

I starting reading some of the forum posts, and these guys are way above my level when it comes to sound, and I'm lost.

[WiWavelength]

Originally Posted by Josh

So my question relates to the volume. Going back to what Big Daddy said about digital volume control, at what level on the player am I starting to lose fidelity? In other words, how high does the volume have to be (1-100 on this player) where I'm getting all the fidelity?

Josh, fill me in on the BDP-95. I have several Oppo players. In fact, that reminds me -- I still have the BDP-103 in the box. I need to get it out and give it a whirl in my system. Regardless, I do not use the analog outs nor the digital volume control capabilities. So, does the BDP-95 not offer a relative volume scale (e.g. -x dB)?

AJ

[Josh]

Originally Posted by WiWavelength

Josh, fill me in on the BDP-95. I have several Oppo players. In fact, that reminds me -- I still have the BDP-103 in the box. I need to get it out and give it a whirl in my system. Regardless, I do not use the analog outs nor the digital volume control capabilities. So, does the BDP-95 not offer a relative volume scale (e.g. -x dB)?

AJ

The volume scale is 0-100. I'll see if there is a way to change that, but a quick google search netted no answers.

[WiWavelength]

Originally Posted by Josh

The volume scale is 0-100. I'll see if there is a way to change that, but a quick google search netted no answers.

So, is 0 mute, then 1 is a significant jump in volume? I wonder if the volume scale could be based on percentages of full scale. Either way, it sounds like the digital volume control will not allow you to reduce volume into the range in which less than 24 bit truncation occurs.

AJ

[Josh]

Originally Posted by WiWavelength

So, is 0 mute, then 1 is a significant jump in volume? I wonder if the volume scale could be based on percentages of full scale. Either way, it sounds like the digital volume control will not allow you to reduce volume into the range in which less than 24 bit truncation occurs.

AJ

Yes, zero is mute and one is around 67-68 dB. At least, for that particular SACD. I put in a DVD-A of The Lord of the Rings soundtrack and it was a much lower volume. So based on the previous info you gave me that 74 dB was the minimum with losing resolution, it is dropping some.

I was able to crank the system, and right now I'm most comfortable at around 95 dB, though that may be more due to the limitations of my current speakers than my ears. Now, you had said that the speakers I was looking at would deliver 92 dB with one watt of input, right? Is that the sensitivity number where it says "Sensitivity (2,83 V/1 m) 92dB"?

[Josh]

So I played with the system a bit more and I'm really enjoying the Oppo. I have to check the removable media playback tonight, but so far it has been nothing but joy!

So back to the issue at hand, I looked up the specs on my current speakers, and they have a sensitivity of 88dB. So that means, all things equal, I will sound levels at "1" will be twice as loud (88dB vs 92dB) as they currently are when I get the Focals? Is the amp going to affect this at all... meaning, is that a variable that would affect what the "1" position sound output is?

[WiWavelength]

Originally Posted by Josh

Yes, zero is mute and one is around 67-68 dB. At least, for that particular SACD. I put in a DVD-A of The Lord of the Rings soundtrack and it was a much lower volume.

I have all of Howard Shore's "The Lord of the Rings" DVD-A score releases, and those may not be a good samples for testing purposes. They are high dynamic range recordings, so their average levels are fairly low. The issue is not necessarily average levels driving your amp into clipping but peak levels (0 dBFS or close to) doing so. You could try some highly dynamically compressed tracks off of CD or iTunes. Or do you possibly have a test CD with a 1 kHz tone at 0 dBFS?

Originally Posted by Josh

Is that the sensitivity number where it says "Sensitivity (2,83 V/1 m) 92dB"?

Correct. The math on that is 2.83 V into 8 Ω equals 1 W (2.83² ÷ 8 = 1), and then the SPL is measured at 1 m.

AJ

[Big Daddy]

Originally Posted by Josh

So I played with the system a bit more and I'm really enjoying the Oppo. I have to check the removable media playback tonight, but so far it has been nothing but joy!

So back to the issue at hand, I looked up the specs on my current speakers, and they have a sensitivity of 88dB. So that means, all things equal, I will sound levels at "1" will be twice as loud (88dB vs 92dB) as they currently are when I get the Focals? Is the amp going to affect this at all... meaning, is that a variable that would affect what the "1" position sound output is?

There is some controversy in how some manufacturers report sensitivty of their speakers. There is a section on this topic in the middle of Post #1 in the Impedance & Sensitivity of a Speaker thread.