[Roger A. Modjeski]

This problem has a simple, low cost solution that will actually improve your sound while giving you the largest range of volume control settings. It will also match your volume settings on your various inputs.

In brief, a volume control is a loss device. It does not control gain, it simply attenuates the incoming signal to the level you desire for your listening. The problem is that most line stages have too much gain and that CDs are often recorded too "hot" for marketing reasons. We need not be at the mercy of either.

Traditionally preamps had 40 dB of gain in the phono section and 20dB in the line. Magnetic cartridges has an output of 5-7 mV and tape decks and tuners had an average output of 0.5 to 0.7 volts. Thus 40 dB of gain (100X) in the phono section made the output of the amplified phono equal to the high level inputs and in general no volume setting change was needed when switching sources. As it happens the preamp people were doing the right thing but things outside the preamp's domain thwared their good intentions. These include: Radio stations that want to be the loudest on the dial using compression and limiting, tuners and tape decks with non standard output levels and cartridges with low output. Note that many power amps of the day had input level adjustments and many preamps had output level adjustments, either of which would allow the user to set gain so that the volume control could be used over its whole range. Unfortunately these pots were often of poor quality and if they were not rotated or cleaned from time to time they would cause distortion. A much better choice would have been a simple rotary switch (gold or silver plated) with fixed resistors. I don't know of any company who chose that, opting for the much less expensive carbon pot that was easy to install and wire up.

We need to re-asses the gain structure in a modern preamp for modern signal sources. Given that modern cartridges are now below 5 mV and that speakers have gotten more sensitive in the last few years we need far less gain in the line and more in the phono section. If I were to make a preamp without internal gain switches I would set the phono gain at 50 dB for MM and 60 dB for MC. I would set the line gain at 10 dB and you would find that your volume control setting would move very little as you changed sources. If you like this idea choose option 6.


For an in-depth treatise on the proper range of volume control please see the post "Volume control setting with CD input"

[DustyC]

This is a very good idea. Marketing pushes the lower settings on a volume control to convince customers that they have lots of headroom when they really don't.
I've been playing around with a preamp (ARC SP-14) that has 2 volume controls and I'm amazed that for most of my input sources I need to use a -18db setting on the coarse attenuator in order to use the regular volume pot at 11:00 position or higher. I figure I'm throwing away most of the 20db gain in the line stage.

Maybe a phono stage with a buffer stage for the line inputs and tape loop?

[Roger A. Modjeski]

This is a very good idea. Marketing pushes the lower settings on a volume control to convince customers that they have lots of headroom when they really don't.
I've been playing around with a preamp (ARC SP-14) that has 2 volume controls and I'm amazed that for most of my input sources I need to use a -18db setting on the coarse attenuator in order to use the regular volume pot at 11:00 position or higher. I figure I'm throwing away most of the 20db gain in the line stage.

Maybe a phono stage with a buffer stage for the line inputs and tape loop?

Do you know if the corse volume is an attenuator or actually changes the gain of the line stage? What are the steps? In either case they were on the right track.

You are correct about throwing away gain. From this designer's point of view the lower the actual active gain the better. It results in lower distortion and lower output noise, the latter of which is becoming a problem in systems with sensitive speakers and sensitive listeners. I have my power amp output noise down to 130 micro Volts. With at gain of 20x in the RM-10 and a gain of about 28x (not dB, actual mulitplication gain) an output noise of 20 microvolts coming out of most preamps the amplified preamp noise will dominate. The amplified preamp noise will be around 400 - 500 mircovolts which swamps my efforts in making a low noise power amp.

Given that information can you hear hiss in your speaker if you get close up? Does this noise go down as you change the course attenuator or the regular volume control?

Here is what I am currently offering in a nice black plastic enclosure. The plastic box is much easier to work with and sounds as good or better than metal. I wanted to keep the price down on these. It there is interest we can double the price and put it in a nice enclosure like the RM-5. The metalwork in most preamps is 50% of the cost. In some case where the aesthetics of the unit is the main thing it can be 90% and I'm not kidding. I can think of several expensive products where the performance suffered too because too much emphasis was placed on the look. I'm sure you can too.

Active Pot in a Box with gain/buffer    $550
Active as above with 2 inputs    $650
Passive Pot in a Box    $155
2 Input Toggle Pot in a Box    $255

Passive pot in a box is perfect for the CD audience.  If you have an outboard phono stage you often need some gain. The standard gain for the active is 12 dB (4x) but I can make is lower. As the gain gets lower the bandwidth goes up, distortion and noise go down and one can drive longer lines.

For reasons I cannot understand or verify or agree with, some listeners find a passive preamp lacks dynamics. Ponder this: The wiper of the volume control travels through a wire (often shielded) to the grid of the tube in the line amp in any preamp. In a passive preamp it goes to the grid of the input tube of the power amp through a short shielded cable. The only difference is the cable and that can be a good one. Short and low capacitance as I provide. I don't see the difference. All my CD systems use a passive pot. An integrated amp is the same as above in many cases where the signal comes into the volume control and goes to the grid of the first tube. That tube can be another gain stage or not depending on the gain of tubes that follow it.
 
If the phono stage has low output impedance a tape output buffer is not needed. High level inputs need no buffer as most high level sources are low output impedance these days.

[bummrush]

For reasons I cannot understand or verify or agree with, some listeners find a passive preamp lacks dynamics.
  my ?With my coda when at unity gain,and not adding gain as i can with this pre amp ,am i or am i not essentially using it as a passive or not?

[Roger A. Modjeski]

It appears you have an active stage.

As to the logic that passive preamps lack dynamics the only other thing to look at is the cables. Unfortunately cable makers know little about their capacitance or other performance parameters when driven by high impedance sources. I have talked to several cable makers and they know nothing about electronics, electricity or any science pertaining to what they do. They just like to make pretty things and take your money. I spoke at length with one noted cable designer who was getting false information through the miss-use of some very expensive HP test equipment. His white paper would have made a nice chapter in Alice in The Wonderland of Audio. His misguided research led to some cables that had very heavy filtering. Of  course this rolled off the highs just as well as a 20 cent capacitor would do.

[DustyC]

Do you know if the corse volume is an attenuator or actually changes the gain of the line stage? What are the steps? In either case they were on the right track.

Looking at the schematic it appears that they have placed resistors inline to reduce the gain. They are switched in -6db increments. The 20db gain in the line stage remains the same.

You are correct about throwing away gain. From this designer's point of view the lower the actual active gain the better. It results in lower distortion and lower output noise, the latter of which is becoming a problem in systems with sensitive speakers and sensitive listeners. I have my power amp output noise down to 130 micro Volts. With at gain of 20x in the RM-10 and a gain of about 28x (not dB, actual mulitplication gain) an output noise of 20 microvolts coming out of most preamps the amplified preamp noise will dominate. The amplified preamp noise will be around 400 - 500 mircovolts which swamps my efforts in making a low noise power amp.

Given that information can you hear hiss in your speaker if you get close up? Does this noise go down as you change the course attenuator or the regular volume control?

What little hiss I hear goes up and down with volume set by either control. I reason that what is going on is they placed 2 volume controls in line with each other.
Some old preamps I remember had a mute switch that would reduce the level by 20db. Such a feature today could prove useful when listening to CD.

Here is what I am currently offering in a nice black plastic enclosure. The plastic box is much easier to work with and sounds as good or better than metal. I wanted to keep the price down on these. It there is interest we can double the price and put it in a nice enclosure like the RM-5. The metalwork in most preamps is 50% of the cost. In some case where the aesthetics of the unit is the main thing it can be 90% and I'm not kidding. I can think of several expensive products where the performance suffered too because too much emphasis was placed on the look. I'm sure you can too.

Active Pot in a Box with gain/buffer    $550
Active as above with 2 inputs    $650
Passive Pot in a Box    $155
2 Input Toggle Pot in a Box    $255

Passive pot in a box is perfect for the CD audience.  If you have an outboard phono stage you often need some gain. The standard gain for the active is 12 dB (4x) but I can make is lower. As the gain gets lower the bandwidth goes up, distortion and noise go down and one can drive longer lines.

For reasons I cannot understand or verify or agree with, some listeners find a passive preamp lacks dynamics. Ponder this: The wiper of the volume control travels through a wire (often shielded) to the grid of the tube in the line amp in any preamp. In a passive preamp it goes to the grid of the input tube of the power amp through a short shielded cable. The only difference is the cable and that can be a good one. Short and low capacitance as I provide. I don't see the difference. All my CD systems use a passive pot. An integrated amp is the same as above in many cases where the signal comes into the volume control and goes to the grid of the first tube. That tube can be another gain stage or not depending on the gain of tubes that follow it.
 
If the phono stage has low output impedance a tape output buffer is not needed. High level inputs need no buffer as most high level sources are low output impedance these days.

[muzak]

The Audio Research SP-11 (circa 1986-1990) also has two volume controls. Here's link the the Audio Research database, which has descriptions of all AR product, and for the SP-11 a schematic. Navigate around and check out also the very first AR preamp, the PAS 2, Look familiar? http://www.arcdb.ws/SP11/SP11.html

[Elizabeth]

My Audio Research SP-15 preamp also has the dual volume control, a mater gain switch in 5 multi-dB steps, along with a notmale volume control for precise adjustment.
I liked it.
Now I use a Bryston BP-26 for a preamp, and it had way way too much gain into the Bryton amp I use. The Volume on the Bryston starts at 7 O'Clock and it is loud by the time it is at 9 O'Clock. Which basically sucks. The phono (also Bryston 1.5) has a value from 10 O'Clock to about 3 O'Clock, which is perfect. Those idiots who designed the CD standard with the two volt output were  A*$%#@**#.
added: The probelm wit passive is only if the source does not have enough current to push. Most sources are not designed to push enough current to make an amp happy.
Though some can.
My Audio Research PH-2 specifically starts it is not suitable for use with passive preamps in it's owners manual..

[Levi]

My BAT VK-51SE has a programmable gain matching for all the inputs.  I think that is a very neat feature.