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Maximizing Your Preamp Performance

 

Gold Member
Username: Mike3

Wylie, Tx USA

Post Number: 1604
Registered: May-06
I was chatting with a web retailer today about cables and such, the fellow builds and sells his own on line. He was very willing to provide information about cables and such, much consistent to what I have learned, but I still learned a few things from him today too.

Ok so what does that have to do with Preamps? Well at the end of our discussion he suggested turning up the volume as high as possible on my Preamp to get best sound out of it. While most folks may not be able to do that I do have a gain switch on my Preamp which I had set to the highest setting and then just worked my Preamp at lower turns on the volume dial. With his suggestion I am able to turn my gain switch to the lowest setting and max out my volume control on the Preamp.

So I will try this out and see if I get it or not, but I am wondering if any of you have done this or anything else to bring more to your sound through your preamp. I've done a few other things too with my Preamp but I will just start with this for now.
 

Silver Member
Username: Soundgame

Richmond Hill Toronto ..., Ontario Canada

Post Number: 334
Registered: Jun-08
Hi Mike,

Doesn't seem intuitive to me. When I turn my preamp up with no input from the source, the minute I get 3/4 up I start to hear some his, which I believe is the preamp just amplifying any noise that it, itself generates. I would think that the higher the volume setting the more potential there is for amplification of inherent noise in the preamp. There must be some optimum volume level of any specific preamp but I question whether that would be in the higher regions but rather in the mid way up region.
I'm not trying to squash the theory but rather, very interested to hear what your results are or what others could share on this.

Cheers!
 

Gold Member
Username: Mike3

Wylie, Tx USA

Post Number: 1605
Registered: May-06
George, I have a gain control which is there to match the settings of various inputs. I have to find what they are again, but for example the lowest setting may be 2.0 db with 0.5 db step ups for each of the 5 switch set points, or up to 2.0 up to 4.0 in increments of 0.5 db. I had been running the switch at the highest level but now have it set to the lowest level. With it at the lowest level and my CD player as the source I am able to max out the volume dial.

I too cannot do this at the higher gain settings due to micro-phonics (hiss) in my tubes which I experienced when running a low gain Micro Benz cartridge (0.3 mv).

There's other things I could experiment with, like leaving the gain dial at 3.0, the middle setting. I will keep you updated.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 13156
Registered: May-04
.

Conventional potentiometers operate best in the upper half of the range. They track better channel to channel in this portion of their operating range* and they tend to sound "best". In the upper range of most simple potentiometers the impedance of the pot is minimized until at its fully open position it is all but non-existent and if the pre amp should not have an input buffer, the lower impedance will allow for more current to flow from the source to the pre amp. This might result in slightly increased dynamic range. In most cases this should be a minimal if at all noticeable improvement as you are trading one condition for another.

Ideally your system should be put togther so levels match well enough that you are always operating the system with the volume control around the 10-2 O'Clock position for a "comfortable" listening level. This hardly ever happens today given the variability of source components, the various choices in pot tapers and the choice of more and more digitally controlled volume controls - not just digital readout but digitally controlled vc's.

If you advance the pot to its maximum position, you have essentially taken it out of the line and your pre amp is merely passing the signal through as a switching device. For some applications where you have another location in the system that allows level control this might be the better choice depending on the quality of each control pot and it's affect on the system sound.

Mike, this is what we talked about when you were choosing cartridges. Gain is gain and you are trying to have all systems operating at the highest level possible that allows a comfortable listening level at midway on the control and still gives full power when the vc is fully advanced. This overall set up of your system will minimize interaction action between components. Adding or removing "gain" will affect the system in some manner.

However, I'm a bit confused about the advice you received from this call. The gain switch is either still functioning by way of placing a set amount of impedance in line or by switching a secondary gain stage into the signal path. The additional gain stage has the chance of introducing more noise and distortion - the result of any active circuit - and you would have to balance the benefits of one source of signal degradation against the potential for another source of problems.

Set the system up to provide full power (with the widest variety of source material) at just under the fully open position on the vc and you should be maximizing the system's operation. This will also give you the ability to make finer adjustments to the overall level.



* That's one reason you have a balance control - because virtually all vc's have channel to channel tracking errors that require balance compensation to perfectly center the image and give the vocalist (or whatever happens to exist center stage) a roundness and a three dimensional "pop" not possible when the vc tracking is off by even a small amount. This is what I've shown you with my dual vc pre amp - at any point in their range both channels are unlikely to be perfectly even in output level due to slight mistracking of the vc's and slight variances in each channel's gain structure or channel variance at the source - this would especially apply to phono st}ages where channel balance is an "iffy" item compared to sources such as CD, DVD, tape or tuner.


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Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 13158
Registered: May-04
.

Here's a lesson in system balance that can be performerd by anyone with an electric guitar and an amplifier or similar set up where you have various locations for controlling overall "volume". Gain is affected by negative feedback - how much of the output of the circuit is fed back into the input of the circuit. The higher the dB of NFB, the higher the gain of the circuit. (This isn't the only thing that affects circuit gain but it is a common source for gain setting in consumer audio.)

Most guitar amplifiers will have both a volume and a "gain" control or "overdrive" control where the "gain control affects the amount of NFB injected back into the circuit's front end. Take your electric guitar and plug into your amp with the master volume control on your guitar at about "2" and amplifier at just beneath mid point and the gain control advanced just far enough to get the system to sound. Strum the guitar and listen for what should be a clean tone no matter which pickup you switch in and out.

Now try to maintain the same overall volume by advancing the guitar's vc to max and the amp's volume to a lower level. Listen for the difference in tonal quality and the sustain of the signal. Then, still trying to maintian a not too loud overall level, advance the gain control on the amp while taking down the volume of the guitar.

The gain (or "overdrive") control on the amplifier's head is controlling the amount of NFB in the (pre) amplifier. By overdriving the NFB circuit and thus the input of the (pre) amplifier, the amp sounds distorted with a long sustain that has a wavering quality. The more you advance the gain control, the more distorted the signal becomes.

Finally advance the guitar's volume control fully to put a higher voltage into the head unit in front of its volume control. Each one of these setings should provide a distinctly different quality of sound. Play with the three points where you can control "gain" by changing from a clean to an overdriven sound simply by adjusting the three points of guitar volume, amplifier head volume and head gain. This should give you an idea of what is happening in your audio system as you adjust gain levels with the various pots and switches available to you.

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Gold Member
Username: Mike3

Wylie, Tx USA

Post Number: 1615
Registered: May-06
New bit of info on my pre-amp. I spoke with Mark O'Brien, Rogue Audio CEO (he keeps answering his phone) and he said that it is subjective but that the volume control potentiometer has (lesser quality) plastic material in play where the gain switch employs high quality resistors so in essence turning the volume control all the way up and using the gain switch at the lowest or next to lowest (depends how loud one wants it) should produce the purer output. Realistically one may still need to trim the volume some with the volume control.

Something of quite interest to me is he informed me that Anthony Gallo utilized the Rogue Audio pre-amp in developing the Reference 3.1 speakers which I own. How about that for marrying up speakers to pre-amp without even being aware of this history? Now how's that for synergy? Way, way cool!!!

Lastly, JV, I do not have individual volume controls on the Rogue as you do on your preamp, however I do have channel volume controls on my amp. Wouldn't those work in the same manner you described for you pre-amp vcs' above?
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 13168
Registered: May-04
.

They do but you would have to adjust them every time you changed discs or adjusted the volume level. (I know, you only listen to Pigs and you have the volume set at max all the time.)

I've never looked. Does your pre amp have a balance control? That's what its for, to balance the two channel's output.

You've heard what a slight adjustment can do in my system. Not every album has a channel imbalance and the vc is not mistracking constantly. But if you are hearing something that sounds slightly sucked out on one side of the center image, then try adjusting your system.

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