Pure Passive vs. Tube Preamp w/Tube Power

[richieb]

It has been said that the best preamp is no preamp at all and having

recently inserted a pure passive preamp (volume) control for my VTL

EL84 mono blocks, that may be true. The custom made passive is about as

simple as it gets, teflon coated solid copper wire direct to all

connections, a 31-step Noble volume control and input switch. I have

heard talk that after a system change or upgrade one can hear things

from a recording that were "never heard before". I am now a believer. I

have never heard my rig have such a clean, clear, un-muddled sound.

Pure is a good word. The most subtle, underlying backgrounds are there,

not heard before. Will a tube preamp give an added dimension and

more texture or just add more sound deadening (blocking) curcuits. I am

real tempted to find what a Merlin would do. Since tubes are powering

the sound and only being restrcited with a volume control why and what

good can an additional tube circuit add.

[Daddy Dee]

RichieB,

In my very lay understanding, whether a setup sounds good with a passive or no preamp depends on the impedance matching of the source and the power amp. Some sources have adequate signal to drive the power amp to full power and others don't. Some power amps require more signal than others.

For example, when I tried doing this with the Wright 2A3 amps, they really needed the preamp to drive the power amp.

I have found both the Peach and Merlin to do a superb job in the preamp slot.

Hope you have a chance to listen to either one of these sweethearts.

[edwinr]

You would have to really suck and see to establish whether a passive pre amp would drive any particular power amp. Some power amps probably require more gain than a passive pre can provide.

I agree that in the case of reproducing music, 'less is more' in the signal chain. It's just that certain technicalities may have to be met so that the power amplifier can work properly.

[leok]

I think what one should strive for is sufficient gain to achieve full power out with the volume control at 3/4 to max setting. More than that simply adds to distortion and noise. The Wright mentioned above is a good example of an amp that won't achieve full output using a 1V line source and passive control .. so a preamp is required. In the case os the Moondogs, there is more than sufficient gain already in the amp and a passive control is a great way to go.

The "noise" I am refering to is not simply a noise floor of humm and hiss, but also noise that accompanies the signal itself: distortion and noise modulating the signal masking lower level details

There are also the issues of impedance matching, but they should be considered in the overall design of the system, not addressed by adding extra gain.

Leo

[SET12]

It has been said that the best preamp is no preamp at all and having recently inserted a pure passive preamp (volume) control for my VTL EL84 mono blocks, that may be true. The custom made passive is about as simple as it gets, teflon coated solid copper wire direct to all connections, a 31-step Noble volume control and input switch. I have heard talk that after a system change or upgrade one can hear things from a recording that were "never heard before". I am now a believer. I have never heard my rig have such a clean, clear, un-muddled sound. Pure is a good word. The most subtle, underlying backgrounds are there, not heard before. Will a tube preamp give an added dimension and more texture or just add more sound deadening (blocking) curcuits. I am real tempted to find what a Merlin would do. Since tubes are powering the sound and only being restrcited with a volume control why and what good can an additional tube circuit add.

Richieb,

Congratulations on your discovery!

I found the same path a few years back and have no desire to spend funds on an expensive line stage better to put in your front end especially with Digital Players that feature line outs with enough juice to drive any power amp.

Still with enough input sensitivty and Klipsch's I don't find it difficult at all, My preamp has been on the shelf for years now and it is a pricy one at that in its day! But it sure covered alot up and restricted my dynamics. Two channel performance is my preferance although I could add a switch to easyly switch in and out my DVD player which I also use direct, I just simply swap IC's

The following is a conversation with some of my local Forum members and by the way I am also a big EL84 fan I have posted some pics on the forum here of it it is yellow brass in color and very good looking if I do say so myself! Also I imagine that your amp has the same circuit as the Manley Stingray or the Mahi Monoblocks in which case for the 50/watts out your sensitivity is in the 300 millivolt range more than enough for Klipschs don't even worry if your passive is all the way up! Front end componets are designed not to clip of course Preamps are rated at clipping but rarely do in real use.

So heres some of my conversation over pre or no pre!

Rzr,

I have been waiting a little bit here before I threw some comments out.

Dennis Had lists your input sensitivity as 950 millivolts in or .950 volts.

I did the math on it using a couple of different primary loads for the 2A3 and I see it more in the range of .750 volts which is good!

Now imagine if you had an input sensitivity of .250 volts in!

That would represent a gain of 9.5db from the .750, my own Motiff line stage is just 10db of gain!

If it went the other way like 2 volts in or lets say 1.5 volts in which isn't uncommon you'd need 6-8.5db more gain to make up the system sensitivity from your .750 that you have now! Yek's!

Now lets take that a step further and say a sensitivity of .125 is dialed in thats another 6db of gain for a total of 15.5db!!

That is very easy to do with just a single 6SN7 triode sections cascaded or in series with one another. The 6SL7 the amp is using now in its configuration is producing a gain of maybe about 50 when an 6SN7 cascaded can do upwards of 250

Even the Western Electric 310 can do 150 and thats one pretty tube especially the mesh plate or even the electrically equivilent 6SJ7

I have an article where Dennis Had redesigned one of his kit 300B front ends to to produce a sensitivity of .130 volts this was done so the guy would get better results dynamicly, In Dennis Had's own words it was "explosive"

The trick to making it really work absoulutely is the right gain for the system.

In mine I do strongly suspect that my Sony is doing more than 2 volts just because I've had other sonys with a 2 volt rating that didn't quite have the reach they did play fine though! the sensitivity of my amps is around .7 volts for 10 watts out.

Most of the time I am at 10 or 11 o'clock on my volume from a control that goes from 8 to 4 with clipping occuring around 2 o'clock with the Titanic sound track I think with the cut, sinking of the titanic the sound track for clipping test is relatively gentle for hard clipping because of the short intense peaks that it has but it is very audiable

The control on my CD player may well be linear type and maybe most are on CD players, rather than a Audio tapper type as most preamps use and most are about 10K and mid settings are of course about 5K output impeadance.

Now here's the clincher do you know how much of the signal is typically fed to the gain stages of a preamp when a typical audio tapper control is used?

I'll tell you! As I measured one in one of Dennis Hads preamps! Just 20% at the 12 o'clock position!from ground! and the rest of it is between the preamp and source!

Not good! something Doc and I disscussed a bit.

Where as with the CD player I am using is more in the 50-60% range of the control, Much better!

So my point is when you have enough gain dialed in the front end of a power amp especially from the gain stage that is already being used anyway why not take advantage of it! And have less gain stages over all in the system! to give you more transperancy and even greater dynamics obviously I certainly am not hurting for that aspect! And I have just 3 valves in the signal path!

So these are the kind of things to think about that make alot of sense to me both subjectively and from a measured point or science point of view but I think I have a better understanding of when and why it will or won't work with a preamp or with out a preamp!

So when I design amps I will need to keep all of this stuff in perspective as to marketing. One can have a happy medium for sensitivity though that can do both although both can be optimized

I don't think I can put it any better!

SET