• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Is there much point in tube preamps? (This isn't a troll)

bigwill

Member
2004-12-25 8:36 pm
UK
As much as I want there to be a good reason to use a tube preamp, they sound good, but hasn't the signal passed through many opamps in the recording process anyway? Does an opamp at line level degrade the signal that much? I really want to believe using tubes sounds better, but my logical reasoning says that your average opamp will have such low distortion it would be pretty much transparent.

FWIW, I am actually building a tube preamp at the moment and I will use it.
 
Well,

This is a really open ended question and should be interesting. The responses will come from all angles and maybe start a few heated debates!

I'm not so sure this is about just op amps. There are many factors that "color" the signal in just about every kind of circuit design from power supplies to capacitors and some say to wire, pcb, power cord and RCA jacks and just about every other choice. This could be a can of worms... be careful what you ask here! LOL

What tube Preamp are you building?

There are a couple of threads right now asking about which would be the best choice in both the Tubes and Chip Amps forums and probably a hundred more dormant here on DIY!

I am interested in the answer too!

Regards//Keith
 
Hi there.

Well actually I had NO hands-on experience with tubes and mostly heard/read internet & retail store "experts" who are insulting to tube users, lots of hype, and opinions from people who never built an amp, etc.

I wondered exactly the same thing you are and decided to separate hype from truth!

Tube circuits are very rare or severely overpriced for car audio and building your own is almost unheard of-especially at high voltage.

So I jumped at the chance at building two 12AX7 tube preamps (along with a +260V power supply) for using in my car or home. It was these:

http://diyaudioprojects.com/Tubes/12AX7_Preamp/index.htm

Here's what I found out:

1. The good tube preamps DO sound different from the 100% solid state!
...however
2. I can't hear the difference if using amplifiers with 'processing' in an amplifier (ex.: home stereo) or with too many preamp stages. Completely took away the effect.

3. I did enjoy the sound most when using my LM3886 amplifiers (where I intentionally have NO preamp stages) because I have a pretty direct audio path.

4. Parts required are stocked on eBay, Mouser, Jameco, Digi-Key, etc. for high-voltage audio (bipolar) capacitors, resistors, and terminals. Got my sockets & tubes on eBay.

5. May be helpful to build your own turn-on & turn-off delay circuits for the heater filaments & audio outputs.. Not very hard.

Hope that helps. Also they were kind of fun to build and were suprising "clean" (very low noise) to the ear. But it had a lot to do with the Silicon Chip magazine's design quality.

I'm not an "expert" by any means so I bet the guys here can help a lot more!

------------------------------------------------------------------------------------
PS: The SMPS & preamps use relatively low current so I eliminated ground loop noise by using an isolated DC-DC +12V power supply
 
For much source material, I believe you're absolutely right. But there are two important exceptions:

1. Vinyl. Tube RIAA amps, properly designed, seem to be kinder on the ears. I theorize that it's because of the dynamic range, freedom from overload, and maybe even some bandwidth limiting. Whatever it is, I find that my worst recordings tend to be more listenable.

2. Vintage recordings. I have hundreds of records that were recorded, mastered, and pressed long before the days of monolithic opamps.
 

cbutterworth

Member
2006-10-03 11:02 pm
My Goodness, what a potential can of worms!

I would venture to say that a well designed preamp regardless of solid-state or tube driven would sound better than a cheaply built and designed preamp. This is evident in my headphone amp - my CMOY does not sound as good as my Meta42 - both are op-amp driven (not that the CMOY is a bad design, it is very good). My $30 solid-state Behringer phono did not sound anywhere as good as my tubed Cornet2 (Hagtech).

As a scientist (my day job), I cannot say whether tubes or op-amps are better because I haven't seen or measured these devices in a comparative manner. I suppose someone could make detailed comparisons with an oscilloscope. BUT, I do know what I discern as sounding better. Also, in order to make a fair comparison, the circuits would have to be as identical as possible so that any differences are the result of the tube or op-amp rather than effects of the peripheral circuitry.

Maybe more important for me is that I love the look of vacuum tubes, and I like the sound of my vacuum tube devices. It gives me a quiet thrill to think of really good sounding music being reproduced via tubes that were manufactured in the 1940's. Could an op-amp sound as good to me? Maybe. Would it look as pleasing to me? Maybe, maybe not.

Just my two cents' worth.

Charlie
 
I should have mentioned that I used my "reference" material which are CDs that I can easily distinguish the sound quality from when using a good audio player.

That made it easier to test.

I was dissapointed at first -couldn't hear any difference-until I switched from my 'average' home stereo to the homemade LM3886 amplifier.

Basically I don't pretend to have all the answers, just my $.02 also.

Hearing those tubes work, and quite well, was really fun!

I guess both solid state & tubes have their place.

:snoopy:
 
MartyM said:
So I jumped at the chance at building two 12AX7 tube preamps


I can't think of many tubes less suited for a preamp (in today's sense) than a 12AX7. You should build something more sensible before drawing conclusions.


Regarding the opamps used in the recording chain, it's a sad fact that at least 90% of all recordings really suck. It makes almost no difference what is the reproducing equipment for those.

Some desperados even use tube buffers with absolutely no purpose but to reduce the intolerable pain those 90% inflict.

Does it make sense to use a tube preamp with high quality digital sources then?

I think it does. Only not any old tube preamp will do. A sensible topology and high quality parts are absolutely essential.
 

bigwill

Member
2004-12-25 8:36 pm
UK
I guess there is something more aesthetic about tube circuits (the physical thing itself and the topology)

I wouldn't get much satisfaction out of putting an opamp in a box but a working tube preamp is a much bigger accomplishment

The tubes certainly don't harm the sound either and possibly enhance since their distortion is low anyway
 
Hi a_s,

I agree about too many bad recordings and I think that problem is getting worse not better despite better abilities. I would say there are three categories, each with different degrees within of about 1/3 each. Very well done, Average and Less than average to just plain unlistenable.

My feeling, and this is not scientific by any means but more of a gut feeling, is a quality system with a tube component somewhere probably allows you to enjoy a higher percentage of the music before your ears bleed somewhere in the unlistenable category. Sometimes that little extra warmth just makes you want more rather than restless.

You know I always look for a high consensus before I make a decision (I hate to waste time and money although this method doesn't always prevent that). But nonetheless, I do respect your input, which preamp tube kit would you recommend? Before thinking about a kit, I was eyeing the Modwright SWLP 9.0SE. So far on the kit side I see the Transcendent, The Bottlehead, and some designs that are being crafted here. Also I see on the SS side, the Pumpkin has a big following.

One thing I would like but could live without is a remote volume control and more steps on the attenuator than less.

Anyone else, I am interested in all the nuances of making this decision! Thanks!

Regards//Keith
 

poynton

Member
2005-03-10 11:57 pm
UK
bigwill said:
As much as I want there to be a good reason to use a tube preamp, they sound good,
A can of worms indeed ....

Do you need to use any preamp, tube or SS ?

Obviously, it depends on the source. Some would say that a 'passive ' preamp is best.


but hasn't the signal passed through many opamps in the recording process anyway? Does an opamp at line level degrade the signal that much? I really want to believe using tubes sounds better, but my logical reasoning says that your average opamp will have such low distortion it would be pretty much transparent.

FWIW, I am actually building a tube preamp at the moment and I will use it.
Those who have heard or own recordings which are made direct to disk using tube equipment would say the quality is unbeatable. Unfortunately, not many make it to CD in their original state.



2.
 
One thing I've noticed, and even started a thread a while back, is this craze for preamps, both tube and SS, that this forum has. What I mean by that is there are a lot of members building preamps with little gain, essentially buffers, and then inserting them into an audio chain that didn't need them in the first place, e.g. a power amp with a high impedance input. Don't get me wrong, preamps make a great beginner project, but a lot of the projects on the forum leave me scratching my head.
 

rdf

Member
2004-06-21 8:04 am
big smoke
Tweeker said:
That is to say, is there much point in preamps?

Yes, but almost entirely for impedance matching. For resistive 'passives' 10kohm pots are about the limit before Zout is too compromised and many tube output stages aren't happy with the load, especially vintage ones. TVC looks like a nice way to go.

SY nails the other half. A world of vintage recordings didn’t use op amps. Many top consoles still don’t. Recording technology has also changed immensely in the last few years. Consoles are digital or just control surfaces for manipulating audio in the digital domain. Many microphone preamps have digital outputs. As do some microphones. The console is often (typically?) only used for monitoring and none of the audio you hear passes through it. The ‘billion of op amps’ argument has more validity in cyberspace than in modern recording facilities. It wouldn’t surprise me that soon most of the op amps in the recording chain will be in the output of your CD player.
 
Hi Keith

I know absolutely nothing about kits. The few configurations using tubes which i've really enjoyed use either choke loading or a step-down output transformer. I have tried practically all tube topologies and found most of them unsatisfactory for my taste. The majority of tube preamps readily fail a bypass test.

The Pumpkin certainly seems intriguing - too bad that thread is impossible for me to follow. Has anyone actually mentioned anything regarding the sound?
 
rdf said:


Yes, but almost entirely for impedance matching. For resistive 'passives' 10kohm pots are about the limit before Zout is too compromised and many tube output stages aren't happy with the load, especially vintage ones. TVC looks like a nice way to go.



Over the years i have shared this opinion (as well as many others, often contradictory :)) but these days i consider the active preamp an essential part of a music system.

Arguably, a great system can be built with passive attenuation, especially if the source is analogue. Digital sources, at least to my ears, demand an active preamp, irrespecive of impedance matching ease.

A good active preamp can really shine subjectively and i have absolutely no explanation why. It can accentuate bass lines, improve dynamics and soundstaging and generally make more complex music "make sense".

Passive preamps, for some reason are always better with simple acoustic music and they accentuate details, air and ambiance.

The TVC i used to have was a compromise of both approaches. Sadly, it didn't have the drive of a good active, nor the transparency of a nice passive attenuator. Over a long period of time i tried to like it in various, mostly tube setups, but ultimately could not live with it.

If you treat the active preamp as a beginner's project you are certainly better off with a passive attenuator.
 
I think the traditional terms "preamp" and "amp" come mainly from ready built stuff you buy in shops. They may already have become outmoded.

The musical signal has no idea what it's going through in terms of the number and type of boxes, except that it goes through a number of gain stages.

When you build your own stuff you can put anything anywhere - an amp can be one or two or three stages. You can have a preamp or a control box or a passive pre or a DAC-Pre where the DAC output goes straight into the grids of the first tube stage. The power supply and/or the filament supply can be onboard or outboard. You can build monoblocks or stereo chassis. You can really do what you like.

I think it's more logical to see the whole "amplification" stage as one thing, to be constructed any way you like. That way you get rid of unnecessary stages, useless buffers etc etc. I'd personally join all the gain stages up with transformers and leave it at that.
 

ray_moth

Ex-Moderator
2004-01-27 8:55 am
Jakarta
Part of the question is how much gain do you need?

That is to say, is there much point in preamps?

I fully agree. All that most people need is a channel selector switch and a volume control. To call these minimal controls a 'preamp' seems silly - by that token, is the on/off switch also part of the 'preamp'?

One thing I've noticed, and even started a thread a while back, is this craze for preamps, both tube and SS, that this forum has.

You've noticed it too, huh? I wonder how much of that stems from beginners being given the advice to "try building a line stage first". Fine if they need one, but I doubt many of them do these days. To me, the concept of a preamp as an in-line component for all inputs is a hangover from the olden days, when signal sources all had different levels, and tone controls were popular - and sometimes necessary, because of the low quality of some broadcasts and recordings.

It seems sensible, nowadays, to 'normalize' the signal as the first step before using it as an input to a general purpose audio amp, and to enclose whatever specialized gain and correction circuits are needed within the signal source units themselves. This approach restricts the complicated circuits to those sources that need them and avoids cluttering the signal path unnecessarily. It also results in all the interconnect cables carrying signals at line level, which is better for signal/noise ratio.

If you're listening to vinyl, then you do need to amplify and correct the signal so that it's at line level and the frequency response is 'flat'. This little unit is a kind of preamp, true, but it has unique application and would be better built into the turntable plinth. The same holds true with other specialized electronics such as the DAC built into the CD player box and the tape-head amplifier and erase head oscillator built into the tape recorder box.