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Old 4th February 2008, 05:38 PM   #1
bigwill is offline bigwill  United Kingdom
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Default Is there much point in tube preamps? (This isn't a troll)

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.
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Old 4th February 2008, 06:20 PM   #2
KP11520 is offline KP11520  United States
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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
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Old 4th February 2008, 06:29 PM   #3
MartyM is offline MartyM  United States
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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/12...eamp/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
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Old 4th February 2008, 06:32 PM   #4
SY is offline SY  United States
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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.
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Old 4th February 2008, 06:38 PM   #5
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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
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Old 4th February 2008, 06:38 PM   #6
MartyM is offline MartyM  United States
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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.

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Old 4th February 2008, 07:07 PM   #7
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Quote:
Originally posted by MartyM
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.
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Old 4th February 2008, 07:14 PM   #8
Tweeker is offline Tweeker  United States
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Part of the question is how much gain do you need?

That is to say, is there much point in preamps?
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Old 4th February 2008, 07:27 PM   #9
bigwill is offline bigwill  United Kingdom
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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
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Old 4th February 2008, 07:33 PM   #10
KP11520 is offline KP11520  United States
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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
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