# DIY tube pre-amp...I wanna build one.



## AWC (Mar 31, 2008)

I am looking at building a tube pre. I don't want to spend very much money the first go round because I'm not overly inclined with this stuff. It's a learning experience. What are your favorite sites to begin with? How do I start? Any suggestions? I have an aold 6 channel analog receiver that is bare bones but built like a tank. Copper chassis, monster power supply, gold connectors....I'm sure it's groovy. I need an active x-over and tube pre DIY kit. Any ideas?


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## AWC (Mar 31, 2008)

home stereo, sorry


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## Mooble (Oct 21, 2007)

You could probably find the room to mount this in the chassis somewhere. I think it does need an isolated power supply though.

http://www.audiodigit.com/?section=81 Not bad for $100.


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## chad (Jun 30, 2005)

Mooble said:


> You could probably find the room to mount this in the chassis somewhere. I think it does need an isolated power supply though.
> 
> http://www.audiodigit.com/?section=81 Not bad for $100.


A 6SL7 wants a plate voltage of around 200V, the 6SN7 CAN be used with 150 (of course they did not use this)

I want to see what they are using to derive a decent plate voltage to the tube.

To the OP, I don't care for these "runs on a 12V adaptor" designs. There are many out there. Find a design with a good-ol iron and copper power supply and build from there, you may want to look at things like the old Dynaco designs for preamps, they are fairly easy.

AND BE CAREFUL because this stuff WILL knock you on your ass.


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## thehatedguy (May 4, 2007)

If this is the first project for you, I would recommend a Bottlehead Foreplay 3 preamp. Awesome kit with great instructions...and the web support on their subsection of Audio Asylum is very good too. Plus...they are great sounding preamps. I think the kits are in the $400 range.


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## silent1 (Jun 2, 2005)

Maybe you could use something from pro audio like...

http://www.musiciansfriend.com/prod...s-Tube-MicrophoneInstrument-Preamp?sku=180643

Just a thought.


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## silent1 (Jun 2, 2005)

or

http://www.musiciansfriend.com/product/Behringer-TUBE-ULTRAGAIN-MIC100-Preamp?sku=182482


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## Spasticteapot (Mar 5, 2007)

silent1 said:


> or
> 
> http://www.musiciansfriend.com/product/Behringer-TUBE-ULTRAGAIN-MIC100-Preamp?sku=182482


These are microphone preamps.

I would look at DIYAudio.com - It's a terrific place full of the best DIYers there are. Nelson Pass - designer of legendary audio equipment for home and car - even has his own section!

Outside of guitar amplification, I avoid tubes whenever possible. That said, I do have a few pieces of advice from my fiddling with older radios.

1. Buy high-quality output transformers whenever possible. While you likely won't need one of these for a pre-amp, a well-made output transformer can make the difference between a mediocre and a stellar amplifier.

2. Buy high-quality tubes. Cheap Chinese tubes have higher tolerances for flaws in performance, and don't last as long. This leaves you two options: New-old-stock (NOS) tubes, or high-end new stuff.

3. Test your tubes whenever possible. Unless you're buying factory-guaranteed high-end tubes (which cost a fortune), you run the risk of a tube having either internal deformations or air leaks. A cheap "tube tester" will alert you to major flaws, but whenever possible a computerized tube measurement device (which costs a small fortune) should be used to test and match them.

4. Don't go in for fancy wire or components - but don't go for total crap, either. Speaker-grade film capacitors should be used whenever possible, and power supply capacitors should always be bypassed by small film caps. 

5. BE VERY CAREFUL WITH CONSTRUCTION AND GROUNDING. Tubes require voltages sometimes as high as 900 volts, more than enough to kill you. 

Here's a simple enough looking preamp I found - it's based off of a popular commercial design.

http://diyparadise.com/simplepreamp.html

Instructions:

http://www.diyparadise.com/preamptutorial.html

Also...you mentioned a six-channel analog reciever. Any thoughts of selling it?


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## chad (Jun 30, 2005)

Spasticteapot said:


> Outside of guitar amplification, I avoid tubes whenever possible. That said, I do have a few pieces of advice from my fiddling with older radios.


I would normally say the same being a lame ass but I will confess that I LOVE to tinker with them! They are very rewarding to build and I find it relaxing... you will NEVER see my buying tube Hi-Fi gear unless it's to gut it for transformers 



Spasticteapot said:


> 1. Buy high-quality output transformers whenever possible. While you likely won't need one of these for a pre-amp, a well-made output transformer can make the difference between a mediocre and a stellar amplifier.
> 
> 2. Buy high-quality tubes. Cheap Chinese tubes have higher tolerances for flaws in performance, and don't last as long. This leaves you two options: New-old-stock (NOS) tubes, or high-end new stuff.
> 
> ...



Great advice!

You can scare up cheap but good tube testers at Hamfests and auctions, as for parts I like the "orange drop" caps for a damn good, reliable, affordable option. As for safety, work with one hand in your pocket, cut an alagator clip in half and put a 470 ohm 5W resistor in line, clip one end to a good ground the other is your "Jesus stick" Use it or meet him. I clamp it on the B+ cap after draining the bias supply, I leave it there till I'm done working.

New Sensor is a great source for tubes, not NOS goodness but not cheap ass Chinese tubes either, mostly Russian (sovtek), a Chinese tube will just give you headaches in microphonics and early failure, in power amps when a tube fails it takes other stuff out most of the time. They are also great people to work with, AND have odd parts you may need. I also get a bunch of my lytics there.

Another thing to watch is unlike SS stuff used in audio as we know it, tubes are MORE THAN HAPPY to operate up into RF frequencies, coupled with the fact that they run at high impedances you have the perfect recipe for HF oscillation, when you first fire it up watch the PS voltage for sudden sagging and monitor the output on a scope before hooking it to ANYTHING.

He was not ****ting about output transformers, a true builder is always watching for that "gem." IT IS a passive component and WILL have it's own sound, especially older ones. the design of the transformer such as input impedance set up design parameters such as how much plate voltage you can safely use, what class you will run in, some are ultralinear, some have feedback taps.

Fortunately preamps are normally cap-coupled so that's down the road.

IF you build one build a real one, use a real HV supply with manly plate voltage, make it look baller and take pride in it, it's won't be you last project of this nature I'll bet.


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## Spasticteapot (Mar 5, 2007)

chad said:


> I would normally say the same being a lame ass but I will confess that I LOVE to tinker with them! They are very rewarding to build and I find it relaxing... you will NEVER see my buying tube Hi-Fi gear unless it's to gut it for transformers


I cannot stand how tubes sound. My favorite pair of speakers I've owned is a pair of studio monitors - the very definition of "cold" and "analytical" sound. 

That said, tubes are loads of fun to work with, look gorgeous, and are generally far less of a headache than solid-state equipment featuring hundreds of miniscule parts including dozens of static-sensitive transistors and integrated circuits that you will inevitably mount backwards, frying the entire amplifier when you turn it on. 




chad said:


> . As for safety, work with one hand in your pocket, cut an alagator clip in half and put a 470 ohm 5W resistor in line, clip one end to a good ground the other is your "Jesus stick" Use it or meet him. I clamp it on the B+ cap after draining the bias supply, I leave it there till I'm done working.


Sage advice. 



chad said:


> a Chinese tube will just give you headaches in microphonics and early failure, in power amps when a tube fails it takes other stuff out most of the time.


He's not kidding about this. In a solid-state amplifier, a failed transistor will generally just cause the amplifier to stop working. In a tube amplifier, a malfunctioning tube can take out the entire amplifier, including the massively expensive output transformers. 

Unlike most of the nonsense ranted about in Stereophile, "microphonics" is actually a very valid issue. A vacuum tube is made of a bunch of tiny metal plates and bits of mesh arranged inside a small glass tube from which all air has been evacuated. Loud noises (such as those made by speakers) can cause vibrations of these tiny bits of metal, causing them to do very strange things indeed.


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## 60ndown (Feb 8, 2007)

there is a z-box for sale at 

www.decware.com 

classifieds section

for $250,

buy that and build a copy and sell the copy 2 me

OVERVIEW:

The ZBOX is designed as a stand-alone tube output stage for CD players or DACs. After offering mod's for a couple of different CD/DVD/SACD players that included a tube output stage, we decided to make the ZBOX so anyone could upgrade their CD player.

The ZBOX is not just another buffer stage, if it were it would only make things sound marginally better and only on certain players/DACs. The ZBOX works by creating a starved voltage condition in the filament of the tube that in turn causes an increase in harmonics.

The results are as follows:

Restores proper frequency balance though better impedance matching.
Improves tone
Relaxes and opens up the music for better detail, imaging.
Reduces listener fatigue.
Enhances the 3D effect of better recordings.
Of course there are no circuit boards and no Chinese parts. There is a lifetime warranty though. Internally the ZBOX uses top grade resistors and poly film & foil capacitors on each channel. The output level control is made by ALPS, internal wiring by MOGAMI. Voltages are low for tube gear so the tube lasts for many years. Because of the lower voltages and lack of heat the ZBOX is a plug in and forget item. Designed for 24/7 operation there is no power switch. This ensures that the unit is always warmed up and at peak performance any time you turn on your CD player.

A final advantage to using a ZBOX is the simple fact that you can tube roll with your choice of 12AX7's, 12AT7's or 12AU7's. Each of these tubes have a different signature as does every brand of each tube so you gain tremendous control over how your system sounds by voicing it to your tastes.


FEATURES:

The ZBOX features an RF proof powder coated steel chassis with removable power cord, one pair of input and one pair of output jacks and a level control. The tube is located so that it can be easily changed without removing any covers. This is a plug it in and forget it solution to that CD sound that always errors towards thinness rather than richness. It removes the underlying stress in the playback of CD's that many people don't even realize is there until they've heard it gone.


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## AWC (Mar 31, 2008)

This is not my first project but it will be my most extensive. I rebuilt a 1961 Fender Princeton Guitar amp when I was younger and it has the sweetest tone now. I enjoyed the process though I admit I have a lot to learn before I even pick up a soldering gun. I'm looking for the right project (thank you very much, all) to have a reference point for learning. I figure if I have the parts in hand when I go to studying it will be easier. I have no problem taking a year to build. It seems like I have a whole box of parts (hammond OT's, NOS 12AX7's) but I am not quite ready to to damage them...or myself. Thanks.


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## chad (Jun 30, 2005)

60ndown said:


> OVERVIEW:
> 
> The ZBOX is designed as a stand-alone tube output stage for CD players or DACs. After offering mod's for a couple of different CD/DVD/SACD players that included a tube output stage, we decided to make the ZBOX so anyone could upgrade their CD player.
> 
> ...


Cool, an RF proof distortion generator 

That Stevie, he's a true audiophole all right


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## Spasticteapot (Mar 5, 2007)

60ndown said:


> there is a z-box for sale at
> 
> www.decware.com
> 
> ...


Aside from the obvious copyright issues and difficulty of construction, this is simply a buffer - it has no gain, and is useless as a pre-amp. If you want it, buy it yourself.



aworldcollision said:


> This is not my first project but it will be my most extensive. I rebuilt a 1961 Fender Princeton Guitar amp when I was younger and it has the sweetest tone now. I enjoyed the process though I admit I have a lot to learn before I even pick up a soldering gun. I'm looking for the right project (thank you very much, all) to have a reference point for learning. I figure if I have the parts in hand when I go to studying it will be easier. I have no problem taking a year to build. It seems like I have a whole box of parts (hammond OT's, NOS 12AX7's) but I am not quite ready to to damage them...or myself. Thanks.


Try the Audio Note design I linked to - Quite a few people have built it, or variants therof.


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## 60ndown (Feb 8, 2007)

chad said:


> Cool, an RF proof distortion generator
> 
> That Stevie, he's a true audiophole all right


i picked up 1 of his modded cd players locally,

he did something with a regular pioneer player and made the output via a tube.

the difference in sound between it and every other cd player ive ever heard was not subtle.

some things make no sense on paper, the only way to now what works is to

'listen to it'

until you get over to decware for a listening session, or build one of his designs, to plans, im gonna take all your scepticism about his ability with large grains of salt.

and even if you do visit him and listen to his reference system, and dont like it, ill assume its because decades of multiple killowatts and beer have damaged your hearing permanently 

'teresa'


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## drake78 (May 27, 2007)

A good warm recording and a nasty bright SS recording?


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## AWC (Mar 31, 2008)

drake78 said:


> A good warm recording and a nasty bright SS recording?


walk into a bar...the digital recording ducks


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## chad (Jun 30, 2005)

60ndown said:


> i picked up 1 of his modded cd players locally,



Here ya go Marge, Mod your own.... http://www.lampizator.eu/


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## drake78 (May 27, 2007)

aworldcollision said:


> walk into a bar...the digital recording ducks


One recording uses all magical analogue cd tube equipment.


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## AWC (Mar 31, 2008)

drake78 said:


> One recording uses all magical tube equipment.


I actually use a tube mike pre on my digital recordings...hey could I use that as cd pre-amp? It seems like the gains may be way too high.


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## chad (Jun 30, 2005)

aworldcollision said:


> I actually use a tube mike pre on my digital recordings...hey could I use that as cd pre-amp? It seems like the gains may be way too high.


Depends on what it is, you can always pad it, is it 2Ch?


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## drake78 (May 27, 2007)

Tubes amps sound like they have the highs rolled off and the lowers warm frequencies boosted?


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## chad (Jun 30, 2005)

drake78 said:


> Tubes amps sound like they have the highs rolled off and the lowers warm frequencies boosted?


They sound like transistors in a well designed circuit and run in a linear state 

It's when you start "starving" or "overdriving" them is when you really start to notice the "tube sound"


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## AWC (Mar 31, 2008)

chad said:


> Depends on what it is, you can always pad it, is it 2Ch?


It is a two channel (dual-path) mic-pre by presonus.
http://www.sweetwater.com/store/detail/BlueTubeDP/


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## drake78 (May 27, 2007)

chad said:


> They sound like transistors in a well designed circuit and run in a linear state
> 
> It's when you start "starving" or "overdriving" them is when you really start to notice the "tube sound"


Tube amps do have a higher resistance output than SS. Wich is also due to the output tansformers on tube amps. Wich alters the the FS response.


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## AWC (Mar 31, 2008)

I'll be damned...says line level right there on the page. Go figger.


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## drake78 (May 27, 2007)

Ohhhh laaa laaa that's sounds so harsh and tubey.


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## chad (Jun 30, 2005)

drake78 said:


> Tube amps do have a higher resistance output than SS. Wich is also due to the output tansformers on tube amps. Wich alters the the FS response.


In OTL designs yes, but in a transformer design they have a MATCHED output impedance via the taps on the OT, grossly mismatch the taps to the driver impedance, buy a new transformer and/or shorten tube life, it ain't like an accumatch.

For all you damping Factor lovers. Calculate the DF of a tube amp


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## drake78 (May 27, 2007)

I'd go with the SS recording because it's so detailed and accurate.


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## chad (Jun 30, 2005)

drake78 said:


> I'd go with the SS recording because it's so detailed and accurate.


I can't dis-agree, I DID love the Neumann and Telefunken mics we had, they just worked, but that's kinda like a guitar amp and the charged diaphram just worked well with the tubes, from there on...SS all the way.


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## AWC (Mar 31, 2008)

drake78 said:


> I'd go with the SS recording because it's so detailed and accurate.


It could be that detailed and accurate are less than desired effects without complete studio silence as is normal in the modern DIY studio. Never really thought about it.


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## drake78 (May 27, 2007)

Yes, don't we all love audiophile quality recordings.


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## silent1 (Jun 2, 2005)

I would love just to hear a tube amp.


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## silent1 (Jun 2, 2005)

Spasticteapot said:


> These are microphone preamps.


I understand, but couldnt these be modded in someway to work? Ive seen people use Behringer processors in there car. Maybe someone could think of way to make these work, plus they're cheap.


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## Spasticteapot (Mar 5, 2007)

silent1 said:


> I understand, but couldnt these be modded in someway to work? Ive seen people use Behringer processors in there car. Maybe someone could think of way to make these work, plus they're cheap.



The processors would work without any modification at all - all that is done is to swap out the switched-mode power supply for one capable of running off 12 volts. 

Modifying a microphone preamp is a much more difficult task - you're better off starting from scratch.


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## thehatedguy (May 4, 2007)

I'm an hour west of Charlotte and will have the HSS Fidelity HT230 tube amp in my car.



silent1 said:


> I would love just to hear a tube amp.


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## AWC (Mar 31, 2008)

thehatedguy said:


> I'm an hour west of Charlotte and will have the HSS Fidelity HT230 tube amp in my car.


 Bastard I've been looking at the HSS stuff but decided I'd rather eat...I know. To each his own. Let me know if the angel's sing or if you want to shoot the off-key wing laden ****-tards!


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