• 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.

What preamp should I build?

OzMikeH

Member
2007-03-18 9:22 am
I've never built a tube project before, I do maintain some simple tube equipment (although it does pull several amps at 6kV). I'm an experienced electronics tech so I'm not afraid of a complex design.

I'm looking for a preamp design or kit, I'd prefer something that can be done point-point because I'm not set up for making PCBs. I will consider kits as well.
I have a faulty Tektronix 545B CRO I can salvage a power supply and sockets from, maybe even tubes.

My requirements:
Some gain, 6dB is plenty.
volume control.
one unbalanced line in, one line out.
Very high sound quality, high resolution, not muddy or overly warm.

Nice to have:
Balanced line out.
no really obscure parts.
an output topology suited to coupling direct to my active crossover without buffers.

Can anyone point me to a few threads or sites? There's plenty of preamps out there, many with boutique parts, but I have no way of knowing which of them actually sound good.
 
Hi Mike,

The other day, I saw someone asking for a decent Tube Phono Stage schematic to build a stage as his first project.

One guy recommended a kit to make it easier for the "First" project and pointed to this site. They make Preamp/Linestages and Amps too. The site looked interesting but I can't vouch for where they sit in the pecking order. Take a look: http://www.bottlehead.com/et/et.html

Oh, like he said, Eileen is not included with any of the products!

You might ask the forum what they think!

Regards//Keith
 
Just my 2 cents....
There are some key things to note....
I would say the power supply is the most critical section of the pre-amp..... ALthough having good PSRR is nice, I still like using very low impedance power supplies.... I usually like to use a triple Darlington arrangement for the pass element...
Most important is to protect your V_reference, whatever you use protect it...for example if you use a Zener string for your reference, make sure to feed it with a PNP constant current source for example....
If you ever add a phono-stage....you will see how critical the power supply can be...
Typically when you say you want high resolution, to me that means a high gm tube....this tends to make the little things jump out more....
As for the output of the pre-amp....the norm is to use the resistor loaded cathode follower....also a high gm tube is good for lower output Z..... The resistor loaded follower is not all that linear for large signal analysis....so a current sink is typically used in the cathode to maintain a constant current, this will greatly help linearize the follower .....

Chris
 
Try this.

I've made a lot of line amps, and this is the daddy so far.

littleMoeb.gif


If interested, let me know, and I'll show you the power supply and stuff.

Hau'oli Makahiki Hou,

Poinz
 

zacster

Member
2003-12-03 10:49 pm
NYC
The Aikido at Tubecad.com is an easy build, but it is board only. You need parts (There may be a kit available) and a power supply, chassis, jacks etc... But you're a tech, so this shouldn't be too hard. Bottlehead is good too. I've built both a BH and an Aikido, and my vote goes to the Aikido on sound, but BH on ease of build, mostly because it is a complete kit.
 

JimW

Member
2004-10-29 11:44 am
Another tube that works well in a low and hot srpp is the ECC99. I have one set up using 91r on cathodes, running 230 volts across the pair (115 per tube) at 17ma. Sounds pretty good, and should have an output z around 800 ohms if I calculated correctly. Don't forget to elevate heater voltage to avoid problems with the uper half or upper tube, as the case may be.
Jim
 

jduffy

Member
2006-10-18 2:40 pm
12AU7

My first from scratch preamp was Bruce Rozenblit's 12AU7 Line Preamp from Glass Audio. Look it up online and you can find the schematic EZ. I built it for under $100 and it works very well. Great learning experience and I've passed it around to my friends to run in their systems, they love the thing.

I've used it with a tube amp, chip amp, SS amp and it never gets in the way of the music.

Good luck with your decision!
 
Hah, got it figured out.  Thank you Netfirms.

In the interests of file and image size, the parts information is a bit terse. If you have questions, ask. Everyt'ing stay bestest kine.

    [IMGDEAD]https://www.audiotropic.net/Demo/big6T4.gif[/IMGDEAD]

Yes, the power transformer is wired unconventionally. I'm burning about ¼ its VA rating, no winding is overvolted, it doesn't even get warm.

Aloha,

Poinz