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Old 9th January 2008, 01:53 AM   #1
OzMikeH is offline OzMikeH  Australia
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Default What preamp should I build?

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.
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Old 9th January 2008, 02:01 AM   #2
arnoldc is offline arnoldc  Philippines
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Old 9th January 2008, 02:25 AM   #3
KP11520 is offline KP11520  United States
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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
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Old 9th January 2008, 02:28 AM   #4
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Default 12b4

Here's a nice thread for you to digest This pre sounds great and can be as simple or complicated as you like: 12b4
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Old 9th January 2008, 02:34 AM   #5
cerrem is offline cerrem  United States
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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
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Old 9th January 2008, 03:22 AM   #6
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Try this.

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

Click the image to open in full size.

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

Hau'oli Makahiki Hou,

Poinz
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Old 9th January 2008, 04:11 AM   #7
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Quote:
Originally posted by Poindexter
If interested, let me know, and I'll show you the power supply and stuff.
I'm interested in anything you do Poinz

dave
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Old 9th January 2008, 04:21 AM   #8
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Thazz why you my idol, Dave.

You want the whole circuit? I'm working up a page about it, but it'll take a little time. I do have various working schems, though.

Best,

Poinz
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Old 9th January 2008, 04:37 AM   #9
zacster is offline zacster  United States
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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.
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Old 9th January 2008, 05:55 AM   #10
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Quote:
Originally posted by Poindexter
Thazz why you my idol, Dave.

You want the whole circuit? I'm working up a page about it, but it'll take a little time. I do have various working schems, though.


Take your time... can't rush the cook...

dave
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