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Old 14th August 2003, 05:12 AM   #1
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Default possible project for me, tube preamp.

i'm an EE student with a little knowledge of circuts, mostly picked up as i go. i think audio is neat, but don't really call myself an audiophile. i hate hiss.

in any case, i'm building an amp for some spekaers for my computer. i'm wondering if a tube amp or tube preamplifer is a feasible thing to try. i already have parts for a gainclone (except for PCB).

since i know about nothing about tubes (and you can insert links that explain their useage and how they work) i am at a slight disadvantage.

in the end, i'm looking for something that will change the sound noticably, hopefully in a good way, and be cheap.

since i am a college student, i have limited funds.

so is a cheap tube preamp feasible?
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Old 14th August 2003, 05:47 AM   #2
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Default Re: possible project for me, tube preamp.

Quote:
Originally posted by theChris
in any case, i'm building an amp for some spekaers for my computer. i'm wondering if a tube amp or tube preamplifer is a feasible thing to try. i already have parts for a gainclone (except for PCB).
You won't need a preamp as the S/C should put out enough voltage to drive a poweramp. Just put a VC at the input.

Quote:
since i know about nothing about tubes (and you can insert links that explain their useage and how they work) i am at a slight disadvantage.
The Grounded Cathode Amplifier article at Tubecad is the best. When you understand that, read the rest of the site.

Quote:
in the end, i'm looking for something that will change the sound noticably, hopefully in a good way, and be cheap.
If you want a tone control, simply design them ito the circuit. A good tube amp won't colour the sound appreciably, unless it's designed to like a guitar amp.

Quote:
since i am a college student, i have limited funds.

so is a cheap tube preamp feasible?
Cheap is relative. If you hunt around for second hand parts like power and output transformers, then it can be done for a modest cost. This will take some time, but there are good new parts in the Hammond iron which are quite cheap. Glass and iron are probably where the bulk of you expense will be, and that will be determined by how much power you want. If you want more than a couple of watts, then also select a less commonly used, but still common tube like the 807 to build around.

I beleive there are also some really cheap kits, but I can't find the link in my biikmarks so someone else hopefully will post.

Our resident 'honorary Scot' (short arms long pockets) Tim will have ideas and resources as he only builds amps that cost $3.

A good parts source is AES. Probably not the absolute cheapest, but good service, shipping and specials and will at least give you an idea of what some parts will cost.
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Old 14th August 2003, 06:33 AM   #3
SHiFTY is offline SHiFTY  New Zealand
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A tube preamp / linestage is very easy to implement, and would only take a few hours to build. You could use a 6SN7 or 12AU7 dual triode (two devices in one glass tube) and a tube rectifier. Do a google search for a 6SN7 linestage schematic and see what you come up with. For better results you could use SRPP with one tube per channel.

A power transformer could be got from an old radio, reel-to-reel or even a couple of back-to-back 6V transformers.

Tubes are easy, look good and sound better...
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Old 14th August 2003, 03:33 PM   #4
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I forgot to include this earlier. Bit of a long read and very informative. Not exactly a beginner work, but will give you plenty to think about if you want to play with tube amps.

http://w3.mit.edu/cheever/www/cheever_thesis.pdf
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Old 14th August 2003, 09:31 PM   #5
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define S/C and VC. no clue on either. also SRPP (PP is push pull?)
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Old 14th August 2003, 10:00 PM   #6
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Hi,

Quote:
define S/C and VC. no clue on either. also SRPP (PP is push pull?)
S/C... Source? CDP, DVD or anything else with a 2V RMS output high enough to drive an amp to full blast?

VC, volume control.

SRPP, Shunt Regulated Push-Pull.
A nice nomer for a not so well regulated PP circuit that can sound really good, offers a nice alternative where cathode followers are not wanted.
It has a lot of mutants, some more complex than others but what most seem to forget is that for the SRPP to shine you really need a very good PSU....which kind of proves that it doesn't regulate itself all that well.

Cheers,
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Old 14th August 2003, 10:03 PM   #7
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S/C = source component. VC = volume control. I think.

What's your budget? The Bottlehead Foreplay (found at www.bottlehead.com) is a pretty nice sounding tube preamp for $150. Not the best thing you can build at that price, but it's really simple to build, the support on the forum is outstanding, and it's a heck of a lot of fun. That was my intro to DIY audio, FWIW.
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Old 14th August 2003, 11:05 PM   #8
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well, the budget is really as low as possible. like i said, i'm looking more for fun with tubes then something that is really good. thats why i asked around first.
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Old 15th August 2003, 02:23 AM   #9
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Sorry. S/C = sound card and VC = volume control. A soundcard will likely put out a couple of volts, easily enough for it to be connected to a power amp through a simple volume control. I think a preamp is a waste of your limited resourves.

SRPP was answered by Frank. But if you want to know more voila!

A second hand fixer upper tube amp might be an option for you too, as you have most of the expensive bits, ie the iron there already. Put ads in the local papers and ask around. Someone will likely have one in their attic/basement they'll let an engineering student have for free. A thorough rebuild will teach you as much, maybe more, than a scratch build.
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Old 17th August 2003, 05:31 PM   #10
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BTW, i've been doing more research on tubes. like pentodes and tetrodes and triodes and all. and then i saw a thread about low voltage tubes and tubes for preamplifers.

in any case, what would some cheap and decent tubes for this use be? i see ecc86 pop up, what about 12au7 or 12au7a?

ADDED Q. as for the power supplies, i usually see a tube diode. is this required or could i use PN diodes of proper rating?
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