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Old 18th April 2012, 11:30 AM   #1
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Default preamp for reciever?

Hey all,
I'm an EE student and want to get my hands dirty on some diy audio equipment for my hifi system at home.
Currently this is my system:

Laptop -> Optical in Yuan Zero DAC -> Yamaha Integrated Reciever rx367 -> stereo paradigm mini monitors.

The yuan zero dac has a preamplifier stage but i have it turned off because I don't think its very good.

I was browsing around for a DIY kit for $100-200USD and found these chinese copy preamp of the Jadis JP-200 and Marantz 7
DIY Kit ref Jadis JP-200 JP200 Tube Pre Amplifier 2 Ch | eBay

I know that these where originally designed for phono line amplification. But im wondering if it would serve any benefit to my system?
I know the rx367 has a preamplifier internally, so is adding another pre-amp overkill?
Im aware that adding a LNA at the start of a cascade drastically reduces noise figure and improves S/N.

Any advice is greatly appreciated
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Old 18th April 2012, 12:22 PM   #2
SY is offline SY  United States
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Stay away from cheap Chinese gear that's sold using stolen trademarks. The designs and implementations are consistent with the ethics.
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Old 18th April 2012, 12:54 PM   #3
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yeah i figured as much after a little more research.
I was thinking getting a Line Stage Preamplifier from Aikido. Unfortunately my knowledge of what im actually doing is minimal...
Im shooting in the dark here.

Any recommendations on an Aikido kit and specific tubes?

Cheers
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Old 18th April 2012, 01:03 PM   #4
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Quote:
Originally Posted by olmeister View Post
Hey all,
I know that these where originally designed for phono line amplification.
Be careful with this stuff: phono inputs are very sensible, and uses a non flat audio response curve, so, using it for other function will be very unsatisfatory: excess in bass response and saturated audio output. You must use a flat preamp.
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Old 18th April 2012, 02:52 PM   #5
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olmeister: As already mentioned, you want a line level pre, not a phono pre. Phono stages have lots more gain (like around 70db) and RIAA eq (not needed for line stages) than line level stages. Line level preamps typically have less than about 20db or so gain, sometimes lots less.

The Aikido preamp is well regarded around here, and quite straightforward to build with lots of threads and support on the forums here. Stuffing a PCB is easier than point to point wiring IMO. The Aikido is very configurable for gain by choice of tube types.

There are many good choices for the Aikido power supply as well. You can roll your own, or buy one of broskie's kits, and there may be a PCB that you can pick up from the vendor forums here (username=Geek) to make a nice PS for the Aikido. There is a long thread here covering that also.

I'm sure there are a few other tube line amp projects around here that may be a little simpler, but stuffing a well-documented PCB based project is hard to beat.

I imagine that Bottlehead also offers a few tube based kits as well........

Do you have a soldering iron and a multimeter? Are you comfortable working around high voltage?
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Old 18th April 2012, 02:55 PM   #6
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Why do you want a preamp? Most DAC outputs don't need any further amplification.
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Old 19th April 2012, 12:27 AM   #7
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@boywonder
Hi, thanks for the reply, yes I have experience with dealing with high-voltage & soldering/multimeter.
Does the octal all-in-one Akido kit (Aikido Octal All-in-One Kit)
require its own power supply? I was under the impression that a linear step down transformer was needed only, which is usually much more stable than switching regulators.

@DF96
I know I want to build something that comes in a kit and I like the idea of vacuum tubes, searching around for complete kits I found these 'preamps'..
But your absolutely right ~$180 dollars is alot to spend on a tube preamp if It does nothing for my sound system..
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Old 19th April 2012, 12:54 AM   #8
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Quote:
Originally Posted by olmeister View Post

Does the octal all-in-one Akido kit (Aikido Octal All-in-One Kit)
require its own power supply? I was under the impression that a linear step down transformer was needed only, which is usually much more stable than switching regulators.
Looks like the all-in-one setup just requires a power transformer, more like a "step-up" as you need to provide B+ for the tubes, as well as filament voltage and current. Broskie spells it out fairly well; you'll need something between 200-250V and 12VCT for filaments. Looks like the board can provide either 6.3V or 12.6V to the tubes. A 40 ma transformer is probably plenty, which is what you will typically find for preamp duty. The 48V that Broskie mentions will work with a few tube types (I don't know much about what tubes are happy at low voltages) but your common types (6SN7/6SL7 etc) will require the 200-250V.

Linear supplies are typically used because they are quieter ie they don't throw a bunch of switching related harmonics on the B+ rail. The smoothing RC stuff is on the PCB.

You actually need to work backwards, and determine how much gain you need, that will determine tube choice, which will determine the power transformer (to some extent). DF96 has a good point......you may not need any gain at all.

Look at Edcor's and Hammond's offerings for this. I'm sure that there are other places as well. You'll need to do a little studying to determine your desired B+ voltage

Last edited by boywonder; 19th April 2012 at 12:57 AM.
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Old 19th April 2012, 01:03 AM   #9
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olmeister,

I believe that your Yamaha unit is an A/V receiver. There is a distinct chance you are pouring money down the drain, in trying to improve things.

Please post a photo of the rear panel. Seeing what the RCA jack labels look like may provide some clues. Is there some sort of bypass that works with 2 channel sources? On a 2 channel receiver or "integrated" amp, the desirable feature is preamp out/amp in. That feature allows an external preamp to drive the power section, without any interference from the internal control circuitry.
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Old 19th April 2012, 02:32 AM   #10
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Yes, you are right, there is no preamp line in, or anything resembling this feature. But this yamaha receiver was only ever a temporary solution, considering i borrowed it from a friend..

Perhaps i could bi-amplify the power amplifiers instead? Are there any good tube power amplifier kits around?
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