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Old 1st April 2002, 05:02 AM   #1
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Default need diy tube preamp (line-stage) recommendation and general tube advice

Sorry if this has been asked before, but some of the other threads were hard for me to follow since I am completely new to both tubes and diy.

I have a pair of Sound Dynamics RTS3 speakers and an Art Dio. I am thinking I would really like to try and introduce tubes into my system.

So, I would love to try and make a cheap diy tube preamp. Unfortunately, I have no idea what to look for in a design.I would reallly appreciate it if anyone could give me a simple design or link to a page with a good project to start.

If I could make a tube preamp with two inputs and enough steps to handle the hot output of my Art Dio I would be set. Of course, a decent headphone circuit for my Sennheiser 580s wouldn't hurt.

I know I may be asking for the impossible, but I really can't afford much so it needs to be cheap. I am thinking something along the lines of the Foreplay preamp by Bottlehead, but I don't think I could even afford that right now and a decent stereo amp, so I would need it to be even cheaper if possible. BTW, right now I'm using a Denon AVR 2400 which I am planning on selling. I have also thought of just making a cheap solid state line stage and using something like the $99 ASL Wave 8 tube monoblocks, but at 10 watts/channel I am worried about them properly driving my speakers. Their efficiency is 89db and I am in a very small room, but I tend to listen to rock and a pretty decent volume.

Thanks,
Ryan
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Old 1st April 2002, 09:49 AM   #2
stigla is offline stigla  Norway
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http://www.users.globalnet.co.uk/~valveamp/

Try that link. Go to "read it" and "line level preamp"

I would go for the Fig. 2 schematic. A pretty common setup, and will work wonderfully with a good tube.

Tubes I would use:
- 6CG7 (6SN7)
- 417A (5842)
- E182CC (7044, 5687)
- 6463

The safest choise would be the 6SN7. Sovtek being the cheapest and pretty OK (some pepole might have quality issues with it.). The 6CG7 is essentially the same tube, but in a different housing.
The E182CC (7044, 5687) might be difficult to find, but would be an excellent choise. An alternatie to these tubes is the ECC99. Also an excellent tube, slightly different specs. but should work OK.
The 417A (5842) is another magnificent tube, but some pepole have quality issues with this one too... Look for the 5842Q. Good tube. Small and cute
I know nothing of the 6463, but the curves looks OK.


If you can't find any of the 13H power supply inductors, 10H will work just fine. (must be 30mA or higher.)


-Stigla
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Old 1st April 2002, 03:29 PM   #3
Asen is offline Asen  Bulgaria
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Hi

Tube pre-amp

If you want to drive headphones check this link:
http://headwize.com/projects/ciuff2_prj.htm

Regards
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Old 2nd April 2002, 02:38 AM   #4
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Stigla, I really appreciate your recommendation and I'm definitely going to look into it.

Since I am just getting into both diy and tubes, I still have a few questions that I could use some help with about the best overall idea

1. How much would you estimate the active preamp would cost with some of the parts you mentioned?

2. Would this be more cost efficient than a Bottlehead Foreplay preamp (which I think is just a passive pre)?

3. How would an active gain stage work with a dac with an extremely hot output? My Art Dio has a 7 volt output which if necessary could be attenuated or fixed with a mod, but I don't know if I would want to change it.

4. Does this have two inputs? What kind of functionality would it have? I would probably be replacing my Denon AVR 2400 receiver with this and a solid state stereo amp from someone like Parasound, Adcom, or Rotel. I don't think I would miss the remote volume and all of the inputs, since all I really need is a vcr input and dac input and my vcr can handle my video inputs.

5. Would this be better than getting some Antique Sound Lab Wave 8 monoblocks? I would probably use them with my Denon until I could make a diy ss preamp. However, although my speakers are in a small room at a distance of probably only about two meters, their efficiency is only 89db and I worry about losing dynamics.
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Old 2nd April 2002, 07:16 PM   #5
stigla is offline stigla  Norway
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;

If youve got 7 volts out, You will most likely NOT need a preamp.
This is nice, since you can cut down the number of elements in the Audio chain.
I will recommend you to go for a Passive Attunator, preferebly stepped.

Sweet Whispers from Bottlehead, a nice box, some gold plated phono contacts (dep. on number of inp. you want...), some wire (silvered copper), a rotary input selector; theres your preamp!
Goldpoint 50k(or lower) stereo would be nice too (112$ from www.tubesandmore.com R-VATKS-50K)!
Or maybe the legendary DACT attunator! (www.dact.com)

The value of the attunator should be around 10-20 times higher than the output-impedance of your DAC. Keep as low as possible...

Readings: http://www.goldpt.com/diy.html
http://www.aloha-audio.com/

Only thing with these is that thay are not as fun to make as active amps

About Antique Sound Lab Wave 8 monoblocks:

8Watts to 89dB will be too little I think. Even for your small room.
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Old 2nd April 2002, 09:08 PM   #6
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stigla,
Thanks for the great responses. I would definitely agree with the idea that less is more, so an attenuator might definitely be the way to go, especially if I decide to go solid state.

But, I was really interested in introducing tubes into my system. With speakers that are only 89db, I don't think I will be able to afford tube amplification that will drive my speakers properly, though those $99 ASL monoblocks look tempting. I have heard great things about the Art Dio in combination with a tube setup, because the Art unit tends to be a little bright and analytical.

First of all, I guess I would like to know how much better a simple passive pre or attenuator with a cheap, solid state stereo amp like something from parasound, adcom, or rotel would be than my Denon receiver (just analog, no ad/da conversion). Or to say it better, what effect would these changes have on my system? Secondly, how could I get that tube sound into my system?
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Old 2nd April 2002, 09:29 PM   #7
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I guess I should clarify something.
It's not like I am only in love with tubes or anything. I mean, I've never actually heard a system with tubes in it, and in actuality I've never heard a system composed of separates. I just want the best possible sound. I think my system is a little bright and many people have reported fantastic results with similar systems and tubes. I am, though, planning on modding my Dio which should add quite a bit of refinement to the sound, so solid state is definitely not out of the question.
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Old 3rd April 2002, 12:19 AM   #8
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Default Bright and 10 watts

ASLs might be great but chances are (WAG here!) the tubes might not be up to par and to retube can cost as much as the amp. Having said that I do think that a tube preamp could help but maybe not as much as you would like. As a recommendation for something that can handle your 89db speakers, is not bright on the top end, has a preamp and tuner built in and has great sound for head phones I strongly recommend a Fisher 400 reciever. I have 2 and love them! I also have SE 300b, and SE 6BQ5 amps that use only gain pots on them as well as a lot of other vintage gear. I also have quite a bit of SS gear but I basically use it for bass and or HT applications. I find bright highs very offensive and love tubes for their soft upper distortions but one thing I do want to point out is that some speakers sound like crap with tube gear and some sound lousy with SS . Of course some sound just plain awfull with both. Before you spend a lot of $$ look at your tweeters. Metal domes can really chew your ears up.
David
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Old 5th April 2002, 08:23 PM   #9
stigla is offline stigla  Norway
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Musiclover:

I know EXACTLY what you feel like, belive you me, I have felt the same thing (and still feels).

The first thing I build was a simple tube preamp, to go with my LEACH amp. This was a preamp just as in the article I recommended you, but I used NOS 30's (DHT). I must say, that I really liked the results!
I also got to test the 30 preamp on a NAD 340, using the power-amp section of the '340. Opened up the sound quite a bit! And I did not use any "fancy" parts like Oil caps, or Black Gates or kiwame's or whatever (though, in a simple design, good quality parts ARE put to good use).
That preamp really got me hoocked on tubes!!!

I think it is a nice (economic) compromise to go for a tube preamp first, but as Thatch_Ear says; the result is dependable on the rest of the system. Only thing is that that 7 volts out of your DAC is WAY to much for a preamp. Your volume pot will be very sensitive, a slight move will make the volume go vvvvoooOOMMMM! For a preamp, the input voltage should be around 1 volt...

If you want "tube sound", a poweramp is really the way to go. To say it like this; If you got "tube sound" from a tube preamp, it is probably a bad tube preamp.
Many people seems to belive that "tube sound" is some kind of cigar shaped; lots of mid's, wobbling bass and behaved highs.
A good tube amp is not like that at all, it is lively and sparky and fast and transparent! Great fun in other words! Makes you want to listen through your entire music collection!

Advice; If you DO go for a tube preamp, the 5687(...) or the 5842 or the 6SN7 will not let you down! These are very good tubes. (do not use long cables between the pre- and the power-amp. 1meter max! btw...)

Surf on the web, there are many manymanymany articles, reports and info about tube amps.
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Old 6th April 2002, 05:34 PM   #10
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Default Tube diy preamp

Hi,
I have built several tube preamps. The one I would reccomend as a first project is at:
http://digilander.iol.it/paeng/projects_frame.htm
This is perfect for a 1st project, as it uses a low voltage power supply. Batterys actually!
24 Volts on the b+, and 12 volts for the filiments . 6.3 volts per tube with filiments wired in series.
It is simple to build, and only uses (1) 7308 tube per channel.
I have built the companion phono stage and it sounds wondetrful. Sweet, detailed and images like a mother!
Good luck in whatever project you decide on.
mg16
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