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Old 22nd April 2009, 10:04 AM   #11
Rewind is offline Rewind  Sweden
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Default Which Pot?

Great that yours is working. Mine is also working, although a little more noise in one channel and of course the stupid blinking of one on the 6N3 driver blue tubes. I can buy another one at this price, anyway.

I found a tube that is american made and is identical to 6N3 except it is supposed to sound much better as a driver tube. They sell these for $7.95 a pair so you can't go wrong. Check Other Items and you will see different kinds. I like the military style tubes. =)

http://cgi.ebay.com/5670-5670W-2C51-...3A1%7C294%3A50



I also want to buy a pot, because a 30W preamp is L O U D. I wonder what kind? I saw a 50W L-pod potentiometer. Is this the right kind? I don't think a 0.02W 100kOhm guitar potentiometer will hold up for the job. Or will it?

Link: http://www.ljudia.se/tillbehor-s8213...0-watt-p79647/


To stray off topic, I contacted Lundahl, since I live two hours drive from their HQ *proud* , however they said they didn't have my kind of tranformer, sadly. I did however buy their Ribbon Microphone transformer for my DIY ribbon mic with really cool results. I will exchange the guitar magnets for Neodym magnets soon. Money saved! A proper ribbon microphone is expensive!
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Old 22nd April 2009, 03:21 PM   #12
Rewind is offline Rewind  Sweden
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This is what I had to do to make it into a micrphone preamp. First I use my rather weak but clean Studio Projects VTB-1 preamp to the microphone or guitar. That gives me a balanced XLR out and a unbalanced TS 1/4" signal. It has a tube, but just as an insert effect tube which is rubbish compared to the real thing.

My DIY tube preamp is unbalanced (as I most recently were told). To use not only the Gain control and High Pass Filter, but also the volume knob and meter on my studio projects preamp, I will have to connect the tip and ring together in a Neutrik TRS 1/4" connector. This is a special function for Studio Projects I guess.

My analog inputs on my Lynx L22,which has a softwar controlled +4dB and -10dB, are XLR. So I have to make an XLR unbalanced. Inside the XLR male which is going into my soundcard from the preamp I move the white cable to the red cable and link the place where the white cable were - to the ground.

On the three preamp audio inputs, ground is in the middle, right channel has both red and white, and Left the same from the other cable.

Done!
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Old 23rd April 2009, 09:58 AM   #13
Rewind is offline Rewind  Sweden
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Default Finally got it. Here's a Guide for n00bs.

I could not wait for an answer and tested the 100k 0.02W Alps stereo potentiometer ($15 in Norway) on the DIY tube amp output and as you said the hum disappeared. This is a really cool preamp. Before my sound was dull and uninspired and weak. It did not work to amplify it with software. Guitar Rig worked, but then it is not your signal any more, just a modelled sound. This preamp amplifies it so I can almost use it out of the box (though the preamp came in a letter). It even kicked some life into my ultracheap Alto mictube.

I am still worried than I should not use a hifi preamp desigend for amplifying signals to power amplifiers, and perhaps not the way I use it - as a mic amp, amping the signal from my weaker mic amp, see picture. I am afraid to burn my soundcard again if the signals does not match.

It preamplifies an unbalanced signal and the soundcard has a -10dB. It should be OK, but it amplifies with 30 W and that seems a lot. My 0.02W potentiometer har survived on the output so I guess those Watts are not in the audio signal. I know so little!

Do a search for "Pre-AMP Amplifier KIT Tube 6N3srpp good for DIY" on Ebay.com if anyone want to test it themselves.

Specs:
30W tube preamp
¤ $54 Chinese 180V-0-180V + 2 x 6V transformer (works ok, but there are better transformers).
¤ $30 prebuilt board with including two 6N3 tubes and one 6Z4 tube.
¤ Free shipping

Recommended: $15 Alps 50k or 100k stereo potentiometer RK18 at the output for reduced hum. See picture for wiring guide.

Temporary Link:
http://cgi.ebay.com/Pre-AMP-Amplifie...3A1%7C294%3A50


Warning: You can die if you don't know what you are doing. High voltages and high currents. Be careful. I have heard that a tube preamp can store energy for hours. Though I was eager to test this I have not...

Hope this helps someone.
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Old 29th May 2009, 03:28 PM   #14
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I'm wondering about trying this tubeamp kit, but is it possible for the tubes not to light blue as in the picture on ebay?

I want it to be glowing red and lovely not blue and fancy!
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Old 29th May 2009, 06:13 PM   #15
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Default Blue tubes

Not sure that this blue light is real: I never met a tube which lights up in blue, but always red.
Maybe it's a "Photoshop" effect, or a blue LED placed somewhere under the tubes - as several years ago a blue LED seemed to improve the sound of a CD player, why not on a tube

Anyway, my 6N3 tube preamp (excellent sounding tube) is orange-red, as any tube on the (blue) earth...

For thye price, it worth to try it out, and if ever the tubes shine blue, buy some others!

- dan
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It is worth to keep your mouth shut and let people think you’re stupid; rather than to open it and thus eliminate any doubts...
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Old 13th February 2012, 08:54 PM   #16
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interesting post. i have the same preamp from China. hehe
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Old 14th February 2012, 10:22 AM   #17
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Default wrong wireing 6z4

Hi,
Carefully look pdf about 6z4.Pin 7 and 3 are anode and 5 is cathode.
According your schematic there is different conection btw.
Regards,
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Old 8th September 2012, 03:54 AM   #18
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These are just awesome little preamps. The green LED in the tubes is cheesy, but you ought to just chuck the tubes and put in something decent. I put a pair of Tung-Sol 2C51 tubes in there, and the little thing simply kicks one whole lot of ***. Mine is dead silent, there are no hum issues whatsoever, and it is an altogether satisfactory piece of audio gear. Just a ridiculously good value.

If you want features, forget it ... there's one input and one volume control. But if you want cryssssstal clear sound, I highly recommend it. Take care to set up the transformer correctly because it's all over if you wire it backwards and then plug it in.
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Old 27th September 2012, 08:56 PM   #19
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I just got something similar from Ebay and connected it up.

I was not going to connect it up to my main rig without a test... So the trusty garage hifi amp - NAD3020 was pressed into service. The NAD has a pre and pwer section and they are normally connected by a simple jumper. Off with the jumper and connecting up the tube pre...
Using a tuner as source. On it all goes. Hmm, nice and quite with no signal - no hum etc... on with the source - wow it plays and actually sounds better than the NAD pre... No too hard I hear you cry. Smoke and function/integration test done.

So, off to the music room and plug it in to the main system.

Again no noise when no signal.
Plays music. Let all the other valves warm up a bit.

Yes the pre tube do get hot as they should.

There's a rather irritating green led under each tube - spoils the tiny bit of warm glow there is...

Actually it sounds pretty amazing for what it is!

Some pics

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

More listening time.

Is it definitely worth spending money on better tubes?

Last edited by Speedysteve7; 27th September 2012 at 09:11 PM.
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Old 28th September 2012, 07:31 PM   #20
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I had no problem disabling the cheesy green lights. You just have to gently stab the LEDs in the center of the tube sockets with a sharp object. Looks so, so much better with the warm natural glow of tubes (that being said, they really don't glow all that brightly in a preamp -- it's not like they are power tubes being cranked up!). (Also, while I could not perceive a difference, I'm told that having LEDs in a preamp is a terrible idea because they add noise. Whatever the case, the preamp is absolutely dead quiet ... you can't hear any hum or other noise no matter how far you turn the volume up.)

I'm not sure whether putting better tubes in there is really worth it. I spent $100 on a pair of NOS Tung-Sols, but being real, the difference is very slight. I am well familiar with changing out power tubes in guitar amps, and those can make a huge difference, but in an audio preamp I guess it's not nearly as critical.

All in all, a killer, killer deal if you can live without remote volume control!!!

A pic of mine is at: https://plus.google.com/u/0/photos/1...CIaY0aXXtsTLBQ
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