12au7 made by Toshiba, Hitachi, Matsushita, RSD, International and Miniwatt?

[Audio Maniac]

Does anyone know one of the listed 12au7 tubes?

I am looking for a 12au7 tube to replace the stock 12au7 used on the MiniMax DAC.

I found some units made by Toshiba, Hitachi, Matsushita, RSD, International and Miniwatt. Is any of them good?

They are retailed for about $20 (NOS).

[GloBug]

Some nice stuff came from Matsushita, the Miniwatt I think is Philips might also be decent.

None of them stand out as a superior tube, like say an old RCA or what have you.

Get a couple and see what you like. AL

[Audio Maniac]

The stock tube of my DAC is a Chinese Shuguang 12au7. Are all those tubes better than the referred one?[


QUOTE=GloBug;2777074]Some nice stuff came from Matsushita, the Miniwatt I think is Philips might also be decent.

None of them stand out as a superior tube, like say an old RCA or what have you.

Get a couple and see what you like. AL[/QUOTE]

[Audio Maniac]

I got a pair of Matsushita but I would like to purchase one more unit. Which one would you choose among Hitachi, Miniwatt and Toshiba?

[ChrisA]

Originally Posted by Audio Maniac

The stock tube of my DAC is a Chinese Shuguang 12au7. Are all those tubes better than the referred one?[


QUOTE=GloBug;2777074]Some nice stuff came from Matsushita, the Miniwatt I think is Philips might also be decent.

None of them stand out as a superior tube, like say an old RCA or what have you.

Get a couple and see what you like. AL

[/QUOTE]

How is the tube used? Is it a cathode follower? I doubt a DAC would be using the Tube for much voltage gain. Is the tube in a feedback loop? Doyouhave a schematic?

The problem is that one person hears a tube in his preamp and says it's good but your DAC might use a completely different part of the tube's curve with a different bias point and maybe even different circuit topology. If so it will sound completely different. You can't compare results.

All that said if it is used as a cathode follower buffer then it is running with a gain of about 0.95 and contributes nearly nothing to the overall sound. In that case any functioning tube will sound the same.

Also don't look down on new production tubes. Good stuff is coming out of Russia and Europe now.

[GloBug]

Without getting complicated, any of those tubes would sound better, in my opinion then a Chinese tube.

I suspect the tube is the "A" in "DAC".

Why hunt around for a Russian tube when there are SO MANY nice NOS 12AU7's??

[GloBug]

Originally Posted by Audio Maniac

I got a pair of Matsushita but I would like to purchase one more unit. Which one would you choose among Hitachi, Miniwatt and Toshiba?

Miniwatt - Likely made in Holand (Philips)
Enjoy!

[Audio Maniac]

I don't have a schematic of the Eatern Electric MiniMax DAC unfortunately.
It uses one unique 12au7 after a pair of opamp which are responsible for I/V conversion and LPF. The DAC has a potentiometer, so it's also works as a preamp.

I can't give you further details. I know a bit about electronics but I didn't learn anything about tubes at technical school.

About those NOS tubes, the advantage of purchasing them is their easy access as they are in my country for a really low price. If I purchased any other model I'd have to get it from European or American stores. It implies that I'll have to pay for international freight as well as a heavy 60% CIF tax.

I don't look down to Russian made tubes certainly.

How is the tube used? Is it a cathode follower? I doubt a DAC would be using the Tube for much voltage gain. Is the tube in a feedback loop? Doyouhave a schematic?

The problem is that one person hears a tube in his preamp and says it's good but your DAC might use a completely different part of the tube's curve with a different bias point and maybe even different circuit topology. If so it will sound completely different. You can't compare results.

All that said if it is used as a cathode follower buffer then it is running with a gain of about 0.95 and contributes nearly nothing to the overall sound. In that case any functioning tube will sound the same.

Also don't look down on new production tubes. Good stuff is coming out of Russia and Europe now.[/QUOTE]

[ChrisA]

Originally Posted by Audio Maniac

I don't have a schematic of the Eatern Electric MiniMax DAC unfortunately.
It uses one unique 12au7 after a pair of opamp which are responsible for I/V conversion and LPF. The DAC has a potentiometer, so it's also works as a preamp.

I can't give you further details. I know a bit about electronics but I didn't learn anything about tubes at technical school.

About those NOS tubes, the advantage of purchasing them is their easy access as they are in my country for a really low price. If I purchased any other model I'd have to get it from European or American stores.

Just the opposite situation here (California) I can buy new production tube from any of several local retail stores that are within a few miles of my house. Each store stocks several brands. But NOS is twice the price and I'd have to pay shipping that adds 50% or more to the price. I think the local Guitar Center has "JJ" brand for about $13 and generic Chinese for just under $10. Then add 9% tax over that.

This being a DIY forum I figured you had built the DAC and then would know how it works. But I think it is save to say the tube in a DAC is not providing a lot of gain. THere are a lot of ways to design a low gain tube stage and it really does not matter because the difference between tubes is hard to notice in low gain sections. All together different story in (say) a phono preamp. You can prove me right (or wrong) Have a buddy flip a coin and change of the 12AU7 for a 12AT7 This is a drastic change, bigger then the difference between brands of 12AU7. So you buddy flips the coin and maybe swaps tubes or not. You listen and tell him which tube is in. Try it 40 times and see if you get more then 20 correct answers. I bet not. Reason is that a cathode follower is in a very strong negative feedback loop. Try it. But is is VERY important that your buddy literally flips a coin each time so there is no pattern to the test.

Then try with a high gain amp section. You will hear the difference is 2 seconds

If you have a technical education in e;ectronics but not tubes then read this web page
http://www.freewebs.com/valvewizard/
It is aimed are guitar amps but really applies to everything Read the links on the left side of the page in order. They are a good technical introduction and the author keep the math at the high school algebra level

[Audio Maniac]

Chris,

Thanks for your comments!

Definetely my DAC is third's project. Who designed the DAC is a Chinese known as Alex. I have no access to its schematics, everything I know about MiniMax DAC was gathered thru internet search.

The MiniMax DAC has 2 ouputs, being the second one a solid state type. I am also rolling the ouput stage op-amp (NE5534) by higher grade models which, according to some, shall outperform the tube output by far. That's one of the reasons I would like to avoid expensive 12au7. Furthermore, with new information given by you, it seems it's not worth investing much money on new tubes. I think I'll make do with those cheap Japanese NOS tubes. They are likely to be more than enough, aren't they?

Regards,

I'll visit the page you posted.

Originally Posted by ChrisA

Just the opposite situation here (California) I can buy new production tube from any of several local retail stores that are within a few miles of my house. Each store stocks several brands. But NOS is twice the price and I'd have to pay shipping that adds 50% or more to the price. I think the local Guitar Center has "JJ" brand for about $13 and generic Chinese for just under $10. Then add 9% tax over that.

This being a DIY forum I figured you had built the DAC and then would know how it works. But I think it is save to say the tube in a DAC is not providing a lot of gain. THere are a lot of ways to design a low gain tube stage and it really does not matter because the difference between tubes is hard to notice in low gain sections. All together different story in (say) a phono preamp. You can prove me right (or wrong) Have a buddy flip a coin and change of the 12AU7 for a 12AT7 This is a drastic change, bigger then the difference between brands of 12AU7. So you buddy flips the coin and maybe swaps tubes or not. You listen and tell him which tube is in. Try it 40 times and see if you get more then 20 correct answers. I bet not. Reason is that a cathode follower is in a very strong negative feedback loop. Try it. But is is VERY important that your buddy literally flips a coin each time so there is no pattern to the test.

Then try with a high gain amp section. You will hear the difference is 2 seconds

If you have a technical education in e;ectronics but not tubes then read this web page
http://www.freewebs.com/valvewizard/
It is aimed are guitar amps but really applies to everything Read the links on the left side of the page in order. They are a good technical introduction and the author keep the math at the high school algebra level