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    Can 12AX7's be used in VTA Driver board?

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    kevco

    Posts: 68
    Join date: 2009-07-16
    Location: Aldan, PA, USA

    Can 12AX7's be used in VTA Driver board?

    Post by kevco on Tue Dec 29, 2009 1:46 pm

    My brother is currently running his VTA modded ST70 without a preamp, as he has not yet found the right unit for his needs. He is running his iPod directly into the amp. The iPod's output is not enough to drive the amp to more than 50-60% of total output in my estimation. I have an ST70 with a DiyTube driver board installed. The DiyTube board uses a 12AX7 in the voltage amplifier position and will take the iPod's output to much higher levels. Can he use a 12AX7 in the VA position to achieve more gain until he gets a preamp? Other modification of the board is not desired at this time, as a preamp is around the corner. Any thoughts are much appreciated...

    LEVLHED

    Posts: 21
    Join date: 2009-10-26

    Re: Can 12AX7's be used in VTA Driver board?

    Post by LEVLHED on Tue Dec 29, 2009 3:58 pm

    I don't know about the 12AX7's, but before I got my Dared SL-2000A preamp I was using a little 9 volt powered CMOY headphone amp to get a little more boost. It wasn't too expensive and it did the job until I got the Dared. It had more boost than needed.

    Sorry, I hate when people don't really answer my question. I hope your not as annoyed as I'd be:)

    kevco

    Posts: 68
    Join date: 2009-07-16
    Location: Aldan, PA, USA

    Re: Can 12AX7's be used in VTA Driver board?

    Post by kevco on Tue Dec 29, 2009 7:48 pm

    LEVLHED wrote:I don't know about the 12AX7's, but before I got my Dared SL-2000A preamp I was using a little 9 volt powered CMOY headphone amp to get a little more boost. It wasn't too expensive and it did the job until I got the Dared. It had more boost than needed.

    Sorry, I hate when people don't really answer my question. I hope your not as annoyed as I'd be:)

    I hate it too, I'm extremely annoyed!
    Just kidding. He's got a working solid state stereo receiver, but unfortunately it doesn't have a preamp out, if it did his dilemma would be solved. And alas, no headphone amp either, and no point in buying one now when he needs to channel his funds toward a preamp. I'd love to try a 12AX7 as I have quite a few, but don't want to blow up his amp in the process...How do you like the little Dared? Is it quiet? I've heard some good stuff about about the Yaqin MS-12B and really like the fact that it's got a phono stage at that price...
    http://cgi.ebay.com/YAQIN-MS-12B-Stereo-Tube-Preamplifier-and-Phono-Stage_W0QQitemZ130355227815QQcmdZViewItemQQptZLH_DefaultDomain_2?hash=item1e59c6eca7

    Only thing is: Where's the front? It's got inputs on both ends!

    LEVLHED

    Posts: 21
    Join date: 2009-10-26

    Re: Can 12AX7's be used in VTA Driver board?

    Post by LEVLHED on Tue Dec 29, 2009 8:43 pm

    I wish I knew enough about the stuff to say for sure that a 12AX7 won't make it blow up. I suspect it won't, but who the hell am I to say.

    I really like my Dared pre. It's quiet to me though I wouldn't say I'm super critical there. I do hear some noise with my ears close to my speakers, but that could be attributed to many other factors as well. I didn't notice any MORE noise when I added it. I really dig that it uses 12AT7's. I just went on a 12AT7 bender and have really got it down to three or four that I'm loving between the pre and the VTA ST70. It was so much nicer only having one kind of tube to buy and roll, but having to try them out in every combination possible has been painstaking.
    I don't use vinyl at all, strictly using a media server so I only use one input! The dual outputs were key so I could run my powered subs. And the remote control volume was the other essential part because my gear sits in a dedicated closet kind of space and I'll be damned if I'm going to get up and adjust the volume. Those were the features I had to have. And I couldn't even think about spending thousands of dollars so its pretty much the perfect pre for me at this stage of the game.

    I read all the reviews and opinions I could find on it before buying it and between the features I needed, the 12AT7s and not really finding *any* negative opinions from anyone who has actually listened to it finally sold me on it. The only negatives I could find were along the lines of people essentially saying its too cheap and a more expensive one would be better, nothing to do with it's actual quality in build and sound!

    I should probably post up a few pics...

    arkivel

    Posts: 6
    Join date: 2009-11-11

    Re: Can 12AX7's be used in VTA Driver board?

    Post by arkivel on Wed Dec 30, 2009 12:32 am

    This doesn't answer your question either, but I had success running a Marantz CD67SE through my ST70. I much preferred this over the Heathkit pre-amp I bought to tide me over until I found a decent replacement. The CD player of course has volume control on the remote.

    What about a DIY pre-amp kit to tide you over? I've seen a few online for really cheap. Or perhaps you could attach a pair of potentiometers to the st70 and use a CD player?

    kevco

    Posts: 68
    Join date: 2009-07-16
    Location: Aldan, PA, USA

    Re: Can 12AX7's be used in VTA Driver board?

    Post by kevco on Tue Jan 05, 2010 1:07 pm

    I'm gonna bump this thread...Hey Bob, what are your thoughts on this one? Will that 12AX7 work in the Voltage Amp position? I haven't been able to find any solid info this and am reluctant to tell my newbie brother to make the swap without some opinion from the gurus. Thanks as always!

    kevco

    Posts: 68
    Join date: 2009-07-16
    Location: Aldan, PA, USA

    Re: Can 12AX7's be used in VTA Driver board?

    Post by kevco on Tue Jan 05, 2010 1:08 pm

    I'm gonna bump this thread...Hey Bob, what are your thoughts on this one? Will that 12AX7 work in the Voltage Amp position? I haven't been able to find any solid info on this and am reluctant to tell my newbie brother to make the swap without some opinion from the gurus. Thanks as always!


    Last edited by kevco on Tue Jan 05, 2010 10:39 pm; edited 1 time in total

    Bob Latino
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    Join date: 2008-11-26
    Location: Massachusetts

    Re: Can 12AX7's be used in VTA Driver board?

    Post by Bob Latino on Tue Jan 05, 2010 1:46 pm

    kevco wrote:I'm gonna bump this thread...Hey Bob, what are your thoughts on this one? Will that 12AX7 work in the Voltage Amp position? I haven't been able to find any solid info this and am reluctant to tell my newbie brother to make the swap without some opinion from the gurus. Thanks as always!

    Hi,

    Yes - A 12AX7 will "work" in the center voltage amplifier position. Actually ANY of the 12A*7 family of tubes will work in there BUT the resistor set as supplied with the VTA kits is optimized for the 12AT7 tube. Using a 12AX7 tube in the voltage amplifier position will increase the gain somewhat in an amplifier that already has a little more gain that the average tube amplifier.(probably not a good idea) The gain factor of the tubes in this 12A*7 family (along with a 5751 tube which also belongs in this family) is listed below.

    12AX7 > 100
    5751 > 70
    12AT7 > 60
    12AY7 > 45
    12AV7 > 41
    12AU7 > 19
    12BH7 > 16.5

    You have to be careful when trying a different tube because some of these draw more current than others and again, the person who designed the circuit optimized the circuit for just one of these tubes. IMHO in any of the VTA boarded amps you could go DOWN in gain factor without much harm although the amp may not be operating at it's best and whether the sound would change for the better or worse - I couldn't say ...

    Bob

    kevco

    Posts: 68
    Join date: 2009-07-16
    Location: Aldan, PA, USA

    Re: Can 12AX7's be used in VTA Driver board?

    Post by kevco on Tue Jan 05, 2010 10:41 pm

    Now that's what I needed to know! As always, Bob, thanks!

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