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In Reply to: RE: Vacuum Tube Audio SP14 posted by John Elison on July 21, 2016 at 11:09:04
John, you are a way smart guy, and I enjoy your informative posts on this forum (I've learned a lot). I am also happy to see that you are delving into hollow state technology. There is no amplifying device more linear than a triode gain stage. Also, I can certainly relate to the joy of making things with your own hands. BTW, the Khozmo attenuators are a really great option.
Just keep in mind, that in spite of a lot of sales pitch, this may not be the end all be all approach to a "preamp". If I get this right, (haven't found a schematic although I've looked) I call this a line stage, preamps have phono stages. Even by line stage standards, this has an unnecessarily complicated attenuation scheme (looks like you've remedied that). This may also be cathode follower topology, as that is the only reason why I could figure it would need 2 6SN7s per channel. In my book, this may not be an "uncompromised design".
In spite of that, hope you're having fun, and enjoy it. Keep on trucking, DIY is big fun.
twystd
Follow Ups:
Are you raining or not????
No John, just want you to explore DIY and tubes even more. I am just trying to say that there are more options out there, please keep on DIY'n.
To be truthful, I don't like slamming any projects. I just get my hackles up about companies that oversell their projects with hyperbole, and yes, I feel that this is what is going on here. Us tube fanatics know that cathode followers aren't "no compromise" designs.
Is that what it is? Well really don't know, but with no schematic available makes me wonder. Believe me, there is NOTHING new about tube schematics, and when companies don't give them, I suspect they may have something to hide.
If you are going to claim a no compromise design you need to show me more than these folks are doing.
twystd
> If you are going to claim a no compromise design you need to show me more than these folks are doing.
I didn't claim it to be a no compromise design. I bought it because it fit my budget. Tube equipment can be very expensive these days and Vacuum Tube Audio products seem like a good value to me. So far I'm very pleased with sound quality from my $680 PH16 phono-stage. The SP14 line-stage cost a little bit more, but still seemed very reasonable to me.
The schematic for the SP14 is available online and is shown below. Do you think this is a compromised design relative to its price?
John, I certainly didn't mean to offend you, and I apologize. I have been nothing but impressed by your posts on this forum. I know you didn't claim it was a no compromise design, but the manufacturer did. They also claimed it is "the best preamplifier kit available at any price." That statement is certainly debatable to say the least. Claiming anything in the audio world is the best is BS. The best according to who?
I'm sure that the design sounds just fine, and I'm glad you enjoy it. I don't think it is a waste of money. The only reason I posted anything negative, which I probably shouldn't have, is that the site selling the SP14 made some pretty strong claims. I feel there is way too much hype involved in our hobby, and hyperbolic claims by sellers, just rubs me the wrong way.
As far as critiquing the design, I think I'll pass on that. I will say this isn't something I would design for the purpose, but I'm a minimalist. This is just my own audio dogma, which is more of my opinion, rather than a proven fact, and you know what they say about opinions. I certainly wouldn't claim any design that I may make, is the best, that is just unsupportable.
Again I apologize, and am very happy to see you getting involved in DIY and tubes. I hope you continue down this path, and I hope you enjoy listening with this preamp. You are right, DIY does offer good value, and has the satisfaction of making something with your own hands. Don't let anything I say discourage your efforts.
twystd
Not meaning to hi-jack your thread but......
The first stage could be seen as a triode gain stage loaded with a triode CCS.
An improvement to the over all design (IMO) would be to eliminate the second stage altogether and take the output off the top of R4 (the "mu" output of the CCS).
A triode doesn't make a very good CCS plate load. It could be replaced with a pentode for better performance or better yet a cascoded pair of depletion mode MosFets like the DN2540.
A step up from that would be Gary Pimm's self biased CCS shown above.
This would give a very low output impedance.
Over all this would be a big improvement and the total cost of the project would be less if the project was designed this way to start with. (one less tube per channel, one less tube socket per channel, less current needed from the power supply, etc..)
If you have to do this on your own......I'm not sure what your cost would be.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Okay! So, in your opinion it's basically a waste of money. Such is life!
Can you recommend another tube preamp that is designed correctly and includes equivalent features with a price that's the same or less? The special Mundorf output caps added $95 and the remote volume control added $290. Then, with a $20 tube upgrade and shipping charges of $30, total cost for this kit was $1355. I don't know anything about amplifier design, but if you know of a better tube preamp at the same price, I might buy it.
What do you think about the M-125 monoblock amplifiers . I estimate the kit price including tubes will run about $2100 a pair. Do you think these amplifiers are worth the money. If not, can you recommend another tube amplifier with at least 125-wpc and better performance that costs the same or less. I'm thinking of building a tube power amplifier kit as my next project and I need a minimum of 125-wpc to drive my Thiel's.
Thanks!
John Elison
Sorry John, I probably shouldn't have said anything to start with.
I build all my own stuff and do not pay attention to what's available, gear wise, so I have no recommendations.
When I do see schematics of available stuff, most of the time I can't help but wonder why they design things the way they do.
I should have kept those thoughts to myself.
When you get to the point where you want to build from scratch, give me a heads up.
When building from scratch your design will be guided by the depth of your understand of theory and the level of performance is only limited by how complete that understanding is.
That is to say, if I knew more my system would sound better.
I don't find much guidance looking at commercial products. Most are built to a price point and are not no holds barred designs.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I seriously doubt I will ever get to the point that I am building amplifiers from scratch. On the other hand, perhaps you know of some manufacturers of tube equipment who design their circuits in accordance with your specifications. Are there any manufacturers you would recommend regardless of price?Thanks,
John Elison
Edits: 07/24/16
It will be nice to read your review of the preamp.I built a Hagerman Clarinet about 5 years ago that I still like,but would love to compare it to the SP14.Do you know if all of the supplied resistors are metal film?
Dave
Yes, all the resistors are metal film. Most of the resistors in the preamp section of the circuit board are precision metal film Dale resistors. They are brown in color with their values stated numerically. The other resistors are also metal film but lower tolerance resistors and use standard color code to depict their values.
I'll definitely keep you posted on how this preamp sounds when it's completed. I'm currently waiting for the enclosure to arrive so I can wire everything together.
Best regards,
John Elison
I know what you mean about saying anything to start with, I feel the same way, and am sorry I started this whole mess. I find it hard to keep my mouth shut.However I am pissed at self serving unsubstantiated claims by commercial interest in this hobby. Not all commercial interests join in on hyperbolic claims. I think there should be ethics involved in commercial advertising, and that extraordinary claims should be backed up with extraordinary evidence.
BTW, for what it's worth, I agree with both your technical observations on the product in question, and your bigger underlying philosophy of understanding. Still working on that one, and hopefully will to the day I die.
twystd
Edits: 07/23/16
"Still working on that one, and hopefully will to the day I die. "
That's the thing about knowledge, the more you learn, the more you understand how much more you need to learn.
The day I stop learning is the day I die.
But for now I'm "Still working the problem".
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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