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I would like to build a tube preamp, but I'm confused by my options. I have done some crappy soldering before (mod chips for cable box, e.g.), but I have never done something this ambitious. The preamp will drive a VTL ST-85 stereo amp, which in turn will drive DeVore Fidelity O/93 speakers.
The Bottlehead BeePre is enticing, because the instructions seem really detailed, and I'm really curious about eventually trying out SET amps. However, I'm told that I will probably have to install attenuators between the preamp and amp, so as to get rid of some of the microphonics and to optimize the listening range of the volume pot. That seems like I'd be buying into an already compromised preamp.
The Audio Note L2 also seems awesome. Again, the instructions provided seem thorough. I have no clue if I will experience the same attenuation need with the VTL amp, and I'm concerned that most of my money would go towards buying the AN brand.
I haven't seen any other kits that provide step-by-step instructions for this ignorant newbie. Do you guys have any suggestions? The Aikido gets a lot of good words, but it seems like I would have to know how to assemble it and where to get a case and other parts for it. I don't.
Thanks for any suggestions you might have.
May the bridges we burn light our way....
Follow Ups:
You might try installing a vol pot in your amp, or have a tech do it for you. 1 less pair of inter-connects, 1 less box for the pot..
I've heard both Bottlehead and AN gear, and think both sound great. My Bottlehead Crack is a delight.
You mention needing an attenuator between pre and amp to minimize microphonics and make the volume pot usable. I think neither will be the case. Attenuators will never reduce microphonics; once a tube has picked up and amplified physical vibrations, the damage is done, and reducing volume reduces the signal along with the microphonics. If the gain-staging is way off making the volume pot hard to use, then you have a problem with gain-staging, not the pot. Actually, I doubt that would be the case, particularly if you run the VTL in triode mode. (It should also be pretty easy to add a resistor after the wiper on the volume pot to give you more usable range on the volume knob.)
I haven't build any AN kits, but the Bottlehead instructions are the best I've ever seen, and Doc Schmalle & company are really great to work with.
Cheers,
WW
"A man need merely light the filaments of his receiving set and the world's greatest artists will perform for him." Alfred N. Goldsmith, RCA, 1922
If the microphonics (or other low-level noises) occur upstream of the attenuator, they will be attenuated. This is the case with a noisy preamp followed by an attenuator at the input of the power amp.
I've never been able to condense the situation into a comprehensible forum post. I did however make a white paper on the subject. It's more than most people want, but it's here if you are interested.
Yes, an attenuator will reduce upstream noise by the same amount that it reduces the (upstream) program level. So, if you hear preamp noise when listening at about an 82dB SPL, attenuating the signal after the preamp will reduce both noise and program. It might be the case that, by the time you're at 72dB, the noise is no longer intrusive, and the lower SPL should reduce the distortion caused by microphonic tubes, if that was part of the problem. I don't see how an attenuator between the preamp and power amp can reduce the level of upstream-induced noise relative to program level without paying the price of listening at a significantly lower level. Am I missing something here?
Paul, I read you paper, and have a couple questions:
1) What is it you accomplish with that process? Is it to have the preamp operating at a level where it has the greatest non-distorting S/N ratio, or is it something else?
2) You write, "Sources should adhere to the -10dB(v) nominal standard, which can be accomplished in the source device, or at the input of the target device (preamp, usually). This is relatively easy. Amplifier/speaker combinations should produce 82dB sound level at the listener’s ear when the input level is -10dB(v). Unfortunately, it is extremely common to find there is too much gain in this part of the chain." Why is it important to hit 82dB at -10dB(v)?
Thanks,
WW
"A man need merely light the filaments of his receiving set and the world's greatest artists will perform for him." Alfred N. Goldsmith, RCA, 1922
Thanks much!
As I understand it, the attenuator is meant to address the gain-staging issue. I probably used the term "microphonics" incorrectly.
You wouldn't happen to remember any specific differences between the Bottlehead gear and the AN gear would you? I got a chance to hear an Ongaku driving DeVore Fidelity O/96's a few weeks ago. Amazing, but I'm sure that's the worst AN device to use as a referent for this decision.
I'm very much looking forward to assembling a preamp myself. I hope I learn a bit about such devices in the process.
Thanks again.
May the bridges we burn light our way....
I just point out again that Audio Note Kits is not the same as Audio Note (You can't compare anything about AN Kits to an Ongaku), and AN Japan is not the same as AN UK. The kit stuff is often on display at audio shows each year. Go on the AN Kit site and ask Brian when the next opportunity is to audition it, or maybe you can find someone on this thread who can let you audition. I think at the end of the day, that's the best appraoch. On the other hand, AN Kit stuff comes up on Audiogon a lot, so there is a market for it. Buy the kit, if you don't like it, resell it.
over on the Tubes4Hifi site there are a few Tube preamp kits. Also The Grounded Grid preamp kit.
www.transcendentsound.com/Transcendent/Products.html
Thanks for the suggestions.
I looked at those, and I didn't notice much in the way of guidance for a first-time builder. The Grounded Grid preamp seems to get a lot of good press.
May the bridges we burn light our way....
Pairing a sensitive pair of speakers with a very sensitive, high power amplifier is a compromised decision before any preamp is added. 0.68V for 60 Watts is hyper sensitive when you have speakers that might play well on a couple of Watts, but would work well on some 87dB sensitive monitors.
If one reasons that you are in the ~10W neighborhood for how much power you're using, you'd need 0.3V out of your preamp. With a 2V source, your maximum volume setting would be at -12dB for 10W out of your amp. If you have a preamp with dB of gain from the circuit, now your down at -24dB on the control for a reasonable listening level.
12dB attenuators are $25, and are going to be a very good idea regardless of your preamp choice.
The amp has an input impedance of 100k ohms, and it does 30 watts per channel into 5 ohms set to triode mode (my favorite for most listening). The folks at Bottlehead cited the input impedance and the speaker sensitivity as the primary factors in recommending an attenuator, so your point makes sense. Seems like the attenuator is, at worst, a bullet I will have to bite if I'm going to stick with a tube preamp.
Thanks much.
May the bridges we burn light our way....
I think K&K has a preamp kit, don't they (they are an Asylum sponsor). On the Bottlehead stuff, I'd be concerned too for the reasons you stated, though I built a Foreplay years ago and it was great. As for Audio Note, remember Audio Note Kits is not the same as Audio Note. IIRC their L2 uses a paralleled 12AU7. 12AU7's are not my favorite tube and I think the process of two sections in parallel is not the best sonic choice. I built the L1 when it first came out and didn't like that aspect of it. I rebuilt it using a 5687 without paralleled sections. I also was not thrilled with the phono section in there, but it's okay - not fantastic. Hope that helps.
Thanks for the K&K info - I had not seen that vendor in my previous searches. The prices are just out of my budget, and the lower-priced, DIY versions seem to require more from the builder than I want to take on. Also, I didn't notice much in the way of instruction.
I'm warming up to the Bottlehead, simply because of the apparent care the manufacturer takes in helping out its customers.
Thanks again!
May the bridges we burn light our way....
All my experiences are that taking as much away as possible cleans up the signal no end. Just use the amplification you need to drive the speakers and not more. There should be very little attenuation needed. As far as tubes are concerned, 2 stages overall are ideal, and 3 only if necessary.
What I'd build is a really good DAC - I'd go over to DIY Audio and look at the latest threads to see what's hot. That could really upgrade the sound. If you mainly listen to digital sources, the volume control is usually in software anyway these days.
I also listen to vinyl and FM. However, my DAC is in dire need of replacing (Perpetual Technologies P-1A/P-3A combo). I was planning on just getting a low-price DAC, since the technology improvements in that category seem to be huge over short periods of time. I was gonna try to run the Musical Fidelity V-90 with my Monolithic P3 power supply! I've heard that a linear power supply helps that DAC a bit. My dealer let me borrow a TEAC 301, and it is definitely an improvement over the Perp. Tech. Its preamp section is uninvolving, however.
Thanks for the suggestions.
May the bridges we burn light our way....
Autoformer Volume Control or TVC usually will provide all of the gain control one needs. I really like the Twisted Pear Buffalo, with its software volume control. However, because I am crazy, I put it through a 10/801a preamp for fun.
Yeah, but don't forget the impedance matching function of a preamp. If you are not starting with a pretty low impedance source (like a DAC) you can really be wasting a lot of money on a passive control. 10:1.
The only thing that does not have a low impedance output is a tube preamp that has a simple plate output. Might be doing better to fit a volume control on that beast and/or an output impedance transformer. The problems that a preamp can solve are mighty rare. It will be a lot better to fix the rare case of a high impedance tube phono preamp.
There are plenty of solid state output stages that have output impedances of a few thousand ohms.
"There are plenty of solid state output stages that have output impedances of a few thousand ohms."
Such stuff is (IMO) very questionable. I strongly believe in accommodating the "lowest common denominator", which is the IHF 10,000 Ω I/P impedance "standard". Therefore, line level O/P impedance must be <= 1,000 Ω.
Eli D.
But still, 2K into a 10K load driving a foot or two of decent cable dissolves into an academic discussion in the faculty lounge.
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