|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
47.147.56.52
Got to a point where I might benefit from having a buffer amp in one rig I'm fooling with, so I was looking at those little tube preamps from eBay that run on a wall-wart power supply. Their main attraction is that are certainly cheaper than anything I can build myself. Then my old tube-design synapses started tingling...
They *can* work but there are critical design considerations. I think the performance potential of a miniature twin triode with 12-25V on the plate is pretty limited. Ultimately I was dissuaded by not wanting electrolytics in the signal chain, which this kind of rig would likely introduce. Unless maybe if it's a cathode follower... A cathode follower is very sensitive to input and output impedances (and power supply) so again, low probability of getting high performance potential.
Whatever the case, if you get one of these and the bias isn't adjustable, you can't "roll" tubes.
This article about the design of these is intelligible and points to the limitations of putting a very low voltage on the plate of a tube designed for at least 100V B+.
Follow Ups:
If you don't need a headphone amp, there is a 3 tube (6n3x2+6z4) preamp that was the subject of a very long thread on audiokarma.org.
I have a Little Bear P1 which sounds ok considering it is very cheap, but it sounds more like a good solid state pre and is not as good as the all tube (but much more expensive) preamps I have owned or heard.
Consider the Schiit Saga preamplifier.
Presently burning in a copy. Will likely post a review later this week
Nice link to begin understanding these little devices...
Do you need a tube preamp or one of the so-called "sweetening" buffers without any controls ? What exactly are you trying to accomplish ? Can you let us know which gear u r matching to which gear ? The responses could become much more helpful, as the little buffers have little utility, no controls and no versatility. Nevertheless, there was a well reviewed and heavily copied Musical Fidelity X-10D "buffer" type in that cool looking, long round can. Of course, many copies of the PCBoard are now available. But, why ? With only Line In and Line Out, you would be either liking or disliking the "added" sonics. For a cold sounding CD player or digital source, this could actually be "helpful."
Then, there are little tube preamps, some with two "special" 7 pin USSR or Chinese triodes. Some keep it simpler with one dual triode. Some of those have some switching and gain available. At least, with these you get a bit of gain, low impedance output, plus a stereo level control. Still, what if the sonics don't help your needs ?
Finally, consider the slightly larger, little tube headphone amp/preamp types which seem to have been "started" by the Indeed company. The Indeed G2, that's Generation 2, began including switching inputs from either a front mounted stereo 3.5mm jack or rear mounted RCA input jacks. Outputs are either the other rear-mounted RCA jacks or switch to headphones by simply plugging headhone in. They have gain, better than decent hybrid sound and their front mounted stereo volume control tracks gain/balance well. Then, they can switch between 6V 6922/6DJ8 types and 12V 12AU7 types ! Sounding versatile yet ? The sound with headphones at 32 Ohms or higher is quite nice. Run through the stereo can be very nice.
What is their best "feature" you ask ? With a good amount of low distortion gain available, for low to high impedances, their drive abilities are admirable. In other words, some of these tube headphone amps, like the even less expensive Bravo or Little Bear, are actually versatile little headphone amps and/or stereo preamps. Now, the crucial question: Will these satisfy your "matching" needs and sound quality needs ? Well, since they can be snatched for $40. to $75. shipped to the USA, a trial might be just what the doctor ordered...
Considering that the "used" market can be a good indicator, if you check the bay for used examples of these hybrid headphone amps, it should not surprise you if only a few are available near now "new" cost. The first one I bought, went to my daughter for her headphone needs. She still keeps it around and uses it a few years later.
The third unit, I kept the second, went to my sunny (son-in-law). He prefers the Indeed G2 headphone sound over any solid-state headphone amp he has heard; he has heard many and he has owned two ss types. When I showed him the preamp ability, that is the new main usage for him. He uses a battery ss h/phone amp for commuting days and plugs in his digital sources to the hybrid at night and on weekends. Thus, his hybrid headphone amp acts like an audio sweetening buffer, plus a sweet sounding preamp to "drive" his stereo EL-84 tube amp. His wife, my other daughter, plays music through it during the day and night as well. They simply enjoy it very much and now thank me for it all the time...
For all the doubters, try it, you might like it...There are two caveats. First, some of these come with switching power supplies, which can cause hum if used on the same house electrical circuit as your record playing system. When spinning records, simply unplug the switching power supply. Also, the heatsink mounted devices do run hot to the touch; but they do not melt the plastic cases or discolor the boards. Try these versatile hybrid headphone amps...
Wonder how an ecc99 would work.
Pick your chosen tube, switch fil to 12V or 6V, connect, plug-in, turn on and see the blue LED glow around the tube thru the clear plastic case. OOOOOhhh...Then wait a moment, turn up the vol. and boogie...
Surprisingly, even the low dollar Little Bear headphone amp uses decent quality parts. Surely, you can upgrade the electros with Silmic II or Muse BP caps which should step it up a notch or two...
Enjoy & SEASON'S GREETINGS !
I heard one driving headphones the other day and was impressed with the low noise.
Think I'll give one a try and see if I could get ECC99s to work.
Thanks and Merry Christmas!
Scott
Why don't you tell us what this rig consists of. I'm leaning toward what others said and it would provide little benefit. What's the goal? Better sound? I can't see that thing bringing much to the table.
What's the source(s) pre, power and speakers now? Maybe you sell your pre and buy a better one or that kit John built and mentions below. But still tell us about the rig.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
Why would you benefit. Buffers as some people call them seldom work. Get a better preamp
Alan
.
I built a tube preamplifier from a Vacuum Tube Audio kit not too long ago and it sounds fantastic in my system. It cost only $1355 and that included upgraded tubes and a remote volume control. If you can build an electronic kit, the VTA SP14 preamp is awesome.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: