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Hi, sfter all this experimentation with DIY passive preamps,transformer implemented and a regular stripped down Dyna PAS this little tube buffer just slays all the others mentioned. Is there anyone out there that could explain what a tube buffer really does to a slow cave man...me? Thanks alot. Remember; Best understood in simpleton form...Mark Korda
Follow Ups:
As viridian has pointed out, the FX and the many similar units that are so popular, are not buffers. They are preamps with gain. So nothing that Nelson Pass has to say about the characteristics of buffers applies to the FX.
The biggest problem with the implementation of the FX is that it operates the tubes at very low voltages.
A poster on the massive FX thread over on AK, linked earlier, measured voltages for me a while back. I was in the process of breadboarding a preamp using a variety of tubes and the same simple (anode follower) circuit. I was curious so I tried the FX tube at stock voltages and then at more "normal" voltages suggested by the tube data sheet.
Not surprisingly, it sounded significantly better at normal voltages but the sound at lower voltage was better than I expected. If you take the triode plate curves (the FX uses a pentode wired in triode) and draw a load line it's truly horrible. Yet it doesn't sound as bad as it looks.
I just breadboarded the FX out of curiosity because I knew it had much more gain than I needed. Most modern systems don't really need any gain at all, since amps can normally be driven to full power by the output of a CD player or DAC alone. Some "tube flavor" is nice, though, and an active stage can often improve dynamics compared to a "passive preamp", aka a volume control.
While many owners like the sound, the gain is probably the biggest problem. There are a lot of complaints about how touchy the volume control is - the useful range is quite limited. So it's difficult to make minor level adjustments, it's often either too quiet or too loud.
I breadboarded several different tube types using the same circuit. Here's a link to what I built, if anyone's interested.
your observations are noteworthy and I might note that the Butler guitar tube preamp from years ago ran the one 12ax7 plate voltage at around 50 vdc for the purpose of significant compression & distortion. I know it's just a guitar preamp but there are more than a few ways of implementing circuits for whatever the intended purpose is.
That's one reason why it's all still alive and doing well. Cheers
Everything below the line is Nelson Pass explaing, among other things, buffers, with regard to his B1 buffered preamp. Link to the full article at the bottom.
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"Is impedance matching an issue? Passive volume controls do have to make a trade-off between input impedance and output impedance. If the input impedance is high, making the input to the volume control easy for the source to drive, then the output impedance is also high, possibly creating difficulty with the input impedance of the power amplifier. And vice versa: If your amplifier prefers low source impedance, then your signal source might have to look at low impedance in the volume control.
This suggests the possibility of using a high quality buffer in conjunction with a volume control. A buffer is still an active circuit using tubes or transistors, but it has no voltage gain - it only interposes itself to make a low impedance into a high impedance, or vice versa.
If you put a buffer in front of a volume control, the control's low impedance looks like high impedance. If you put a buffer after a volume control, it makes the output impedance much lower. You can put buffers before and after a volume control if you want.
The thing here is to try to make a buffer that is very neutral. Given the simple task, it's pretty easy to construct simple buffers with very low distortion and noise and very wide bandwidth, all without negative feedback."
Viridian and Shovel, thanks, that was just what I was looking for. That Nelson Pass article was easy to understand too...Mark K.
Hi Viridian, thanks for that site on the FX01! If the first guy liked it better than the Bottlehead I might not be going insane.I got the better tubes right off and they were 20 bucks.As good as it sounds,and I read about the new power supply mod, the tubes glow a MacIntosh aqua blue and the power supply or adapter projects a planetarium light effect when playing in the dark.My best test cd is Sammy Davis Live at the Coconut Grove.He says right on the concert that their recording this with some new techniques described on the cd case or album cover.I've used this again and again testing which preamp sounds best.At the start of the cd you can hear Sammy trying to clear up a frog in his throat.You can hear him sipping whiskey and his throat continually improving and it's full of great songs and impersonations all while president Kennedy was still alive.I gave up for a while my turntable restoration projects when I heard this.Thanks Viridian.....Mark Korda......You too Shovel!
I don't think Sammy, or any of the other Rat Pack, sipped whiskey during a show. There are plenty of interviews with both Dean Martin (who's trademark was a drink in hand) and Frank Sinatra that debunked those claims (much later in their careers). Both have said that it would be impossible to sing while drinking. Although it was amazing to see Dean puff away on a cigarette and sing. Ahhh, those were great days!
I'm sure that after the show was a different story.
Sorry about the spelling. Dean Martin did drink apple juice, claiming it was Jack. He often was out early the next morning, that morning(?), for a round of golf. Per one of his Bios, Frank, on the other hand, drank 3 dozen glasses of Jack daily. A full day to Frank was a movie scene in the AM, a recording session in the afternoon, a gig at night, followed by an occasional late night fist fight. Gordy Howe had nothing on Frank.
Hi Airtime,
I heard the same thing about the rat pack.Sammy starts out with For Once in a Lifetime and he struggles with the notes.That's where I mentioned a frog in his voice.I don't know what he did to recover lest put his hand over the mike and hack his guts into some sort of spittoon.That's why I thought a little nip of whiskey might have loosened his vocals, not being drunk...yet.Like you said probably after the show. He was a heavy smoker and I know all about that.His voice keeps getting sharper and sharper thru the recording.
I've been on the wagon for 7 years but vividly remember a shot of Jack cleansing the old gizzard for a rendition of One for my Baby down at the Eagles in front of 4 people on Kareoke night.It loosens up your vocal chords....Mark Korda
Already have some nice JAN tubes, NOS, and a linear power supply that would fit right in.
Enjoy! All the best, Marty.
...-.used for improving impedance mismatches in components, or for driving long cable runs. A buffer presents a high input impedance to the driving component and a very low output impedance to the component that is driven. The FX01 is actually not a buffer in the classical sense, as it adds gain and has a volume knob, so it is actually what most would call a single input preamp.
There is long thread on the device at AK linked below:
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