AVForums South Africa

Audio/Video Hardware => Valves/Tubes => Topic started by: Bruce M on August 14, 2018, 07:37:57 PM

Title: Cheap valve pre amps - any good?
Post by: Bruce M on August 14, 2018, 07:37:57 PM
Hello valve chaps,

I was looking at this litte valve pre amp on Massdrop (the FX Audio TUBE-03 Preamp Buffer), and read the below comment. Is this accurate, and if so is it true of all valve pre amps, or just the cheap ones...


"To understand the merit of this thing, you have to realize it is NOT an amplifier.  It is a buffer.  Meaning, all it does is pass a signal through a tube with almost no appreciable amplification.  The catch is that it is preying on people thinking that simply having a tube in the chain is what makes the sound better.  That's not the point.  "Adding warmth" or "adding color" is not the point.  The point of a tube - what makes it better for audio than a transistor - is the way a tube distorts when it amplifies a signal.   Yes, the even-order distortion produced by overdriven tube circuits is more musically pleasant than the odd harmonics produced by an overdriven (clipping) transistor.  (you can google using terms like "tube transistor distortion odd even harmonics" to better understand this)

If you're not amplifying the signal with the tube, there is no point.  You're just adding the distortion inherent to the tube to whatever else in your chain you're already using to amplify.  So if you're not REPLACING a transistor with a tube for the various steps in your signal chain, you are not gaining sound quality, period.  In the case of this thing, you're also adding the distortion of an extra volume knob, and the bass and treble controls."

Title: Re: Cheap valve pre amps - any good?
Post by: fdlsys on August 14, 2018, 07:55:31 PM
As you quoted below - it's NOT a preamp, it's a buffer circuit. It's role is to adjust ("buffer") the input-output impedance of whatever comes before and after it. As the author of the quote said, chances that a tube buffer would sound appreciably different from solid state buffer are small to none.
Title: Re: Cheap valve pre amps - any good?
Post by: Hi-Phibian on August 14, 2018, 09:24:25 PM
Most of these are clones of the Musical Fiddle Tea X10D. 

Here is an excerpt from Stereophile about the X10D and it explains it’s reason for existence.  Basically it gives lesser designed line level output stages an easier time. 

“Musical Fidelity X-10D line-level preamplifier
Sam Tellig Various | Nov 6, 1996
"Musical Fidelity X-10D" it said on the box. No, this is not bathtub mildew remover or laundry detergent. Actually, it's hard to figure out exactly what it is. The box is little help. Musical Fidelity calls the X-10D "the missing link," a "pure Class A CD-player accessory."
image: https://www.stereophile.com/images/archivesart/mf10dla.jpg

I'll reveal the true identity of X-10D in a moment. But I'll say straight off that for those of you with such CD players as the Marantz CD 63, RadioShack Optimus CD-3400, etc., this may be the most cost-effective CD upgrade ever to come down the pike.

Digital processors?

Nah. Do you want to spend $500 to $1000 (for starters) on a processor, only to be faced with paying $200 for a good digital cable to run between your player and processor? And what else do you get by separating the two boxes, besides having to buy cable? You get jitter, that's what.

I say forget processors. Anthony Michaelson, Managing Director of the British Musical Fidelity company, appears to agree—even though he makes processors. In a phone conversation, Anthony referred to outboard processors as "commerce"—which I take to mean he can sell 'em but you should perhaps not buy 'em.

According to Anthony, though there's nothing wrong with the DACs in many modestly priced players, their analog output stages are another matter: cheap op-amps, wimpy power supplies, and the like. Much of the improvement in sound that you get with an outboard DAC may be due to the DAC's better analog output stage.

So why not just buy a better analog output stage?

That, essentially, is what the X-10D is—for about a third of what you'd likely pay for even a budget outboard DAC. Cost-effective? You bet!

The X-10D thing looks neat—a long, narrow cylinder supported along its sides by two rails running the length of the unit. Anthony tells me that, in-house, they've nicknamed it "the piglet." Additional products using the same chassis will be forthcoming, including a tubed headphone amp, an outboard phono stage, and a line stage—although whether these or other Musical Fidelity products make it to these shores remains up in the air.

So...what exactly is this thing that I am suggesting—nay, urging—you to shell out 200 bucks for?

It's a tubed output stage and buffer. The X-10D has two sets of RCA jacks, input and output (you'll need an extra set of interconnects). You put the X-10D between your CD player and your preamp, active or passive. Or you can put it after your preamp, active or passive. Or you can put one X-10D before the preamp and another one after, if you like—which would have the effect of tubing everything before it goes to your power amp.

"Voilà!," says Anthony, whose products are all the rage in France. "You have turned your solid-state preamplifier into a tube preamplifier" with "the ineffable magic of tubes.

"Essentially, the unit is an impedance-matching device," he explains. "It has a very high input impedance, of about half a meg [500k ohms—Ed.], and quite a low output impedance—we rate it at 200 ohms or less, but in fact it's about 15 or 20 ohms. What this does is allow a CD player to operate perfectly. You can take almost any old CD player, bang an X-10D on the end of it, and you can't believe the results you get."

If my own experiences with the Marantz CD 63SE and the Optimus CD-3400 are any indication, Anthony is right. With the CD63SE in particular, the X-10D transformed the sound, especially in those areas where the CD-63SE itself is weak. There was more body, more bloom. Dynamics were vastly improved. There was more there there.

One caveat: The X-10D is probably not for every CD player, and the two extra sets of RCA connectors, plus the cabling and everything else that will now be in the signal path, will probably compromise the sound ever so slightly. I did not hear any great improvement using the X-10D with my Meridian 508, perhaps because the Meridian player has such a superb (and tubelike) analog output stage already. Nor would I use the X-10D with the YBA 3 CD player, feeling that the X-10D made the sound ever so slightly less transparent. But with the Marantz CD63SE? Holy smoke! Talk about transformations!

Anthony swears up and down that the X-10D does not add distortion or alter frequency response (footnote 1). "The figures we're getting from this thing have never been achieved with tubes before," he crows. "Distortion is less than 0.01% from 10Hz to 100kHz. Signal/Noise ratio is way better than 90dB. Frequency response is flat from 10Hz to 100kHz." I would assume that any slight loss of information is due to the cabling and connectors.

The key with the X-10D is versatility. Hell, you could use this thing even if you do have a DAC—put it after the DAC or after the preamp. Music, especially digital music, almost always sounds better after it's passed through bottles. Put it into the tape loop of your preamp and tube it on the cheap.

Inside, the unit has two 6DJ8s, each mounted in a tube socket so tube replacement should be no problem. The unit is meant to be left on all the time—which, contrary to what you might expect, may actually prolong the useful life of the tubes. (This would not be true of tube amplifier output tubes, of course.) If you open the unit to change tubes, be aware that Musical Fidelity considers this "tampering"; if they catch you at it, they void your warranty. Oh, hell, just be careful, and remember that the top hex screw holds the ground wire—you'll have to carefully put it back in place when reassembling. In any event, I haven't tried messing with the tubes, and I don't suggest you do, either, until it becomes a necessity.”
Title: Re: Cheap valve pre amps - any good?
Post by: kenvanraas on August 14, 2018, 11:04:05 PM
I have the Little Bear P5 pre.I was very sceptical @ first til i read this...


(I made a cool power supply and its still going strong  :2thumbs:)
Title: Re: Cheap valve pre amps - any good?
Post by: Dubya Jay Dee on August 15, 2018, 12:52:22 AM
Have been using the Schiitt Audio Saga pre for a couple of months now and it is very good. Switchable between fully passive (i.e. no powered electronics) - or going through the 6SN7 valve buffer with no gain but improved ability to drive power amp inputs optimally.

Driving a T-Rex power amp there is a distinct difference between the two modes with the buffered option sounding stronger in the bass and slightly increased volume vs the passive option.

Driving a Schiitt Vidar power amp or my Adcom power amp there is very little if any discernible difference between the two modes - both sounding full, neutral and balanced.

Highly recommended for what is a very affordable option for a passive/buffer pre with remote control for input selection, volume and mode.


Title: Re: Cheap valve pre amps - any good?
Post by: Curlycat on August 15, 2018, 06:53:09 AM
There is the Darkvoice 336SE as well. Lovely preamp or headphone amp.


(https://s19.postimg.cc/vm484c95f/415sh_LINe9_L.jpg) (https://postimages.org/)
Title: Re: Cheap valve pre amps - any good?
Post by: Bruce M on August 15, 2018, 10:46:55 AM
Thank you all for the input, very informative.

Based on what I've read:

"The key with the X-10D is versatility. Hell, you could use this thing even if you do have a DAC—put it after the DAC or after the preamp. Music, especially digital music, almost always sounds better after it's passed through bottles. Put it into the tape loop of your preamp and tube it on the cheap."

Could one put something like the above mentioned devices (obviously the Little Bear is really well priced) in line between my intergrated amps pre-outs and its line in. There are currently bridging jumpers between the two?

It's a Yamaha AX-1095 (stereo integrated, 145wpc) with a "direct through" function, which would bypass any of the on board pre amp signal processing.

Obviously the Little Bear's volume knob would have to be adjusted through trial and error.

Forgive me if the above idea is ridiculous!

What I'm trying to achieve is warming up the sound a bit, and perhaps more bass at lower volume levels.

FRom the above review: "There was more body, more bloom. Dynamics were vastly improved. There was more there there."

I'm driving a pair of CM9's with this Yamaha, and although it's got plenty of power required by these speakers, I'm finding it a bit bright with some music (far better when playing vinyl). A bit like it needs more bass at reasonable volume levels. Obviously these speakers can produce plenty of base.

Perhaps I'm just not used to large 3 ways, it seems they deliver plenty of precise high's and mids, that I suppose is to be expected!

With certain music it does sound great as it is.
Title: Re: Cheap valve pre amps - any good?
Post by: Ampdog on August 15, 2018, 11:07:18 AM

All of this sounds interesting, but what with several contradictions coming out of the woodwork it is not easy to express a better opinion than what came with all the subjective views.

Is there any possibility that someone can find us a schematic?  I googled briefly but was unsuccessful. As others said, something does not suddenly become a 'valve' amplifier because a valve is hidden somewhere in the works (the 'valve sound' myth flourishes and sells all over the play-field). 
Title: Re: Cheap valve pre amps - any good?
Post by: Hi-Phibian on August 15, 2018, 11:10:02 AM
Chances are, in the end you will still change speakers or amplifier anyway if the two don’t gel for you. 

The buffers may add some warmth but it even depends on their design.

You could try some cables with a known mellower tone too.   
Some sellers like myself would let you try some. 

But these things may help but ultimately may not keep you happy and the itch to change remains. 

Title: Re: Cheap valve pre amps - any good?
Post by: Ampdog on August 16, 2018, 12:34:23 AM
Okay ......  I will leave some of the erroneous opinions* in the quoted paragraphs there; I did find a schematic plus spectrum analysis of a Musical Fidelity X10D 'buffer'.

The circuit is a twin triode (ECC88) - full amplification, with about unity NFB.  (The gain is about 1,5dB.)  This is  likely to cure some (a lot of) loop distortion caused by the very low operating voltage (some 60V only). As such the triodes work quite outside their normal conditions (on the bends of Va-Ia graphs), but one must admit that, accepting the distortion analysis (and I have no reason to doubt that), the goal is achieved.

The maligned small power transformer must supply only about 5W, and with the h.t. (though the term barely applies here!) being regulated, the results seem to be believable. My greatest concern is that 6DJ8/ECC88 heaters can have a quite large variation in current drawn. (They were not intended for series operation). Thus series operation of the heaters may cause unequal voltage division of heater voltages.

Thus: Finding that valve distortion can be unacceptable at low voltages, so applying some 50dB of NFB to cure that, cannot really be criticised, though it is unusual. There is the use of an extra valve, over cathode follower operation requiring a single triode.

* Regarding some comments, I might remark that
1. Overloadiing/clipping of triodes does not cause even order harmonics as stated. It causes odd order distortion, same as semiconductors (clipping). 

2. I am amazed that (good) potentiometers are listed as a source of distortion.

3. Keeping valves under power continuously will hardly extend their life span.

4. and valve sound?  Not to re-open an argument on that, but that as said before, is an overrated factor. Such is more often caused by the total circuit design than valves per se.

But not to appear smart-ass about these .....   
Title: Re: Cheap valve pre amps - any good?
Post by: Bruce M on August 16, 2018, 05:32:26 PM
Thanks for the insight gents.

Interesting to hear someone in the know confirming that it may have some merit, and isn't just hype and cool looking valves sticking out.

Although HiPhian's comment is probably quite accurate about upgrading anyway.

Out of interest, which of the better known cables (in the realms of reality, considering this 100% second hand system!) would you suggest for a mellower tone?