120studio.com 4/14/2015
Copyright 2015.  All rights reserved.





Intro

Vacuum tube audio has traditionally been expensive in this modern age of transistors.  For a while, it was only a niche for the most dedicated enthusiasts.

Today, the vacuum tube sound has found new life again.  A lot of people are realizing that there's a genuine difference in the sound.   And now there's affordable tube gear on the market.

As you'll see by reading the rest of this article, we're talking about a hybrid tube / solid-state design here.  If you're looking for all-tube, then this is not it.   With that said, I hope you'll keep reading anyway, because this is an interesting little device.

In this article we're going to look at the Bellari VP-130 from Rolls Corporation.   It's a combination phono stage and headphone amp, built around a 12AX7 vacuum tube.



A Quick Note


This article is made possible only by the support of readers like you, when you use the links on here to purchase your gear.

The small commissions from sales are what allow me to keep this site going.   Thank you in advance for your help.


In This Article


Some Specs

General Characteristics


Circuitry

Connectors

Audio Quality

Power Supply Noise

Spectrum Analysis

Pros & Cons

Fun Stuff

Upgrade Path

Conclusion



Circuit board



Some Specs

Case Material:  Steel
AC Voltage:  Wall adapter takes 110/120V AC
Cartridge Compatibility:  Moving Magnet only
DC Voltage:  Wall adapter supplies +15V DC,  300 mA
Dimensions:  6" x 5.4" x 2.5"
Gain:  30 dB @ 1 KHz
Headphone Jack:  1/4" stereo (do not use a mono plug!!)
Input Impedance:  50 K ohms
Made In:  USA
Output Impedance:  8 ohms for headphones, 100 ohms for RCA line-out
Price (typical):  $275 US
RCA Inputs:  one pair (stereo), for un-amplified phono signal
RCA Outputs:  one pair (stereo), line-level output
Signal to Noise Ratio:  80 dB
THD:  0.02% @ 1 KHz
Vacuum Tube:  12AX7 or direct substitute (ECC83, 7025, etc.)
Voltage Input Range:  12 to 15 volts DC
Weight:  2 lbs






General Characteristics

This is a dual-purpose device.  It's a headphone amplifier and a phono-stage preamp.  It amplifies the phono signal according to the RIAA equalization curve, which means it increases certain frequencies (the lows) and decreases others (the highs).  If you just straight-up amplified the signal of a record player, it would sound unbelievably tinny and would have almost no bass.

The VP130 brings the phono signal up to what's called "line level".   That means it has been amplified enough that you can listen to the turntable through a receiver or amp that doesn't have its own phono stage.  That describes quite a few of them.

The VP130 is a vacuum tube device, at least partially.  There is a 12AX7 vacuum tube in the amplification circuit.   The 12AX7 is a small-signal tube, because a phono preamp is a small-signal amplifier.  You're not going to see big power-tubes, massive high-voltage capacitors, or anything like that in here.   That also explains why you don't see a big, heavy transformer.  (That's what makes power amps so heavy.)


(Back to top)


Circuitry


IC's and Transistors

The device has four BA4560 op-amps.  That tells me, quite obviously, that not all the amplification is being done by the tube.   Here's the good news:  (A.) the BA4560 is an analog IC, and (B.) it's a low-noise component. 

The VP130 is not an all-tube amp, but it appears to be an all-analog device. 

I see a hex inverter IC in there.  (Analog.)  Near it there's an FQP 3N30, which is a power MOSFET.  I'm guessing this and the hex inverter are part of a circuit to convert DC to AC.  (The VP-129 had a power adapter that supplied AC, but the VP-130's adapter supplies DC.)


Signal Amplification

Various sources claim the audio signal goes only through the tube, without using any integrated circuits (IC's).  Initially I thought that, too, but now I'd say otherwise. 

Looking at the circuit board, I then assumed the op-amp IC's were receiving the output from the tube and amplifying it further. 
 
That would go like this:  Input Signal --->  Tube --->  Op-amps --> Output Signal.    It could be happening in that order, but I don't think it has to.

There was a schematic for the earlier VP-129 on a Norwegian audio forum, but the file doesn't seem to be there now (and I don't speak Norwegian).  Here's what I can gather about this circuit.


Vacuum Tube

First, here's what the pins do on a 12AX7....

Pin 1:  Plate
Pin 2:  Grid
Pin 3:  Cathode
Pins 4-5:  Heater
Pin 6:  Plate
Pin 7:  Grid
Pin 8:  Cathode
Pin 9:  Heater common

Now, here were the voltages on the 12AX7 that's used in this unit.  Do not try this at home;  live 12AX7's can be up to 330 volts.

Input voltage (from power supply):  14.8 volts DC

Plate (Pin 1) to Chassis.....  67 volts DC
Cathode to Plate:   Pin 3 to Pin 1...... 72 volts DC
Grid to Plate:   Pin 2 to Pin 1...... 64 volts DC

Plate (Pin 6) to Chassis........64 volts DC
Cathode to Plate:   Pin 8 to Pin 6.....  68 volts DC
Grid to Plate:  Pin 7 to Pin 6....  61 volts DC

Pins 4 to 5:   12.8 volts when the unit is getting 14.8 volts DC;  10 volts when the unit is getting 12 volts DC. (Pin 4 to 9 is 5 volts and Pin 5 to 9 is -5 volts).

On a conventional design, the plate voltages would be higher:  150 to 300 volts, not 60 to 70.   So it's a "starved plate" design.  That means the 12AX7 tube is getting less voltage than usual. 

When I first fired up this device, I wondered why the tube didn't glow as brightly as the ones in old radios I used to have.   Even the small-signal tubes would glow more than this.  That explains why.

When you adjust the output control, the tube's glow never gets brighter or dimmer.  The DC voltages also do not change on the tube pins;  I checked.  That suggests the level controls are working on the op-amps, not the tube.   You can have constant-voltage on a tube while changing the overall power through it, but if that were the case, the glow should still get brighter or dimmer.

Maybe that's why there are two pairs of op-amps, one for the RCA-out and one for the headphone-out.


Design Rationale

Here's why they chose a starved-plate design, probably.  At lower-than-spec voltages, tube output is non-linear.  That allows you to get the "tube sound" without having as many tubes.  It also allows you to make a nice, compact unit without big, heavy transformers. 

Some people will say that's cheesy, because it messes up the sound.  I disagree. 

In theory the distortion of a starved-plate / hybrid device would be more third-order than second-order harmonics, and that's not as good.... but the vacuum tube character you get with the VP130 is subtle.  Through headphones, it sounds like a high-quality receiver amp, not a distortion pedal.  You're not running this device at clipping levels.

This design is using both of the triodes in the 12AX7.  The voltage is higher than a lot of starved-plate designs, but not all the way up into "normal" voltage.  They probably chose this to give the best balance of sound:  clean, yet with a hint of vacuum-tube. 

As I found, changing out the tube does affect the audio characteristics.  That means the tube definitely does something other than act as a decoration.  That something can take a trained ear to detect, and you won't always notice it.  But then, sometimes you will, and many people do. 

And right now, there aren't any all-tube devices that do what the VP-130 does, while staying in this price bracket.




Analog op-amp IC

(Back to top)


Connectors


Ground: 
- Binding post with banana-plug jack, also through-hole in post.

Input: 
- Phono In:  RCA stereo (1 pair)

Outputs:
- Line Out:  RCA stereo (1 pair)
- Headphone Out:  1/4" stereo (1 jack)

Power: 
- DC plug jack (center-negative)


(Back to top)


Audio Quality Tests

I tested this amp carefully with a couple different LP's. 

Listening order:  first, the stock power supply,  then a new power supply, and then a new (Electro-Harmonix) 12AX7 tube. 

Music with high sibilance, punctuated with spike transients (clicks and pops), had a noticeable improvement by using the better power supply.  The improvement continued by switching to an Electro-Harmonix tube.     Your mileage may vary, which I'll explain later.

The power supply upgrade was a natural here.  A linear supply has lower-noise than a switching-mode. Actually you can make a very low-noise switching supply, but it's a little easier to make a low-noise linear.

There's another thing you can do, for any amp, which may improve your sound quality.  Get a real surge protector (series mode), which has built-in line conditioning (handy, and awesome.)  Plug your power supply into that, not the wall.  And definitely not one of those cheesy "power strip" things.

Now, the listening tests:

Test 1:  Stock power supply;  Stock tube. 


Results:   Some noticeable hum at higher playback levels.  It wasn't that bad, though.  I expected the main problem to be the 300 mA power supply;  the manual calls for a power supply of 700 mA.   Then again, that could be for an earlier version of the VP-130.

The music had a somewhat muffled quality. The bass was a bit muddy.   The pops and clicks were nastier than usual.  Just to be sure, I tried the power supply on a different outlet.  Same result, with or without a power conditioner.

After about ten minutes of listening, I was fatigued.   This was not normal for this LP;  usually I could listen to it a couple times through. 

To be fair, this problem seemed to lessen after a burn-in period of using the device for a while.  In fact, after a couple hours of burn-in, the stock supply wasn't really that bad.  (See "Power Supply Noise", below).  Switching between them still yielded a difference, but not as dramatic as initially.


Test 2:  Upgraded power supply;  Stock tube. 


Results:  With a better power supply, I noticed the VP-130 was still drawing less than 250 mA, even with the headphone output at max.  Thus, current supply wasn't a bottleneck.  However, the new supply seemed to give an improvement in sound quality. 

Pops and clicks lost some of their edge.  The music sounded better overall.  After burn-in, the difference wasn't enormous, but it was there.

Varying the DC supply voltage between 12.0 and 15.0 volts didn't have any real effect on the sound.  The VP130's circuitry handled the variation without a hiccup.  The manual says you can use a 12V power supply.

By this stage of the test, I could listen to a whole side of the LP without wanting to go do something else.

But wait, there's more...



Upgraded 12AX7 tube.


Test 3:  Upgraded power supply;  Upgraded tube.


Results:  Now the bass lines sounded better and clearer.  The best way I could describe the sound at this stage is to say that now, I could listen to the whole LP three or four times the whole way through. 

I think this little headphone amp is dialed in now.  It might be even better with a NOS tube.  (That's "new old stock", not the same as "used".)  However the Electro-Harmonix seems better than the stock tube.   However, as this points out, the variation in modern tubes is great enough that you could get very different results even within the same brand.  Some people say the stock tube in their VP130 wasn't that great, but others say it's just fine.  Part of that's going to be subjectivity, but I think a lot of it is also the variation in modern tubes.  That, and burn-in.  The Chinese 12AX7 tube may actually be pretty good;  it just needs some hours on it.

(Back to top)




Power Supply Noise

I measured the stock supply at 3.5 millivolts RMS, which is considered "ultra-low noise" for a switching power supply.  The RMS voltage fluctuates, which is not surprising for a switch-mode unit.

Normally, 3.5 mV of noise would not be a concern, but since we're amplifying a phono signal, it's worth looking for lower noise. 3.5 millivolts is in the same range as what a phono cartridge puts out.  I'm not saying both voltages will be amplified to the same extent (obviously, they're not supposed to be), but a lower-noise supply is probably not a bad idea.

The linear power supply that I tried tests far lower (0.5 to 0.7 millivolt). 

(Back to top)




Spectrum Analysis

Like the audio test, this is mainly just for fun.  If I wanted to run a "real" test, I'd run five or ten different samples of 12AX7's from each manufacturer, a bunch of different samples of each power supply, and at least three or four different types of music. 

This was actually with a different LP than I used in the listening comparison.  It was a short section of music, mostly rather quiet without much sibilance.  Sure enough, this LP did not produce quite as dramatic a difference when I changed the components.
 
Differences in amp circuitry are most pronounced when you have very high-amplitude portions of audio.  That's where I heard the biggest differences in switching to a better power supply.  That's also where I heard the biggest differences by switching to a different tube.
 

These spectra are not aligned on amplitude, as you can see.  Changing out the power supply did not change the volume of the overall sound.  Compare the shapes here, that's all.  This is just to show that the spectra are similar, though very slightly different.



For some reason, the graph makes me think of this.


Notice what happened to the frequencies lower than 40 Hz, though.  At 20 Hz it changed from about -39 dB to -45 dB.  That's the biggest change here from using a better power supply. 

Below 30 Hz is mostly "rumble", so it's better to attenuate that unless you're listening to cathedral organ.

There are also a lot of very small differences elsewhere.  These are the differences you can't see unless you zoom way in on the graphs, but they're the kinds of differences that can change the listening characteristics slightly.     

Here's why the changes should be slight.  Really obvious changes in frequency distribution would mess up the sound, not improve it.  With tubes, it's all about the subtleties.

So anyway, here's a summary of the differences.  (Step 2 not shown in spectra.)

Step 1.  Upgraded power supply: 
 -Decrease in sub-40-Hz frequencies.  At 20 Hz there was a 6 dB cut by using a better power supply.  The amp had the "Rumble Filter" on at all times.
 -Slight increase in some other frequences:  near 800 Hz, 1000 Hz, etc.
 -Very slight changes at other frequencies

Step 2.  Upgraded the stock tube to an Electro-Harmonix:
 -Slight increase at 140 Hz
 -Very slight changes in spectrum at other frequencies

This was only with one particular type of music.  There's a lot of possibility for variation here.

With extended burn-in, the differences might diverge even more.  Keep the old tube for your VP-130, and once in a while swap between them.  As you rack up some hours on each of them, each will probably develop more of its own character.

(Back to top)




VP130 vs. All-Transistor Amp


I recorded a short passage of music through the Bellari and then through an all-transistor stereo receiver.   Everything else was kept the same.

Here's a difference-graph of the spectra.  These are aligned on the 1 KHz audio peak, because... well, 1 KHz is the center of most graphic equalizers, so it seemed as good a place as any. 



The differences are not uniform.  The 700 to 2,000 Hz region overlaps very closely.  Then, the differences sort of stretch out on either side of that region. 

Now, let's look more closely at the high-frequency region:



Again, this is a difference graph.  The jagged line represents the difference between the amplitude peaks of two spectra.   The thicker that line, the more the two spectra are different. 

And here again, there's good overlap in the mids... and then increased divergence later on.   Just as we want here, the sound is "basically" the same;  the differences are subtle. We don't want a device that's going to alter anything drastically in the sound, unless of course that's what we're trying to do (such as with a distortion pedal).

Everything was the same in these tests, except for the RIAA equalization device.  "Bellari" was the VP130;  "Transistor" was the all-transistor phono stage of a stereo receiver.

(Back to top)



Pros & Cons

First, the cons.  There aren't many.

The anodized aluminum tube guard was not well-finished.  The edges were ugly, and sharp.  With as nice a job as they did on everything else, it seemed out of place.


No way I was gonna leave it this way.
Photo at the top of page has the sanded version.


At least it doesn't detract from the amp function, and at least it's user-fixable.  (Don't sand it while it's attached to the amp... but you knew that already.)

The other thing I didn't like so much was the power supply.  It doesn't feel like it belongs on a headphone tube amp this nice.   As I found in the audio tests, though, it's not that bad.   It seemed to add a slight harshness to the audio, but it wasn't apparent on every audio track.

Swapping out the tube is difficult at first.  That connector really doesn't want to let go of the pins.  And when you try to put a different tube there, it's equally tough.  After about three or four times of switching between the stock tube and a Russian 12AX7, the connector finally seemed to be... semi-tolerable.  I guess it's better than having the tube fall out, or develop a contact resistance on one of the pins.


Now, the pros.

This amp is beautiful.  The red enamel paint is gorgeous.  The white letters on the red enamel are gorgeous.  The construction is solid. 

The solder joints look good.  There are no surface-mount devices that I can see (and glad of it).   If you ever want to replace any components, this is the kind of circuit board you want.  They used quality materials here.

The knobs are plastic but high-quality.  They look and feel like the black phenolic knobs of early-vintage gear.   The pushbutton toggles are plastic but are metal-capped on top.  They are about on par with mid-range stereo gear from 1980, which is very good compared to most of what's out there today.

The connectors are all very solid, with no jiggle.  They look gold-plated.

There is a ground connector for the chassis, and yes, I checked... it really makes electrical connection to the chassis.  I've seen brand-new automobiles where they couldn't even get this simple thing right.

Rolls paid attention to the details here.  If you've ever tried to build something, you know that it's the seemingly little features that add quickly to the cost.  This device has a lot of features and qualities that you won't find on cheap electronics of any kind. 

(Back to top)



Fun Stuff

This pre-amp brings the phono output up to line-level.  That allows you to run the output into your computer's sound card.

Get an RCA-female-to-3.5mm-male stereo adapter.  Run the RCA cables from the output of the VP-130 to that adapter, then plug the 3.5mm plug into the "Line In" jack of your sound card.  

While the computer is recording, you can listen to the LP through headphones plugged into the VP-130.    The headphone-level and output-level controls are independent of one another.  If you adjust the headphone volume, it will not affect the output level.  (Just pay attention to which knob you're adjusting. )

On your computer's software, set the sampling rate to at least 48 KHz or better yet, 96 KHz.  This will give you the best recordings.  Lower sampling rates will not even sample the highest frequencies at all.

Here's another fun thing you can do with this phono stage:  mini stereo system!  Get the VP-130 for your turntable, and get these speakers.  They have their own power amp, so you don't need to buy one.  Don't mind the "extreme gamer" design... the sound quality is worth it, and the control layout is tops.   Connect the RCA out from the VP-130 to the RCA inputs of the speaker set, and you can produce room-shaking sound from your vinyl LP's.    And when you're not using that, you can always go back to listening to headphones.

(Back to top)




Upgrade Path

At first I thought it would be nice to have an all-tube phono stage.  Problem is, most all-tube phono stages lack their own headphone amp.  Meanwhile, most all-tube headphone amps aren't phono stages, because they can't do RIAA equalization.

One of the best things about the VP-130 is that it's not going to be redundant.  If you later get an all-tube mini amp such as a Little Dot, you will be able to hook the VP-130 output to it.  An amp like the Little Dot requires a separate phono stage anyway.  Unless your turntable has one built-in, you'll still need the VP-130 to bring the turntable output up to line-level. 

Even if I were using a turntable with onboard phono-stage, I'd prefer to bypass that one and use the Bellari.  Not many turntables are going to have phono stage circuitry as good as what's on here.

This is a device that stays useful even when you upgrade. 

(Back to top)



Conclusion

The VP-130 is made in the USA, it's impressively well-built, and it's even pretty to look at.  The bright red enameled steel case and the overall build give this unit a classic feel.   In a world of plastic stuff, it's nice to see something built this nicely.

The sound is good:  perhaps a hint of "tube" coloration, but overall it's still a faithful, clear sound.  In other words, you don't need to worry about it sounding like a distortion pedal.

The VP-130 is pleasant to use and pleasant to have on your desk, because it's so nicely made.   And if you decide to get an all-tube mini amp later, that still requires a phono pre-amp if you want to listen to vinyl through it.  Use the VP-130 as a phono stage, and bypass the one that's in your turntable (if there is one).

And the ability to listen to your vinyl on headphones, directly through the VP-130, is great.

Overall, I think we have a winner here.

I hope you found this page useful, informative, or entertaining.  If so, please help me out by purchasing your stuff through these links.   Your help is greatly appreciated and is the only way I can keep this website going.

Thanks for visiting this page!





    


Contact me:

3 p o.t o . 1 2 0 s t u d i o.. c o m


This won't directly copy and paste.  Please manually type it into your mail program.
No spaces between letters.





Home Page


What's New



Disclaimer

All photos on this site are Copyright 2010-2015.  Please feel free to share links to this site.  However, copying or re-distributing page contents or photos for any purpose, electronic or printed, is prohibited without express written permission
.





 



Back to Top of Page