From The Bench


by Tom Lees

Arnold Schnitzer

This Article Was Originally Published On: June 3rd, 2015 #Issue 16. 

Introduction

If you are over 40 years old like I am, there’s an off chance that you are turning into a curmudgeonly complaining fool, right? [Fist pumping in the air] “Kids, get off my lawn!” has become a familiar war chant. However, your biggest complaint is likely drawn from nostalgia. “They don’t make them like they used to.” Da-gum, we sure do like our indefinite pronouns, don’t we. Okay, grammar aside, today we are going to see if the new can really live up to the old. Squaring off is a beloved 1970s V-4B with all its battle scars, but not a lick of maintenance, going head-to-head (literally) with the new V-4B reviewed herein.

General Observations

Before getting started, it is worth pointing out that the new V-4B is not an electrical clone of our beloved old V-4B. For instance, due to the modern realities of tube availability, reliability, and cost, the new V-4B was re-designed to use easily obtainable tubes. As an aside for you tube amp geeks out there keeping score, the new V-4B also features a cathodyne phase inverter and custom-wound transformers. The power and output transformers were selected by Ampeg engineers to strike a balance between performance, tone, weight, and authenticity to vintage Ampeg tone.

Despite some notable electrical differences, there are some similarities that deserve honorable mention. The new V-4B preserves the rocker switches arrayed just above the equalizer knobs as seen in Photo A. This to me is one of the definitive signature stylings of the vintage V-4B, so kudos for that. The new V-4B also preserves several notable internal telltales of the vintage V-4B. For instance, the new V-4B preserves the fully passive midrange equalization circuit of the vintage V-4B.

Photo A Amps stacked

The new V-4B also preserves the floating chassis suspension system, which is intended to isolate the tubes and other sensitive components from vibration. Taking a look at Photo B, looking inside the head cab, you see a “C” shaped metal bracket that sits on top of a wooden frame. There is one bracket on each end of the amp. These brackets serve two main functions. The brackets secure the chassis to the head cab. The brackets also support the chassis via a series of rubber bumpers that space the chassis from the brackets. These rubber bumpers absorb vibration and help provide isolation to the chassis. Referring to Photo C, the braket and bumpers can be seen with the chassis outside the head cab. In an age of cost-cutting, it is notable to call attention to this detail, as this is a corner that Ampeg could have cut, but opted not to. Good on them!

Photo B Inside look at the suspension system

 

Photo C outside look at the suspension system

Explanation of how the Tests Were Performed

Okay, now a little bit about this comparison. I am going to break the analysis down into a series of rounds, declaring a winner for each round. When all is said and done, I will tally up the scores and crown a non-official, purely subjective champion.

For performance-based testing, each V-4B, new and old, will be plugged into our Audio Precision APx521 test analyzer. Each will receive the identical drive signal at the same time. Each will be plugged into its own independent and isolated 4-ohm non-inductive dummy load. The V-4Bs will be plugged into adjacent electrical wall outlets on the same 20 Amp circuit. As such, these amps will be tested side-by-side at the exact same time, under as close to the exact same conditions as I can muster. For all traces, green is the new V-4B and purple is the old V-4B.

Okay, here is one disclaimer. The old V-4B has two channels, each channel featuring a single gain knob. The new V-4B has a single channel, featuring gain and master volume, as well as two inputs, labeled 0 dB and -15 dB. As noted in my review of the new V-4B herein, the inputs of the new V-4B not only have different gain characteristics, but also different impedances. Given this key set differences, the two amps could not be calibrated based upon a visual setting of the gain knob alone. I tried to match the amps up with close to the same gain structure, but this proved difficult. As such, it is possible that different gain settings may provide different results. But hey, this is just for fun, so let’s roll on.

The Testing Rounds

Form Factor

Dimensions:

New V-4B:  23 ¾” W x 10” H x 11” D

Old V-4B:   26 ¾” W x 10” H x 11 ¾” D

(Note: our old V-4B did not include feet, so our measurement here of the new V-4B is also without feet).

 

Weight:

New V-4B: about 42 lbs.

Old V-4B: about 62 lbs.

 

Front Panel Notable Features:

New V-4B:

Single channel, 0 dB passive input and a -15 dB padded active input;

Gain and Master volumes;

Power and Standby on metal toggle switches;

Midrange Frequency selection 220, 800, 3000; and

Controls left to right – Bass, Mid, Treble.

 

Old V-4B:

Two channels, one input jack per channel;

Gain for each channel, no master volume;

Power and Standby on rocker switches;

Midrange Frequency selection 300, 1000, 3000; and

Controls left to right – Treble, Mid, Bass.

 

Back Panel Notable Features:

New V-4B:

IEC socket for detachable power cable;

No Courtesy 120 V outlet;

No Hum Balance;

Preamp Out;

Power Amp In;

Slave Amp out;

DI with Ground Lift;

2 x 2-ohm Speaker Jacks;

2 x 4-ohm Speaker Jacks; and

1 x 8-ohm Speaker Jacks.

 

Old V-4B:

Integral power cable;

Courtesy 120 V outlet;

External Hum Balance;

Two External Amp Jacks (Equivalent to Preamp Out and Slave Out);

No Power Amp In Jack;

No DI;

2 x 1/4” Speaker Jacks; and

Impedance selector switch (2-ohm, 4-ohm, and 8-ohm settings).

 

Tube Compliment:

New V-4B

4x6L6GC

3x12AX7

1x12AU7

 

Old V-4B

4x7027A (similar to a 6L6GC tube, with a slightly different pin out)

1x12AU7

1x12DW7

2x12AX7

On the new V-4B, when throwing the rocker switches, the user is greeted with a satisfying “chunk” letting them know that the switch is functioning properly. The old V-4B rocker switches simply slide into place, leaving the user to question whether the switch actually fully engaged.

Comparatively, I much preferred the feel to the knobs of the old V-4B. I am not sure if it was 40+ years of built up crud and gunk, or just the potentiometers themselves. The old V-4B potentiometers had a little “resistance” and “substance” to them. The turn is smooth, controllable and feels “high end.” Comparatively, the new V-4B potentiometers felt “light” and too easy to turn.

Form Factor Winner: New V-4B

Here, the slightly smaller head cab and the weight were huge factors. I also much prefer independent output jacks for each impedance, compared to a common jack and impedance switch. That is a personal preference, though. I also appreciate the modernization of tube selection to make it easier to upgrade. Still further, the DI is almost a necessity to many gigging musicians.

That said, there is something for tubes that are 40+ years old and still sound great, as in our old V-4B. The idea of a courtesy outlet seems better in idea than usefulness, and most modern backlines have plenty power drops. If I could put the old V-4B potentiometers into the new V-4B, I would do so in a heartbeat. Also, I prefer the visual aesthetic of the old V-4B name badge, which uses non-italic, lower case font.

Calibration

As noted above, differences in input jack configuration and gain control presented a challenge in calibrating the two amps for a side-by-side comparison. So, I turned on the tone generator for each amp (each amp received a signal from an independent, but gain and phase-synchronized source). I then tweaked the gain of each amp until the measured output was within 0.01 Vrms of each other. For initial testing, on the new V-4B, I turned the master up, varying the gain control. After consulting available schematics for both amps, cranking the master and only varying the gain on the new V-4B seemed most likely to give an even comparison.

Referring to Fig. 1, the calibration process fleshed out our first difference. The new V-4B has an output that is 180 degrees out-of-phase with the input at 1kHz. Our old V-4B has an output that is in-phase with the input.

Fig 1. Calibration

Calibration Winner: Old V-4B

I realize that this is a subtle difference. I am unsure whether this was intentional, e.g., based upon listening tests, or whether this is an artifact of the design changes. However, as an old timer electrical engineer myself, my subjective preference is to preserve phase.

Frequency Response

Referring to Fig. 2, with all controls at “noon” and the amps calibrated to a 100 mVrms 1kHz sin input, the Old V-4B shows an overall flatter response through the low frequencies, especially in the 100Hz to 400Hz range. The old V-4B also shows better low end extension below 40Hz. In comparison, the new V-4B shows an extended top end, with a slightly steeper cutoff. However, in our 80Hz to 8kHz “optimally flat” range, the new V-4B response is +/- 0.261dB, compared to the old V-4B response of +/- 0.417dB (which is due to the high end roll-off on the old V-4B).

FIG.2 “All controls at noon” frequency sweep

Referring to Fig. 3, engaging the Ultra Hi switch yields familiar curves. However, the old V-4B provides about double the high end boost (about 16dB boost), compared to the new V-4B.

FIG.3 “All controls at noon” Ultra Hi

Referring to Fig. 4, engaging the Ultra Lo switch fleshes out a key distinction. The new V-4B provides a midrange dip, a slight low-end boost, a low-end extension and a high-end extension. Comparatively, the old V-4B Ultra Lo provides an overall gain reduction, a deep low-end reduction and a drastic high-end reduction. It appears that the Ultra Lo in the old V-4B clearly seeks to emphasize the low mids.

FIG.4 “All controls at noon” Ultra Lo

Referring to Fig. 5, engaging both the Ultra Lo and Ultra Hi switch yields completely different EQ responses, due to the key differences in the Ultra Lo performance. The new V-4B provides a nice low-end bump, a midrange cut and a nice high-end boost that is larger than the low-end boost. This response is similar to “enhance” or “shape” filters of other manufacturers, so this tone is likely to be familiar and recognizable by many artists. Comparatively, on the old V-4B, engaging both the Ultra Lo and Ultra Hi switches results in strong low midrange and low-end rolloff for deep lows.

FIG.5 “All controls at noon” Ultra Lo and Ultra Hi engaged

Referring to Fig. 6, returning the Ultra Lo and Ultra Hi switches to their “off” positions, the Bass control of each amp was swept. Note that the Old V-4B is capable of more boost and the new V-4B is capable of more cut. However, the Bass control of each amp is in the same ballpark.

FIG.6 Low sweep

Referring to FIG. 7, the low midrange control is swept. Note again that the old V-4B provided greater boost, whereas the new V-4B provides greater cut. Otherwise, despite a slight difference in center frequency, the low midrange control of both amps appears reasonably in the same ballpark.

FIG.7 Midrange sweep position 1

Referring to Fig. 8, the middle midrange control is swept, revealing a similar pattern that is beginning to emerge. The old V-4B provides greater boost, whereas the new V-4B provides greater cut. The middle midrange position shows the new and old V-4B circuits are about 100Hz off from each other, but reasonably in the same ballpark.

FIG.8 Midrange sweep position 2

Referring to Fig. 9, the high midrange control is swept, revealing that the similar pattern continues. The old V-4B provides greater boost, whereas the new V-4B provides greater cut. The high midrange position shows the new and old V-4B circuits are centered pretty close to one another, thus providing a frequency curve that is reasonably in the same ballpark.

FIG.9 Midrange sweep position 2

Referring to Fig. 10, the treble is swept. Here, the new V-4B and the old V-4B tracked reasonably well, except for the extreme cut.

FIG.10 Table sweep

Frequency Response Winner: Draw

In our frequency testing, the old V-4B had more boost on tap when the Treble, Mid and Bass controls were dimed. However, being a little less extreme on the boost yielded results that were extremely close to the new V-4B. Likewise, the new V-4B had more cut on tap when the Treble, Mid and Bass controls were dimed. However, being a little less extreme on the cut yielded results that were extremely close to the old V-4B.

The new V-4B had a more aggressive Ultra Lo response, providing a nice midrange cut, low-end boost and high-end boost in a single switch. This represents a great bang-for-the-buck control that should provide a modern tone that many rock players will like. Comparatively, for those looking for a more low-end heavy, midrange tone with no top end (e.g., country players, R&B players, etc.), the response of the Ultra Lo on the old V-4B may be more to your liking.

Distortion

Referring to Figs. 11-18, sample distortion characteristics are provided for the new V-4B. Fig. 11 shows a 1kHz wave with 1 % THD+N and Fig. 12 shows the corresponding distortion products. Note the strong odd-order emphasis relative to the neighboring even-harmonic (e.g., the 3rd harmonic is stronger than the 2nd harmonic, etc.). Fig. 13 shows that at 5% THD+N, the wave looks more rounded, but there are no signs of hard clipping. Referring to Fig. 14, the rounding of the waveshape due to compression manifests itself in even stronger odd-order harmonics, compared to the neighboring even harmonics. Referring to Fig. 15, the THD+N was pushed to 10%. Note the lack of perpendicular bisector symmetry beginning to develop (draw an imaginary vertical line through the middle of the positive peak; note that the two vertical halves are not mirror images of one another). Fig. 16 shows the trend in the odd-order harmonics, with the 3rd order down only 20dB from the fundamental. Referring to Fig. 17, the signal is shown at 15% THD+N. Note that despite such drastic amounts of distortion, the waveshape still looks reasonable, with no clear hard clipping. Referring to Fig. 18, note that the emphasis on odd-order harmonic remains consistent, with a strong distinction between odd and neighboring even-order harmonics.

FIG.11 New V-4B scope 1 kHz 1% THD+N

 

FIG.12 New V-4B distortion products 1 kHz 1% THD+N

 

FIG.13 New V-4B scope 1 kHz 5% THD+N

 

FIG.14 New V-4B distortion products 1 kHz 5% THD+N

 

FIG.15 New V-4B scope 1 kHz 10% THD+N

 

FIG.16 New V-4B distortion products 1 kHz 10% THD+N

 

FIG.17 New V-4B scope 1 kHz 15% THD+N

 

FIG.18 New V-4B distortion products 1 kHz 15% THD+N

Referring to Figs. 19-26, sample distortion characteristics are provided for the old V-4B. Fig. 19 shows a 1kHz wave with 1 % THD+N and Fig. 20 shows the corresponding distortion products. Note that odd-order harmonics do not consistently dominate, compared to the same plot for the new V-4B. For instance, the 3rd harmonic edges out the 2nd harmonic. However, the 4th harmonic is stronger than the 5th harmonic, etc. Fig. 21 shows that at 5% THD+N, the wave looks more triangular, with signs of hard clipping on the peaks. Referring to Fig. 22, the result is a shift in balance to a clear emphasis on odd-order harmonics relative to corresponding neighboring even harmonics. Referring to Fig. 23, the THD+N was pushed to 10%. Note the lack of perpendicular bisector symmetry, as well as the distortion in the crossover region (see the area about -5dB). Fig. 24 shows the odd-order harmonics dominate the neighboring even-order harmonic up to about the 6th harmonic. The 6th harmonic is about the same as the 7th harmonic. Thereafter, the even harmonics dominate the neighboring odd-order harmonic. Referring to Fig. 25, the signal is shown at 15% THD+N. Note the clear signs of hard clipping (e.g., clipped rails, overshoot on the positive-going transition of each peak, etc.). Referring to Fig. 26, note that the harmonic levels appear much more consistent across even-order harmonics and odd-order harmonics.

FIG.19 Old V-4B scope 1 kHz 1% THD+N

 

FIG.20 Old V-4B distortion products 1 kHz 1% THD+N

 

FIG.21 Old V-4B scope 1 kHz 5% THD+N

 

FIG.22 Old V-4B distortion products 1 kHz 5% THD+N

 

FIG.23 Old V-4B scope 1 kHz 10% THD+N

 

FIG.24 Old V-4B distortion products 1 kHz 10% THD+N

 

FIG.25 Old V-4B scope 1 kHz 15% THD+N

 

FIG.26 Old V-4B distortion products 1 kHz 15% THD+N

To get a better sense of the distortion range of the new V-4B, the gain was adjusted to produce 100w of power, and the results are illustrated in Figs. 27-29. Referring to Fig. 27, the power was first adjusted in the new V-4B by setting the Master to full on and adjusting the Gain. This represents the “cleanest” 100w that the new V-4B generated. Referring to Fig. 28, the Master was turned to noon. To obtain 100w, the Gain was turned up to compensate. Note that the new V-4B’s curves are rounder, with slightly flatted peaks, showing more compression compared to Fig. 27. Referring to Fig. 29, the Gain on the new V-4B was turned fully on and the Master was adjusted to yield 100w. Note that the new V-4B trace is showing signs of hard clipping at the peaks. In this manner, the clipping is significantly more intense than the clipping on the old V-4B.

FIG.27 Scope 100 W both amps version 1

 

FIG.28 Scope 100 W both amps version 2

FIG.29 Scope 100 W both amps version 3

Distortion Winner: New V-4B

Here, the old V-4B provided an extremely consistent and definitive transition from clean to overdrive. In this regard, our testing saw the onset of clipping with as little as 2.5% THD+N. Once this transition was breached, the distortion increases predictably as the signal increases. However, there were also signs of crossover distortion or some other artifact that is undesirable distortion.

Comparatively, the new V-4B offered more natural tube compression, thus extending the levels of measurable distortion before hard clipping took place. Moreover, having separate gain and master volumes, as well as having two different inputs with different impedance and attenuation characteristics, allowed the customization of a broad range of distortion characteristics. The new V-4B takes more time and effort to dial in, but is overall more versatile, compared to the old V-4B.

Power

Once this calibration was set, our normal power and dynamic test algorithms were run, testing maximum output and maximum dynamic power of each amp simultaneously. In our first test, we ran each amp to 8% THD+N.

Maximum:

New V-4B: 112w; 8% THD+N filtered 20Hz-20kHz; 827 mVrms 1kHz sin Input; 4-ohm load.

Old V-4B: 123w; 8% THD+N filtered 20Hz-20kHz; 803 mVrms 1kHz sin Input; 4-ohm load.

Dynamic:

New V-4B: 113w; 8% THD+N filtered 20Hz-20kHz; 1kHz CEA 2006; 781 mVrms Input

Old V-4B: 136w; 8% THD+N filtered 20Hz-20kHz; 1kHz CEA 2006; 747 mVrms Input

Power Winner: Old V-4B

Referring to Fig. 30, the new V-4B is generally cleaner for a given input at relatively low output levels. For instance, for measured levels under 10 Vrms, the new V-4B measures lower overall THD+N compared to the old V-4B. However, the new V-4B begins a steep and linear rise in distortion levels (e.g., starting at about 6.5 Vrms in this example). This linear rise continues to distortion levels well over 20% THD+N.

Comparatively, the old V-4B has two transitions into distortion. Note the first transition from about 4 Vrms to just under 20 Vrms, where we see a knee at about 2.5% THD+N. After that point, the distortion level rises more steeply. Note for signals over 20 Vrms (over 100w into a 4-ohm load), the distortion is significantly less than the new V-4B. This is due to the natural compression that leads to an almost limiting type of effect in the new V-4B. Incidentally, if we measure the maximum output of the old V-4B at its knee at 2.5% THD+N, we measured 109w; 2.5% THD+N filtered 20Hz-20kHz; 798 mVrms 1kHz sin Input; 4-ohm load.

In this regard, if we do not try to match target THD+N, but rather rate each amp based upon it’s own distortion characteristics, the output of the new and old V-4B are closely matched. Forcing both amps to the same target distortion level though, favors the old V-4B, albeit at a cost of different distortion characteristics.

Conclusion

By a narrow margin, the overall winner is the new V-4B. The size and weight, alone, are a big deal these days. However, the more flexible EQ, thanks to the different Ultra Lo curve, DI, and more common tube compliment, make the new V-4B a more usable and serviceable amp. Also, sacrificing the second channel of the old V-4B allowed the use of two different input jacks, a gain and a master volume, which allows gain characteristics that simply cannot be recreated with the old V-4B. Honestly, at the end of the day, I would not hesitate to perform with eith