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Hafler DH-200
100 WPC MOSFET Stereo Amplifier
Made in USA (1979-1982)
© 2014 KenRockwell.com. All rights reserved.

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Hafler DH-200

Hafler DH-200 (rated 100 watts per channel into 8Ω, 26 lbs./11.8 kg, measured 75 watts idle power draw, about $125 used). enlarge. I got this mine at this link directly to them at eBay (see How to Win at eBay).

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Hafler DH-200, rear

Rear, Hafler DH-200. enlarge.


August 2014   Hafler reviews    audio reviews    all reviews


Introduction         top

Adorama pays top dollar for your used gear.

B&H Photo - Video - Pro Audio

Intro   Specifications   Measurements   Compared

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The Hafler DH-200 is a 100 watts-per-channel MOSFET class AB stereo power amplifier. MOSFETs are solid-state devices that work on principals more similar to vacuum tubes than bipolar transistors — and it sounds great!

35 years ago when the DH-200 was introduced, it astounded the world in having performance so high that it exceeded the abilities of most laboratory equipment of its day. It was also reasonably priced, making this Hafler amplifier astounding both for its incredible performance and unheard of price.

Today I have the modern laboratory equipment to allow me to test exactly how good is this 35-year old sample, which I purchased in 1988. I also have an even older one that I built from a kit after getting it from Santa Claus for Christmas in 1981. Both have served me well for all these decades.

Like most made-in-USA audio gear, it easily outperforms its rated specification. This 30-year-old sample easily put out 116 WPC continuous and 164 W burst power into 8Ω.

The DH-200 was sold as a kit or fully assembled. The kits came with the two amplifier modules completely assembled and tested; kit assembly was assembling the case then wiring the power supplies, switches and connectors together.

Assembled versions came with a full 1-year warranty, and the kits came with a 1-year warranty on parts. In reality, I built a DH-200 from a kit in 1981, and about 15 years later I had a small problem and phoned Hafler. They recognized the problem and sent me two new transistors, free of charge. That fixed it and it's run perfectly ever since.

The amplifier tested here was purchased used in 1986 in Thousand Oaks, and I'm testing it today in 2014. It still easily exceeds its specifications nearly 30 years later, and I doubt it's ever been serviced.

This amplifier is from the very pinnacle of home High Fidelity. Products got better and better ever since home amplifiers were invented in the 1920s, but video took over home entertainment by the late 1980s, and home Hi-Fi equipment never evolved past this stage. Newer Hafler amplifiers, and the home audio market in general, has been neglected for lack of interest ever since the VCR became affordable to everyone in the late 1980s. There are newer amplifiers, but few are better than this Hafler DH-200.

David Hafler was one of the founders of Dynaco in 1954, and started the Hafler company in 1977.


Circuit Design

It's a traditional class AB linear power amplifier in a sheet metal steel case.

It has a traditional unregulated linear power supply with a big power transformer in the middle of the case, a bridge rectifier and two 10,000 µF 75V capacitors on which I measure ±55 VDC.

The "loose" regulation of the power supply gives it much greater burst power than continuous (perfect for music), and also means that power output doesn't completely double as speaker impedance halves.

It has eight power MOSFETs (4 per channel) in TO-3 packages mounted to two big anodized aluminum heat sinks on opposite sides of the case.

There's a neon pilot light in the power switch as well as a yellow overtemperatgure light on the front.

The DH-200 has one 5 ampere 3AG slow-blow power-input fuse, and 5A 3AG fast-blow fuses on the B+ and B- rails of each of the two power amp modules.

It has speaker fuses to protect your speakers from you doing something stupid. Most amplifiers don't have speaker fuses. Unique to the DH-200, the speaker fuses are inside the feedback loop to maintain high damping factor and null any sonic degradation form the fuses.


Specifications         top

Intro   Specifications   Measurements   Compared

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Output Power


Less than 0.02% THD at any power level up to 100 watts per channel, both channels driven continuously, from 20-20,000 Hz.


Audio Input

One stereo pair of 1/4" RCA jacks with individual potentiometers.

22 kΩ.

1.5 V RMS input for 100 watts into 8Ω.


Audio Output Connectors

Standard 5-way binding posts on standard 3/4" centers.

Total four pairs or 8 posts.


SMPTE Intermodulation Distortion

< 0.005% from 1 - 100 watts into 8Ω.


THD at 100 WPC into 8Ω (typical)

1 kHz: 0.0015%

10 kHz: 0.005%

20 kHz: 0.012%


Frequency Response into 8Ω

10 - 40,000 Hz at 100 watts ±0.5 dB.

1 - 100,000 Hz at -3 dB at 1 watt.


Crosstalk (typical)

66 dB at 20 Hz.

66 dB at 1 kHz.

60 dB at 20 kHz.


Signal to Noise Ratio

>100 dB unweighted, referred to 100 watts.


Damping Factor

150 at up to 1 kHz into 8Ω.

50 at up to 10 kHz into 8Ω.


Rise Time

2.5 µS from 10% to 90% with a 60 V p-p 10 kHz square wave.


Slew Rate

30 V/µS with a 60 V p-p 10 kHz square wave.



8 power MOSFETs: two pairs of complementary Hitachi 2SK134 and 2SJ49 lateral MOSFETs per channel.

Each of these power MOSFETs was individually tested, graded and sorted by Hafler. Each was stamped with a number from one to five and assembled accordingly into amplifier modules.

26 transistors.

24 diodes.

4 Zener diodes.

1 bridge rectifier.


Power Input

120 VAC, 60 Hz (US version).

Rated 370 VA maximum, marked 600 W maximum.

Actual power consumption is much less.



Made in the United States of America (Pennsauken, New Jersey).



Corrugated cardboard box.

Amplifier supported by cleverly multiple-folded inner corrugated cardboard insert.



5-1/8 x 16 x 10-1/2 inches, HWD.



26 pounds (11.8 kg).

30 pounds (13.6 kg) shipping weight.


Price, USA

1979: $299.95 assembled (DH-200A), $199.95 as a kit (DH-200K). ($1,000 or $650 considering inflation in 2014.)

1980: DH-200A $429.95, DH-200K $329.95. ($1,125 or $875 considering inflation in 2014.)

1981: DH-200A $429.95, DH-200K $329.95.

2014: about $125 used.


Measurements         top

Intro   Specifications   Measurements   Compared

Usage   Recommendations   More

Gain   Input Levels   Channel Balance   Power Output

Damping Factors   Noise   SNR   DC Offset

Frequency Response   Square Waves   THD    DFD

Actual Power Consumption   4Ω Operation


These measurements were made with a $50,000 Rohde & Schwarz UPL laboratory analyzer. The traces from the Rohde & Schwarz UPL laboratory analyzer are color coded for the Left Channel and for the Right Channel. When they don't lie on top of each other, it's due to channel imbalance. When they do lie on top of each other, the trace turns blue.

Unless otherwise specified, all measurements are RMS at 1 watt continuous output per channel at 1 kHz with an 8 Ω load, both channels driven with 120 VAC 60 Hz supply.

Made on paddle-switch sample bought in 1986.


Gain     measurements        top

25.511 dB left, 25.412 dB right.


Input Levels     measurements        top


Stereo 8Ω

150 mV for 1 W output.

480 mV for 10 W output.

1.51 V for 100 W output.

1.665 V for 120 W output at 0.1% THD.

2.0 V for 164 W output in 10mS bursts at clipping.


Stereo 4Ω

107 mV for 1 W output into 4Ω.

1.07 V for 100 W output into 4Ω (5A fuse limit).

1.41 V for 175 W output into 4Ω (beyond 5A speaker fuse limit; at 6.6A, a 5A AGC fuse ought to last about 15 seconds before blowing).

1.91 V for 290 W RMS in 10mS bursts at clipping into 4Ω at 1 burst per second.


Channel Balance     measurements        top

The left channel has 0.0986 dB more gain than the right.


Power Output     measurements        top

All are continuous RMS measurements at 0.1% THD at 1 kHz into 8Ω with a 120 VAC supply unless otherwise noted:


116 watts per channel into 8Ω, both channels driven continuously at 1 kHz at 0.1% THD.


Burst Power

164 W into 8Ω at clipping in 10ms bursts of 1 kHz at one burst per second.


175 watts per channel into 4Ω, both channels driven continuously at 1 kHz at 0.1% THD (note: 5A speaker fuse will blow in about 15 seconds at 175 W into 4Ω).


Burst Power

290 W into 4Ω at clipping in 10ms bursts of 1 kHz at one burst per second.


Damping Factors     measurements        top

Output Source Impedance
4Ω Damping Factor
8Ω Damping Factor
50 Hz
24.6 mΩ
1 kHz
23.1 mΩ
20 kHz
69.4 mΩ


Output Noise    measurements        top

Hafler DH-200 output noise

DH-200 noise spectral analysis.


A Weighted
-84.2 dBV A
-75 dBV
-74.9 dBV A
-66.6 dBV


Signal to Noise Ratio (SNR)     measurements        top

88.6 dB A-weighted SNR (14.4 effective bits) referred to 1 watt into 8Ω (2.83 V or +9.031 dBV).

108.6 dB A-weighted SNR (17.7 effective bits) referred to 100 watts into 8Ω (28.3 V or +29.031 dBV).

109.4 dB A-weighted SNR (17.9 effective bits) referred to 120 watts into 8Ω (31.0 V or +29.82 dBV).


Output DC Offset     measurements        top

-0.85 mV left, -26.4 mV right.


Frequency Response     measurements        top

Hafler DH-200 frequency response

DH-200 frequency response into 8Ω.


Hafler DH-200 frequency response

DH-200 frequency response into 8Ω, expanded scale.


Hafler DH-200 frequency response

DH-200 frequency response into 8Ω, greatly expanded scale.

The two curves are separate due to an 0.1 dB channel imbalance.

Here's a closer look at the infrasonic response. I increased the value of the input coupling capacitor in one of my samples of DH-200; I forget which one. This one is -3 dB at 0.9 Hz and drops at about 12 dB/octave:

Hafler DH-200 infrasonic frequency response

DH-200 infrasonic frequency response into 8Ω, 1 - 20,000 Hz.


Let's look out to 110 kHz:

Hafler DH-200 ultrasonic frequency response

DH-200 ultrasonic frequency response into 8Ω, 10 - 110,000 Hz.

Not bad; -1 dB at 75 kHz.

This is driving an 8Ω resistor, which doesn't count in the real world. Let's see what it does driving a real loudspeaker:

Hafler DH-200 frequency response driving a B&W 805 loudspeaker

DH-200 driving an 8Ω resistor and driving a B&W Matrix 805 loudspeaker (yellow).

Marvelous, there's only a ±0.1 dB variation. The only reason there seems to be an 0.1 dB overall difference is due to channel imbalance, not the different loads.


Square Waves     measurements        top

Hafler DH-200

50 Hz square wave. (HP 209A, Tek TDS3052, Tek P6139A.)


Hafler DH-200

1 kHz square wave. (HP 209A, Tek TDS3052, Tek P6139A.)


Hafler DH-200

10 kHz square wave. (HP 209A, Tek TDS3052, Tek P6139A.)


Hafler DH-200

50 Hz square wave driving a B&W Matrix 805 loudspeaker. (HP 209A, Tek TDS3052, Tek P6139A.)


Hafler DH-200

1 kHz square wave driving a B&W Matrix 805 loudspeaker. (HP 209A, Tek TDS3052, Tek P6139A.)


THD: 0.001% (-100 dB)     measurements        top

All these THD measurements are measuring pure distortion components only (THD only), not noise and distortion (THD+N). THD+N numbers would be worse than THD alone shown here.


Harmonic Distortion Components at 500 microwatts

Hafler DH-200 THD

DH-200 harmonic distortion content at 500 µW.

Perfect! even at nearly zero output (one-half of one one-thousandth of a watt), there's only 0.004% THD.


Harmonic Distortion Components at 10 milliwatts

Hafler DH-200 THD

DH-200 harmonic distortion content at 10 mW.

At 10 milliwatts, where much of the inner detail of music lies, distortion is vanishing at only 0.001%. You can't get that from crappy class-D amplifiers!


Harmonic Distortion Components at 1 watt

Hafler DH-200 THD

DH-200 harmonic distortion content, 1 kHz at 1 watt, 8Ω load.

Magnificent, and the distortion is mostly musical second harmonic distortion, just like tube amplifiers, but an order of magnitude or two less!


Harmonic Distortion Components at 100 watts

Hafler DH-200 THD

DH-200 harmonic distortion content at 100 W.

Nearly no distortion at full power.

The right channel has extra second harmonic distortion in the range of about 10 W as you'll see next; probably from wire routing errors.


THD versus Power into 8 Ω

Hafler DH-200 THD vs. power

DH-200 THD versus power output at 1 kHz, 8Ω load.

Curious about the greater distortion in the right channel between 1 W and 100W, i looked into it and it's all second harmonic distortion, which might go away with careful rerouting of the internal wiring. I didn't build this one, and Hafler cautions to follow the instructions exactly otherwise audio wires routed incorrectly near power supply wires will lead to extra distortion at higher power levels.


THD versus Frequency into 8 Ω

Hafler DH-200 THD

DH-200 THD versus frequency at 1 watt, 8Ω load.


Hafler DH-200 THD

DH-200 THD versus frequency at 10 watts, 8Ω load.


19+20 kHz Difference-Frequency Distortion (DFD)

per DIN IEC 268-3 or 118:

DH-200 DFD

DFD at 1 W RMS total output.

The 1 kHz component is in the noise, excellent.


DH-200 DFD

DFD at 10 W RMS total output.

The 1 kHz component is around -105 dB, which is superb.

The close-in 18 kHz and 21 kHz skirts are at -100 dB, which are also swell.


DH-200 DFD

DFD at 50 W RMS total output.

The 1 kHz component is at about -101 dB, which is excellent.

The close-in 18 kHz and 21 kHz skirts are at -90 dB, which are also swell at this high power level.


Actual Power Consumption     measurements        top

The DH-200 runs moderately warm. It's always comfortable to touch and never gets hot if well ventilated.

Power Consumption
Power off
Idle, warm
75 W (0.86 A)
83 W (0.96 A)
10 WPC
148 W (1.67 A)
100 WPC
388 W (4.1A)


4Ω Operation    measurements        top


DH-200 DFD

Frequency response driving 4Ω.

We have 0.2 dB loss at 20 kc versus 0.1 dB at 8Ω. No big deal, obviously the output source impedance rises a little at 20 kc.


DH-200 DFD

THD driving 4Ω at 1 watt.


DH-200 DFD

THD driving 4Ω at 10 watts.


Compared         top

Intro   Specifications   Measurements   Compared

Usage   Recommendations   More

Compared to most (bipolar) transistor amplifiers, this MOSFET amp draws more power and runs hotter at idle. Think of it as a larger class-A area, and that the FETs are operating under similar principles to vacuum tubes — but with much higher performance.

The DH-200 of 1979 is David Hafler's first amplifier under his own company.

Next came the DH-220 (110 WPC) of 1982. The DH-220 was a slightly more powerful version of the DH-200 of 1979 (100 WPC). The DH-500 was the beastly 255 WPC version that came next.

The DH-120 of 1984 was a smaller version of the DH-220.

The DH-220 and DH-120 have rounded heat sink fins which are much more comfortable for carrying compared to the sharp, square fins if this DH-200. All perform excellently

All these amplifiers are 100% Made-in-USA and were sold both as kits or fully assembled.

I'm amused that even at 30 years old it easily outperforms modern state-of-the-art class D amplifiers like the Musical Fidelity M1PWR.

This 30-year-old DH-200 has more power output, much less noise, much less distortion, flatter frequency response, higher damping factors and better sound than a brand-new M1PWR. The only advantage to the M1PWR is that it draws less power at idle, but the M1PWR draws much more power when turned off. The DH-200 draws no power at all when off.

The ADCOM GFA-545 and GFA-545 II are very similar to the DH-200, with similar prices, audio performance, size, weight, appearance and power output. The ADCOMs are a little newer and add some very dim clipping indicators, while these Haflers offer integrated speaker fuses and sturdier construction. I don't find the clipping indicators as useful as integrated speaker fuses, so I prefer these Haflers.


Usage         top

Intro   Specifications   Measurements   Compared

Usage   Recommendations   More

There's a neon pilot light in the power switch.

It comes with 2-ampere speaker fuses. This is about right for most speakers. Use a maximum of 5 ampere fuses for lab testing. On my desktop, I use 1 ampere fuses to protect my ears as well as speakers if I do something stupid!


Recommendations         top

Intro   Specifications   Measurements   Compared

Usage   Recommendations   More

The DH-200 is a great amplifier.

I've been using mine for over 35 years to drive everything to my Quad ESL, ESL-63 and B&W 801. For about $125 used today (see How to Win at eBay), it is far superior to most new amplifiers costing far more.


More Information         top

Intro   Specifications   Measurements   Compared

Usage   Recommendations   More

Hafler DH-200 Manual.


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(1981 rocker switch sample)

80W idle warm power consumption.

All measured driving an 8 Ω load at 1 Watt at 1 kHz unless otherwise stated.

All fed from the 5 Ω source impedance and measured with an R&S UPL laboratory audio analyzer unless otherwise stated.


Maximum Output Power at 1 kHz into 8 Ω load

126W at 120.3 V AC power input at 0.1% THD (1.66V RMS input).

135W at 120.6 V AC power input at 1% THD (1.738V RMS input).


10 mS burst of 1 kHz (10 cycles) at 1 per second: 50V Pk = 35.3V RMS = 156W Pk at 122.1V AC power input. Burst Input level: 1.85 V RMS.


Gain: 25.6 dB (19.07x)

Measured at 1 kHz, 1 Watt output into an 8 Ω load:

25.450 dB
25.763 dB

This calculates out to 19.07x gain.

148 mV in is 1W out into 8 Ω.

1.48 V is 100 W out into 8 Ω.


Frequency Response: +0, -0.1 dB

1 Watt output into an 8 Ω load:

Hafler DH-200

Hafler DH-200 Frequency response, ±1 dB scale.

Note about 0.3 dB channel imbalance, otherwise, easily within +0, -0.1 dB from 10 Hz - 20 kHz.


Hafler DH-200

Hafler DH-200 Infrasonic response, 0.1 Hz - 100 Hz.

-3 dB point: 0.53 Hz.


Hafler DH-200

Hafler DH-200 frequency response to 110 kHz.

-1 dB at 70 kHz.

-3 dB point in excess of 110 kHz, probably around 180 kHz.


DC offset: < 50mV

+29 mV
+48 mV


Noise: -83 dBV A

Hafler DH-200

Hafler DH-200 Output noise spectrum.

As fed from a 5 Ω source impedance, the Hafler DH-200 has more noise than an ADCOM GFA-545 II, but I've still never heard it, even with my head held to a loudspeaker.


A-weighted noise:

Input fed from 5 Ω source impedance
-81.2 dBV
-84.9 dBV
No input connection
-73.8 dBV
-77.6 dBV


Unweighted noise:

Input fed from 5 Ω source impedance
-77.8 dBV
-68.7 dBV
No input connection
-76.0 dBV
-57.9 dBV


Distortion: 0.0005% THD


Hafler DH-200

THD versus frequency, Hafler DH-200.


Hafler DH-200

THD versus power level, Hafler DH-200.

Note extended scale to 0.0003% THD.


Hafler DH-200

THD at maximum output levels: Hafler DH-200.



Hafler DH-200

SMPTE IMD, Hafler DH-200.


19+20 kHz DFD

Hafler DH-200

DFD at 1 Watt RMS, Hafler DH-200.

Difference-frequency distortion is extremely low at -104 dB, while a typical amp is at -90 dB.


Hafler DH-200

DFD at 50 Watts RMS, Hafler DH-200.

Exceptionally good performance at -100 dB. A typical amp might be around -95 dB here.


Driving a pair of B&W Matrix 805

Frequency Response

Hafler DH-200

Hafler DH-200 driving a pair of B&W Matrix 805 at 100 milliWatts.

Extremely enlarged vertical scale.



Hafler DH-200

Hafler DH-200 driving a pair of B&W Matrix 805 at 100 milliWatts.

Distortion at low power seems to rise from levels seen at 1 Watt above driving a resistive load, however these readings are a result of the amplifier's noise at a lower power level.

My ears prefer not to tolerate driving the B&W Matrix 805 at 1 watt with sine waves in the lab; even at 100 milliWatts its louder than I'd prefer.


Damping Factors and Output Impedances

Output Impedances

50 Hz
59 mΩ
29 mΩ
1 kHz
61 mΩ
29 mΩ
10 kHz
98 mΩ
46 mΩ
20 kHz
160 mΩ
85 mΩ


Damping Factors at 8Ω

50 Hz
1 kHz
10 kHz
20 kHz


Method and raw data

Voltage drop when applying an 8 Ω load:

50 Hz
-0.0635 dB
-0.0310 dB
1 kHz
-0.0665 dB
-0.0319 dB
10 kHz
-0.1061 dB
-0.0503 dB
20 kHz
-0.1718 dB
-0.0920 dB

R source = (R load/attenuation ratio) - R load.


August 2014