Home  Donate  New  Search  Gallery  Reviews  How-To  Books  Links  Workshops  About  Contact

Quad 34 Preamplifier
Made in England (1982-1996)
© 2011 KenRockwell.com. All rights reserved.

Intro   Specifications   Measurements   Usage   Recommendations

Please help KenRockwell..com

Quad 34 Preamplifier

The Quad 34 Preamplifier. enlarge.

 

Quad 34 Preamplifier

Rear, Quad 34 Preamplifier. (about $350 used). enlarge. This free website's biggest source of support is when you use these links, especially this link directly to the Quad 34 Preamplifier at eBay (see How to Win at eBay), when you get anything, regardless of the country in which you live. Thanks! Ken.

September 2011   Audio Reviews   All Reviews

 

Good:

Optimized for astoundingly accurate symphonic music reproduction in concert with the very finest loudspeakers, the Quad 34's exceptional TILT control allows the listener to choose his own seat in the hall. The unique TILT control also allows one to compensate precisely for overly bright or dull recordings. Want a little more warmth, or a little more detail? The TILT control delivers this without colouring the sound.

The stereo volume control tracks within an astounding tenth of a dB, ensuring that the stereo image never shifts as the volume is changed.

The BASS LIFT control does the best job I've ever heard at low-level loudness compensation in 40 years. It also compensates well for smaller loudspeakers, acting as an electronic subwoofer, boosting only the very lowest bass without altering the mid- and upper-bass. The BASS STEP control removes bass boom or bloat caused by placing loudspeakers too close to the wall in a small home. The smooth HF filters eliminate high-frequency zing or distortion.

Very compact, and therefore ideal for today's desktop audio use.

 

Bad:

For use in the USA, it may require a licensed technician to alter it for use on 120 VAC.

The output levels are optimized for Quad's own power amplifiers, like the matched Quad 306. For use with ordinary American power amplifiers, it will require a licensed technician to alter it for use with larger audio output voltage levels. Be sure to see my warnings under Usage.

 

Introduction         top

Intro   Specifications   Measurements   Usage   Recommendations

Ritz Camera

I use Adorama, Amazon, eBay, Ritz, Calumet, J&R and ScanCafe. I can't vouch for ads below.

This popular (at least in the UK) and compact (only 12½" or 32cm wide) Quad 34 preamp is optimized for the enjoyment of symphonic music through the world's finest loudspeakers, namely the QUAD ESL-63 electrostatic in its day, or today, Harbeth.

The Quad 34 preamp excels in having the world's most useful tone controls which allow a listener to choose his favourite seat in the hall, regardless of where the recording's producer thought he should sit.

The Quad 34's most astounding innovation is its TILT control. The TILT control is an eight-pole filter which allows subtle optimization of the relative brightness or warmth of the music's original performance space to your listening room, without adding any colouration. Unlike conventional tone controls, its effects are very subtle — and therefore very powerful.

Selecting inputs and filters is easy: just tap the electronic buttons on the left. The signals are switched electronically, with no relays or distortion-inducing mechanical switches needed.

Of course all music sounds great through this preamp; when I mention symphonic music that's because live acoustic performances are the most difficult to reproduce, and it is for these performances that the Quad 34 is designed.

 

Perspective         top

This Quad 34 replaced the earlier Quad 33 in 1982.

The first versions of this Quad 34 had an AUX input and had 5-pin DIN connectors for most inputs and outputs.

The newest versions of this Quad 34, as seen here, used RCA connectors and relabeled the AUX input as CD.

Most Quad 34 came with an extra interchangeable moving-coil (MC) DISC input module. Different modules allowed for different pickup loading.

About 40,000 were sold across 14 years. It was gone from catalogues by late 1996.

 

Sound         top

The TILT control is this preamp's claim to fame. Serious music lovers are at the symphony every week, unless they're performing and rehearsing daily, and know that there is no such thing as one unique "sound of a live performance."

These musical people are intimately and regularly familiar with actual live performances, and know that every seat sounds different. Some listeners prefer the front rows, others the middle rows, while others prefer the rear of the hall. Every seat presents a different perspective. The TILT control allows one to optimize the reproduced perspective to suit one's taste if the recording's producers and engineers had a different opinion.

For instance, while London and Decca's UK recordings tend to be neutral, Deutsche Grammophon's tended to be forward, and USA's Telarc tend to be more distant. With the TILT control, you can put yourself where you want to be.

The TILT control also allows subtle correction of other equipment, cables, connectors, power cords, Shatki stones, recordings, speakers and acoustics that are slightly too bright or analytical, or that are too dull and reserved.

The TILT control really works. No, its action is not as obvious as old-fashioned bass and treble controls, and therein lies its power. It corrects subtle variations in perspective, equipment, cabling or anything in the signal chain and can restore perfect balance to reproduced music. Remember, Quad make the world's finest loudspeaker, the ESLs, and this preamplifier is designed to extract the most musical enjoyment out of them for serious music listeners, even if audio hobbyists are chasing other things.

As Quad says, "The results obtained from any programme source depend on the aggregate effect of the listening room and the recording environment together with the corrections applied by the recording engineer, and the equipment of the reproducing chain."

The real kicker is where Quad adds "…it is extremely unlikely that the arbitrary combination of these variables when listening at home will will yield the closest approach to the original sound," and therein lies the need for this subtle control.

The TILT control can improve the subjective quality of musical reproduction, while adding no colouration, just a simply slight increase or decrease in overall warmth or brightness.

Likewise, the BASS LIFT control is brilliant. It really makes a world of difference with small speakers, boosting only the missing low bass like an electronic subwoofer, and adding back in low bass missing at low playback levels.

The BASS STEP control drops low bass response by precisely 5.5 dB to correct for boomy rooms or bloated recordings. The 100 Hz, 170 Hz and 300 Hz positions merely change the transition frequency, not the ultimate reduction.

The smooth-rolloff HF filters eliminate high-frequency zing, tizz or distortion. Unlike most high filters, these are brilliantly slow in rolloff so that they don't add honk or artifacts related to a sharp cutoff.

As critical as any or all of the above is a volume control which keeps the channels precisely balanced at every level. The Quad 34 is extraordinary as having the most tightly-specified tracking of any preamp at 0.5 dB, and it exceeds this by a factor of about five. Most preamps are so sloppy that they deliberately don't specify channel tracking. At low levels, most preamps are fifty times worse than this Quad 34.

The inputs switch instantly, so if they are active with signal, there can be very mild clicks.

The Quad 34 is non-inverting, meaning that the polarity of your source is never changed.

 

Aesthetics         top

Quad 34 Preamplifier

The Quad 34 Preamplifier. enlarge.

It's painted in two tones of semi-metallic brown that looks much better in person than it does in my illustrations.

It looks great paired with wood, and of course we all have our own preferences. I love its simple, pure, and to-the-point design.

 

Ergonomics         top

It feels great: a light tap is all it takes to select an input or filter.

The input LEDs are your pilot light. They make it easy to see how it's set from a distance.

The tone and volume controls are double-premium Alps precision stepped attenuators. They feel perfect. The volume control knob is the perfect diameter and depth, and the pot has just the right detents and damping. By comparison, the Apt Holman Preamp's volume control pot and knob has too much damping and is too thin.

Just like professional mastering equipment, every setting (except Balance) is detented and numbered for easy logging and recall.

Be careful not to bang the BASS and TILT control knobs; the shafts are thin for aesthetics.

The volume control tracks incredibly well, however with only 21 steps and 57 dB of maximum attenuation, lacks the lower-level positions of other preamps like the Apt Holman Preamp, with its 31 steps and 66 dB range.

Just like 1940s broadcast console knobs, I feel that the engraved index on the volume control ought to be filled with white paint.

The little Balance control lever is weird and a little hard to move precisely, but it does its job. Aesthetically, it vanishes, as befits a rarely used control.

There is no headphone jack because music reproduction of the quality which is expected by the Quad user isn't available thorough ordinary 1/4" or 3.5mm-plug dynamic headphones. It is expected that this preamp will be used only with electrostatic headphones, like the Stax, which are fed from their own dedicated power amplifiers connected to the OUTPUT or unmarked spare TAPE REC outputs.

There's no need for a MUTE control; when the volume is set to zero, the output is completely muted at 98 dB below maximum gain.

 

Mechanical         top

The case is heavy-gauge sheet metal, with felt pads on the inside top and bottom to dampen vibration.

The preamplifier slides out of the case after removing two rear screws.

The knobs are all metal, except for the power button on the lower right, which is a plastic shaft that reaches back to the internal power switch.

The front plate is painted cast aluminum.

 

Electronics         top

The circuit boards are dual-layer with plated through-holes. ICs are soldered directly without sockets.

Amplification is with discrete transistors at low levels, and plenty of TL071 and TL072 FET op amps. These FET op amps have extremely high input impedances, just like tubes, and therefore allow realization of very precise active filters. These FET op amps help maintain a warm, tube-like sound compared to traditional bipolar-input op amps, for those who care.

Signal selection is via 4066 CMOS switches, with Motorola MC14066BCP and Philips ICs.

 

Gain Structure         top

The Volume Control is designed into the feedback loop of an operational amplifier so it varies the actual gain of that stage, with the appropriate benefits to noise and distortion.

The Quad 34 offers many weird gain options for inputs and outputs.

Sadly, the Quad 34 always runs the rest of its internal circuits at full gain, and reduces gains for inputs or outputs as needed with resistive pads, not by eliminating gain stages or reducing actual amplifier gain.

 

Electrical         top

The Quad 34 only consumes 2¾ Watts of power as measured, so it runs cool and ought to last a long time.

The amplifier supply rails only run +8.6 and -9.6 volts, not the more common ±15 V, so the active devices ought to last several lifetimes.

It has a switched power outlet on the back.

 

Rated Specifications         top

Intro   Specifications   Measurements   Usage   Recommendations

Schematic Diagram   Price

Since Quad redesigned the circuitry many times over the years, you'll see different rated specifications.

All voltages are RMS.

 

Inputs

Quad 34 preamp THD

Input Selector and Filters, Quad 34 Preamplifier. enlarge.

 

RADIO

Rated 100 mV, 5 V maximum. 100 kΩ load.

Not variable.

 

DISC (phono cartridge)

Usually rated 3 mV (150 mV maximum), 47 k Ω, 220 pF. Other values often programmable.

Moving coil module rated 100 µV (5 mV maximum), 100 Ω, 22 nF. Sometimes rated 200 µV (10 mV max.), 100 Ω, 22 nF, and variable.

 

CD (a.k.a. AUX on earlier models)

AUX rated 100 mV (5V Maximum), 100 k Ω.

CD usually rated 300 mV, variable with plug-in resistors.

 

TAPE REP

Marked REP under TAPE, for Tape Reproduce (professional parlance) or Tape Replay (hobby parlance).

Rated 300mV (15 V maximum), 120 k Ω. Often adjustable with plug-in resistors.

 

Gain, Polarity and Volume Control         top

Interchannel balance rated as ± 0.5 dB over the entire range of the volume control, the tightest specification I've ever seen. Most preamps aren't good enough even to list this specification.

Non-inverting.

 

Outputs         top

OUTPUT

The main output to the power amplifier is labeled OUTPUT.

Rated 0.5 V, 830 Ω source impedance.

The earliest samples were rated 1.5 V.

 

TAPE REC

The output to a tape recorder is marked REC under TAPE.

Rated 100 mV, 2.2 k Ω source impedance. Altered with plug-in resistors.

 

Frequency Response         top

RADIO, CD or TAPE at OUTPUT or TAPE REC: ± 0.3 dB.

DISC RIAA Frequency Response: ± 0.5 dB.

Frequency range was listed as 30 - 20,000 Hz, and then 20-20,000 Hz as of 1989.

 

Distortion         top

0.05%, worst-case, any input, 30-10,000 Hz.

First rated as an unqualified 0.005%.

 

Noise         top

-105 dB, A-weighted, Volume Control at minimum.

That sounds impressive, unless you realize that this is a meaningless specification!

Turning off the volume control means even the noisiest preamp ought to be quiet, and worse, the dB rating is made without any reference, making it a meaningless, undefined number. Whoops!

 

The signal-to-noise ratios were rated as follows, relative to rated inputs, with inputs loaded:

Input
A-weighted
RADIO
88 dB
DISC MM
75 dB
DISC MC
68-80 dB
AUX
88 dB
TAPE REP
87 dB

 

Power         top

50-60 Hz via standard IEC C14 (HP) power connector.

 

Mains Voltage

The mains voltage had been rated at 110-120V or 220-240V, and later as 200-240V or 100-127V.

Some units have a rear-panel switch, while newer ones require a licensed technician to resolder internal jumpers.

 

Power consumption

Rated: 4.5 to 7 Watts maximum depending on year.

Measured: 2.6-2.9 Watts depending on output level (average 2¾ Watts) for the sample tested here.

It consumes but 30 mA at 120V AC with a 76% power factor.

 

Fuse

The 240 V version uses a 5x20mm T63 mA fuse.

I'm guessing that the 120V version mostly likely uses a T100 mA fuse. Since this version seen here only draws 30mA after changing its jumpers to 120V operation, you're probably OK with the original 63 mA fuse for 240V operation.

 

Size         top

321 x 64 x 207 millimeters, WHD (including knobs, but excluding rear RCA connectors and bottom feet).

12.64 x 2.52 x 8.15 inches, WHD (including knobs, but excluding rear RCA connectors and bottom feet).

 

Weight         top

Rated 3.2 kg or 4 pounds, depending on where you read it.

 

Quality         top

Hand-made in Huntingdon, England.

 

Schematic Diagram         top

Quad 34 Preamplifier

The Quad 34 Preamplifier. enlarge.

 

Quad 34 Preamplifier

The Quad 34 Preamplifier. enlarge.

Quad 34 Schematic Diagram.

Quad 34 Service Manual.

Quad 34 Instruction Book (User's Guide).

QUAD 34 MK II Instruction Book.

 

Price         top

 
Catalog price*
(in period dollars)
1982
$1,450
$625
1983
$1,350
$595
1984
$1,300
$595
1985
$1,250
$595
1986
$1,225
$595
1987
$1,375
$695
1988
$1,525
$795
1989
$1,450
$799
1990
$1,375
$799
1991
$1,325
$795
1992
$1,450 w/o MC input
$849 w/o MC input
1993

$1,250, w/o MC input

$1,350 w/MC input

$795 w/o MC input

$870 w/MC input

1994
$1,150 w/MC input
$749 w/MC input
1995
$1,025
$695
     
2011

*corrected for inflation in 2011.

 

Measurements         top

Intro   Specifications   Measurements   Usage   Recommendations

Frequency Response   Maximum Input   Maximum Output   Distortion   

Gain & Balance   Noise   Crosstalk   Tone Controls   Filters   

Tape Outputs   Tape Loop (EPL)   Phono Preamp  Lifting the 1kΩ Shunt

 

A state-of-the-art Rohde &Schwarz UPL was employed for these laboratory measurements.

All voltages are RMS.

The traces are colour 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.

 

Frequency Response: ± 0.12 dB         top

Quad 34 frequency response

Frequency Response 20-20,000 Hz, Quad 34 Preamplifier.

It's flat to ± 0.12dB from 20 - 20,000 Hz.

 

Quad 34 frequency response

Infrasonic Frequency Response 0.1 - 20,000 Hz, Quad 34 Preamplifier.

- 1 dB at 8.5 Hz, -3 dB at 5.6 Hz.

It rolls off at about 12 dB per octave below about 6 Hz, perfect design.

I have a more detailed curve plotting 2-20 Hz under TAPE monitor.

 

Quad 34 frequency response

Ultrasonic Frequency Response 10 kHz - 110 kHz, Quad 34 Preamplifier.

Still flat at 30 kHz, it's intelligently designed to resist radio interference and prevent driving power amplifiers into slew-rate limiting by being 1 dB down at 40 kHz, 3 dB down at 52 kHz, 6 dB down at 68 kHz, 10 dB down at 85 kHz, 12 dB down at 95 kHz and 14 dB down at 110 kHz.

I'll cover the response of the Filters and Tone Controls below.

 

Maximum Input Levels      measurements    top

Maximum Input Levels for 0.1% THD at OUTPUT output

RADIO: 5.040 V.

DISC: 151.1 mV.

CD: > 10 V.

TAPE: > 10 V.

 

Maximum Input Levels for 0.1% THD at TAPE REC output.

The TAPE REC output hits 0.1% THD at 5.09 V. Here are the input levels which will drive this output to this level:

RADIO: 1.610 V.

DISC: 48 mV.

CD: 5.200 V.

 

Maximum Output Levels      measurements    top

Maximum Output Levels at 0.1% THD, 200 k Ω load

Op amp supply rails are +8.6 VDC and -9.6 VDC.

OUTPUT: 0.649 V (fed from a 15.4 dB internal pad: 2.7k+2.2k in series, 1k shunt).

OUTPUT: 2.626 V (lifting 1k Ω shunt resistors; raises output impedance to 5k Ω).

TAPE REC: 5.09 V.

 

Maximum Volume Control Settings    top

If sine waves are your thing, here are the maximum Volume Control settings that will not exceed 0.1% THD for the stated input signals. For reference, the maximum output of most CD players is 2V, and most iPods and iPads have a 1V maximum output.

RADIO input
Max Volume Control
(with 1k load lifted)
5.04 V
7
6
5 V
7
6
3 V
9
8
2 V
10
9
1V
13
11
500 mV
15
14
300 mV
17
16
200 mV
19
18
138.2 mV
21
100.0 mV at VC 21

 

CD or TAPE input
Max Volume Control
(with 1k load lifted)
10 V
9
7
2 V
14
13
1V
17
16
500 mV
20
19
447 mV
21

323.2 mV at VC 21

 

At 20.4 Hz with BASS at +3 dB (+12.27 dB additional gain at 20.4 Hz)

There is enough internal headroom to allow bass boost at the same maximum input levels as unboosted operation. Of course, the maximum output level is the same, so we cannot crank the Volume Control as far:

RADIO input
(with 1k load lifted)
5.26 V
3
5 V
3
3 V
4
2 V
4
1V
7
500 mV
9
300 mV
11
200 mV
12
100 mV
15

 

CD or TAPE input
(with 1k load lifted)
10 V
4
2 V
8
1V
11
500 mV
13
200 mV
17
100 mV
19

 

At 42Hz with maximum bass TILT and BASS at +9 dB (+16.97 dB additional gain)

Even at full boost, there is still enough internal headroom to allow the same maximum input levels as unboosted operation.

RADIO input
(with 1k load lifted)
5.16 V
2
5 V
2
3 V
3
2 V
3
1V
5
500 mV
7
300 mV
9
200 mV
10
100 mV
13

 

CD or TAPE input
(with 1k load lifted)
10 V
3
2 V
6
1V
9
500 mV
11
199 mV
15
100 mV
17

 

Distortion      measurements    top

THD vs. Frequency      measurements    top

Quad 34 preamp THD

THD, RADIO input at 200 mV and Volume Control at 15, Quad 34 Preamplifier.

 

Quad 34 preamp THD

THD, CD input at 200 mV and Volume Control at 19, Quad 34 Preamplifier.

 

THD vs. Level      measurements    top

Quad 34 preamp THD

THD vs. input level, RADIO input, Volume Control at 15, Quad 34 Preamplifier.

 

Quad 34 preamp THD

THD vs. input level, CD input, Volume Control at 19, Quad 34 Preamplifier.

 

Gain, Tracking and Balance      measurements    top

Maximum Gain    Attenuator   Channel Tracking   Balance Control

Quad 34 preamp THD

Volume Control at 12, Quad 34 Preamplifier. enlarge.

 

Maximum Gain         top

 
OUTPUT*
TAPE REC
OUTPUT
(1k Ω shunts lifted)
RADIO
13.49 dB
10.102, 10.082 dB
28.662 dB (37mV = 1V)
DISC
43.96 dB
40.55, 40.58 dB
59.13 dB (1.08mV = 1V)
CD
3.31 dB
-0.07, -0.125 dB
18.478 dB (119mV = 1V)
TAPE
3.29 dB
n/a
18.470 dB (119mV = 1V)

*Output is fed from a 15.4 dB internal pad: 2.7k+2.2k in series with 1k shunt.

 

The Attenuator: Gain & Volume Control         top

The most important thing a preamplifier does is amplify. The most critical part is the volume control, or attenuator, which can lead to distortion and channel imbalance.

These are measurements of the various steps of the attenuator (volume control).

As measured, the nominal step sizes are :

Volume Control Settings
Nominal step size
1-5
5 dB
5-16
2.5 dB
16-21
2 dB

These exact measurements are at 1 kHz as the average of both channels, and were measured with a precision of 0.001 dB. The highlighted numbers are the Volume Control step closest to unity gain.

Volume Control Setting
Relative attenuation
from maximum gain
Gain, RADIO input
Gain, CD or TAPE input
Gain, RADIO input (1k Ω load lifted)
Gain, CD or TAPE input (1k Ω load lifted)
21
0.00 dB
13.49 dB
3.29 dB
28.662 dB
18.478 dB
20
-1.825 dB
11.66 dB
1.47 dB
26.845 dB
16.653 dB
19
-3.89 dB
9.59 dB
-0.60 dB
24.777 dB
14.582 dB
18
-5.96 dB
7.52 dB
-2.67 dB
22.706 dB
12.51 dB
17
-8.20 dB
5.29 dB
-4.90 dB
20.469 dB
10.278 dB
16
-10.49 dB
3.00 dB
-7.20 dB
18.18 dB
7.99 dB
15
-12.72 dB
0.77 dB
-9.42 dB
15.95 dB
5.76 dB
14
-14.99 dB
-1.505 dB
-11.69 dB
13.68 dB
3.49 dB
13
-17.50 dB
-4.01 dB
-14.20 dB
11.17 dB
0.976 dB
12
-19.81 dB
-6.33 dB
-16.52 dB
8.85 dB
-1.33 dB
11
-22.28 dB
-8.79 dB
-18.98 dB
6.39 dB
-3.80 dB
10
-24.78 dB
-11.29 dB
-21.49 dB
3.89 dB
-6.30 dB
9
-27.16 dB
-13.67 dB
-23.86 dB
1.51 dB
-8.68 dB
8
-29.60 dB
-16.11 dB
-26.30 dB
-0.92 dB
-11.12 dB
7
-32.18 dB
-18.69 dB
-28.89 dB
-3.51 dB
-13.70 dB
6
-34.77 dB
-21.28 dB
-31.47 dB
-6.10 dB
-16.29 dB
5
-37.21 dB
-23.72 dB
-33.92 dB
-8.54 dB
-18.73 dB
4
-42.30 dB
-28.81 dB
-39.01 dB
-13.62 dB
-23.82 dB
3
-47.22 dB
-33.73 dB
-43.93 dB
-18.55 dB
-28.74 dB
2
-52.29 dB

-38.80 dB

-49.00 dB

-23.62 dB

-33.81 dB

1
-57.20 dB
-43.70 dB
-53.91 dB
-28.53 dB
-38.72 dB
0
-97.63 dB
-83.81 dB
-93.88 dB
-68.61 dB
-78.76 dB

At Volume Control 0, the attenuation is sufficient so that there is no audible output, eliminating the need for a MUTE button.

13.49 dB maximum gain is a linear amplification of 4.727x.

3.29 dB maximum gain is a linear amplification of 1.4605x.

28.662 dB maximum gain is a linear amplification of 27.108x.

18.478 dB maximum gain is a linear amplification of 8.3927x.

 

 

Tracking (Left-Right channel balance versus volume control setting)         top

Tracking

Right channel level versus left channel, vs. volume control setting. (positive means image moves to right. Volume Control 1 = -57 dB, Volume Control 23 = 0 dB. See Attenuator and Gain Structure for other Volume Control.)

The stereo image never varies as the volume is changed. Poorer amplifiers often skew the stereo image several dBs or more at the lowest volume settings, while the superb channel tracking of the Quad 34 Preamplifier keeps the channels balanced to within a tenth of a dB or better at almost every setting.

 

MONO Mode

When in MONO mode, the Quad 34 sums the channels after the balance and volume controls.

Therefore, in MONO mode, the balance is locked at 0.0025 dB more gain in the left channel regardless of the position of the other controls.

In MONO mode, the BALANCE control is used to mix or select which of the two input channels one would like to here; it no longer adjusts the relative levels of your speakers.

 

Balance Control      measurements    top

Quad 34 preamp THD

Balance Control at centre, Quad 34 Preamplifier. enlarge.

 

The balance control alters the gain of both channels. As one channel is attenuated, the other channel's gain will rise by up to 2 dB at either end of the control's adjustment range. For the first couple of dB of the control's range, the two channels' levels vary about equally in dB, for instance, at the first division, each channel varies up or down by about a dB.

The balance control is actually a linear potentiometer moved by means of a mechanical linkage to the front panel control lever. Don't force the lever or you could break the pot-metal internal cast levers. The balance control is not a rotary potentiometer concentric with the gain control as you'd expect.

Here is the level difference imparted by the balance control at various positions:

Position
Level difference between channels
BAL — (center)
± 0.0 dB (reference)
± 1 division
1.9 dB
± 2 divisions
3.6 dB
± 3 divisions
7.2 dB
ends of recessed area
10 to 20 dB
ends of travel
70 dB

 

Noise      measurements    top

Measured as fed from the muted output of the Rohde &Schwarz UPL, with its 5Ω unbalanced source impedance. The highlighted numbers are unity gain for each input:

Volume Control Setting
Relative attenuation
from maximum gain
Output noise, A-weighted, RADIO input selected
Output noise, A-weighted, CD or TAPE input selected
Output noise, A-weighted, DISC input selected
RADIO input, 1 k Ω shunts lifted
CD or TAPE input, 1 k Ω shunts lifted
21
0.00 dB
-96.6 dBV
-94.4 dBV
-84 dBV
-82.0 dBV
-79.7 dBV
20
-1.825 dB
-98.3 dBV
-96.2 dBV
-85 dBV
-83.5 dBV
-81.3 dBV
19
-3.89 dB
-100.3 dBV
-98.3 dBV
-88 dBV
-85.5 dBV
-84.4 dBV
18
-5.96 dB
-102.1 dBV
-100.2 dBV
-90 dBV
-87.3 dBV
-85.3 dBV
17
-8.20 dB
-104.1 dBV
-102.2 dBV
-92 dBV
-89.3 dBV
-87.3 dBV
16
-10.49 dB
-105.9 dBV
-104.2 dBV
-94 dBV
-91.0 dBV
-89.5 dBV
15
-12.72 dB
-107.5 dBV
-106.0 dBV
 
-93.0 dBV
-91.3 dBV
14
-14.99 dB
-109.0 dBV
-107.6 dBV
 
-94.4 dBV
-93.0 dBV
13
-17.50 dB
 
-109.3 dBV
-101 dBV
95.0 dBV
-95.0 dBV
12
-19.81 dB
-111.3 DBV
-110.5 dBV
 
-97.5 DBV
-96.2 dBV
11
-22.28 dB
 
-111.5 dBV
   
-97.7 dBV
10
-24.78 dB
-112.6 dBV
-112.3 dBV
 
-98.7 dBV
-98.2 dBV
9
-27.16 dB
 
-113.0 dBV
   
-99.0 dBV
8
-29.60 dB
-113.3 dBV
-113.1 dBV
-110 dBV
-100.0 dBV
-99.3 dBV
7
-32.18 dB
         
6
-34.77 dB
         
5
-37.21 dB
         
4
-42.30 dB
         
3
-47.22 dB
-113.9 dBV
-113.9 dBV
-113.9 dBV
-100.4 dBV
-100.4 dBV
2
-52.29 dB
         
1
-57.20 dB
         
0
-97.63 dB
-114.0 dBV
-114.0 dBV
-114.0 dBV
-100.4 dBV
-100.4 dBV

 

TAPE REC output noise, as fed from the muted output of the Rohde &Schwarz UPL, with its 5Ω unbalanced source impedance. A-weighted:

 
Left
Right
RADIO
-102.7 dBV
-102.5 dBV
DISC
-92.5 dBV
-89.0 dBV
CD
-99.4 dBV
-99.3 dBV

 

Crosstalk      measurements    top

Idle Input Rejection

When one input is selected, but other unselected inputs are providing signals, how much feeds through to the output?

 

Input applied to RADIO, OUTPUT output

CD selected: -102 dB gain at 1 kHz.

TAPE selected: -73/-76 dB gain at 1 kHz.

DISC selected: -84 dB gain at 1 kHz. (mostly noise).

 

Input applied to RADIO, TAPE REC output

CD selected: -104 dB gain at 1 kHz.

DISC selected: -94 dB gain at 1 kHz (mostly noise).

 

Input applied to CD, OUTPUT output

RADIO selected: -64/-57 dB gain at 1 kHz.

TAPE selected: -74/-78 dB gain at 1 kHz.

 

Input applied to CD, TAPE REC output

RADIO selected: -63/-57 dB gain at 1 kHz.

 

Tape Loop Independence

If I punch up the TAPE input, how much signal leaks through from the CD input? In other words, if used as an external processor loop, how much of the source leaks through?

In this case, I didn't terminate the inputs of the TAPE REP input.

Quad 34 preamp THD

Leakage through unconnected tape loop, CD input at 1V, Volume Control at 13, lifted 1k Ω shunts.

 

Tone Controls      measurements    top

BASS   BASS LIFT    BASS STEP    TILT    Filters

Quad 34 preamp THD

BASS LIFT/STEP and TILT Controls at centres, Quad 34 Preamplifier. enlarge.

 

BASS LIFT/STEP Control     tone     measurements    top

Quad 34 preamp THD

BASS LIFT/STEP Controls at 0 dB, Quad 34 Preamplifier. enlarge.

 

Quad 34 TILT Control

Infrasonic Frequency Response 2 (two) Hz to 20,000 Hz, Quad 34 Preamplifier BASS controls.

 

BASS LIFT     tone     measurements    top

Quad 34 TILT Control

Frequency Response, Quad 34 Preamplifier BASS LIFT control.

+3 dB: +3.00 dB at 82.5 Hz, +12.27 dB at 20.4 Hz.

+6 dB: +6.03 dB at 82.5 Hz, +14.00 dB at 27.0 Hz.

+9 dB: +10.26 dB at 82.5 Hz, +15.26 dB at 36.7 Hz.

 

BASS STEP Control     tone     measurements    top

Quad 34 TILT Control

Frequency Response, Quad 34 Preamplifier BASS STEP control.

 

TILT Control     tone     measurements    top

Quad 34 preamp THD

TILT Controls at neutral, Quad 34 Preamplifier. enlarge.

 

Quad 34 TILT Control

Frequency Response, Quad 34 Preamplifier TILT control.

 

Filters     tone     measurements    top

Quad 34 preamp THD

Input Selector and Filters, Quad 34 Preamplifier. enlarge.

 

QUAD 34 filter frequenct responses

Filter Responses, Quad 34 Preamplifier.

The top trace is with no filters.

The next two traces are the F1 (11 kHz) filter. The lower of these two traces is with SL (increased slope) engaged.

The bottom two traces are the F2 (7 kHz) filter. The lowest trace is with SL engaged.

 

Tape Rec Output      measurements    top

Gain measured from the RADIO input at 1 kHz is 10.102 dB (left) and 10.082 dB (right).

Gain measured from the DISC input at 1 kHz is 40.55 dB (left) and 40.58 dB (right).

Gain measured from the CD input is -0.070 dB (left) and -0.125 dB (right).

 

Frequency Response

Quad 34 frequency response

TAPE REC output frequency response from CD input, Quad 34 Preamplifier.

The RADIO input is similar; down 1 dB at 10 Hz and flat 20 - 20,000 Hz.

 

THD

Quad 34 preamp THD

THD, TAPE REC output from CD input at 1V, Quad 34 Preamplifier.

 

Tape Loop (EPL)      measurements    top

If the TAPE REC output is connected to the TAPE REP input, we can investigate the transparency of using the TAPE monitor input as an external processor loop (EPL).

 

Gain Change

This is the change in gain when the TAPE REP input is selected, as fed from the TAPE REC output:

Left
Right
-0.3474 dB
-0.3006 dB

So we lose a third of a dB kicking-in the EPL, which is largely inaudible, but watch for it if you're doing tests.

 

Channel Balance Shift

As seen above, the stereo image shifts an inaudible 0.0467 dB to the right. This is less than the attenuator's own tracking error.

 

Frequency Response

HF frequency response is unchanged.

At subsonic frequencies, one more pole (capacitor) is added to the circuit at about 5 Hz, adding another 6 dB/octave to the rolloff:

Quad 34 Tape Loop Response

Subsonic response, CD input to OUTPUT output, 1 V input, Volume Control at 13.

Top trace: normal operation. Bottom trace: adding TAPE monitor loop.

 

Distortion

I can't measure any significant change in distortion when feeding a signal through the TAPE loop.

 

DISC (Phono) Preamplifier      measurements    top

Gain

Gain measured from the DISC input to the TAPE REC output at 1 kHz is 40.55 dB (left) and 40.58 dB (right).

 

Maximum Input Levels at 0.1% THD at 1 kHz

151.1 mV.

48 mV, if using the TAPE REC outputs.

 

Noise

Signal-to-noise, A-weighted, OUTPUT output at Volume Control 15, referred to 5 mV at 1 kHz: 75 dB left, 87 dB right.

Signal-to-noise, A-weighted, TAPE REC output, referred to 5 mV at 1 kHz: 74 dB left, 88 dB right.

TAPE REC output noise, as fed from the muted output of the Rohde &Schwarz UPL, with its 5Ω unbalanced source impedance. A-weighted:-92.5 dBV (left), -89.0 dBV (right).

 

Frequency Response

DISC input measured at TAPE REC output.

Quad 34 Preamplifier

DISC frequency response (showing RIAA curve), Quad 34 Preamplifier.

 

1 kΩ Shunt Lifting      measurements    top

As shipped, the OUTPUT level (500-650 mV RMS maximum) is insufficient to drive most American power amplifiers to full output. They need about 1.5 V RMS, so if driven by most unmodified QUAD 34s, the Quad 34 will clip while driving an ADCOM 545-II to only 27 Watts of output — and the amp's self-monitoring LEDs won't know to light.

A professionally licensed technician can endeavour to change the resistive output pad to provide more output voltage. The easiest way it to lift either end of the 1kΩ shunt resistors, which increases output to 2.6 V RMS and output source impedance to 5 kΩ.

Frequency response is unchanged, save for the effects of a 5 kΩ source impedance.

I can't see any difference in THD either:

THD, Quad 34

THD versus input level at unity gain (VC at 8, RADIO input), 1 kHz, 1 kΩ shunt resistors lifted, Quad 34 Preamplifier.

 

Usage         top

Intro   Specifications   Measurements   Usage   Recommendations

 

WARNING 1: Have your technician ensure that the rear switch or internal jumpers match your local mains power.

 

WARNING 2: Be sure to buy a unit which has your choice of connectors, be they DIN (Europe) or RCA (rest-of-world). You can make adapters if you got the wrong version.

 

WARNING 3: Have your technician ensure that the audio level options are set for your usage. For instance, most versions don't have enough output to drive an American power amplifier to full output unless internally modified.

 

Quad 34 Preamplifier

Quad 34 Preamplifier. enlarge.

 

Power Switch         top

Press the little button on the lower right.

 

Inputs         top

When turned on, it always wakes in the RADIO position.

As this and many units are configured, the RADIO input has 10 dB more gain than the CD or TAPE inputs, so it will sound about twice as loud.

While the CD and TAPE inputs usually can have their sensitivity adjusted with plug-in resistors (often set to "300 mV" as labeled by Quad), the RADIO input always operates at the same sensitivity, labeled as "100 mV" by Quad.

Therefore, you might want to plug an iPod, with its typically 1V maximum output into the RADIO input, and use the CD and TAPE inputs for your CD, SACD, DVD players or Mac Pros, which usually have 2V maximum outputs.

Weirder still is that the more sensitive RADIO input is direct, while the CD and TAPE inputs use input amplifiers with resistive pads in front of them to allow various, and usually lower, input sensitivities. The RADIO input is therefore both more sensitive and cleaner, and my Measurements confirmed that! Sadly, the RADIO input is so sensitive that if used with most audio sources that one may need the Volume Control set farther down than convenient, limiting one's ability to enjoy music at lower levels — but feel free to preface it with a 10 dB pad, and it's still slightly cleaner than the other inputs.

 

MONO         top

MONO sums the two channels after the Balance and Volume controls.

MONO lets one use the Balance control as a selector/mixer to enjoy either the left or right inputs, or a mixture of them, as a mono programme.

In MONO, the Balance control selects between the two input channels, it does not vary the apparent balance between speakers.

 

Filters         top

Press F1 (11 kHz) or F2 (7 kHz, more filtering).

Pressing SL (steeper slope) adds even more filtration above the chosen frequency.

 

BASS LIFT         top

Try the +3 position for all small speakers.

Try the +6 position for low-level enjoyment.

Try the +9 position for listening at very low background levels.

 

BASS STEP         top

If you put your speakers too close to the walls, move them, or try any of the STEP positions.

Likewise, as this preamp is expected to be used with the very finest wide-range reproduction systems, if the recording is too bass-heavy or loaded with rumble, try the STEP positions.

 

TILT         top

Adjust to taste.

Clockwise adds warmth, smoothness and depth. It moves you farther from the orchestra.

Counter-clockwise adds definition, speed and detail. It moves you closer.

 

Unmarked Output         top

The unmarked pair of rear connectors between CD and TAPE REP are a second TAPE REC output.

They are connected directly to the other TAPE REC output via internal plug-ins X1 and X2.

 

Headphones         top

There is no common 1/4" or 3.5mm headphone jack. Use the OUTPUT output (or the unlabeled second TAPE REC output) and an outboard headphone amplifier.

Common dynamic headphones like AKG, Sennheiser or Ultrasone which would use such a jack lack the quality demanded by the Quad listener.

For the serious listener who uses Quad electrostatic speakers, for headphones, it is expected that the listener will demand only electrostatic headphones to enjoy his music. Unlike speakers, proper headphones will take you back into the original performance space.

 

Recommendations         top

Intro   Specifications   Measurements   Usage   Recommendations

If you're prepared to swap 120V jumpers and/or tweak internal pads to get the levels where you need them, there's a reason this has been such a popular preamplifier for many, many years, especially for careful listeners.

 

More Information

Quad 34 Instruction Book (User's Guide).

QUAD 34 MK II Instruction Book.

Quad 34 Service Manual.

Quad 34 Schematic Diagram.

 

Help me help you         top

I support my growing family through this website, as crazy as it might seem.

The biggest help is when you use any of these links to Adorama, Amazon, eBay, Ritz, Calumet, J&R and ScanCafe when you get anything, regardless of the country in which you live. It costs you nothing, and is this site's, and thus my family's, biggest source of support. These places have the best prices and service, which is why I've used them since before this website existed. I recommend them all personally.

If you find this page as helpful as a book you might have had to buy or a workshop you may have had to take, feel free to help me continue helping everyone.

If you've gotten your gear through one of my links or helped otherwise, you're family. It's great people like you who allow me to keep adding to this site full-time. Thanks!

If you haven't helped yet, please do, and consider helping me with a gift of $5.00.

As this page is copyrighted and formally registered, it is unlawful to make copies, especially in the form of printouts for personal use. If you wish to make a printout for personal use, you are granted one-time permission only if you PayPal me $5.00 per printout or part thereof. Thank you!

 

Thanks for reading!

 

 

Mr. & Mrs. Ken Rockwell, Ryan and Katie.

 

Home  Donate  New  Search  Gallery  Reviews  How-To  Books  Links  Workshops  About  Contact