Sugden A28 amplifier

The Sugden A28 once again gives you the unsurpassed quality of pure Class "A"

This is how we regard the Sugden A28 amplifier. Based upon well proven Sugden output circuitry, we now bring you an Amplifier which is second to none in its sound reproducing quality.

Let's start with the input circuitry, accessed via easy to use phono plugs and sockets and selected by four simple push-on, push-off switches. On the disc input not only do we have the facility for an internal plug in Moving Coil Module (the A 28 CTHA) deriving its power from within the Amplifier, but also a brand new "series-shunt" disc Amplifier with precision RIAA equalization and two level gain adjustment. In fac, everything to suit the cartridge of your choice.

Next the Tuner, Auxiliary and Tape inputs. All these three have identical input impedances, allowing a wide range of ancillary equipment to be used without interface problems.

The Tape output signal can, of course be fed from any of the input signals. For those people with 3 head Tape Machines, the Tape button will allow immediate post tape recording/replay through the Amplifier, i.e. Tape Monitor.

 

No tone controls here to marr distortion figures, just volume and balance controls with simple but effective filter circuits for hiss and rumble attenuation. Don't forget the Mono Button. Still essential for much recorded material.

Observe the neat, unfussy and easy to clean case style. Front and rear sections are matt black extrusions, whilst the side and top plates are covered in grey textured "Nextel" paint, giving a very attractive two tone finish.

As to how it sounds, well the specification, amy give you some clue, but we believe you will be delighted at the clear transparent sound.

The very low harmonic distortion of a class "A" Amplifier gives fatigue free listening to please even the most discerning ear. All this and more. Sugden expertise brings you the "S.Q.C" circuitry to give an amazingly compact pure class "A" output stage with up to 35 watts in class "B" allowing all but the most inefficient loudspeakers to be driven. Backed by the Sugden workmanship for life guarantees, we are justifiably proud to present this high quality British product.

 

Features:

20 watts pure Class "A" per channel

Continuous reserve capability of 35 watts per channel

Budget price (top quality sound at a price you can afford)

With additional module, can be used with Moving Coil cartridge

Variable gain disc input

Very low distortion

New precision RIAA equalisation network

Built to Sugdens uncompromising standards

Carries Sugden workmanship "for life" guarantee

 

S.Q.C. is short for Switched quiescent Current

And its development gives new potential to the cless "A" amplifier. We at Sugden have always believed in the class "A" amplifier and , in fact, were the first company in the world to produce the all transistor class "A" amplifier in 1968. it was only the demand for more output power which forced us away from the 12 watt A21 pure class "A" amplifier into the higher power "AB" amplifiers, such as the A48 and the P51 in the majority of casses were music is played through reasonably efficient 8 Ω  loudspeakers, the average power used is probably not more that 3 to 4 watts with excursions to higher levels depending upon the dynamic rrange of the recorded material.

Also what is the point of burning off power when it is not required. This then is the philosophy around which the S.Q.C. circuit has evolved. The availability of high speed, low level, switching components enables us to control the "AB" circuit to its very best advantage.

The A28 operates continuously at a quiescent level of 10 watts in Class A, i.e. with a current in the output transistors of about 800 mA. By looking at the incoming signal level, after the potentiometer, we can determine whether the 10 watt output level will be exceeded and should this be the case increase the quiescent current level up to 1,2A or 20 watts. The current will stay at this level for as long as the heavy signal exists and also for a short time afterwards, before reverting back to the lower quiescent level. There is, however, a finite switching time of the S.Q.C. circuit, admittedly it is only about one millionth of a second, but under some very fast transient signal conditions there is just a possibility that if the switch sensing point is set at the same level as the quiescent current level, the Amplifier may slip momentarily into class "B" before reverting back to class "A". This is obviously unacceptable and in order to prevent it, we set the sensing a elactronics to switch at a level of 7 watts allowing a 3 watts reserve, giving time for the output stages to react to the increased demand.

Using this technique we can absolutely guarantee a full 20 watts in class "A" at all times.

The additional overhead level between 20 and 35 watts in class "B" allows for the wide dynamic range of some recorded material and since it is far into the linear range of the devices, there is little increase in distortion right up to 35 watts.

 

Specifications

Disc Input Magnetic

Sensitivity :  Internally Selectable to 1,7 mV or 3,5 mV for 35 watts into 8 Ω

Signal-to-Noise Ratio :  better than 65 dB unweighted

Frequency Response:  Equalised to within ±0,5 dB of RIAA characteristics 20 Hz to 20 kHz

Input Impedance:  47 k Ω  in parallel with approx. 50 pF

Overload :  margin better than 35 dB at all frequencies

Moving Coil Amplifier

Provision is made with the A28 to lift the A28-CTHA Moving Coil Amplifier Module.

Inputs sensitivities for this unit are 40 µV, 90 µV, 180 µV depending upon the internal sensitivity switch position in the Module and also in the main Amplifier.

This head amp. Uses a novel input circuitry which obviates the need for impedance matching.

Tuner, Aux, Tape Inputs:

Sensitivity :  100 mV into 180 k Ω  for 35 watts into 8 Ω

Tape output

Dependent upon input selected Typically 100 mV from disc Amplifier

Tape Monitor

Allows direct "AB" comparison from Tape Recorder on 3 head Machines

Filters

Low Filter:  is a rumble filter with attenuation of 18 dB /octave below 30 Hz

High Filter :  is a hiss filter with an attenuation of 18 dB/octave above 10 kHz

Mono Button:

Allows the incoming signal to be mixed and applied equally to both channels

Loudspeakers:

The Amplifier is suitable for any 8 to 16 Ω  loudspeaker - 4 Ω  speakers can be driven with reduced power output.

Connection is via 4 mm "banana" plugs

Headphones

Any headphones of 8 Ω  to 2 k Ω  impedance may be operated. Connection is by standard 1/4" stereo jack socket on the front panel. The loudspeakers are automatically muted when headphones are used.

Frequency Response:  20 Hz to 20 kHz ±1 dB referred to 1 kHz

Cross Talk (stereo):  better than -35 dB at all levels

Load Stability:  Unconditional

Damping Factor: better than 35 into 8 Ω

Power Output (Both Channel):

20 watts in Class "A" into 8 Ω

35 watts in Class "B" into 8 Ω

Distortion

Class "A" :  0,04 at 1 kHz (20 watts)

Class "B" :  0,06% at 1 kHz (35 watts)

Power Supplies:  Internally adjustable to 110, 120, 220, 230, and 240 V AC

Mains Supply Frequency:  48 / 60 Hz

Total Power Consumption:  220 watts

Auxiliary Power Output:  a 3 pin IEC socket with mating plug is provided. The output is switched live via the Amplifier power on switch. Max. Load from socket is 250 watts

Power ON Lamp:  indication that the Amplifier is operating is given by a light emitting diode on the front panel adjacent to the power on switch.

Dimensions (W x H x D):  400 x 88 x 267 mm

Weight:  6,5 kg

 

Sugden A 48 mkII (1976) amplifier

Circuit Configuration

The amplifier is electrically and physically in two sections, the pre-amplifier or control unit and the power amplifier. The pre-amplifier is again in two electrical sections. The first section is a feedback triple of high gain transistors forming the disc amplifier. The output of the disc amplifier or one of the high level inputs is selected and fed to an emitter follower circuit which in turn feeds the tone control, filter snd output stages. Each power amplifier has a low noise input transistor coupled to a high voltage bootstrapped stage to convert the input EMF to a high amplitude EMF approx equivalent too the required output voltage. The voltage amplifier is followed by a bootstrapped medium power emitter follower stage working into a resistive load. This circuit is followed by twin complementary pairs of output emitter followers with emitter coupled drivers. The quiescent current is fairly high at 100 mA. This method has been found to produce a linear output even without feedback thus only 30 dB or so of negative is used with  a much greater attendant stability into complex loudspeaker loads. The output stage is protected by reverse  fast diodes across the output devices and  curent limiting cicuiry. Cartridge fuses protect against over  dissipstion from a sustained short circuit.

Construction and finish

The basic chassis is a U section front panel joined to a U section rear panel with two tray section side members and a lateral U section member also joining the two side members. One side member caries the large main transformer, the lateral member the power smoothing and loudspeaker coupling capacitors together with the two bridge rectifiers, the front panel carries the pre-amplifier and the rear panel the power amplifier. The pre-amplifier components except for the controls which are mounted on the front panel are carried on a printed circuit board supported on special nylon stand off pillars. The entire pre-amplifier is screened in a two part cover formed from 22 gaue steel. All other steel parts are formed from 18 or 16 gauge mild steel. The power amplifier circuits are mounted on nylon stand off pillars carried by the rear panel and the power transistors are mounted on four massive heatsinks carried outside the rear panel and machined from from a special aluminium extrusion produced for JE Sugden by Alcan Booth Aluminium. The heatsinks are anodized matt black and all the ferrous metalwork is zinc plated and chromate passivated for maximum corrosion resistance. The chassis is clad in the "trim" consisting of a nextel finished strip behind the knobs and two aluminium trims which carry the front lettering. These trims are acid etched and anodized and printed with an epoxy ink. The top and sides trims are made from aluminium and finished in Nextel - a very durable paint with a suede effect feel to it. The push button knobs are of hard moulded black plastic and the rotary knobs are centre collet fixing (for perfect positioning and for not coming loose) in a rather pleasing matt black finish. The rear trims are aluminium faced with matt white PVC upon which the connector details are printed using a scratch resistant vinyl solvent ink. Non-staining soft plastic feet are fitted to the bottom.

Specification

Power Output (from Loudspeaker Sockets): 

8 Ω Loads :  45 W RMS per channel (90 W from both channels simultaneous operation)

16 Ω Loads :  35 W RMS per channel

4 Ω Loads :  50 W RMS per channel

Headphone Output:  600, 300 and 8 Ω (from TRS jackk socket on front panel, fed via an attenuator network from the loudspeaker circuits)

Tape Recorder Outputs:  '

DIN 5 Pin : 200 mV / 100 k Ω

Harmonic Distortion:  less than 0,1% into 8 Ω at 1 kHz (just prior to clipping)

Output Impedance:  0,2 Ω (in series with 10,000 µF)

Frequency Response:  30 Hz - 20 kHz ±1 dB

Power Response:  15 Hz - 35 kHz (at constant input level the output is -3 dB relative to 45 W at 1 kHz)

Load Stability:  Unconditional (reactive loads such as electrostatic loudspeakers will not cause malfunctioning of the power amplifier section)

Input Selection:  Disc 2; Dosc 1; Radio; Tape 1; Tape 2

Input Connections:  by 5 pin DIN sockets on the rear panel

Input Sensitivity (ref. To 25 Watt output level, 8 Ω loads):

Disc :  2,5 mV/47 k Ω

Radio :  100 mV/180 k Ω

Tapes :  100mV/200 k Ω

Signal-to-Noise Ratio: 

Disc Input :  75 dB

Aux, Radio, Tape :  85 dB

Disc Equalization: to BS1928 i.e. RIAA

Filter Controls

Low :  70 Hz / 12 dB per octave

High :  choice of 4, 7, 10 kHz / 18 dB or 6 dB per octave

General function

Mains Supply Required:  110  - 120 - 220 - 230 - 240 V AC 50/60 Hz (set by adjustment on transformer)

Dimensions (W x H x D):  400 x 130 x 290 mm (15,8" x 4,9" x 11,4")

Weight:  10,7 kg 23,5 lbs

I like

Sugden T48 tuner

The T48 is a tuner of novel concept to match and be used with the new A48 amplifier. The circuitry is a new dsign featuring the latest techniques including a front end with four tuned circuits and dual gate FET's, an I.F. strip using two ceramic filters with a quadrature detector and a phase locked loop multiplex decoder.

Its most radical departure from convention is the complete absence of a dial. Tuning is accomplished by six push buttons in a similar manner to the tuning of a TV unit. When a particular button is pressed it may then be tuned as desired, subsequent pushing of this button and the selected frequency will always be realised. Five lower push buttons selectt audio off, afc, stereo, muting and stereo noise filter. The last button trades a certain amount of separation for a reduction in switching noise as may be found on a weak or distant signal. A stereo transmission is indicaated by a lamp adjacent to the stereo push button.

Specifications

Sensitivity:  2,0 mV

Alt. Channel Selectivity:  60 dB

Requency Range :  88 to 108 MHz

Capture Ratio:  2 dB

Distortion:  0,5%

Output Level:  0,5 V

I like

Sugden A21 serie Two amplifier

The original A21 amplifier was hailed by many leading authorities as the most significant advance in amplifier design technique for many years.

The Series Two version incorporates certain improvements to the original model, including increased power output, improved input sensitivites and disc overload factor, headphone socket, nad superb new styling.

Construction is to very high standards, and the interior illustration indicates the neat layout. High quality components only are used to ensure long term reliability - note particularly the large electrolytic capacitors and mains transformer which immediately instill a feeling of confidence.

Unconditionally stable, superbly styled, a nd elegantly presented in a handsome teak case, this amplifier sets entirely new standards of high quality reproduction not only withinm but well beyond its price range.

Power Output

The rated power output of 12 watts RMS per channel is more than adequate for the vast majority of domestic situations even when using relatively insensitive loudspeakers. Once again it must be stressed that it is the quality of the watts which is important. With the current trend towards lower impedance loudspeakers, the A21 series two has been designed to produce its full output into 8 ohms, although it may be used with absolute safety to drive loudspeakers of higher impedance (at reduced total output)

Specifications

Power output:  12 watts RMS per channel (24 watts RMS both channels simultaneous operation)  at clipping  level into 8 Ω

Output to Tape Recorder:  Direct connection from raadio and aux, inputs, 150 mV from disc amplifier when correctly loaded.

Input Sensitivity

Magnetic cartridge :  2,5 mV into 68 k Ω, equalized to RIAA

Caramic cartridge :  50 mV into special input circuit

Radio, Tape, Aux :  150 mV into 200 k Ω flat response

Overload Capabilities:  25 dB on disc inputs; infinite on radio, aux, and tape inputs

Total Harmonic Distortion:  better than 0,25% at 10 watts, mainly 2nd and 3rd harmonic, negligible proportion of high order harmonics and reducing in proportion with reducing power to give less than 0,01% at 1/2 watt  - i.e. the average power listening level.

Frequency and Power response:  30 Hz to 20 kHz ±1 dB

Signal-to-Noise Ratio:

Radio, tape, Aux :  80 dB

Disc :  70 dB

Interchannel Crosstalk:  typically 40 dB 20 Hz to 19 kHz, dependent upon input load impedance

Control Knobs

Bass :  ±14 dB at 40 Hz

Treble ;  ±14 dB at 10 kHz

Volume:  Logarithmic (channel balance ±1 dB maintained to 50 dB attenuation)

Balance :  ±6 dB for 180° rotation, either channel eliminated at limits of rotation

Push Buttons to select

Inputs :  Disc, Radio, Aux, Tape

Rumble Filter :  Built in on disc input, 18 dB/octave below 30 Hz

High Frequency Filter :  12 dB / octave above 7 khz

Function :  Mono, Stereo, Input Right, Input Left

Power Consumption:  70 watts max

Dimensions (W x H x D):  394 x 127 x 229 mm (15-1/2" x 5" x 9")

Weight:  11,3 kg (24 lbs)

I like

Sugden A48 amplifier (1973)

The A48 integrated stereo amplifier is a "Luxury" development of the A21 amplifier. It is in many ways similar , almost identical in size and appearance , except for the 10 buttonn push button banl instead of 6. briefly the facilities are varied as follows:

Power Output

Doubled to 40 W RMS per channel ( 80 W from both channels simultaneous operation)

Filter Facilities

L.F. filter - switchable and operating on all inputs with a terminal slope of 18 dB/octave

H.F. filter - single turnover point and slope replaced by three turnover points of 4 kHz, 7 kHz and 10 kHz with a choice of two slopes -6 dB or 18 dB/octave

Disc Input Sensitivity

A further sensitivity position of 10 mV is available in addition to the 2,5 mV position to cater for such high output cartridges as the ortofon with transformer. The overload factor also increases by the same scale of four.

Quiet Facility

A switch position providing a quiet listening facility with an attenuation at mid frequencies of 16 dB only 8 dB low frequencies with the response contoured to the difference in the equal loudness curves of the ear. This facility, where normal volume is set and then 'quiet" selected is to be preferred to the so called :loudness" compensation of a volume control which has no relevance to the incoming signal level.

Specifications

Power Output: 40 watts RMS per channel(both channel driven at clipping  level into 8 Ω)

Total Harmonic Distortion:  less than 0,1% mainly 2nd and 3rd harmonic, negligible proportion of high order harmonics and reducing in proportion with reducing power

Frequency Response:  30 Hz - 20 kHz ±1 dB

Output to Tape Recorder:  Direct connection from radio and aux, input, 200 mV from disc amplifier when correctly loaded at average modulation

Input Sensitivity (25W level 8 Ω):

Radio, Tape, Aux :  100 mV into 200 k Ω flat response

Phono Magnetic Cartridge:  2,5 mV into 47 k Ω equalized RIAA standard

Overload Capabilities:  100 mV on magnetic disc input; infinite on radio, aux, tape

Signal-to-Noise Raatio (30 phon weighting): 

Radio, Tape, Aux :  80 dB

Phono :  70 dB

Interchannel Crosstalk:  typically 40 dB 20 Hz - 10 kHz, dependent upon input load impedance

Rumble Filter:  Buil in on disc input, 12 dB/ovctave below 30 Hz

Control Knobs:

Bass : ±14 dB at 40 Hz

Treble :  ±14 dB at 10 kHz

Volume :  logarithmic (Channel balance ±1 dB maintained to 40 dB attenuation)

Balance :  ±6 dB for 180° rotation, either channel eliminated at limits of rotation

Push Buttons to select

Inputs :  Disc, Radio, Aux, Tape

L.F. Filter :  18 dB/octave below 70 Hz

H.F. Filter :  turnover 4, 7 or 10 k Hz, slope 6 or 18 dB / octave

Function :  Mono, Stereo, Input Right, Input Left

Power Consumption:  140 watts max

Dimensions (W x H x D):  400 x 130 x 230 mm (15-1/2" x 5" x 9")

Weight:  11 kg (24 lbs)

I like