~ QUAD 22 Pre–Amplifier Control Unit ~ Modernisation & Modification ~

The QUAD 22 is very compact for its functionality because it does not have its own power supply ~ When it was introduced in 1959 the functions of a good pre–amplifier or control unit were more complex compared to some pre–amps today ~ Like many valve pre–amps up to the 1970s the QUAD 22 made maximum use of all components because they cost a lot both to buy to stock and to fit

The 1959 Hi–Fi year book that featured the "New QUAD22 control unit" was a "special tape edition" featuring many tape recorders but also many "tape decks" which were tape reply devices similar to "record decks" or turntables and which required an equalised tape reply pre–amplifier ~ Hence the TAPE plugin on the QUAD 22

The DISC or Pickup P.U. adaptor was another QUAD 22 "complexity" that allowed connection of various types of ceramic or crystal or magnetic cartridges ~ This coupled with switched equalisation for most manufacturers 78rpm discs as well as RIAA and an excellent variable "noise" filter made it a good choice for the serious record collector at the time

QUAD22 Control Unit new phono connectors If you own an original QUAD22 control unit in very good condition you may not wish to modify it and I would agree with you ~ Operating all the controls and switches and re-seating the valves and adaptors regularly can prevent some of the faults and noises that vintage valve amps develop

One thing you will eventually have to admit is the horrible tin plated phono connectors on the rear panel will need replacing

Pictured above is a QUAD 22 where the phono connectors have been replaced with Red Neutrik/Rean NYS367-2 and White NYS367-9 phono connectors ~ I like these because they are good quality and fit the large holes in the 22 back plate ~ And the part numbers follow the resistor colour code

A MONO pickup input or TAPE out was not required for this project ~ The line inputs were made Yellow channel is left with input connectors at the top which is an "industry de–facto standard" but on the QUAD 22 this makes the balance control work back–to–front unless the power amps or balance connections are swapped

The old phono connectors are removed by drilling the rivets with a 3mm drill or they can be cut with flush wire cutters from the inside of the panel (best use an old pair of cutters) ~ The job is much easier if the back panel is removed from the rest of the chassis and this will be required to fit the new phono connectors anyhow

The holes in the back plate are about 10mm and are not evenly spaced ~ The NYS367– have an 8mm thread and are supplied with 2x 12mm gold plated nuts and solder tag and 2 insulated washers

The insulated washers cannot be used for the line inputs and the nuts are too close to be turned so the connectors have to be screwed onto the nuts

If 4 nuts are soldered together on a flat surface and the outside "corners" of holes are filed where shown the connectors can be screwed onto the nuts and should fit neatly in a line

The Middle 2 connectors should be fitted first and can be tightened from the rear using the "flats" on the threaded section assisted by turning the connector from the front with your fingers ~ A small 7mm spanner may just fit ~ If the filing of the outside "corners" is correct the edges of each row of 4 connectors should just clear the QUAD nameplate

If the connectors do not clear the edge of the nameplate first try filing the "corners" more and check that the middle 2 connectors touch the top or bottom edges of their holes in the directions shown above ~ All 4 holes can be filed along the outside edges or the name plate can be filed to profile the connectors which can look good

A nice option for an original QUAD QC222 is to fit Blue and Yellow NYS367–6 and NYS367–4 phono connectors and stick with the QUAD handbook scheme ~ yellow for right hand channel blue for left

Note the mains input connection has an earth wire which is connected to the chassis for safety ~ There is a chassis connection below the output cables which had been kept free for the record deck

If you often listen to 33rpm or 45 rpm vinyl you may like the QUAD QC22 / QUAD II "valve sound" but not the stereo image ~ The various DISC equalisations available only on the Yellow channel are derived using series and parallel 5% resistors and horrid metalised paper capacitors which don't age well even if they were good when new

The section of QUAD 22 schematic below shows the Yellow (or right hand channel) of the DISC / TAPE amplifier set for DISC playback with the 4mV output magnetic cartridge Adaptor A and RIAA equalisation ~ Unless you want to listen to any 78rpm discs or use a ceramic or crystal pickup this is the only setting you will want

QUAD Hi Fi QUAD22 RIAA schematic

If you decide that you will never be using a ceramic or crystal cartridge and you only require RIAA equalisation which is the standard for 45rpm and 33rpm vinyl discs made after 1954 then you can dispense with the often troublesome TAPE and DISC plugins and build the DISC EQ inside the QC22 chassis around the EF86 valve bases and make a reliable and modern Pre–Amp based on the schematic below

QUAD Hi-Fi QUAD 22 modification

Note there are changes to component values on the above schematic to make the RIAA more accurate while using readily available 1% standard value components and also to give the cartridge a lower 47kΩ load

Removing components and rewiring around the bases of V1 and V2 can be awkward and time consuming so I made a replacement PCB to accommodate the RIAA circuit

The DISC amplifier stage should have a few MΩ on its output to eliminate switching spikes ~ The CD input can be attenuated about 10dB with respect to RADIO with 32kΩ input impedance as shown on the schematic above ~ The TAPE input acts as a Tape Monitor if operated in conjunction with the other input buttons ~ It was switched in and out to check the source and tape output while recording but this is tricky to do and using the MON button is a better option for this feature ~ see QUAD Switching A
In 1983 I got a Sony CDP 101 and was already using a Philips CD104 and wanted another identical CD level input to compare them

My QUAD 22 was further modified to have 2x 300mV inputs using the TO and MIC + RADIO2 sockets

QUAD Hi Fi new rear panel
QUAD HiFi input switching In 1983 I also had a Lenco turntable with Mono Magnetic cartridge so my variation on the schematic above switched Mono coarse groove DISC equalisation with all buttons out and I could record my mums 78 collection

If only using RIAA more inputs can be provided by the arrangement in the diagram shown on the left

I chose to use all 4 contacts on the MIC switch so that the RADIO button could still switch the HT to the RADIO 1 sockets for an FM1 I had at the time ~ The sensitivity of the 2 CD inputs was made –12dB wrt the Radio input and had 20kΩ impedance as above

Making the TAPE or MON button a 'Tape Monitor' the other switches could provide up to 7 inputs but you will need a new back panel [See below] ~ This efficient use of changeover switches is often referred to as a "Clapham Junction" after the numerous track switching points at a famous railway station in Clapham London UK

My schematics give a "pictorial" view of the switchbank which may be useful when wiring it and making connections to the rear panel

There is little or no clearance between the bottom row of red NYS367 connectors and the chassis base so I fit PTFE sleeving over the wires and the series resistors for the attenuated inputs which are connected directly to the NYS367 centre pins as shown

Second nuts are added to 2 phonos to fit the solder tags supplied with them and a wire formally connects the solder tags to the base solder tag

It is often best to completely remove the back panel even if you are going to re–use it ~ changes to the switchbank and fitting the RIAA PCB requires a lot of work but the end results are worth it

The picture opposite shows where old stand off posts need to be removed to make way for the RIAA PCB ~ The cut out at the top of the picture is for a 5pin DIN socket for Tape in and out

There is only one way to work on the QUAD 22 input selection switch and that is to completely remove it and clean off all the old solder and flux

The switch bank pictured is wired to my drawing QUAD 22 Switching B but there are other options you could explore like QUAD 22 Switching C which uses the original back panel and Tuner HT switching but makes the TO an input if no recording device is required

A possible drawback of the clampham junction switching is that the signal passes through more than one switch and audiophool purists prefer a direct signal path ~ To get more than 4 inputs with the original QUAD 22 switch bank the back contacts of the changeover switches need to be used for some inputs ~ See QUAD 22 Switching B or the 2016 revised QUAD 22 Switching A

This severe modification to the QUAD 22 provides 6 inputs and a buffered output Tape monitor but dispenses with the HT and Mains switching ~ It uses the MON button as a "Record" Monitor and the STEREO button for Source monitoring ~ The Blue channel mains switch was removed to make MON switching smoother

The volume control is replaced by an ALPS 500k log pot and the balance control fitted on the rear panel ~ the QUAD 22 still operated as a control unit switching mains to the power amps with each QUAD II power amp supplying the Heater and HT voltages separately to each channel [only 3 made]

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~ Some babies grow in a peculiar way ~ It changed it grew and everybody knew ~