Quad 22 preamp revived.

[Audioflyer]

Quad 22 preamp.



The picture above is in it restored state.

I was give this preamp last year and as part of my scrapyard refurbish, I decided to see what it would take to get it to work in a modern set-up

First thing first it needed a power supply and after rummaging around I found all the bits.
Well first thoughts listening to it using the standard inputs, it had a soft warm sound with a lack of bass when plugged into my Linn Intek.

Years ago when I used to use the Quad 22 I use to feed line level equipment into the tape output with all the input buttons switched out,
this feeds the signal into the volume control removes the veil sound from it by bypassing the EF86's.

When connected to my Intek and using the Quad 22 tape output as the input the sound open up but it still had a lack of bass.
The big problem is matching the Quad 22 output with any thing less than 1M ohm input impedance as the ECC83 has a very high anode impedance.

More to come....

Quad 22 preamp revived...

Modification...

Mods please feel free to move it Past Master if needed.

Sharif.

[Audioflyer]

This is the third Quad 22 preamp that I've owned and it was not in the best of conditions.

First mod was to replaced the back panel and get rid of the umbilical cords.



Next up was to look at the input to selector switch wiring, as I didn't need the EF86 input stage thus greatly simplified the connections.
The output from the selector switches now feed a 470nf capacitor (C34-C35 were 47nF) that is then connected to the volume control.



Resistor R20 was disconnected to remove the supply to the EF86 stage.
All the old carbon resistors were replace around the ECC83 as most of them were out of spec.
The brown Hi-stab resistor didn’t need replacing.

I was in two mind whether to to keep the tone controls or not in the end I kept them.



Again I replace the resistor and capacitors.



Volume and balance controls were not working properly so I replace them with alps pots.



The balance control need a bit more work I had to make a bracket.



The connecting rod was made from a medium sized paper clip



Volume Control need an extension and was drilled and tapped.





Now for the PSU.




So how did it sound.

It sounded like a ECC83 line stage very neutral none of that old school valve sound when feed into a load greater than 1M ohm.
Now the problem was how to make it work with an amp with a 10K ohm input.
Capacitor C16-C17 restricts the bass response in the past I’ve tried increasing them to 470nF but the ECC83 protested with the low loads.

In the early eighties I played with adding a cathode follower but I didn’t like the results.
Then I discovered VFET and successfully used it as a source follower.

So this time I've revisited the source follower I've used a high voltage MOSFET which eliminates the extra parts for the VFET psu.

I've found a few site where this mod has been done mainly to valve guitar amps with good results.





Now with a 470nF cap on the output of the MOSFET follower it drive a 10K ohm input of my amp properly.
I'll need to up the 470nF cap to get the low frequency response down.

Final mod was to replace the main electrolytic cap C12 – C15.









Almost there.

Front panel resprayed and lettering sorted I used T-cut to wipe the excessive paint form the lettering.





Case with dents removed and resprayed.



At last the end.

[Firebottle]

Fantastic job Sharif, well done.
Thanks for posting so many pics, we all love lots of pics

The input selector switch contacts look remarkably clean, did you clean them or were they as is?

Alan

[Gordon Steadman]

I love the look of these old Quads. I have the facia from an old non-worker mounted in a frame as 'art'. The 33 too is a great piece of industrial design.

Yours looks superb.

[Audioflyer]

Fantastic job Sharif, well done.
Thanks for posting so many pics, we all love lots of pics

The input selector switch contacts look remarkably clean, did you clean them or were they as is?

Alan

I used Servisol Switch & Contact Cleaner on the selector switches and the rotor filter switch, followed with electrolube contact oil.

Sharif

[Audioflyer]

I love the look of these old Quads. I have the facia from an old non-worker mounted in a frame as 'art'. The 33 too is a great piece of industrial design.

Yours looks superb.

Thank you, it has take about three weekend to finish the front panel.
Modern car paints are crap they need so long to days to full cure before you can apply the finishing lacquer.

[Audio Al]

Very worthwhile project

You are the man

[DSJR]

Very well done, but PLEASE bin that awful Intek thingy - bloody thing should have been stillborn - ugh!

[Audioflyer]

Very well done, but PLEASE bin that awful Intek thingy - bloody thing should have been stillborn - ugh!

It the only amp that safe for the missus to use.