audioflyer
No going back once you heard a ceramic cartridge
I've owned a few Quad 22 preamp this being the third one and it was not in the best of conditions.
First mod was to replaced the back panel and get rid of the umbilical cords and replace it with 6 pin plug.
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 didnt need replacing.
I was in two mind whether to to keep the tone controls or not in the end I kept them.
Then I replace the resistor and capacitors in the tone network.
Volume and balance controls were not working properly so I replace them with Alps pots.
The balance control need a bit more work and I had to make a bracket this mod was similar to the one that Quad did.
I need a connecting rod and this was made from a medium sized paper clip
The short shaft on the Alps pot need an extension best idea I could think of was to drilled and tap it.
Separate PSU.
So how did it sound.
It sounded like a ECC83 line stage very neutral none of that old school valve sound.
The main problem was the ECC83 drive abilities into a load of less than 1M ohm.
So I needed a solution to make it work with an amp with a 10K ohm input.
In the original circuit capacitor C16-C17 restricts the bass response and in the past Ive tried increasing them to 470nF but the ECC83 protested with any load less than 1M ohm.
In the early eighties I played with adding a cathode follower but I didnt 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 in 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, only problem is it 5db down a 20Hz. I'm planing to stack two 470nF cap to get the low frequency response down.
The last mod was to replace the main electrolytic cap C12 C15, nothing in spares box so resorted to making one.
Front panel was resprayed and lettering sorted using artist acrylic paint. After it dried I used T-cut to wipe the excessive paint form the lettering.
The case had a few dents which were removed and then it was resprayed.
Well that's it.
One restored/modified Quad QC 22.
It now quite at home with my Quad II's.
Sharif.
First mod was to replaced the back panel and get rid of the umbilical cords and replace it with 6 pin plug.
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 didnt need replacing.
I was in two mind whether to to keep the tone controls or not in the end I kept them.
Then I replace the resistor and capacitors in the tone network.
Volume and balance controls were not working properly so I replace them with Alps pots.
The balance control need a bit more work and I had to make a bracket this mod was similar to the one that Quad did.
I need a connecting rod and this was made from a medium sized paper clip
The short shaft on the Alps pot need an extension best idea I could think of was to drilled and tap it.
Separate PSU.
So how did it sound.
It sounded like a ECC83 line stage very neutral none of that old school valve sound.
The main problem was the ECC83 drive abilities into a load of less than 1M ohm.
So I needed a solution to make it work with an amp with a 10K ohm input.
In the original circuit capacitor C16-C17 restricts the bass response and in the past Ive tried increasing them to 470nF but the ECC83 protested with any load less than 1M ohm.
In the early eighties I played with adding a cathode follower but I didnt 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 in 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, only problem is it 5db down a 20Hz. I'm planing to stack two 470nF cap to get the low frequency response down.
The last mod was to replace the main electrolytic cap C12 C15, nothing in spares box so resorted to making one.
Front panel was resprayed and lettering sorted using artist acrylic paint. After it dried I used T-cut to wipe the excessive paint form the lettering.
The case had a few dents which were removed and then it was resprayed.
Well that's it.
One restored/modified Quad QC 22.
It now quite at home with my Quad II's.
Sharif.
