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Old 13th June 2008, 03:21 PM   #1
johnm is offline johnm  United Kingdom
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Join Date: Sep 2003
Location: Hampshire
Default Zen Quad 22

Hi folks!

To complement my pair of Quad IIs (currently being restored), I decided to build a stripped down version of a Quad 22 pre-amp - what better design to partner the IIs? I know some mock the 22s sound, but I've always respected Peter Walker's designs, and - for nostalgia reasons more than anything else - I wish to build one for my Quad IIs.

This is a totally ground up design - I don't own a Quad 22 and won't shell out for one on Ebay as the prices are insane.

As mentioned, this will be a 'Zen' Quad 22 - I don't need the complicated switch-bank, or any of the balance/filter/tone controls. As most all of my sources provide 2V output I believe I am correct in thinking I can dispense with the EF86 stage of the circuit as well and have the sources go directly to the 500K volume control? (Got a nice stepped attenuator from China for this). The EF86 stage is present in the attached diagram, but I shall probably remove it for the next revision. Actually if you follow the original circuit diagram you can see that the Radio 2 bypasses the EF86 stage also and runs direct into the 500K pot.

As my Quad IIs use their original circuit values (apart from the dual section cap uprated to 2 x 32uF) I want to do the same with the 22 - no 'improvements', just stock values.

The problem I have at present - not being an expert in these matters - is how to imlement the required feedback to this circuit so it meets the Quad 22s original design? I know its feedback was part of the balance control section, but I have dispensed with this. Could some kind soul possibly draw onto the attached diagram the correct way to implement the required feedback?

The original diagram maybe found here: http://www.dc-daylight.ltd.uk/Valve-...-Schematic.pdf

Thanks so much!

- John
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