H/K Citation 11 grounding issues
I am very close to finishing my H/K Citation 11, 12 & 15 restoration. Citation 15 needed only basic recapping of electrolytics and grounded mains lead. I recapped 12 with correct dia CDE computer grade electrolytics at 12 000UF/63V and used decent quality smaller electrolytics. Grounded mains lead was installed. I twisted live and neutral leads inside chassis for lower radiated hum. Also second ground lift resistor was added, as chassis is now grounded by mains cable. There is considerable DC offset on both outputs, but it seems that there is not too much trouble about this issue.
11 proved to be more troublesome. My unit seems to be similar to Sir Byrd´s Citation 11/HK 430 recap tread and H/K Technical manual starting serial no. 2060001.
There was considerable ground loop hum. It took some time to find that 10 ohm ground lift resistor was added between main filter cap and chassis ground. For some odd reason there were two black wires running from chassis end of ground lift resistor to output and high level input RCA:s, even inputs were already grounded to signal ground. Cutting these wires cured the ground loop hum.
As sound was edgy and switches and pots performed well, I considered output relay must be cause for edginess. I simply bypassed relay connection to output by wire link. This cured most of edginess and had no adverse effect for output muting.
Two under chassis 500 UF axial electrolytisc were grounded to right channel output ground, even one cap was used for smoothing left and other one right channel line stage supply. I added two way turret and second ground return wire to left channel output ground and performance improved clearly.
I noticed also that both L and R channel Line stage inputs are grounded directly L channel EQ board... this seems a bit odd... but it is difficult to trace where all ground wires go.
Everything except ground lift resistor seems to be original. Most likely there has also been faulty ground lift conversion bulletin available somewhere, as Sir Byrds 11 does have exactly same faulty conversion. Somehow I think that there is still some unsolved grounding problem.
As Citation 12 is performing quite well now... maybe slight edginess and not too good image depth, but pretty involving and dynamic. Citation 15 is very good by any standard. Therefore I suppose that it is reasonable to expect that 11 will be performing close to this standard, but my 11 is quite far from this now. Maybe David or somebody else do have any suggestions or idea how to proceed.
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