Refurbishing and upgrading the AU-D11 II

[Hyperion]

They are sensitive especially if left unplugged, they will hugely affect DC offset adjustments. The screens of the input connectors are additionally grounded to the rear panel earth terminal. This is a weakness because the copper plated chassis acquires a resistive coating which interferes with grounding all over the amplifier.

My solution is a stout ground wire soldered from the rear panel earth terminal across the rear panel leftwards past the main heatsink and then forward to the star ground on the chassis member underneath the amplifier. This seems to improve things a lot.

 

[ConradH]

I'm thinking the connectors are subject to oxidation or something, but what I don't understand is the input to the driver board is high impedance, so why should it be so darn sensitive to the connectors? I did check the grounding of the various chassis parts and it looks OK, probably because everything was recently unscrewed and remounted. I'll report back in a couple days when I can get back to it.

 

[phonomac]

I agree with Hyperion about the need to improve the grounding of the driver boards. In my case I ran a fresh ground wire from each driver board to the star point on the chassis.

Also check the solder connections on the base of each driver board into the main board, and especially those on the two brackets per driver which look like they are only support for the driver - they carry the feedback line from the output of each half of the driver back to the respective inputs. Check the solder joints for these on both the main board and the driver board. If these are flaky then it plays havoc with trying to set things up (ask me how I know - even though on inspection they looked fine they weren't )

 

[ConradH]

I pulled a driver board to clean it, so those joints are good. I should probably pull the other one. All sorts of strange brown fuzz in the flux. Thanks!

edit- BTW, I use SN62 silver solder for joints between boards because the tensile strength is much higher and the joints are less likely to fail.

 

[quadklipsh]

The toroidal cant be an EI inside .because if it was so the round casing would have to be a lot bigger . The EI maybe the same as in 707xcd or the 907x.
And they are bigger.
Heck my 9500 has a monster trafo. If they were to round it up the casing would be something huge like in krells. Imho

 

[Plattensp]

Hey phonomac,
First of I would like to take my hat of to you after reading this thread. A remarkable job!
A year ago I became the proud owner of a D11 II but had to put it into storage until recently. It is now paired up with a Arcam CD-17 and Infinity Reference Six speakers.
I bought it from the original owner with the matching TU-S77X tuner, manuals and the sales brochure from 82'. He was using it regular.
Unfortunately I don't know the first thing about electronics but do like the quality reproduction of good music!
When I first powered up the volume dial had a few crackles to it but that completely dissipated after a few dozen dials. At 100% volume there is a faint hiss when you put your ear up to the speaker, at 7/8 nothing. Everything else seems to be OK.
Now here are my questions:
1) Can I do some damage if I use the amp the way it is without having it checked by a pro due to it's age?
2) If I open it up for a visual and don't see any evidence of "hot spots" on the boards, leaky caps etc. should I leave it alone? (aka if it works don't fu.. with it)
3) What is your opinion on a good speaker for this?
Thank you upfront for any help

 

[Hyperion]

When I first powered up the volume dial had a few crackles to it but that completely dissipated after a few dozen dials. At 100% volume there is a faint hiss when you put your ear up to the speaker, at 7/8 nothing. Everything else seems to be OK.

This is normal.

Now here are my questions:
1) Can I do some damage if I use the amp the way it is without having it checked by a pro due to it's age?

It should be checked over - there are many internal adjustments to ensure it is working at its best, with age many, if not all of these will have drifted.

2) If I open it up for a visual and don't see any evidence of "hot spots" on the boards, leaky caps etc. should I leave it alone? (aka if it works don't fu.. with it)

You aren't likely to 'see' anything amiss - other than the presence of glue used to secure larger components to the PCB's - this glue will look brown and 'toffee like' in appearance. Unfortunately this glue deteriorates with age and becomes corrosive, and can also become conductive - both of which are very bad for the amplifier. The only cure is to remove the glue completely which requires quite extensive work on the amplifier. This, and restoration, and dealing with the maintenance issues of this particular amplifier is generally beyond most novices, and is best left to a pro.

3) What is your opinion on a good speaker for this?

Any 'good' speakers will sound good, I own a fully reconditioned AU-D11 II and use modern 2-way floorstanders.

 

[Plattensp]

Hey John,
thanks for the advice. Always appreciated. I will start looking for a reputable repair shop in my area. Updates will follow.