Humming asl 2004dt wave pre amp - diyAudio
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Old 17th February 2009, 11:56 AM   #1
webby is offline webby  United Kingdom
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Unhappy Humming asl 2004dt wave pre amp

Hi all,
Can you guys help please. I have a pair of wave 8 amps and matching wave pre amp. The wave amps do hum, but with a passive pre it is exceptable. With the wave pre its too much and is really annoying. The passive pre is much a cleaner sound, but looses dynamics from the phono stage. I would like to try and remove the humming from the wave pre and get it back in the system.
The story so far;
I swapped the valves for better quality
swapped c2,4,7 & 8 for auricaps
Better diodes in the PSU
ALPS 100k vol pot
The sound quality did improve, but still spoilt by too much noise.
Hum was the same as before.
I have stripped the pre down and my plan is to rewire with better signal wire and follow advice for grounding. can you guys explain the correct grounding method and describe how to wire this pre for best results?
In the picture you can see the yellow earth is connected to the chassis but the signal ground is a different point (screw near PSU pcb) and this has ground cable back to this point from the rca ground and wrapped around signal wires. Is this correct, or is there a best practice with Pre amps?
The signal wires are single core with copper shielding, the shield is connected to the rca grounds only at the rca end and the vol pot grounds, which in turn connect to the chassis ground point.
Confused, i am!!!
I have taken some photos to help.
Does anyone have a circuit diagram for this pre, i cant find one?
Any advice you can offer
Thanks
ian
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Old 17th February 2009, 11:57 AM   #2
webby is offline webby  United Kingdom
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Some more photos
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Old 17th February 2009, 12:02 PM   #3
webby is offline webby  United Kingdom
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Old 18th February 2009, 06:50 AM   #4
pchw is offline pchw  United States
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This http://www.tubehifi.com/Circuit/C_204.JPG ?
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Old 18th February 2009, 03:06 PM   #5
webby is offline webby  United Kingdom
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Hi all,
Thanks phcw, is looks like the right diagram, but some components have different values. Do you have experience of this pre, do i need to just buy a better pre?
i am just guessing though.
Cheers

Ian
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Old 18th February 2009, 04:17 PM   #6
pchw is offline pchw  United States
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Hi Ian,

I haven't modified this pre. Mine has a imbalance of the channels and a little hum as well. FWIW, John Broskie had a write up on how to fix up all wrongs of this preamp which was the motivation of his Aikido. Unfortunately, there is no search on his site, and it will need some efforts to dig it out. I have a print out of that, let see I can find it and and give you the article number.

Edit: here is the link to the article:
http://www.tubecad.com/april_may2001/page28.html
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Old 19th February 2009, 05:54 PM   #7
webby is offline webby  United Kingdom
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Hi Fred, Thanks so much for the link. It has convinced me to just buy a new preamp, probably this kit;
http://wduk.worldomain.net/acatalog/info_WDPRE3.html

I will try a few things out in the meantime, but I can see cables aren't going to cure design problems.
Many thanks
Ian
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Old 20th February 2009, 08:21 AM   #8
pchw is offline pchw  United States
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Hi Ian,

I bought my AQ-2004DT used. It came with 3 x 12AU7, and I wondered why until I saw JB's article .......
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