Hi guys,
I was wondering if you guys could help me out:
Recently I picked up a small lot of Dual turntables that needed fixing up.
Two of those came with the HS39 plinth with built in amplifier.
One of them is busted up pretty bad but the other one looks mint and worked after some small fixes. ( they all have a cap that blows up after ±30 years)
Now my problem is the following: Although the amp works fine, it buzzed pretty loudly when playing.
It's pretty noticeable through the speakers.
Buzzing goes up with volume. Also, when I touch the volume knob, I can hear some changes in the some as if I'm grounding the amp by touching it. The noise stays, though. It's not a 60Hz or 120Hz hum, I compared the sound with some tutorial on PS Audio's site. Noise stays the same with TT attached or without.
So far I've checked all ground connections and they all check out.
Major electrolythic caps have also been replaced, with no improvement.
I know this isn't a very good amp to begin with, but I can't imagine this is what it would have sounded like when new.
I'd like to add a simple preamp to the amp so I can use MM cartidges in the TT (Dual 1215), but I'd rather it didn't make so much noise to start with. I really like the look and it would make a great compact setup for my bedroom.
Any ideas on what could be causing this? Maybe a failing transistor? Something about the transformer? I have the SM and schematics.
All help is appreciated.
EDIT:
There appears to be 85VAC running from chassis ground to earth ground.. not good.
Any idea what could cause this?
I was wondering if you guys could help me out:
Recently I picked up a small lot of Dual turntables that needed fixing up.
Two of those came with the HS39 plinth with built in amplifier.
One of them is busted up pretty bad but the other one looks mint and worked after some small fixes. ( they all have a cap that blows up after ±30 years)
Now my problem is the following: Although the amp works fine, it buzzed pretty loudly when playing.
It's pretty noticeable through the speakers.
Buzzing goes up with volume. Also, when I touch the volume knob, I can hear some changes in the some as if I'm grounding the amp by touching it. The noise stays, though. It's not a 60Hz or 120Hz hum, I compared the sound with some tutorial on PS Audio's site. Noise stays the same with TT attached or without.
So far I've checked all ground connections and they all check out.
Major electrolythic caps have also been replaced, with no improvement.
I know this isn't a very good amp to begin with, but I can't imagine this is what it would have sounded like when new.
I'd like to add a simple preamp to the amp so I can use MM cartidges in the TT (Dual 1215), but I'd rather it didn't make so much noise to start with. I really like the look and it would make a great compact setup for my bedroom.
Any ideas on what could be causing this? Maybe a failing transistor? Something about the transformer? I have the SM and schematics.
All help is appreciated.
EDIT:
There appears to be 85VAC running from chassis ground to earth ground.. not good.
Any idea what could cause this?
Last edited:
