2. amps-preamps
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Newbie Troubleshooting Question


I am new to using a separate amp and preamp so I apologize in advance if this question has an obvious answer. I recently purchased an ADCOM GFA-555 amp and a Hafler DH-101 preamp. Both are older units and work but... When the volume is turned all the way down, there is a slight hum in the right speaker that I can hear up to about 10 feet away but the left channel seems fine. There is also a very small amount of hiss coming from both speakers if you hold your ear within a foot of the speaker and the volume is all the way down. Using the balance control on the preamp to cut off the right or left channel does not make the hum go away. I read a little about ground loops and tried inverting the plug on the preamp and even moving it to a different outlet but it didn't seem to make any difference. I also tried switching cables from/to the amp/preamp. I also tried using a different inputs on the preamp. I did not try moving/switching speaker wires/channels.

MY QUESTION.....
Is there a simple method for me to determine whether the problem is in the amp or in the preamp? I'm hoping it's the preamp because I don't have much invested in it and can probably still get my money back on it.

Any suggestions will be greatly appreciated.

One other very minor issue which I'm pretty sure is the preamp. When you turn the volume all the way down the music is still audible. Not in a bleeding or feedback kind of way but just like the volume POT is not adjusted right. Again this is a minor issue I can live with but if it is a simple, idiot proof adjustment, I might be tempted to make it.

Thanks again for any input...
grundig
dgaylin
255 posts
 
The hiss sounds perfectly normal. The hum does not. A few suggestions:

- plug all equipment into the same outlet (using a decent power strip), assuming this won't overload the circuit.

- try plugging interconnects into a different channel on the pre-amp.

- try some better (shielded) interconnects, or better yet, switch to XLR (balanced) interconnects if the equipment has balanced inputs/outputs.

- try (only for a short time) using a cheater plug on the outlet to see if it is a ground loop

- make sure power cords and interconnects are separated and not crossing one another

- try getting a decent inexpensive power conditioner
rwwear
2,873 posts
 
Swap left and right inputs on the amp. If the hum stays in the right channel, it's the amp.
dgaylin
255 posts
 
Yes, absolutely what Rwwear said. I meant to question you if the hum is really coming out of one speaker (make sure you don't hear it in the other one -- even if a bit softer). If it is only coming out of the one speaker, then the problem could be an interconnect cable and not the amp, but if you do the swap and the hum stays in the right channel (with no problem on the left) you've got amp issues, that should sort that out pretty quickly.
grundig OP
8 posts
 
Rwwear and Dgaylin,

THANK YOU! for your responses. I tried the easiest thing first (swapping the left and right inputs on the amp). The hum moved from the right speaker to the left speaker so I guess that means the preamp has an issue.

I'll get it back to the person I bought it from. It seems like a nice preamp. If I knew about circuitry and things I would probably try and track down the issues because I only paid about $65 dollars for it but if it doesn't work right, it's not a bargain for me.

THANK SO MUCH for your helpful responses.
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