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
rodman99999
6,132 posts
 
If you enjoy the DH-101: Find a DH-110 on eBay. It was more transparent than the 101, and(being somewhat newer) you'll have some time before the caps start to show their age. Here's one with Hafler's MC phono head-amp built in already too: (http://cgi.ebay.com/Hafler-DH-110-Pre-amp-Preamplifier-Moving-coil-Phono_W0QQitemZ140300566034QQihZ004QQcategoryZ12050QQssPageNameZWDVWQQrdZ1QQcmdZViewItem) Like the 101: There are many upgrade paths offered for the 110(perhaps even more).
grundig OP
8 posts
 
Thanks for the suggestions again Rodman and Rwwear. Since I fiddled with the inside of the unit, it seems like all the hum is now gone. Most likely something was just loose. This was not a true fix but let's see how long it lasts. The only remaining problems the unit has is that the volume will turn down most of the way but not all the way. There is still some hiss with the volume off and no sound being input through the preamp. I contacted
http://www.angelfire.com/art2/stereorepair117/highend.htm
to see what they could do to the unit and they responded with:
"We replace all electrolytic caps with upgrade parts and change the power rectifiers to HEXFRED type. The cost is 175.00 and includes normal cleaning of all controls and switches."
I don't know anything about these guys and wonder how these modifications might change the Hafler's sound. The Hafler already sounds better than I can imagine. Could it really sound any better? Maybe I better leave well enough alone.

I may keep my eyes open for the Hafler DH-110. Again, I'm not sure it could sound any better that the 101. If it did, my brain would not be able to handle it and would probably overload. It's not hard to overload two brain cells. ;)
Thanks again for your help and suggestions.
rodman99999
6,132 posts
 
You can upgrade to CREE Silicon Carbide Schottky Diodes(better than HexFREDs) yourself, and install the previously suggested capacitor kit off eBay for about $70.00 total(plus your labor). If you can replace a resistor(like you said before), you can do the upgrade. (http://www.partsconnexion.com/catalog/semiconductors.html) It would do wonders for the sound of the Hafler, and your confidence.
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