Newbie Troubleshooting Question

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.

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.

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).

www.avahifi.com/index.htm

Well I opened the preamp up, inspected what I could, moved wiggled and jiggled and the hum dropped about 90% which I can live with for now. I hooked up the Kenwood preamp I paid $12 for the other day thinking the sound difference wasn't as vast as I had imagined and could give the Kenwood a second chance. Guess what? I was wrong! It's amazing how much difference in sound there is between the two. I swear it's like night and day. The Kenwood is quieter at low volumes but the sound difference is drastically worse than the Hafler. It's hard for me to understand that there is as much difference in sound quality as there is because I'm certain that the Hafler is not in 100% working order. Maybe I should send the Hafler and have it completely rebuilt. Are newer designs markedly better sounding than a 23 year old Hafler that is in good working order. Maybe I should just plunk down the cash for a new preamp and forget about worrying about worn out capacitors etc. Hmmm....

P.S. Free Download of Hafler Manuals Here:
http://www.hafler.com/techsupport/index.asp?ID=3

Thanks for the advice Rodman. By the way I used to live in Orlando before I moved to the Dallas area. I had seen that kit and another on that website. Do you think this kit would eliminate the hiss and the hum? I'm thinking the hum is from a loose ground related to the right channel, but what I know about electronic circuitry wouldn't fill a thimble. Gosh I hate being so stupid about something that I know is ultimately very simple. I would probably end up soldering one of those parts in backwards and frying my preamp, amp and setting the house on fire. There's an electronic shop down the way from me... Maybe I could get one of those guys to put those pieces in for me. I don't think it would take more than about 20 minutes to do.

I actually have the assembly/owner's manual I found somewhere on the internet. Anybody wanting a copy can send me a message and I'll email you a copy.

The capacitors in the unit are past the 20 year old mark by a very comfortable margin(going on 30). No doubt- Ripe for replacement. I'd start with the power supply caps. Were you provided with a manual when you bought the unit? If not- Buy one on eBay. That will give you a complete list of parts, and the full construction instructions that originally came with the piece. The circuit board was pre-assembled, but the parts layout, and schematic are included in the manual. Then too- A few people offered power upgraded power supplies for the 101. Some are still available. Here's something on eBay that may interest you: (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260359603612&ssPageName=MERCOSI_VI_ROSI_PR4_PCN_BIX&refitem=260350575646&itemcount=4&refwidgetloc=closed_view_item&refwidgettype=osi_widget&_trksid=p284.m185&_trkparms=algo%3DSI%26its%3DI%26itu%3DUCI%26otn%3D4%26ps%3D42) BTW: The S/N ratio was high enough that no hiss should be audible, especially with the volume turned down. I was the Hafler dealer in Orlando/Winter Park, FL for a few years, and used the 101(modded) in my demo system back in the day(early 80's). No noise at all would have tolerated in my audition room. RE: The power supply fuse- That's just what some slo-blo fuses look like. RE: Getting electrocuted by a cap- The voltages in a SS pre-amp are too small to worry about. If you can solder, you can handle the DH-101 upgrade. It would be a great way to get involved in the DIY electronics/modding hobby(It's highly addictive).

OK... So I got a $12 Kenwood preamp (no kidding) and even though it was more modern and quiet, the sound was not as good as the Hafler DH-101. Don't ask me to explain it but the Hafler just had a better sound. At any rate I think I want to keep the Hafler but it has a hum in the right channel that you can hear at low volume levels which is where I do most of my listening. It is only in the right channel. Also there is some hiss with the volume all the way down. Additionally the sound will not turn all the way down like maybe a bad pot or something. The balance was off which is part of the volume control but loosening a hex bolt and repositioning the knob took care of that problem. I have found some places on the internet that will go through the unit for $150 to $300 but I hate to pay somebody that much just to replace a resistor or capacitor.

My question... Does anybody have any suggestions on what I might look for or do to eliminate this problem? Is this a common problem with an easy fix? I could probably replace a resistor or a wire but even that would be at the far limits of my expertise. I always worry about getting electrocuted by a capacitor or something. Now I did open the case up the other day just to see if there was something obvious like a loose wire or something but didn't see anything. The unit did have a glass type fuse by the power supply which looked like it had a resistor inside of it. Never seen that before. So if any of you have any suggestions I would greatly appreciate it. I already tried the previously mentioned suggestions. (Thanks RWWEAR & DGAYLIN)
Thanks in advance for any help or advice you might have.

The saga continues
HERE

You bet, but note it could be as simple as the interconnect cable. Try replacing the one that seems to be indicated based on your swapping.

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.

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.

Swap left and right inputs on the amp. If the hum stays in the right channel, it's the amp.

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