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Old 13th August 2015, 06:39 PM   #1
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Default Hafler DH-110 problem

A couple years ago, a guy who worked for me gave me a Hafler DH-220 power amp and a DH-110 pre-amp. Iím just getting around to trying them out. Havenít tried the power amp yet, but the pre-amp seems to have a problem. The right output is about half as loud as the left, and sounds subdued, or muted. I tried swapping the inputs from the source and the right channel is still the problem. I tried swapping the outputs to the power amp and the problem moves to the left speaker. I tried this with the source in both AUX and Tuner modes. Any ideas?

I don't know much about electronics, I'd just like this thing to work.

Appreciate any help I can get.

Thanks,

grym
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Old 13th August 2015, 06:48 PM   #2
anatech is offline anatech  Canada
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Hi grym,
That is a really nice sounding combination. It is well worth keeping in top shape. Unless you are an audio tech, I would recommend you visit a good one. There are things the amplifier needs to have done, and the same goes for the preamp.

Most DIY attempts end with wrecked PC boards and equipment that is rough even repaired. In addition to capacitors, there are transistors that need replacing with matched pairs. The difference in sound quality is worth while. This is detail work that only good, professional audio techs do, and advanced hobbyists. It can be difficult to sort them out from the hackers because everyone thinks they are "great"!

Stay away from shops that specialize in modifications. They are the most harmful breed that destroys more equipment every year than any other cause.

-Chris
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Old 13th August 2015, 06:50 PM   #3
rayma is offline rayma  United States
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Quote:
Originally Posted by grymster View Post
DH-110 pre-amp. The right output is about half as loud as the left, and sounds subdued, or muted.
Probably it's a bad part that will require an electronics tech to find and fix.
Any local friends that can look at it?
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Old 13th August 2015, 07:07 PM   #4
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Sounds like I can either pay a bunch to have someone fix this thing, or wreck it by attempting the repairs myself! .... or shove it back into the basement and worry about it some other day.

I did just fire up the 220 and so far so good! I just have it on low volume now, letting it run. I'll crank it up later when Mrs. Grymster goes shopping, see if my tired old ears can distinguish the sound from the Onkyo amp I have in that system.
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Old 13th August 2015, 07:38 PM   #5
anatech is offline anatech  Canada
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Hi grym,
You haven't heard anything yet. Once gone over, your Hafler equipment will be a joy to listen to. I have serviced many over the years, and each of my customers have been extremely happy with both the price and the equipment.

It's not cheap to have a good job done, but cheaper than having a bad job done. These will last a very, very long time. Once you hear these things in fighting form, you will understand. Right now, they aren't anything to write home about. All you need is an honest tech who services audio only. I hope you can find one close to where you live.

-Chris
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Old 13th August 2015, 08:14 PM   #6
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Thanks Chris!
There doesn't seem to be much locally. Seems most people I know these days have some 5.1 or 7.1 home theater system and don't much care about old school, two channel stuff. And if something breaks, they seem to just toss it and go buy another one.

There is a place in Alameda (about 50 miles from me). Not sure that I'll want to mess around with this at this time, but at least you've kept me from digging into the preamp with my less than stellar electronics skills! I suppose if I do take it to someone I could ask what they recommend, then run that by you folks before committing?

grym
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Old 13th August 2015, 08:43 PM   #7
anatech is offline anatech  Canada
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Hi grym,
By all means, we would love to help. Too bad I don't live down there. I actually enjoy rebuilding these little amplifiers, and the preamp is the same for me.

The best techs these days are probably working from home, like myself now. They will be in their 50's (the young ones), and have a pretty nice bench. I find that the guys who know the most are generally pretty helpful people. Many are members here, so possibly one may catch your thread and respond. The cranky old guys are a minority, but they exist too.

-Chris
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Old 13th August 2015, 09:37 PM   #8
amp_guy is offline amp_guy  United States
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So first thing to do with the 110 is to get a can of Caig laboratories "deoxIT" and clean all the switches. As for the differing levels problem, there is a JFET in each channel that performs a de thumping mute function on power up. you need to replace both of them. When I repaired these under warranty this was the most common problem ( actually about the only problem) I have simply just removed the JFETS in a number of 110's and have not had any thumping issues at all. Due to the age of these units a replacement of power supply caps is in order here with larger uf values preferred . The 110 has electrolytic output coupling caps bypassed with a small film type a polypropylene cap of your prefferred flavor here makes a dramatic upgrade , you will need to mount them offboard as there is not much room.
As for the DH220 there is a wealth of upgades and advice out there ( and in diyaudio.com) The 110 got some bad press in the beginning as being coarse sounding and the switches are an issue - way too many contacts in the signal path. but with very little work they can be great! have fun!
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Old 14th August 2015, 02:54 AM   #9
anatech is offline anatech  Canada
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Hi amp_guy,
What are your thoughts about replacing the muting JFets with relay contacts to signal ground?

-Chris
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Old 14th August 2015, 05:06 PM   #10
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Thanks amp_guy!

As I said before, I donít know a whole bunch about electronics (I was a mechanical manufacturing guy before I retired), but I do have some experience. A couple years ago, I almost completed a tube amp from a kit. Was actually two mono amps from S5. Iíve also soldered a number of other kits together (little amplifies and power supplies and such), and built a pair of Overnight Sensation speakers. We put the house on the market before I finished the tube amp, and while the speakers work great, I didn't get to finishing the boxes, so all that stuff is still packed away in the basement.

Replacing a couple of JFETs sounds like something I could do though. My problem will be identifying the components that I need to replace. For instance, the muting JFETs you mentioned are not completely obvious to me. The ďcomponent valuesĒ list in the 110 manual lists 15 transistors, but only one is designated a FET (J112).
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