Hafler DH101 preamp repair and mods? - diyAudio
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Old 29th April 2006, 06:54 PM   #1
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Default Hafler DH101 preamp repair and mods?

I've just purchased a Hafler DH101 preamp kit build. It is in decent working order, however, there is some "bleeding" of input sources. What I mean by that is that I can hear the aux and tape sources (if they are active) while listening to phono. Can anyone recomend what to look for to cure this problem? Also, i was wondering if anyone could recomend some mods. I read something about a moving coil upgrade, but i'm not sure what that is or how it would benefit me.
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Old 29th April 2006, 09:17 PM   #2
anatech is offline anatech  Canada
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Hi jarrettl,
That's a design "feature" of many older products. If there are leads from the jacks to the switch, you may have luck moving them around. Nothing will eliminate this save turning off the other sources.

-Chris
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Old 30th April 2006, 06:16 AM   #3
Leolabs is offline Leolabs  Malaysia
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Get yourself new switches and shielded wires and rewire the whole thing.
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Old 30th April 2006, 07:33 PM   #4
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Could someone maybe give me some clues as to what type of hook-up wire to use? I don't mind spending $5-$10/foot on some decent wire...and if i'm lucky, could someone maybe rattle off a some places to purchase such stuff (as wire and switches).
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Old 1st May 2006, 02:06 AM   #5
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I used a modified DH-101 for many years, it was a pretty good design.

The best thing to do with it is what I did, pull out the main pcb, slice apart the phono and line stages separately, and build them into a new case with all new controls, wire, capacitors, jacks, and regulated power supply. Of course that's a bit of a major project, but you really do have an excellent preamp when you are done.

The Audio Amateur lists mods in the Feb. 1979 and April 1980 issues. They include; changing the ground wiring to remove crosstalk and ground loops, removing the phono input selector switches by wiring directly from the phono jacks to the pcb phono inputs, removing the tone control circuitry, and correcting the phono RIAA bass response as well as some other minor circuit changes.

I strongly recommend replacing the electrolytic bypass capacitors with something better, and upgrading the resistors would help too. Replacing the power supply makes a huge difference.

I have some extremely poor photocopies from some of the AA articles as well as the original owner's manual with schematics if you need them. DH-110 as well.

Quote:
I read something about a moving coil upgrade, but i'm not sure what that is or how it would benefit me
That would be for using with a low-output moving coil type cartridge on your turntable, so that you didn't need a step-up amp or transformer.

Take care,
Doug
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Old 1st May 2006, 07:05 AM   #6
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Thanks for the info! Tinkering with this preamp will actually be my first ever amp/preamp project. I thought it might be a good starting point since my last preamp just fizzled out because it needs a lot of work. (HK Citation 17...why am I not fixing it?...) Anyway, the DH101 came with the original manual and schematics, but if itís not too much trouble, those AA articles it would be greatly appreciated. In fact, ANY other info would be greatly appreciated.

-Jarrett
jarrett23@comcast.net
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Old 1st May 2006, 12:22 PM   #7
Zen Mod is offline Zen Mod  Serbia
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your mail server is hysteric,I send you those articles,but mail bounced.....("send unblocking request with your mail server IP addy....")
any other mail addy?
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Old 1st May 2006, 02:15 PM   #8
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Quote:
Originally posted by jarrettl
Could someone maybe give me some clues as to what type of hook-up wire to use? I don't mind spending $5-$10/foot on some decent wire...and if i'm lucky, could someone maybe rattle off a some places to purchase such stuff (as wire and switches).
I use CAT5 wire for hookup. Inexpensive, high quality and color-coded.

The DH101 was quite well regarded in its day.

http://www.borbelyaudio.com/special_articles.asp
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Old 1st May 2006, 07:58 PM   #9
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-Choky
I'm not sure why your email got blocked, but thanks for trying. The Peasant sent the articles, so i think that will do. Thanks for the help. Hopefully this gives me something to start with, and other (numerous) questions can be addressed later.
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Old 10th May 2006, 09:25 AM   #10
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One of the articles mentions a grounding modification (John Philpot TAA 2/79) to reduce noise and crosstalk. Does anyone know the specifics of this mod, or have any suggestions.
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