Preamp Buzz/Hum

[Tony Reed]

I'm working on a Hafler 101 preamp that has a buzz/hum through both channels. It happens with any amplifer and it's variable with the volume on the amplifer. In other words, if I keep the volume on the amp (Super T) low, it's not as noticable as when the volume is turned up on the amp to a higher level. I've grounded the unit. Anyone out there have any ideas as to where to start. Anyone out there work on these things?

Thanks,

Tony

[thebes]

I've got one of these and they were mostly kit built so over time one of the wires or solders joints might have come loose or failed.

First, though, if you already haven't, check the obvious. Remove and reconnect the speaker wires, same with the rca's, try to seperate the power cords from the everything else, reverse the preamp wall plug. If you're using Aux as your out try "Tuner". Switch out the cd player if you have a spare or a dvd player.

Nothing doing? Disconnect it and wait a day to let that spare electricity go wherever it goes. Then open it up and take a real close look inside especially at those small wires around the selector gizmo. I had 3 of those come loose on mine while doing a recap.

From there it get's more complicated. I'll see if can track down the link to an online manual. It's got great pictures of the innards.

[Guest " "]

Is the pre-amp a two prong cord?

[thebes]

Is the pre-amp a two prong cord?

Yes

[thebes]

Is the pre-amp a two prong cord?

double

[thebes]

Here's the manual:

http://www.hafler.com/techsupport/pdf/DH-101_preamp_man.pdf

[Tony Reed]

Thanks Guys... I'll poke around inside this weekend and let you know what I find.

Tony

[Tony Reed]

I opened up the Hafler... not a wire out of place. Could the power supply be going bad?

Thanks,

Tony

[NOSValves]

I'd start by replacing all the Electrolytes including the none polarized. The manual has a complete list but compared the pysical sizes before you order replacements. It should be pretty easy to accomplish. I bet one if not all are the culprits.

Craig

[fini]

'd start by replacing all the Electrolytes including the none polarized.

Yeah, drink a lot of Gatorade. ;^)

As an aside, I finally got the pCats fired up last night. No critical listening: We had a party with about 40 people! I think I have a tube gone microphonic in the BBX. I'll do a little exploratory surgery later today...

[Guest " "]

If replacing the caps do not work..try replacing the speaker wires....no I'm just kidding....the buzz vs the hum question below is a good point.

Also, it's not clear how long it has been since the unit was in use. If your the first person to turn this thing on in a few years....there's a proceedure to re-form the caps that you may need to look into. If reforming and leaving on for a while reduces the noise...and turning it back off and later turning it back on brings the noise back...agree with the cap problem angle.

[Tony Reed]

I guess it's more of a buzz. It sounds like it's coming mainly from the mids to me. This thing has been in storage for awhile now. I've tried this preamp at 3 different locations... same buzz. Leaving it on for awhile or turning it off doesn't seem to affect it in any way. I'm stumpted.

Thanks,

Tony

[Tony Reed]

Yes, the buzz does increase when you turn up the volume on the amp. I can only run the Super T at about 1/4 volume before it becomes "noisy". On amps without a volume (amp running wide open), the buzz is unbearable. No other symptoms.

Thanks,

Tony

[Tony Reed]

The volume on the preamp does not affect the buzz level. In other words, if the amp is all the way up, the buzz level is unaffected by the volume on the preamp.

Thanks,

Tony

[NOSValves]

Mark,

Realize this is an SS preamp and most likely some of these electrolytics are in the signal path (most likely the none polarized types). Hard to say which ones for sure so without a schematic, so I say replace them all and be done with it. Besides I've seen electrolytic failure cause all kind of noises over the years beyond humming especially in later filter stages in the power supply. Many times if it just shorts out (open) and becomes total disconnected down the chain in the power supply it can cause buzzing more then it will hum since most of the ripple is already filtered out early in the stages.

Craig

[LarryC]

http://cgi.ebay.com/Hafler-DH-101-Preamplifier-MINT-RACK-MOUNT-RARE_W0QQitemZ110200044778QQihZ001QQcategoryZ12050QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[thebes]

No doubt that can be true. I wonder if this was ever used SUCCESSFULLY with the T-amp in the past? I bet not. These amps have some peculiar grounding I found out.

It might be cheaper (like 50 bucks) to just get another one:

http://cgi.ebay.com/Hafler-DH-101-Preamplifier-MINT-RACK-MOUNT-RARE_W0QQitemZ110200044778QQihZ001QQcategoryZ12050QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Or, try using it with a different amp - - just to see.

They usually go for about $100. For about $60 you can recap them and have some fun. These were sold primarily as kits so they are easy to work on.

Thanks to some detailed suggestions and help from MikeBSe I recapped mine and noticed quite a difference. He had me pull a couple of tantalum caps and replace them with those small round orange thinies, parrallel some 1uf's with the power supply cans and swap out the coupling caps and some others parts, 22 pieces in total. For SS it sounds quite nice, and after the rebuild almost as good as my unrestored Marantz 7T. Musical, detailed and tight bass.

Here's a pic. The little orange thingies are between the the big cans at left, the four small blue cans to the right of them were also replaced, and the power supply changes are somewhat visible at the upper right. I used Dayton caps but made a mistake in ordering and used 1% tolerance caps. The 5%'s will be fine and cost less.

The great thing is that using the manual I posted earlier in this thread (take a look Craig and Mark) makes this a snap, especially since there are detailed photgraphs and a parts list.

I'd be happy to work up a parts list and walk you through this. Just take a couple of pictures before you start because you can count one or two of those small wires coming loose and it's nice to know where they should go.

Stil some things to try. Try different outs on the back, move all knobs back and forth a bunch of times, and push the buttons in an out several times. Also try the "Tone" button both off an on because it's a bypass for the tone controls.

Here's how I rate the skill levels involved, one being the highest.

1. Craig building a VRD and Mark building a Blueberry.

2. MikeBSE building a SET amp.

3. Dean building a crossover

4. A caveman hitting an amplifier with a club

5. Burning Down the House Thebes recapping a Halfer

[Tony Reed]

No doubt that can be true. I wonder if this was ever used SUCCESSFULLY with the T-amp in the past? I bet not. These amps have some peculiar grounding I found out.

It might be cheaper (like 50 bucks) to just get another one:

http://cgi.ebay.com/Hafler-DH-101-Preamplifier-MINT-RACK-MOUNT-RARE_W0QQitemZ110200044778QQihZ001QQcategoryZ12050QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Or, try using it with a different amp - - just to see.

I tried it with other amps, as well... same problem. I thought about buying another 101, but I could end up with 2 preamps with the same or similar problems... you never know what you'll get.

Thanks,

Tony

[thebes]

Well geez Tony if you are just going to toss it back into the closet send it to me and I'll see if I can fix it. I've still got the old caps here so I can test and substitute, and see if I can get it up and running.

[Tony Reed]

Well geez Tony if you are just going to toss it back into the closet send it to me and I'll see if I can fix it. I've still got the old caps here so I can test and substitute, and see if I can get it up and running.

I might just take you up on that. I'd be more than happy to pay for parts and labor. I just need someone who knows something about this sort of thing.

Thanks,

Tony