Hafler DH-100 upgrade

[Feanor]

Very recently I notice a Hafler DH-100 preamp for sale here in Canada on eBay; since I had no back up preamp, I decided to bid for it. At the same time I knew that I could by an upgrade kit from another eBay seller. Once I'd got the preamp home and it tested OK, I ordered the upgrade kit from ray17760 ... here.

I didn't audition the preamp much before doing the mods, just enough to get rough idea of the sound. The upgrade kit consisted entirely of capacitors, viz. the major ones in the power supply and most in the line stage signal path; (not all, but the seller insists the originals are as good as any). Kit contents ...



The kit included desoldering wick and rosin solder, but I had my own solder sucker and silver core solder which I used instead.

The upgrade sound was basically as advertised though "dramatic" might be a slight hyperbole. Nevertheless the new sound as detailed, reasonably spacious, with a slight prominence in the low-mid bass vs. my main preamp. The highs pretty grain-free but tiny bit bright or shrill.

But lo! I figured I might have the solution for the slightly bright highs in a couple of OPA627 opamp pairs. These I had abandoned from an earlier project; they were from Gigawork, a eBay seller in China ... here.

I installed the OPA627's for a significant (but not "dramatic") smoothing of the highs. Now I have a very tolerable backup preamp! Also some fun and a total cost under $175. The modded Hafler DH-100 preamp vs. my Sonic Frontiers Line 1, (final MSRP $3500):

• Slightly warm low-mid bass, otherwise a neutral balance
• Clean, non-grainy sound
• Very good detail & resolution, close to, but not as good as the SF
• Smooth highs with the OPA627 opamps, though not as refined as the SF
• Acceptable soundstage & depth, but much inferior to the SF -- this is where the latter rules big-time.

My upgraded Hafler DH-100 ...

[Hyfi]

That is a pretty clean pc. Nice job and pics. I had one in my system years ago as a loaner from a friend. I prefered my Hafler 945 and Sound Valves 101i over the DH100 but it was in original condition and slightly beat up.

All in all, since my brother built Hafler kits on the kitchen table when I was a kid, they were quality components. David Hafler used to be right across the bridge in Pensauken NJ and my brother spent a lot of time together.

Thanks for the writeup.

[Feanor]

That is a pretty clean pc. Nice job and pics. I had one in my system years ago as a loaner from a friend. I prefered my Hafler 945 and Sound Valves 101i over the DH100 but it was in original condition and slightly beat up.

All in all, since my brother built Hafler kits on the kitchen table when I was a kid, they were quality components. David Hafler used to be right across the bridge in Pensauken NJ and my brother spent a lot of time together.

Thanks for the writeup.

Thanks for noticing and commenting, Hyfi.

I really like the spacious layout of the Hafler PCB and also the easy accessibility of their case, (top and bottom both remove, so no need to remove the board). This made it mechanically easy to upgrade, and I guess it would have made it relatively easy kit.

I never build any Hafler kits, but I did build several Dynaco kits back in the day.

By the way, I'm thinking of swapping the OPA627's for a pair of OPA2134 opamps, another well-regarded audio opamp which I also just happen to have lying around -- I will report.

[jrhymeammo]

Feanor,

DAMN that looks clean.
I wish I had your skills. When I add a pair of bypass capacitors on my Hagerman, it took me about an hour...

Nice job and a score!!!

[Feanor]

Well I did some futher tweaking (beyond the original kit) for some subtle improvement.

I replaced a pair of original capacitors in the interstage signal path with Solen polyproylenes and I did once again swap the opamps: original 5532-types => pairs of OPA627 => OPA2134. (I happened to have all the new components laying around, so I had no additional cash outlay.)

These improvements have many effected the highs and perhaps solidified the bass a bit. I found the OPA627's, relatively very expensive for opamps, were just too mellow, IMO. The Hafler is now a clean, pleasant, fairly detailed preamp though is much lower league in terms of depth and soundstage to my Sonic Frontiers.

Note to E-Stat: one of these fine days I'm going build a passive volume control using a decent quality stepped attenuator.

[Craigo87]

New guy here!

I have this same preamp and have decided to do a similar mod to the one you did. I've ordered the kit from Ray, as well as a Burr Brown OPA2134 dual Op amp (which has already arrived). Just wondering which additional caps you replaced in the interstage. Could you tell more? I've also downloaded the schematics from the Hafler website, so if you could just let me know which ones, that'd be fantastic.

Thank you,
Craig

[Feanor]

New guy here!

I have this same preamp and have decided to do a similar mod to the one you did. I've ordered the kit from Ray, as well as a Burr Brown OPA2134 dual Op amp (which has already arrived). Just wondering which additional caps you replaced in the interstage. Could you tell more? I've also downloaded the schematics from the Hafler website, so if you could just let me know which ones, that'd be fantastic.

Thank you,
Craig

Hi, Craig,

Other than the opamps, the only things I changed were the C11 & C111 capacitors that are between the stages. I replaced them with Solen Fast Caps of the same value as the originals, i.e. 1.0 uF; (they have a higher voltage rating than the 100 V specified, but that's no issue).

Ray says I doubts this replacement is really necessary but that he might try it himself. He also told me he'd try the opamps.

[E-Stat]

Note to E-Stat: one of these fine days I'm going build a passive volume control using a decent quality stepped attenuator.

Given the scope of this and other projects you've done, it would be a piece of cake! Ten years after building my first one, I'm still a happy camper.

rw

[Feanor]

Given the scope of this and other projects you've done, it would be a piece of cake! Ten years after building my first one, I'm still a happy camper.

rw

I'm still liking the idea of passives. I recently acquired a Jolida JD50A, ALPS pot-based passive which is a pretty flexible unit and sounds good. See my discussion HERE.





BTW, the Hafler is currently for sale on eBay -- nothing wrong with it, it's just redundant to my needs at the moment; see HERE.

[bobsticks]

Arthru,

être juste clair, ceci est un forum audio et tandis que nous apprécions la nouvelle entrée c'est la seconde telle signalant vous ont énuméré avec des informations sur tout mais l'acoustique.

Vous venez dangereusement près de violer notre politique de Spamming. Veuillez se rendre compte de ceci.

Nous attendons avec intérêt votre interaction dans toutes les matières liées à l'acoustique.

Beaucoup mercis,
gestion

[Mash]

?? Does Hormel know about all this free spam??

[Mash]

Awww, gee... Now we will not learn more about Mr. Oxilyworryrok's new dress:

" I was so happy once I received this dress I love the colour plus the design, very gorgeous "