Modding Hafler Amps?

Hi all. I've been away from the boards here for about a year, but I've got the audio bug...again.

The power switch on my Hafler DH-500 broke last month, giving me the lame excuse I needed to fork out the bucks to have it modded. An internet search found not only John Hillig (Musical Concepts), who I already knew about, but also Van Alstine. Has anyone compared the mods to recommend which company I should use to mod the amp? I'm not looking for all the exotic stuff- I just want the most bang for my buck.

Then the next problem: I also have a McCormack .5 amp (Rev A) that I love with my McCormack RLD-1. I could do a number of things - bi amp using both amps (Hafler for bass and McCormack for mid/high), toss the .5 (which I'd hate to do) and use either the Hafler by itself or purchase another used Hafler 500 and have it modded as well for biamping.

I can't really assess power needs right now, as I won't upgrade to speakers that really need the Hafler's power for another year, and I have no idea what speakers I'll buy. I'm thinking if I have more power than I need, no problem. Some day I'll probably want/need all that power, even if not in the near future.

Sorry this is so long, but thanks in advance for your advice!

Van Alstine probably has a greater degree of design experience although he is just learning about the differences in passive parts ( caps, resistors, etc... ). Hillig has probably modified WAY more gear but has more experience with the various sonic attributes of the passive parts that one would normally work with when modding gear. Only thing is, John may not have the technical design prowess that Frank has. So long as one is simply doing direct parts substitutions i.e. upgrading caps, etc.. Hillig may be the way to go. Then again and in your specific case, Van Alstine used to work directly with David Hafler ( if i remember correctly ) and may have greater insight into the actual design of these amps. Obviously, these are just my personal thoughts and ramblings, so take them for what they are worth. Sean
Pooge. If you are a DIY type, you may want to get ahold of the POOGE articles from Audio Amateur.
let me transform your DH500, 200, 220 etc. you will not be disappointed.
I can send you a modified one to listen too and you can
decide for yourself. There are many levels to mod too.

My major mod takes you way beyond pooging and passive part
replacement. I can explain all the mods if you care to
listen. The major requirement is a solid running amp
to start with!!! I can also repair if necessary.

Please feel free to ask questions I will try to explain.

I guess i was "thinking inside the box" on that one. I agree with the others. That is, there are GOBS of info available about modifying these amps. Much of what either of these guys would do and charge a high hourly labor rate, you can do yourself. That is, it is simply a matter of unsoldering one part and replacing and resoldering with another higher grade part. That part could be capacitors, resistors, wiring, etc... There's nothing hard about doing something like this, but it can seem VERY scary at first. Just take your time and make notes along the way. Having a schematic and then looking at how the schematic equates to the actual parts layout on the board can help you with signal flow and what parts play key roles. Sean
Something I should have mentioned in my original post. If they are not soldered in, VERY CAREFULLY remove each mosfet and clean the pins. Of all the things I did to improve the sound of my old DH 200, I don't think anything I did made as big a difference. I got that advice from some post on a Hafler user group site. P.S. I was satisfied with my Hafler until I got an original Son of Ampzilla. The Ampzilla is better in everyway.
Hi Aggielaw -

The previous responses here have provided a lot of good information about upgrading your Hafler amp, but have not addressed the question of bi-amping with your DNA-0.5 Rev A. Whether this can be made to work well (or at all) depends on what you have in mind. If you are thinking of "passive bi-amlification" (using the speaker's own internal crossover networks), this works best with a matched pair of amps. It can be made to work with 2 different amps, but this is far more difficult and rarely works well unless the crossover point is very low - around 100Hz. Even then you will need some way to independently adjust the input level to the amp with higher sensitivity - almost certainly the DNA-0.5 in this instance.

Some of the problems I have mentioned can be overcome by using an adjustable electronic crossover, but this introduces a whole new set of issues, some of which are technically difficult.

So, the "mix-and-match" approach to bi-amping is rather problematic, in my estimation. On the other hand, it can work very well indeed with a matched amplifier pair. You may want to consider moving in this direction in the long run. Another DNA-0.5 or Hafler can be arranged to match what you have now, and I believe this will give you the most flexibility and best performance. In addition, the DNA amps can be converted to true balance monoblock operation, delivering over 400 Watts per into 8 ohms. That should satisfy your taste for more power ;-)

Please give me a call if you would like to go over the various options.

Happy holidays,

Steve McCormack
Great info - thanks all!

Short term I will mod the Hafler. Then in January '06 when I get my bonus from Uncle Sam I'll use some of that to match a pair of your DNA amps and have my RLD-1 upgraded, Steve. That'll probably be they last sum of money I spend on amps and preamps...ever. :)

Happy holidays, all!
I had John Hillig mod my DH-500, did the dual mono upgrade and signature level mods plus a few other tweaks. It was a pricey leap in the dark, based on stuff I read on this forum and elsewhere online. I have to say I am very impressed and very happy with the sound. I have listened to the same CD on some really pricey systems (McIntosh, Krell, etc.) and to my ear my system sounds a good or better. Huge sound stage and depth, a really "live" sound, great bass and clarity, very musical. Don't know about Van A, but to correct an earlier post I believe Hillig worked with Hafler, and his redesigned circuit boards are much more than a passive swap-out of parts. In any case, whether you go Van A or JH, you are buying the guy's ear... I only know JH's and I like it - a lot! That's my two cents.
If you're going to mod your DH-500 yourself, I highly recommend The POOGE Chronicles. They outline modding in general, and the DH-200 specifically, along with a number of other pieces. The principles they use could be applied to anything you were modding, and cover both the theory and the implementation. I bought my copy here:

Well worth the price.

Hi guys,
I am new to this site, but I wanted to comment on Hafler products modded by John Hillig at Musical Concepts in St Louis.
I am a "Golden Age" audio dinosar that goes way back to the Eicos, Pilots and Dynaco.I have had a lot of "hi end" stuff over the years such as Dynaco,GAS,ARC,Mac and I thought I have heard it all, until I purchased a Hafler 500 modded by John Hillig.I am hearing things that I have NEVER heard before and I didn't have to spend a fortune.The depth, width and detail of the soundstage is so much more than I expected.I am extremely impressed, especially considering the investment.Well worth it!

Yes, there are more exotic, and expensive amps out there that may sound better but look at what you have to pay.
I read somewhere that Hillig had been an engineer for the Hafler co. but not sure if it is true.