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Phono section on Hafler DH-101 - Tweaking?

willyrover

willyrover

Super Member
A while ago I bought a Hafler DH-101 preamp and a DH-200 amp. I've done some tweaking on the amp. Capacitors, binding posts, phono jacks, improved grounding, etc.

Now I would like to do some work on the preamp. The thing that is bugging me is that the phono section seems to be lacking gain. I am using a Shure M97xe cartridge. On CD source, the volume control is at about 1/4 and it's loud. On Phono, the volume needs to be on 1/2 to be loud enough and some records even higher.

I am planning to recap the phono board. Could this improve gain? Also, Hafler used a Tantalum capacitor on the input to the phono board. I thought Tantalum was not good for audio...or am I wrong.

Any suggestions, best tweaks for the buck, would be appreciated.
 
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Recap could help the gain but maybe not. Still worth the effort as I think you will hear a difference.
Tantalum used to be considered good stuff but today a lot of folks are not keen on it.
Try some non-polar poly caps. Daytons are pretty good and cheap but there are also others.
 
Changing the caps won't change the gain - the circuit values for the caps and more importantly the resistors determine the gain. You're not far off, CDPs always seem to have higher output.

I upgraded my 101 years ago and the best improvement was to replace all the resistors with metal film equivalents. Unit got very quiet and was spooky black where the music popped in - very startling.

Next easy steps are replace the PS diodes with shottkeys and replace the before and after caps of the regulator with newer ones.

lastly, replace the caps. Here you'll have a problem with the larger replacements - where to put them. electrolytics and tantalums are very small compared to film types.

And if you still have the energy, replace the RCAs with better quality ones.

have fun
Bob
 
What have been peoples' experience with electrolytic capacitors in Hafler preamps? Have they held up well or do they generally need replacing by now? I'd be interested because I own a DH-100 that seems to work with no problems, but if I can improve it relatively simply, I will.
 
shocley said:
What have been peoples' experience with electrolytic capacitors in Hafler preamps? Have they held up well or do they generally need replacing by now? I'd be interested because I own a DH-100 that seems to work with no problems, but if I can improve it relatively simply, I will.
Click to expand...

Ooooh, I did a heavy-duty rebuild/mod on a DH-100. Easy to do, mostly cheap!

I'll add details later, maybe in another thread. Then again, I also have DH-101 sitting here I could look through to contribute a bit on this thread.
 
A couple of things:

- There were quite a few articles on the Hafler gear in Audio Amateur (now AudioXpress) commonly known as the POOGE articles. I _think_ that the Hafler preamp was addressed in a couple of them. I think back issues are still available. Might also want to check with Old Colony Labs as they reissued many of those articles in book form.

- Also, contact John Hillig at Musical Concepts. I used many of his parts to update a Hafler DH-110 about 15 years ago or so. He's got simple transistor replacements all the way to a full gut-the-innards-and-replace-all kits. I believe his stuff has been discussed here in the past, too.

Cheers,

David
 
Be careful changing caps in the phono section as they set the RIAA curve response. They are probably silver colored polystyrenes which are pretty good caps to begin with.

The DH200 should have the 100mf caps replace on the driver boards at a minimum. Also the 47 ohm resistor used to open up and should be replaced.
 
Talking to the maker of the best phono amp that I've ever heard, he matched not only resistors but capacitors. That's not an easy thing to do but it sure worked for his product.
 
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