Refreshing a DH-200 Hafler

[jakelm3075]

Hello folks.

Its time to refresh my older hafler 200.

I have noticed in the past few years, the SQ has gone downhill. The highs are raspy (harsh) and the bottom end is fading to non existant.

I am going to replace the C1 coupling caps located at the input. And also replace the PS 10,000uF large caps.

I have little experience in upgrading or refreshing amps, so I thought this amp would be a good project to start learning.

Any ideas on what to replace the caps with and what else I might want to look at to get this fine little amp back to specs?

Thanks

Jake

[MaxS]

Have a search

[jakelm3075]

Did a search. Mods mostly and addons.

Greek to me. Those guys were speaking way above my head.

Nothing about simple cap change or refreshing gear to "original" specs.

Just talk about modding bias and changing voltage values and loop feed back etc.

But I'll keep reading.

Jake

[jakelm3075]

I know myself and a few others who own this amp, who would like to read something on this subject, that is put in alittle more laymens terms...lol

I'm just looking for simple upgrade like the thermal cap on the power switch I did. That was simple and easy.

[djk]

The cap most people miss in the one in the feedback loop to ground.

First the bass starts going away, then the gain.

Replace the input cap, the feedback cap, and add 0.1uF film bypass caps to these, then add a 47uF bypass to each of the 10,000uF caps. Now listen to it. If you want to spend a bunch of money you could replace the 10,000s, but most of the time they are still OK.

[jaycee]

Replace all the electrolytic capacitors with new ones. The main PSU capacitors may need to be replaced but leave them until all the others have been and judge. Electrolytic caps don't age well, especially when exposed to heat. My guess is this is what has caused the noticeable degredation in sound quality for you.

It may also be worth unmounting all of the output MOSFETS and cleaning off the old heatsink paste, and applying fresh paste, but if in doubt, leave them alone.

Re adjusting the bias my also have a beneficial effect, and it's fairly simple to do.. but if you only do one thing, I'd say replace all electrolytic capacitors.

[jakelm3075]

Thanks guys..thats excatly the info I needed..I appreciate all the help..


Jake

[jakelm3075]

Originally posted by jaycee

Re adjusting the bias my also have a beneficial effect, and it's fairly simple to do.. but if you only do one thing, I'd say replace all electrolytic capacitors.

Whats a simple way to adjust the bias?

I have a multi meter, but unexperienced in bias adjustment.

[djk]

Yank one of the DC rail fuses for one channel, clip in your DVM set to 2A, turn the amp on, adjust to 250mA. Wait a half hour and re-check. Repeat for the other channel.

The main filter caps sound quite bad as they age, but adding 47uF bypass caps takes care of the sound. If it can put out full power I wouldn't replace the main filters (unless I had money to burn).

[Upupa Epops]

And whatabout refreshing your ears, Jake ?