Hafler DH-220 rebuild

[Plcamp]

I do have some unresolved questions about how to connect grounding in this amp.

I would appreciate any comments folks have about this

a) I would like to bring a 3 wire power cord into the picture and safety ground the chassis. I believe it is correct that a tight binding post at power entry tie to chassis, and a wire should run from there to the chassis ground point between the input jacks.

b) As originally wired, the input jacks tie directly to the chassis ground point between them. But I have seen other papers advocating these input grounds be lifted with a fusible resistor that is bypassed with an rf suppression cap. I don’t know how to gauge the importance of this. I can of course just try it and see.

c) As originally wired, the driver board ground routes first to speaker output return, and then to single pt ground between the bulk caps. Is it better to connect the driver board ground to spg first?

d) should a wire be soldered to the transformer ground and connected to chassis ground?

that’s all for now!

 

[elak]

Quite long time passed since last reply, but I found occasion to buy Hafler D 220 in good shape for 200 euro. How does it sound comparing to ncore 250? Is there sense in buying such old equipment, when sound quality is most important? Greetings

 

[H-713]

Quite long time passed since last reply, but I found occasion to buy Hafler D 220 in good shape for 200 euro. How does it sound comparing to ncore 250? Is there sense in buying such old equipment, when sound quality is most important? Greetings

$200 (conversion is almost 1:1 IIRC) is pushing it for a DH220. The ncore will be more powerful and have somewhat lower distortion (though DH series Haflers tend to be below 0.01% if they're operating well), in most cases I really don't feel that it's particularly audible.

I have a DH120, and I can't reliably hear a difference between it and an MC650 (which I consider to be pretty much transparent). The main thing is the condition of the DH220 and how well it was built (these are kits).

You want to know my opinion? Once distortion gets really low (say below 0.05%) it's really hard to hear a difference. I can't reliably pick out the difference in a blind test. Because it's so subtle, picking out which one sounds better is impossible.

Me? I'd take the DH220. Schematics are publicly available, and they are super easy to work on. There are a few upgraded driver boards available as well, including some from Bob Cordell, so you can "hotrod" the amplifier if you feel inclined. I also happen to like the look of the DH220, and I think lateral MOSFETs are interesting devices.

 

[Plcamp]

FYI…This is the Bob Cordell driver board (matched fet front end).

 

[Sal1950]

Is there sense in buying such old equipment, when sound quality is most important? Greetings

What's your soldering skill level?
Unless you go thru the amp, replacing all caps and testing resistors, etc for proper function you'll have no idea how it will sound or how long it will continue to work in an "as is" condition. Also no idea what the parts cost will be to get it fully restored.
If you enjoy this type of thing go for it.
If not your probably better off with a new ncore.

 

[H-713]

What's your soldering skill level?
Unless you go thru the amp, replacing all caps and testing resistors, etc for proper function you'll have no idea how it will sound or how long it will continue to work in an "as is" condition. Also no idea what the parts cost will be to get it fully restored.
If you enjoy this type of thing go for it.
If not your probably better off with a new ncore.

I agree, but only to some degree. These amps don't run super hot, and my DH120 (which lived in a rack, powered up 24/7 for 30 years before I got it) didn't need any caps. A lot of people like to assume that "any amp over 20 years old needs recapping!!!11", and I find that more often than not, they're just fine.

I think the bigger concern is that a lot of these were kits, so some of them weren't built all that well to begin with.

But since this is the DIY subforum, I would expect someone posting to be willing/interested to do some soldering.

 

[tomelex]

Quite long time passed since last reply, but I found occasion to buy Hafler D 220 in good shape for 200 euro. How does it sound comparing to ncore 250? Is there sense in buying such old equipment, when sound quality is most important? Greetings

I would say some things to consider in the idea of keeping your hafler or just going with the ncore is whether you are an appliance operator (you just want an amp to amplify) or you also get a satisfaction from the looks and lineage of your gear (the hafler looks great and vintage and has a supurb record of listenability and rugged construction).

As a hobbyist, the hafler probably would be more satisfying sitting in your cabinet than an eqully superb but not easy to repair nor an established track record of reliability product such as ncore. Haflers are running going over 40 years and are repairable by any qualified electronics technician, the only issue would be the need to scavenge the output transistors from other haflers as they have not been made for 30 years or so, but obsolete parts are a problem with most any vintage gear.

So, depending on your speakers, the sound could be nearly the same from both amps. If they sound about the same, then its an emotional decision, that is which one makes you feel good looking at it and knowing it is in your system.

In any case, if you are an audiophile you probably will change amps a few more times in your life anyway. Some, like me, have stuck with their haflers, in my case bridged mono DH220 amps capable of 440 ultra clean in specification watts each, going over 35 years. Those amps are my long term reliable friends.

However, electronics has been my life's work so there is no fear of repairing my units. I have replaced the two large storage caps in each unit, the other smaller electrolytics just a few were changed about a decade ago as they were on the low side of their tolerances. The feedback in the amps corrects for a lot of cap weaknesses anyway.

 

[H-713]

I would say some things to consider in the idea of keeping your hafler or just going with the ncore is whether you are an appliance operator (you just want an amp to amplify) or you also get a satisfaction from the looks and lineage of your gear (the hafler looks great and vintage and has a supurb record of listenability and rugged construction).

As a hobbyist, the hafler probably would be more satisfying sitting in your cabinet than an eqully superb but not easy to repair nor an established track record of reliability product such as ncore. Haflers are running going over 40 years and are repairable by any qualified electronics technician, the only issue would be the need to scavenge the output transistors from other haflers as they have not been made for 30 years or so, but obsolete parts are a problem with most any vintage gear.

So, depending on your speakers, the sound could be nearly the same from both amps. If they sound about the same, then its an emotional decision, that is which one makes you feel good looking at it and knowing it is in your system.

In any case, if you are an audiophile you probably will change amps a few more times in your life anyway. Some, like me, have stuck with their haflers, in my case bridged mono DH220 amps capable of 440 ultra clean in specification watts each, going over 35 years. Those amps are my long term reliable friends.

However, electronics has been my life's work so there is no fear of repairing my units. I have replaced the two large storage caps in each unit, the other smaller electrolytics just a few were changed about a decade ago as they were on the low side of their tolerances. The feedback in the amps corrects for a lot of cap weaknesses anyway.

New production lateral MOSFET output devices are available from Exicon / Profusion. They aren't cheap, but they aren't insane either.

 

[rompstar]

haha, this thread might go on forever... new member here, I just got the hafler 220 as well, all new to me, I've replaced the power caps and also the input RCA plugs with nice gold ones... but I heard that this amp might benefit from the "by pass cap" trick ? does anyone have any pictures showing that ? and also which capacitors should I buy ?

I love my Hafler 220, reminds me of the Heathkit days!

Cheers!

 

[precisionav]

Well I was enjoying reading this old thread OP until it got hijacked. Was looking forward to your end result.

 

[phoenixdogfan]

haha, this thread might go on forever... new member here, I just got the hafler 220 as well, all new to me, I've replaced the power caps and also the input RCA plugs with nice gold ones... but I heard that this amp might benefit from the "by pass cap" trick ? does anyone have any pictures showing that ? and also which capacitors should I buy ?

I love my Hafler 220, reminds me of the Heathkit days!

Cheers!

Built both a Halfler DH 200 and a Heathkit AR-1500 in my day. Great gear in their day. But unless you like to tinker, better off going with something like an NCore or a Purifi.

 

[PurpaSmart]

Well I was enjoying reading this old thread OP until it got hijacked. Was looking forward to your end result.

Unfortunately, life got in the way. I had to give up the room where I did my work. I did get the amp running though, only for it to thermally shut down as it did before. I'm pretty sure it is one of the lateral mosfets, since one out of the four on the left channel gets super hot, thus causing the thermal shutdown. Could also be a bad pot, since I was also having fluctuating bias readings on the left channel. Last thing I did was buy some Exicon lateral mosfets a couple years ago, but right now the project is on hold until then.

 

[precisionav]

Thanks for the update. Keep me (us) posted when you get back at it again. I'm almost done restoring my third Hafler amp over this winter. Two DH-220, one DH-500 and actually picked up a mint condition, one owner factory built XL-280. They're all great sounding amps and fun to work on. I'm sure with some perseverance you'll get that amp singing and all your efforts will be rewarded.
Take Care