Hafler DH-220 rebuild

[PurpaSmart]

Well my dad had a bought a hafler dh220 in the mid 80's along with the hafler dh 101 preamp and the kef reference 104/2, however in 2003 it stopped working in the left channel because my dad had left it on for like a few days, well ever since that it had been sitting in a closet , until now..
First pic is original vanilla, second pic is wip brand new board with 1-0.1 % resistors, new wima and vishay polypropylene caps and nichicon KZ electrolytic capacitors and one bipolar nichicon muse capacitor

New power capacitors

New binding posts

Here is another shot of the board

 

[tomelex]

That's a very good amplifier, there are plenty for sale all the time, and it has audio grade mosfets, no longer made. New replacements for the electrolytic caps and new input and output connectors and sometimes some folks use multiple caps instead of the two large storage caps but just restoring her as is will give you another 20 years of service. For some reason, I found that when I purchased a second amp, and then operated each amp in bridged mode, the music sounded better to me. That mode gets you over 400W at published specs per channel, pretty good IMO. The only thing is that it loses p0wer into lower ohms loads, ie dipping below 4 ohms, but that is to be expected when bridging. Nice pics.

 

[DonH56]

Brings back memories! Built and modified a ton of these way back in the day. It runs on the hot side so I would use 105 degC caps instead of 85 degC... Way back when I tweaked the feedback network and boosted the power supply caps to improve the bass. Replacing the electrolytic input coupling cap was a very popular mod, along with bypassing the large power supply caps with a couple (or more) smaller values. I still have mine, someplace...

 

[restorer-john]

Looking good. So the new boards are re-productions or NOS?

I'd like to see the power switch live terminals insulated/heatshrunk, for that time down the track, when the plastic retaining clips let go and the switch falls forward and drops onto the front panel or chassis...

Gotta love those old Hitachi MOSFETs.

 

[PurpaSmart]

That's a very good amplifier, there are plenty for sale all the time, and it has audio grade mosfets, no longer made. New replacements for the electrolytic caps and new input and output connectors and sometimes some folks use multiple caps instead of the two large storage caps but just restoring her as is will give you another 20 years of service. For some reason, I found that when I purchased a second amp, and then operated each amp in bridged mode, the music sounded better to me. That mode gets you over 400W at published specs per channel, pretty good IMO. The only thing is that it loses p0wer into lower ohms loads, ie dipping below 4 ohms, but that is to be expected when bridging. Nice pics.

Thanks, I plan on getting it up and running once the rest of parts from mouser arrive, after it works, I will plan on modifying even more such as adding bypass caps and some bleeder resistors

Looking good. So the new boards are re-productions or NOS?

I'd like to see the power switch live terminals insulated/heatshrunk, for that time down the track, when the plastic retaining clips let go and the switch falls forward and drops onto the front panel or chassis...

Gotta love those old Hitachi MOSFETs.

Yes, the board is NOS, which is for the left channel, however I'm using the existing board for the right channel. because those NOS boards cost like $25, and I wanted to save some money.

 

[PurpaSmart]

Here is my super messy setup, not ideal but it works.

 

[PurpaSmart]

Heres the right channel, just replacing the caps and some resistors, maybe some diodes

 

[Speedskater]

Two thoughts:
1] A 3 wire power cord with the Safety Ground connected to the chassis near where the cord entries the chassis would be nice.
2] The bus wire between the two large electrolytic capacitors could be much larger.

 

[DonH56]

I used to have some circuit boards I made to connect the two main power caps plus mounting for another pair. Nice wide, thick copper, and then a thick braid to ground and heavy wires to the rest of the circuit.'

 

[PurpaSmart]

I used to have some circuit boards I made to connect the two main power caps plus mounting for another pair. Nice wide, thick copper, and then a thick braid to ground and heavy wires to the rest of the circuit.'

That's exactly what I am doing, using 8 awg copper wire, I am also planning putting a three prong power cable, also bought rfi and efi filter for the mains, I'm adding a ground, so I'm kinda worried I'm adding a ground loop.

 

[PurpaSmart]

New ground bus, the one on the left took much more time since the ring terminal broke, so I had to retrofit a washer for the hole by soldering it to the broken terminal. But I got it, also no cold joints at all

 

[PurpaSmart]

Almost done with the left channel board, getting better wire wound resistors, reusing some the bjt's and the trim pots, and also one metal film resistors that's rated for 1W, oh and the output inductor, all caps are polypropylene except for the three electrolytic caps. Oh yeah and that big wima cap was like $15, it did not even need to be rated at 400v but that's only one that fit that spot, the original capacitance was 2 uf, but again most were to small, so went with 2.2 uf, not going to make a huge difference

 

[Speedskater]

That's exactly what I am doing, using 8 awg copper wire

That big bus looks good.

I am also planning putting a three prong power cable, also bought rfi and efi filter for the mains, I'm adding a ground, so I'm kinda worried I'm adding a ground loop.

Connect the new Safety Ground to the chasses near where the power cord enters the chassis. Connect the audio circuit common (aka ground) to the chassis near the input connectors.

Tell us more about the EMI & RFI filters. Effective & safe EMI filters can be huge.

 

[PurpaSmart]

That big bus looks good.


Connect the new Safety Ground to the chasses near where the power cord enters the chassis. Connect the audio circuit common (aka ground) to the chassis near the input connectors.

Tell us more about the EMI & RFI filters. Effective & safe EMI filters can be huge.

Here's the rfi/efi mains filter
https://www.mouser.com/ProductDetail/592-10EH4C

 

[Speedskater]

That is a very small filter, indeed.

 

[DonH56]

Keep the EMI filter's return path to the safety ground very short and as low in impedance as possible.

Signal ground can be isolated by a low-value resistor, at least per our code, but I don't have the requirements off-hand (someone probably does -- it specifies a max value and resistor wattage, must be flameproof). That can break a ground loop. I cannot recall if the DH-220 already has that (many components do).

I have a vague memory of building a mu-metal shield around the transformer on some builds. It dropped the noise floor measurably but not really audibly IIRC. I also put a braid shield around the AC input line and used coax for the input signal lines. Again not sure how much any of it helped... I think mine does have coax input lines and maybe the AC shield but not the transformer shield. I know I added some bypass caps for line noise due to some issues I had with that in one (very old) house; that was long before the inlet EMI filters were common so I rolled my own for a while.

 

[PurpaSmart]

Well I've got both channels working, bias is set at 280mv, dc offset set as low as possible, which isn't that low at all, planning on getting two sets of matched pairs of 2N5401 and 2N5550, any idea where i can get pre matched sets without having to buy like a hundred of each?

 

[Plcamp]

For those with old Hafler power amps like 200 and 220, a Bob Cordell designed circuit and 4 boards are available in DIY mode here...there are two listings...one with and one without the required matched jfets included

I ordered my boards yesterday, there is a maintained Mouser BOM that accompanies your order, along with extensive assembly and bring up procedures.

I love my old Haflers...and can’t wait to implement this!

https://www.ebay.com/itm/David-Hafl...pgrade-using-the-DH-220C-design-/223993422898

 

[Sal1950]

I love my old Haflers...and can’t wait to implement this!

Sounds like fun, good luck with the build!

 

[phoenixdogfan]

I put together a DH 200 in the '70s. Great little amp. Guy named Ken Rockwell did a review complete with Amir like measurements.

https://www.kenrockwell.com/audio/hafler/dh-200.htm

As you can see, it's performance more than holds its own, even by today's standards. And they're floating around everywhere for dirt cheap.