Hafler DH-200/220 Mods

[abraxalito]

Originally Posted by Jacques Merde

It might be easier to get an isolation transformer which will step the mains voltage down to 110.

Or even, as isolation isn't required, a variac. Out shopping recently I was surprised how cheap a 1kVA variac was. Cased up, it listed a bit lower than what I paid for a custom 1kVA toroidal.

[abraxalito]

Originally Posted by scott wurcer

I thought there is a dual winding transformer that simply requires the change of a couple of jumpers.

The man. shows two possible transformer types - the 'domestic' (T401) and 'international' (T402). If the OP has the domestic US variant, it has a single primary.

[alexg]

Originally Posted by Jacques Merde

Other than the mains voltage, is there another reason you want to replace the EI transformer with a toroidal? It might be easier to get an isolation transformer which will step the mains voltage down to 110.

Actually, the price of the toroidal and the price of a decent step down (1KVA) is almost the same locally.

So, am more inclined to replace the transformer to avoid clutter.

Another option that I am thinking is having the EI transformer, re-wound for 220VAC primary. Labor in our country is so inexpensive.

Am trying to avoid having a 110V audio equipment, am a klutz and I might plug it on my mains outlet and burn the Hafler.

[abraxalito]

Originally Posted by alexg

Another option that I am thinking is having the EI transformer, re-wound for 220VAC primary. Labor in our country is so inexpensive.

Copper's not though so hopefully you'll get scrap value back on the 120V windings (which will be thicker wire as fewer turns).

[alexg]

Originally Posted by abraxalito

Copper's not though so hopefully you'll get scrap value back on the 120V windings (which will be thicker wire as fewer turns).

Actually, copper is not that expensive, the core is more expensive.

I just talked to a friend who owns a transformer factory, he will wind for me and just give me the bobbin with the windings, I will try to recover the core from the original transformer and stack it myself to the new bobbin...

[abraxalito]

Originally Posted by alexg

Actually, copper is not that expensive, the core is more expensive.

It certainly seems relatively expensive here, when I bought a 100m reel of wire it was more than lunches for a week.

I just talked to a friend who owns a transformer factory, he will wind for me and just give me the bobbin with the windings, I will try to recover the core from the original transformer and stack it myself to the new bobbin...

Sounds like a fun exercise. I still remember the old days when RS sold transformer kits for building your own EI. Only had to wind the secondary though - doing your own primary is more challenging I think. Stacking the laminations and not getting any rattles or hum may be an even bigger one...

[alexg]

I just replaced the 4 100uf electrolytics on the driver board with 4 220uf Panasonics (I have on hand used for bypassing tube projects, the Hafler is my first SS project). Sound is pretty much imporoved.

The board have a 470uf bi-polar cap, I cannot find better replacements, how low of a capacitance can I go? I have a bunch of polypropylene and polyester caps, the highest is 20uf... I wonder if I can use these instead.

Thanks.

[abraxalito]

Originally Posted by alexg

... I wonder if I can use these instead.

You certainly can, but bass performance will suffer. This cap determines the low frequency roll-off of the amp. Reducing it by a factor of 20 sounds rather drastic... But try it and see what it sounds like. You could try substituting back-to-back 1000uF polarised electrolytics if you don't like the sound of your 20uF.

[alexg]

Originally Posted by abraxalito

You certainly can, but bass performance will suffer. This cap determines the low frequency roll-off of the amp. Reducing it by a factor of 20 sounds rather drastic... But try it and see what it sounds like. You could try substituting back-to-back 1000uF polarised electrolytics if you don't like the sound of your 20uF.

Back to back, does it mean, - connected to the -?

I asked if I can lower it because in vacuum tube circuits, hardly I would go beyond 2.2uf for an output cap.

Thanks.

[djk]

"hardly I would go beyond 2.2uf for an output cap."

Calculate the RC corner.

The R is 150 ohms. 20µF would then be 53hz.