Hafler DH200 / Zen / Aleph conversion - diyAudio
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Old 12th April 2005, 06:17 PM   #1
pixpop is offline pixpop  United States
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Default Hafler DH200 / Zen / Aleph conversion

I began this about a week ago, and now have the output stage of the first channel working. Thought I'd share what I've done so far.

I wanted to re-use the power devices and obviously the heatsinks. My plan was to find out what was the maximum class A power I could manage with this arrangement.

I decided to use the P channel devices as the current source, very similar to what is shown in Fig 2. of the original Zen article on the Pass DIY website. I'm using a different BJT for Q3, salvaged from the Hafler PCB. I have two MOSFETs in parallel, and a single current sense resistor (R1) of 0.1 Ohm. My R3 is 1K, and I've set the bias to run at 3A total, 1.5 A per device.

I wanted to use the Aleph style current source, so I added a resistor to the base of Q3, and scaled it so that it would modulate the current source appropriately.

For the current feedback signal, I placed a 0.75 Ohm resistor between the load and ground. This develops a ground referenced voltage proportional to the current in the load. I feed this via a capacitor into the base of Q3. I've scaled it so that when 1.5A flows into the load, the current source is sourcing 3.75A. When the load current is -1.5A, the current source generates 2.25A.

Obviously, I needed to replace the power transformer. I have a temporary one installed at the moment while I wait for my toroid kit to arrive. When it arrives, I'll wind it to exactly the voltage I need, to get rails of about +/- 15VDC. Currently, I'm running at about +/- 13.5, but my transformer is maxed out, getting very hot, and I have lots of hum.

I don't have any good way of measuring the temperature. I have the original thermostat installed on the heatsink, and it doesn't trip, but I don't know what temp it is set for. I also have another thermostat set for 85C, and it doesn't trip. I can hold my hand on the heatsink for 5 to 10 seconds. I can hold my finger on the power devices for 3 to five seconds.

For the lower section, I built something like the circuit in Zen variations part 2, figure 1. I tweaked it a little bit, and adjusted the pot until I had no output offset. It wanders around by about 100mV as the temp changes, but seems to stay within +/- 100mV.. I'm running it without feedback at the moment.

By my estimates, I should get about 12W RMS into 8 Ohms. I haven't connected a signal yet. I plan to do that tonight. I have connected a cheap speaker via 10uF, and I hear noticeable hum. If I connect the speaker across either of the supply rails, I hear exactly the same hum, so I think this is my transformer being overworked. I'm not going to worry about it until I get my toroid wound. I don't hear any noise through the speaker, only hum.

Next step is to build an input stage to go with it. I'm thinking I'll do one like the Aleph 30, but haven't decided yet. I have a bunch of BJTs that I originally bought for restoring the Hafler, but now they won't be needed. Maybe I'll use some of those.

So far, so good!
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Old 12th April 2005, 06:26 PM   #2
pixpop is offline pixpop  United States
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Hehe.. I just thought of a cool name for this project..

It's the "Haf Nelson"
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Old 12th April 2005, 09:53 PM   #3
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Variac sent me one of his Haflers, which is being converted
(slowly) into a JLH variant.
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Old 12th April 2005, 10:08 PM   #4
pixpop is offline pixpop  United States
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OK, I'll let you call that one a Haf Nelson, as well.
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Old 13th April 2005, 12:10 AM   #5
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...and as everyone knows, two halves make a whole...

Grey
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Old 13th April 2005, 01:33 AM   #6
lcleven is offline lcleven  Canada
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Quote:
Originally posted by GRollins
...and as everyone knows, two halves make a whole...

Grey

That would be a full Nelson
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Old 13th April 2005, 05:44 AM   #7
eLarson is offline eLarson  United States
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Okay... then let's see a suplex or a sunset flip.
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Would a woodchuck bother to chuck MDF?
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Old 21st April 2005, 05:08 PM   #8
pixpop is offline pixpop  United States
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Update on the Haf-Nelson..

Last night, I made my first attempt at winding the power toroid.

I'm currently running the amp as a Zen, with 2A bias. I hooked up the finished toroid, and measured.. 28 volts. A bit low, I was expecting more like 32. I thought I'd better measure the current. Ay carrumba! there was 6A flowing.

After correcting a wiring problem in the CCS, I got my 2A back, and now I have the expected 32 Volts. I get about 800mV ripple, but the hum at the output is acceptable (haven't measured it).

As a Zen, it sounds OK, though not much bass, and not enough power. I'm driving it directly from my preamp, and even on max volume, I don't get enough drive to clip the Zen. The gain seems very low.

For reference, I'm comparing it to my Bottlehead SEX amp, which is about 2 Watts, and plays much louder on the same (4 ohm) speaker.

Anyway, it looks like the basic concept is sound. All the power devices seem equally hot. The heatsink is well under 50 Celsius.

Next step: convert back to Aleph-like configuration, and make an imput stage.
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Old 21st April 2005, 06:01 PM   #9
paulb is offline paulb  Canada
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Where did you get the toroid kit from?

I'm interested in what you're doing here. I may adapt a Technics SE-A5 to something else, reusing the transformer, heatsinks, and power meters. The transformer has lower-voltage taps which I will use. Picture:
http://www.diyaudio.com/forums/attac...amp=1078202143
Nelson advised against a Zen, but I may try a small Aleph.
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Old 21st April 2005, 06:27 PM   #10
pixpop is offline pixpop  United States
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I got the toroid kit from Toroid corp of Maryland

They give you everything you need, including info on how to compute number of turns, etc. Nice folks to deal with. They also stock standard toroidal transformers at reasonable prices.
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