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Hafler P-230 recondition
Hafler P-230 recondition
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Old 19th October 2008, 06:47 PM   #1
joetama is offline joetama  United States
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Default Hafler P-230 recondition

I'm working on a Hafler P-230 and I'm having trouble finding information on it. One channel was destroyed, had a serious melt down, and I wanted to build the PC-19 boards with good quality components.

I see the PC-19 is also used in the DH-220, but I don't know if the schematics are exactly the same since the 230 uses 6 MOS-FETS and the 220 uses 4.

I am also wondering if there are any good upgrades or changes in design to make the amplifier sound and work better.

Thanks,
JT
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Old 19th October 2008, 07:08 PM   #2
Stormrider is offline Stormrider  United States
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There are no differences between the P230 and DH220 amps except for the extra pair of mosfets, and the heavier duty power cord.

The PC19 card was a result of the various mods that people normally did to the DH200 circuit. As a result, there isn't much you can add to the PC19 cards. If you are going to start from scratch with blank PC19 PCB's use good quality parts and you will be good to go.
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Old 19th October 2008, 07:11 PM   #3
joetama is offline joetama  United States
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Hey great thanks for the information.

I figured they were the same just with the extra pair of mosfets.

I don't really have access to K134, do you think it would work ok with K135 or something equivalent from Exicon?
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Old 19th October 2008, 08:38 PM   #4
eyoung is offline eyoung  United States
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hello again...

ditto stormrider. there are some folks on Ebay selling replacement output transistors,just search 2sk134/2sj49. Everything else is available from Mouser/Digikey.


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Old 19th October 2008, 09:13 PM   #5
jaycee is offline jaycee  United Kingdom
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Don't risk it - get the Exicon devices. You risk getting fakes etc from eBay. You'd be best using them for both channels.
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Old 19th October 2008, 09:19 PM   #6
joetama is offline joetama  United States
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I must say that I have been really impressed with Exicon and Profusion. They were easy to order from, quick, and really weren't that expensive.

I've always been afraid of getting ripped off on the transistors. So, I think I might stick with the Exicon Mosfets.

The schematic for the Hafler uses capacitors to match gate capacitance, should I change the numbers of the caps to match the different transistors? I haven't looked at the specs closely, but any ideas or help on that front?
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Old 19th October 2008, 11:27 PM   #7
Dick West is offline Dick West  United States
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I am sorry to give you some possible bad news. The 3 N-channel devices on each channel must be matched on Vgs to within 10%. Ditto for the P-channel devices.

The numbers on the MOSFETs in Hafler amps reflect their grading (1-7) of their Vgs. You need matched triplets for the P-230.

I have used Exicons, etc., with no apparent change in sound but, again, they must be used in matched pairs (or triplets) and not mixed in with Hitachi devices.

Do you really need to replace MOSFETs? They are very rugged and rarely fail. Also, you can always use your amp with just a pair of N-channel/P-channel devices instead of a triplet. Heck, you could even use it with just one N/P-channel per side if needed -- after you reset the bias accordingly.
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Old 20th October 2008, 12:24 AM   #8
jaycee is offline jaycee  United Kingdom
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Might be simpler to just put some low ohm resistors eg 0.22R 3W in the drains and have done with it. The lost power wont be much of a loss in a domestic amp.

Feel free to tell me i'm a moron but it would save a hell of a lot of cost (the mosfets are expensive) for very little loss.
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Old 20th October 2008, 04:11 AM   #9
joetama is offline joetama  United States
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Quote:
Originally posted by jaycee
Might be simpler to just put some low ohm resistors eg 0.22R 3W in the drains and have done with it. The lost power wont be much of a loss in a domestic amp.

Feel free to tell me i'm a moron but it would save a hell of a lot of cost (the mosfets are expensive) for very little loss.
By no means am I going to call you a moron.

I am just curious of why you would put the resistors there? So the output from each one is more balanced or something?
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Old 20th October 2008, 04:46 AM   #10
jaycee is offline jaycee  United Kingdom
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The resistors make the mosfets share the load. In the Hafler factory, this was obtained by matching the output devices so the characteristics were similar. This basically meant having a load of them, and testing them individually to see how well they matched. To get a good set of matched pairs you'd have to buy 25 of each device at least.

Most amps have such resistors anyway, so it is not such a big deal.

If the devices are not made to share, and not matched, then one of them ends up doing more work than the others. This can lead to device failure.
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