Hafler DH-200/220 Mods - Page 4 - diyAudio
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Old 26th May 2004, 04:40 AM   #31
thanh is offline thanh  Viet Nam
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fab! i saw your post 22! Have you succeed in building that shematic?
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Old 27th May 2004, 02:58 AM   #32
fab is offline fab  Canada
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Quote:
Originally posted by thanh
fab! i saw your post 22! Have you succeed in building that shematic?
Thanh,

Yes I Have succeeded!! and it works very well too. All the mods I indicate on this thread works prefectly. Every mods have been validated in 3 different DH-200 amps. For the input stage, it is installed for more than 1 year with no problem. I used 2 modified DH-200 amps in a bi-amp system.

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Old 27th May 2004, 03:13 AM   #33
thanh is offline thanh  Viet Nam
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wooooooow!Really? i think i will build a input stage like that!
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Old 31st May 2004, 03:30 PM   #34
larryg is offline larryg  United States
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Default thermistor

Slowhands, in post #23 does the thermistor go after the fuse in series with the ac?
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Old 16th August 2004, 07:24 PM   #35
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Default balanced-inputs on the dh-200/220 series?

is this a waky idea?

maybe based on the application, it isn't. I want to get the benefits of balanced line operation on the input stage of my hafler.

I have some experience in the car audio area and balanced lines are quite popular, to reduce pickup-noise from nearby fields.

my amp might be located farther away from my preamp than I'd like. so I'm thinking of running balanced cables from the preamp to the amp - BUT - of course modifying both so that the input stage of the amp and the output of the preamp both 'speak' balanced.

I had an interesting idea - why not get a quality balanced line receiver and just install it INSIDE the hafler. there's a bit of room inside and it would save me having to put some clunky adapter box outside.

I like zapco stuff. they have something called 'symbilink' that runs the analog cables and the power in one mini-din cable. quite elegant, really. works well. you can get a balanced transmitter that takes in RCA and puts out this symbilink stuff. then a receiver box on the other side to do the inverse. the transmitter also 'transmits' power to the receiver box, so you really do use only 1 cable from Tx to Rx.

ok, with me so far? done laughing yet?

the zapco stuff can be found cheaply enough on ebay and is small enough that it -can- fit inside the hafler chassis. then I could take the mini din and panel mount it somehow and that would be my new amp input.

OR - before I get too far - is the hafler 200/220 input already floating?? so that really, I wouldn't even have to install a 'receiver' circuit? its been a while since I've opened my DH but I think the inputs are not floating (are they?)

comments on this whole idea?
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Old 17th August 2004, 07:39 PM   #36
Sigmo is offline Sigmo  United States
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Default Thanks

I've just found this thread and I'm really glad to see the good info about the Haflers. I've been using a pair of them for a long time and I just want to let you all know that there are others of us out here who appreciate the effort aimed at these good old amps.

Both of mine have the stereo/mono bridge boards in them and I set that up from the get-go to use a switch so I can quickly change them from bridged to stereo. That's worked well over the years.

I hope I'll have something useful to contribute to the thread at some point, but for now let me just add my encouragement to those of you who are showing us your ideas.
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Old 18th August 2004, 02:17 AM   #37
fab is offline fab  Canada
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Hi linux-works

I am not familiar with the zapco stuff. However, I can respond that the Hafler inputs are not floating. The driver boared would need some resistors removed and added with the amp inverted input available for balance connection.


Hi Sigmo

I am glad that you find some interest in this thread. If you want more ideas you can see a follow-up (Lavardin) in the latest posts of this thread: http://www.diyaudio.com/forums/showt...70#post455770.

Fab
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Old 18th August 2004, 02:32 AM   #38
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zapco is just one example - one that I'm pretty familiar with. its a plug and play module (sort of - needs +12vdc though) that does a function and does it very well.

http://memimage.cardomain.com/member.../200585_45.jpg

that is a picture of what the small modules look like, the Tx and Rx boxes are
similar.

I figure if I remove the box and mount the pc board inside my hafler, I can use the symbilink (balanced line - ignoring the dc lines in that cable) as my amp's input
and disconnect the rca jacks and have the zapco's output go directly to the pc boards of the hafler amp.

then I just need to get a clean +12v for the zapco.

OR - how about fully passive? some balanced audio transformers (like from jensen) might work. no power and no changes to the amp.

jensen stuff is high end and expensive. but would the 'sound' of the input transformers be counter-productive vs. the electronic balanced inputs of the zapco, for example? or any other balanced->unbal converter?
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Old 23rd August 2004, 06:20 AM   #39
thanh is offline thanh  Viet Nam
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Quote:
slowhand
I have done the current mirror mod to the Citation MF12, with very excellent results
Can you give me that schematic?
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Old 20th November 2004, 06:53 PM   #40
Davet is offline Davet  United States
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Default Hafler are like 55 Chevy's

I stumbled upon this thread yesterday and I am glad to know that I am not the only Hafler modder out there. There is a certain degree of comfort in numbers.

I built a Hafler DH200 kit with the original PC6 boards in the early 1980s. This amp has served me well over the years. A couple of years ago I embarked on some of the Marsh/Jung Audio Amateur Pooge mods. These mods included new wiring, star grounding new input jacks and polypropylene/metal film bypass caps, etc. The sound, to my ears, seemed to have improved.

I have since purchased two additional DH200 amps and two sets of PC19 boards. A few of the transistors dropped off the PCB on one channel of one of the purchased amps. This prompted the purchase of the PC19 boards. I have purchased all the MF resistors and polystyrene caps suggested in th AA article, but the comments in this thread have given me reason to pause and consider other alternatives.

I believe, the MOSFETs may be blown on the one channel where the transistors fell off. Obviously cold solder joints and age aggrevated by shipping were contributing factors to the transistors falling off. So replacement or upgrading the power MOSFETs is a consideration. Suggestions would be appreciated for a course of action in this regard.

So, is it worth upgrading/replacing the resistors on the PC19 board for the functional amps?

Ideas on where to purchase replacement MOSFETs/transistors.

Great thread!
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