Hafler DH-200/220 Mods

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#601
The PC-7 board is a phase inverter that enables the DH-200 to be bridged. Things I have read told me that this amp never sounded very good bridged. You might put this PC-7 board up on eBay. In one of the manuals available in the Tech archives at Hafler.com is a schematic of the board and instructions on its hook up.
 
#604
I have been working on a DH200 that has been out of service
for a long time. After replacing 3 of the fuse holders that were
broken and checking the bias I found that one side has ~ 150mv
on the output the other side has ~ 260mv. What would be the
most likely cause for this.
 
#606
My manual says pc6. I removed a B+ fuse and inserted an amp meter the bias is 200ma. I am talking about the dc offset voltage
at the speaker terminals. It is my guess the 470uf 6.3v bi-polar
cap (c5) is going bad any way to reform a bi-polar cap.
 
#608
This is strange. While I had it open and powered up I added a
2.2uf mylar across each power supply cap. As soon as I did this
the dc offset droped to ~35mv on both sides. I guess one of the
grounds at the power supply buss had failed and when I soldered
the caps in I re soldered the bad joint.
 
#610
Re: Replacing the Main Boards with P101 Boards

emmettr said:
Has anyone considered replacing the Hafler circuit boards with Rod Elliot's P101 boards and reworking the power supply accordingly?
Click to expand...


What you should consider is a board for Nat Semi's LME49811 -- this is the single version of their LM4702. The LM4702 sound is just incredible. This chip should drive lateral MOSFET's as Rod has in P101 quite well.
 
#611
Is there a thread here discussing the use of the LM4702 you mentioned?

Does anyone have a PCB available for an amateur?

I am reading the Application pdf at National's web site. This chip certainly seems promising. For example:


RENESAS 2SK1058/2SJ162 pair were biased at 115mA for the output stage.
The 115mA bias current was very stable with
changes in case temperature. A benefit of these Renesas
devices is the integration of gate protection diodes eliminating
the need for external gate protection components
Click to expand...

Thanks
 
#614
jackinnj said:

I had some boards made for the LM4702 -- but not the LME49830 or LME49811. The LM4702 boards are on my website.

The LM4702 won't quite work in a DH-200 chassis as it is the stereo chip and you have those hulking caps and trafo in the center of the box.
Click to expand...


please - gimme a hint - where is easiest to buy these chips for (almost) European residents ?
 
#619
I answered this one several pages back. Mouser has the exact part for about $3-4 or so. I gave their part number at the time, but it's a non-trivial number and I don't carry it around in my head. The older switches were rated for 10A and roasted pretty regularly. The newer ones are 15A and tend to last a great deal longer.
Don't skip the disc caps across the terminals of the switch. They reduce arcing at turn-on/off.

Grey

EDIT: I searched out the post...it's Mouser part number 691-LTA201TRB/125N.
Now you see why I don't carry it around in my head.
 
#620
I couldn't find the dh220 repair thread so will ask this here. I
have an old dh200 that has a lot of DC off set. I am measuring
175mv left chanel and 298mv right chanel. I thought the 470uf
bipolar caps might be going bad and replaced the one on the
right chanel but still get 298mv. If I connect the power supply
ground to the chassis this offset drops to 100mv left chanel and
60mv right chanel but it's not suposed to wired that way.
What could be wrong?
 
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