Hafler DH-200/220 Mods

[Dick West]

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.

 

[GRollins]

I think you'll find that the IRFs will exhibit negative temperature coefficients, too. It's all a question of bias. If everyone abandoned devices with positive tempco, you'd never see a bipolar amp again.

Grey

 

[woody]

There is a discussion about this in the ( 200 watt Lateral Mosfet
amp and Irfp/240/9240 ) thread. It is mentioned that the irf240
has a positive temp coeficent till it reaches 11A where it changes
to a negative temp coeficent.

 

[woody]

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.

 

[eyoung]

HELLO WOODY,

WHERE ARE MEASURING BIAS??? AND WHICH DRIVER BOARDS ARE IN YOUR DH200???

REGARDS, ELWOOD

 

[woody]

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.

 

[Stormrider]

"It is my guess the 470uf 6.3v bi-polar
cap (c5) is going bad any way to reform a bi-polar cap."

Buy a new, preferably a 25-35v rated one. No sense in trying to reform a .75c cap.

 

[woody]

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.

 

[emmettr]

Replacing the Main Boards with P101 Boards

Has anyone considered replacing the Hafler circuit boards with Rod Elliot's P101 boards and reworking the power supply accordingly?

 

[jackinnj]

Re: Replacing the Main Boards with P101 Boards

Has anyone considered replacing the Hafler circuit boards with Rod Elliot's P101 boards and reworking the power supply accordingly?

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.

 

[Dick West]

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

Thanks

 

[Dick West]

OK. I did a search and found several threads. Time to do some reading.

diyAUDIO is a great resource!!

 

[jackinnj]

Does anyone have a PCB available for an amateur?
Thanks

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.

 

[Zen Mod]

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.

please - gimme a hint - where is easiest to buy these chips for (almost) European residents ?

 

[jackinnj]

please - gimme a hint - where is easiest to buy these chips for (almost) European residents ?

I have the chips and driver boards here -- http://www.tech-diy.com/LM4702_Kits.htm but the LM4702 is probably not the right chip for the Hafler.

 

[Zen Mod]

I have the chips and driver boards here -- http://www.tech-diy.com/LM4702_Kits.htm but the LM4702 is probably not the right chip for the Hafler.

tnx for answering


what I need , and not for Haf , are LME49830 ;

....... are ....... hehe , because I need them in pairs ;

any info regarding that chip - where and how much?

TIA

 

[Sideout]

Hafler DH-220 Power Switch

I have a Hafler DH-220 with an intermittant power switch. Anyone have a suggestion on a replacement switch and where to buy it?

Tom

 

[djk]

It's a hardware store item, Home Depot type places have them too. About $5.

 

[GRollins]

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.

 

[woody]

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?