Hafler dh-200 switch

[Zen Mod]

from one of Hafler amps;
there you can see how switch is connected

little play with multimeter will tell ya how to connect switch

always use suppressor cap,as others tells ya already

[slowhands]

Originally posted by jakelm3075
...a Dh-200 with a bad on\off switch. I went to radio shack and bought another 3 prong switch. Replaced the switch the exact same way the bad switch was. Plugged the amp in and blow the main fuse. The switch I bought is a 3 prong switch similar to the original, different look but same 3 prong. I'm lost as to what went wrong.
.....
I also plan on bridging this amp for a sub amp. Is this a good idea? Does Hafler still make the bidgeing kit? Also, is there a way to bridge it without the kit?

There may be a reason the switch was burned out. The amp could have serious problems that cause it to draw lots of juice and blow the fuse. Or the cheapo switch from RS might not be able to handle the load. Or you might have hooked up the switch wrong. Switches are not standard in their pinouts, sorry to say.

You can tell if the amp is OK or not by just bypassing the switch, and seeing if the fuse blows again. People do this when the switch fails, and just plug and unplug the power cord instead. If fuses blow again, leave it for a tech, it's probably more than you can fix.

If not, figure out which two pins on the switch connect together when you close the switch. Those are the lugs to connect to. You should be able to figure out what two lugs to use by measuring the switch resistance with an ohmmeter as you move it on and off.

I have a hunch your RS switch can't take the load. It's a 15A rating demanded. I wrote up a fixit list for this amp two years ago here, and the first thing I mentioned is the switch is bad on most of the amps I see. Anyway, you need a beefy 15A switch, and it will still fail in a few years again, sorry about that. My patch for the switch is a thermistor, but I don't recommend you put this in unless you really know what you are doing.

Here is what I wrote about this in Feb 2004:

"First, here is my list of the most common failures in these amps, with causes. The power switch fails, due to excessive inrush currents (see fix below). The output transistors do burn out, probably due to insufficient cooling coupled with oversized fuses on power. The input pairs go leaky due to overdriven inputs. When the outputs fail, they generally take out drivers and possibly inputs, as you would expect. That's what I see most often, so those are the areas I check first.

There is not a lot you can do to hugely improve the sound of this amp, in my opinion. Here are some small mods that preserve the essential character of the design while adding reliability.

The first mod is simply an NTC thermistor (5 ohm cold) on the AC power. This is needed to prevent the switch from failing due to high inrush current. On most of the amps I see, the power switch is toast and has to be replaced, but it will just fail again unless you do this mod. If you do nothing else, do this mod!"

I don't know if your amp is seriously blown or just the switch is toast, you will have to do the switch bypass to see. If the fuses blow again, quit while you are ahead and turn this over to a tech. Probably the outputs MOSFETs are shorted, but there is no sense in you causing a fire trying to chase it down. You're dealing with a 30 year old amp that could have other issues, so walk softly.

As far as bridging this, once you get it working it's easy if you are a competent tech. A couple of wire pairs have to be connected in a particular way from each board to a new switch on the back. I do it all the time to the amps I modify. I put it in, and bingo, a monoblock is born. I get the feeling most people use these for subs, but they are still good amps in my book. Just no frills, which I like. Anyway, good luck!

[jakelm3075]

Thanks slow. I'm trying another switch tonight. But if that doesn't work, what wires do I hook together to bypass the switch? There is a small wire from the fuse, a large black wire from the plug, another small black wire to the light and another blue wire from the right channel board.

[jakelm3075]

Well I just ordered the Carling rocker switch that was refered. 2nd day fedex. Picked up extra fuses as well.. Wish me luck..lol


Jake

[slowhands]

Originally posted by jakelm3075
Thanks slow. I'm trying another switch tonight. But if that doesn't work, what wires do I hook together to bypass the switch? There is a small wire from the fuse, a large black wire from the plug, another small black wire to the light and another blue wire from the right channel board.

I will probably regret this, but...

To see if it is just the switch, connect the two wires together that do not go to the light. In other words, connect the wire from the fuse to the wire from the plug. This is just temporary. If it works, use the new switch when you get it.

If the fuse blows again, it's not just the switch. You have a big problem somewhere else. Quit while you are ahead and have a tech finish the job.

[jakelm3075]

Originally posted by slowhands


I will probably regret this, but...

I will take full responsibility for my actions..

Lets hope the fuse blows before my house...lol

[jakelm3075]

Another thing I think might have happened. The prongs on the switch are so close together, the current might have arced and blew the fuse. Not much I can do about thet though, unless my soldering skill was off abit.

[jakelm3075]

I do remember now that there was a unnormal hummm when I plugged the amp in the wall. Then fuse blew when I flipped the switch.

The amp was in perfect working order when I got it. It was just that the old switch was frozen in the on position.

[Dick West]

You need to get up close and personal with the Hafler DH-200 schematic and wiring diagrams. You can get these at WWW.HAFLER.COM. Go to the Archive library and download the pdf file for your amp.

The switch has three prongs. Two are to switch the AC, the 3rd is to light the pilot light. The proper switch has the numbers 1, 2, 3 embossed on its back side. The Hafler wiring diagram shows the switch wiring complete with the numbers 1, 2, 3. If you study the diagrams and get the proper switch and match up the 1, 2, 3 connections installing the switch is as simple as "1, 2, 3."

Install a ceramic cap across the AC connections and make it a .01 uF cap as previously suggested.

The other stuff you referred to, the resistor, etc., are part of a little circuit that makes the yellow indicator lamp blink if the amp overheats and one of the thermal switches opens up. Again, study the schematic and wiring diagrams and firgure it out. It is a simple circuit.

Don't even think about bridging the DH-200. Reports from those who did said the amp did not really like being bridged. To bridge it requires a special add on circuit card that no longer is available. Any amp channel has distortion and when you bridge an amp you add up the distortion from each channel together so the mono output has twice the normal amount of distortion. This, plus the impedance load limitations, make bridging a very poor solution. If you need more watts, get a larger amp.

When you get the Mouser switch, tell us about it. The Carling variety I purchase locally has the 1, 2, 3 numbers molded in. Does the Mouser switch have the numbers?

Good luck.

[anatech]

Well, that seems to be at least three solid votes not to mess around bridging your amplifier. It takes a lack of understanding the technical issues at hand to think this is a good idea.

-Chris