Hafler dh-200 switch

[jakelm3075]

I do have the technical schematics manual for the amp. The amp seems to be a pretty easy design. I just want , with the help from you guys, to make sure I do things right, the first time (or second time in this case).

I take this project as the perfect oportunity to learn more about circuits and schematics. I am good at part changing but I do have alot to learn on how everything works. That was the main reason for joining up here. Hopefully I can learn alittle, then give my opinion to someone in the future who is in the same boat as I am right now.

I am more familiar with speaker design and audio\video calibration than actual hands on repairs. So I appreciate everyones patients and help.

Jake

P.s. I will let you know on the switch

[anatech]

Hi Jake,
The last comment I made was not aimed at anyone, but rather intended to keep you from making an error.

To test the amplifier, I have a real problem with just shorting the wires and juicing it up. At least use a variac or light bulb in series.

For a permanent inrush limiter, consider using a 2~4 ohm resistor in series that is shorted out by relay contacts, coil energized by the secondary DC supply. That will give you the best solution and lowest supply impedance in the "run" state. This method is used in many large amplifiers.

-Chris

[GRollins]

I find it difficult to believe this thread has gone on this long. It's really a very simple fix.
Oh, well. I'm having a bad day so I'm grumpy. Ignore me if I fuss too much.
The Mouser part number I gave earlier is the Carling Mini-Tippette (or whatever they call the silly thing) direct replacement for the original switch, albeit with a 50% higher current rating than the early version of the switch. Jeez, guys, did you think I'd send you off on a wild goose chase? I've rebuilt four or five of these things in the past eight months or so and have yet another lying open on the floor behind my workbench, ready for Evil Experiments of a JFET nature. I also sold scads of the things back when I was in retail.
Yes, the switch will come in with the 1 2 3 connections stamped on the side. DO NOT IGNORE THE NUMBERS. Connect it as per the original Hafler schematic and you'll be fine.
If you want to upgrade the thing, go through and replace all the electrolytics with film caps. People did so for years. Then Hafler finally got smart and started a production version that did the same thing called the DH-220. It's relatively cheap (assuming that you don't use really, really expensive caps) and very effective, sound quality-wise. That said, the stock units still sound decent. As I detailed in another thread, they beat the pants off my la-di-dah Pioneer Elite receiver in my AV system, and that's without any updates, mods, increasing of bias, etc. Shameful, the sound that AV people think is acceptable, but there it is.
As I believe I mentioned earlier, the power switches in the DH-200 were prone to failure. They usually failed in the closed (i.e. "on") position, but every once in a while you'd get one that froze open. They don't like being hit, either. The red plastic rocker will break if you bump it against a table or shelf. The one booger is that you're going to be working in a tight space getting the new one put in. Be patient and it will work out okay. When doing repairs on these things I would sometimes use push-on connectors so as to make switch replacement faster and easier. The idea is worth what it cost you. If you get some bozo who has managed to kill three switches during the course of a year, it starts sounding like a good idea.
Regarding bridging:
--As I believe someone mentioned earlier, it's not a good idea to use a bridged DH-200 for low impedance loads. In this case, interpret low impedance as anything below 8 Ohms.
--The bridging boards may be unavailable, but that's not a problem. All the add-on board did was serve as a phase splitter. Nothing fancy. It was, as I recall, just a simple differential on a circuit board about an inch or two square. It's trivial to whip up something like that. Use, say, MPSA42s or ZTX453s. This would be a good time to use a current source, although a resistor will do nearly as well and be a lot simpler. Might even sound better. Something like a 15k 1/2W (or 1W if you want to be more conservative) would give you 2mA per side bias.
--For those who believe in opamps, it would be simple enough to use opamps to do the phase splitting, but remember that the Hafler rails are on the order of 60V. You're going to need to drop the voltage so that the opamp doesn't pop.
Regarding gain: There are far too many variables to guess about something like that. Try it. If it works, fine. If not, then we'll talk about possible solutions.

Grey

[jakelm3075]

For the inrush limiter I picked up a small box of .01uF disk. I'm not too thrilled about "hard" wiring this amp either. I wont. I will just wait a couple of days for the Carling switch to come in. Tonight I'll go ahead and try my other switch again. If I blow a fuse, I blow a fuse. I looked at the switch again last night. Its not the switch I posted. That switch was for something else. The switch I bought from RS but is a much bigger toggle switch. The only difference in the switch I bought from RS and the Carling I bought was (becides the light) I believe the amps are different and the style.

[anatech]

Hey Grey,
Yup, a bit touchy. You answered the question in your post #17 rather completely. Other concerns came up. The power switch thing should be in bed.

-Chris

[Zen Mod]

I have PCB pattern somewhere...

[Zen Mod]

II page

[jakelm3075]

My dad had this amp driving 2pairs of Polk Monitor 7a's stacked. Which stacked dropped the ohms down to 3, this amp did a wonderfull job. Thats why I'm so excited to get it workign again. I have only one pair of Monitor 7b's I would love take them off of my Onkyo tx-502 and hook them up to the Hafler, use my onkyo as preamp. But for the long run, I am rebuilding two seperate subs and would use this amp to drive them. It has to be 10 times better than that little plate amp the subs came with.

[jakelm3075]

Choky I have this. But thanks.

Grey, Thanks for the input. I think of this more like a conversation rather than a botheration. If it offends you or anyone here I appologize for dragging this thread out so long.

[GRollins]

Some conversations have more meat on their bones than others. Speaking purely for myself, unless we're due for tornadoes, hurricanes, and blizzards, all on the same day, I get bored with conversations about the weather. What's tomorrow's high going to be and is it going to rain? Mid-70s and 0% chance of rain. Conversation over. Move on to other things. Alcohol, naked ladies, you know...the usual. Given the choice, I prefer them 'nekkid' to 'nude.' As the humorist Lewis Grizzard used to say, "nude" is art--"nekkid" means you're up to something.
I regard inrush limiting as about the same sort of thing. You can use an active circuit, thermistors, relays, or lightbulbs, your choice. Will it make the switch last longer? Presumably. But my experience has been that the 15A version of the switch is pretty reliable as long as it's got the spark suppression caps on it and you don't bash it mechanically. Next topic.
The bridging thing is potentially more interesting, but to take it much further than "not lower than 6-8 Ohms or so" would get into questions of bias current, heatsinking, and whether the DH-200 power supply could handle that sort of thing. However, that seems to have been settled fairly efficiently and that's all to the good.
Jake, I'm not bothered by your posts. They're completely understandable--particularly when faced with some rather random and contradictory responses to your original questions. It's just that I wonder whether some of the posters in this thread really bothered to think about what they wrote, hence my somewhat less-than-cheerful tone (aside from the fact that I had a lousy afternoon, which is certainly not the fault of anyone here--those following the power JFET story will not be at all surprised to hear that I had another run-in with the USPS whilst trying to take care of some of our Canadian members).
Oh, and for the record, I'm not particularly wild about hot-wiring the power switch. Not necessarily for any reason that might first occur to anyone, though. My main objection is the spark you get when the plug first makes contact with the socket. It's an arc. It will pit the plug and the contacts in the socket, which will lead to poor contact in the future. That interface wasn't designed to handle a hot make/break current flow.
Me grumbly? Certainly. It's this unrequited wish to strangle certain nitwits at the post office that keeps bubbling over.

Grey