hafler dh-200 rebuild

[BrianGT]

I picked up an old hafler dh-200 over the weekend with one channel working. I got it and an old heathkit tubeamp for $85, so I figured that I would try to get it working, and if not, use the case for a leach amp, since it is almost the same as my first leach amp case.

For now, I am just working on getting the one channel sounding better, then I will fix the other channel the same way. I did the following modifications last night:

-changed the power plug to an IEC connector, getting rid of the old 2-prong connector. I tied the ground to the transformer centertap. This improved the sound.
-swapped out the power switch and re-wired the power supply wiring with 16ga silver-coated teflon covered wire and 18ga for other wires. (i got the wire cheap from apexjr)
-changed the input jack to a much heavier gold plated dayton one and used shielded co-ax for the wiring
-wired terminal blocks to the power supply so that I could swap out transformers. I tried it with the original EI core transfomer and a new toroid transformer that I have for my leach amp. I didn't hear much difference... I will do more listening later.

The one channel sounds much better. Initially, it had a significant hum. Swapping the input jacks, adding the ground and re-wiring almost totally removed this. I have compared the toroid and the ei core transformers and I couldn't hear much difference. I will do more extensive testing on this later. This is a decent sounding amplifier, and on par with my leach amp.

Future plans and questions:
-swap power supply caps: originally 10,000uF... what is a good replacement? I figured 20,000-30,000uF for each rail
-swap speaker terminal jacks: I didn't have any that would fit the chassis
-swap old components on the boards for newer ones. I figured swap the caps for now. Any suggestions on other components? How do I adjust the pot on the board? I am assuming that it is for adjusting the bias, but I am unsure what to make this, or where to measure to adjust it.

Anyone have any more suggestions on upgrades to this amplifier?

I took about 30 pics of this process... but I erased them by accident when I downloaded them from my camera. I will post pictures later. The schematic is on my website at:
http://brian.darg.net/dh200rebuild
I will put more pictures there, once I retake them.

--
Brian

 

[Nelson Pass]

You could gut it and stick the Halcro circuit inside.

 

[Fred Dieckmann]

You could gut it and stick the Halcro circuit inside

I couldn't have said it better myself. And if I did, the moderators would have been on me like a swarm of locust.

Ah..... the the glories of executive privilege.....


I think I hurt myself laughing
Fred

P.S. If you printed pretty small I bet the stack of schematics for the Halco would just about fit in the Hafler, if you packed them in real tight......but only if you left out the patent document.

 

[BrianGT]

Interesting idea... but I was figuring that since the transformer is still good and so are the output devices, why not bridge it and use it for a subwoofer amplifier. Hafler has a schematic for the bridging circuit on their website:

http://www.hafler.com/techsupport/pdf/DH-202_PC-7_bridgeKitForDH-200.pdf

I am concerned about the the stability of the DH-200 in bridged mode, since the subwoofer is 4 ohms and when bridged, I assume that each channel will be driving half of the impedence, making each channel driving a 2 ohm load... I can experiment with it.

Anyone have any experiences with the hafler amplifiers? I noticed that Smart Devices licensed the hafler circuit and is selling their version of the amplifier. I will talk to their engineer and see how they modified the hafler circuit.
http://www.smartdev.com/2x150vt.html

--
Brian

 

[1/137]

I bridged a dh-200 a long time ago. I don't even remember what I was using for speakers then but I do remember that the two I had did not like being bridged. They ran very hot and didn't sound very good at all. That's all I remember as it was 20 plus years ago. I ended up building 4 A-40's mono amps and was very happy with them! I believe I just "unbridged" the dh-200's and never bothered to do anything further with bridging the amps. I still have 3 or 4 of them and it would be fun to try and do something with them.

rt

 

[1/137]

Also...I believe that Audio Amateur did at least one article on dh-200 mods. I do not remember the issue (all of mine are packed along with the Audios that contain the Cordell Distortion Analyzer articles).

rt

 

[mlloyd1]

how much are you willing to do?

Stuffed with a Halcro... indeed!

How much modification do you want to do? If I was modding a DH200, I'd study the Borbely site. He has a number of amp projects/kits that would be great upgraded and updated driver boards for the DH200. If you don't want to go with any the "all-FET" modules, I can personally vouch for the Servo 50 being a very nice sounding amp (pics on my web page). The board comes with the option of using on card regulators for the front end.

Note: You have to make some changes to use this board with the supply rails of the DH200. And personally, I'd like more output devices to feel comforatble rating the amp at 100W continuous into 8 ohms.

Hope this helps. Ask more questions if you like...

 

[HDTVman]

I've had several Hafler amps over the years. The only one I ever had trouble with was a new one that was fixed and returned to me overnight. I have owned DH-200s and DH-220s and have been very happy with both models The only mods I've done to them are about what you describe (PS upgrades and better connectors)

Will I try to tell you that they are the best amp in the world? NO WAY! But they are a good everyday amplifier that will set there and play, not give a lot of trouble and sound good too. They do run hot and always have. I still have one I use for the rear channels of my 5.1 system. I have a Dynaco ST400 for the low frequencys of the front channels and a pair of MK IIIs for the top. (David Hafler worked at Dynaco for years and did a lot of the design work there.)

Later
Bruce

 

[mlloyd1]

Brian:
The Smartdev site says the output stage has voltage gain. This would have to be different topology from the DH200 (slightly less than untiy gain output stage). Maybe they actually licensed the TransNova circuit???

Anyone have any experiences with the hafler amplifiers? ...
Brian [/B]

 

[BrianGT]

Will I try to tell you that they are the best amp in the world? NO WAY! But they are a good everyday amplifier that will set there and play, not give a lot of trouble and sound good too. They do run hot and always have. I still have one I use for the rear channels of my 5.1 system. I have a Dynaco ST400 for the low frequencys of the front channels and a pair of MK IIIs for the top. (David Hafler worked at Dynaco for years and did a lot of the design work there.)

I know that the Hafler won't even touch the sound quality of the passlabs aleph 2 project that I am finishing up. I just figured that it would be an interesting project, restoring and old amplifier and having a halfway decent 2-channel amplifer for under $100.

Regarding the boards and circuit. I would like to keep the transformer and output devices, as they seem to still be good. I the old EI core to a new toroid and there didn't seem to be much sound difference, and I don't think that it worth putting another $60 into it, since that is all that I paid for it anyway. If there is a better circuit that I can use with the transformer and output devices, that I can easily redesign the board.

I forgot to mention, I also replaced the rectifier bridge with a new one and a new smaller .1uF 250V cap instead of the old 1uF cap (ceramic) and that made a huge difference. I am going to order some polypro. caps and mica to replace the film and ceramic caps on the board.

I was also planning on replacing the bi-polar electrolytic C1 with a polypro cap. Complete manual is here:
http://www.hafler.com/techsupport/techsupport.asp?ID=3

--
Brian

 

[Nelson Pass]

On a more practical note:

Since you are only keeping the outputs and transformer,
I suggest that you wire the transformer for 240V primary,
run it at 120V, and make a nice Class A amp out of it. I
did this once, and had great results with the Hafler.

Who wants the schematic?

 

[BrianGT]

On a more practical note:

Since you are only keeping the outputs and transformer,
I suggest that you wire the transformer for 240V primary,
run it at 120V, and make a nice Class A amp out of it. I
did this once, and had great results with the Hafler.

Who wants the schematic?

That was an idea that I had at first, until I opened the case and realized that the transformer only had a single primary.... leaving me stuck at a ~82VCT transformer putting out around +/- 56v DC

I think that this is one of the older DH-200 from the very early 80s.

--
Brian

 

[1/137]

I am certain at least two of my dh-200 have the 240 V winding....any details on the mod would be appreciated.
thank you,
rt

 

[BrianGT]

If you have the newer transformer, here is a picture of the wiring that you would do to change it to 240v. This will just cut the output voltages in half, allowing you to use lower voltage designs, such as a class A amplifier. You should get around +/- 28-29v from it once you change the wiring.

Picture from the manual on the website:
http://www.hafler.com/techsupport/techsupport.asp?ID=3

--
Brian

 

[planet10]

On a more practical note:

Since you are only keeping the outputs and transformer,
I suggest that you wire the transformer for 240V primary,
run it at 120V, and make a nice Class A amp out of it. I
did this once, and had great results with the Hafler.

Who wants the schematic?

I have 2 DH200s and what was originally planned was to lose a channel so as to effectively double the size of the power supply (and make room for more caps), but this is more interesting. i'll have to dig the beasts out and see if they are the single or dual primary trafos.

dave

 

[HDTVman]

Hi Nelson;

Ya, I'd be interested on the class A mod for the Hafler. What have you got for the old ST400? Big transformer there.

Later
Bruce

Well heck, I'm old too ya know.

 

[Fred Dieckmann]

Hafler

Do I see the beginning of the "Hack the Hafler" contest. Might be very interesting to start a thread for a design for a given power supply, heatsink capacity, and output configuration. I might even play as I have have a couple "Bonk the B and K" adventures that were simular in scope to this.


Fred

 

[mlloyd1]

OK Nelson,
I know this was a trick question, so I'll bite:

Me, Me!

mlloyd1

.... make a nice Class A amp out of it. I
did this once, and had great results with the Hafler.
Who wants the schematic?

 

[mlloyd1]

yes, DH200, DH220, XL280 run hot! but...

It's normal for these amps to run fairly hot. The rails are +/- 65 volts when not driving a load and each MOSFET is biased to about 100mA to hit the zero tempco point Hitachi designed the devices to.

I won't touch the comment about the sound for obvious reasons

.... They ran very hot and didn't sound very good at all.

 

[Variac]

I've got a DH 220 with one channel out, was wondering what to do with it.... Sounds like there are a LOT of disfunctional DH amps out in the world!

Will check for dual trans input wires
Let's see that schematic!- might become the most ubiquetous Pass amp ever!