Hafler DH-200/220 Mods

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D

Dick West

Member
Joined 2004
zcables said:
Any link to a high current switch that would work in the DH200? I'm not against getting large filter caps (twice bypassed) and calling it a day coupled with the upgraded bridge rectifier.
Click to expand...

I agree with the other posts here. No magic in the PS board you show. It is not two halves. The 4 diodes shown make up one diode bridge. Think the PS caps might be fakes at that low price.

My DH-200 pair of mono blocks each have a pair of 39K mfd caps suitably bypassed with quality film caps. No changes were made to switch, diode bridge, etc. No change was needed because I use a soft start circuit.

My soft start is mounted in a separate metal cabinet that has AC sockets into which an amp can be connected. The soft start circuit is realized using a time delay relay and a 50 ohm power resistor. About 8 seconds are used when turned on until the amps' PC capacitance is fully charged.

So, you could swap in a pair of higher capacitance good quality PS caps, and maybe even find a way to shoe horn in a 2nd pair of caps. No muss, no fuss, when using an outboard soft start box. I soft start 156K mfd of PS capacitance for this pair of amps with nary a whimper.
 
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Stormrider

Stormrider

Member
Joined 2006
Dick West said:
My soft start is mounted in a separate metal cabinet that has AC sockets into which an amp can be connected. The soft start circuit is realized using a time delay relay and a 50 ohm power resistor. About 8 seconds are used when turned on until the amps' PC capacitance is fully charged.
Click to expand...

8 seconds? That must be a very large power resistor. I think a typical soft start circuit would trigger in a second or less, and this is typically long enough.

Rod Elliot has a basic one detailed on his website sound.westhost.com
 
D

Dick West

Member
Joined 2004
Stormrider said:
8 seconds? That must be a very large power resistor. I think a typical soft start circuit would trigger in a second or less, and this is typically long enough.

Rod Elliot has a basic one detailed on his website sound.westhost.com
Click to expand...

You are correct. The 8 seconds is too slow. A 20 ohm resistor might be more suitable. I went with the power resistor I had handy, plus I did not know at the time how many amps might be soft started at one time. Building a soft start circuit is simple to do if one wants to do it. I went for a more plug n' play approach. Here is my wiring diagram and a picture of the power resistor, a stand off connector, and the time delay relay.

The trick is to find an AC powered relay suitably sized for the occasion. I got mine off (where else) eBay.
 

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Z

zcables

Member
Joined 2008
A more realistic and circuit stable approach I've composed: Parallel a pair of 6800uf and a bypass (2.2uf?) cap to replace each original 10000uf filter cap. This would allow for a little more capacitance, but hopefully not enough to cause issues; plus lower resistance thanks for the split overall value. All the caps would be soldered tabs, but I'd strap all the caps together before making to electrical connection, so it would have a clean look with solid connections.

Am I missing something with this design? Did I forget something? This would still be in coordination with upgraded 35A bridge rectifier.
 
Stormrider

Stormrider

Member
Joined 2006
zcables said:
A more realistic and circuit stable approach I've composed: Parallel a pair of 6800uf and a bypass (2.2uf?) cap to replace each original 10000uf filter cap. This would allow for a little more capacitance, but hopefully not enough to cause issues; plus lower resistance thanks for the split overall value. All the caps would be soldered tabs, but I'd strap all the caps together before making to electrical connection, so it would have a clean look with solid connections.

Am I missing something with this design? Did I forget something? This would still be in coordination with upgraded 35A bridge rectifier.
Click to expand...

That would be a fine upgrade.

Not really necessary, but you may also want to fit a ~6.8K 2W resistor in parallel with each cap bank to discharge the caps at power off. With this fitted I find they discharge more evenly reducing turn off thumps, and it's convenient when working on the amp (setting bias, etc).
 
R

rsavas

Member
Joined 2012
I have been working on this AC soft-start ckt as well. I am basing it on the old Pioneer SX-1250 design, since I have acquired a used SX-1250 transformer. You can down-load the SM from.
Main scan page
I have attached my schematic and BOM. Note I have not fabricated this ckt yet, but it is rather simple.
Regards
Rick
 

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rsavas

Member
Joined 2012
Soft-start ckt's

Oop's previous schematic has been updated, see attached. I welcome feedback as well.
I have the other sections designed and laid out too, but off topic for this discussion.
I based this stuff from the SX-1250 & other Pioneer amplifier designs as well as the National power supply app note as used for thr LME498xx series of parts
1) main rectifier & filter
2) regulators & protection ckt
3) LME49830 + Lateral MOSFET

Thx Rick
 

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rsavas

Member
Joined 2012
C1, according to National ap1849, to protect against turn-on/off spikes, Pioneer did not use it = optional
C3, Nationals idea, another optional, yes a film cap would do as well= better. I used 5mm lead spacing.
Thinking of adding 2 triacs, controlled by opto's, in series with the line & in parallel with K1 so that I can add MCU control option, would require separate power for MCU, more PS what can I say.
 
djk

djk

R.I.P
Joined 2001
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djk

djk

R.I.P
Joined 2001
While in theory it could be done, I would not recommend trying it at all.

The bias circuit would have to be redesigned for the much higher gate voltages, and temperature compensation. The pin-outs are different. Source resistors would need to be added. The device threshold voltages would need to be matched. The frequency compensation would need to be changed. Fold-back current limiting would be a good idea, the IRF type do not protect themselves like the Hitachi type do. Etc.

But yes, it is possible.
 
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