Balance operation
Hi Tony
See an example of a Pass amp with balanced and unbalanced switch. You can probably apply the same principle to the DH-200/220 amp.
http://cygnus.ipal.org/mirror/www.passlabs.com/images/a75f9a.jpg
Good luck
Fab
Hi Tony
See an example of a Pass amp with balanced and unbalanced switch. You can probably apply the same principle to the DH-200/220 amp.
http://cygnus.ipal.org/mirror/www.passlabs.com/images/a75f9a.jpg
Good luck
Fab
Mod on fuses location?
Hi Hafler fans!
One mod that could be interesting to do is to move the power supply fuses (+V and V- for both channels) between the diode bridge and the power capacitors. In 2 of my other amps, it has improved the bass response so it is more "fast". One explanation might be the non negligeable resistance of the fuse between the power caps and the mosfets... However, in my 2 amps I have a 700ma and 1.3A class A current compared to the DH-200 which is originally about 220ma or so.
My friends have my DH-200 amps so I wonder if one member could try this mod and report its findings. It would be good to specify if the modified amp has its original power caps or new ones (which ones).
Thanks
Fab
Hi Hafler fans!
One mod that could be interesting to do is to move the power supply fuses (+V and V- for both channels) between the diode bridge and the power capacitors. In 2 of my other amps, it has improved the bass response so it is more "fast". One explanation might be the non negligeable resistance of the fuse between the power caps and the mosfets... However, in my 2 amps I have a 700ma and 1.3A class A current compared to the DH-200 which is originally about 220ma or so.
My friends have my DH-200 amps so I wonder if one member could try this mod and report its findings. It would be good to specify if the modified amp has its original power caps or new ones (which ones).
Thanks
Fab
fuses
Hi Fab!
This mod is suggested also in the famous "Pooge" article but I never tried it. I'm sceptical about trying it, not for the sonic benefits rather for the reduced effectiveness of the protection of the fuses when placed before the diode bridge. The energy stored in the capacitor banks is not irrilevant. Moreover I use to get rid of the output fuse, so I prefer to keep the other fuses as near as possible the output of the amp. Another reason is that the fuse rating, if placed before the diode bridge, should be quite higher respect to the normal rating, due to the cold switch on peak current that charges the empty capacitor bank. This also reduces the protection effectiveness.... The original fuses are 5A, the fuses suggested in the Pooge article are 7A...
Nonetheless, it is wort a try! I do not have access to an original Hafler, and the ones I do are actually clones quite far from the original
Ciao!
Paolo
Hi Fab!
This mod is suggested also in the famous "Pooge" article but I never tried it. I'm sceptical about trying it, not for the sonic benefits rather for the reduced effectiveness of the protection of the fuses when placed before the diode bridge. The energy stored in the capacitor banks is not irrilevant. Moreover I use to get rid of the output fuse, so I prefer to keep the other fuses as near as possible the output of the amp. Another reason is that the fuse rating, if placed before the diode bridge, should be quite higher respect to the normal rating, due to the cold switch on peak current that charges the empty capacitor bank. This also reduces the protection effectiveness.... The original fuses are 5A, the fuses suggested in the Pooge article are 7A...
Nonetheless, it is wort a try! I do not have access to an original Hafler, and the ones I do are actually clones quite far from the original
Ciao!
Paolo
Hi Fab!
This mod is suggested also in the famous "Pooge" article but I never tried it. I'm sceptical about trying it, not for the sonic benefits rather for the reduced effectiveness of the protection of the fuses when placed before the diode bridge. The energy stored in the capacitor banks is not irrilevant. Moreover I use to get rid of the output fuse, so I prefer to keep the other fuses as near as possible the output of the amp. Another reason is that the fuse rating, if placed before the diode bridge, should be quite higher respect to the normal rating, due to the cold switch on peak current that charges the empty capacitor bank. This also reduces the protection effectiveness.... The original fuses are 5A, the fuses suggested in the Pooge article are 7A...
Nonetheless, it is wort a try! I do not have access to an original Hafler, and the ones I do are actually clones quite far from the original
Ciao!
Paolo
Hi Paolo
I never had the chance to get a copy of ths pooge article. Is the 7A fuse suggested for the 2 original caps of 10000uf or for more capacitance?
I am not too worried about the location change of these fuses. They do not protect that much. The output mosfets are very robust. In fact these mosfets can support a vey high current for several seconds.... By this time, the main fuse will probably blow. How many peoples have experienced one of these DC power supply fuses blown for a real circuit failure (other than the aged fuse failure itself)?
Why did you remove the output fuse since it is located in the feedback path of the amp. Its series resistance is negligable in that location...
If someone wants to try it please raise your hand?
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Hi Fab,
7A is for the stock 10mF original cap. I naively suppose that removing the output fuse I could still have a "speaker protection fuse" if I leave this fuse after the filter bank.
I know, the output fuse is in the feedback loop, but it is in any case in the output signal path
...Ciao
Paolo
My estimation, from memory, based on temp and power measurements it is in the range of about 0.55 C/W
I ran my Pooged 200 at 500 ma per rail per side. Heatsinks got very warm!. I used the speaker fuse holders inline between Trannie and bridge with ground to massive copper bar running between 4x10000uf grnd terminals. Outputs were wired straight to binding posts and spkr returns straight to above copper bar. Never had any problems with 7A fuses unless playing Dark Side Of The Moon too loud..... I don't miss twisting all that wire though!
I get about 50-55 deg C or so at about 50W dissipation in the heatsink. At 500ma you get about 60W so it should be about [55 -60] deg C or so...
Are you saying that you have changed the location of the rails fuses so they are not between the capacitor bank and the Trannie anymore?
"By this time, the main fuse will probably blow. How many peoples have experienced one of these DC power supply fuses blown for a real circuit failure "
I have, and on more than one Hafler amplifier.
The time-lag main fuse will pass about 1.2KW for one hour before opening.
The rail fuses are fast-blow types and open with shorted outputs.
If you have the correct speaker fuse, they will open on speaker wire shorts, or speaker faults.
I have, and on more than one Hafler amplifier.
The time-lag main fuse will pass about 1.2KW for one hour before opening.
The rail fuses are fast-blow types and open with shorted outputs.
If you have the correct speaker fuse, they will open on speaker wire shorts, or speaker faults.
Pooge 2 article
Thanks msb64 but another forum member gave it to me recently and I thank him very much.
fab
Thanks msb64 but another forum member gave it to me recently and I thank him very much.
fab
If an output shorts, the speaker fuse should blow first.
The amplifier output is now stuck to one rail.
Now the feedback loop causes the outputs on the other rail to turn on to bring the DC to zero. At that point one of the rail fuses will go open to limit damage.
The main power fuse generally opens only on rectifier/filter cap/transformer faults.
The amplifier output is now stuck to one rail.
Now the feedback loop causes the outputs on the other rail to turn on to bring the DC to zero. At that point one of the rail fuses will go open to limit damage.
The main power fuse generally opens only on rectifier/filter cap/transformer faults.
If the output fuse opens then its parallel 2k resistor is still in the feedback loop and should normally avoiding to switch to one rail...
Even if the rail fuse opens it does not necessary justifies its mandatory use if the expensive parts (mosfets) of the amplifier circuitry can survive long enough to have the main fuse to blow. Anyway, having said that, if one places a higher value fuse between the bridge and cap - as it seems was already done successfully - then it should satisfy everybody.
Hybrid Hafler DH220
Has anyone considered turning a Hafler DH220 or DH200 into a tube hybrid amp? Not to get anyone upset but they are inexpensive to acquire and pretty wide up for a mod of this type once you gut the interior circuit board and it is not like there are not many others available so you are not killing a really rare collectable.
Thoughts
Has anyone considered turning a Hafler DH220 or DH200 into a tube hybrid amp? Not to get anyone upset but they are inexpensive to acquire and pretty wide up for a mod of this type once you gut the interior circuit board and it is not like there are not many others available so you are not killing a really rare collectable.
Thoughts
"If the output fuse opens then its parallel 2k resistor is still in the feedback loop and should normally avoiding to switch to one rail..."
R25 in series with R23 form a voltage divider with R35, providing about half the rail voltage to the bases of Q2 and Q6. Let's say the positive rail FET has shorted. Q6 is cut off and Q5 is turned on. Q5 turns on the negative rail FET to try and reduce the DC at node 9. The negative rail FETs now have to dissipate whatever the supply can source until a fuse blows.
Do you want to have the FETs have to open a 5A fast-blow fuse on a 60V rail, or the 5A slow-blow fuse on the 120V main?
It has been my experience that the Vas transistors can sink enough current to burn up the gate protection zeners and that the FETs on the good rail then lose their gates (low resistance from gate-to-source), and the only surviving FET is the one in parallel with the shorted FET.
I guess an audiophile won't mind having to buy a set of four new outputs.
R25 in series with R23 form a voltage divider with R35, providing about half the rail voltage to the bases of Q2 and Q6. Let's say the positive rail FET has shorted. Q6 is cut off and Q5 is turned on. Q5 turns on the negative rail FET to try and reduce the DC at node 9. The negative rail FETs now have to dissipate whatever the supply can source until a fuse blows.
Do you want to have the FETs have to open a 5A fast-blow fuse on a 60V rail, or the 5A slow-blow fuse on the 120V main?
It has been my experience that the Vas transistors can sink enough current to burn up the gate protection zeners and that the FETs on the good rail then lose their gates (low resistance from gate-to-source), and the only surviving FET is the one in parallel with the shorted FET.
I guess an audiophile won't mind having to buy a set of four new outputs.