Currently working on a DH-200 I picked up for cheap and am having trouble biasing it. I can get zero volts at the outputs using P1 but cannot get anything but zero mA and adjusting P2 does nothing at the fuse blocks as described in the bias instructions. Amp plays but does not get warm. It has new boards from que...as part of the upgrade kit and new power supply.
The instructions I thought deleted C401 (220 schematic) but I put the stock 390pf cap back in as I saw no images online with that cap not in place.
Thanks. I have read a bunch on this issue on this forum and others and am just stumped as to where the issue is.
The instructions I thought deleted C401 (220 schematic) but I put the stock 390pf cap back in as I saw no images online with that cap not in place.
Thanks. I have read a bunch on this issue on this forum and others and am just stumped as to where the issue is.
Can you post the que schematic? It's likely a problem with the Vbe multiplier.
I will post the schematic when I get home. I did get it with the kit.
HAFLER DH200 HIGH END AUDIOPHILE UPGRADE KIT TOSHIBA JFET CASCODE TOPOLOGY | eBay
HAFLER DH200 HIGH END AUDIOPHILE UPGRADE KIT TOSHIBA JFET CASCODE TOPOLOGY | eBay
Schematic here:
http://www.hafler.com/pdf/archive/DH-200_amp_man.pdf
Q9 likes to fail for some reason. A PN2222A (plastic package version) replaces it. Also watch for P1's wiper having gone open circuit - replace with a good quality trimpot
http://www.hafler.com/pdf/archive/DH-200_amp_man.pdf
Q9 likes to fail for some reason. A PN2222A (plastic package version) replaces it. Also watch for P1's wiper having gone open circuit - replace with a good quality trimpot
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IMO the commonest problem with setting bias is 1)not using the right connection on the meter (Amps, not volts - requires different connections on meter) and that meter fuses can blow, especially if using mA connections. My practice is to use a 1 ohm resistor with clip leads across one of the fuse connectors, and to measure the voltage drop across it.
My
My
I took a blown fuse and soldered a 1ohm 5 watt resistor to it and put in the plus side of each fuse block and measured mV there for bias and set it at 250 for now. I think that math works right? 
I did this with 8 ohm 20 watt load resistors as dummy speaker loads as thats how I do the vacuum tube amps I work on.
Whatever I was doing before just wasnt working.
I did this with 8 ohm 20 watt load resistors as dummy speaker loads as thats how I do the vacuum tube amps I work on.
Whatever I was doing before just wasnt working.
IMO the commonest problem with setting bias is 1)not using the right connection on the meter (Amps, not volts - requires different connections on meter) and that meter fuses can blow, especially if using mA connections. My practice is to use a 1 ohm resistor with clip leads across one of the fuse connectors, and to measure the voltage drop across it.
My
Great minds think alike! I posted before I refreshed this. Thanks!
So all day replacing the rectifier, putting in a buss bar, cleaning and resetting the output devices, new feet, the speaker terminals in the kit werent so nice so the stock are still there. New inputs and carefully routed the cabling. Cleaned the fuses and sockets for the outputs as well as the output terminals. It has the 18k power supply caps which I bypassed with 47uf electrolytics and .1 uf film capacitors.
Bias at 275, the heat sinks get to 98F, and the noise floor is almost down to my mcintosh mc240's neighborhood but I did not go soup to nuts on the hafler. Started listening this evening and comparing to the mc240 with my klipsch chorus ii with rebuilt xovers and titanium tweeter diaphragms. I used a Dynaco pas3 and a marantz thx2 certified 7.1 do everything receiver as preamps. So, not knowing what the hafler is really suppsed to sound like I have to say that with the super efficient klipsch the bass slam is too much. I am going to try it with some jbl 4410 studio monitors which could use some help there. I also wired the additional power supply capacitance to be easily removed so I will try that first. The mc240 has a fatter than stock power and bias supply and it seems to match up better with the klipsch, more balanced through the whole range. Again, I dont know what the hafler is supposed to sound like. The original boards played but the right channel was weaker. When I pulled them the right board had a burnt resistor dead center so I am also going to fix it and swap those boards back in to test whether I goofed up buikding the new boards.
to close the loop on the bias, using the dropping resistor really simplifies the bias adjustment and the new boards allow very precise adjustments with p1 and p2.
Bias at 275, the heat sinks get to 98F, and the noise floor is almost down to my mcintosh mc240's neighborhood but I did not go soup to nuts on the hafler. Started listening this evening and comparing to the mc240 with my klipsch chorus ii with rebuilt xovers and titanium tweeter diaphragms. I used a Dynaco pas3 and a marantz thx2 certified 7.1 do everything receiver as preamps. So, not knowing what the hafler is really suppsed to sound like I have to say that with the super efficient klipsch the bass slam is too much. I am going to try it with some jbl 4410 studio monitors which could use some help there. I also wired the additional power supply capacitance to be easily removed so I will try that first. The mc240 has a fatter than stock power and bias supply and it seems to match up better with the klipsch, more balanced through the whole range. Again, I dont know what the hafler is supposed to sound like. The original boards played but the right channel was weaker. When I pulled them the right board had a burnt resistor dead center so I am also going to fix it and swap those boards back in to test whether I goofed up buikding the new boards.
to close the loop on the bias, using the dropping resistor really simplifies the bias adjustment and the new boards allow very precise adjustments with p1 and p2.
The boards are breaking in for sure. Initial review was premature. Intersting that it has more hum with the cover on than with it off by a big margin. Still need to upgrade the power cord and do the chassis ground. Further listening has made the comparison with the tubes apparent. Much faster response/attack with the hafler. Warmer and less hard edges with the tubes.
So another symptom early on before I placed C-13 back in (new boards had that deleted but I saw no images on the web without that in place) when I attempted to take a voltage reading in that location with the probe there was so much radio affect it made sound out of the speakers without them even being connected to the amp and my DMM went nuts. This is my first work with a SS circuit so I know I sound like a total hack but more information is better than less...
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