Any way to cool a Hafler DH 200 ?
I have a DH 200 power amp I built long ago and modified using a Musical Concepts kit (early 80's maybe?). It is the power for my computer sound and has been fed by a Tascam US-122 audio/midi USB interface. Since upgrading my OS the Tascam no longer works (64 bit) so I wanted to start using my DH 101 (also modded in the 80's by Musical Concepts kit) as the control center for audio from the Mac. There is a question coming ....The DH 200 pretty much is on 24/7 and when I picked it up to move it today I was surprised by how hot it was. Hot enough that I had to wait a couple minutes to let it cool. I don't remember it being that hot. I did recently replace the 2 big main caps with some from ebay that were represented as suitable replacements. They sure sound good.
The question is, is there anything I can do to make this amp run cooler. I seem to remember something you could do inside that altered the amount of heat produced. I really appreciate any thoughts/guidance on this.
*I have moved the amp to an area with more free airflow. It was kind of confined in it's previous space.
I have a DH 200 power amp I built long ago and modified using a Musical Concepts kit (early 80's maybe?). It is the power for my computer sound and has been fed by a Tascam US-122 audio/midi USB interface. Since upgrading my OS the Tascam no longer works (64 bit) so I wanted to start using my DH 101 (also modded in the 80's by Musical Concepts kit) as the control center for audio from the Mac. There is a question coming ....The DH 200 pretty much is on 24/7 and when I picked it up to move it today I was surprised by how hot it was. Hot enough that I had to wait a couple minutes to let it cool. I don't remember it being that hot. I did recently replace the 2 big main caps with some from ebay that were represented as suitable replacements. They sure sound good.
The question is, is there anything I can do to make this amp run cooler. I seem to remember something you could do inside that altered the amount of heat produced. I really appreciate any thoughts/guidance on this.
*I have moved the amp to an area with more free airflow. It was kind of confined in it's previous space.
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I noticed when trying to figure this out that the speakers connected to the amp (Alesis Monitor One) are 4 ohm. Could that cause the heat? Is the DH200 able to handle those 4 ohm loads without damage?
Thanks.
Thanks.
The heatsinks for this amplifier should be OK for a 4 ohm load -- check to see if the bias isn't high.
Thanks for leaving a message jackinnj. I am a home hobbyist at best and as such can follow detailed instructions, but that's the end of my ability.
How does one check and adjust the bias? That is exactly the term I was trying to remember. I think some time in the past I was informed that changing the bias would create some improvement in the sound. That was long ago and now I'm more concerned with the excessive heat.
Care to try and guide me in checking and adjusting the bias?🙂
How does one check and adjust the bias? That is exactly the term I was trying to remember. I think some time in the past I was informed that changing the bias would create some improvement in the sound. That was long ago and now I'm more concerned with the excessive heat.
Care to try and guide me in checking and adjusting the bias?🙂
beefing up the bias is a common practice to achieve more watts in class A from this amplifier ( there is a very good chance that this was a suggestion while the amp was getting upgraded )
obviously this will increase some amount of quality but will also make the amp run hot
if you don't have technical skills to measure the bias you may as well pop the hatch and carefully trim both trimmers existing on amplifier boards marked as P1 to a 30% down or counterclockwise
if you have a dvm there is more accurate ways to do that .
Then again "running hot" amplifiers .... DH 200 in particular kills capacitors very easy so there is a chance that the """Running hot issue"" is not an actual bias problem but some kind of failure
sampling small capacitors inside to measure the conditions will be also a proper thing to do even a small 10USD capacitance meter will put you in the picture and give you an idea on what is going on ...
Kind regards
sakis
obviously this will increase some amount of quality but will also make the amp run hot
if you don't have technical skills to measure the bias you may as well pop the hatch and carefully trim both trimmers existing on amplifier boards marked as P1 to a 30% down or counterclockwise
if you have a dvm there is more accurate ways to do that .
Then again "running hot" amplifiers .... DH 200 in particular kills capacitors very easy so there is a chance that the """Running hot issue"" is not an actual bias problem but some kind of failure
sampling small capacitors inside to measure the conditions will be also a proper thing to do even a small 10USD capacitance meter will put you in the picture and give you an idea on what is going on ...
Kind regards
sakis
Remove the B+ fuse. This fuse is in the line from the ’+’
capacitor terminal to hole #3 on the board. Connect an ammeter’s ' + ' !ead to the fuse clip nearest the large filter capacitors. Connect the’ - ’lead to the other side of the fuse clip. Avoid intermittent connections, and do not short the leads together. Turn the amplifier on, and if possible adjust the line voltage to 120 volts. Adjust P1 to 250-275 mA. Turn the amplifier off, and when the current drops to zero, then remove the ammeter and replace the fuse.
You can bias it higher into Class A. Just DO NOT exceed say 350mA. Musical Concepts says don't go past 400mA, but I think anything beyond 350mA is too high. The higher it is set, the hotter it will run!
capacitor terminal to hole #3 on the board. Connect an ammeter’s ' + ' !ead to the fuse clip nearest the large filter capacitors. Connect the’ - ’lead to the other side of the fuse clip. Avoid intermittent connections, and do not short the leads together. Turn the amplifier on, and if possible adjust the line voltage to 120 volts. Adjust P1 to 250-275 mA. Turn the amplifier off, and when the current drops to zero, then remove the ammeter and replace the fuse.
You can bias it higher into Class A. Just DO NOT exceed say 350mA. Musical Concepts says don't go past 400mA, but I think anything beyond 350mA is too high. The higher it is set, the hotter it will run!
If you don't have a current meter just plug it in through a light bulb. Adjust the bias to dim the bulb a bit.
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