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Old 16th August 2011, 06:03 AM   #971
rfj5106 is offline rfj5106  United States
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How do you determine the optimum value for the choke?
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Old 16th August 2011, 06:59 AM   #972
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The choke is for high-frequency noise, not hum.
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Old 16th August 2011, 06:45 PM   #973
rhr9 is offline rhr9  France
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Hi ,

Here is a topic , ( on the french Elektor forum ) , about PI filtering :
alim et filtre en PI - ELEKTOR.fr | Électronique : Analogique Numérique Embarqué Microcontrôleurs Audio Test Mesure

@ + Philippe.
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Old 25th September 2011, 01:56 AM   #974
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I did a bad thing... I bought a dh220 on fleabay. I have not got it yet to see what kind of basket case it is , I have not bought anything on ebay electronics that was working when I got It ....That said I have been lucky that I have been able to fix everything reasonably cheap. Stay tuned It looks like a pawn shop special (was working the last time I plugged it in)...

I am an amplifier addict. the fact that i happen to be drinking when I buy these wonderful amps means nothing....

Does anyone know how deep in class A you can bias or is there a sweet spot(to paraphrase another)

Burning in South Carolina... EL
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Old 25th September 2011, 02:14 AM   #975
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Quote:
Originally Posted by eyoung View Post
I did a bad thing... I bought a dh220 on fleabay. I have not got it yet to see what kind of basket case it is , I have not bought anything on ebay electronics that was working when I got It ....That said I have been lucky that I have been able to fix everything reasonably cheap. Stay tuned It looks like a pawn shop special (was working the last time I plugged it in)...

I am an amplifier addict. the fact that i happen to be drinking when I buy these wonderful amps means nothing....

Does anyone know how deep in class A you can bias or is there a sweet spot(to paraphrase another)

Burning in South Carolina... EL
Normal BIAS for the DH-200 is 250mA. For the DH-220, it is 275mA.

You can go higher, but at the expense of more heat, and a slightly shortened life span. I'm not sure what the maximum you can go before something smokes, but I wouldn't go higher that 300mA.
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Old 25th September 2011, 04:48 AM   #976
fab is offline fab  Canada
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Quote:
Originally Posted by ouimetnick View Post
Normal BIAS for the DH-200 is 250mA. For the DH-220, it is 275mA.

You can go higher, but at the expense of more heat, and a slightly shortened life span. I'm not sure what the maximum you can go before something smokes, but I wouldn't go higher that 300mA.
Hi eyoung

For more clarification, the output Lateral Fets are self protected against over temperature. The temperature coefficient (about 110-130 ma range per mosfet) change after some bias current value, so the more the temprature rises the more the current drops. Therefore, even if you try to increase the bias current, after some times, it will automatically reduces due to high temperature. The amount of reduction is also function of the size of the heatsink. I remember noticing that effect around 300ma ( bias for 2 pairs) or more - I think. I have already described it earlier in the thread.

The "sweet spot" for these Lateral mosfets is high bias current thus would require a bigger heatsink...or to reduce the voltage (I remember Nelson Pass indicating that this design can make a nice sounding class A amp)

Also, these amps have thermal cutoff switches when heatink temperature exceeds 70C thus you can try different bias current values without too much risk.

Good luck

Fab

Last edited by fab; 25th September 2011 at 04:51 AM.
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Old 25th September 2011, 06:48 PM   #977
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Quote:
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...Does anyone know how deep in class A you can bias or is there a sweet spot(to paraphrase another)
I asked the same "class 'A' question elsewhere on this thread. They advised me (on an XL280) "pull back on the finals PS voltage to about 30; adjust bias until you can't touch the sinks." Also asked the question: "Would it be worth it?"

cheers tony
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Old 22nd October 2011, 08:44 AM   #978
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Here is another idea. Convert the power supply from a full wave BRIDGE to a simple full wave supply. This way instead of having + and - 60v you would only have about 60v. Then use the type circuite used in one of the Quad amps to make a + and - supply from one voltage. Use the first circuite to get the 60V dc then the last 1/2 of the next circuite to get the split supply voltages. Then we should be able to run the bias a whole lot higher.
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Old 22nd October 2011, 03:05 PM   #979
fab is offline fab  Canada
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Default Class A higher current

Quote:
Originally Posted by woody View Post
Here is another idea. Convert the power supply from a full wave BRIDGE to a simple full wave supply. This way instead of having + and - 60v you would only have about 60v. Then use the type circuite used in one of the Quad amps to make a + and - supply from one voltage. Use the first circuite to get the 60V dc then the last 1/2 of the next circuite to get the split supply voltages. Then we should be able to run the bias a whole lot higher.
You mean a virtual ground for a power amp and using half de power capacity of the actual tranformer.... why not change the transformer to a smaller voltage with same power rating then...
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Old 22nd October 2011, 03:22 PM   #980
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Default Class A

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You mean a virtual ground for a power amp and using half de power capacity of the actual tranformer.... why not change the transformer to a smaller voltage with same power rating then...
Yes FAB, that's what I did. Worked out very well. I use it as a tweeter amp, running 17.5 VDC on each rail.
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