Here are the Aragon bias adjustment instructions, from some unconfirmed tech support document. See my very important (of course) comments below:
I realize now this is a very ambiguous document. What exactly does "run amps under load" mean, how much power output, continuous sine or music test, and into what load or efficiency speakers? And what is the "operating temperature" ?
This is far more important that a reader might assume. The heatsinks in the 8008 and Palladium series amplifier have very large thermal mass. If they are heated up sufficiently, 2 minutes is no where near long enough to cool down enough to approach the stable bias level.
An hour or more might be required. While I determined my outer channel emitter resistor voltage approaches 26mV in a long term idle warmup, when I run my amp for 30 minutes at moderate level into killer load (Acoustat !+1's) it gets hot enough to roll the voltage to 14mV for a many minutes; I watched it for 15 minutes or so and it hadn't significantly moved upwards. This is because high heatsink temperature causes the bias compensation transistor to cut back the idle current to some minimum level. Only when the heatsinks have cooled down sufficiently is the normal idling bias restored.
So if you start out with heasinks at a relatively high temperature, and allow only two minutes, what you may be setting is actually the minimum bias level, not the long term level.
2000 & 3000 4-6 mV EACH CHANNELSERIES8008ST & BB INNER CHANNEL-12mVand MKII OUTER CHANNEL- 8mV8008X3 & X3B 8-10mV EACH CHANNEL8002 8-10mV EACH CHANNELPALLADIUM II INNER CHANNEL-25mV& 1K OUTER CHANNEL-20mVW/ TOP COVERS ON-HEATSINK TEMP-118 DEG. F.4004 6-8mV EACH CHANNEL2004 4-6mV EACH CHANNELA100,A100X3A200,A200X3DIA150,A125X5 6mV EACH CHANNELIMPORTANT NOTE: RUN AMPS UNDER LOAD UNTIL HEATSINKS REACH OPERATING TEMPERATURE. REMOVE SIGNAL AND LET AMP TO IDLE AT LEAST 2 MINUTES TO STABILIZE. RESET BIAS TO INDICATED VALUES
I realize now this is a very ambiguous document. What exactly does "run amps under load" mean, how much power output, continuous sine or music test, and into what load or efficiency speakers? And what is the "operating temperature" ?
This is far more important that a reader might assume. The heatsinks in the 8008 and Palladium series amplifier have very large thermal mass. If they are heated up sufficiently, 2 minutes is no where near long enough to cool down enough to approach the stable bias level.
An hour or more might be required. While I determined my outer channel emitter resistor voltage approaches 26mV in a long term idle warmup, when I run my amp for 30 minutes at moderate level into killer load (Acoustat !+1's) it gets hot enough to roll the voltage to 14mV for a many minutes; I watched it for 15 minutes or so and it hadn't significantly moved upwards. This is because high heatsink temperature causes the bias compensation transistor to cut back the idle current to some minimum level. Only when the heatsinks have cooled down sufficiently is the normal idling bias restored.
So if you start out with heasinks at a relatively high temperature, and allow only two minutes, what you may be setting is actually the minimum bias level, not the long term level.
Would you be kind enough to email me how to adjust bias on my 8008BB? My email is tahmid@yahoo.com
ReplyDeleteMuch appreciated. I follow your blog and like it a lot. Thanks.