Hi!
After having sold off my Yammy M-80 quite a while back, and then an episode of lost funds with a previous diyA purchase, was finally able to get a reasonable deal on an Aragon 8002. Big difference in design/layout that I like; super clean. Nice noticeable improvement in sound quality.
Anyway, noticed one channel was running a touch warmer than the other, so I dived in and did the "check the bias thing). One channel read 18mv over the resistor, the other was ~30mv.
I re-set them to 10mv just as a starting base point (seems to be the magic number for a lot of amps. Runs cold and still sounds great. I know that this amp supposedly is supposed to run warm~hot, so the question is...
What is the ideal bias for the 8002?
Thanks.
bluesmoke
SMALL EXTRA: One odd thing (lucky me; like always with amps), I've noticed that when I've listened to the amp at low levels from a cold start, about 1 hour in the left channel seems to break up. As soon as I turn up the volume and run it for a while, things are fine when back down to quiet listening levels. Weird... It FEELS like a relay problem (me and relays... starting to hate them), but both channels seem to be making solid contact. Could still be a relay problem (oxide from arcing~ I can't see), but just wondering if there might be any alternative suggestions. Can live with the weirdness for now, but this is just shouting "fix me!".
After having sold off my Yammy M-80 quite a while back, and then an episode of lost funds with a previous diyA purchase, was finally able to get a reasonable deal on an Aragon 8002. Big difference in design/layout that I like; super clean. Nice noticeable improvement in sound quality.
Anyway, noticed one channel was running a touch warmer than the other, so I dived in and did the "check the bias thing). One channel read 18mv over the resistor, the other was ~30mv.
I re-set them to 10mv just as a starting base point (seems to be the magic number for a lot of amps. Runs cold and still sounds great. I know that this amp supposedly is supposed to run warm~hot, so the question is...
What is the ideal bias for the 8002?
Thanks.
bluesmoke
SMALL EXTRA: One odd thing (lucky me; like always with amps), I've noticed that when I've listened to the amp at low levels from a cold start, about 1 hour in the left channel seems to break up. As soon as I turn up the volume and run it for a while, things are fine when back down to quiet listening levels. Weird... It FEELS like a relay problem (me and relays... starting to hate them), but both channels seem to be making solid contact. Could still be a relay problem (oxide from arcing~ I can't see), but just wondering if there might be any alternative suggestions. Can live with the weirdness for now, but this is just shouting "fix me!".
bluesmoke said:
We aim for some target CURRENT.
now:
Volt = Resistance x Current
( U = R x I )
so,
1. you should try to measure or see what resistance Those emitter resistors have.
for example 0.22 Ohm
2. you decide what current you want to bias to
for example 60mA = 0.060 Ampere
3. You adjust until you get a voltage across this resistor
that corresponds to 60 mA :
for example:
Volt = Ohm x Ampere
Volt = 0.22 x 0.060
Volt = 0.0132 Volt .... ~13 mV
====================
How much bias current for this Aragon 8002amplifier?
We need to know 2 things:
a) What power transistors? What is the text on those?
b) How many of them?
Only 2 per channel? Or maybe 4?
Generally, we can say, that Bipolar power amplifier normal Class AB
would want to have an idle current of something like
50-90 mA in each output transistor.
Can vary a little bit between different devices.
But I am sure someone at this forum has used EXACTLY the same output Transistors
that are used in Aragon 8002.
And so would be able to give you a good advice.
Regards, lineup
The Aragon is basically a Krell.
The 8002 is a successor of the 2004, sort off a class AB version of the KSA50, 4 TO3/Ch output devices.
First series 2004 used Krell type Motorolas, MKII had Japanese metal can output devices.
The 8002 had 4 2SA1302/2SC3281 devices per channel, also designed by another guy instead of DanniO.
The 8002 sounds a whole lot better with the bias bumped up a bit, at the factory setting it already does a few watts in A. Best for that would be to have the heatsinks breath open air, instead of covered.
To keep the precious Toshibas in the 2004 alive, better to have them cool instead of wearing them down hot. You're not going to find replacements. (unless you feel the urge to pay my bill for a fancy dinner)
The 8002 is a successor of the 2004, sort off a class AB version of the KSA50, 4 TO3/Ch output devices.
First series 2004 used Krell type Motorolas, MKII had Japanese metal can output devices.
The 8002 had 4 2SA1302/2SC3281 devices per channel, also designed by another guy instead of DanniO.
The 8002 sounds a whole lot better with the bias bumped up a bit, at the factory setting it already does a few watts in A. Best for that would be to have the heatsinks breath open air, instead of covered.
To keep the precious Toshibas in the 2004 alive, better to have them cool instead of wearing them down hot. You're not going to find replacements. (unless you feel the urge to pay my bill for a fancy dinner)
Just contact Mondial(now owned by Klipsch). I contacted them a few months ago because I was interested in the schematics for the Aragon 4004. I also recontacted them last week to get an owners manual for the Aragon Soundstage processor I recently purchased. They sent everything right over plus the bias setup procedure for the 4004 mkII.
Here is the email address, Support.Mondial@klipsch.com. I talked with a guy named Steve Philips.
I would do this even if your going to just set it up by temp. You never know when you may need a copy of the schematic in the future and who knows how long Klipsch will continue to keep these materials around now that Aragon/Acurus is a thing of the past...
Here is the email address, Support.Mondial@klipsch.com. I talked with a guy named Steve Philips.
I would do this even if your going to just set it up by temp. You never know when you may need a copy of the schematic in the future and who knows how long Klipsch will continue to keep these materials around now that Aragon/Acurus is a thing of the past...
the other way to set the bias is to operate the amp at one watt with a 20khz sine wave, and while monitoring the output with a distortion analyzer, and viewing the analyzer residual on an o-scope, adjust the bias untill the crossover notches just barely disappear. this does not always give the same bias even with two of the same model amp, or even both channels of the same amp, but many manufacturers use this method.
as far as the distortion problem you describe, you could have an intermittant emitter resistor or driver, or output transistor.
as far as the distortion problem you describe, you could have an intermittant emitter resistor or driver, or output transistor.
unclejed613 said:
thank you very much, unlclejed613
I have been wondering what level/frequency for adjust bias.
I was thinking that maybe higher freq, like 20kHz, could be used.
Because,
Douglas Self findings was that 'bad biasing'
had the most clear effects at higher frequencies.
Distortion in Power Amplifiers - by D. Self
Regards
lineup
Was a pretty easy tweak, except for lifting the thing... yeesh!
Emitter resistors read 0.5ohms (tested a few), putting it to the enjoyably easy math...
= A setting range of 25~45mV for the 50~90mA desired current range.
I set it to 30mA (in matching with the 60ma original calculation), get's lightly warm to the touch (enough for me; want to keep it alive for a loooong time). After re-connecting it to my system I was surprised, there was a quite noticeable audible difference, for the better.
Hardest part for me was keeping the room at the same temperature when setting bias. Had a drafty window nearby.
Hadn't noticed the channel breakup in the last recent plays, hoping it stays that way, as it would be a real pain to source down something so rarely intermittent.
Had avoided contacting Mondial, after looking at the aged forums it looked like they didn't want to reveal any technical details to those who inquired. Will give them a shout now, seeing that they may be more giving.
Wish I had a scope, and a dist-analyzer, and a lot more goodies. Gotta brush up on my electronics understanding more before I invest in anything serious like that though.
Nothing much left to fiddle with now... Sadly it was the only thing keeping me from doing real work.
Maybe I should vacuum...
Cheers, and thanks all!!!
bluesmoke
Emitter resistors read 0.5ohms (tested a few), putting it to the enjoyably easy math...
= A setting range of 25~45mV for the 50~90mA desired current range.
I set it to 30mA (in matching with the 60ma original calculation), get's lightly warm to the touch (enough for me; want to keep it alive for a loooong time). After re-connecting it to my system I was surprised, there was a quite noticeable audible difference, for the better.
Hardest part for me was keeping the room at the same temperature when setting bias. Had a drafty window nearby.
Hadn't noticed the channel breakup in the last recent plays, hoping it stays that way, as it would be a real pain to source down something so rarely intermittent.
Had avoided contacting Mondial, after looking at the aged forums it looked like they didn't want to reveal any technical details to those who inquired. Will give them a shout now, seeing that they may be more giving.
Wish I had a scope, and a dist-analyzer, and a lot more goodies. Gotta brush up on my electronics understanding more before I invest in anything serious like that though.
Nothing much left to fiddle with now... Sadly it was the only thing keeping me from doing real work.
Maybe I should vacuum...
Cheers, and thanks all!!!
bluesmoke
bluesmoke said:
jacco vermeulen said:
Great! 'And easy tweak'Nothing is really difficult, when we know what we do & how to do it.
I would ALSO try jacco_vermeulen nice information:
The 8002 sounds a whole lot better with the bias bumped up a bit,
at the factory setting it already does a few watts in A.
It might very well be, that Aragon 8004 is so much alike Aragon 8002
that it would benefit with bit higher than normal bias.
normal: 50-90 mA
a bit higher bias: 150-300 mA
... a few watts in Class A
Compare with Nelson Pass www.fristwatt.com
where he tries the concept of the first 1 or 2 watts = low level
are the most important watts of an amplifier
==========================
Technical.
Info from lineup.
To bias Aragon 8004 for Class A operation into 8 Ohm speakers
0-1 Watt: set bias 275mA ...... ( actually 250mA + 10% )
0-2 Watt: set bias 390mA
275mA bias = 1 Watt Class A into 8 Ohm.
If resistor is 0.5 Ohm, this will mean 0.137 Volt across 0.5 Ohm.
But if you have 4 BIG Transistors per channel (=total 8 for stereo)
You make it 50% .... 68mV per Resistor 0.5 Ohm.
--------
Final Comment and something to think about, in life:
This is of course because they do 50%-50% of the job, compared to a Single Transistor.
When two persons do a job, they only have to make half of it.
This is why CO-operation is so good, to do Instead of making things more difficult for others
we should try to support and help eachother!
lineup
Hi Blue,
you are in Winter just now.
I suggest you periodically check your bias setting as Summer approaches.
Hopefully, your bias will hold steady as the heatsink warms up following the increasing ambient temperature.
You may find that the bias falls slightly, indicating a safe overcompensated bias arrangement.
What you must watch out for is increasing bias as the temperatures rise.
If your amp falls into this category you must set the bias when the amp is hot and accept a low bias value when conditions are cooler.
If the manufacturer is giving a range of 50 to 90mA, I suspect that is total bias. You must calculate the equivalent Vre for each emitter resistor so that the total bias through all the NPN output devices = recommended range. With the speakers disconnected the total bias through all the PNP devices (Ib PNP) = Ib NPN.
eg. 10mV across 0r5 gives emitter current =20mA.
Total bias for a 2pair output stage = 2*20mA, Iq=40mA.
I hope that makes sense.
you are in Winter just now.
I suggest you periodically check your bias setting as Summer approaches.
Hopefully, your bias will hold steady as the heatsink warms up following the increasing ambient temperature.
You may find that the bias falls slightly, indicating a safe overcompensated bias arrangement.
What you must watch out for is increasing bias as the temperatures rise.
If your amp falls into this category you must set the bias when the amp is hot and accept a low bias value when conditions are cooler.
If the manufacturer is giving a range of 50 to 90mA, I suspect that is total bias. You must calculate the equivalent Vre for each emitter resistor so that the total bias through all the NPN output devices = recommended range. With the speakers disconnected the total bias through all the PNP devices (Ib PNP) = Ib NPN.
eg. 10mV across 0r5 gives emitter current =20mA.
Total bias for a 2pair output stage = 2*20mA, Iq=40mA.
I hope that makes sense.
" Had avoided contacting Mondial, after looking at the aged forums it looked like they didn't want to reveal any technical details to those who inquired. Will give them a shout now, seeing that they may be more giving."
Actually they have been quite receptive and quick at supplying me with any info I requested including schematics. Send them an email at the address I posted before and let them know what your doing and what you need. It never hurts to ask!
Actually they have been quite receptive and quick at supplying me with any info I requested including schematics. Send them an email at the address I posted before and let them know what your doing and what you need. It never hurts to ask!
Confused enuff?
If you are not confused already... here's another method.
Adjust the Bias till you get thermal equilibrium around 40C (for cold ambients) and about 36C for warmer rooms. Measured about an inch from any OP device directly on the heatsink.
It should remain at that temp with no signal played (DC offset +/-10mV max), and self regulate after 5 mins of hard play with 4 ohm load....
During hard play, the heatsink can go up to 65C without major issues. (Measured less than 1" from any OP device).
This method will usually max out the class-A you can get without subjecting the OP devices to thermal stresses during hard play.
From personal experience, OP temperature has a higher affect on sonics than voltage across the BE or the ER. This and having a constant Current across the device (Both are achieved via this method) have in my experience made listening a more pleasant experience.
There will be many who will dissent this view, it is up to you to test it out yourself.
HTH.
If you are not confused already... here's another method.
Adjust the Bias till you get thermal equilibrium around 40C (for cold ambients) and about 36C for warmer rooms. Measured about an inch from any OP device directly on the heatsink.
It should remain at that temp with no signal played (DC offset +/-10mV max), and self regulate after 5 mins of hard play with 4 ohm load....
During hard play, the heatsink can go up to 65C without major issues. (Measured less than 1" from any OP device).
This method will usually max out the class-A you can get without subjecting the OP devices to thermal stresses during hard play.
From personal experience, OP temperature has a higher affect on sonics than voltage across the BE or the ER. This and having a constant Current across the device (Both are achieved via this method) have in my experience made listening a more pleasant experience.
There will be many who will dissent this view, it is up to you to test it out yourself.
HTH.
Think I'll going to email Klipsch/Mondial before any more action, and see what specs they figured... I'd crank it up a bit more since it is only mildly warm, but will wait for the real info.
When setting bias I wait at least 20 minutes for it to stabilize, adjust, wait another 5 minutes for it to bounce around, adjust, and on and on... until it barely floats less than 0.5mv
I agree with the importance of the first watt or two concept, thought I was already at that point, but may still be a touch under..? The 8002 has 6 transistors per channel (or 3 pair). So I'm hitting a cumulative value of 360ma per channel..? Maybe I don't need to touch anything...
Will spend tomorrow relaxing and just watch the snow!
Cheers,
bluesmoke
When setting bias I wait at least 20 minutes for it to stabilize, adjust, wait another 5 minutes for it to bounce around, adjust, and on and on... until it barely floats less than 0.5mv
I agree with the importance of the first watt or two concept, thought I was already at that point, but may still be a touch under..? The 8002 has 6 transistors per channel (or 3 pair). So I'm hitting a cumulative value of 360ma per channel..? Maybe I don't need to touch anything...
Will spend tomorrow relaxing and just watch the snow!
Cheers,
bluesmoke
I just went back and looked at the info Mondial sent me about the 4004 amp and realized they actually sent me the info for ALL of their amps. I feel pretty stoooopid now!
Its in a word doc so I just cut and pasted it, here you go.
ARAGON & ACURUS AMPLIFIER BIAS ADJUSTMENTS
2000 & 3000 4-6 mV EACH CHANNEL
SERIES
8008ST & BB INNER CHANNEL-12mV
and MKII OUTER CHANNEL- 8mV
8008X3 & X3B 8-10mV EACH CHANNEL
8002 8-10mV EACH CHANNEL
PALLADIUM II INNER CHANNEL-25mV
& 1K OUTER CHANNEL-20mV
W/ TOP COVERS ON-HEATSINK TEMP-118 DEG. F.
4004 6-8mV EACH CHANNEL
2004 4-6mV EACH CHANNEL
A100,A100X3
A200,A200X3
DIA150,A125X5 6mV EACH CHANNEL
IMPORTANT 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.
Its in a word doc so I just cut and pasted it, here you go.
ARAGON & ACURUS AMPLIFIER BIAS ADJUSTMENTS
2000 & 3000 4-6 mV EACH CHANNEL
SERIES
8008ST & BB INNER CHANNEL-12mV
and MKII OUTER CHANNEL- 8mV
8008X3 & X3B 8-10mV EACH CHANNEL
8002 8-10mV EACH CHANNEL
PALLADIUM II INNER CHANNEL-25mV
& 1K OUTER CHANNEL-20mV
W/ TOP COVERS ON-HEATSINK TEMP-118 DEG. F.
4004 6-8mV EACH CHANNEL
2004 4-6mV EACH CHANNEL
A100,A100X3
A200,A200X3
DIA150,A125X5 6mV EACH CHANNEL
IMPORTANT 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.
bluesmoke said:
that's a shame, since Blue has already found a sound quality improvement at a higher bias setting.
Go very easy if you intend exceeding the manufacturer's settings.
Can I suggest you reduce the bias Vre back down to 15mV (that range of 15 to 25mV for optimum bias) and await the warmer weather before doing anything higher.
Jacco... I have heard the 4004/2004's which were Aragon's reason to fame... didnt like the sound a whole lot.... I see why they are not that fab anymore... I owned a 4004 (actually 2)... they were built like a Tank... thats about the only thing I liked about them...
Also Manufacturer's are more interested in $$$ than getting the consumer the last ounce of performance. They happily err on the conservative side while specifying bias current... with the exception of a few, they usually like to do to the minimum.
I have asked neslon on biasing a few of his amps and his private replies have always given me numbers higher than were published. In private he is giving good advice, on the spec sheet... someone is playing it safe... (I mean whoever owns those designs now). e.g. the Adcoms, the Fortes etc.
Also Manufacturer's are more interested in $$$ than getting the consumer the last ounce of performance. They happily err on the conservative side while specifying bias current... with the exception of a few, they usually like to do to the minimum.
I have asked neslon on biasing a few of his amps and his private replies have always given me numbers higher than were published. In private he is giving good advice, on the spec sheet... someone is playing it safe... (I mean whoever owns those designs now). e.g. the Adcoms, the Fortes etc.
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