Is the Audiolab 8000A integrated amplifier designed as a Class A or A/B amplifier?
I have owned two of these amps for many years (in England), and enjoyed them immensely. I moved to the USA seven years ago, and only recently went back to visit friends and family. Whilst I was there I dug up up one of my Audiolabs and brought it back with me. I have rigged a 240v supply from an A/C unit in my listening room and I am currently enjoying it's sonic abilities - neutral and very confident output, if a tad cold at times. It seems so far to fit well with my other equipment - Sony PSE-4000 turntable, Sony PUA-1500L Tonearm, Denon DL-103 cartridge, Pro-Ject Tube Box II phono stage, JBL Stadium speakers.
I mostly marvel at this amplifiers ability to be transparent. I recall it's legendary status from many years ago and this made me curious. What was different about this amp in the late 80's that generated so many awards? So for the first time I removed the cover and discovered a double pair of Sanken 2SA1216 power transistors.
Is there some magic to these epitaxial transistors? And are they operating in Class A, or Class A/B in this design?
Your thoughts and technical comments are most welcome.
Ian
I have owned two of these amps for many years (in England), and enjoyed them immensely. I moved to the USA seven years ago, and only recently went back to visit friends and family. Whilst I was there I dug up up one of my Audiolabs and brought it back with me. I have rigged a 240v supply from an A/C unit in my listening room and I am currently enjoying it's sonic abilities - neutral and very confident output, if a tad cold at times. It seems so far to fit well with my other equipment - Sony PSE-4000 turntable, Sony PUA-1500L Tonearm, Denon DL-103 cartridge, Pro-Ject Tube Box II phono stage, JBL Stadium speakers.
I mostly marvel at this amplifiers ability to be transparent. I recall it's legendary status from many years ago and this made me curious. What was different about this amp in the late 80's that generated so many awards? So for the first time I removed the cover and discovered a double pair of Sanken 2SA1216 power transistors.
Is there some magic to these epitaxial transistors? And are they operating in Class A, or Class A/B in this design?
Your thoughts and technical comments are most welcome.
Ian
Commercial, UK built class A amplifiers are seldom more than 30W/channel and even they will literally pour heat out at you from large heatsinks because of the constant dissipation necessary to maintain class A operation throughout the power range. This is specified as a 60W model and has only a small, shared heatsink so it will assuredly be class AB. Audiolab 8000A | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
The number 8000A only denotes Amplifier, since the cousin, 8000P means Preamplifier.
The number 8000A only denotes Amplifier, since the cousin, 8000P means Preamplifier.
there is a very long issue next to these amps .... read this:
http://www.diyaudio.com/forums/solid-state/220588-audiolab-8000-bias-issues.html
it might become handy ....
As about the principal of operation the class is strictly AB but next to any japanese amplifier the Audiolab is highly biased but not class A
Though from the above if you cannot make an assumption let me make it for you ....
The principal of operation for a highly biased class AB amplifier will only operate in the specific room temperature of about 22 degrees .
when room temperature is 25-27 degrees expect the drivers to rise to 58-62 degrees
when room temperature is 32 degrees expect the drivers to boil at 67-72 degrees
and goes on
At this point and in room temperature the double VBE multiplier will overcompensate resulting very very low bias if memory serves its dropping from 100 ma to 12 ...( 12 ma is marginal class AB don't even think of class A at 12ma )
solution is to drill fins of ventilation above the drivers which is done by me so far on 10 of these amps to very happy ( now ) owners ..ventilation of the drivers preserves far more stable bias versus room temperature and far more less time from start up to normal operating temperature .
To add one more detail the original concept was to set up the amplifier on start up on very high bias and when the amplifier reach to an operating temperature the VBE multiplier will drop it to a normal operating level ....point is that this is only working in a low room temperature .
The all problem starts in an Sziklai amplifier where the heat compensation lays on the drivers and not on the output combos One that wants the benefits of an Sziklai should preserve a better environment for the operation of the drivers ....
Sorry for the long post but all had to be written
Kind regards
sakis
http://www.diyaudio.com/forums/solid-state/220588-audiolab-8000-bias-issues.html
it might become handy ....
As about the principal of operation the class is strictly AB but next to any japanese amplifier the Audiolab is highly biased but not class A
Though from the above if you cannot make an assumption let me make it for you ....
The principal of operation for a highly biased class AB amplifier will only operate in the specific room temperature of about 22 degrees .
when room temperature is 25-27 degrees expect the drivers to rise to 58-62 degrees
when room temperature is 32 degrees expect the drivers to boil at 67-72 degrees
and goes on
At this point and in room temperature the double VBE multiplier will overcompensate resulting very very low bias if memory serves its dropping from 100 ma to 12 ...( 12 ma is marginal class AB don't even think of class A at 12ma )
solution is to drill fins of ventilation above the drivers which is done by me so far on 10 of these amps to very happy ( now ) owners ..ventilation of the drivers preserves far more stable bias versus room temperature and far more less time from start up to normal operating temperature .
To add one more detail the original concept was to set up the amplifier on start up on very high bias and when the amplifier reach to an operating temperature the VBE multiplier will drop it to a normal operating level ....point is that this is only working in a low room temperature .
The all problem starts in an Sziklai amplifier where the heat compensation lays on the drivers and not on the output combos One that wants the benefits of an Sziklai should preserve a better environment for the operation of the drivers ....
Sorry for the long post but all had to be written
Kind regards
sakis
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Thank you both for your excellent responses.
I have measured external temperatures, at the main heat sink and the top of the case towards the front where I feel a hot spot. Does this hot spot correspond with the drivers on the board?
With a room temp of 25.8c the case temp is 34.0c and 40.1c at the heat sink after one hour at idle/no input/zero volume control.
At twelve hours with a room temp of 24.4c the case is 35.4c and the heat sink is 40.3c (Idle).
Previously when I ran this amp in a much colder climate, it seemed to sound "grainy" when cold and I would seemly hear an improvement after about an hour of pre-heating. I am confused as to weather I should be running this amp hot or cold.
I live on the Gulf of Mexico, so next summer the ambient temps will rise somewhat as my listening room is not part of the main building's thermostatically controlled A/C environment.
This amplifier performs well at the 8 o'clock to 10 o'clock vol position. The sound seems to get bigger through this range. After this when approaching 12 o'clock (vertical) the output starts to sound "loud" and does not have the same character. Could this be the amp moving into class B operation and I am hearing crossover distortion? Or am I merely challenging the room acoustics?
Ian
I have measured external temperatures, at the main heat sink and the top of the case towards the front where I feel a hot spot. Does this hot spot correspond with the drivers on the board?
With a room temp of 25.8c the case temp is 34.0c and 40.1c at the heat sink after one hour at idle/no input/zero volume control.
At twelve hours with a room temp of 24.4c the case is 35.4c and the heat sink is 40.3c (Idle).
Previously when I ran this amp in a much colder climate, it seemed to sound "grainy" when cold and I would seemly hear an improvement after about an hour of pre-heating. I am confused as to weather I should be running this amp hot or cold.
I live on the Gulf of Mexico, so next summer the ambient temps will rise somewhat as my listening room is not part of the main building's thermostatically controlled A/C environment.
This amplifier performs well at the 8 o'clock to 10 o'clock vol position. The sound seems to get bigger through this range. After this when approaching 12 o'clock (vertical) the output starts to sound "loud" and does not have the same character. Could this be the amp moving into class B operation and I am hearing crossover distortion? Or am I merely challenging the room acoustics?
Ian
You have put in everyday terms what Sakis has detailed about the wayward bias control on these amplifiers. There are others of that era too, which just weren't fully understood or thought through for reliability in their potential worldwide market.
Bias is the DC current running through the output stage to bring the junctions toward the point of conduction. This minimises crossover distortion as the signal switches between the output transistors on positive and negative voltage excursions. The voltage is small and very temperature dependent but critical to sound quality so it must have accurate control to set and maintain the amplifier at its lowest distortion point in whatever ambient temp. and power level the amplifier has to work at. Another issue is safety, as an out of control bias system often leads to amp.death, fire even.
When you hear the sound go from grainy to smooth, the bias is dropping from very high initially towards the optimum but then as it gets really hot, the bias falls too low and crossover distortion then becomes obvious. To keep an amplifier in its sweet spot by manipulating ambient temp. and power level is a frustrating and needless distraction for an owner, I should think. I've seen it in several older up-market UK products and whilst some owners thought it a quaint and endearing quality, I think it's a disgrace, since it benefits no one to have such a narrow or unstable band of good sound quality.
Sakis has detailed a cunning way of cooling the driver transistors so that they work better in his (Athens) climate. It seems good to me and might be just as appropriate in the Gulf area. At least read his interesting linked thread and consider if you are up to it.
Bias is the DC current running through the output stage to bring the junctions toward the point of conduction. This minimises crossover distortion as the signal switches between the output transistors on positive and negative voltage excursions. The voltage is small and very temperature dependent but critical to sound quality so it must have accurate control to set and maintain the amplifier at its lowest distortion point in whatever ambient temp. and power level the amplifier has to work at. Another issue is safety, as an out of control bias system often leads to amp.death, fire even.
When you hear the sound go from grainy to smooth, the bias is dropping from very high initially towards the optimum but then as it gets really hot, the bias falls too low and crossover distortion then becomes obvious. To keep an amplifier in its sweet spot by manipulating ambient temp. and power level is a frustrating and needless distraction for an owner, I should think. I've seen it in several older up-market UK products and whilst some owners thought it a quaint and endearing quality, I think it's a disgrace, since it benefits no one to have such a narrow or unstable band of good sound quality.
Sakis has detailed a cunning way of cooling the driver transistors so that they work better in his (Athens) climate. It seems good to me and might be just as appropriate in the Gulf area. At least read his interesting linked thread and consider if you are up to it.
Once more let us not forget that the specific amplifier doesn't operate like the ones we know ...Temperature in the heatsink is not a ""bias indication" IE normally consumer amps when hot in heatsink at idle normally means that its a highly biased amp .
Point is that the specific amplifiers senses temperature from the drivers so cooling down the drivers will actually increase the bias, speed up the preheat process , and bring the amp generally to original operation bias .
Small remark
many of you know that i am not in the class A thingy ...some time though i have to learn about this also .so far been working with some class A ( some big names also ) and i think that the sound is horrible ( excuse my French ) i even tried to bias my P3A to something like 300-400 ma with also not so nice results
Point is that my everyday listening is soulful house music includes plenty and variety of vocals, always high BPM between 122-132, plenty of electronic sounds KB style , often strings and with both elements of Jazz and soul music .
I think though for this type of music class A sucks big time ...highly biased amps also ... sound looses punch there is a feeling that there is no "air" and speed on the sound and sound stage becomes far too smaller .Still i think that middle is far better but only this is not enough to my taste .
I d'like very much someone to comment on the above
So far i have been modifying 10 of the Audiolab 8000A operating in Greece under teh mods and conditions described ...Costumer's reference say that the qualities of the specific amp remain untouched and far better soundstage and crisp was increased together with some "air" it was specifically said : "I could listen to music that previously was impossible to play with this amplifier ""
Not to forget that with the above goes a complete recaping and resoldering of the amp
Kind regards
sakis
Point is that the specific amplifiers senses temperature from the drivers so cooling down the drivers will actually increase the bias, speed up the preheat process , and bring the amp generally to original operation bias .
Small remark
many of you know that i am not in the class A thingy ...some time though i have to learn about this also .so far been working with some class A ( some big names also ) and i think that the sound is horrible ( excuse my French ) i even tried to bias my P3A to something like 300-400 ma with also not so nice results
Point is that my everyday listening is soulful house music includes plenty and variety of vocals, always high BPM between 122-132, plenty of electronic sounds KB style , often strings and with both elements of Jazz and soul music .
I think though for this type of music class A sucks big time ...highly biased amps also ... sound looses punch there is a feeling that there is no "air" and speed on the sound and sound stage becomes far too smaller .Still i think that middle is far better but only this is not enough to my taste .
I d'like very much someone to comment on the above
So far i have been modifying 10 of the Audiolab 8000A operating in Greece under teh mods and conditions described ...Costumer's reference say that the qualities of the specific amp remain untouched and far better soundstage and crisp was increased together with some "air" it was specifically said : "I could listen to music that previously was impossible to play with this amplifier ""
Not to forget that with the above goes a complete recaping and resoldering of the amp
Kind regards
sakis
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