Sorry the title should read new class A, I couldn't edit it. How do I go about biasing this amp there is no manufacturers recommended setting,it has the left & right pots to set it but to what? milliamps or millivolts and how much? it is a technics SU-V650.
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CORRECT ...there is no info in existing schematics on the internet there is pages missing from the schematic ..... from experience anything between 30-70ma per amplifier will be just fine
start from 40 for example and monitor temperature .... then you will see
There is going to be some trouble though measuring it since everything is inside the IC so one practice will be to set one trimmer in the middle check the voltage given in the test point A and then adjust for the exact same measuring the point B ..
Alternative will be to cut a trace of + power supply on the main amp root and insert an A meter to see how it goes
start from 40 for example and monitor temperature .... then you will see
There is going to be some trouble though measuring it since everything is inside the IC so one practice will be to set one trimmer in the middle check the voltage given in the test point A and then adjust for the exact same measuring the point B ..
Alternative will be to cut a trace of + power supply on the main amp root and insert an A meter to see how it goes
Arent these using a STK/SVI module ? if so, theres no way of adjusting bias as its all done within the module.
And as i've understood it, these are not actually class A at all, but rather standard class AB, but with a special circuit that prevents the output transistors from switching off completely.
And as i've understood it, these are not actually class A at all, but rather standard class AB, but with a special circuit that prevents the output transistors from switching off completely.
what are the IC Quiscent adjustments on the left and right channels for then? You might be mistaken for the automatic dc adjustment (servo)
Sakis,I will try that and get back to you, I didn't want to start fiddling with it with out having some idea of what I was doing. Been there done that! LOL.
I have just measured it and both sides are 5ma? it has the test points to measure from, so I didn't have to cut the tracks.Oh well it looks like I will have to hunt down the missing page of the SM.
Hi, If both sides are the same I'd assume it is correct and leave it alone, rgds, sreten.
Technics new class A I know how it works, its good but not cheap. Technics new class
AA I don't other that what it claims, and if that is true the standing current can be low.
Technics new class A I know how it works, its good but not cheap. Technics new class
AA I don't other that what it claims, and if that is true the standing current can be low.
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I'm not going to assume anything Sreten, until I know what the correct setting is? Ive read a lot of threads on other forums about new class A bias but nowhere does it mention a ballpark setting?
Hi,
New class A is a combination of a low voltage class A amplifier
and a further class B amplifier that modulates the mid point
voltage the class A amplifier is working in. complex, not cheap.
For new class AA details are hard to find, presumably because
its a lot simpler. It seems to be a sliding bias scheme "that
never turns off". If so the required standing current is low.
If both channels measure the same then its best to assume that
it is correct until you know otherwise, a reasonable assumption.
rgds, sreten.
New class A is a combination of a low voltage class A amplifier
and a further class B amplifier that modulates the mid point
voltage the class A amplifier is working in. complex, not cheap.
For new class AA details are hard to find, presumably because
its a lot simpler. It seems to be a sliding bias scheme "that
never turns off". If so the required standing current is low.
If both channels measure the same then its best to assume that
it is correct until you know otherwise, a reasonable assumption.
rgds, sreten.
Absolutely.
The circuit details are locked up in special chips or power modules etc, according to the models as they changed and became cheaper over the years, in the SU series.The class B amp is the same in my 70W SUV-50 (4mA) and the only class A amplifier is a TO126 pair in the middle of a complex PCB.
If it works, don't touch it because you can't tweak it and you can't replace the critical parts if you make mistakes. It is not class A, but akin to class S and I understand as Sreten says, that sliding bias is involved because the straight class S amps were not successful.
PS the arbitrary small bias is necessary to give lowest distortion figures - JLH
The circuit details are locked up in special chips or power modules etc, according to the models as they changed and became cheaper over the years, in the SU series.The class B amp is the same in my 70W SUV-50 (4mA) and the only class A amplifier is a TO126 pair in the middle of a complex PCB.
If it works, don't touch it because you can't tweak it and you can't replace the critical parts if you make mistakes. It is not class A, but akin to class S and I understand as Sreten says, that sliding bias is involved because the straight class S amps were not successful.
PS the arbitrary small bias is necessary to give lowest distortion figures - JLH
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Thanks for explaining it for me fellas, I understand whats happening! The bias is set low because the sliding system keeps the current low through-out to keep the heat down,or something like that? LOL Anyway the main thing is its working OK. ;BANANA!!!
Hi,
Now the arguments can begin 😉.
Class A+ is clearly (IMO) a variation of class A but complex and expensive.
Two amplifiers per channel, two complementary supplies per channel, the
class A one totally floating and the Class A amplifier needs to be able to
support the full load current albiet with low voltage rails.
New class A is an entirely different beast. The output devices are prevented
from switching off, which no doubt will reduce "high frequency switch-off/on
distortion". But does it avoid (as class A and A+ does) the variations of final
stage gain ( always < 1) that causes x/o distortion ? I don't think it does.
IMO the first version works and does what it says on the tin. The second
carried on Technics class A marketing, but is not proper class A, that has
no gain variation at x/o, and is clearly a far cheaper topology / technology.
rgds, sreten.
Confusingly, Class A+ was called new class A, new class A was called class AA.
Now the arguments can begin 😉.
Class A+ is clearly (IMO) a variation of class A but complex and expensive.
Two amplifiers per channel, two complementary supplies per channel, the
class A one totally floating and the Class A amplifier needs to be able to
support the full load current albiet with low voltage rails.
New class A is an entirely different beast. The output devices are prevented
from switching off, which no doubt will reduce "high frequency switch-off/on
distortion". But does it avoid (as class A and A+ does) the variations of final
stage gain ( always < 1) that causes x/o distortion ? I don't think it does.
IMO the first version works and does what it says on the tin. The second
carried on Technics class A marketing, but is not proper class A, that has
no gain variation at x/o, and is clearly a far cheaper topology / technology.
rgds, sreten.
Confusingly, Class A+ was called new class A, new class A was called class AA.
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Hi,
I thought New class A and class AA were different. Or does Mos Class AA differ from Class AA? Mos Class AA being a class A amp driving the load (bridge) and any output from the bridge means helping current from the class B (AB) amplifier.
Excerpt from block diagram (Technics SE-A2000)
Attachments
Class AA was the Sandman bridge. It is an integrated module. MOS Class AA is a discrete version using MOSFET output devices. Got an amp of each here and have poked about inside.
New Class A is different and can be either sliding bias or the modulated scheme sreten mentioned.
New Class A is different and can be either sliding bias or the modulated scheme sreten mentioned.
I think you will find a much larger and inconsistent range of model/series variations than the sample
covered in those pages suggests (thanks AKN)
There are even similar copycat class names by JVC and others using very different ideas.
Super A, AA, AA+, AAA+ and SUZ series just for Technics, to start with.
You could even say the confusion was intentional 😀
covered in those pages suggests (thanks AKN)
There are even similar copycat class names by JVC and others using very different ideas.
Super A, AA, AA+, AAA+ and SUZ series just for Technics, to start with.
You could even say the confusion was intentional 😀
Yes,
JLH about Sandman/Technics: Valve and Transistor Audio Amplifiers - John Linsley Hood - Google Böcker
JLH about Sandman/Technics: Valve and Transistor Audio Amplifiers - John Linsley Hood - Google Böcker
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