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BA-F1 Crossover distortion

ghamilton

ghamilton

Super Member
Audio magazine (March 1980) did a review of the BA-F1. It was a great review.
I remember that they were not able to detect any crossover (notch) distortion which was very good for a class A/B amp. They even compared it to some tube equipment and preferred the BA-F1.
I have read that class A and tubes are prefered over class A/B by other reviewers.
Does this make the BA-F1 better than the average class A/B design?
 
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Crossover distortion is a myth for modern (vintage now) SS amps, you wont see it on any class AB amp with the negative feedback used in typical designs, its applicable for all makes of amplifiers not just Sansui.....
Some people say if the bias is off, you'll have crossover distortion, but I have never seen any on the output at all on a typical modern (vintage now) design....
The only time I have seen it is on class AB tube amps when the bias is off.....
You can however, see crossover distortion if you look at the gain stages in a power amp before the negative feedback, and this is actually a good way to set the bias right in the sweet spot, which is what I do wherever I can.....
 
kevzep said:
Crossover distortion is a myth for modern (vintage now) SS amps, you wont see it on any class AB amp with the negative feedback used in typical designs, its applicable for all makes of amplifiers not just Sansui.....
Some people say if the bias is off, you'll have crossover distortion, but I have never seen any on the output at all on a typical modern (vintage now) design....
The only time I have seen it is on class AB tube amps when the bias is off.....
You can however, see crossover distortion if you look at the gain stages in a power amp before the negative feedback, and this is actually a good way to set the bias right in the sweet spot, which is what I do wherever I can.....
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The only way that I know to set the bias is by the SM. Is there another (better) way?
 
Some manufacturers want you to set the bias by using a distortion analyzer. I use the current through the output transistors. When I worked at Harman Electronics I looked at the effect of bias current on distortion. I found that above 40mA, if you increase the current there is minimal effect on distortion. So if you have no service manual, and a nice big heat sink in the unit, 40mA is a good target. 20mA if the heat sink is small or if the bias won't stabilize at 40mA.
 
dr*audio said:
Some manufacturers want you to set the bias by using a distortion analyzer. I use the current through the output transistors. When I worked at Harman Electronics I looked at the effect of bias current on distortion. I found that above 40mA, if you increase the current there is minimal effect on distortion. So if you have no service manual, and a nice big heat sink in the unit, 40mA is a good target. 20mA if the heat sink is small or if the bias won't stabilize at 40mA.
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It may be more safe for me to just stick with the service manual. My amp is the AU-919.
 
ghamilton said:
It may be more safe for me to just stick with the service manual. My amp is the AU-919.
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Unless you know what you're doing and understand how what you're doing can affect things, just stick with the service manual.....Its adequate, and to be honest bias is a little like the idle mixture on a carburettor, once you're running you're off the idle circuit and its pretty meaningless....
People make way too much out of setting bias, its a fairly approximate thing and doesn't need to be any more than that...
 
kevzep said:
Unless you know what you're doing and understand how what you're doing can affect things, just stick with the service manual.....Its adequate, and to be honest bias is a little like the idle mixture on a carburettor, once you're running you're off the idle circuit and its pretty meaningless....
People make way too much out of setting bias, its a fairly approximate thing and doesn't need to be any more than that...
Click to expand...
Got it. Now the reason for this thread is to determine why class A is said to be better than class A/B if the crossover notch distortion has been removed.
 
ghamilton said:
Got it. Now the reason for this thread is to determine why class A is said to be better than class A/B if the crossover notch distortion has been removed.
Click to expand...
I think its a bit of an old world thing to be honest, before class AB designs were refined, Class A by nature has no crossover distortion, so was the go to for many years because of it.
Since the 70's when Class AB designs really came into their own, there were as many reason to use class AB as there were to use Class A.
It comes down to personal preference in my opinion.
Class AB amplifiers can be far more powerful than a Class A amplifier for one thing.

Remember those Yamaha integrated amps, CA1000/2000 or something, they had a switch on them so you could run them in class A if you wanted, but after working on a few of them, I can see it was a marketing gimmick, running them in Class A would most certainly shorten the life of them due to all the extra heat.....

But I suppose the battle rages on and some people are going to swear by Class A, others wont care........
 
kevzep said:
I think its a bit of an old world thing to be honest, before class AB designs were refined, Class A by nature has no crossover distortion, so was the go to for many years because of it.
Since the 70's when Class AB designs really came into their own, there were as many reason to use class AB as there were to use Class A.
It comes down to personal preference in my opinion.
Class AB amplifiers can be far more powerful than a Class A amplifier for one thing.

Remember those Yamaha integrated amps, CA1000/2000 or something, they had a switch on them so you could run them in class A if you wanted, but after working on a few of them, I can see it was a marketing gimmick, running them in Class A would most certainly shorten the life of them due to all the extra heat.....

But I suppose the battle rages on and some people are going to swear by Class A, others wont care........
Click to expand...
Nelson Pass makes both A & A/B.
Wonder why?
 
The real problem, IMO, is that "Class A" is equated with "Grade A". It's not a grading system, though, they're merely identifiers. You can have a crappy Class A design, too.
 
With most well designed class AB amps, even if you turn the bias pot to minimum you will not actually get zero bias as there is a fixed resistor in series with the pot to prevent damage if the pot goes open or closed circuit.

I was tidying up the other day and came across an old book full of 60s and 70s amplifier designs (some Nelson Pass projects were in it). Interesting reading.
There were valve and solid state designs and the thing that struck me was how different modern solid state amplifiers are when compared to these 60s designs. Very few even had long tailed pair front ends.
The specifications, acceptable then, certainly wouldn't pass muster now. Full load 30 watts at less than 1% distortion anyone?

Things have moved on - a lot.
 
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