AB100 Class AB Power Amplifier

[osscar]

I also noticed that the bias difference between each the Darlington transistor (MJ11015 and MJ11016 from ON semi) ar minimal - in range of few mA.
Standard ON semi MJ 15003/004 bipolars which I use im my leach amps - their individual bias difference is much greater - even up to 15-20mA.

 

[wrenchone]

A correction - the Puccini amp has two pair of output Darlingtons...

 

[osscar]

AB100 amplifier was operated continuously 10h by me at moderate volume.I checked parameters now - bias stable compensated from 100mA per transistor to 90 mA. Offset - from 3mV dropped to 1.2mV and 12mV on other channel. (diff pair transistors was matched by hfe) .sounds very good - the low end also impressive.

 

[mpmarino]

Thanks for bringing this back up. It blew right by me it the first time around.

This could easily displace some of the commercial ~100w amps kicking around

 

[gaborbela]

AB100 amplifier was operated continuously 10h by me at moderate volume.I checked parameters now - bias stable compensated from 100mA per transistor to 90 mA. Offset - from 3mV dropped to 1.2mV and 12mV on other channel. (diff pair transistors was matched by hfe) .sounds very good - the low end also impressive.

How you match the darlingtos, do you use some circuit etc. With a simple DMM you can not do it.
Please let me know
Thank you

 

[osscar]

Hello,
I matched only the input pair transistors not darlingtons, but they are already pretty close to each other from the store shelf - maybe I'm lucky. (Which I doubt ..)
I think its possible to reduce Re to some 0.33R instead of 0,5R .

 

[linuxguru]

In between enjoy the schematic ....This is a commercial design existing in the market for a number of years and also features a patch of 150Pf in the upper side Only ! relatively low next to known other schematic .

Thanks - It's (vaguely) a Blameless clone with a cascoded VAS and Darlington OPs. They have gone through some pains to include an elaborate Vbe bias limiter to reduce the possibility of thermal runaway - perhaps the added cost of such a limiter was much lower than the price of discrete non-Darlington outputs + drivers in that era (maybe even today, even with inexpensive C5200/A1943 clones from the likes of ST).

The discrete darlington VAS of 2x BC560 is wasted. They should have used a true Blameless-style emitter follower, with collector going to ground. Perhaps you can do that mod, though the extra open-loop gain may tip it into instability.

 

[osscar]

In the last few months ab100 has become my everyday amplifier - I like everything, especially the bottom end is very punchy and fast - also sound stage is very good. Stable as a rock even if you lose one supply rail - you will not fire speakers - there will be only small amount of DC at output (instead of chipamps for example).
In addition I installed small heat-sinks fors VA and CCS transistors, maybe they can do without them (approx 0,5W dissipation) -but it's better to be on the safe side.

 

[gaborbela]

In the last few months ab100 has become my everyday amplifier - I like everything, especially the bottom end is very punchy and fast - also sound stage is very good. Stable as a rock even if you lose one supply rail - you will not fire speakers - there will be only small amount of DC at output (instead of chipamps for example).
In addition I installed small heat-sinks fors VA and CCS transistors, maybe they can do without them (approx 0,5W dissipation) -but it's better to be on the safe side.

 

[Nelson Pass]

In the last few months ab100 has become my everyday amplifier.

 

[osscar]

Thank you,
I know that it's been a while ... I've added the actual circuit of my amplifier.Of course, a lot of things can be changed according to the taste and possibilities
I think the amplifier is worth it to be built.

 

[mpmarino]

... I've added the actual circuit of my amplifier.Of course, a lot of things can be changed according to the taste and possibilities .

I like your simplification of the output stage with the big darlingtons.

Have you built the amp both ways?

I can't get space heaters off my mind, but I should be looking into a Summer amp. I have plenty of AB commercial stuff, but the ones we build are so much better

 

[richard_pc]

Hello guys

As you know, the degeneration for differential input stage can greatly improve linearity, but seems most Papa's design without it(or rare), is there any special reason ?

Thanks!

 

[vdi_nenna]

Anyone make boards for the AB100 amp?
If you have a working example, I'll buy a pair, if you have spares.

Thanks,

Vince

 

[osscar]

I

Have you built the amp both ways?

No..just to3 version

Hello guys

As you know, the degeneration for differential input stage can greatly improve linearity,?

Thanks!

I performed a quick simulation - with degeneration thd at high F getting worse..

regarding PCB:
I do not think someone has ordered a professional PCB for this amp - I only saw home made PCB and some nice PCB layouts in this topic.My PCB also is a "kitchen table" DIY for my needs and adapted to3 transistors.

 

[Nelson Pass]

the degeneration for differential input stage can greatly improve linearity, but seems most Papa's design without it(or rare), is there any special reason ?

Papa is too cheap to use two extra resistors.

 

[osscar]

 

[bogdan_borko]

Papa is too cheap to use two extra resistors.

Really, what is the reason for this, I noticed that too?

 

[vdi_nenna]

The ST TIP35C and TIP36C.

Complimentary, 3Mhz, 100V, 25A, high gain and pretty cheap in bulk.

What do you think?

Wait, they are not Darlingtons. Would they still work? Specs seem the same.

 

[richard_pc]

Papa is too cheap to use two extra resistors.

Hi Papa

If possible, please give us some hints.

Thanks!