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-   -   Class AB .... is it all done ? (http://www.diyaudio.com/forums/solid-state/204442-class-ab-all-done.html)

east electronics 13th January 2012 03:36 PM

Class AB .... is it all done ?
 
I wonder is it all done in class AB ?

while repairing an average of 350 amps per year i think i ve heard pretty much everything ...from Musical Fidelity to Goldmund and from Adcom to Ampzillas plus almost any available Japanese ....name it i 've been working with it ....

well ? what is the next step ? Go to class A ? focus on an extreme design ?

My latest idea ( havent put to practice yet ) is a class AB 4 outputs but with 4 drivers on EFP topology aim is to be more stable than CFP full discrete so you can have playful drivers and outputs and as claimed from other designers 4 drivers and 4 outputs if stabilized will provide extra kick and nice drive ability .

Still my favorite remains the P3A but i may also say that many typical class AB amplifiers can perform equal or close if made the same way ( good semis ,large caps , no limiters , light filtering and so on )

so what is next to listen ? should i go for the quad EFP ? or should i try a fully regulated power supply next to a P3A ?

opinions please ?

shaan 13th January 2012 04:36 PM

How about SSA? The one by Lazycat. I've built it and listened to it, for a long time. To my ameteur ears it's better than P3A. But with so much eperience I guess you already have tried SSA.

indianajo 13th January 2012 04:55 PM

Considering the propensity that split supply class AB transistor amps have to blow up all the time and take the speakers with it, I think proper class AB design work is just begun. I own a tube amp that has worked reliably and either compentently or feebly depending the state of the capacitors & tubes for 40 years. I own 4 more 43 year old tube amps, all working, one quite loudly with new caps, others feebly due to overage electrolytic caps or rectifier. No tube amp has damaged its speaker. I own 3 transistor amps which are contiunally blowing up all the time. Admittedly I bought them as junk, just as the tube amps were. I have now gotten one, the 1966 design dynakit ST120, to work stably and beautifully for over a year, using the djoffe bias design, and my own heat wasting design (mickey mouse ears fans). As the St120 blew up the 2nd & 3rd times, it never hurt a set of $300 a pair speakers (used) because it has output caps. My second amp, the Peavey CS800s, sounded great for 8 months but is blowing the breaker now. Probably 14 year old electrolytic caps have damaged the switcher power supply. You convinced me to use it on my $600 speakers because it has output relays. a DC diac-triac crowbar, and microprocessor controlled current sense on the output. So far so good, no damage to speakers, but it is so complicated that if it takes a lightning hit (as the ST70 and ST120 both have done, and probably the Hammond that lived on a hill above Cincinnati) all the fancy protection stuff will be gone with the wind. I've been monkeying with a Peavey PV1.3k split supply amp which has convinced me with burned PC lands how useless diac-triac protection is, and I have gotten one channel to run 20 seconds so far before blowing up again. I'm only playing it into a car radio speaker protected by a 50 uf 1000 v film cap, so the damage has been limited.
So in my opinion, there are only 4 designs of class AB amp I will trust to replace the tube amps in my organs. 1. dynakit ST120 with djoffe bias board mod and much better heatsinks. Series output cap doesn't cross through zero, so it sounds good. Sounds just like the CS800s to me, despite being quasi-comp O.T. and incredibly primitive 2. Leak Stereo 70. Bias and design is more primitive than the djoffe dynakit. Has + biased output caps. 3. MJR7 and MJR8 fet amps. Has + biased output caps. Not very powerful and has output transistors not available in the United States except from a different vendor and in TO3 instead of TO220. 4. The sample amp in the LM3886 datasheet. Has an output cap biased +all the time. Limited to about 60 w/channel 5. Any split supply amp with a film output cap of at least 3300 uf and volts > supply voltage. So far I have gotten the cap cost down to $900 apiece and a cubic foot, so that project doesn't look viable. I've tried back to back 6600 uf electrolytic caps on the CS800s when it was working, the sound was stupidly distorted on top octave piano.
So right now my best candidate for a reliable stupid proof amp with low parts count is a 1966 design with 2010 tweaks. The original has the benefit that it produces a lot more than 60 w/channel until the heat sink heats up. There is no design of a 500 w or 1000 w stupid proof class AB amp that I have seen. Stupid proof has to take any sort of output wire error and not blow up. Stupid proof doesn't have to work after a lightning strike, it just has to not blow up the speakers afterwards. It would be nice if there were more than one source of the parts after a lightning strike. And the St120 and ST70 both took a power line lightning surge and lost only the power switch and turn off pop capacitor, so I'm in favor of large iron transformers instead of switching power supplies. So, if anybody understands the need for long life no damage and repairability, it should be you. This PV1.3k is driving me nuts on the repairability front - the ST120 was way easier & I didn't even have a schematic diagram.

east electronics 13th January 2012 05:39 PM

indiana jo ....i think you are in another tune ....

system7 13th January 2012 05:57 PM

Quote:

Originally Posted by indianajo (Post 2860227)
Split supply class AB transistor amps tend to blow up all the time and take the speakers with them. I think proper class AB design work is just begun.

I own a tube amp that has worked reliably and competently, or feebly, depending the state of the capacitors & tubes for 40 years. I own 4 more 43 year old tube amps, all working, one quite loudly with new caps, others feebly due to overage electrolytic caps or rectifier. No tube amp has damaged its speaker.

I own 3 transistor amps which are continually blowing up all the time. Admittedly I bought them as junk, just as the tube amps were. I have now gotten one, the 1966 design dynakit ST120, to work stably and beautifully for over a year, using the djoffe bias design, and my own heat wasting design (mickey mouse ears fans). As the St120 blew up the 2nd & 3rd times, it never hurt a set of $300 a pair speakers (used) because it has output caps.

My second amp, the Peavey CS800s, sounded great for 8 months but is blowing the breaker now. Probably 14 year old electrolytic caps have damaged the switcher power supply. You convinced me to use it on my $600 speakers because it has output relays. a DC diac-triac crowbar, and microprocessor controlled current sense on the output. So far so good, no damage to speakers, but it is so complicated that if it takes a lightning hit (as the ST70 and ST120 both have done, and probably the Hammond that lived on a hill above Cincinnati) all the fancy protection stuff will be gone with the wind.

I've been monkeying with a Peavey PV1.3k split supply amp which has convinced me with burned PC lands how useless diac-triac protection is, and I have gotten one channel to run 20 seconds so far before blowing up again. I'm only playing it into a car radio speaker protected by a 50 uf 1000 v film cap, so the damage has been limited.

So in my opinion, there are only 5 designs of class AB amp I will trust to replace the tube amps in my organs.

1. Dynakit ST120 with djoffe bias board mod and much better heatsinks. Series output cap doesn't cross through zero, so it sounds good. Sounds just like the CS800s to me, despite being quasi-comp O.T. and incredibly primitive.

2. Leak Stereo 70. Bias and design is more primitive than the djoffe dynakit. Has + biased output caps.

3. MJR7 and MJR8 fet amps. Has + biased output caps. Not very powerful and has output transistors not available in the United States except from a different vendor and in TO3 instead of TO220.

4. The sample amp in the LM3886 datasheet. Has an output cap biased +all the time. Limited to about 35 w/channel.

5. Any split supply amp with a film output cap of at least 3300 uf and volts > supply voltage. So far I have gotten the cap cost down to $900 apiece and a cubic foot, so that project doesn't look viable. I've tried back to back 6600 uf electrolytic caps on the CS800s when it was working, the sound was stupidly distorted on top octave piano.

So right now my best candidate for a reliable stupid proof amp with low parts count is a 1966 design with 2010 tweaks. The original has the benefit that it produces a lot more than 60W/channel until the heat sink heats up. There is no design of a 500W or 1000W stupid proof class AB amp that I have seen.

(Stupid proof has to take any sort of output wire error and not blow up. Stupid proof doesn't have to work after a lightning strike, it just has to not blow up the speakers afterwards. It would be nice if there were more than one source of the parts after a lightning strike.)

And the St120 and ST70 both took a power line lightning surge and lost only the power switch and turn off pop capacitor, so I'm in favor of large iron transformers instead of switching power supplies. So, if anybody understands the need for long life no damage and repairability, it should be you. This PV1.3k is driving me nuts on the repairability front - the ST120 was way easier & I didn't even have a schematic diagram.

Yes, that was quite hard work to read. So I've edited it, and it's still hard...:D

Ability to withstand lightning aside, Class A is always going to work and sound better at every level than Class AB. But in the real world, power consumption matters.

But that Rod Elliot P3A design looks well thought out.
60-80W Power Amplifier
An element of current drive within a simple voltage feedback differential input amplifier. He's got the input impedances for common-mode rejection about right too. (Say, 1k and 22k on both the + and - inputs, if you know how to balance a differential amp at the inputs for Common-mode rejection...LOL)

VladimirK 13th January 2012 06:10 PM

I support your doubts, whether we should try another million of modifications within AB class or not.
We should remember, final sound is most affected by a weakest part of an amp.
On the other hand, definite parts or features are inevitably inherent to definite amp topologies.
We can try another millions of modifications to AB amps, one feature is inherent to all of them - output signal current passes through power supply. Since we usually pay less attention to PS than to main schematics - in most cases we listen to far from ideal PS.
There are also other features, inherent to one topology and not to another.

However, AB and D class will remain main topologies forever, since final users are happy with them, as well as with MP3.

Only for some individuals your question can matter, but in no way it could touch an industry.

indianajo 13th January 2012 06:25 PM

P3a is another split supply direct coupled amp with output protection. The emperor has no clothes. That won't last 50 years without damaging expensive speakers, not in the midwest. There is a reason the Russians built the MIG21 with tubes. Lightning is a lot like EMP. Just because they don't have lightning in California or the East Coast or UK much, people keep building this split supply trash. There are 100's of us rebuilding and playing hammond organs with tube amps, because they just keep working and working. Why has nobody designed a 400 V rail transistor AB push pull amp with transformer outputs? Transformers are great speaker protection, and decent ones are back in production again. It would be less "efficient" than a P3a, but at least you would save the 200 watts of tube heaters the St70 etc have. I own a transformer interstage coupled transistor amp, the Hammond PR10 tone cabinet, but everybody agrees that is silly. At least the PR10 still works. The Wurlitzer 4500 organ is another case of a blown up split supply transistor amp I own. Two blown up power amps, actually.

Coconuts 500 13th January 2012 06:36 PM

What's the best Japanese ab-amp you've heard?

shaan 13th January 2012 06:45 PM

Nice flames indianajo! People will keep building the split supply trash and feel happy about it. Please suggest the thread opener a practical and non 400V amplifier plan if you have one more.
BTW, P3A doesn't have output protection. ;)

TheShaman 13th January 2012 06:59 PM

Quote:

Originally Posted by VladimirK (Post 2860333)
However, AB and D class will remain main topologies forever, since final users are happy with them, as well as with MP3.

Lack of real arguments is oh so evident when people have to resort to mixing their subjective opinion with facts/objective data in one sentence.


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