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Old 28th November 2013, 10:26 AM   #101
AJT is offline AJT  Philippines
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Quote:
Originally Posted by AndrewT View Post
Leach Lo Tim already has CCS.
The tails of both LTPs are CCS.
you are correct, i was referring to the active CCS proposed by Lazy Cat...

those resistor tails are good enough for me, i wouldn't change them....
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Old 28th November 2013, 10:27 AM   #102
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Quote:
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Leach Lo Tim already has CCS.
The tails of both LTPs are CCS.
There's no CCS present in sch from post #65
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Old 28th November 2013, 11:22 AM   #103
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Many people's consensus on their's subjective opinions becomes objective.
Sorry, but thats nonsense.
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Old 28th November 2013, 11:46 AM   #104
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Not if we're talking about SQ. No numbers of evidence there.
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Old 29th November 2013, 07:26 AM   #105
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I think the leach amp is a totally proven, tested, in large numbers and found to be quite high quality.

I am of course open to new things, but before going for some other design, I would want it to be tested properly, a prototype made, many comparisons by as many people as possible to make sure not only that it does work right, always, and that there are actual improvements that were made and that brought something more.

We can't go wrong with the leach as it is right now.

We can make a few minor alterations without leaving the realm of the philosophy behind it.

The changes that revert the low tim aspect to some other "type" of concept makes that amp some other amp and it's no longer leach's amp.

One thing that was done purposely in that amp to aim for low tim, was to reduce gain at each stage and apply a moderate feedback overall. Each stage thus has local feedback that's calculated specifically to reduce that gain, with other few benefits in the process, and leach has even added a feedback from an intermediate stage. Everything he has done was well thought out and very carefully considered and tested.

I don't think anyone out there who has built the leach amp has ever found its sound quality wanting.

Of course nothing is ever perfect and I'm sure we can probably improve on things. So if such improvements do indeed bring something, then why not. But before simply switching to it, I'm sure most will agree that proper testing must be done and proper comparisons will tell.
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Old 29th November 2013, 09:54 AM   #106
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Hi Spookydd you have a great project going. Remember you cannot please everyone, nor can you factor in everything in a single design. The Leach amp has a long history, many engineers were taught using that amplifier. Do try it out. You have come pretty far. There will be time more for other designs including Lazy Cats and SYMEF.

kind regards,

Harrison.
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Old 29th November 2013, 10:46 AM   #107
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Remember you cannot please everyone, nor can you factor in everything in a single design.
That's what I'm thinking, and I'm trying not to deviate too much from the intended design. My small alterations are really minor and don't detract from the soul behind it, I hope.

This may please a fair number of amateurs of that amp, so why try to go into uncharted territory right now and lose interest?

Quote:
Originally Posted by OnAudio View Post
The Leach amp has a long history, many engineers were taught using that amplifier. Do try it out.
If it wasn't as good as it is, I doubt it will still be so popular now, after all these years. I'm sure this one will still be built by many in many years from now, and many new designs from this current period will have long been forgotten along the way.

Unless I can find something truly better, not just because someone says it, but because it was tried and proven by many, I don't see any others that are up to the standard right now. And as I mentioned before, I am not interested in mosfet based ones, and although I think some "classes" are rather interesting, such as G/H, A and for some, even D, I'm sticking with AB for now.

Quote:
Originally Posted by OnAudio View Post
You have come pretty far. There will be time more for other designs including Lazy Cats and SYMEF.
Absolutely! I am considering those possible "updates", but that would be for a future version, and it needs testing and prototype.

I think such changes can rather easily be brought in the design without having to radically change everything. I like this current design. I gave it a lot of thoughts.

It's not easy to find all the right compromises. I'm trying to make it as elegant as possible, as easy as possible to repair if need be. And hopefully making it good enough so repairs would be as unlikely needed as they possibly can be.

I think the extensive testing and research done by our friend Bonsai on the mosfet based SSRs is excellent and well documented. He's done a great job and I am convinced now to make use of this. So I am changing all the relays and fuses for SSRs (although not crowbars), because I do think it's superior and far better and efficient protection. With a good protection and things like input muting and perhaps input limiter or even compressor to prevent clipping, this amp can be as indestructible as for example the crown amps.
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Old 29th November 2013, 11:00 AM   #108
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btw: The is one concept that I find quite interesting (sch attached).

Although this is more of a testing circuit to simulate and perhaps it could be built as a prototype to find out how it works in reality. This has certain aspects that I find very interesting. The SQ remains to be seen and tested.

Perhaps this could be done all discrete and remove that opamp, and eventually a more conventional topo (such as leach's) could be adapted to this scheme.

I'm unfortunately not geared for such prototyping and research, but perhaps there are other enthusiasts that could tackle this.

Interesting this, is that like in a grounded bridge, the output is grounded!

One very interesting feature, is the fact that all outputs have their collectors, not only together, but also grounded. This is great for heatsinking, the cases, no need for insulation, no danger of touching high voltages on the transistors, etc...

This is nice, because TO3s can be used directly without shims (no mica or other), so we can have a better heat exchange situation, possibly reducing the required heatsink size.

The wiring can also get interesting, with the amp's output becoming the central star ground and the speaker's other end goes to the center tap on the psu...

Many cool things to learn from this. (thanks QSC)
Attached Files
File Type: pdf QSCgrounded source topology schema.pdf (20.6 KB, 85 views)
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Old 23rd February 2014, 06:49 AM   #109
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I haven't been working much on this project lately because I've been working on a grounded bridge with 2N3055.

I am however giving it some thoughts and I have decided to do away with the VI limiter type of protection and replace this with a more comprehensive protection scheme, using solid state switches as eminently described by our friend Bonsai:

Solid State Loudspeaker Relays for Audio Amplifiers

His research work on this subject has convinced me that this is a much better way to protect amps than any other methods.

Thus I will not use any output relays and VI limiters, in favor of solid state switches on the output and on both rails as well. Plus I want to add an input muting, with the proper logic to have proper timing for switching those in the right order.
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Old 23rd February 2014, 12:44 PM   #110
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Different protections. Bonsai's SSR protects the speaker from an amp failure, the VI limiter protects the amp from improper loads. You don't absolutely have to have either one as long as your amp doesn't fail and you don't short your speaker leads. A bit safer to use both.
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