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Old 14th September 2008, 03:38 PM   #61
PB2 is offline PB2  United States
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Interesting amplifier.

What are you using for driver transistors Q1 and Q2?

Do you know what the output stage bias level was in the original amplifier? There is essentially no thermal compensation in this amp. +/- 80V is mighty high for so few outputs, you might want to limit it to 8 ohm loads.

It may work into 4 ohm cold, for a while, but when it is hot it will probably fail. Do you plan to use forced air cooling?

C10 and C11 zobels are not so commonly used but are an interesting way of improving stability.

Pete B.
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Old 14th September 2008, 04:16 PM   #62
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Default at this point

yeah its a fairly simple and nice amp .....

this what you see is the basic schematic
-there is a complete zobel in the output
-in earlier models this network C10-R10 C11-R11 was ommited
- in my version except 2drivers exist also 3pairs of outs 1943+5200 and a few other cahnges
- about thermal stabilize in erlier models on parallel of 220R (R7) was added a thermistor attached to the heat sink
-fully regulated psu for 15+15 volts ( even though the schematic say 16.5+16.5 ( havent tested this yet but i am working on this also )

- ive also designed a pcb that includes the main board with all the heavy power stuff and a piggy board that includes all the small things like op amp and so on ( extremelly very compact and size of only 4cm x20 cm ) you can look at the picture ....

-also bench tests are doing just fine with only problems that this amp like many others was kinda sensitive to wiring and layout so you cannot make tests with 4 klm of cables arround you....

-finally let us not forget that this is an amp class AB+B so top of quality is not the target here but compact easy cheap and power full is more like it

real life tests are coming any day now and after that updated schematic ( and pcb why not !!!!) with a full set of wave forms will be presented in a few days
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 14th September 2008, 04:51 PM   #63
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Default another picture

another picture without the inductor yet ....
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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Old 14th September 2008, 05:36 PM   #64
PB2 is offline PB2  United States
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I asked about the original bias point because the output stage bias is not very well defined, being dependent on the driver bias point, driver & output beta, temperature, etc. It will be dependent on component to component variation without some form of feedback.

You mention a thermister that you might want to duplicate from the original design. A diode string or Vbe multiplier are other solutions as I'm sure you know.

Larger emitter resistors on the outputs will also help thermal stability but are not a complete solution.

Just noticed that drivers and outputs are the same devices, that is some overkill on the drivers, but on the other hand I think that they're often undersized when temp and SOA are considered.

Pete B.
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Old 15th September 2008, 11:51 AM   #65
jez is offline jez  United Kingdom
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As promised, here's the circuit diagram, (in a new thread as an adjunct to this one because the original title doesn't mention the Chameleon and so many people who may be interested in this amp may pass it by....that's my reasoning anyway) Here's the Hill Audio Chameleon Schematic
Good luck to Sakis with the practical implementation of this, it looks like some good work so far
Jez.
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