Here's the Hill Audio Chameleon Schematic

[jez]

Hi Folks, As a follow on from Sakis's thread

help wanted in this schematic

I have reverse engineered a Chameleon 1400S so please find attached schematic.
Any odd looking values such as the Zobel resistor of 1R and 0R47 in parallel are how it is....
I don't have the original output transistors in Multisim so the MJL's are used instead. There is also some doubt over the varacity of the NE5534 model as compensation usually goes between pins 5 and 8 whereas only pins 1 and 5 are shown on the model.
I haven't yet had time to try out simulation of simple NE5534 circuitry on it's own and verify either that the Multisim model works correctly but mistakenly shows pin 8 as pin 1 or that it is not correct...
The simulation works great so long as you set the Zobel network values to be more "normal", it oscillates with the values used in the real thing, but the inductance of the 5 Watt wirewounds is not modeled (coudn't find any valid data on this believe it or not....non of the resistor manufacturers gives any figures for the self inductance of their wirewounds)

Also of course these are not the transistors used in the "real thing"
I'm guessing that the trimmer at the input is to match gain/phase at the inputs in order to get channel matching and best bridge mode performance (and yes, one end is left disconnected).
A brief check of distortion showed 0.005% at 1KHz and about 50 Watts output and -3dB at around 85KHz. These figures are just what I recall from late last night and not gospel truth, as it were..... It's only a simulation anyway so it could be out by a mile.

Jez.

[jez]

Ahem.....that should read "0.005% AT 50 Watts output", not "and 50 Watts output".

I'm sure it is capable of high output power but I haven't yet simmed the clipping point.
Jez.

[sakis]

about the voltage psu of the op amp ?????

standard voltage for op amps is 15+15 volts though in this schematic 17+17 is stated or in my schematic it says 16.5+16.5

any comments on that ????

[jez]

The 5534 can stand a max of + and - 22 Volts, on many amps which have a simple zener diode arrangement using 15V zeners to give the op amp supplies, it is found that they actually measure anywhere from ABOUT 15.8 to 17.5 (very approximate!) because they are run "hot" (literally as well as meaning at a high current!) to give lower impedence and also the temp co is not goood.
I am guessing that your friend measured the supplies as 16.5 V on his amp. It is not in any way critical and I merely rounded it up to a whole number......same with the output stage supplies. I can't make actual measurements on the amp as it is not "a runner"
Jez.

[sakis]

check this out ......
as we speak the amp is in real life test meaning ....board fully constructed heat sinked and ventilated

but:

Rails are 60+60 volts
1 khz sine wave + 8R dummy load
the only changes i have in the schematic is R22-23 = 52.3 R and R 27+26 = is now 10Kohm and emmiter resistors are 0.47 R

i have placed one millivolt meter across R12 emmiter resistor in one of the output transistors to monitor bias ......

here is what happend

with out the ventilator and with my electric thermo torch producing a lot of heat against the heat sink the bias increased from original reading about 70mv to something 90+ mv at this point got afraid and stopped ......

then added ventilator......... bias stabilized at 70mv at all times at this point no load ....

then added dummy load 1 khz sine and power up while still monitor the bias .....power up for 2 minutes at FULL power and then power down to monitor any changes in the bias ....

what happen is that the reading i had was some 45 milivolts that slowly slowly builted up to the original 70 mv

any comments ??????

[sakis]

was done with the R26-27 moded from original 15K to 10 K to force more bias in the output transistors and then see or make bias drifts more obvious .....

some few minutes later the resistors R26-27 are back to normal 15K resulting only 1.1 mv across emmiter resistors that drifts more or less between 0.2-0.3 volts after operating the amp at full power for a few minutes ....( pls notice that all this is 1khz sine dummyload 8R and ventilator )

any comments ????

[richie00boy]

What are the actual transistors used then? I thought they were MOSFETs?

[sakis]

2 drivers and 3sets of outputs all of them 1943+5200

[sakis]

for this rail voltage i think and seems that a slight crossover distortion appears ...a value between 10-15K is going to be calculated for a bit more bias .....

[jez]

Sakis,
Do you have thermistor (R20 1K NTC in my diagram) fitted??
It is physically located in the centre of the output devices i.e. 3 devices to each side of it. The drivers are right at one end and quite long pcb tracks go from the driver area to the thermistor.
The output devices are arranged NPN PNP NPN PNP NPN PNP
in a row. R10 on my diagram appears to be a "select on test" (SOT) item, probably to set the initial quiescent current at the factory....?

Richie00boy,
They are Sanken 2SC3264 and 2SA1295 BJT's. See the schematic.

Jez.