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Old 21st September 2008, 01:16 AM   #1
ReiMomo is offline ReiMomo  Puerto Rico
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Default Lowering temperature to the C300

Hi all

I did what would be called the C300.3 into a vero board
but the vas and drivers are running very hot,
I changed R31, R32 and R24 to 100
But the vas still too hot.
I'm using 2SC2333/2SB633 for vas and drivers.
outputs 2SA1094x6 at 49volts.

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Old 21st September 2008, 03:43 AM   #2
lineup is offline lineup  Sweden
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what would be nice to know
is the voltage you have across R24 & R31
this way we can know like what current you have in stages
--------

What sets the voltage across R24 is the RED LED.
Most RED LEDs have 1.7 Volt at 7 mA
so the voltage across R24 normally should be ~1.0 V
But there are RED LEDs with higher Voltage than 1.7V.
And these can be used just a well. See below.

With original 56 Ohm for R24, we get a bit less than 20 mA in this stage
--------

Voltage across R31 (and R32) can be something like 0.9 Volt

With original 33 Ohm, this may give something like
35-40 mA in Q15 and Q16 at idle

AS the 2SA1094 have good gain, the base current into those 8 transistors is only a few mA, of that 35-40 mA value.
If you have normal Class AB bias: 50-100 mA into each Output transistor
Gives 20-40 mV across those Emitter resistors.
---------

I would recommend you use the orignal values for R31,R32.
And you should try to get ~18-20 mA through R24.
Depending on your used LED and so the voltage across R24,
you may have to adjust the value of R24 (56 Ohm),
until you get like 18-20 mA.
---------

It is nothing wrong those VAS driver transistors get a bit hot.
Q15, 2SC2333 is one 15 Watt TO220
Q16, 2SB633 is one 40 Watt TO220
(as what I got from datasheets)
With small separate heatsinks they can take a couple of Watt.
40 mA x 50 Volt = 2 Watt
20 mA x 50 Volt = 1 Watt
---------

The reason I should want to use original current levels in VAS driver
is that this is probably tested to work well.
At least I would not change, reduce the current, too much.

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Old 21st September 2008, 03:51 AM   #3
lineup is offline lineup  Sweden
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Q11 should be placed onto Main Heatsink
close to those 8 Output transistors.

I do not see any BASE stoppers resistors.
Not even to the 8 output transistors.
And not to Q15, Q16.

for the 8 power devices, you may use 8x10 Ohm resistors into Base
and put as close as practically possible to the base pin of each T
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Old 21st September 2008, 04:08 AM   #4
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Location: Albany , NY (smallbany)
I built C200 and 300 ...
1.Put the drivers on the main heatsink.

2.make sure red led is 1.6-1.7v (most are 1.9+ except deep red
low brightness-low current Al-GA-AS .I use red led CSS on ALL
my amps.)

3.large VAS heatsinks/change r16 to 10K-2w (helped me).

I eventually scrapped the c300 because I didn't like the sound
but it never blew up and seems to be a
stable design...good luck..OS

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Old 21st September 2008, 05:10 PM   #5
ReiMomo is offline ReiMomo  Puerto Rico
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Ok for some reason R19 went into a flame after some seconds
I power it. I don't dare to keep using this now at least
on this vero board. I did two channels of this amp before
on a breadboard and never had problems only the heat.

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My favorite amp is this one
n55n.com_86DKCckL0A.jpg
the Melody 400 but I need to know how to do it quasi
I will do a new topic about it later.

Thanks ppl for the quick help.
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Old 21st September 2008, 05:39 PM   #6
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Quote:
reimomo:My favorite amp is this one
That amp is
very similar to the Leach amp, same triple darlington outputs
but with a different CSS.

I never had problems with amps blowing up
mainly because I make boards. All those wires up in the
air greatly increases the chances of noise and instability.

I draw these amps out on graph paper first:
Click the image to open in full size.
lay the graph paper on top of the board, center punch the pads
use the design as a drawing guide and get:
Click the image to open in full size. etch it,
Click the image to open in full size.
very low tech, but cheap and the amps don't blow up.
BTW , amp above is similar (QUASI) to c300 but a better design.

To do the melody Quasi (pnp) reverse the layout of this:
http://www.ampslab.com/c200qc.htm
same as you did to your c300 but add 10 ohm basestoppers
to all output devices.
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