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Old 21st May 2003, 07:43 PM   #1
nanhifi is offline nanhifi  Malaysia
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Default problem in mje2955 to 2sa1943

I have modified my own old circuit that use a output transistor of MJE2955 to 2SA1943. I found that the sound seem to be big different. The bass seem to over blown and treble lack and limited. Why this happend. I change the MJE2955 to get rid of the metal mounted to a plastick type 2SA1943. It make my job simple on mounting at big heat sink.

Any body have any idea why this happend. I try set on the gain, the compenstion VAS capacitor and it still the same.

I found that mje2955 is a slow transistor than the fast 2SA1943. Is there anything wrong in here?

The Amp is a CLass A bias at 2.6A of 20W per channel.

Any suggestion to change the MJE2955 to a different package like the 2SA1943 ..

regard.
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Old 22nd May 2003, 12:55 PM   #2
moamps is offline moamps  Croatia
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Default Re: problem in mje2955 to 2sa1943

Quote:
Originally posted by nanhifi
I have modified my own old circuit that use a output transistor of MJE2955 to 2SA1943. I found that the sound seem to be big different. The bass seem to over blown and treble lack and limited. Why this happend. I found that mje2955 is a slow transistor than the fast 2SA1943. Is there anything wrong in here?
The Amp is a CLass A bias at 2.6A of 20W per channel.
Any suggestion to change the MJE2955 to a different package like the 2SA1943 ..
Hi,

Some class A design have oscillation problem when fast transistors are used. On http://www.gmweb.btinternet.co.uk/index.htm (The Class-A Amplifier Site) you can find very interest papers about this. Anyway, similar replacement for MJE2955 is BD250.

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