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Old 9th March 2005, 02:14 PM   #31
tmblack is offline tmblack  United Kingdom
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Here is the schematic of the modded amp.
A well proven LIN design but with current mirror.

Tom
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Old 9th March 2005, 04:49 PM   #32
MikeB is offline MikeB  Germany
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What transistors are you using ?
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Old 11th March 2005, 06:56 AM   #33
thanh is offline thanh  Viet Nam
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Quote:
I haven't tried the TDA7295.
Is that a smooth sounding one?
I dont also know!
A magazine said it like that. Who have listend its sound?
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Old 11th March 2005, 02:22 PM   #34
tmblack is offline tmblack  United Kingdom
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I have used common Motorola transistors, MPSA06/56 for inputs,MJE15030/31 and MJ15003/4 for output.

The TDA7295 uses DMOS outputs and might sound smoother.
The cost of the TDA7295 is reasonable to try.

Tom
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Old 11th March 2005, 02:36 PM   #35
MikeB is offline MikeB  Germany
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And what did you use for vas ?
You can speed up your LTP by ~3 by not using mpsa06/56, these
devices are incredible slow...
You could use mpsa8099/8599 or 2n5551/5401.

Mike
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Old 12th March 2005, 03:49 PM   #36
tmblack is offline tmblack  United Kingdom
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I use MJE15030/31 for VAS.
You must mean MPS8099/8599. Not always in production but 2SA1015/2SC1815 is low noise, fast and available.

Tom
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Old 12th March 2005, 04:12 PM   #37
MikeB is offline MikeB  Germany
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Sorry, yes of course mps8099...
The 2n5551/5401, should be easy to get and are cheaper than
japanese transistors.

Mje15031 in vas ? Unbuffered connected to a currentmirror ? Ouch !
Mje15031 has very big inputcapacity, giving large reactive load
to the currentmirror having nearly infinite zout. This combined with
the 100pF cdom gives enourmous dynamic phaseshifts.
You could replace q5 with a normal signaltransistor and cascode it
with a mje15031 (or better suitable), this removes a lot of dynamic
phaseshift.

Mike
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Old 12th March 2005, 08:09 PM   #38
tmblack is offline tmblack  United Kingdom
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I agree and pondered on MJE350 for VAS.
No room to cascode or add a buffer, but how about 2SB649A video transistor for VAS?

Tom
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Old 15th March 2005, 06:39 AM   #39
ilimzn is offline ilimzn  Croatia
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Quote:
You can speed up your LTP by ~3 by not using mpsa06/56, these
devices are incredible slow...
You could use mps8099/8599 or 2n5551/5401.
2N5551/5401 are fast and high voltage but have a relatively low gain. If the 90V Vceo of the MPS8099/8599 is suitable, they would be a far better choice.
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Old 21st March 2005, 05:31 AM   #40
tmblack is offline tmblack  United Kingdom
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I am using MPS8099 is LTP now.
Question is what is the best for VAS?

I have examined popular op-amps and all use current mirror loads and many with single transistor VAS.

So maybe there is hope in the design.

Tom
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