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Old 14th August 2006, 12:30 PM   #1
AMV8 is offline AMV8  United Kingdom
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Default Best transistors for preamps

Hi

I am trying to update the transistors in two preamps that I built about ten years ago. I do not know what the current best transistors for a preamp are as there so many choices now - and I am hoping that this may be of interest to others also.

ALL HELP WILL BE APPRECIATED.

The transistors that I would like to replace with modern/updated equivalents are;

ZTX384 NPN transistor. ( Is 2SC2547E a good replacement - the specs look OK but I do not know how it sounds.)

ZTX214 PNP transistor. ( Is 2sa1085E a good replacement. Again the specs look OK but I do not know how it sounds.)

LM394CM - a matched pair dual NPN transistor

Both preamps are all disrete component and are based upon Kelvin labs designs. They operate in class A with dual +15 0 -15 power supplies. One uses an emitter follower first stage ( using the ZTX384 ) and the other has a dual differential first stage ( using LM394 ).

In the phono stage the preamp uses TLO72CP. Is there a better equivalent for that for use in the phono stage?

It would be nice to "just drop in" some replacement transistors but I do not mind doing some resistor replacement to get a better preamp.

I would appreciate any help#

Don
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Old 14th August 2006, 12:33 PM   #2
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One single transistor type can't fit all your needs so if you show us where there transistors are in your circuit it is easeir for us to help you.
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Old 14th August 2006, 12:59 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
the 2S transistors are high voltage.

It is normal for there to be compromises between; gain, fT, voltage, linearity and cost By dropping needless voltage ability you can probably achieve a better mix of other specs.

Can you post a schematic?
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Old 14th August 2006, 02:03 PM   #4
sreten is offline sreten  United Kingdom
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Default Re: Best transistors for preamps

Quote:
Originally posted by AMV8


LM394CM - a matched pair dual NPN transistor

In the phono stage the preamp uses TLO72CP. Is there
a better equivalent for that for use in the phono stage?

Don
Hi,

The NE5332 would probably drop straight into the phono stage.

The LM394M, I have seen updated "low noise supermatched pairs"
(presumably its in the MC stage), Analogue Devices I think, MAT02
series I think, don't know if they would be better, also they are
not in DIL from.

/sreten.
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Old 14th August 2006, 03:45 PM   #5
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Old 14th August 2006, 03:56 PM   #6
AMV8 is offline AMV8  United Kingdom
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Peranders, Andrew, streten.

Thanks for the replies.

I did think about adding a schematic to help replies as I do have them for both pre amps.

I also have schematics for the power amps that I use. The power amps are class A monoblocks I have both 30w and 60 watt class A monoblocks.

The pre amps and the power amps that I have used for some years are all based upon Kelvin Labs circuits - but modified to various extents by me. Kelvin labs made gear from about 1988 to 1994 or so and then disapeared. I have tried to contact them but failed so I have not been able to get any agreement to publish the circuits. Do I need permission? Can I put the circuits on a thread? Any views?

Don
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Old 14th August 2006, 04:10 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
posting your modified version should not cause a problem.
If you have tried to contact them and they have not responded, then I think that opens the door to posting the unmodified version.
Let them or their succesor ask you to remove the posting. Our Mods can do this if this happens.

I suspect the 394 will be hard to improve on.

OOPs this does not apply to the 5532. The 5534 has an unusual comp and pin out. Check it's compatibility with the 072 socket.
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Old 14th August 2006, 04:18 PM   #8
AMV8 is offline AMV8  United Kingdom
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Andrew

Thanks for the reply.

I do not have a drafting programme so I will scan the circuits and try posting the preamp circuits. They are simple circuits in concept but just sound good. I have owned Krell, Musical Fidelity and various other high end gear but never found any that approach these for sound.

Don
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Old 14th August 2006, 04:25 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

I tried an early kelvin labs 20W proper class A integrated.

CD sounded sublime when it wasn't giving up the ghost on bass notes.

The MC + MM phono input was a real dissapointment, not good.

Compared to my AudioLab 3000A.

/sreten.
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Old 14th August 2006, 04:45 PM   #10
AMV8 is offline AMV8  United Kingdom
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Streten

The "giving up the ghost on bass notes" I believe was due to resistence in the power supply after the main filter capacitors that resulted in a high pass filter acting at around -3db at 30hz. One of my mods was to reduce the resistence in the power supply and lower the filter frequency.

The mm and mc circuits all used tantalum capscitors in the circuit, had very poor power supply rejection and used noisy voltage regulators. More of the items I modified.

I spent time on them because as you commented I found they sounded good.

Don
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