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
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
AMV8 said:
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.
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
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
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.
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.
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
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
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
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
Hi,
Having also heard the Sugden class A 15 watter, bass quality is
very good up to a point, when this "also gives up the ghost".
The bass quality of the Kelvin was very good, up to a given level.
But neither amplifier can drive my typical speakers (87dB/W 8R) to
levels in the bass I'd find acceptable, whilst the midrange was fine.
I agree the power amplifiers are certainly worth the effort, the lack
of midrange "clutter" and "strain" on complex passages compared
to my Audiolab was surprising, as was unclipped midrange levels.
/sreten.
Having also heard the Sugden class A 15 watter, bass quality is
very good up to a point, when this "also gives up the ghost".
The bass quality of the Kelvin was very good, up to a given level.
But neither amplifier can drive my typical speakers (87dB/W 8R) to
levels in the bass I'd find acceptable, whilst the midrange was fine.
I agree the power amplifiers are certainly worth the effort, the lack
of midrange "clutter" and "strain" on complex passages compared
to my Audiolab was surprising, as was unclipped midrange levels.
/sreten.Sreten
I also found the Kelvin Labs pre amps and power amps good to listen to. There is no confusion in the music and the sound is clear with no audible distortion.
The weak area I also found was that the base was lacking - but clear. After some research I have found that in the pre amps it is due to resistence in the power supplies and also in the signal inputs.
I am still playing with the power amps but the lack of power in those seems to be due to the small size of the transformer and the capacitors and again some added resistence which is creasting a high pass filter. As I modify these aspects the bass becomes correct.
I have also modified a few other parts in the circuuit, generally in line with current thinking. However I have made changes step by step - one at a time - to aviod loosing the strenghts of the amplifiers.
The pre amp circuits I posted are my current versions of the pre amp circuits.
Don
I also found the Kelvin Labs pre amps and power amps good to listen to. There is no confusion in the music and the sound is clear with no audible distortion.
The weak area I also found was that the base was lacking - but clear. After some research I have found that in the pre amps it is due to resistence in the power supplies and also in the signal inputs.
I am still playing with the power amps but the lack of power in those seems to be due to the small size of the transformer and the capacitors and again some added resistence which is creasting a high pass filter. As I modify these aspects the bass becomes correct.
I have also modified a few other parts in the circuuit, generally in line with current thinking. However I have made changes step by step - one at a time - to aviod loosing the strenghts of the amplifiers.
The pre amp circuits I posted are my current versions of the pre amp circuits.
Don
Hi,
Kelvin like their cascodes!
Q10 has me perplexed. The cascode cannot be there to allow voltage tolerance for the VAS, they must have used the cascode to remove the influence of non linear Cob of the VAS and to then speed up the VAS as a consequence. They undo all the good work by wrapping a Miller compensation cap around the VAS/cascode stage. Bonkers.
If the Miller comp cap does as badly here as it does in a conventional power amp then that might in part explain why the phono stage sounds bad in comparison to other pre-amps.
Kelvin like their cascodes!
Q10 has me perplexed. The cascode cannot be there to allow voltage tolerance for the VAS, they must have used the cascode to remove the influence of non linear Cob of the VAS and to then speed up the VAS as a consequence. They undo all the good work by wrapping a Miller compensation cap around the VAS/cascode stage. Bonkers.
If the Miller comp cap does as badly here as it does in a conventional power amp then that might in part explain why the phono stage sounds bad in comparison to other pre-amps.
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