Leach wide bandwidth preamp.

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beppe61

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Joined 2005
Dear Udip,

Thank you very much indeed for your kind and valuable reply.
That is the one.
How do you rate is line section ?
I am not interested in LP listening anymore.
I am too lazy and clumsy for black disks.
What intrigues me is the fact that is made out just two BJT.
May be is becoming my obsession.
Which line preamp is possible from just two BJT.
I strongly think that is possible a lot indeed.

Any your suggestion, information and opinion would be greatly appreciated here.

Kind regards,

beppe61
 
udip

udip

Member
Joined 2004
beppe61 said:

What intrigues me is the fact that is made out just two BJT.
May be is becoming my obsession.
Which line preamp is possible from just two BJT.
I strongly think that is possible a lot indeed.

Any your suggestion, information and opinion would be greatly appreciated here.
Click to expand...


Hi again,

You were refering to the first one with the two BJT's line amp,
I actually built the FET version (look at page 10-11 in
the article) were both the MC preamp and line preamp are
the same (except for the feedback compoments) - they are
actually a discrete opamp so you can use it in any application
you want... and the sound is very good indeed..at least
I liked it...and also they are very quiet!
I haven't tried the two BJT's version so I can't tell you
how it sounds... but I guess it should be pretty good as a line amp with not too much gain...
If you decide to try the discrete opamp version, you can
check the thread I'v posted and modify it for +-15 supply.

Regards,

Udi.
 
R

rayfutrell

Member
Joined 2004
I bought the both Leach preamps, the line stage and power supply from Dr. Leach in the late 1970s. I bought them built to avoid the hassel of ordering and matching parts. Most parts houses had a minimum order amount, both quantity and price. One time I wanted 4 transistors and had to buy a bag of 25. I prefer the JFET version of the preamp and replaced most of the caps in it with polystyrene caps. The JFET preamp has a much higher slew rate and much lower input capacity than the BJT version. High inductance MM cartridges require low terminating capacity.
 
M

Mikett

Member
Joined 2003
I bulit both the BJT and FET versions. The line sections are a little veiled and certainly not as dynamic as compared to Walt Jung's AD744-811 design.

Unfortunately, I am comparing the Leach sections with a "Sulzer" type regulator versus Jung's high performance regulators on the 744-811 section.
 
B

beppe61

Member
Joined 2005
Mikett said:
I bulit both the BJT and FET versions. The line sections are a little veiled and certainly not as dynamic as compared to Walt Jung's AD744-811 design.

Unfortunately, I am comparing the Leach sections with a "Sulzer" type regulator versus Jung's high performance regulators on the 744-811 section.
Click to expand...

Dear Mikett,

Thank you very much for your kind and valuable reply.
Could you please give me some more info on this Sulzer type regulator or some useful link ?
I intend to use 24V fixed voltage regulators or the 117-317 pair for the +/- 24V dual power supply.
I am very intrigued by the simplicity of this line stage (something called Sziklai pair I guess), just two BJTs, and the high voltage rails (for a preamp of course).
I am sure that this simple stage deserves a good power supply.

As soon as I will build it I will report.

Kind regards,

beppe61
Torino__ITALY
 
B

beppe61

Member
Joined 2005
andy_c said:
Here's Walt Jung's article on the "Super Regulator" design. This was developed both by Walt and by Jan Didden (janneman), and is an enhancement to Sulzer's original regulator design (which was published in The Audio Amateur around 1979 or 1980).

http://home.comcast.net/~walt-jung/wsb/PDFs/Improved_PN_Regs.pdf
Click to expand...

Thank you Andy,

You have given me something to study.
Even if it is just a little complex for my taste.
I am very basic by attitude.
I will try to understand.

Thank you very much again
Kind regards

beppe61
 
H

HKC

Member
Joined 2003
Leach wide bandwidth preamp

Hi Rayfutrell

I would like to know the value of the polystyrene caps you used to replace the electrolytic capacitors as the value of electrolytic capacitors are much higher than polystyrene capacitors I even can not find any close.
Your reply will be much appreciated.
 
B

beppe61

Member
Joined 2005
udip said:
Hi beppe61,

If you prefer a simpler regulator, you can try this one
It's is the pooge regulator, and suppose to be very good,
when comparing to the lm317/337.

Regards,

Udi.
Click to expand...

Dear Udip,

Thank you very much for the link, very interesting indeed.
But I still think that if a couple of 317/337 is good enough for the well reviewed Bryston top of the line preamps that could be no that bad.
This monolithic voltage regulators are just too much handy not to be considered.
And I am very bad ad implemeting complex circuits.
Nevertheless I will be very interested in knowing in which aspect the discrete regulators are better than monolithic when feeding pure class A circuit (so with constant current draw).

Thank you very much indeed.

Kind regards,

beppe61
 
B

beppe61

Member
Joined 2005
roger-k said:
I want to build this preamp too.

The pot for bass and treble should have revers log taper, but I can't find any pot with shaft and reverse log thaper.

How can I solve this problem?
Click to expand...

Dear Roger,

The pot for bass and treble?
Please don't do that !
I am just joking eh, eh.
But seriously if you are looking for the best sound you really should avoid to build the tone control section.
Bypassing it leads always to better sound.
If you look at the top of the line preamps of any brand you can see no tone controls.
We need flat frequency response for the amplification.

If you build the line preamp section I would be very interested to know your opinion.

Kind regards,

beppe61
 
R

rayfutrell

Member
Joined 2004
I replaced the plastic and ceramic caps with the polystyrene caps. I did not replace the electrolytic caps. It is difficult or impossible to find high value plastic caps and they are big. I have some 5 mfd mylar caps and they are about 25 mm diameter and 75 mm long.

I could only obtain 5% tolerance caps and used an RLC meter to match the caps in the right and left channels. Be careful. Polystyrene caps are fragile and melt easily

Regards,
Ray
 
udip

udip

Member
Joined 2004
beppe61 said:
Dear Udip,

Thank you very much for the link, very interesting indeed.
But I still think that if a couple of 317/337 is good enough for the well reviewed Bryston top of the line preamps that could be no that bad.
This monolithic voltage regulators are just too much handy not to be considered.
And I am very bad ad implemeting complex circuits.
Nevertheless I will be very interested in knowing in which aspect the discrete regulators are better than monolithic when feeding pure class A circuit (so with constant current draw).

Thank you very much indeed.

Kind regards,

beppe61
Click to expand...


Hi beppe61,


I agree that the LM317/337 are a much easier solution,
and they are not bad either, but as far as I can tell
the discrete regulators sound better, and have lower noise
than the monotholics, specially for pure class a designs.
Maybe for line level applications the lower noise is not a
major improvement, but for preamps it is.

Regards,

Udi.
 
B

beppe61

Member
Joined 2005
udip said:



Hi beppe61,


I agree that the LM317/337 are a much easier solution,
and they are not bad either, but as far as I can tell
the discrete regulators sound better, and have lower noise
than the monotholics, specially for pure class a designs.
Maybe for line level applications the lower noise is not a
major improvement, but for preamps it is.

Regards,

Udi.
Click to expand...

Dear Udip,

Ok, I give in.
This is to much difficult for me. I am very unexperienced in DIY.
I understand that low noise is very fundamental especially with small signal.
I guess that the magic of a preamp can be in the quality of its power supply (like the Tom Evans "The groove" equipped with those Lithos ultra-low noise regulators).
Or even power supplies based on batteries.

Thank you very much for your kind and valuable advices.

Kind regards,

beppe61
 
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