Leach Low Tim frontend tweak - Page 3

Bonsai · 04:53 AM

No I would not do that. In the context of the output signal levels, I doubt you have a noise problem with the Leach. The 317's (or 337's) are slow and their line and load regulation is not up to a Zener CCS that has been carefully designed. For a tweak, you could split r13 and r14 into 2 resistors and then decouple the junction to ground with a decent cap. This will help to keep rail noise off the Zener anode. Another tweak is to place a low value resistor (eg 10 Ohms) between the Zener anode and the bases of the transistors, and then to decouple the bases to GND with a cap (eg 10 uF). This will take care of the Zener noise- but, as I said earlier, in the big scheme of things, this is not an issue.

This is a fine amplifier that has stood the test of time. Don't mess with a classic - build and listen as Prof Leach intended!

Good luck!

Bonsai · 27th July 2011, 04:59 AM

Quote:

Originally Posted by djk

They do.

But the ear is an interesting instrument, after a while it can 'tune out' certain sounds, ignore them if you will. Whenever I play in a new venue it always takes a while to get used to the room. After a while you start thinking to yourself 'it really doesn't sound as bad as what I though originally'.

Fully agree!

I do wish some people would acknowledge that! I remember Bob Cordell commenting, something to the fact (and I am paraphrasing here) that there were a whole bunch of people raving about a SE 5W tube amp at a show and after he heard it, he could not work out what the fuss was all about.

Now, you can take that both ways, but sure illustrates the point about dogmatism in audio

gmphadte · 7th November 2012, 05:31 AM

I never liked the zeners at the bases of the LTP and knowing my quick fix for these with LM3x7 regulators was not recommended for their slow speed, I turned to a shunt regulator.
I assembled a shunt regulator designed for the RMI-FC100 with a 39volts zener simply because the parts r easy to find here, connected it in place of the 20Vx2 zeners and removed the two filter caps across it.

The low level highs are considerably improved now.

Gajanan Phadte

Tony · 7th November 2012, 05:36 AM

how about the ltp running on 20volts instead of 40v? anyone care to do simulation?

gmphadte · 7th November 2012, 05:58 AM

Now that u have asked, I would also want to add...

How about connecting appropriate RC across R36 like in RMI-FC100.

Gajanan Phadte

27th July 2011, 04:50 AM	#21
Bonsai diyAudio Member Join Date: Aug 2006 Location: Taipei, Taiwan	No I would not do that. In the context of the output signal levels, I doubt you have a noise problem with the Leach. The 317's (or 337's) are slow and their line and load regulation is not up to a Zener CCS that has been carefully designed. For a tweak, you could split r13 and r14 into 2 resistors and then decouple the junction to ground with a decent cap. This will help to keep rail noise off the Zener anode. Another tweak is to place a low value resistor (eg 10 Ohms) between the Zener anode and the bases of the transistors, and then to decouple the bases to GND with a cap (eg 10 uF). This will take care of the Zener noise- but, as I said earlier, in the big scheme of things, this is not an issue. This is a fine amplifier that has stood the test of time. Don't mess with a classic - build and listen as Prof Leach intended! Good luck! __________________ bonsai Amplifier Design and Construction for MUSIC! http://hifisonix.com/ Last edited by Bonsai; 27th July 2011 at 04:53 AM.

7th November 2012, 05:36 AM	#24
Tony diyAudio Moderator Join Date: May 2003 Location: Palatiw, Pasig City	how about the ltp running on 20volts instead of 40v? anyone care to do simulation? __________________ http://www.elab.ph/forum/index.php?topic=32688.0

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7th November 2012, 05:31 AM	#23
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	I never liked the zeners at the bases of the LTP and knowing my quick fix for these with LM3x7 regulators was not recommended for their slow speed, I turned to a shunt regulator. I assembled a shunt regulator designed for the RMI-FC100 with a 39volts zener simply because the parts r easy to find here, connected it in place of the 20Vx2 zeners and removed the two filter caps across it. The low level highs are considerably improved now. Gajanan Phadte

7th November 2012, 05:58 AM	#25
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	Now that u have asked, I would also want to add... How about connecting appropriate RC across R36 like in RMI-FC100. Gajanan Phadte