Leach Low Tim frontend tweak

[Bonsai]

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]

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]

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

 

[TonyTecson]

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

 

[gmphadte]

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

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

Gajanan Phadte

 

[spongeman]

WM Leach felt the passive CCS (resistor from a regulated supply) sounded better than an active CCS.

MacIntosh uses a resistor pulled to a very high voltage instead of an active CCS in many of their pieces.

Just because something may measure better, doesn't mean it always sounds more like music.

what mcintosh,mister? all?

 

[djk]

MC250, MC2505, MC2100, MC2105, MC2300, all pull to HV.

MC502, MC2120, MC2125, MC2200, MC2205, all pull to a regulated supply.

MA6100



Diff pair pulling to 110V.

 

[spongeman]

MC250, MC2505, MC2100, MC2105, MC2300, all pull to HV.

MC502, MC2120, MC2125, MC2200, MC2205, all pull to a regulated supply.

MA6100



Diff pair pulling to 110V.

what type and watt resistor used at that amplifier,mister?

 

[djk]

1W carbon composition.

The 3.6K for the Vas is a 5W wirewound.