I have assembled a Leach amp to drive my Klipsch RB 81 and am in the process of chasifying(engrish) it. But before completing it, I would like to know if anybody has modified the frontend by incorporating a ccs and can I get the schematic of the same.
Can't wait too long to listen to them through Leach amp
Thanks and regards,
Gajanan Phadte
Can't wait too long to listen to them through Leach amp
Thanks and regards,
Gajanan Phadte
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.
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.
Actually, I did some simulation on zener reference based LTP current generator a la Leach, and a number of the more conventional current sources for LTP use. Below a few KHz, the active current sources are better by about 8dB (in sim 156dB vs 148dB) when I t comes to rail noise rejection. But the Zener based reference rejection performance is flat out to 100's of KHz. The Zener noise issue can easily be fixed with filtering. My view: the Zener current source is more than a match for active current sources, so I would not fiddle with the Leach design in this area.
you can add resistive bootstrap to the tail R for a huge increase in common mode impedance with just 2 added R (and changing the 2 tail R value)
basically connect a new R from the output (feedback take-off point) to each diff pair, calculate the ratio of the added R with the tail R to equal the feedback ratio
then the "voltage source" providing the "CCS" thru the tail R (Thevenin equivalent) is a blend of the Zener V and the output - which is set to closely match the input common mode V from the positive input/non inverting amp structure
you also have to calculate the parallel R, divided bootstrap V to get the original current setting
I am highly skeptical of people offering advice that circuit change X gives Y sound change in basically good amplifier circuits - amps are way behind source, Loudspeaker, Room, volume setting, EQ, listener's mood, ect. in effect on perceived "sound" – you have to ask how they controlled for any of those effects – ask if they ever actually had 2 complete circuits with only the one variable changed to listen to at the same time – human auditory memory is really poor too
basically connect a new R from the output (feedback take-off point) to each diff pair, calculate the ratio of the added R with the tail R to equal the feedback ratio
then the "voltage source" providing the "CCS" thru the tail R (Thevenin equivalent) is a blend of the Zener V and the output - which is set to closely match the input common mode V from the positive input/non inverting amp structure
you also have to calculate the parallel R, divided bootstrap V to get the original current setting
I am highly skeptical of people offering advice that circuit change X gives Y sound change in basically good amplifier circuits - amps are way behind source, Loudspeaker, Room, volume setting, EQ, listener's mood, ect. in effect on perceived "sound" – you have to ask how they controlled for any of those effects – ask if they ever actually had 2 complete circuits with only the one variable changed to listen to at the same time – human auditory memory is really poor too
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I'm also think that the Leach amp does not need improvement, its sounds good (I have two Leach amps) , you speakers are quite sensitive- there is lot of power in Leach amp. Some believe that Leach sounds better with higher bias than in original article - around 150mA or even 200mA-I can not confirm that.
according to B. Cordell book protection circuit can be a problem in certain circumstances ...but this is not a problem for home listening imho.
amplifier is very quiet-there is no hiss or hum with professor boards.
in my second Leach I place output coil near resistor instead wounding around resistor.
according to B. Cordell book protection circuit can be a problem in certain circumstances ...but this is not a problem for home listening imho.
amplifier is very quiet-there is no hiss or hum with professor boards.
in my second Leach I place output coil near resistor instead wounding around resistor.
"I am highly skeptical of people offering advice that circuit change X gives Y sound change in basically good amplifier circuits - amps are way behind source, Loudspeaker, Room, volume setting, EQ, listener's mood, ect. in effect on perceived "sound" – you have to ask how they controlled for any of those effects – ask if they ever actually had 2 complete circuits with only the one variable changed to listen to at the same time – human auditory memory is really poor too "
I am Absoloutely 100% in agreement with this JCX.
I am Absoloutely 100% in agreement with this JCX.
Running a service department for a hi-fi store I could do some interesting mods. One time I modded six of the same piece of equipment with a series of mods. I had originally done several mods to one piece all at once and the unit sounded quite different. Doing them one at a time I was able to see what gave the biggest bang for the buck.
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'.
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'.
The foldback current limiting on a Leach is to protect it from shorts and being driven hard into clipping on low impedance loads. A friend can make his produce 'farting' sounds when driving more than 6dB into clipping on a 2Ω load. Other than that, I have never heard the foldback limiter.
If you mean a DC protection relay, that's a different function. I prefer both.
If you mean a DC protection relay, that's a different function. I prefer both.
Yes, I mean the dethump and dc protection circuit with a relay.
I intend to protect the speaker only and the amp should sound good.
As far as the frontend bias goes, I find that the consensus is that it sounds good.
Can the zener noise be reduced if I make zener from transistors.
Gajanan Phadte
I intend to protect the speaker only and the amp should sound good.
As far as the frontend bias goes, I find that the consensus is that it sounds good.
Can the zener noise be reduced if I make zener from transistors.
Gajanan Phadte
No, the reverse BE junction is just as noisy.
Transistors can be used when you need a ~7V zener, you can but a cheap transistor for less than a zener.
Audio Amateur had a noise generator project the amplifier a BE junction noise.
On the other hand, Nelson Pass used the BE junctions with 0.1µF in many of his designs.
Transistors can be used when you need a ~7V zener, you can but a cheap transistor for less than a zener.
Audio Amateur had a noise generator project the amplifier a BE junction noise.
On the other hand, Nelson Pass used the BE junctions with 0.1µF in many of his designs.
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