Compare Crecendo and Leach Amp

[swede]

Hi there,

Have any of you any idea on the main differenced between the (Elektor's) Crecendo and the Leach Amp.

I'm currently building the Leach Amp and are really curious about the pros and cons comapred to the Crecendo, which I'm probably about to build in a not too distant future.

Have a good day,
//magnus

[djk]

Are we talking about the original 1984 Crescendo? It had a reputation as an oscillator. The new 2001 version may be better. I don't like plastic outputs and I don't like the sound of L-MOS for bass. I have owned several Leach amps. They are well worth the effort.

[fcel]

A lot of people mentioned Leach Amp on this web site. What is the high light of these amps? Easy to built? Low parts count? Or .....

[GRollins]

fcel,
Once upon a time, it was thought that TIM (Transient Intermodulation Distortion) and slew rate were the cures for the audible problems with amps that measured well, yet didn't sound all that good.
The Leach amp is a design that seeks to minimize TIM by having a high slew rate. It's a fairly complicated circuit as such things go, so the parts count is high and there's a lot of assembly and fiddle-factor involved.
I haven't heard a current version, but the last one I heard (I don't know what revision it might have been) didn't seem all that remarkable to me. However, lots of people seem to like them.

Grey

[swede]

Well,

For me, since I'm a newbie, the Leach Amp is close to perfect, since it requires some hard work and prof. Leach has a lot of explanaitions on his website. It has, this far, been a goldmine for learning about the different parts of an amp.

I hope I'll be able to finnish the project in reasonable time.

But, it was an article about the Crecendo (just recentrly, the "upgraded" version") that got me hooked on building an amp. from the beginning, so I'm still curious if it is worth the effort to build it as well.

//magnus

[jteef]

I think one of the main features that the leach amp has, is that it is pretty much rock solid. Prof. Leach oversees the construction of at least 20 amps / year from just students. Not counting DIYers elsewhere. This gives him first hand knowledge of any problem that can arise and he has done well in fixing them in the 20+ years of the designs life.

I built one as a student under his supervision that I am very anxious to listen to. Its first test was on a pair of martin logan monolith III's. I liked the sound a lot, but the guy's krell fsb 600 had quite a bit of an edge of my amp(for 13 grand, it better). I have been unable to find employment since i graduated and have no money to buy a good pair of speakers. They are 2nd on my list after i do find a job tho!

jt

[Damon Hill]

I take issue with Grey's perceptions about the Leach amp; it is fairly typical of modern amplifier design and even relatively simple as it has no constant current sources or current mirrors. I'd hardly call it 'fiddly' in terms of building and adjusting; there's only a bias pot.

While having a good slew rate, it also avoids slew
limiting by having an input filter. The symmetrical
design and plenty of power supply decoupling helps to give
it very high ripple rejection. Indeed, the symmetrical
design from input to output was one of the attractive
features when I originally chose to build it.

I'd call it a straightforward and even slightly conservative design that's well-documented and thoroughly
debugged over the years. You DO have to follow the instructions closely and be careful about wiring and grounding, but that's true of any high-performance amplifier.

It might benefit from a few tweaks; I've installed a 1 uF
capacitor between the driver transistor emitters to improve
the output device turnoff at high frequency, as per Self
and Sloan's books. Perhaps there's room for improvement in the bias tracking. I'm installing ver 4.5 boards to update my amplifier, pending arrival of some Black Gate and Nichicon Muse capacitors; I used metal film resistors throughout, and matched all mirror-image parts for tolerance or gain as closely as I could. Also used better
quality parts for the wire-wound emitter resistors instead
of the typical sandcast parts--lower Tc, I hope.

At some point I may substitute 2SA1302/2SC3281 transistors
for the MJ15003/4 devices; the former have much better linearity at higher current and a much higher Ft. But I'll
have to change the physical design of the amplifier to
mount the new transistors on new heatsinks, if I can find
suitable units at a good price. But I'm going to brassboard
this before I commit to a major overhaul of the chassis; I'd
like to be sure these new transistors are stable.

As for sound quality; I can't really comment as I've never
had much of a chance to compare it to other amplifiers. I'm
fairly pleased with the amplifier over the nearly twenty years I've been using it and hope the newest version boards will constitute an audible improvement.

I haven't seen any other amplifier designs that intrigue me enough to try them, as far as Class B amplifiers go. Class
A amplifiers probably have lower distortion, but the heat
dissipation and related complications make them impractical
for my use. It's a trade-off between absolute quality and
practicality.

I've also been working on a tube amplifer project, but it's stalled for lack of parts, money for parts, and a choice
of driver circuit design.

[peranders]

Originally posted by swede
Hi there,

Have any of you any idea on the main differenced between the (Elektor's) Crecendo and the Leach Amp.

I'm currently building the Leach Amp and are really curious about the pros and cons comapred to the Crecendo, which I'm probably about to build in a not too distant future.

Have a good day,
//magnus

I improved the original Crescendo a lot and published it in the swedish (now dead) magazine called Audio-Video. My amp at home has done excellent service since 1989 together (since 1996) with my Martin Logan SL3 electrostatic speakers.

You can read a short piece at my homepage about the QRO amp as I called it.

My point of view is that the Leach amp is well tested for years and is bipolar and Crescendo is a MOSFET but you can put MOSFET's on the Leach and vice versa.

[Vivek]

Hi,
Where can I get the schematic for the Crescendo amp?

Vivek

[bawang]

An extremely good feature of the Leach Amp is that if one of the fuses on the supply rails blew, the output stays at zero ie no swinging to the other live rail!