Modified Leach Super Amp

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Modified Leach Super Amp

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

110 V rails,Choke Regulated , Dual Mono with 2 X 1KVA transformers,

Output stage MJ21195 and MJ21196 8 pairs per channel.

Driver stage MJE15034 NPN,MJE15035 PNP.

During initial testing with a speaker during a loud musical peak i saw an input current draw of 6 Amps.Is this OK?
could you post details of your choke regulated PSU.
Some design calculations to go with it would be nice.
There were a couple of threads recently that could not be fully answered due to lack of knowledge.

Re your output current.
6A into 8R is only 48V. You have about 100V available as drive voltage so output currents approachung 12A into 8R are possible and your stages should be designed to cope with this.
However 8ohm speakers can have impedance dips to below 6ohms in parts of the frequency range (mostly in bass) then your peak current could exceed 17A.

Were you talking about output current or PSU current before the choke?
If before the choke then 6A in and 17A out proves that the choke regulation is working and using stored magnetic energy.
I would assume 6A input current is at 240V, about 1.5KVA.

This would be about right for this amp driving an 8 ohm load per channel on music. If it is a choke input filter (as opposed to a Pi filter) I would expect the output to be about 600W at 8 ohms per channel.
I hate to seem pedantic about detail, but a finned heatsink actually functions FAR more efficiently when mounted vertically and in heights of around 125-150mm. Also the heat draw from your mounted devices is optimised when they are mounted centrally on the heatsink. Why waste value. If only for resource/environment/future generations/... reasons.

It's probably because I'm a physicist, it's entrenched.

jacco vermeulen said:
Mr Ball,

i suppose this is just a test setup.
Notice the attention to detail, the number of devices that have their legs sleeved.
If not, this is the best arrangement for stewing components and boards.:clown:

Yes it is a test setup. I wanted to make sure everything works before i install it in my monoblock Aluminium Case.

I also got new PCB with integrated support for 8 pairs of TO-247 output devices. :D

I plan to do 3 Box setup with 1 PSU, 2 monoblock Amplifiers.
OK I get it, Mura.

It's decidedly scary as is. In fact, this type of open web layout usually tends to have issues of it's own so I never do these.

You've certainly tamed the beast.

On the subject of heatsinks and final pkg, it is best to raise the vertical fins well above the mounting surface (base) and to count on 25C+ rise as heatsinks need a good temp differential to extract heat efficiently. I say this because I note you are in India and kanwar has previously advised of 50C temps there.

About the heatsinks (Local Made cost about 5$ each)
I plan to mount them vertically and it will be coupled with a solid 10mm Aluminium base.

Also i plan of using forced cooling for extended high power use.

I am still tuning the sound right now and do different input caps like Auricap make a difference?

Thanks all for your valuable inputs.

if I were to be ask, it is better to place those output devices on the
on the center channel of your heatsinks so that heat is EQUALLY
distributed side ways to the fins. most importantly that the Leach Amp
dissipates a lot of heat:hot: when driven at low impedance loads.

Sometimes we like nice looking arrangements on the chassis because we like it to be like that but sometimes the materials used do not
appear to want it.



for tunning the Leach Amp for a deeper, clean and tight output,
I would also prefer using the Class AB+B output topology which actually
used by Crown power amps and which I'm also using for my Leach
Amp (modified),

yet I'm not still satisfied with this, since the LTP are using a psuedo
type of current source.

Active current sourcing is rather better for so many aspects,
like improve THD, PSRR, CMRR, and rounder dynamic soundstage.

such modification makes the amp more complicated but very rewarding.

to joan2:
May know if where could we purchase MJL21195 and MJL21196 in Manila, but are these available here.
by this time I'm using MJL4281 and MJL4302 for my projects,
and I want to change these for a higher SOA, I have with me here
some numbers of MJL21196's but without the MJL21195's..


Audiophilenoob said:
did you use this design:

for your boards?? I'm assuming you changed components to make it very high power like it is....
what exactly is different about your leach amp, as in what parts did you change from his design?

Yes it is the same design......

I will list out all the mods in a few days time.(too many to remember now);)

I am working on a new linear PSU design which features the same transistors used in Output stage for active current sourcing.


I think going the Class AB+B way will make the amp sound deep clean and tight as you tell but not delicate.

I prefer a A+AB bias.

This way i get a clean deep and fast amp wich still manages to sound delicate in low volume and hugely powerful in high volume.

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