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jleaman 27th February 2005 09:21 PM

Smaller Leach Amp V1
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Jens Rasmussen Has passed along to me this smaller version of the leach amp. Picture posted .. I am wondering if any one is interested in the smaller version ? Any Comments and suggestions ?

Jean 27th February 2005 09:34 PM

Depending on the price, i'll take 2 :)

jleaman 27th February 2005 09:38 PM

Me my self i want 6 the more people that want them the cheaper they are..

I'm also Thinking about a kit and also a group Buy on some of the parts used..

Mikett 27th February 2005 10:19 PM

Personally, if the amp were to be used with lower impedance speakers as in many MTMs today, and subwoofers the voltage used should be reduced for the 4 transistor board if you want to be cautious since SOA can vary from device to device. But is that a good compromise? I say no.
By simply adding at least one more pair of output transistors, the output stage remains quite close to the original. When you consider the additional cost of a couple of pairs of outputs over the total cost of the amp it's really minute. What do you gain, higher rail voltages giving you higher power and headroom and a safety factor.
There's another thread discussing the equivalency of plastic versus metal output transistors and I gather that it take three plastics to two metal outputs.
I'll pass on the 4 output version. It is not good engineering IMHO.
The 10 might be overkill but it needs more than 4.

JensRasmussen 28th February 2005 05:32 AM

First of all I Okayed this thread to Jason because someone out there might find the 4 transistor version useful.

Secondly, before anybody decides if a 4 transistor version is good engineering or not, I have a little background regarding the design.

1) The big 10 transistor version was designed for full range or the bass channels in an active speaker, using rail voltages above the original level; I aim for +-75V.

2) The smaller version was designed for small speakers and the midrange and tweeter channels in an active system. The rails would be slightly lower then the original, say +-53V.

In general the 4 transistor version will be ok for full range use with rails of about +-50V or so, but the protection circuit needs to be redesigned to make sure that the transistors will not be damaged if the output is shorted. If you want an equivalent circuit to the original Iím pretty sure that 3 parallel plastic devises will do the job nicely.

On a slightly different note, I donít think itís polite or very helpful to comment on the level of engineering before knowing the reasons for a design. Clearly no one could, but this is the reason why I was a bit reluctant in releasing the design for a group buy in the first place.

Now you know, so Iíll leave you alone to decide what to do.


jleaman 28th February 2005 06:00 AM

For me 10 is over kill way to much power or money for me to build. But 4 is perfect for any sub that i would be able to listen to and handle with out going deaf. Personally 4 transistors is to much but should be good enough to get good results with the distortion level low.

Second I like these small amps there perfect for a compact speaker or a nice small powered speaker : O )

Mikett 28th February 2005 02:10 PM

Keep this in mind. Jens also sees that the amp is good for a little over 50 volts or around 50 and that is what I eluded to. Why is that significant? Consider the power supply capacitors and what voltage ratings they come in generally. 50 volts is available but for long term reliability, it is not recommended that caps are used at the rated voltage since if you happen to have a higher than normal line voltage in your area that could be exceeded easily. What's the next step? It's over 60 volts for sure, higher voltage ones also generally have lower ESR too.. And that's the ones you should use. Now comes the issue, if the caps and everything else on the design is rated for those higher voltages, might as well use it especially if all it will take is two extra output transistors and a few resistors. The cost of the transformer will be the same since they are generally priced by VA ratings.
Just going by experience. You've gained a lot more power too for very little money ( Voltage Squared) and you've gained long term reliability. Since you're using this for subs, remember that at low frequencies there is a lot of relected complex impedances from subs and they are not purely resistive. This also necessitates a strong output section for the complex impedances. At the high rail voltages Jens intended to use for subs, the 10 transistor package is NOT overkill but prudence.

jleaman 2nd March 2005 08:39 PM

So is any one interested ?

JensRasmussen 2nd March 2005 08:48 PM

I'd like 6 boards if the price is right.....


Mikett 2nd March 2005 08:52 PM

jens I am sorry if you were offended by my saying it is not good engineering. I was just pointing out that much more was to be gained by simply adding another pair of outputs and the extra cost of doing so would essentially be just those components alone.
How about redesigning it for 6. The redesign is very well done and this 6 transistor board could become a classic in a sense.
If a 6 transistor was offered, I'd be in for 2.

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