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From: Eeyore on 15 Dec 2008 16:49


Dan Kuechle wrote:

> I am just a hobbyist. I am not am amplifier designer, but I don't see how
> this amp would work. If you move the ground symbol to the other side of the
> speaker you get something that looks more like an amp to me.

Agreed.

But it has no voltage gain. Hence it would need a high voltage ~ 10V rms input.
Use an IC op-amp for that stage perhaps ?

Graham

From: Eeyore on 15 Dec 2008 16:57


morris.slutsky(a)gmail.com wrote:

> > Are you sure you have the ground in the right place?
> >
> > Dan
>
> Yep. I'm pretty sure that's where I want it.

You're wrong.


> It's based on a MOSFET design of John Broskie's from his Tubecad.com
> site. I didn't believe it when I saw it either. But SPICE seems to
> think it should work, and I like the simple feedback network.

There is no 'feedback', other than using transistors in emitter follower
mode is a form of feedback in its own right. The 2N2222 and 2N2907 are a
bit puny as drivers btw allthough you might just get away with it here.
Not to mention hugely expensive for the genuine metal can item. At least
get the PN TO-92 versions but something newer than 40 yrs old might be
more appropriate.

Also 'bypass' R2 and R3 with something like 10uF electrolytic caps.

Graham

From: Eeyore on 15 Dec 2008 18:28


Bob Eld wrote:

> Yes, well I didn't notice where the ground was. Funny I missed it. I've
> hooked up op-amps this way with the output grounded and the signal taken
> from the power supply leads in a similar manner.

I just realised this is very like the 'classic' QSC output stage they used for
years but they arranged the driver and output devices as a Sziklai pair with the
main output device collectors physically grounded, requiring no insulation pad
which was clever.

Compare with this.
http://www.qscaudio.com/support/library/schems/Current/RMX%20Series/rmx850.pdf

Graham

From: Bob Eld on 15 Dec 2008 21:50

"BobW" <nimby_GIMME_SOME_SPAM(a)roadrunner.com> wrote in message
news:PO-dnSSzONAHndrUnZ2dnUVZ_sPinZ2d(a)giganews.com...
> >
Snip.....
> I recently went to see a band that some friends play in. They played for
> about 2 hours and spent about 3 hours setting it up and tearing it down.
> Cables and mixers and effects boxes and amplifiers and more cables and
patch
> panels and boxes and cables and more boxes. Sheesh! How to they keep track
> what equipment belongs to whom? I made a comment similar to yours: "Why
> can't everyone plug into ONE box?"
>
> The answer, ultimately, will probably be wireless. Wireless mics, wireless
> control box, and wireless powered speakers. 10 minutes of setup and
> teardown. Buddabing!
>
> Bob
> --

I went to one show where they were using wireless mics and all of a sudden
somebody was ordering a hamburger and a coke. A bit of fm interference from
the joint across the street. They switched out to wired mics for the next
set.



From: BobW on 15 Dec 2008 23:07

"Bob Eld" <nsmontassoc(a)yahoo.com> wrote in message
news:4IE1l.6954$hc1.3726(a)flpi150.ffdc.sbc.com...
>
> "BobW" <nimby_GIMME_SOME_SPAM(a)roadrunner.com> wrote in message
> news:PO-dnSSzONAHndrUnZ2dnUVZ_sPinZ2d(a)giganews.com...
>> >
> Snip.....
>> I recently went to see a band that some friends play in. They played for
>> about 2 hours and spent about 3 hours setting it up and tearing it down.
>> Cables and mixers and effects boxes and amplifiers and more cables and
> patch
>> panels and boxes and cables and more boxes. Sheesh! How to they keep
>> track
>> what equipment belongs to whom? I made a comment similar to yours: "Why
>> can't everyone plug into ONE box?"
>>
>> The answer, ultimately, will probably be wireless. Wireless mics,
>> wireless
>> control box, and wireless powered speakers. 10 minutes of setup and
>> teardown. Buddabing!
>>
>> Bob
>> --
>
> I went to one show where they were using wireless mics and all of a sudden
> somebody was ordering a hamburger and a coke. A bit of fm interference
> from
> the joint across the street. They switched out to wired mics for the next
> set.
>
>

That's pretty funny. I would have liked to have seen their faces.

The wireless stuff would have to be a fairly sophisticated technology like
spread spectrum to avoid that type of interference. I haven't done any
checking, but I would bet that it's already available.

Bob
--
== All google group posts are automatically deleted due to spam ==


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