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ostripper 17th November 2008 06:49 AM

The Frugalamp by OS
It's been a while since joined , and thanks to the forum and
good material (D. Self's handbook), I've finally gotten this far.

There are good amps here, ..and great amps here. But none
as good as one you do yourself. (DIY "spirit")

Well , here it is , not simulated, but a real working amp... )

Another "blameless" design ,but with economical considerations.
(amp in picture below cost $21 US dollars)

I am continuing my work on the board layout in eagle 5 (source
of schematic) and would be very thankful if someone could
help me with some of the layout issues.
I have a full protection package in the design stage as well
as the layout for the PS completed.

Also ,comments or suggestions are always welcome.

lineup 17th November 2008 07:18 AM

You need to simulate this
to be able to tell the specs :) in a more impressive way :D

I say you are a very quick learner, OS
And when being as interested and active as you are
you become good .. quickly.

Who knows where you will be in you designs in say 20 years.
Having the experience like Curl / Self / Pass.
If I may live as long to see .. I will know

Great job! Well done!

ostripper 17th November 2008 07:34 AM

Thanks, lineup. I have done simple sims in spice but
dont know where to get models or how to import them
into spice for my devices.

I spent too much time with eagle and doing real world
sims with real parts.

I have scoped it ,(picoscope), it performs very good in
squarewave and sine tests.

>125w 8R0 (> 200w peaks with music content)

I was too impatient and after biasing hooked it right
to a speaker.(sounds great)

lineup 17th November 2008 07:39 AM

yes, this is the hook, to get those models
most of the time I have to stick to 'similar' components
of course, I was ironic when say you have to sim ;)
we should not tease the man in brasil too much ...

And nothing beats real life test results ... or better Music with your own Amp :cool:
... even dummy load test is questionable .. as this is not same loading as speakers

ostripper 17th November 2008 08:05 AM

I got as far as simulating this with old 15003/4 devices
, but I use the new njw0302/0281's which are more
linear, lower Cob, (and cheap).This also helped me set
the currents of LTP and VAS.

I used picoscope to choose Cdom @68pf (best squarewave).
little ringing and NO oscillations. (don't like burning amps)

KLe 17th November 2008 09:42 AM

OS, where's your 3T current mirror? ...

lineup 17th November 2008 09:57 AM

How much bias do you use for those .22 Ohm resistors?

jam 17th November 2008 01:58 PM

Yeah! Where is the improvrd mirror?:D

Good looking design, Cascoding the current source on the differential usually helps.


ostripper 17th November 2008 05:34 PM


by jam - Yeah! Where is the improvrd mirror?
I didn't want to threadjack that from the CM thread.
What I'm going to do is incorporate the extra pads
in my final board layout to accept ALL the mods discussed in
the CM thread.:)

As a "base" design it has a neutral quality and is very
sound (derated , failure anticipation).
Example :If the Vbias wiper fails - outputs go underbias,
baker clamps,OP section fails - only 100R resistors burn,etc.

But , here is the mod....

by lineup - How much bias do you use for those .22 Ohm resistors
35ma per device (Xover "glitch" disappears at 20ma).

For that "eerie" (depth and decay) sound. :D

sandyK 17th November 2008 09:10 PM


Are you able to post the LTP collector voltage readings, before and after the 3 transistor CM ? THis would give a very good idea of the differences between the 2 types, and the degree of balance achieved.


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