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Old 17th November 2008, 06:49 AM   #1
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Default 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...

Click the image to open in full size. )
Click the image to open in full size.

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

Click the image to open in full size.

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.

Click the image to open in full size.



Also ,comments or suggestions are always welcome.
OS
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Old 17th November 2008, 07:18 AM   #2
lineup is offline lineup  Sweden
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You need to simulate this
to be able to tell the specs in a more impressive way

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!
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Old 17th November 2008, 07:34 AM   #3
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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)
OS
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Old 17th November 2008, 07:39 AM   #4
lineup is offline lineup  Sweden
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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
... even dummy load test is questionable .. as this is not same loading as speakers
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Old 17th November 2008, 08:05 AM   #5
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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)
OS
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Old 17th November 2008, 09:42 AM   #6
KLe is offline KLe  Australia
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OS, where's your 3T current mirror? ...
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Old 17th November 2008, 09:57 AM   #7
lineup is offline lineup  Sweden
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How much bias do you use for those .22 Ohm resistors?
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Old 17th November 2008, 01:58 PM   #8
jam is offline jam  United States
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Yeah! Where is the improvrd mirror?

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

Regards,
Jam
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Old 17th November 2008, 05:34 PM   #9
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Quote:
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....
Click the image to open in full size.
Quote:
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.
OS
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Old 17th November 2008, 09:10 PM   #10
sandyK is offline sandyK  Australia
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Default Frugalamp

ostripper

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.

Regards
SandyK
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