The Frugalamp by OS

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ostripper

ostripper

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Joined 2008
(see below)
OS
 

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Steve Dunlap

Steve Dunlap

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Joined 2008
ostripper said:


I didn't mean to point out a problem , but I don't want to be
a contributer to burning amps .:hot: :hot:


I've tried both including or omitting the diamond current
stage in the NFB loop with little effect other than ,with the
isolated current stage, no change with load. (As you pointed out.)

Another interesting note is that by degenerating the darlington
(470r - 2.2k) like a standard EF type 2, "tames" a little
bump at 5MHz (I think that is where this thing "likes" to oscillate)
and sets the phase margin.

I already did the carlos thing and no :hot: fire , so I know it works. I tested what would happen if my vbias died and it
is the safest I could imagine.. just 300ma (severely overbiased).
Idiot proof, much better than a typical amp. A total short at
the output would just burn the basestopper resistors.:cool:

It seems DIYaudio has gone "krill crazy" these days, even
carlos (no trashbin or buckshot) likes it, 3 seperate diamond
topology threads... you started it all ,steve, thanks!
BTW..., yours(krill) is most like the Nakamitchi 620, except they use an EF'ed diamond which is the thermal compensation .
(attached)
OS
Click to expand...


Anything that contributes to the stability of the amp is welcome. I certainly have no issue with you pointing it out.

I haven't seen the bump at 5 Meg in the open loop design.

Audio Research placed the input pair on the hear sink for compensation in the solid state amps they released in the mid 70s.

I am glade I stirred up a little interest. I really appreciate the reception my design has received here.
 
ostripper

ostripper

Member
Joined 2008
Thank you for the baker clamp link , I sucked the articles into
my pdF creator and cropped them so they will read nice.:D

I went to the Knoxville TN. Eagles concert and listened to 24
QSC 1KW amps. At first they sounded strained , later in
the show I saw the engineer "fiddling" with the board and
the sound became more to my liking.

Compared to my last concert , RUSH , in 1985 - albany, N.Y.,
with Altec lansings and 4.1 surround at 50KW+ ,the eagles
sound system "blew chunks". The performance was good,
considering the age of Henley and Walsh.

Dang ticket cost a fortune for a 3.5 hour show.(see below)
OS
 

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J

jkeny

Banned
Joined 2007
Os If you get a chance I would recommend catching a Leonard Cohen concert - excellent value for money by superb musicians - memorable experience. Don't know what sound system was used but the sound was intimate in an open air venue which says a lot for the sound engineers.

Your amp has me intrigued - is the magic in the input stage or the whole circuit. I'm interested in an output stage only which my tube based input stage will feed.

You are using global feedback which I would lose so would there be much advantage to yours Vs the Krill output stage?
 
ostripper

ostripper

Member
Joined 2008
is the magic in the input stage or the whole circuit
Click to expand...

No magic, but the cfp inPut stage and holman (apt) based
front end is the best as compared to a standard topology.

The krill /nakamitchi diamond OPS has slightly better
distortion figures with global feedback but as Steve pointed
out it would go "open loop" if it burned out ,also NFB would be affected BY differences of loading on the output.

The sound of the diamond seems to be the same either
way as I have tried it.

The whole circuit is one of the best I've done both simulated
or prototyped. Only basic matching is desirable for the
diamond itself (ksa1381/ksc3503).
os
 
jaycee

jaycee

Member
Joined 2004
Hi OS,

Looks good on the sim to me :D

A few points though...

1) MPSA42/92 ? They're a bit slow, only 50MHz fT. OnSemi also do the MPSW42/92 which are extended TO-92 packages that do 1W - might be better.

2) For Q11/Q12 - check out the dissipation on them, hardly any. I switched to KSA992/KSC1845 here.

3) The R-C-R filter in the current source for the LTP produces a hell of a turnon thump by the look of it - the output goes nearly full +VE rail until the current source turns on. I nicked an idea from the Cambridge A3i amp on this score.

There is also quite a difference on the sim between taking feedback from the output, and feedback from the VAS - it's a lot worse from the VAS, with a lot higher THD figure and much more prominent H2/H3/H4. I'm debating trying the "split feedback" system that's in the Leach Amp.
 

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ostripper

ostripper

Member
Joined 2008
by JC - Looks good on the sim to me
Click to expand...
build it , man!!!



3) The R-C-R filter in the current source for the LTP produces a hell of a turnon thump by the look of it - the output goes nearly full +VE rail until the current source turns on. I nicked an idea from the Cambridge A3i amp on this score.
Click to expand...

Now that is strange, I kept the same CCS from FA1 and 2,
with 4 in the house now..NO Thump. In fact , I was surprised
when first turned on the first FA1.. I thought I would have
hum and/or a little thump like I read about from other threads,
but no..nothing.

Of the 3 frugalamps , the 3-x series, even through it appears
unbalanced LTP wise, balances within .01mA (even better
than FA2) in the 2 tails Ic wise.

the only anomily is when you shut down the FA1/2 ,you hear a
little bit of crackle (distortion) as the rails collapse in the last
1/2 second..

If you build the FA3k (diamond) first, being untested, and like
it, I will build it ,too and make the board for it. But if you don't,
I going to make a pair of FA3's as I already have protoyped the
LPT/VAS/CCS and it rocks.

OS
 
jaycee

jaycee

Member
Joined 2004
ostripper said:

build it , man!!!
Click to expand...

I know - what's putting me off is that I still don't have a 'scope, nor the funds to splash out for one :(

ostripper said:

Now that is strange, I kept the same CCS from FA1 and 2, with 4 in the house now..NO Thump. In fact , I was surprised when first turned on the first FA1.. I thought I would have hum and/or a little thump like I read about from other threads, but no..nothing.
Click to expand...

It only seems to do it with the diamond - look at the first 5ms or so of the sim, using ".tran 0 10 0 startup uic" which simulates poweron. With the cascoded FA3, it doesnt happen - the output stays at 0 until the current source starts.

ostripper said:

Of the 3 frugalamps , the 3-x series, even through it appears unbalanced LTP wise, balances within .01mA (even better than FA2) in the 2 tails Ic wise.
Click to expand...

I really like the Holman arrangement here. A very elegant solution for the VAS :)

Personally though I still like the "symasym" style "differential" VAS.

ostripper said:

the only anomily is when you shut down the FA1/2 ,you hear a little bit of crackle (distortion) as the rails collapse in the last 1/2 second..
Click to expand...

Same with pretty much any power amp.

ostripper said:

If you build the FA3k (diamond) first, being untested, and like it, I will build it ,too and make the board for it. But if you don't, I going to make a pair of FA3's as I already have protoyped the LPT/VAS/CCS and it rocks.
Click to expand...

We will see... I've got two heatsinks, 2x15000uF 80V, and a 2x35V 500VA toroid waiting to go... as well as most of the transistors... just wish i hada scope!
 
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